Tungsten oxide as an alternative to conventional acidic PEDOT:PSS has attracted much attention in organic solar cells (OSCs). However, the vacuum-processed WO3 layer and high-temperature sol–gel hydrolyzed WOX are incompatible with large-scale manufacturing of OSCs. Here, we report for the first time that a specific tungsten oxide WO2.72 (W18O49) nanowire can function well as the anode buffer layer. The nw-WO2.72 film exhibits a high optical transparency. The power conversion efficiency (PCE) of OSCs based on three typical polymer active layers PTB7:PC71BM, PTB7-Th:PC71BM, and PDBT-T1:PC71BM with nw-WO2.72 layer were improved significantly from 7.27 to 8.23%, from 8.44 to 9.30%, and from 8.45 to 9.09%, respectively compared to devices with PEDOT:PSS. Moreover, the photovoltaic performance of OSCs based on small molecule p-DTS(FBTTh2)2:PC71BM active layer was also enhanced with the incorporation of nw-WO2.72. The enhanced performance is mainly attributed to the improved short-circuit current density (Jsc), which benefits from the oxygen vacancies and the surface apophyses for better charge extraction. Furthermore, OSCs based on nw-WO2.72 show obviously improved ambient stability compared to devices with PEDOT:PSS layer. The results suggest that nw-WO2.72 is a promising candidate for the anode buffer layer materials in organic solar cells.Keywords: anode buffer layer; efficiency; organic solar cells; stability; WO2.72 nanowire;

Ternary bulk heterojunction (BHJ) blends have been demonstrated as a promising approach to increase the power conversion efficiencies (PCEs) of organic solar cells. Currently, most studies of ternary organic solar cells are based on blends of two donors and one acceptor, because of the limitation in acceptor materials. Here, we report that high-performance ternary solar cells have been fabricated with a wide-bandgap polymer donor (PDBT-T1) and two acceptor materials, phenyl-C70-butyric acid methyl ester (PC70BM), and nonfullerene acceptor (ITIC-Th). The addition of ITIC-Th into the BHJ blends dramatically increases the light absorption. Consequently, the champion ternary solar cell shows a high PCE of ∼10.5%, with an open-circuit voltage (Voc) of 0.95 V, a short-circuit current (Jsc) of 15.60 mA/cm2, and a fill factor (FF) of 71.1%, which largely outperforms their binary counterparts. Detailed studies reveal that the ternary solar cells work in a parallel-like device model (ITIC-Th and PC70BM form their own independent transport network) when ITIC-Th loading is >30% in the ternary blends. The results indicate that the combination of fullerene derivative and appropriate nonfullerene acceptor in a ternary blend can be a new strategy to fabricate high-performance ternary organic solar cells.

•Star-shaped S/Se-annulated perylene diimide are used as non-fullerene acceptors.•The OPV devices achieve high power conversion efficiencies of up to 6.10%.•The PCE of 6.10% is among the highest values based on star-shaped non-fullerene acceptors so far.•From sulfur to selenium, the heteroatom annulation improves the device performance.Three novel star-shaped S/Se-annulated perylene diimide (PDI) small molecule acceptors with triphenylamine as the core, namely TPA-PDI, TPA-PDI-S and TPA-PDI-Se, were designed and synthesized. Using the wideband-gap polymer PDBT-T1 as the donor and Se-annulated perylene diimide (TPA-PDI-Se) as the acceptor, power conversion efficiencies (PCE) of up to 6.10% was achieved, which is 38% higher than the reference of TPA-PDI without heteroatom annulation. Impressively, the S/Se-annulated perylene diimides as acceptors showed high open-circuit voltage (VOC) of 1.00 V. The high efficiency for TPA-PDI-Se can be attributed to complementary absorption spectra with the donor material, relatively high-lying LUMO level, balanced carrier transport and favorable morphologies. To the best of our knowledge, this PCE of 6.10% is among the highest values based on star-shaped non-fullerene acceptors so far.Star-shaped S/Se-annulated perylene diimide as non-fullerene acceptors achieve high power conversion efficiencies of up to 6.10%. From sulfur to selenium, the heteroatom annulation improves the device performance.

