Co-reporter:Na ZhangWai-Yip Lo, Zhengxu CaiLianwei Li, Luping Yu
Nano Letters January 11, 2017 Volume 17(Issue 1) pp:
Publication Date(Web):December 5, 2016
DOI:10.1021/acs.nanolett.6b04110
Inspired by transistors and electron transfer in proteins, we designed a group of pyridinoparacyclophane based diodes to study the through-space electronic gating effect on molecular rectification. It was shown that an edge-on gate effectively tunes the rectification ratio of a diode via through-space interaction. Higher rectification ratio was obtained for more electron-rich gating groups. The transition voltage spectroscopy showed that the forward transition voltage is correlated to the Hammett parameter of the gating group. Combining theoretical calculation and experimental data, we proposed that the change in rectification was induced by a shift in HOMO level both spatially and energetically. This design principle based on through-space edge-on gate is demonstrated on molecular wires, switches, and now diodes, showing the potential of molecular design in increasing the complexity of single-molecule electronic devices.Keywords: Molecular diode; rectification; STM-BJ; through-space gate;
Co-reporter:Qinghe WuDonglin Zhao, Jinghui Yang, Valerii Sharapov, Zhengxu Cai, Lianwei LiNa Zhang, Andriy NeshchadinWei Chen, Luping Yu
Chemistry of Materials 2017 Volume 29(Issue 3) pp:
Publication Date(Web):January 6, 2017
DOI:10.1021/acs.chemmater.6b04287
This paper describes the synthesis and application of βTPB6 and βTPB6-C as electron acceptors for organic solar cells. Compound βTPB6 contains four covalently bonded PDIs with a BDT-Th core at the β-position. The free rotation of PDIs renders βTPB6 with varying molecular geometries. The cyclization of βTPB6 yields βTPB6-C with high rigidity of the molecular geometry and enlarged conjugated skeleton. The inverted solar cells based on βTPB6-C and PTB7-Th as the donor polymer exhibited the highest efficiency of 7.69% with Voc of 0.92 V, Jsc of 14.9 mAcm–2, and FF of 0.56, which is 31% higher than that for βTPB6 based devices. The larger fraction of βTPB6-C and PTB7-Th than that of βTPB6:PTB7-Th in a blend film takes a face-on orientation packing pattern for π-systems that benefits the charge transport and hence higher PCE value than that for βTPB6:PTB7-Th. It was also found that a proper DIO:DPE additive further enhances this trend, which results in an increase of the PCE value for βTPB6-C:PTB7-Th while decreasing the PCE value for βTPB6:PTB7-Th.
Co-reporter:Na Zhang;Wai-Yip Lo;Anex Jose;Zhengxu Cai;Lianwei Li
Advanced Materials 2017 Volume 29(Issue 28) pp:
Publication Date(Web):2017/07/01
DOI:10.1002/adma.201701248
Single-molecular electronics is a potential solution to nanoscale electronic devices. While simple functional single-molecule devices such as diodes, switches, and wires are well studied, complex single-molecular systems with multiple functional units are rarely investigated. Here, a single-molecule AND logic gate is constructed from a proton-switchable edge-on gated pyridinoparacyclophane unit with a light-switchable diarylethene unit. The AND gate can be controlled orthogonally by light and protonation and produce desired electrical output at room temperature. The AND gate shows high conductivity when treated with UV light and in the neutral state, and low conductivity when treated either with visible light or acid. A conductance difference of 7.3 is observed for the switching from the highest conducting state to second-highest conducting state and a conductance ratio of 94 is observed between the most and least conducting states. The orthogonality of the two stimuli is further demonstrated by UV–vis, NMR, and density function theory calculations. This is a demonstration of concept of constructing a complex single-molecule electronic device from two coupled functional units.
Co-reporter:Wai-Yip Lo, Na Zhang, Zhengxu Cai, Lianwei Li, and Luping Yu
Accounts of Chemical Research 2016 Volume 49(Issue 9) pp:1852
Publication Date(Web):August 30, 2016
DOI:10.1021/acs.accounts.6b00305
As the semiconductor companies officially abandoned the pursuit of Moore’s law, the limitation of silicone-based semiconductor electronic devices is approaching. Single molecular devices are considered as a potential solution to overcome the physical barriers caused by quantum interferences because the intermolecular interactions are mainly through weak van der Waals force between molecular building blocks. In this bottom-up approach, components are built from atoms up, allowing great control over the molecular properties. Moreover, single molecular devices are powerful tools to understand quantum physics, reaction mechanism, and electron and charge transfer processes in organic semiconductors and molecules.So far, a great deal of effort is focused on understanding charge transport through organic single-molecular wires. However, to control charge transport, molecular diodes, switches, transistors, and memories are crucial. Significant progress in these topics has been achieved in the past years. The introduction and advances of scanning tunneling microscope break-junction (STM-BJ) techniques have led to more detailed characterization of new molecular structures. The modern organic chemistry provides an efficient access to a variety of functional moieties in single molecular device. These moieties have the potential to be incorporated in miniature circuits or incorporated as parts in molecular machines, bioelectronics devices, and bottom-up molecular devices.In this Account, we discuss progress mainly made in our lab in designing and characterizing organic single-molecular electronic components beyond molecular wires and with varied functions. We have synthesized and demonstrated molecular diodes with p–n junction structures through various scanning probe microscopy techniques. The assembly of the molecular diodes was achieved by using Langmuir–Blodgett technique or thiol/gold self-assembly chemistry with orthogonal protecting groups. We have thoroughly investigated the rectification effect of different types of p–n junction diodes and its modification by structural and external effects. Through a combination of structural modifications, low temperature study, and quantum mechanical calculations, we showed that the origin of the rectification in these molecules can be attributed to the effect of dipolar field. Further studies on charge transport through transition metal complexes and anchoring group effect supported this conclusion. Most recently, a model system of molecular transistor was synthesized and demonstrated by STM-BJ technique. The gating effect in the molecular wire originated from the tuning of the energy levels via dipolar field and can be turned on/off by dipolar field and chemical stimulation. This is the first example of gated charge transport in molecular electronics.
Co-reporter:Zhengxu Cai, Wai-Yip Lo, Tianyue Zheng, Lianwei Li, Na Zhang, Yubing Hu, and Luping Yu
Journal of the American Chemical Society 2016 Volume 138(Issue 33) pp:10630-10635
Publication Date(Web):August 4, 2016
DOI:10.1021/jacs.6b05983
A series of ladder-type fused heteroacenes consisting of thiophenes and benzothiophenes were synthesized and functionalized with thiol groups for single-molecule electrical measurements via a scanning tunneling microscopy break-junction method. It was found that this molecular wire system possesses exceptional charge transport properties with weak length dependence. The tunneling decay constant β was estimated to be 0.088 and 0.047 Å–1 under 0.1 and 0.5 bias, respectively, which is one of the lowest β values among other non-metal-containing molecular wires, indicating that a planar ladder structure favors charge transport. Transition voltage spectroscopy showed that the energy barrier decreases as the length of the molecule increases. The general trend of the energy offsets derived from the transition voltage via the Newns–Anderson model agrees well with that of the Fermi/HOMO energy level difference. Nonequilibrium Green’s function/density functional theory was used to further investigate the transport process in these molecular wires.
Co-reporter:Qinghe Wu; Donglin Zhao; Alexander M. Schneider; Wei Chen
Journal of the American Chemical Society 2016 Volume 138(Issue 23) pp:7248-7251
Publication Date(Web):May 24, 2016
DOI:10.1021/jacs.6b03562
A cluster type of electron acceptor, TPB, bearing four α-perylenediimides (PDIs), was developed, in which the four PDIs form a cross-like molecular conformation while still partially conjugated with the BDT-Th core. The blend TPB:PTB7-Th films show favorable morphology and efficient charge dissociation. The inverted solar cells exhibited the highest PCE of 8.47% with the extraordinarily high Jsc values (>18 mA/cm2), comparable with those of the corresponding PC71BM/PTB7-Th-based solar cells.
Co-reporter:Lianwei Li; Zhengxu Cai; Qinghe Wu; Wai-Yip Lo; Na Zhang; Lin X. Chen
Journal of the American Chemical Society 2016 Volume 138(Issue 24) pp:7681-7686
Publication Date(Web):June 2, 2016
DOI:10.1021/jacs.6b03472
Developing highly efficient photocatalyts for water splitting is one of the grand challenges in solar energy conversion. Here, we report the rational design and synthesis of porous conjugated polymer (PCP) that photocatalytically generates hydrogen from water splitting. The design mimics natural photosynthetics systems with conjugated polymer component to harvest photons and the transition metal part to facilitate catalytic activities. A series of PCPs have been synthesized with different light harvesting chromophores and transition metal binding bipyridyl (bpy) sites. The photocatalytic activity of these bpy-containing PCPs can be greatly enhanced due to the improved light absorption, better wettability, local ordering structure, and the improved charge separation process. The PCP made of strong and fully conjugated donor chromophore DBD (M4) shows the highest hydrogen production rate at ∼33 μmol/h. The results indicate that copolymerization between a strong electron donor and weak electron acceptor into the same polymer chain is a useful strategy for developing efficient photocatalysts. This study also reveals that the residual palladium in the PCP networks plays a key role for the catalytic performance. The hydrogen generation activity of PCP photocatalyst can be further enhanced to 164 μmol/h with an apparent quantum yield of 1.8% at 350 nm by loading 2 wt % of extra platinum cocatalyst.
