Stability Study Of Two-dimensional Perovskite And Interfacial Property Regulation In Devices

3D perovskite materials have many excellent photoelectric properties,such as strong optical absorption,small exciton binding energy,bipolar charge transfer and long carrier diffusion length.These advantages make the photoelectric conversion efficiency of 3D perovskite solar cells break through from 9.7%to 25.2%in a few years.The perovskite solar cells have become an important research topic in the field of photovoltaics.At present,the bottleneck for commercialization of perovskite solar cells(PSCs)lies in the stability,especially the stability of perovskite materials.2D perovskite material has better stability than 3D ones.Using it as perovskite absorbing layer or interface modification layer can significantly improve device stability,which is an effective strategy to solve the stability problem of PSCs.Firstly,the thermal stability of a typical two-dimensional perovskite material is systematically studied.Then,the effects of Br doping,the length of carbon chain of ammonium salts and the types of ammonium salts on the interfacial properties of 2D/3D stacking structure and the photoelectric performance and stability of the cell are studied respectively.The main contents are as follows:(1)Thermal stability is one of the important characteristics of perovskite materials.For a typical 2D perovskite material(CH3NH3)2Pb(SCN)2I2,we studied its thermal degradation process by thermogravimetry and mass spectrometry.At the same time,with help of theoretical calculation,we speculated the reaction path of some products in the degradation process,and obtained the detailed degradation path of MA2Pb(SCN)2I2.The effect of SCN-on the crystallization process of 3D perovskite was also studied.The results show that SCN-can regulate the crystallinity of 3D perovskite by increasing the grain size of perovskite and decreasing the grain boundary.The ultimate photoelectric conversion efficiency(PCE)was increased by 10%.In addition,due to the improvement of crystallinity,the stability of perovskite film in humid environment has been significantly improved.The surface of 3D perovskite film turns yellow completely after 3.5 hours in the environment of 99%humidity,but the surface of SCN-doped Perovskite film has little change.(2)In the 2D/3D stacking structure,the 2D perovskite layer is so thin that it may introduce new defects while passivating the surface defects of 3D perovskite at the bottom.In this part,we studied a more effective control strategy,that is,Br doping in the 2D perovskite layer to further reduce defect states,and ultimately achieve better interface passivation effect.The results of steady-state fluorescence(PL)and time-resolved fluorescence spectroscopy(TRPL)show that the exciton lifetime of the Br-doped 2D/3D stacked structure is longer.Furthermore,the analysis of electrochemical impedance(EIS)measurement shows that the charge recombination in the new 2D/3D stacking structure is effectively suppressed.Based on this,the open-circuit voltage(Voc),filling factor(FF)have been significantly enhanced.The PCE was increased from 18.01%to 20.07%.In addition,the efficiency of 3D perovskite cells decreased by 30%after 80 days in 38%humidity environment,while the efficiency of Br-doped 2D/3D cells still maintained 90%of its original,showing excellent stability.(3)The length of organic amine carbon chain has an important influence on the interface characteristics of 2D/3D stacking structure.By means of PL,TRPL and EIS characterization,it is proved that the passivation effect of 2D perovskite interface layer corresponding to HAI(hexamine hydroiodate)is better than that of BAI(butyl iodide amine).Compared with BAI-based devices,the charge recombination at the interface of HAI-based devices is further suppressed,and the PCE is increased from 18.83%to 20.67%.In addition,the contact angle and device stability monitoring experiments show that the surface of 2D perovskite layer based on HAI is more hydrophobic,which can prevent water vapor from corroding the bottom 3D perovskite,and improve the stability of devices in air.After 50 days in the air with humidity of 55%-75%,the efficiency of 3D perovskite based PSCs decreased to below 80%,while the efficiency of 3D+HAI counterpart has little change.Moreover,the thermal stability has also been improved due to the existence of 2D perovskite,which effectively prevents ion migration channels.After 600 hours in an 85? oven,the efficiency of the 3D perovskite based PSCs decreased to below 60%,while the efficiency of the 3D+HAI counterpart still maintained 80%of its original.(4)A new ammonium salt HD ADI(1,6-hexamethylenediamine hydroiodate)was used to synthesize 2D perovskite and was applied in 2D/3D stacking structure.It is shown that the introduction of HDADI-based 2D perovskite interface layer can greatly improve the ultraviolet resistance of perovskite.At the same time,the 2D perovskite interface layer can passivate the surface defects of the bottom 3D perovskite,effectively inhibit the charge recombination inside the device,and the corresponding PCE is up to 19.44%.In addition,water contact angle experiments show that the surface of 3D+2D perovskite is more hydrophobic,resulting in an improved stability in air.After 60 days in the air with humidity of 55%-75%,the efficiency of 3D perovskite based PSCs decreased to below 30%,while the efficiency of 3D+2D counterpart still maintained 80%of its original.Moreover,due to the existence of 2D perovskite,which can effectively prevent ion migration channels,the thermal stability of the PSCs has also been improved.After 350 hours in an 85? oven,the efficiency of the 3D perovskite based PSCs decreased to less than 40%of the original,while the efficiency of the 3D + 2D counterpart still maintained 60%of the original..