Research On The Perovskite Films Of CH₃NH₃PbI₃ And Devices For High Performance Solar Cells

Semiconductor perovskite material MAPbI₃?MA⁺=CH₃NH₃⁺?has the suitable band gap,long carrier migration distances and high mobility which make the solar cell device based on its film has wide spectral response range and high photoelectric conversion quantum efficiency.At present,MAPbI₃ film is mainly prepared by solution method,which has the advantages of low temperature,simple operation and low cost.However,the perovskite film prepared from DMF solution has greatly high void ratio,resulting in poor performance of the solar cell device.On the other hand,the energy level differences and contact problems among the layers of the devices have a strong impact on the carriers transport in the whole device,and thus affect the device performance.Therefore,the performance of solar cells can be effectively improved by adding additives to improve the quality of MAPbI₃ films and using interface modification to optimize the energy level matching and interface contact quality of devices.Furthermore,MAPbI₃ contains lead,which is harmful to humans.As a result,it is another important research direction for perovskite device to prepare lead-free perovskite solar cell device with high efficiency and stability.To deal with these problems,this paper mainly studies the following aspects:The quality of perovskite films was improved by adding unconjugated polyacrylonitrile?PAN?to the precursor solution of MAPbI₃.When the PAN concentration was 20 mg/mL,MAPbI₃:PAN film had the highest quality.Based on this film,perovskite solar cell with a small area?0.12 cm²?had the photoelectric conversion efficiency of 14.48%,and the device with a large area?1 cm²?also had the efficiency of7.32%.Comparing the non-conjugated polymer PAN with the conjugated polymer poly-3-hexylthiophene?P3HT?,it is found that the device with P3HT had poor performance because charge transfer between P3HT and MAPbI₃ results in carrier recombination.In order to reduce the limitation of PAN retained in perovskite film on improving device performance,volatile organic amine hydrochloride was added into MAPbI₃precursor solution.The organic amine hydrochloride can improve the quality of the perovskite film by increasing the number of nucleation during film formation,promoting the space occupation competition among organic groups,and the recrystallization of perovskite film,so as to improve the film compactness and smoothness.Among the organic amine hydrochlorides,aniline hydrochloride?BACl?and diethylamine hydrochloride?DEACl?are most beneficial to the improvement of the quality of MAPbI₃ film.By studying effects of the hydrochloride concentration and annealing time on film performance,the optimal process for film preparation was obtained,that is,the hydrochloride concentration was 0.4 M,the spin coating rate was4000 rpm,the spin coating time was 30 s,and the annealing process was performed at90°C for 10 min.Based on this process,the efficiencies of devices with BACl and DEACl were increased to 14.76%and 14.15%,respectively.In order to improve the energy level matching and interface contact among the various layers in the solar cell device,the surface work function of ITO was significantly increased and the quality of the perovskite film deposited on the ITO was improved,when indium tin oxide?ITO?was modified with polyethylene glycol?PEG?:graphene oxide?GO?composite.Thus,a hole transport layer-free perovskite solar cell with an efficiency of 9.27%was obtained.On the basis of this,PEG:GO was used to modify PEDOT:PSS,which improved the surface work function of PEDOT:PSS and promoted the growth of perovskite film grains.In addition,the PCE of planar heterojunction perovskite solar cell,which was modified with 2D material MoS₂ at PCBM/Ag interface,was improved from 16.89%up to 19.14%,along with the open circuit voltage increasing from 0.96 V to 1.14 V.In order to further improve the light absorption and charge transport properties of perovskite thin films,the laminated perovskite thin films with different grain sizes were prepared by applying the effect of organic amine hydrochloride on solubility of MAPbI₃in aniline solvent.Based on this film,a device without modified layer was obtained with an efficiency of 18.09%.On this basis,the PEG:GO and MoS₂ modified layers were introduced into the solar cell,and the efficiency of the device was further improved to 20.68%,and the filling factor was up to 80.8%.Meanwhile,the increase of grain size of laminated thin film further improves the stability of the device.To prepare lead-free perovskite solar cell devices with high stability,the antioxidant triphenyl phosphite?TPPi?was applied to inhibit the oxidation of Sn²⁺in CsSnI₃.The stability of CsSnI₃ solution was enhanced,and the solution would not decompose after being stored for 90 days.The stable CsSnI₃ film was prepared from this precursor solution,and this film has low concentration of tin vacancy doped carriers.Based on this film,the lead-free perovskite solar cell device with PCE up to 5.03%was prepared.