Zero drift can severely deteriorate the stability of the light–dark current ratio, detectivity, and responsivity of photodetectors. In this paper, the effects of a [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)-doped perovskite-based photodetector device on the inhibition of zero drift under dark state are discussed. Two kinds of photodetectors (Au/CH3NH3PbIxCl3–x/Au and Au/CH3NH3PbIxCl3–x:PCBM/Au) were prepared, and the materials and photodetector devices were measured by scanning electron microscopy, X-ray diffraction, photoluminescence, ultraviolet absorption spectra, and current–voltage and current–time measurements. It was found that similar merit parameters, including light–dark current ratio (∼102), detectivity (∼1011 Jones), and responsivity were obtained for these two kinds of photodetectors. However, the drift of Au/CH3NH3PbIxCl3–x:PCBM/Au devices is negligible, while a drift of ∼0.2 V exists in Au/CH3NH3PbIxCl3–x/Au devices. A new model is proposed based on the hindering theory of ion (vacancy) migration, and it is believed that the dopant PCBM can hinder the ion (vacancy) migration of perovskite materials to suppress the phenomenon of zero drift in perovskite-based photodetectors.Keywords: ion migration; perovskite; photodetectors; zero drift; [6,6]-phenyl-C61-butyric acid methyl ester;

Recently, low temperature solution-processed tin oxide (SnO2) as a versatile electron transport layer (ETL) for efficient and robust planar heterojunction (PH) perovskite solar cells (PSCs) has attracted particular attention due to its outstanding properties such as high optical transparency, high electron mobility, and suitable band alignment. However, for most of the reported works, an annealing temperature of 180 °C is generally required. This temperature is reluctantly considered to be a low temperature, especially with respect to the flexible application where 180 °C is still too high for the polyethylene terephthalate flexible substrate to bear. In this contribution, low temperature (about 70 °C) UV/ozone treatment was applied to in situ synthesis of SnO2 films deposited on the fluorine-doped tin oxide substrate as ETL. This method is a facile photochemical treatment which is simple to operate and can easily eliminate the organic components. Accordingly, PH PSCs with UV-sintered SnO2 films as ETL were successfully fabricated for the first time. The device exhibited excellent photovoltaic performance as high as 16.21%, which is even higher than the value (11.49%) reported for a counterpart device with solution-processed and high temperature annealed SnO2 films as ETL. These low temperature solution-processed and UV-sintered SnO2 films are suitable for the low-cost, large yield solution process on a flexible substrate for optoelectronic devices.Keywords: electron transport layer; low temperature processing; perovskite solar cells; tin dioxide; UV irradiation;

The development of solution processable perovskite solar cells (PSCs) has progressed rapidly, and the their highest power conversion efficiency (PCE) has recently surpassed 22%. Further studies to promote market-oriented PSCs call for further reducing the manufacturing cost of the device and addressing the concerns about the possible outflow of toxic lead. To reduce the level of environmental pollution and prevent the health hazard caused by degraded devices (solid waste) and possible lead outflow and to conserve resources, we adopted low-temperature solution-processed, multirecycled glass/FTO/c-TiO2 (m-TiO2) substrates from the degraded devices to fabricate efficient planar heterojunction (PH) and mesoporous (M) PSCs in an environmentally friendly and energy-conserving manner. This is realized by simple and low-temperature processes, including organic solvent washing, ultrasonic cleaning, and UV–ozone treatment. After two rounds of substrate recycling, the PH PSC and M PSC still exhibited peak efficiencies of 11.87% and 11.03%, respectively, indicating the feasibility of recycling used substrates for sustainable, energy and resource conservation-oriented, and environmentally friendly energy production.Keywords: Degraded devices; Environmentally friendly energy production; High performance; Low-temperature processing; Perovskite solar cells; Recycled substrates;