The past decade has witnessed significant advances in the field of organic solar cells (OSCs). Ongoing improvements in the power conversion efficiency of OSCs have been achieved, which were mainly attributed to the design and synthesis of novel conjugated polymers with different architectures and functional moieties. Among various conjugated polymers, the development of wide-bandgap (WBG) polymers has received less attention than that of low-bandgap and medium-bandgap polymers. Here, we briefly summarize recent advances in WBG polymers and their applications in organic photovoltaic (PV) devices, such as tandem, ternary, and non-fullerene solar cells. Addtionally, we also dissuss the application of high open-circuit voltage tandem solar cells in PV-driven electrochemical water dissociation. We mainly focus on the molecular design strategies, the structure-property correlations, and the photovoltaic performance of these WBG polymers. Finally, we extract empirical regularities and provide invigorating perspectives on the future development of WBG photovoltaic materials.

•Two perylenediimide-based polymer acceptors named PF-PDI and PBDT-PDI were successfully designed and synthesized.•The donor unit plays an important role in determining the optical and electronic properties of polymer acceptors.•All-PSCs based on PDBT-T1:PF-PDI exhibited a PCE of ∼4.5%, which is much higher than that of devices with PDBT-T1:PBDT-PDI.Perylenediimide (PDI)-based small molecules have significantly contributed to the development of non-fullerene acceptors, whereas the development of PDI-based polymer acceptors is relatively lagging behind. In this study, we designed and synthesized two PDI-based n-type polymers named as PF-PDI and PBDT-PDI, in which PDI was used as electron-deficient unit and fluorene (F) or benzodithiophene (BDT) were used as electronrich components. The density functional theory (DFT) calculations and grazing incidence wide-angle X-ray scattering (GIWAXS) results indicate that the PF-PDI shows larger steric hindrance and relatively weaker lamellar packing than that of PBDT-PDI. Comparing with PBDT-PDI, PF-PDI shows red-shift absorption and lower-lying HOMO level, which agrees well with the DFT results. A well-known wide bandgap polymer donor, PDBT-T1 was employed to fabricate polymer solar cells (PSCs) with the two acceptors. The all polymer solar cells (all-PSCs) based on PDBT-T1:PF-PDI showed a high power conversion efficiency (PCE) of 4.47%, which is approximately 2-fold larger than that of devices with PDBT-T1:PBDT-PDI (PCE = 2.70%).Two perylenediimide (PDI)-based polymer acceptors named as PF-PDI and PBDT-PDI were synthesized, in which PDI was used as electron-deficient unit and fluorene (F) or benzodithiophene (BDT) were used as electron-rich unit. All-PSCs base on PF-PDI acceptor exhibited a high efficiency of ∼4.5%.Download high-res image (233KB)Download full-size image

•A pair of two-dimensional non-fullerene acceptors, named as TVIDTPDI and TVIDTzPDI, were successfully synthesized.•They have same perylene diimide end-capping groups, but different in two-dimensional conjugated central core.•We focused on evaluating the effect of replacing thiophene to thiazole on the bulk properties and device performances.•The TVIDTzPDI/PTB7-Th-based OSCs showed a higher PCE of 2.09% than that of TVIDTPDI/PTB7-Th-based devices (1.50%).A pair of linear two-dimensional conjugated non-fullerene acceptors, named as TVIDTPDI and TVIDTzPDI, which have the same perylene diimide end-capping groups, but different in two-dimensional conjugated central core (the dithienyl vinylene-fused indacenodithiophene or dithienyl vinylene-fused indacenodithiazole), were successfully synthesized and evaluated as acceptor materials in organic solar cells (OSCs). Such core units in these small acceptors play a decisive role in the formation of the nanoscale separation of the blend films, which were systematically investigated through absorption spectra, electrochemical properties, density functional theory calculations, AFM images, and charge mobility measurement by space-charge-limited current SCLC method. By incorporation of the dithienyl vinylene-fused indacenodithiazole-based core, TVIDTzPDI showed better planarity in the core unit with a dihedral 45.4° and 49.6° angle of between central core and the PDI. Moreover, the TVIDTzPDI blend with PTB7-Th displays higher and more balanced mobilities (μh = 4.56 × 10−4 and μe = 6.12 × 10−4 cm2 V−1 s−1) in comparison with those of TVIDTPDI blend with PTB7-Th. Therefore, the TVIDTzPDI/PTB7-Th based OSCs showed a higher PCE of 2.09% than that of the TVIDTPDI/PTB7-Th devices (1.50%). The purpose of this study is to provide a facile strategy to design PDI-based two-dimensional conjugated small molecular acceptors and understand the impact of installing the two dimensional core and more electron-deficient thiazole unit in such small molecular acceptors.A pair of linear two-dimensional conjugated non-fullerene acceptors, named as TVIDTPDI and TVIDTzPDI were successfully synthesized and evaluated as acceptor materials in organic solar cells (OSCs). By blending with PTB7-Th, the TVIDTzPDI-based OSCs showed a higher PCE of 2.09% than that (1.50%) of TVIDTPDI-based devices.Download high-res image (142KB)Download full-size image