Co-reporter:Donglin Zhao, Qinghe Wu, Zhengxu Cai, Tianyue Zheng, Wei Chen, Jessica Lu, and Luping Yu
Chemistry of Materials 2016 Volume 28(Issue 4) pp:1139
Publication Date(Web):January 20, 2016
DOI:10.1021/acs.chemmater.5b04570
Perylene diimide (PDI) derivatives functionalized at the ortho-position (αPPID, αPBDT) were synthesized and used as electron acceptors in non-fullerene organic photovoltaic cells. Because of the good planarity and strong π-stacking of ortho-functionalized PDI, the αPPID and αPBDT exhibit a strong tendency to form aggregates, which endow the materials with high electron mobility. The inverted OPVs employing αPDI-based compounds as the acceptors and PBT7-Th as the donor give the highest power conversion efficiency (PCE) values: 4.92% for αPBDT-based devices and 3.61% for αPPID-based devices, which are, respectively, 39% and 4% higher than that of their β-substituted counterparts βPBDT and βPPID. Charge separation studies show more efficient exciton dissociation at interfaces between αPDI-based compounds and PTB7-Th. The results suggest that α-substituted PDI derivatives are more promising electron acceptors for organic photovoltaic (OPV) components than β-isomers.
Co-reporter:Thomas J. Fauvell, Tianyue Zheng, Nicholas E. Jackson, Mark A. Ratner, Luping Yu, and Lin X. Chen
Chemistry of Materials 2016 Volume 28(Issue 8) pp:2814
Publication Date(Web):April 8, 2016
DOI:10.1021/acs.chemmater.6b00734
Organic semiconductors have garnered substantial interest in optoelectronics, but their device performances exhibit strong dependencies on material crystallinity and packing. In an effort to understand the interactions dictating the morphological and photophysical properties of a high-performing photovoltaic polymer, PTB7, a series of short oligomers and low molecular weight polymers of PTB7 were synthesized. Chain-length dependent optical studies of these oligomers demonstrate that PTB7’s low-energy visible absorption is largely due to self-aggregation-induced ordering, rather than in-chain charge transfer, as previously thought. By examining molecular weight and concentration dependent optical properties, supplemented by molecular dynamics simulations, we attribute polymeric PTB7’s unique midgap fluorescence and concentration independent absorption spectrum to an interplay between low molecular weight unaggregated strands and high-molecular weight self-aggregated (folded) strands. Specifically, we propose that the onset of PTB7 self-folding occurs between 7 and 13 repeat units, but the aggregates characteristic of polymeric PTB7 only develop at lengths of ∼30 repeat units. Atomistic molecular dynamics simulations of PTB7 corroborate these conclusions, and a simple relation is proposed which quantifies the free-energy of conjugated polymer folding. This study provides detailed guidance in the design of intra- and interchain contributions to the photophysical and morphological properties of polymeric semiconductors.
Co-reporter:Lianwei Li, Ryan G. Hadt, Shiyu Yao, Wai-Yip Lo, Zhengxu Cai, Qinghe Wu, Bill Pandit, Lin X. Chen, and Luping Yu
Chemistry of Materials 2016 Volume 28(Issue 15) pp:5394
Publication Date(Web):July 11, 2016
DOI:10.1021/acs.chemmater.6b01477
Developing photocatalytic systems for water splitting to generate oxygen and hydrogen is one of the biggest chemical challenges in solar energy utilization. In this work, we report the first example of heterogeneous photocatalysts for hydrogen evolution based on in-chain cobalt-chelating conjugated polymers. Two conjugated polymers chelated with earth-abundant cobalt ions were synthesized and found to evolve hydrogen photocatalytically from water. These polymers are designed to combine functions of the conjugated backbone as a light-harvesting antenna and electron-transfer conduit with the in-chain bipyridyl-chelated transition metal centers as catalytic active sites. In addition, these polymers are soluble in organic solvents, enabling effective interactions with the substrates as well as detailed characterization. We also found a polymer-dependent optimal cobalt chelating concentration at which the highest photocatalytic hydrogen production (PHP) activity can be achieved.
Co-reporter:Lianwei Li, Wai-Yip Lo, Zhengxu Cai, Na Zhang and Luping Yu
Chemical Science 2016 vol. 7(Issue 5) pp:3137-3141
Publication Date(Web):26 Jan 2016
DOI:10.1039/C6SC00152A
The manipulation of charge transport through single molecules so that electronic information can be controlled is a basic challenge that is important for both fundamental understanding of the mechanisms and the potential applications in single-molecule technologies. This paper reports the influence of protonation on the gating effect in a series of molecular wires utilizing a pyridinoparacyclophane (PPC) moiety as the edge-on gate. It was found that the molecular conductance, transition voltage, and the corresponding tunnelling barriers can be reversibly switched by the protonation/deprotonation process of the nitrogen atom on the PPC pyridine ring. It was found that protonation levels off the tunnelling barrier of different molecules and converts p-type molecular wires into n-type, reversibly.
Co-reporter:Lianwei Li, Wai-yip Lo, Zhengxu Cai, Na Zhang, and Luping Yu
Macromolecules 2016 Volume 49(Issue 18) pp:6903-6909
Publication Date(Web):September 13, 2016
DOI:10.1021/acs.macromol.6b01764
Porous conjugated polymer (PCP) is a new kind of photocatalyst for photocatalytic hydrogen production (PHP). Here, we report the importance of the electronic properties of acceptor comonomer in determining the reactivity of 4,8-di(thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene (DBD)-based PCP photocatalyst for PHP application. It was found that the incorporation of nitrogen-containing ligand acceptor monomers into PCP network is an effective strategy to enhance the PHP activity. These moderately electron-deficient comonomers enhanced the dipole polarization effect. These PCPs exhibit appropriate solid-state morphology for charge transport. Powder X-ray diffraction (XRD) studies demonstrate that these PCP materials are semicrystalline materials. A strong correlation between the crystalline property and PHP activity is observed. The replacement of nitrogen-containing ligand acceptors with ligand-free strong acceptors is proved to be detrimental to the PHP process, indicating the proper choice in the electronic properties of monomer pair is important for achieving high photoactivity.
Co-reporter:Zhengxu Cai, Lianwei Li, Wai-Yip Lo, Donglin Zhao, Qinghe Wu, Na Zhang, Yu-An Su, Wei Chen, and Luping Yu
Macromolecules 2016 Volume 49(Issue 14) pp:5172-5178
Publication Date(Web):July 5, 2016
DOI:10.1021/acs.macromol.6b00860
A novel series of amphiphilic TC-PEG molecules were designed and synthesized based on the orthogonal cyclophane unit. These molecules were able to self-assemble from 1D nanofibers and nanobelts to 2D ultrathin nanosheets (3 nm thick) in a controlled way by tuning the length of PEG side-chains. The special structure of the cyclophane moiety allowed control in construction of nanostructures through programmed noncovalent interactions (hydrophobic–hydrophilic interaction and π–π interaction). The self-assembled nanostructures were characterized by combining real space imaging (TEM, SEM, and AFM) and reciprocal space scattering (GIWAXS) techniques. This unique supramolecular system may provide a new strategy for the design of materials with tunable nanomorphology and functionality.
Co-reporter:Bill Pandit
The Journal of Physical Chemistry C 2016 Volume 120(Issue 8) pp:4189-4198
Publication Date(Web):February 8, 2016
DOI:10.1021/acs.jpcc.5b10291
Rational design strategies for controlling the energetics of conjugated “donor–acceptor” copolymers are ubiquitous in the literature, as they allow for simple energy-level tuning strategies to be employed for photovoltaic and transistor applications. Utilizing the recently reported PTRn series of conjugated polymers closely related to the widely implemented material PTB7, we investigate the effect of local copolymer block energetics on the generation of transient excitonic and charge carrier species. It is clearly demonstrated that local copolymer block energetics play a much larger role than is apparent from simple energy-level tuning arguments, and drastically affect the ultrafast generation of free-charge carrier and trap state populations. Specifically, we observe an almost complete reversal in the efficient generation of free-charge in PTB7 to the ultrafast creation of a high percentage of trapped pseudo charge-transfer states. The implications of this secondary effect of “donor–acceptor” energy level tuning are discussed, along with strategies for avoiding the generation of trap states in “donor–acceptor” copolymers.
Co-reporter:Luyao Lu, Tianyue Zheng, Qinghe Wu, Alexander M. Schneider, Donglin Zhao, and Luping Yu
Chemical Reviews 2015 Volume 115(Issue 23) pp:12666
Publication Date(Web):August 7, 2015
DOI:10.1021/acs.chemrev.5b00098
Co-reporter:Wai-Yip Lo, Wuguo Bi, Lianwei Li, In Hwan Jung, and Luping Yu
Nano Letters 2015 Volume 15(Issue 2) pp:958-962
Publication Date(Web):January 20, 2015
DOI:10.1021/nl503745b
This work demonstrates edge-on chemical gating effect in molecular wires utilizing the pyridinoparacyclophane (PC) moiety as the gate. Different substituents with varied electronic demands are attached to the gate to simulate the effect of varying gating voltages similar to that in field-effect transistor (FET). It was observed that the orbital energy level and charge carrier’s tunneling barriers can be tuned by changing the gating group from strong electron acceptors to strong electron donors. The single molecule conductance and current–voltage characteristics of this molecular system are truly similar to those expected for an actual single molecular transistor.
Co-reporter:Tianyue Zheng; Zhengxu Cai; Rosina Ho-Wu; Sung Hei Yau; Valerii Shaparov; Theodore GoodsonIII
Journal of the American Chemical Society 2015 Volume 138(Issue 3) pp:868-875
Publication Date(Web):December 31, 2015
DOI:10.1021/jacs.5b10175
A series of ladder-type thienoacenes based on benzo[1,2-b:4,5-b′]dithiophene (BDT) have been synthesized and characterized. They were shown to be p-type semiconductors with wide band gaps and able to support multiple stable cationic states. As the conjugation lengthens, these oligomers become more emissive, showing high quantum yields. They were shown to be good two-photon absorbers, exhibiting high two-photon absorption coefficients.