•The SnO2-TiO2 composite layers are low-temperature-processed.•The composite layer for efficient perovskite solar cells was demonstrated.•The composite layer improves the band-alignment and interface-contact.•The composite layer facilitates charge extraction and reduces carrier recombination.•The solar cell based on SnO2-TiO2 layer acquires an efficiency of 14.8%,Inorganic metal oxide electron-transport layers have the potential to promise perovskite solar cells with improved stability and high efficiency, but generally require high temperature to enhance conductivity and reduce defect. Here, low-temperature solution-processed inorganic SnO2-TiO2 composite layer for efficient planar heterojunction perovskite solar cells is demonstrated. The SnO2-TiO2 composite layer brings better bandgap matching at the perovskite/FTO interface that facilitates charge extraction and reduces surface recombination. Cyclic voltammetry, steady-state photoluminescence spectroscopy and electrical impedance spectroscopy were conducted to reveal the energy band alignment and charge carrier dynamics. The SnO2-TiO2 composite films based solar cells acquire a high power conversion efficiency (PCE) of 14.8%, which is higher than PCEs of devices based on individual SnO2 layer and sintered TiO2 layer.Low-temperature solution-processed inorganic SnO2-TiO2 composite layer brings perfect band-gap matching and closes interface-contact between perovskite layer and FTO substrate, which contributes to facilitating charge extraction and reducing carrier recombination, leading to device efficiency as high as 15%.Download high-res image (159KB)Download full-size image

•Pseudo-planar heterojunction perovskite solar cell was reported for the first time.•The device was fabricated by a solution-saving one-step dip-coating method.•The device shows PCE close to that of a conventional spin-coated one.•Models of the abnormal hysteresis, roll-over and current peak were proposed.Rough dense sol-gel-derived titanium dioxide (TiO2) electron-transport layers (ETLs) and smooth organolead halide perovskite (PVK) films for pseudo-planar heterojunction perovskite solar cells (P-PH PVKSCs) were fabricated by a facile one-step dip-coating method. The highly compact TiO2 ETLs and uniform PVK films endow the device a high power conversion efficiency (PCE) of over 11%, which was nearly identical to that of a reference device (12%) fabricated by conventional spin-coating. Furthermore, the device showed no pronounced hysteresis when tested by scanning the voltage in a forward and backward direction, showing the potential of facile and waste-free dip-coating in replacing of spin-coating for large area perovskite solar cells preparation. Lastly, the hysteresis was compared and discussed and models regarding the abnormal hysteresis, roll-over and current peak phenomena were proposed as well.Efficient and hysteresis-less pseudo-planar heterojunction perovskite solar cell fabricated by a facile and solution-saving one-step dip-coating method was proposed for the first time. The device shows a high power conversion efficiency of over 11%, closing to that of a reference device (12%) fabricated by conventional spin-coating. Models regarding the abnormal hysteresis, roll-over and current peak phenomenons were proposed as well.Download high-res image (301KB)Download full-size image

In this paper, polycrystalline perovskite (CH3NH3PbIxCl3−x) photodetectors with a structure of Au/CH3NH3PbIxCl3−x/Au are prepared and are shown to have good performance. The measured electrical parameters demonstrate that the current behavior of the perovskite photodetectors is dependent of work temperature from 300 K to 350 K. We find that only space charge limited conduction mechanism fits the current–voltage (I–V) curves under small external voltage (0.1–0.7 V) both under darkness and illumination. The lattice vibration scattering plays the major role in the dark, leading to a decreased current as the temperature increases under the same external voltage, and an enlarged current increasing with the temperature is due to the leading role of the ionized impurity scattering. At each temperature, the rising slope of the I–V curves decrease with the increase of voltage both under dark and illumination. The values of on/off ratio, responsivity and detectivity increase with the measured temperature, which indicates that the polycrystalline perovskite photodetector can work with better performance at high temperature. However, the stability in the dark gradually becomes weak as the temperature increases, especially at 330 K and above.