In this work, we demonstrated the synthesis and characterization of two novel donor–acceptor type conjugated polymers, IDT-T1 and IDTT-T1, which consist of indacenodithiophene (IDT) and indacenodithieno[3,2-b]thiophene (IDTT) donor and 1,3-bis(5-bromothiophen-2-yl)-5,7-bis(2-ethylhexyl)-4H,8H-benzo[1,2-c:4,5-c]dithiophene-4,8-dione (T1) acceptor building blocks. The resulting copolymers exhibited a wide bandgap of about 1.90 eV with a comparatively low-lying highest occupied molecular orbital (HOMO) energy level. However, IDTT-T1 with an extended fused-ring unit was found to have better coplanarity and higher carrier mobility (0.11 cm2 V−1 s−1). As a consequence, organic solar cells employing IDTT-T1 as the donor material afforded a power conversion efficiency (PCE) of 6.58%, while IDT-T1-based devices yielded a relatively lower PCE of 6.26%.

The open-circuit voltage (Voc) is one of the important parameters that influence the power conversion efficiency (PCE) of polymer solar cells. Its value is mainly determined by the energy level offset between the highest occupied molecular orbital (HOMO) of the donor and the lowest unoccupied molecular orbital (LUMO) of the acceptor. Therefore, decreasing the HOMO value of the polymer could lead to a high Voc and thus increasing the cell efficiency. Here we report a facile way to lower the polymer HOMO energy level by using methoxyl substituted-benzodithiophene (BDT) unit. The polymer with the methoxyl functionl group (POBDT(S)-T1) exhibited a HOMO value of–5.65 eV, which is deeper than that (–5.52 eV) of polymer without methoxyl unit (PBDT(S)-T1). As a result, POBDT(S)-T1-based solar cells show a high Voc of 0.98 V and PCE of 9.2%. In contrast, PBDT(S)-T1-based devices show a relatively lower Voc of 0.89 V and a moderate PCE of 7.4%. The results suggest that the involvement of methoxyl group into conjugated copolymers can efficiencly lower their HOMO energy levels.

Ladder-type dithienocyclopentacarbazole (DTCC) cores, which possess highly extended π-conjugated backbones and versatile modular structures for derivatization, were widely used to develop high-performance p-type polymeric semiconductors. However, an n-type DTCC-based organic semiconductor has not been reported to date. In this study, the first DTCC-based n-type organic semiconductor (DTCC–IC) with a well-defined A–D–A backbone was designed, synthesized, and characterized, in which a DTCC derivative substituted by four p-octyloxyphenyl groups was used as the electron-donating core and two strongly electron-withdrawing 3-(dicyanomethylene)indan-1-one moieties were used as the terminal acceptors. It was found that DTCC–IC has strong light-capturing ability in the range of 500–720 nm and exhibits an impressively high molar absorption coefficient of 2.24 × 105 M−1 cm−1 at 669 nm owing to effective intramolecular charge transfer and a strong D–A effect. Cyclic voltammetry measurements indicated that the HOMO and LUMO energy levels of DTCC–IC are −5.50 and −3.87 eV, respectively. More importantly, a high electron mobility of 2.17 × 10−3 cm2 V−1 s−1 was determined by the space-charge-limited current method; this electron mobility can be comparable to that of fullerene derivative acceptors (μe ∼ 10−3 cm2 V−1 s−1). To investigate its application potential in non-fullerene solar cells, we fabricated organic solar cells (OSCs) by blending a DTCC–IC acceptor with a PTB7-Th donor under various conditions. The results suggest that the optimized device exhibits a maximum power conversion efficiency (PCE) of up to 6% and a rational high VOC of 0.95 V. These findings demonstrate that the ladder-type DTCC core is a promising building block for the development of high-mobility n-type organic semiconductors for OSCs.