Co-reporter:Luyao Lu, Tianyue Zheng, Tao Xu, Donglin Zhao, and Luping Yu
Chemistry of Materials 2015 Volume 27(Issue 2) pp:537
Publication Date(Web):December 19, 2014
DOI:10.1021/cm5042953
Bulk heterojunction (BHJ) polymer solar cells (PSCs) are a popular research subject currently pursued by many groups around the world. The state-of-the-art PSCs are composed of a polymer donor and a fullerene acceptor as the active layer, and their overall photovoltaic performance is dependent on many factors, such as the electrical and optical properties of donor polymers, device architectures, and interfacial layers used. Among them, the nature of donor polymer is without doubt one of the determining factors in performance of PSCs. In this work, we report for the first time the study of the influence of polymer dispersity (Đ) on the performance of PSCs composed of PTB7 and PC71BM as the active layer materials. It was found that polymers exhibiting large Đ contained structural defects that played the role of energy transfer and charge trapping/recombination centers. The power conversion efficiency of PTB7 devices decreased from 7.59% to 2.55% with increased Đ. The results highlighted the importance of controlling Đ of donor polymers for PSCs.
Co-reporter:In Hwan Jung, Donglin Zhao, Jaeyoung Jang, Wei Chen, Erik S. Landry, Luyao Lu, Dmitri V. Talapin, and Luping Yu
Chemistry of Materials 2015 Volume 27(Issue 17) pp:5941
Publication Date(Web):August 17, 2015
DOI:10.1021/acs.chemmater.5b01928
Several electron accepting polymers having weak accepting–strong accepting (WA-SA) and strong accepting–strong accepting (SA-SA) monomer alternation were synthesized for studies of structure/property relationship in all-polymer solar cells. Two kinds of cyclic amide monomers, 4,10-bis(2-butyloctyl)-thieno[2′,3′:5,6]pyrido[3,4-g]thieno-[3,2-c]isoquinoline-5,11-dione (TPTI) and 5,11-bis(2-butyloctyl)-thieno[2′,3′:4,5]pyrido[2,3-g]thieno[3,2-c]quinoline-4,10-dione (TPTQ), were synthesized as weak accepting monomers (WA). Difluorinated TPTQ (FTPTQ) and well-known perylene diimide (PDI) monomers were synthesized as strong electron accepting monomers (SA). By using 1-chloronaphthalene (CN) as a cosolvent, the morphology of the polymer blended films can be finely tuned to achieve better ordering toward face-on mode and favorable phase separation between electron donor and acceptor, resulting in significant enhancement of short circuit current (Jsc) and fill factor (FF). The fluorination in the TPTQ unit reduced the dipole moment of the D–A complex and gave a negative effect on a polymer system. PFP showed worse electron accepting property with lower electron mobility than PQP. It is reasoned that the internal polarization plays an important role in the design of electron accepting polymers. As a result, PQP having TPTQ monomer exhibited the best photovoltaic performance with power conversion efficiency (PCE) of 3.52% (Voc = 0.71 V, Jsc = 8.57 mA/cm2, FF = 0.58) at a weight ratio of PTB7-Th:PQP = 1:1, under AM 1.5G.
Co-reporter:Alexander M. Schneider, Luyao Lu, Eric F. Manley, Tianyue Zheng, Valerii Sharapov, Tao Xu, Tobin J. Marks, Lin X. Chen and Luping Yu
Chemical Science 2015 vol. 6(Issue 8) pp:4860-4866
Publication Date(Web):04 Jun 2015
DOI:10.1039/C5SC01427A
We report the properties of a new series of wide band gap photovoltaic polymers based on the N-alkyl 2-pyridone dithiophene (PDT) unit. These polymers are effective bulk heterojunction solar cell materials when blended with phenyl-C71-butyric acid methyl ester (PC71BM). They achieve power conversion efficiencies (up to 5.33%) high for polymers having such large bandgaps, ca. 2.0 eV (optical) and 2.5 eV (electrochemical). Grazing incidence wide-angle X-ray scattering (GIWAXS) reveals strong correlations between π–π stacking distance and regularity, polymer backbone planarity, optical absorption maximum energy, and photovoltaic efficiency.
Co-reporter:Sung Cho, Brian S. Rolczynski, Tao Xu, Luping Yu, and Lin X. Chen
The Journal of Physical Chemistry B 2015 Volume 119(Issue 24) pp:7447-7456
Publication Date(Web):January 26, 2015
DOI:10.1021/jp5111345
Using ultrafast polarization-controlled transient absorption (TA) measurements, dynamics of the initial exciton states were investigated on the time scale of tens of femtoseconds to about 80 ps in two different types of conjugated polymers extensively used in active layers of organic photovoltaic devices. These polymers are poly(3-fluorothienothiophenebenzodithiophene) (PTB7) and poly-3-hexylthiophene (P3HT), which are charge-transfer polymers and homopolymers, respectively. In PTB7, the initial excitons with excess vibrational energy display two observable ultrafast time constants, corresponding to coherent exciton diffusion before the vibrational relaxation, and followed by incoherent exciton diffusion processes to a neighboring local state after the vibrational relaxation. In contrast, P3HT shows only one exciton diffusion or conformational motion time constant of 34 ps, even though its exciton decay kinetics are multiexponential. Based on the experimental results, an exciton dynamics mechanism is conceived taking into account the excitation energy and structural dependence in coherent and incoherent exciton diffusion processes, as well as other possible deactivation processes including the formation of the pseudo-charge-transfer and charge separate states, as well as interchain exciton hopping or coherent diffusion.
Co-reporter:Luyao Lu
Advanced Materials 2014 Volume 26( Issue 26) pp:4413-4430
Publication Date(Web):
DOI:10.1002/adma.201400384
Solution processed single junction polymer solar cells (PSCs) have been developed from less than 1% power conversion efficiency (PCE) to beyond 9% PCE in the last decade. The significant efficiency improvement comes from progress in both rational design of donor polymers and innovation of device architectures. Among all the novel high efficient donor polymers, PTB7 stands out as the most widely used one for solar cell studies. Herein the recent development of PTB7 solar cells is reviewed. Detailed discussion of basic property, structure property relationship, morphology study, interfacial engineering, and inorganic nanomaterials incorporation is provided. Possible future directions for further increasing the performance of PTB7 solar cells are discussed.
Co-reporter:Tao Xu, Luping Yu
Materials Today 2014 Volume 17(Issue 1) pp:11-15
Publication Date(Web):January–February 2014
DOI:10.1016/j.mattod.2013.12.005
Organic photovoltaic cells are promising in terms of their light weight, mechanically flexibility, ease of processing and low cost. Establishing a predictive understanding between the chemical structures and physical properties of polymers is still challenging, and continuous effort is needed to progress toward full commercialization. In this review, recent progress in polymer/fullerene systems is highlighted and four synthetic principles are summarized to engineer the bandgap and tune the energy levels and the solubility of the targeted polymers.
Co-reporter:Jodi M. Szarko;Brian S. Rolczynski;Sylvia J. Lou;Tao Xu;Joseph Strzalka;Tobin J. Marks;Lin X. Chen
Advanced Functional Materials 2014 Volume 24( Issue 1) pp:10-26
Publication Date(Web):
DOI:10.1002/adfm.201301820
Exciton dissociation is a key step for the light energy conversion to electricity in organic photovoltaic (OPV) devices. Here, excitonic dissociation pathways in the high-performance, low bandgap “in-chain donor–acceptor” polymer PTB7 by transient optical absorption (TA) spectroscopy in solutions, neat films, and bulk heterojunction (BHJ) PTB7:PC71BM (phenyl-C71-butyric acid methyl ester) films are investigated. The dynamics and energetics of the exciton and intra-/intermolecular charge separated states are characterized. A distinct, dynamic, spectral red-shift of the polymer cation is observed in the BHJ films in TA spectra following electron transfer from the polymer to PC71BM, which can be attributed to the time evolution of the hole–electron spatial separation after exciton splitting. Effects of film morphology are also investigated and compared to those of conjugated homopolymers. The enhanced charge separation along the PTB7 alternating donor–acceptor backbone is understood by intramolecular charge separation through polarized, delocalized excitons that lower the exciton binding energy. Consequently, ultrafast charge separation and transport along these polymer backbones reduce carrier recombination in these largely amorphous films. This charge separation mechanism explains why higher degrees of PCBM intercalation within BHJ matrices enhances exciton splitting and charge transport, and thus increase OPV performance. This study proposes new guidelines for OPV materials development.
Co-reporter:Tao Xu;Luyao Lu;Tianyue Zheng;Jodi M. Szarko;Alexer Schneider;Lin X. Chen
Advanced Functional Materials 2014 Volume 24( Issue 22) pp:3432-3437
Publication Date(Web):
DOI:10.1002/adfm.201303688
This paper describes the synthesis of low bandgap copolymers incorporating an artificial sweetener derivative, N-alkyl, 3-oxothieno[3,4-d]isothiazole 1,1-dioxide (TID). This new TID unit is identical to the well-known thieno[3,4-c]pyrrole-4,6-dione (TPD) unit except that one carbonyl has been replaced by a sulfonyl group. Semi-empirical calculations on the local dipole moment change between ground and excited states (Δμge) in the repeating units of the new polymer indicate that the replacement of the carbonyl by a sulfonyl group leads to larger Δμge values. The resulting polymers exhibit a diminished power-conversion efficiency (PCE) compared to a bulk heterojunction (BHJ) solar cells with PC71BM as an acceptor, which extends the correlation between PCE and Δμge of single repeating units in p-type polymers to a new regime. Detailed studies show that the strongly electron-withdrawing sulfonyl group is detrimental to charge separation in alternating copolymers containing a TID unit.