Organic–inorganic metal halide perovskites are promising semiconductors for optoelectronic applications. Despite the achievements in device performance, the electrical properties of perovskites have stagnated. Ion migration is speculated to be the main contributing factor for the many unusual electrical phenomena in perovskite-based devices. Here, to understand the intrinsic electrical behavior of perovskites, we constructed metal-oxide-semiconductor (MOS) capacitors based on perovskite films and performed capacitance–voltage (C–V) and current–voltage (I–V) measurements of the capacitors. The results provide direct evidence for the mixed ionic–electronic transport behavior within perovskite films. In the dark, there is electrical hysteresis in both the C–V and I–V curves because the mobile negative ions take part in charge transport despite frequency modulation. However, under illumination, the large amount of photoexcited free carriers screens the influence of the mobile ions with a low concentration, which is responsible for the normal C–V properties. Validation of ion migration for the gate-control ability of MOS capacitors is also helpful for the investigation of perovskite MOS transistors and other gate-control photovoltaic devices.

•A facile synthesis of perovskite microcrystals was demonstrated.•A tetragonal crystal structure was tested by XRD and FE-SEM.•Red shift and thermal stability were investigated by PL and DSC-TGA, respectively.•CH3NH3PbI3 microcrystal promises a candidate for optoelectronic applications.The organic–inorganic hybrid perovskite CH3NH3PbI3 is becoming an interesting material in the field of optoelectronic application. Most of the previous research focused on thin film and crystal growth of this material. Here we describe the rapid preparation of perovskite CH3NH3PbI3 microcrystals using a facile synthesis method at room temperature. By using ultrasound assisted solutions of PbI2 and CH3NH3I precursors in acid solvents, a single-phase perovskite was obtained. X-ray diffraction data reveal that the prepared CH3NH3PbI3 crystals possess a tetragonal structure. FE-SEM and TEM images show the morphology and grain size of CH3NH3PbI3 crystals. UV-VIS-NIR and PL measurements indicate that the perovskite crystals show a slight reduced bandgap, accompanying with red shift, compared with the perovskite polycrystalline films. DSC-TGA demonstrates that the perovskite microcrystals show the better thermal stability than that of the perovskite films, which suggests the wide potential application.

•Polymer assisted growth of high-quality perovskite films was demonstrated.•Polymer PMMA can retard nucleation and crystal growth of perovskite.•The interaction between the perovskite films and PMMA was addressed.•Planar-heterojunction solar cells with efficiencies of 15% were achieved.Long-chain insulating polymers dissolved in perovskite precursor solution can assemble the polymer scaffold acted as the function of TiO2 porous layer to improve the quality of the perovskite films. Here, perovskite films with high electronic quality were prepared by mediating nucleation and crystal growth. Polymer post treatment can induce Lewis acid-base reaction with PbCl2, which alleviates the reaction velocity between PbCl2 and CH3NH3I, and then retard perovskite crystallization. The interactions between the perovskite films and polymer with different concentration are addressed to interpret the function and evolution of the polymer long-chains during the annealing process. These solar cells exhibit efficiency more than 15% with small variation. Our work demonstrates the value of retarding nucleation and crystal growth by Lewis acid-base adducts for high-quality perovskite films.

Currently, most efficient perovskite solar cells (PVKSCs) with a p–i–n structure require simultaneously electron transport layers (ETLs) and hole transport layers (HTLs) to help collecting photogenerated electrons and holes for obtaining high performance. ETL free planar PVKSC is a relatively new and simple structured solar cell that gets rid of the complex and high temperature required ETL (such as compact and mesoporous TiO2). Here, we demonstrate the critical role of high coverage of perovskite in efficient ETL free PVKSCs from an energy band and equivalent circuit model perspective. From an electrical point of view, we confirmed that the low coverage of perovskite does cause localized short circuit of the device. With coverage optimization, a planar p–i–n++ device with a power conversion efficiency of over 11% was achieved, implying that the ETL layer may not be necessary for an efficient device as long as the perovskite coverage is approaching 100%.Keywords: electron-transport layer; energy band structure; equivalent circuit model; full coverage perovskite; perovskite solar cells; ultraviolet-ozone treatment;