Perylene bisimide (PBI) based molecules have recently attracted tremendous interest as acceptors in non-fullerene organic solar cells. However, most PBI-based acceptors possess deep LUMO energy levels (−3.9 ∼ −4.0 eV) and show an open-circuit voltage (Voc) below 0.90 V, thus limiting the improvement of device efficiency. Here, we report two novel ring-fused PBI dimers, SdiPBI-BT and diPBI-BT, with thienobenzene fused to the bay region of the PBI subunits. Conventional bulk-heterojunction (BHJ) solar cells based on SdiPBI-BT show a power conversion efficiency (PCE) of 6.71% with a high Voc value of 0.95 V, a short-circuit current density (Jsc) of 10.31 mA cm−2 and a high fill factor (FF) of 68.7%. Devices based on diPBI-BT show a PCE of 5.84% with a high Voc value of 0.99 V. These results demonstrate that ring-fused PBI derivatives are promising materials for non-fullerene cells.

A series of propeller-shaped triperylene hexaimide (TPH) non-fullerene acceptors, featuring branched alkyl side chains with different lengths (TPH-4, TPH-5, TPH-6, and TPH-7), have been designed and synthesized. The effects of the branched alkyl chain length on the physical properties, thin-film microstructure, molecular packing, charge transport and the resulting photovoltaic properties of these materials have been systematically investigated. It was found that TPH-7 with the longest alkyl side chain showed the best photovoltaic performance compared with three other TPH molecules, and an outstanding power conversion efficiency (PCE) of 8.6% under AM 1.5G irradiation (100 mW cm−2) has been obtained using a wide-band-gap polymer PDBT-T1 as the electron donor. These results demonstrate that finely tailoring alkyl substituents on TPH-based small molecular acceptors critically impacts the structural order of thin films and molecular orientation, and thus the photovoltaic performance.

Three perylenediimide (PDI) acceptors (P2O2, P2N2 and P4N4) were synthesized by functionalizing the bay positions of PDI with benzil, 2,3-diphenylquinoxaline and 2,3,7,8-tetraphenylpyrazino[2,3-g]quinoxaline as linkers, respectively. The photovoltaic properties of the three acceptor molecules have been investigated. The different PDI linker units show different physical and chemical properties of the PDIs. The three PDIs display different non-planar geometrical structures because of the different linker units, which affect the corresponding morphology of the blend films and also influence the charge mobility and fill factor (FF) of the organic solar cells (OSCs). Furthermore, the gradient energy levels of the three PDIs provide an efficient research model for the relationship of device open-circuit voltage (Voc) and energy levels. As the result, the P4N4 based non-fullerene devices show the best photovoltaic performance with a power conversion efficiency (PCE) of 5.71%, whereas the P2O2 and P2N2 based non-fullerene devices show relatively lower PCEs of 2.53% and 3.86%, respectively.

Extending the π-conjugation length of the polymeric backbone is an effective way to enhance the photovoltaic performance of polymer solar cells (PSCs). Here, the donor–donor–acceptor (D–D–A) molecular strategy has been used to design and synthesize two wide-bandgap conjugated copolymers, in which 2,2-bithiophene (BT) or thieno[3,2-b] thiophene (TT) is introduced to the D–A polymer as a third component to investigate the influence of the conjugation backbone on photovoltaic properties. The structure–property relationship and photovoltaic performance of the polymer have been investigated. Compared to P2 (TT as the third unit), P1 (BT as the third unit) exhibits a deeper highest occupied molecular orbital (HOMO) level and a more planar backbone structure with slightly higher mobility. Based on a conventional device structure with PC70BM as the acceptor material, P1-based solar cells exhibit a maximum power conversion efficiency (PCE) of 6.93%, an open-circuit voltage (VOC) of 0.86 V, a short-circuit current (JSC) of 11.06 mA cm−2, and a fill factor (FF) of 72.9%, which are much better than those of P2-based solar cells (PCE 3.92%). These results demonstrate that extending the effective π-conjugation structure of the polymer backbone could improve the photovoltaic performance of PSCs by inserting an additional appropriate donor unit in the D–A polymer.