Co-reporter:In Hwan Jung, Wai-Yip Lo, Jaeyoung Jang, Wei Chen, Donglin Zhao, Erik S. Landry, Luyao Lu, Dmitri V. Talapin, and Luping Yu
Chemistry of Materials 2014 Volume 26(Issue 11) pp:3450
Publication Date(Web):May 8, 2014
DOI:10.1021/cm500832h
New electron withdrawing monomers, thieno[2′,3′:5′,6′]pyrido[3,4-g]thieno[3,2-c]isoquinoline-5,11(4H,10H)-dione (TPTI) and fluorenedicyclopentathiophene dimalononitrile (CN), have been developed and used to form 12 alternating polymers having different monomer combinations: (a) weak donating monomer–strong accepting monomer, (b) weak accepting monomer–strong accepting monomer, (c) weak accepting monomer–weak accepting monomer, and (d) strong donating monomer–strong accepting monomer. It was found that lowest unoccupied molecular orbital (LUMO) energy levels of polymers are significantly determined by stronger electron accepting monomers and highest occupied molecular orbital (HOMO) energy levels by the weak electron accepting monomers. In addition, fluorescent quantum yields of the TPTI-based polymers in chloroform solution are significantly decreased as the LUMO energy levels of the TPTI series of polymers become deeper. The quantum yield was found to be closely related with the photovoltaic properties, which reflects the effect of internal polarization on the photovoltaic properties. Only the electron accepting polymers showing SCLC mobility higher than 10–4 cm2/(V s) exhibited photovoltaic performance in blend films with a donor polymer, and the PTB7:PNPDI (1:1.8 w/w) device exhibited the highest power conversion efficiency of 1.03% (Voc = 0.69 V, Jsc = −4.13 mA/cm2, FF = 0.36) under AM 1.5G condition, 100 W/cm2. We provide a large set of systematic structure–property relationships, which gives new perspectives for the design of electron accepting materials.
Co-reporter:Tianyue Zheng, Luyao Lu, Nicholas E. Jackson, Sylvia J. Lou, Lin X. Chen, and Luping Yu
Macromolecules 2014 Volume 47(Issue 18) pp:6252-6259
Publication Date(Web):September 9, 2014
DOI:10.1021/ma501152v
This work describes an efficient synthetic method for creating ladder-type, oligomeric donor monomers with fused thienobenzothiophene structures. These monomers are copolymerized with fluorinated thieno[3,4-b]thiophene ester to form a series of polymers which are investigated as donor materials in polymer/fullerene solar cells. Photophysical and electrochemical characterizations are used in conjunction with quantum-chemical calculations to identify the interplay of quinoidal and charge transfer character in the optical gaps of conjugated copolymers, providing broadly applicable design rules for tuning the excitation character of conjugated copolymers. X-ray diffraction, mobility measurements, and solar cell device characterization are used to analyze neat films and bulk heterojunctions of these copolymers, demonstrating the importance of the spatial symmetry of the donor and acceptor unit in determining the charge transport characteristics of conjugated copolymers.
Co-reporter:Luyao Lu ; Tao Xu ; In Hwan Jung
The Journal of Physical Chemistry C 2014 Volume 118(Issue 40) pp:22834-22839
Publication Date(Web):September 16, 2014
DOI:10.1021/jp5036663
The interfacial energy level alignment is shown to play an important role in determining solar cell performance. Replacing hole transport layer poly(3,4-ethylene dioxythiophene)–(polystyrene sulfonic acid) (PEDOT:PSS) with vanadium pentoxide (V2O5) leads to a simultaneous improvement in short-circuit current density (Jsc), open-circuit voltage (Voc) and fill factor (FF) for two donor polymers with deep HOMO energy levels, resulting in a power conversion efficiency (PCE) of 7.03% and 4.14%. This is 18% and 106% increase in PCE over the 5.97% and 2.01% achieved with PEDOT:PSS. V2O5 is shown to increase Jsc and FF by enhancing hole mobility, reducing bimolecular recombination, and facilitating charge collection and to maximize Voc by providing a better ohmic contact. We also demonstrate that PEDOT:PSS still works better for donor polymers with a HOMO energy level around 5.1 eV, such as PTB7.
Co-reporter:Brian S. Rolczynski, Jodi M. Szarko, Hae Jung Son, Luping Yu, and Lin X. Chen
The Journal of Physical Chemistry Letters 2014 Volume 5(Issue 11) pp:1856-1863
Publication Date(Web):May 13, 2014
DOI:10.1021/jz5005957
Charge-transfer copolymers with local electron density gradients, systematically modified by quantity and position of fluorination, result in widely variable (2–8%) power conversion efficiencies (PCEs). Ultrafast, near-infrared, transient absorption spectroscopy on the corresponding films reveals the influence of exciton polarity on ultrafast populations and decay dynamics for the charge-separated and charge-transfer states as well as their strong correlation to device PCEs. By using an excitation energy-dependent, dynamic red shift in the transient absorption signal for the polymer cation, the exciton polarity induced by push–pull interactions within each polymer fragment is shown to enhance charge dissociation on time scales of tens to hundreds of picoseconds after excitation. These results suggest the important role played by the local electronic structure not only for exciton dissociation but also for device performance.Keywords: carrier diffusion; charge-transfer polymer; exciton dissociation dynamics; organic photovoltaics; polarized exciton; ultrafast transient absorption;
Co-reporter:Hae Jung Son;Luyao Lu;Wei Chen;Tao Xu;Tianyue Zheng;Bridget Carsten;Joseph Strzalka;Seth B. Darling;Lin X. Chen
Advanced Materials 2013 Volume 25( Issue 6) pp:838-843
Publication Date(Web):
DOI:10.1002/adma.201204238
Co-reporter:Luyao Lu, Zhiqiang Luo, Tao Xu, and Luping Yu
Nano Letters 2013 Volume 13(Issue 1) pp:59-64
Publication Date(Web):December 13, 2012
DOI:10.1021/nl3034398
This article describes a cooperative plasmonic effect on improving the performance of polymer bulk heterojunction solar cells. When mixed Ag and Au nanoparticles are incorporated into the anode buffer layer, dual nanoparticles show superior behavior on enhancing light absorption in comparison with single nanoparticles, which led to the realization of a polymer solar cell with a power conversion efficiency of 8.67%, accounting for a 20% enhancement. The cooperative plasmonic effect aroused from dual resonance enhancement of two different nanoparticles. The idea was further unraveled by comparing Au nanorods with Au nanoparticles for solar cell application. Detailed studies shed light into the influence of plasmonic nanostructures on exciton generation, dissociation, and charge recombination and transport inside thin film devices.
Co-reporter:Luyao Lu, Tao Xu, Wei Chen, Ju Min Lee, Zhiqiang Luo, In Hwan Jung, Hyung Il Park, Sang Ouk Kim, and Luping Yu
Nano Letters 2013 Volume 13(Issue 6) pp:2365-2369
Publication Date(Web):May 1, 2013
DOI:10.1021/nl304533j
This paper reports an improved solar cell performance of 8.6% by incorporation of N-doped multiwall carbon nanotubes (N-MCNTs) into BHJ solar cells composed of PTB7 and PC71BM. It was demonstrated for the first time that incorporation of N-MCNTs leads to not only increased nanocrystallite sizes but also smaller phase-separated domain sizes of both PTB7 copolymers and PC71BM from X-ray scattering study. The results show that N-MCNTs could serve as both exciton dissociation centers and charge transfer channels. The enhanced charge dissociation probabilities and effective charge carrier lifetime in the active layer material offer evidence to support the conclusion that N-MCNTs facilitated charge separation and transport.
Co-reporter:Hae Jung Son, Bridget Carsten, In Hwan Jung and Luping Yu
Energy & Environmental Science 2012 vol. 5(Issue 8) pp:8158-8170
Publication Date(Web):19 Apr 2012
DOI:10.1039/C2EE21608F
In this perspective article, we discuss the development of organic photovoltaic (OPVs) solar cells. Our focus will be on discussing the development of new donor polymers and device technologies, which resulted in enormous progress in OPV performances with power conversion efficiencies (PCEs) of 8–9%. However, for the wide spread usage of OPVs, high module efficiencies (>10%) and lifetimes suitable for commercial applications are required. To achieve such goals, interdisciplinary advances in the development of new light-harvesting materials, the improvement of device structures, and the development of cost effective device processing methods are crucial. In particular, new donor polymers overcoming the drawbacks of current polymer solar cells can play an important role to further improve the PCEs and device stability. This perspective article addresses the polymer design criteria that have been distilled out from the research of the past 20 years: energy level matching, nano-morphology of polymer/acceptor blend films, local dipole moments of the polymer chains, and stability. Also, we introduce representative donor polymers and describe the research progress in the polymers development to move beyond certain milestones. We emphasize the importance of the synergetic research efforts in developing new materials, such as the design of new polymers with improved physical properties, the development of device technologies and a fundamental understanding of OPV mechanisms, which will help to continuously enhance the performance of OPVs.
Co-reporter:Jingbi You;Chun-Chao Chen;Letian Dou;Seiichiro Murase;Hsin-Sheng Duan;Steven A. Hawks;Tao Xu;Hae Jung Son;Gang Li;Yang Yang
Advanced Materials 2012 Volume 24( Issue 38) pp:5267-5272
Publication Date(Web):
DOI:10.1002/adma.201201958
Co-reporter:Brian S. Rolczynski ; Jodi M. Szarko ; Hae Jung Son ; Yongye Liang ; Luping Yu ;Lin X. Chen
Journal of the American Chemical Society 2012 Volume 134(Issue 9) pp:4142-4152
Publication Date(Web):February 6, 2012
DOI:10.1021/ja209003y
Record-setting organic photovoltaic cells with PTB polymers have recently achieved ∼8% power conversion efficiencies (PCE). A subset of these polymers, the PTBF series, has a common conjugated backbone with alternating thieno[3,4-b]thiophene and benzodithiophene moieties but differs by the number and position of pendant fluorine atoms attached to the backbone. These electron-withdrawing pendant fluorine atoms fine tune the energetics of the polymers and result in device PCE variations of 2–8%. Using near-IR, ultrafast optical transient absorption (TA) spectroscopy combined with steady-state electrochemical methods we were able to obtain TA signatures not only for the exciton and charge-separated states but also for an intramolecular (“pseudo”) charge-transfer state in isolated PTBF polymers in solution, in the absence of the acceptor phenyl-C61-butyric acid methyl ester (PCBM) molecules. This led to the discovery of branched pathways for intramolecular, ultrafast exciton splitting to populate (a) the charge-separated states or (b) the intramolecular charge-transfer states on the subpicosecond time scale. Depending on the number and position of the fluorine pendant atoms, the charge-separation/transfer kinetics and their branching ratios vary according to the trend for the electron density distribution in favor of the local charge-separation direction. More importantly, a linear correlation is found between the branching ratio of intramolecular charge transfer and the charge separation of hole–electron pairs in isolated polymers versus the device fill factor and PCE. The origin of this correlation and its implications in materials design and device performance are discussed.
