Pseudohalide(SCN)-based Perovskite Solar Cells

The efficiency of perovskite solar cells(PSCs)is advancing by leaps and bounds.At present,the highest efficiency of single-cell perovskite solar cells is close to that of commercial monocrystalline silicon thin film solar cells.The efficiency of perovskite solar cells is very good,but the stability has not been ideal so far.In addition to many external factors such as damp heat,I-ions in perovskite materials may have some negative effects on stability.Based on the above considerations,this paper designs the device structure from the perovskite material itself,and uses solvent engineering,band gap engineering,intramolecular exchange reaction to prepare high quality perovskite film,and successfully prepare halogen-like(SCN-)based perovskite solar cells:FAPb(SCN)2I,FA0.98K0.02Pb(SCN)2I based non-hole transport layer perovskite solar cells,CsPb(SCN)I2 based all inorganic perovskite solar cells.Further,magnesium phthalocyanine(MgPc)is used as a hole transport layer material(HTM)of a perovskite solar cell,and a carbon-based perovskite solar cell having high efficiency and high stability is obtained.The main research results obtained in this paper are as follows:1)Herein,we report a method for the design of new perovskite materials that involves the replacement of the halide ions with pseudohalide ions in formamidinium lead halide(FAPbX3,X=Cl,Br,I).Furthermore,in order to improve the stability of the metal halide perovskites(with the general formula ABX3),organic cations(FA+)at A sites was partially replaced by potassium cations.In this study,we developed a new perovskite material,FA0.98K0.02Pb(SCN)2I,for PSCs synthesized through a convenient two-step sequential solution-phase process.All the fabrication steps of FA0.98K0.02Pb(SCN)2I based PSCs were conducted in ambient air without the humidity control.This new mixed-cation perovskite has a well suitable band gap(1.51 eV)in room temperature,and high absorption coefficient even reaches the near-infrared absorption range.The carbon electrode-based FA0.98K0.02Pb(SCN)2I non-hole transport layer perovskite solar cell exhibits excellent work conversion efficiency(PCE)as high as 13.39%.Importantly,the PSC based on FA0.98K0.02Pb(SCN)2I exhibited only 12%PCE loss after continuous heat treatment at 100? for 1020 hours,showing good long-term stability.Further,a solar cell based on a FA0.98K0.02Pb(SCN)2I film exhibits good resistance of heat and moisture.This work helps solve difficult problems such as thermal and moisture instability of the perovskite material itself,and is a step toward achieving efficient and stable perovskite solar cells for further research and practical purposes.2)Exploring magnesium phthalocyanine(MgPc)as a hole transport layer material of a perovskite solar cell,and obtaining a carbon-based perovskite solar cell device with high efficiency and high stability.Under continuous heating at 100? for more than 2,100 hours,the PCE of the perovskite solar cell based on MgPc as HTM showed no attenuation and exhibited excellent stability.In addition,MgPc does not require an additional additive such as a lithium salt as a hole transport layer material,has high hole mobility,is simple to use,is easy to handle,and is relatively inexpensive to obtain raw materials compared to Spiro-OMeTAD.Efforts have been made to explore new hole transport layer materials for perovskite solar cells.3)In the inorganic perovskite material,replace one of the CsPbI3 ions with a halogen-like SCN-to obtain a CsPb(SCN)I2 inorganic perovskite material,and use the carbon electrode as the back electrode of the perovskite solar cell.The hole transport layer material was fabricated into a carbon-based all-inorganic perovskite solar cell of CsPb(SCN)I2,which has a band gap of 1.73 eV similar to that of CsPbI3,and has high efficiency and better stability.It provides new ideas and directions for the exploration of new inorganic perovskite materials,and lays a foundation for the preparation of more efficient and stable all-inorganic perovskite solar cells.