Two kinds of conjugated C3-symmetric perylene dyes, namely, triperylene hexaimides (TPH) and selenium-annulated triperylene hexaimides (TPH-Se), are efficiently synthesized. Both TPH and TPH-Se have broad and strong absorption in the region 300–600 nm together with suitable LUMO levels of about −3.8 eV. Single-crystal X-ray diffraction studies show that TPH displays an extremely twisted three-bladed propeller configuration and a unique 3D network assembly in which three PBI subunits in one TPH molecule have strong π–π intermolecular interactions with PBI subunits in neighboring molecules. The integration of selenophene to TPH endows TPH-Se with a more distorted propeller configuration and a more compact 3D network assembly due to the Se···O interactions. A single-crystal transistor confirms that both TPH and TPH-Se possess good electron-transport ability. TPH and TPH-Se acceptor-based solar cells show high power conversion efficiency of 8.28% and 9.28%, respectively, which mainly results from the combined properties of broad and strong absorption ability, appropriate LUMO level, desirable aggregation, high electron mobility, and good film morphology with the polymer donor.

A planar fused-ring electron acceptor (IC-C6IDT-IC) based on indacenodithiophene is designed and synthesized. IC-C6IDT-IC shows strong absorption in 500–800 nm with extinction coefficient of up to 2.4 × 105 M–1 cm–1 and high electron mobility of 1.1 × 10–3 cm2 V–1 s–1. The as-cast polymer solar cells based on IC-C6IDT-IC without additional treatments exhibit power conversion efficiencies of up to 8.71%.

Two new polymers, PDTPO-IDT and PDTPO-IDTT, are synthesized through copolymerization of 4-(2-octyldodecyl)-dithieno[3,2-b:2′,3′-d]pyridin-5(4H)-one (DTPO) with indacenodithiophene (IDT) or indacenodithieno[3,2-b]thiophene (IDTT). The rational combination of the planar DTPO unit with ladder-type IDT and IDTT units endows the resulting copolymers with wide optical bandgaps of ca. 2.05 eV, low HOMO energy levels of ca. −5.32 eV and good hole-transporting abilities with a hole mobility of 1.0 × 10−3 cm2 V−1 s−1. The polymer solar cell (PSC) in a conventional structure based on PDTPO-IDT as donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as acceptor achieves a high power conversion efficiency (PCE) of up to 7.33%, the highest value for PSCs based on polymers with optical bandgap over 2.0 eV to date, along with a remarkable open-circuit voltage (Voc) approaching 0.97 V. The performance of the PDTPO-IDTT based PSC is slightly behind this with a moderate PCE of 5.47% under the same conditions. The relationship between the copolymer structures and optoelectronic properties as well as photovoltaic performance are comprehensively investigated by experiments and theoretical simulations.

Extensive efforts have been focused on the study of wide-band gap (WBG) polymers due to their important applications in multiple junction and ternary blend organic solar cells. Herein, three WBG copolymers named PBDT(X)-T1 (X = O, S, Se) were synthesized based on the benzodithiophene (BDT) donor unit and 1,3-bis(5-bromothiophen-2-yl)-5,7-bis(2-ethylhexyl)-4H,8H-benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (T1) acceptor unit. Different aromatic heterocycle groups (furan, thiophene and selenophene) were introduced to modify the BDT unit to investigate the influence of conjugated side chains on the photovoltaic properties of conjugated polymers. Photophysical properties, electrochemistry, charge transport and crystalline properties of the polymers were studied to discuss the role of chalcogen atoms on the performance of conjugated polymers. Solar cells based on these three WBG copolymers were fabricated. Among them, the PBDT(Se)-T1-based solar cell shows the best photovoltaic performance with the highest power conversion efficiency (PCE) of 8.52%, an open-circuit voltage (Voc) of 0.91 V, and a high fill factor (FF) of 72%. The high crystallinity and preferential face-on orientation in the blend film partially explain the superior photovoltaic performance achieved in PBDT(Se)-T1-based solar cells. The results indicate the important role of chalcogen atoms in conjugated side chains and that high photovoltaic performance can be realized through side chain engineering of BDT-based WBG conjugated polymers.

