Interfacial Regulation And Performance Study Of High Efficiency And Low Hysteresis Perovskite Solar Cells

In recent years,perovskite solar cells（PSCs）have been extensively studied for the advantages of high efficiency,low cost and solution processing.PSC uses ABX₃perovskite material as the core of light absorption,which produces electron-hole pairs and converts solar energy into electricity under AM 1.5G irradiation(100 mW cm^-2).Meanwhile,the interface modification between electron-transporting layer（ETL）and perovskite layer can optimize its interface energy level,induce the growth of perovskite,and ultimately improve the corresponding performance and stability of device.Therefore,it is of great scientific significance and application values to study the grain boundary of perovskite layer and the ETL/perovskite interface for the construction of high efficiency,low hysteresis and high stability PSC.Based on these,this dissertation focuses on the grain boundary of perovskite layer and the ETL/perovskite interface,and a series of work are carried out by new methods,new additives and multifunctional interface materials.The specific research contents of this dissertation are as follows:（1）An in situ dissolution-recrystallization method（DRM）was provided for the preparation of high efficiency,and high stability PSC.The in situ DRM with mixed solvent dimethylsulfoxide（DMSO）and chlorobenzene（CB）treating the perovskite film could effectively promote the perovskite grain growth and suture the perovskite grain boundary,which improved the quality of perovskite film by reducing the defects such as pinhole and grain boundary.Through optimization,the short-circuit current density(J_sc)and open-circuit voltage(V_oc)of DRM2-treated（4μL DMSO and 96μL CB）PSC were increased compared with the CB-treated device under a standard sun irradiation,and the DRM2-treated device showed a remarkable photoelectric conversion efficiency（PCE）of 16.76%.（2）A low cost(1 RMB g^-1)4-methylbenzenesulfonic acid（4-MSA）additive was introduced into perovskite precursor to control perovskite crystallization and suture grain boundaries.Furthermore,the sulfonic acid group of 4-MSA could be chemically bonded with mesoporous TiO₂（mp-TiO₂）,and the benzene ring had a?-conjugated structure,which were conducive to the carrier transport at perovskite grain boundary.Consequently,the optimal PCE of PSC based on 6 mg mL^-11 4-MSA doped perovskite thin film was 17.58%and the hysteresis was negligible（HI=0.05）under a standard solar irradiation.Under the same test conditions,the PCE of PSC based on the 4-MSA undoped perovskite thin film was 14.08%,and the HI of corresponding device was 0.42.（3）An eco-friendly and low-temperature CsI interface modification layer was introduced to passivate the interface between mp-TiO₂ and MAPbI₃,and thus improved the stability of TiO₂/MAPbI₃ interface.Furthermore,CsI interface modification could fill the partial grain boundaries of mp-TiO₂ and induce the growth of large-grain and low-defect MAPbI₃ perovskite film.Simultaneously,CsI interface modification could reduce the work function（W_F）of TiO₂,increase the built-in potential of device,and facilitate the internal carriers separation,transport and collection.Ultimately,the performance of the device based on CsI interface modification was significantly improved,and the optimal PCE of the corresponding device was increased from 14.38%（reference device）to 17.10%.In addition,the PSC based on CsI interface modification exhibited negligible hysteresis and good stability.（4）A pyridine sulfonic acid interfacial layer was introduced to improve the ETL/perovskite interface.Based on these,low-defect perovskite thin films were prepared.Next,the effect of functional group position changes of two isomers of pyridine sulfonic acid（2-PA and 3-PA）on the performances of PSCs were investigated.Under a standard sunlight condition,the PCE of the reference device was 14.65%,and the HI of the corresponding PSC was 0.31.The PCEs of devices based on 2-PA and 3-PA interface modification were 16.54%and 16.88%,respectively,and the HI of both devices were0.02.The results showed that the performance of device based on 3-PA interface modification was better than that of based on 2-PA interface modification.This is because pyridine nitrogen atom of 3-PA molecule had greater local charge than that of the 2-PA molecule.Furthermore,the valence band edge(E_CB)of TiO₂ based on 3-PA interface modification more negatively shifted than that of TiO₂ based on 2-PA interface modification,which were beneficial to the photon-generated carrier transport from perovskite to TiO₂.（5）A bifunctional 4-picolinic acid（4-PA）self-assembled monolayer（SAM）was introduced as the interface linker of ETL/perovskite.Further,the effects of 4-PA SAM on the interfacial electrical properties,grain growth of perovskite,and the photoelectric performance of the PSC were investigated.Finally,under a standard solar irradiation,the PCE of PSC based on 4-PA SAM modification reached 18.90%,and the HI was 0.03.Under the same test conditions,the PCE of device without 4-PA SAM modification was only 14.65%,and the corresponding HI was 0.31.It can be concluded that the 4-PA SAM modified device exhibited significantly improved device performance and negligible hysteresis were due to the bifunctional 4-PA SAM could be grappled with the TiO₂ and perovskite,respectively,and preferably balance electrons and holes transfer.