Co-reporter:Haythem A. Saadeh, Luyao Lu, Feng He, Joseph E. Bullock, Wei Wang, Bridget Carsten, and Luping Yu
ACS Macro Letters 2012 Volume 1(Issue 3) pp:361
Publication Date(Web):February 14, 2012
DOI:10.1021/mz300004t
Herein we describe the synthesis of a new series of copolymers (PSeBx) containing selenopheno[3,4-b]selenophene and benzodiselenophene, which exhibited a high power conversion efficiency (PCE) of 6.87% in a bulk heterojunction (BHJ) solar cell device (PSeB2/PC71BM). In comparison with its thiophene analogue, PTB9, the new polyselenopheno[3,4-b]selenophene-co-benzodiselenophene (PSeB2) showed a lower band gap and improved charge carrier mobility as high as 1.35 × 10–3 cm2 V–1 s–1.
Co-reporter:Shengwen Yuan;Desiree White;Alex Mason;Briana Reprogle;Magali S. Ferron;Di-Jia Liu
Macromolecular Rapid Communications 2012 Volume 33( Issue 5) pp:407-413
Publication Date(Web):
DOI:10.1002/marc.201100797
Abstract
The design and synthesis of a new porous organic polymer (POP) incorporated with cobalt carbonyl complexes through built-in bipyridinic coordination sites for hydrogen storage are described. A thermal activation process was developed to remove the ligated carbonyl and carbon dioxide in order to expose the cobalt atomically inside of porous structure. Various spectroscopic and physical characterization techniques were used to study the coordinated Co sites and the POP's surface property. Upon thermal activation, this new cobalt-containing POP showed improved hydrogen uptake capacity and isosteric heat of adsorption.
Co-reporter:Mayank Mayukh;In Hwan Jung;Feng He
Journal of Polymer Science Part B: Polymer Physics 2012 Volume 50( Issue 15) pp:1057-1070
Publication Date(Web):
DOI:10.1002/polb.23102
Abstract
The power conversion efficiency of an organic solar cell has now exceeded the 10% mark, which is a significant improvement in the last decade. This has been made possible due to the development of low-band-gap polymers with tunable electron affinity, ionization potential, solubility, and miscibility with the fullerene acceptor, and the improved understanding of the factors affecting the critical device parameters such as the VOC and the JSC. This review examines the latest strategies, results, and trends that have evolved in the design of solar cells with better efficiency and durability. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012
Co-reporter:Zhuo Wang, Shengwen Yuan, Alex Mason, Briana Reprogle, Di-Jia Liu, and Luping Yu
Macromolecules 2012 Volume 45(Issue 18) pp:7413-7419
Publication Date(Web):September 17, 2012
DOI:10.1021/ma301426e
This article describes the synthesis of four porous polymers containing Ni–porphyrin units with Brunauer–Emmet–Teller (BET) specific surface areas up to 1711 m2/g achieved. The isotherm gas adsorptions of hydrogen, methane and carbon dioxide over these polymers were measured. The adsorption selectivity for methane and carbon dioxide over nitrogen were also investigated. While the initial isosteric heat of adsorption (ΔHads) was around 8–9 kJ/mol for hydrogen, it reached 23 kJ/mol for methane and 29 kJ/mol for carbon dioxide. CO2/N2 selectivity as high as 19 (calculated from single gas adsorption isotherms) was also achieved with one of these four polymers.
Co-reporter:Bridget Carsten, Jodi M. Szarko, Luyao Lu, Hae Jung Son, Feng He, Youssry Y. Botros, Lin X. Chen, and Luping Yu
Macromolecules 2012 Volume 45(Issue 16) pp:6390-6395
Publication Date(Web):August 2, 2012
DOI:10.1021/ma3011119
We report synthesis and characterizations of two novel series of polymers, namely the PBTZ and PBIT series. The PBTZ1 polymer was synthesized as a copolymer of 4,8-bis(2-butyloctyl)benzo[1,2-b:4,5-b′]dithiophene (BDT) along with 2,5-bis(2-ethylhexyl)-3,6-bisthiazol-2-yl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (TzDPP), while PBTZ2 was a copolymer of TzDPP and 2-(1-butylheptyl)thieno[3,4-d]thiazole (TTz). The PBIT series based on dithienopyrrolobenzothiadiazole (DPBT), and BDT was also synthesized. The PBIT series of polymers showed enhanced ground and excited state dipole moments (μg and μe) when compared to the previously reported PBB3 polymer, while PBTZ1 showed the largest dipole change (1.52 D) from ground to excited state (Δμge) in respective single polymer units. It was found that the power conversion efficiencies of the polymer series were strongly correlated to Δμge. The results reported demonstrate the utility of the calculated parameter Δμge of single units of the polymers to predict the performance of donor–acceptor copolymers in photovoltaic devices. We rationalize this result based on the large degree of polarization in the excited state, which effectively lowers the Coulomb binding energy of the exciton in the excited state and leads to faster charge separation kinetics, thus facilitating the full separation of electron and hole.
Co-reporter:Bridget Carsten, Feng He, Hae Jung Son, Tao Xu, and Luping Yu
Chemical Reviews 2011 Volume 111(Issue 3) pp:1493-1528
Publication Date(Web):February 11, 2011
DOI:10.1021/cr100320w
Co-reporter:Huidong Zang;Yongye Liang;Bin Hu
Advanced Energy Materials 2011 Volume 1( Issue 5) pp:923-929
Publication Date(Web):
DOI:10.1002/aenm.201100304
Abstract
This article reports experimental studies on internal charge dissociation, transport, and collection by using magnetic field effects of photocurrent (MFEPC) and light-assisted dielectric response (LADR) in highly-efficient organic solar cells based on photovoltaic polymer PTB2 and PTB4 with intra-molecular “donor–acceptor” interaction. The MFEPC at low-field (< 150 mT) indicates that intra-molecular “donor-acceptor” interaction generates charge dissociation in un-doped PTB2 and PTB4 films, which is similar to that in lightly doped P3HT (Poly(3-hexylthiophene)) with 5 wt% PCBM (1-(3-methyloxycarbonyl)-propyl-1-phenyl (6,6) C61). After PTB2 and PTB4 are mixed with PCBM to form bulk-heterojunctions, the MFEPC at high-field (> 150 mT) reveals that the charge-transfer complexes formed at PTB2:PCBM and PTB4:PCBM interfaces have much lower binding energies due to stronger electron-withdrawing abilities, as compared to the P3HT:PCBM device, towards the generation of photocurrent. Furthermore, the light-assisted dielectric response: LADR indicates that the PTB2:PCBM and PTB4:PCBM solar cells exhibit larger capacitances relative to P3HT:PCBM device under photoexcitation. This reflects that the PTB2:PCBM and PTB4:PCBM bulk heterojunctions have more effective charge transport and collection than the P3HT:PCBM counterpart. As a result, our experimental results indicate that intra-molecular “donor-acceptor” interaction plays an important role to enhance charge dissociation, transport, and collection in bulk-heterojunction organic solar cells.
Co-reporter:Wei Chen, Tao Xu, Feng He, Wei Wang, Cheng Wang, Joseph Strzalka, Yun Liu, Jianguo Wen, Dean J. Miller, Jihua Chen, Kunlun Hong, Luping Yu, and Seth B. Darling
Nano Letters 2011 Volume 11(Issue 9) pp:3707-3713
Publication Date(Web):August 8, 2011
DOI:10.1021/nl201715q
PTB7 semiconducting copolymer comprising thieno[3,4-b]thiophene and benzodithiophene alternating repeat units set a historic record of solar energy conversion efficiency (7.4%) in polymer/fullerene bulk heterojunction solar cells. To further improve solar cell performance, a thorough understanding of structure–property relationships associated with PTB7/fullerene and related organic photovoltaic (OPV) devices is crucial. Traditionally, OPV active layers are viewed as an interpenetrating network of pure polymers and fullerenes with discrete interfaces. Here we show that the active layer of PTB7/fullerene OPV devices in fact involves hierarchical nanomorphologies ranging from several nanometers of crystallites to tens of nanometers of nanocrystallite aggregates in PTB7-rich and fullerene-rich domains, themselves hundreds of nanometers in size. These hierarchical nanomorphologies are coupled to significantly enhanced exciton dissociation, which consequently contribute to photocurrent, indicating that the nanostructural characteristics at multiple length scales is one of the key factors determining the performance of PTB7 copolymer, and likely most polymer/fullerene systems, in OPV devices.