Two perylene bisimides based non-fullerene small molecules, H-DIPBI and B-DIPBI, are applied into inverted planar heterojunction perovskite solar cells. The power conversion efficiency up to 11.6% has been achieved for device with B-DIPBI, indicating that non-fullerene acceptor can function as the electron transport layer to replace PCBM in perovskite solar cells.

Perylenediimide (PDI)-based materials exhibit great potential as non-fullerene acceptors in bulk-heterojunction (BHJ) organic solar cells (OSCs). Recent investigations have revealed that PDI molecules with a twisted structure could disrupt aggregation of perylene unit. Here, we present a PDI monomer via bay-substitutions with four fused naphthalene units by three-step reactions, named TN-PDI. The introduction of four fused naphthalene rings into the bay positions of PDI unit leads to a strong steric hindrance with a twist angle of 33° between the two PDI subplanes. Blended with a wide-band gap polymer donor (PDBT-T1), the TN-PDI based non-fullerene solar cells show power conversion efficiency (PCE) of 3.0%. Our results indicate that the bay-substitutions with fused aromatic substitutions could be an efficient approach to develop monomeric PDI acceptors.近年来, 本体异质结型有机太阳能电池领域中, 苝酰亚胺类衍生物作为富勒烯类电荷受体材料的最佳替代材料而得到广泛关注. 很 多研究表明扭曲构型的分子结构设计可以明显地抑制苝酰亚胺的聚集行为. 本研究在苝酰亚胺的四个湾位同时共轭引入萘基官能团, 从 而合成一种简单结构的苝酰亚胺单分子型电荷受体材料TN-PDI. 四个共轭萘基的引入使苝酰亚胺平面骨架扭曲至33°. 分别以TN-PDI和一 种宽带隙聚合物PDBT-T1为电荷受体材料和给体材料构筑本体异质结型有机太阳能电池, 其光电转换效率可达3.0%. 研究结果表明, 四个 湾位同时共轭取代苝酰亚胺是一种制备简单高效苝酰亚胺单分子型电荷受体材料的有效方法.

A novel perylene bisimide (PBI) dimer-based acceptor material, SdiPBI-S, was developed. Conventional bulk-heterojunction (BHJ) solar cells based on SdiPBI-S and the wide-band-gap polymer PDBT-T1 show a high power conversion efficiency (PCE) of 7.16% with a high open-circuit voltage of 0.90 V, a high short-circuit current density of 11.98 mA/cm2, and an impressive fill factor of 66.1%. Favorable phase separation and balanced carrier mobilites in the BHJ films account for the high photovoltaic performance. The results demonstrate that fine-tuning of PBI-based materials is a promising way to improve the PCEs of non-fullerene BHJ organic solar cells.

Non-fullerene acceptors have recently attracted tremendous interest because of their potential as alternatives to fullerene derivatives in bulk heterojunction organic solar cells. However, the power conversion efficiencies (PCEs) have lagged far behind those of the polymer/fullerene system, mainly because of the low fill factor (FF) and photocurrent. Here we report a novel perylene bisimide (PBI) acceptor, SdiPBI-Se, in which selenium atoms were introduced into the perylene core. With a well-established wide-band-gap polymer (PDBT-T1) as the donor, a high efficiency of 8.4% with an unprecedented high FF of 70.2% is achieved for solution-processed non-fullerene organic solar cells. Efficient photon absorption, high and balanced charge carrier mobility, and ultrafast charge generation processes in PDBT-T1:SdiPBI-Se films account for the high photovoltaic performance. Our results suggest that non-fullerene acceptors have enormous potential to rival or even surpass the performance of their fullerene counterparts.

An efficient gradient annealing approach is demonstrated to improve the surface morphology and coverage of perovskite films. Gradient annealed perovskite films exhibit more uniform and smooth surface with improved coverage compared to directly annealed films. The resulting perovskite solar cells show enhanced device performance with a high efficiency of 14%, indicating that the gradient annealing process is a useful way to improve the efficiency of perovskite solar cells.