•UVO treatment greatly affected perovskite coverage and structure.•UVO treatment of FTO substrate resulted in high-efficient perovskite solar cells.•The best device showed an efficiency of 10.67%.Planar perovskite solar cells with a p–i–n structure use both hole-transport layers and electron-transport layers to promote collection of photogenerated holes and electrons for achieving high performance, wherein a high temperature processed compact and mesoporous titanium dioxide are usually required. We report here efficient perovskite solar cells grown directly on ultraviolet–ozone treated fluorine-doped tin oxide (FTO) substrates without using any electron-transport layers. The morphology, structure, optical–electrical properties of perovskite films deposited on FTO substrates with and without ultraviolet–ozone treatment and their corresponding devices׳ performance have been studied and compared. Ultraviolet–ozone treatment of FTO substrates improves the smoothness and coverage of CH3NH3PbI3−xClx films, which avoids direct contact between FTO and hole-transport layer. A planar electron-transport layer free device with a power conversion efficiency of over 10% has been achieved, suggesting that the widely adopted electron-transport layer is not a requirement for an efficient device.In this article, simple-structured and electron-transport layer free planar perovskite solar cells with power conversion efficiency of over 10% by simple one-step solution process under sub-100 °C temperature has been achieved.

•N, N-Dimethylformamide (DMF) can easily dissolve the perovskite films of the degraded devices.•The obtained glass/FTO substrates can be easily rinsed clean with low-energy solution processes.•The cleaned glass/FTO substrates can participate in the new round of devices preparation.•The best device showed an efficiency of 9.97% after 2 times of glass/FTO substrates recycling.Perovskite solar cells (PVKSCs) are an attractive technology that finds their potential in the field of renewable energy sources. Transparent conductive oxides including fluorine-doped tin dioxide (FTO) and indium tin oxide (ITO) with high optical transmittance and low electrical resistivity are key components in PVKSCs. While commercial FTO or ITO either requires high temperature and high vacuum process or contains rare indium element, which will increase the production cost of PVKSCs. Here we report efficient electron-transport layer (ETL) free planar PVKSCs using the recycled FTO/glass substrates from degraded devices. By simple and low-temperature processes including organic solvent washing, ultrasonic cleaning and UV ozone treatment, the discarded substrates can be readily reused for fabricating ETL-free planar PVKSCs. The UV–vis optical transmission, crystal structure, sheet resistance, surface morphology, elemental composition and static contact angles measurement of the original and recycled FTO/glass substrates (one time and two times) were measured and compared. Planar ETL-free devices with power conversion efficiencies of about 10% have been achieved by adopting the recycled FTO/glass substrates, which are comparable to that of the devices based on the original FTO substrates, suggesting the feasibility of recycling the FTO/glass substrates from degraded devices for fabricating ETL-free PVKSCs.In this article, efficient electron-transport layer-free planar perovskite solar cells with power conversion efficiencies of about 10% have been achieved by recycling low-energy solution processed one time and two times used Glass/FTO substrates from degraded devices, establishing an instructive model towards an attractive technology for sustainable, scalable, energy and resources-conservation-oriented as well as environmentally-friendly energy production.

•Perovskite materials were developed via microwave radiation.•Perovskite solar cell using microwave radiation exhibits an efficiency of 10.29%.•Perovskite solar cell were performed in air condition under high humidity (∼60%).•A fast and less energy-intensive process was introduced in device fabrication.A rapid annealing technique for fabricating perovskite materials via microwave radiation in air condition is presented. A planar-heterojunction perovskite device via microwave radiation within 6 min exhibits an efficiency of 10.29%, compared to 11.08% for a 90 min heating-annealed device in inert atmosphere, which is higher than that (8.04%) of a heating-annealed device in air condition under high humidity (∼60%). We believe that the microwave annealing technique provides a fast and less energy-intensive process for fabricating ideal perovskite active layers for high performance solar cells.