Co-reporter:Bridget Carsten ; Jodi M. Szarko ; Hae Jung Son ; Wei Wang ; Luyao Lu ; Feng He ; Brian S. Rolczynski ; Sylvia J. Lou ; Lin X. Chen
Journal of the American Chemical Society 2011 Volume 133(Issue 50) pp:20468-20475
Publication Date(Web):November 12, 2011
DOI:10.1021/ja208642b
A new low band gap copolymer PBB3 containing [6,6′]bi[thieno[3,4-b]thiophenyl]-2,2′-dicarboxylic acid bis-(2-butyloctyl) ester (BTT) and 4,8-bis(2-butyloctyl)benzo[1,2-b:4,5-b′]dithiophene (BDT) units was synthesized and tested for solar cell efficiency. PBB3 showed a broad absorbance in the near-IR region with a substantially red-shifted (by more than 100 nm) λmax at 790 nm as compared to the PTB series of polymers, which have been previously reported. The PBB3 polymer also showed both a favorable energy level match with PCBM (with a LUMO energy level of −3.29 eV) and a favorable film domain morphology as evidenced by TEM images. Despite these seemingly optimal parameters, a bulk heterojunction (BHJ) photovoltaic device fabricated from a blend of PBB3 and PC71BM showed an overall power conversion efficiency (PCE) of only 2.04% under AM 1.5G/100 mW cm–2. The transient absorption spectra of PBB3 showed the absence of cationic and pseudo charge transfer states that were observed previously in the PTB series polymers, which were also composed of alternating thienothiophene (TT) and BDT units. We compared the spectral features and electronic density distribution of PBB3 with those of PTB2, PTB7, and PTBF2. While PTB2 and PTB7 have substantial charge transfer characteristics and also relatively large local internal dipoles through BDT to TT moieties, PTBF2 and PBB3 have minimized internal dipole moments due to the presence of two adjacent TT units (or two opposing fluorine atoms in PTBF2) with opposite orientations or internal dipoles. PBB3 showed a long-lived excitonic state and the slowest electron transfer dynamics of the series of polymers, as well as the fastest recombination rate of the charge-separated (CS) species, indicating that electrons and holes are more tightly bound in these species. Consequently, substantially lower degrees of charge separation were observed in both PBB3 and PTBF2. These results show that not only the energetics but also the internal dipole moment along the polymer chain may be critical in maintaining the pseudocharge transfer characteristics of these systems, which were shown to be partially responsible for the high PCE device made from the PTB series of low band gap copolymers.
Co-reporter:Feng He ; Wei Wang ; Wei Chen ; Tao Xu ; Seth B. Darling ; Joseph Strzalka ; Yun Liu
Journal of the American Chemical Society 2011 Volume 133(Issue 10) pp:3284-3287
Publication Date(Web):February 18, 2011
DOI:10.1021/ja1110915
A series of semiconducting copolymers (PTAT-x) containing extended π-conjugated tetrathienoanthracene units have been synthesized. It was shown that the extended conjugation system enhanced the π−π stacking in the polymer/PC61BM blend films and facilitated the charge transport in heterojunction solar cell devices. After structural fine-tuning, the polymer with bulky 2-butyloctyl side chains (PTAT-3) exhibited a PCE of 5.6% when it was blended with PC61BM.
Co-reporter:Hae Jung Son, Feng He, Bridget Carsten and Luping Yu
Journal of Materials Chemistry A 2011 vol. 21(Issue 47) pp:18934-18945
Publication Date(Web):06 Oct 2011
DOI:10.1039/C1JM12388B
Over the last ten years, polymer solar cells have been developed as an attractive alternative to the traditional silicon photovoltaic devices. Remarkable progress has been made in polymer-fullerene solar cells and several polymers have shown power conversion efficiencies (PCEs) greater than 7%. The most important recent development has been the synthesis of new low bandgap polymers with optimal properties for the solar cells. Herein we provide an overview of the key strategies of optimization of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels in the design of new low bandgap conjugated polymers. Detailed examples of representative donor polymers, the current state of the art in their solar cell performances and possible future directions for development of new polymers with improved efficiencies are discussed.
Co-reporter:Feng He and Luping Yu
The Journal of Physical Chemistry Letters 2011 Volume 2(Issue 24) pp:3102-3113
Publication Date(Web):November 22, 2011
DOI:10.1021/jz201479b
The photovoltaic effect in organic materials is an interesting research area because it offers fundamental knowledge, waiting to be explored, and the potential to offer low-cost technology to replace traditional inorganic solar cells. Worldwide research effort in this area is largely motivated by the desire to develop a new technology platform to cost-effectively harvest solar energy. Currently, researchers from different disciplines are focusing on developing new materials, performing physical studies to gain basic understanding of charge separation and transport mechanisms in these disordered soft material systems, and formulating new device structures and processing conditions in order to push the solar energy conversion efficiency above threshold for commercialization. This Perspective reviews some of the work that has been done over the past 20 years and describes the efforts in materials development to move beyond certain milestones. We emphasize the importance of a synergistic approach in developing new materials to continuously enhance the performance of organic photovoltaic cells.
Co-reporter:Ian P. Murray, Sylvia J. Lou, Laura J. Cote, Stephen Loser, Cameron J. Kadleck, Tao Xu, Jodi M. Szarko, Brian S. Rolczynski, James E. Johns, Jiaxing Huang, Luping Yu, Lin X. Chen, Tobin J. Marks, and Mark C. Hersam
The Journal of Physical Chemistry Letters 2011 Volume 2(Issue 24) pp:3006-3012
Publication Date(Web):November 12, 2011
DOI:10.1021/jz201493d
Organic photovoltaic (OPV) materials have recently garnered significant attention as enablers of high power conversion efficiency (PCE), low-cost, mechanically flexible solar cells. Nevertheless, further understanding-based materials developments will be required to achieve full commercial viability. In particular, the performance and durability of many current generation OPVs are limited by poorly understood interfacial phenomena. Careful analysis of typical OPV architectures reveals that the standard electron-blocking layer, poly-3,4-ethylenedioxy-thiophene:poly(styrene sulfonate) (PEDOT:PSS), is likely a major factor limiting the device durability and possibly performance. Here we report that a single layer of electronically tuned graphene oxide is an effective replacement for PEDOT:PSS and that it significantly enhances device durability while concurrently templating a performance-optimal active layer π-stacked face-on microstructure. Such OPVs based on graphene oxide exhibit PCEs as high as 7.5% while providing a 5× enhancement in thermal aging lifetime and a 20× enhancement in humid ambient lifetime versus analogous PEDOT:PSS-based devices.Keywords: bulk heterojunction; GO; interfacial layer; lifetime; PTB7; reliability; solar cell;
Co-reporter:Joshua Hihath, Christopher Bruot, Hisao Nakamura, Yoshihiro Asai, Ismael Díez-Pérez, Youngu Lee, Luping Yu, and Nongjian Tao
ACS Nano 2011 Volume 5(Issue 10) pp:8331
Publication Date(Web):September 20, 2011
DOI:10.1021/nn2030644
Designing, controlling, and understanding rectification behavior in molecular-scale devices has been a goal of the molecular electronics community for many years. Here we study the transport behavior of a single molecule diode, and its nonrectifying, symmetric counterpart at low temperatures, and at both low and high biases to help elucidate the electron–phonon interactions and transport mechanisms in the rectifying system. We find that the onset of current rectification occurs at low biases, indicating a significant change in the elastic transport pathway. However, the peaks in the inelastic electron tunneling (IET) spectrum are antisymmetric about zero bias and show no significant changes in energy or intensity in the forward or reverse bias directions, indicating that despite the change in the elastic transmission probability there is little impact on the inelastic pathway. These results agree with first principles calculations performed to evaluate the IETS, which also allow us to identify which modes are active in the single molecule junction.Keywords: IETS; inelastic electron tunneling spectroscopy; molecular electronics; single-molecule conductance; STM-break junction
Co-reporter:Youngu Lee;ShengWen Yuan
Science China Chemistry 2011 Volume 54( Issue 2) pp:410-414
Publication Date(Web):2011 February
DOI:10.1007/s11426-010-4206-6
Charge transport through single molecular neutral mono- and di-cobalt(II) complexes with π-conjugated macromolecular wire was investigated. Scanning tunnelling spectroscopy (STS) studies revealed that the mono-cobalt(II) complex showed a pronounced rectifying effect with a large rectification ratio and finely featured NDR peaks, while the di-cobalt(II) complex showed a relatively symmetric electron transport without clear NDR peaks. The results are explained based on the dipolar and electronic effects.
Co-reporter:Matthew R. Hammond, R. Joseph Kline, Andrew A. Herzing, Lee J. Richter, David S. Germack, Hyun-Wook Ro, Christopher L. Soles, Daniel A. Fischer, Tao Xu, Luping Yu, Michael F. Toney, and Dean M. DeLongchamp
ACS Nano 2011 Volume 5(Issue 10) pp:8248
Publication Date(Web):September 22, 2011
DOI:10.1021/nn202951e
We report quantitative measurements of ordering, molecular orientation, and nanoscale morphology in the active layer of bulk heterojunction (BHJ) organic photovoltaic cells based on a thieno[3,4-b]thiophene-alt-benzodithiophene copolymer (PTB7), which has been shown to yield very high power conversion efficiency when blended with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). A surprisingly low degree of order was found in the polymer—far lower in the bulk heterojunction than in pure PTB7. X-ray diffraction data yielded a nearly full orientation distribution for the polymer π-stacking direction within well-ordered regions, revealing a moderate preference for π-stacking in the vertical direction (“face-on”). By combining molecular orientation information from polarizing absorption spectroscopies with the orientation distribution of ordered material from diffraction, we propose a model describing the PTB7 molecular orientation distribution (ordered and disordered), with the fraction of ordered polymer as a model parameter. This model shows that only a small fraction (≈20%) of the polymer in the PTB7/PC71BM blend is ordered. Energy-filtered transmission electron microscopy shows that the morphology of PTB7/PC71BM is composed of nanoscale fullerene-rich aggregates separated by polymer-rich regions. The addition of diiodooctane (DIO) to the casting solvent, as a processing additive, results in smaller domains and a more finely interpenetrating BHJ morphology, relative to blend films cast without DIO.Keywords: bulk heterojunction; crystallinity; organic photovoltaics; orientation; polymers
Co-reporter:Wei Wang and Luping Yu
Langmuir 2011 Volume 27(Issue 6) pp:2084-2087
Publication Date(Web):January 27, 2011
DOI:10.1021/la104002s
A novel diode molecule consisting of α-hydroxyphenyl pyridine motif was synthesized. Molecular self-assembly onto gold electrode surface leads to moderate rectifying behavior. The replacement of the hydroxyl proton by a methyl group leads to the disruption of intramolecular hydrogen bonding and yields a twisted molecular conformation. Comparing the current−voltage characteristics between these two compounds reveals that the presence of intramolecular hydrogen bonding substantially improves the molecular conductivity.