Two new polymers, PDTPO-IDT and PDTPO-IDTT, are synthesized through copolymerization of 4-(2-octyldodecyl)-dithieno[3,2-b:2′,3′-d]pyridin-5(4H)-one (DTPO) with indacenodithiophene (IDT) or indacenodithieno[3,2-b]thiophene (IDTT). The rational combination of the planar DTPO unit with ladder-type IDT and IDTT units endows the resulting copolymers with wide optical bandgaps of ca. 2.05 eV, low HOMO energy levels of ca. −5.32 eV and good hole-transporting abilities with a hole mobility of 1.0 × 10−3 cm2 V−1 s−1. The polymer solar cell (PSC) in a conventional structure based on PDTPO-IDT as donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as acceptor achieves a high power conversion efficiency (PCE) of up to 7.33%, the highest value for PSCs based on polymers with optical bandgap over 2.0 eV to date, along with a remarkable open-circuit voltage (Voc) approaching 0.97 V. The performance of the PDTPO-IDTT based PSC is slightly behind this with a moderate PCE of 5.47% under the same conditions. The relationship between the copolymer structures and optoelectronic properties as well as photovoltaic performance are comprehensively investigated by experiments and theoretical simulations.

Extending the π-conjugation length of the polymeric backbone is an effective way to enhance the photovoltaic performance of polymer solar cells (PSCs). Here, the donor–donor–acceptor (D–D–A) molecular strategy has been used to design and synthesize two wide-bandgap conjugated copolymers, in which 2,2-bithiophene (BT) or thieno[3,2-b] thiophene (TT) is introduced to the D–A polymer as a third component to investigate the influence of the conjugation backbone on photovoltaic properties. The structure–property relationship and photovoltaic performance of the polymer have been investigated. Compared to P2 (TT as the third unit), P1 (BT as the third unit) exhibits a deeper highest occupied molecular orbital (HOMO) level and a more planar backbone structure with slightly higher mobility. Based on a conventional device structure with PC70BM as the acceptor material, P1-based solar cells exhibit a maximum power conversion efficiency (PCE) of 6.93%, an open-circuit voltage (VOC) of 0.86 V, a short-circuit current (JSC) of 11.06 mA cm−2, and a fill factor (FF) of 72.9%, which are much better than those of P2-based solar cells (PCE 3.92%). These results demonstrate that extending the effective π-conjugation structure of the polymer backbone could improve the photovoltaic performance of PSCs by inserting an additional appropriate donor unit in the D–A polymer.

A series of propeller-shaped triperylene hexaimide (TPH) non-fullerene acceptors, featuring branched alkyl side chains with different lengths (TPH-4, TPH-5, TPH-6, and TPH-7), have been designed and synthesized. The effects of the branched alkyl chain length on the physical properties, thin-film microstructure, molecular packing, charge transport and the resulting photovoltaic properties of these materials have been systematically investigated. It was found that TPH-7 with the longest alkyl side chain showed the best photovoltaic performance compared with three other TPH molecules, and an outstanding power conversion efficiency (PCE) of 8.6% under AM 1.5G irradiation (100 mW cm−2) has been obtained using a wide-band-gap polymer PDBT-T1 as the electron donor. These results demonstrate that finely tailoring alkyl substituents on TPH-based small molecular acceptors critically impacts the structural order of thin films and molecular orientation, and thus the photovoltaic performance.

Perylene bisimide (PBI) based molecules have recently attracted tremendous interest as acceptors in non-fullerene organic solar cells. However, most PBI-based acceptors possess deep LUMO energy levels (−3.9 ∼ −4.0 eV) and show an open-circuit voltage (Voc) below 0.90 V, thus limiting the improvement of device efficiency. Here, we report two novel ring-fused PBI dimers, SdiPBI-BT and diPBI-BT, with thienobenzene fused to the bay region of the PBI subunits. Conventional bulk-heterojunction (BHJ) solar cells based on SdiPBI-BT show a power conversion efficiency (PCE) of 6.71% with a high Voc value of 0.95 V, a short-circuit current density (Jsc) of 10.31 mA cm−2 and a high fill factor (FF) of 68.7%. Devices based on diPBI-BT show a PCE of 5.84% with a high Voc value of 0.99 V. These results demonstrate that ring-fused PBI derivatives are promising materials for non-fullerene cells.