Quasi-solid-state dye-sensitized solar cells (DSSCs) fabricated with the mixed-plasticizer (MP) modified polymer electrolyte are reported in this paper. The mixture of hydroxyethyl methylacrylate (HEMA) and ethylene glycol (EG) as plasticizer are added into the original composite polymer electrolyte (CPE) based on poly(ethylene oxide)/poly(vinylidene fluoride-hexafluoropropylene) (PEO/P(VDF-HFP)) and KI/I2. The olefinic bonds in HEMA and hydroxyl bonds in EG provide strong molecular polarity to effectively reduce the crystallinity of the polymer electrolyte, thus largely improve the ionic conductivity of the CPE. On account of MP, the decrease of crystallinity provides a better photovoltaic performance, the best photon-to-current conversion efficiency is 6.79% with a short current density Jsc of 15.23 mA cm−2 under AM 1.5 illumination. Fourier transforms infrared (FT-IR), differential scanning calorimetry (DSC), ionic conductivity, electrochemical impedance spectroscopy are test to analyze superior property of DSSCs assembled with MP-modified CPEs. It shows that the performance of the CPEs can be largely improved by MP.

•Perovskite films treated by two annealing methods were compared.•Annealing temperature and duration greatly affected perovskite films.•Slow annealing resulted in high-efficient perovskite solar cells.•The slow annealing device showed the best efficiency of 13.58%.The morphology, structure, optical and electrical properties of perovskite films treated by two different annealing methods with different annealing temperature ramp and their corresponding device performance have been studied and compared. Annealing temperature ramp significantly influences the surface morphology and optical properties of perovskite films which determines the performance of solar cells which determines the performance of solar cells. The perovskite films treated by one-step direct annealing method tend to exhibit irregular and weak ultraviolet–visible absorption spectrum, which can easily result in great variation in the final performance of solar cells. While multi-step slow annealing is beneficial for preparing highly uniform and well-crystallized perovskite films, and thus these devices present tightly-distributed performance parameters. The best device treated by multi-step slow annealing method showed a short circuit current density of 21.49 mA/cm2, an open circuit voltage of 0.988 V, a fill factor of 64.86%, and a power conversion efficiency (PCE) of 13.58%, which is a 57% enhancement of the overall PCE relative to 8.65% of the device treated by one-step annealing method. These findings suggest that optimized slow temperature ramp is necessary to prepare high-efficient and well-reproducible perovskite solar cells.In this article, multi-step slow annealing is adopted for preparing highly uniform perovskite films and high-efficient and well-reproducible planar perovskite solar cells that present tightly-distributed performance parameters.

Depositing pinhole-free perovskite films is of vital importance for achieving high performance perovskite solar cells, especially in a planar heterojunction device. Here, perovskite films with coverage approaching 100% and with highly oriented crystal domains were obtained by carefully controlling the annealing temperature and duration. Perovskite solar cells with an average efficiency of 12% and a maximum efficiency of 15.17% were achieved in a planar heterojunction structure. Comprehensive characterization and analysis showed that appropriate annealing temperature and duration allowed the perovskite crystals to grow slowly, resulting in highly oriented crystal domains without any internal voids or pinholes. The anisotropic transport properties of perovskite crystals ensure efficient electron and hole transport to their corresponding electrodes.

•ITO-free polymer solar cells (PSCs) were fabricated by dip coating method.•Highly conductive PEDOT:PSS films used as anode were prepared.•The ITO-free PSCs performance was comparable with that of the spin coated devices.•Our results suggest the possibility of replacing ITO with dip coated PEDOT:PSS.The fabrication of anodes and active layers by dip-coating in indium tin oxide (ITO)-free polymer solar cells (PSCs) is investigated. A highly conductive poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) layer was used as an anode while a blend film of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) was employed as an active layer. The transmittance and sheet resistance of dip-coated PEDOT:PSS layers prepared with different thickness were studied. These layers were integrated into PSCs. The PSCs with the dip-coated PEDOT:PSS and P3HT:PCBM films exhibited power conversion efficiencies of 3.21% and 3.03% on glass and polyethylene terephthalate substrates, respectively, comparable to those of conventional ITO-based cells. Our research results suggest the feasibility of fabricating PSCs without a traditional spin-coating process and the possibility to substitute the ITO electrodes for conducting polymer films using the facile dip-coating method.