Co-reporter:Jodi M. Szarko, Brian S. Rolczynski, Jianchang Guo, Yongye Liang, Feng He, Michael W. Mara, Luping Yu, and Lin X. Chen
The Journal of Physical Chemistry B 2010 Volume 114(Issue 45) pp:14505-14513
Publication Date(Web):May 21, 2010
DOI:10.1021/jp101925b
Conjugated oligomers containing a common central thienothiophene unit symmetrically connected to two identical thiophene oligomers were studied as model systems for a series of low bandgap organic diblock copolymers. The oligothiophene side chain fragments were varied in length as a means to tune the electronic coupling between the thienothiophene and oligothiophene moieties. The fragment length dependence of both the ground- and excited-state electronic and structural properties of a series of diblock oligomers were investigated in detail. The charge transfer character in these diblock oligomers, revealed by their optical absorption and fluorescence spectra, is responsible for their low band gap and energy gap tunability compared with their homooligomer counterparts. The electronic spectra and theoretical analysis indicate a partially localized central charge in the first excited state. Using experimental results and comparing them with theoretical calculations, we estimate that the electronic effects from a single thienothiophene unit spreads over seven to nine adjacent units through π-conjugation along the oligomers.
Co-reporter:Yongye Liang, Danqin Feng, Jianchang Guo, Jodi M. Szarko, Claire Ray, Lin X. Chen and Luping Yu
Macromolecules 2009 Volume 42(Issue 4) pp:1091-1098
Publication Date(Web):January 21, 2009
DOI:10.1021/ma8023969
A regioregular conjugated oligomer (MF) and its polymer counterpart (PF) containing a thieno[3,4-b]thiophene moiety have been developed. The existence of thieno[3,4-b]thiophene extends the absorption of the molecules to longer wavelengths and increases the current density of solar cell devices using these materials. The regioregularity of the polymers from the incorporation of regioregular oligothiophene fragments also enhances hole mobility. Consequently, the polymers show higher solar energy conversion efficiencies in bulk heterojunction (BHJ) solar cells than the low molecular weight oligomers. Spectroscopic and structural studies reveal that composite films prepared from the polymer exhibit a larger charge carrier density and smaller domain sizes for the electron donor and acceptor than the oligomer counterpart. These results rationalize the origin for the higher solar cell efficiency.
Co-reporter:Youngu Lee, Brian Carsten and Luping Yu
Langmuir 2009 Volume 25(Issue 3) pp:1495-1499
Publication Date(Web):December 16, 2008
DOI:10.1021/la802923a
This paper describes the anchoring group effect of molecular diodes on rectifying behavior. Two molecular diodes with different anchoring groups, which are based on diblock co-oligomeric structures, have been synthesized and characterized. Scanning tunneling spectroscopy (STS) measurements revealed the correlation of rectifying effects in these molecular diodes with anchoring groups such as thiol and isocyanide. The combination of theoretical calculation and experimental results on these molecular diodes demonstrated that the rectifying effect could be affected by the nature of anchoring groups due to the bond dipoles at the interface and internal polarization inside the molecules.
Co-reporter:Lin Gan, Jennifer L. Olson, Clifton W. Ragsdale and Luping Yu
Chemical Communications 2008 (Issue 5) pp:573-575
Publication Date(Web):22 Nov 2007
DOI:10.1039/B714278A
A series of poly(β-aminosulfonamides) was synthesized and demonstrated to be efficient in vitro transfection reagents.
Co-reporter:Youngu Lee, Shengwen Yuan, Arturo Sanchez and Luping Yu
Chemical Communications 2008 (Issue 2) pp:247-249
Publication Date(Web):24 Oct 2007
DOI:10.1039/B712978E
This communication reports an asymmetric charge transport with a large rectification ratio and finely featured NDR (negative differential resistance) by d-orbitals of a neutral ruthenium(II) complex with a C2 axis of symmetry.
Co-reporter:Yongye Liang ; Shengqiang Xiao ; Danqin Feng
The Journal of Physical Chemistry C 2008 Volume 112(Issue 21) pp:7866-7871
Publication Date(Web):April 11, 2008
DOI:10.1021/jp711623w
A series of copolymers based on thieno [3,4-b]thiophene and thiophene unit have been synthesized. By controlling the ratio of thieno [3,4-b]thiophene to alkyl thiophene in the copolymer composition, the electro-optic properties of the copolymers can be fine tuned. It was shown that the energy gap of copolymers narrowed when the content of thieno [3,4-b]thiophene increased, brought by the decrease in lowest unoccupied molecular orbital and increase in highest occupied molecular orbital energy levels. When these copolymers were blended with [6,6]-phenyl-C61-butyric acid methyl ester to form solar cell’s active layer, an optimized copolymer composition was found that gave the best photovoltaic performance.
Co-reporter:Yongye Liang, Hengbin Wang, Shengwen Yuan, Youngu Lee, Lin Gan and Luping Yu
Journal of Materials Chemistry A 2007 vol. 17(Issue 21) pp:2183-2194
Publication Date(Web):10 Apr 2007
DOI:10.1039/B702271A
This article reviews the progress in conjugated block copolymers and co-oligomers. The discussion focuses on recent advances in the synthesis and supramolecular assemblies of conjugated diblock copolymers. New knowledge in supramolecular chemistry learned from studies of rod–coil conjugated diblock copolymers is discussed. This article also points out the limited success in obtaining unique electronic properties brought about by the conjugated nanostructures and discusses progress in another important class of block copolymers, rod–rod diblock copolymers. Progress in synthesis and characterization of the rod–rod block co-oligomers is summarized. Unique rectification effects in conjugated diblock co-oligomers are illustrated with several molecular systems.
Co-reporter:Hae Jung Son ; Wei Wang ; Tao Xu ; Yongye Liang ; Yue Wu ; Gang Li
Journal of the American Chemical Society () pp:
Publication Date(Web):January 25, 2011
DOI:10.1021/ja108601g
Herein, we describe the synthesis of fluorinated polythienothiophene-co-benzodithiophenes (PTBFs) and the characterization of their physical properties, especially their performance in solar cells. Fluorination of the polymer backbone lowered both the HOMO and LUMO energy levels and simultaneously widened the energy bandgap of the polymer (0.1−0.2 eV). Incorporation of fluorine into the various positions of the polymer backbone significantly affected the solar cells’ power conversion efficiency from 2.3% to 7.2%. Detailed studies revealed that the polymer containing mono-fluorinated thienothiophene gave the best solar cell performance. Perfluorination of the polymer backbone led to poor compatibility with PC71BM molecules, thus poor solar energy conversion efficiency. This is possibly due to the enhanced self-organization properties of the polymer chains and the fluorophobicity effect. Furthermore, it was found that perfluorination of the polymer backbone resulted in poor photochemical stability against singlet oxygen attack. Theoretical studies indicated that the internal polarization caused enhancement of the negative charge density on thienothiophene rings, which rendered them vulnerable to [2+4] cycloaddition reaction with singlet oxygen.
Co-reporter:Youngu Lee, Shengwen Yuan, Arturo Sanchez and Luping Yu
Chemical Communications 2008(Issue 2) pp:
Publication Date(Web):
DOI:10.1039/B712978E
Co-reporter:Lin Gan, Jennifer L. Olson, Clifton W. Ragsdale and Luping Yu
Chemical Communications 2008(Issue 5) pp:NaN575-575
Publication Date(Web):2007/11/22
DOI:10.1039/B714278A
A series of poly(β-aminosulfonamides) was synthesized and demonstrated to be efficient in vitro transfection reagents.
Co-reporter:Lianwei Li, Wai-Yip Lo, Zhengxu Cai, Na Zhang and Luping Yu
Chemical Science (2010-Present) 2016 - vol. 7(Issue 5) pp:
Publication Date(Web):
DOI:10.1039/C6SC00152A
Co-reporter:Hae Jung Son, Feng He, Bridget Carsten and Luping Yu
Journal of Materials Chemistry A 2011 - vol. 21(Issue 47) pp:NaN18945-18945
Publication Date(Web):2011/10/06
DOI:10.1039/C1JM12388B
Over the last ten years, polymer solar cells have been developed as an attractive alternative to the traditional silicon photovoltaic devices. Remarkable progress has been made in polymer-fullerene solar cells and several polymers have shown power conversion efficiencies (PCEs) greater than 7%. The most important recent development has been the synthesis of new low bandgap polymers with optimal properties for the solar cells. Herein we provide an overview of the key strategies of optimization of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels in the design of new low bandgap conjugated polymers. Detailed examples of representative donor polymers, the current state of the art in their solar cell performances and possible future directions for development of new polymers with improved efficiencies are discussed.
Co-reporter:Yongye Liang, Hengbin Wang, Shengwen Yuan, Youngu Lee, Lin Gan and Luping Yu
Journal of Materials Chemistry A 2007 - vol. 17(Issue 21) pp:NaN2194-2194
Publication Date(Web):2007/04/10
DOI:10.1039/B702271A
This article reviews the progress in conjugated block copolymers and co-oligomers. The discussion focuses on recent advances in the synthesis and supramolecular assemblies of conjugated diblock copolymers. New knowledge in supramolecular chemistry learned from studies of rod–coil conjugated diblock copolymers is discussed. This article also points out the limited success in obtaining unique electronic properties brought about by the conjugated nanostructures and discusses progress in another important class of block copolymers, rod–rod diblock copolymers. Progress in synthesis and characterization of the rod–rod block co-oligomers is summarized. Unique rectification effects in conjugated diblock co-oligomers are illustrated with several molecular systems.