In aiming to build novel wide band-gap high-performance photovoltaic donor materials, a vertical benzo[1,2-b:4,5-b′]dithiophene-2,6-dicarboxylate (V-BDTC) with a weak electron-withdrawing character was primarily developed. And its wide band-gap (WBG) copolymers PV-BDTC1 and PV-BDTC2 were designed and synthesized, which contain a traditional electron-donating unit of 4,8-disubstituted benzo[1,2-b:4,5-b′] dithiophene (BDT) derivative with diethylhexyloxy for the former and diethylhexylthiophenyl for the latter. It is found that the weak electron-withdrawing V-BDTC unit endows its copolymers with a WBG up to 2.09 eV and a deep HOMO energy level of ∼5.67 eV. Furthermore, PV-BDTC2 exhibits much better photovoltaic properties than PV-BDTC1 in the solution-processing polymer solar cells (PSCs) with a higher open-circuit voltage (Voc) of 1.03 V and an increased power conversion efficiency (PCE) of 7.49%. To the best of our knowledge, this PCE value is the highest level recorded for copolymers with a WBG over 2.0 eV in the PSCs to date, along with a remarkable Voc over 1.0 V. This work provides a feasible strategy to develop a novel promising electron-withdrawing building block and its high-performance WBG copolymers based on the BDT unit.

Ladder-type dithienocyclopentacarbazole (DTCC) cores, which possess highly extended π-conjugated backbones and versatile modular structures for derivatization, were widely used to develop high-performance p-type polymeric semiconductors. However, an n-type DTCC-based organic semiconductor has not been reported to date. In this study, the first DTCC-based n-type organic semiconductor (DTCC–IC) with a well-defined A–D–A backbone was designed, synthesized, and characterized, in which a DTCC derivative substituted by four p-octyloxyphenyl groups was used as the electron-donating core and two strongly electron-withdrawing 3-(dicyanomethylene)indan-1-one moieties were used as the terminal acceptors. It was found that DTCC–IC has strong light-capturing ability in the range of 500–720 nm and exhibits an impressively high molar absorption coefficient of 2.24 × 105 M−1 cm−1 at 669 nm owing to effective intramolecular charge transfer and a strong D–A effect. Cyclic voltammetry measurements indicated that the HOMO and LUMO energy levels of DTCC–IC are −5.50 and −3.87 eV, respectively. More importantly, a high electron mobility of 2.17 × 10−3 cm2 V−1 s−1 was determined by the space-charge-limited current method; this electron mobility can be comparable to that of fullerene derivative acceptors (μe ∼ 10−3 cm2 V−1 s−1). To investigate its application potential in non-fullerene solar cells, we fabricated organic solar cells (OSCs) by blending a DTCC–IC acceptor with a PTB7-Th donor under various conditions. The results suggest that the optimized device exhibits a maximum power conversion efficiency (PCE) of up to 6% and a rational high VOC of 0.95 V. These findings demonstrate that the ladder-type DTCC core is a promising building block for the development of high-mobility n-type organic semiconductors for OSCs.

Three perylenediimide (PDI) acceptors (P2O2, P2N2 and P4N4) were synthesized by functionalizing the bay positions of PDI with benzil, 2,3-diphenylquinoxaline and 2,3,7,8-tetraphenylpyrazino[2,3-g]quinoxaline as linkers, respectively. The photovoltaic properties of the three acceptor molecules have been investigated. The different PDI linker units show different physical and chemical properties of the PDIs. The three PDIs display different non-planar geometrical structures because of the different linker units, which affect the corresponding morphology of the blend films and also influence the charge mobility and fill factor (FF) of the organic solar cells (OSCs). Furthermore, the gradient energy levels of the three PDIs provide an efficient research model for the relationship of device open-circuit voltage (Voc) and energy levels. As the result, the P4N4 based non-fullerene devices show the best photovoltaic performance with a power conversion efficiency (PCE) of 5.71%, whereas the P2O2 and P2N2 based non-fullerene devices show relatively lower PCEs of 2.53% and 3.86%, respectively.