•ZnO prepared by MOCVD was used in inverted polymer solar cells.•The effects of ZnO thickness on device performance were investigated.•The effects of boron doped ZnO on device performance were investigated.•ZnO layer controls the tradeoff between Jsc, Voc and FF.We report on the photovoltaic properties of inverted polymer solar cells (IPSCs) where the transparent indium tin oxide (ITO) electrode was modified by a ZnO layer using metal organic chemical vapor deposition (MOCVD). The intrinsic ZnO (i-ZnO) layers were deposited with varying thicknesses from 0 to 1500 nm. The work function and surface morphology of ITO/i-ZnO were found to be dependent on the i-ZnO thickness. When the thickness of the i-ZnO layer was 80 nm, optimized IPSCs with a power conversion efficiency (PCE) of 2.93% was achieved. Furthermore, the i-ZnO layer doped with boron (BZO) was investigated. The best IPSC with a BZO layer showed a PCE of 3.26%, which is higher than that (2.93%) of the device with the i-ZnO layer. The better performance is due to combined effects of improvement in charge collection and conductivity of BZO/ITO electrode.

•An ultrathin and discrete TiO2 (u-TiO2) was fabricated at low temperature.•High-performance perovskite solar cells based u-TiO2was realized.•u-TiO2 between perovskite and FTO functions as a bridge for electron transport.•u-TiO2 accelerates electron transfer and alleviates charge recombination.A compact TiO2 (c-TiO2) layer fabricated by spin coating or spray pyrolysis following a high-temperature sintering is a routine in high-performance planar heterojunction perovskite solar cells. Here, we demonstrate an effective low-temperature approach to fabricate an ultrathin and discrete TiO2 (u-TiO2) for enhancing photovoltaic performance of perovskite solar cells. Via hydrolysis of low-concentration TiCl4 solution at 70 °C, u-TiO2 was grown on a fluorine doped tin oxide (FTO) substrate, forming the electron selective contact with the photoactive CH3NH3PbI3 film. The perovskite solar cell using u-TiO2 achieves an efficiency of 13.42%, which is compared to 13.56% of the device using c-TiO2 prepared by high-temperature sintering. Cyclic voltammetry, steady-state photoluminescence spectroscopy and electrical impedance spectroscopy were conducted to study interface engineering and charge carrier dynamics. Our results suggest that u-TiO2 functions as a bridge for electron transport between perovskite and FTO, which accelerates electron transfer and alleviates charge recombination.

Depositing pinhole-free perovskite films is of vital importance for achieving high performance perovskite solar cells, especially in a planar heterojunction device. Here, perovskite films with coverage approaching 100% and with highly oriented crystal domains were obtained by carefully controlling the annealing temperature and duration. Perovskite solar cells with an average efficiency of 12% and a maximum efficiency of 15.17% were achieved in a planar heterojunction structure. Comprehensive characterization and analysis showed that appropriate annealing temperature and duration allowed the perovskite crystals to grow slowly, resulting in highly oriented crystal domains without any internal voids or pinholes. The anisotropic transport properties of perovskite crystals ensure efficient electron and hole transport to their corresponding electrodes.

Organic–inorganic metal halide perovskites are promising semiconductors for optoelectronic applications. Despite the achievements in device performance, the electrical properties of perovskites have stagnated. Ion migration is speculated to be the main contributing factor for the many unusual electrical phenomena in perovskite-based devices. Here, to understand the intrinsic electrical behavior of perovskites, we constructed metal-oxide-semiconductor (MOS) capacitors based on perovskite films and performed capacitance–voltage (C–V) and current–voltage (I–V) measurements of the capacitors. The results provide direct evidence for the mixed ionic–electronic transport behavior within perovskite films. In the dark, there is electrical hysteresis in both the C–V and I–V curves because the mobile negative ions take part in charge transport despite frequency modulation. However, under illumination, the large amount of photoexcited free carriers screens the influence of the mobile ions with a low concentration, which is responsible for the normal C–V properties. Validation of ion migration for the gate-control ability of MOS capacitors is also helpful for the investigation of perovskite MOS transistors and other gate-control photovoltaic devices.