Co-reporter:Alexander M. Schneider, Luyao Lu, Eric F. Manley, Tianyue Zheng, Valerii Sharapov, Tao Xu, Tobin J. Marks, Lin X. Chen and Luping Yu
Chemical Science (2010-Present) 2015 - vol. 6(Issue 8) pp:NaN4866-4866
Publication Date(Web):2015/06/04
DOI:10.1039/C5SC01427A
We report the properties of a new series of wide band gap photovoltaic polymers based on the N-alkyl 2-pyridone dithiophene (PDT) unit. These polymers are effective bulk heterojunction solar cell materials when blended with phenyl-C71-butyric acid methyl ester (PC71BM). They achieve power conversion efficiencies (up to 5.33%) high for polymers having such large bandgaps, ca. 2.0 eV (optical) and 2.5 eV (electrochemical). Grazing incidence wide-angle X-ray scattering (GIWAXS) reveals strong correlations between π–π stacking distance and regularity, polymer backbone planarity, optical absorption maximum energy, and photovoltaic efficiency.
.jpg)
![Poly[[2,2'-bipyridine]-5,5'-diyl[4,8-bis(decyloxy)benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]]](/data/chemimg/3726600/2001010-43-9.png)
![Poly[[2,2'-bipyridine]-5,5'-diyl[4,8-bis(decyloxy)benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]]](/data/chemimg/3726600/2001010-43-9_b.png)
![Poly[[2,9-bis(1-hexylheptyl)-1,2,3,8,9,10-hexahydro-1,3,8,10-tetraoxoanthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-5,12-diyl][2,2'-bipyridine]-5,5'-diyl]](/data/chemimg/3726600/2001010-41-7.png)
![Poly[[2,9-bis(1-hexylheptyl)-1,2,3,8,9,10-hexahydro-1,3,8,10-tetraoxoanthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-5,12-diyl][2,2'-bipyridine]-5,5'-diyl]](/data/chemimg/3726600/2001010-41-7_b.png)
![Poly[[2,2'-bipyridine]-5,5'-diyl[4,8-bis[2-[2-(2-methoxyethoxy)ethoxy]ethoxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]]](/data/chemimg/3726600/2001010-40-6.png)
![Poly[[2,2'-bipyridine]-5,5'-diyl[4,8-bis[2-[2-(2-methoxyethoxy)ethoxy]ethoxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]]](/data/chemimg/3726600/2001010-40-6_b.png)
![Anthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetrone, 5,12-dibromo-2,9-bis(1-hexylheptyl)-](/data/chemimg/152100/1174418-72-4.png)
![Anthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetrone, 5,12-dibromo-2,9-bis(1-hexylheptyl)-](/data/chemimg/152100/1174418-72-4_b.png)
![[4-hexyl-5-(3-hexyl-5-trimethylstannylthiophen-2-yl)thiophen-2-yl]-trimethylstannane](http://img.cochemist.com/ccimg/869600/869556-90-1.png)
![[4-hexyl-5-(3-hexyl-5-trimethylstannylthiophen-2-yl)thiophen-2-yl]-trimethylstannane](http://img.cochemist.com/ccimg/869600/869556-90-1_b.png)
![4,4-di-n-octyl-2,6-bis(trimethylstannyl)dithieno[3,2-b:2',3'-d]silole](http://img.cochemist.com/ccimg/1160200/1160106-15-9.png)
![4,4-di-n-octyl-2,6-bis(trimethylstannyl)dithieno[3,2-b:2',3'-d]silole](http://img.cochemist.com/ccimg/1160200/1160106-15-9_b.png)
![PROPANENITRILE, 3-[(4'-BROMO[1,1'-BIPHENYL]-4-YL)THIO]-](http://img.cochemist.com/ccimg/864000/863997-45-9.png)
![PROPANENITRILE, 3-[(4'-BROMO[1,1'-BIPHENYL]-4-YL)THIO]-](http://img.cochemist.com/ccimg/864000/863997-45-9_b.png)
![[1,1'-Biphenyl]-4-thiol, 4'-bromo-](http://img.cochemist.com/ccimg/220900/220805-21-0.png)
![[1,1'-Biphenyl]-4-thiol, 4'-bromo-](http://img.cochemist.com/ccimg/220900/220805-21-0_b.png)
![2,9-Di(tridecan-7-yl)anthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetraone](/data/chemimg/339200/110590-84-6.png)
![2,9-Di(tridecan-7-yl)anthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetraone](/data/chemimg/339200/110590-84-6_b.png)
![2-Bromothieno[3,2-b]thiophene](http://img.cochemist.com/ccimg/25200/25121-82-8.png)
![2-Bromothieno[3,2-b]thiophene](http://img.cochemist.com/ccimg/25200/25121-82-8_b.png)
![Stannane, 1,1'-[4,8-bis[5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]bis[1,1,1-trimethyl-](/data/chemimg/139400/1352642-37-5.png)
![Stannane, 1,1'-[4,8-bis[5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]bis[1,1,1-trimethyl-](/data/chemimg/139400/1352642-37-5_b.png)
![Pyrrolo[3,4-c]pyrrole-1,4-dione, 3,6-bis(5-bromo-2-thiazolyl)-2,5-bis(2-ethylhexyl)-2,5-dihydro-](/data/chemimg/3782300/1392832-52-8.png)
![Pyrrolo[3,4-c]pyrrole-1,4-dione, 3,6-bis(5-bromo-2-thiazolyl)-2,5-bis(2-ethylhexyl)-2,5-dihydro-](/data/chemimg/3782300/1392832-52-8_b.png)
![Benzo[1,2-b:4,5-b']dithiophene, 2,6-dibromo-4,8-bis[(2-ethylhexyl)oxy]-](/data/chemimg/380400/1226782-13-3.png)
![Benzo[1,2-b:4,5-b']dithiophene, 2,6-dibromo-4,8-bis[(2-ethylhexyl)oxy]-](/data/chemimg/380400/1226782-13-3_b.png)
![Thieno[3,4-b]thiophene-2-carboxylic acid, 4,6-dibromo-, 2-ethylhexyl ester](/data/chemimg/189600/1160823-81-3.png)
![Thieno[3,4-b]thiophene-2-carboxylic acid, 4,6-dibromo-, 2-ethylhexyl ester](/data/chemimg/189600/1160823-81-3_b.png)
![Octyl 4,6-dibromo-3-fluorothieno[3,4-b]thiophene-2-carboxylate](http://img.cochemist.com/ccimg/1160900/1160823-76-6.png)
![Octyl 4,6-dibromo-3-fluorothieno[3,4-b]thiophene-2-carboxylate](http://img.cochemist.com/ccimg/1160900/1160823-76-6_b.png)
![(4,8-Bis(octyloxy)benzo[1,2-b:4,5-b']dithiophene-2,6-diyl)bis(trimethylstannane)](http://img.cochemist.com/ccimg/1098200/1098102-95-4.png)
![(4,8-Bis(octyloxy)benzo[1,2-b:4,5-b']dithiophene-2,6-diyl)bis(trimethylstannane)](http://img.cochemist.com/ccimg/1098200/1098102-95-4_b.png)
![Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)]](/data/chemimg/102300/920515-34-0.png)
![Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)]](/data/chemimg/102300/920515-34-0_b.png)
![Benzene, 1,4-dibromo-2,5-bis[(2-ethylhexyl)oxy]-](/data/chemimg/3049700/191867-85-3.png)
![Benzene, 1,4-dibromo-2,5-bis[(2-ethylhexyl)oxy]-](/data/chemimg/3049700/191867-85-3_b.png)
![21H,23H-Porphine, 5,10,15,20-tetrakis[4-[2-(trimethylsilyl)ethynyl]phenyl]-](/data/chemimg/2944500/145362-97-6.png)
![21H,23H-Porphine, 5,10,15,20-tetrakis[4-[2-(trimethylsilyl)ethynyl]phenyl]-](/data/chemimg/2944500/145362-97-6_b.png)
![Silane, trimethyl[5-(tributylstannyl)-2-thienyl]-](http://img.cochemist.com/ccimg/128100/128055-72-1.png)
![Silane, trimethyl[5-(tributylstannyl)-2-thienyl]-](http://img.cochemist.com/ccimg/128100/128055-72-1_b.png)
![3-Thiophenecarboxylic acid, 2,5-dihydro-4-[[(4-methylphenyl)sulfonyl]oxy]-, methyl ester](/data/chemimg/1916000/67525-75-1.png)
![3-Thiophenecarboxylic acid, 2,5-dihydro-4-[[(4-methylphenyl)sulfonyl]oxy]-, methyl ester](/data/chemimg/1916000/67525-75-1_b.png)
![Thieno[3,4-d]isothiazol-3(2H)-one, 1,1-dioxide](http://img.cochemist.com/ccimg/59400/59337-79-0.png)
![Thieno[3,4-d]isothiazol-3(2H)-one, 1,1-dioxide](http://img.cochemist.com/ccimg/59400/59337-79-0_b.png)
![Thieno[3,4-b]thiophene](/data/chemimg/417100/250-65-7.png)
![Thieno[3,4-b]thiophene](/data/chemimg/417100/250-65-7_b.png)
![Stannane, 1,1'-[4,8-bis[(2-butyloctyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]bis[1,1,1-trimethyl-](/data/chemimg/154400/1271439-08-7.png)
![Stannane, 1,1'-[4,8-bis[(2-butyloctyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]bis[1,1,1-trimethyl-](/data/chemimg/154400/1271439-08-7_b.png)
![Thieno[3,4-b]thiophene-2-carboxylic acid, 4,6-dibromo-3-fluoro-, 2-ethylhexyl ester](/data/chemimg/1642600/1237479-38-7.png)
![Thieno[3,4-b]thiophene-2-carboxylic acid, 4,6-dibromo-3-fluoro-, 2-ethylhexyl ester](/data/chemimg/1642600/1237479-38-7_b.png)
![2-Ethylhexyl 4,6-dibromo-3-fluorothieno[3,4-b]thiophene-2-carboxylate](http://img.cochemist.com/ccimg/1237500/1237479-39-8.png)
![2-Ethylhexyl 4,6-dibromo-3-fluorothieno[3,4-b]thiophene-2-carboxylate](http://img.cochemist.com/ccimg/1237500/1237479-39-8_b.png)
