Study On Efficient And Stable Methylammonium-free Perovskite Solar Cells

In the past ten years,perovskite solar cells（PSCs）have made amazing progress.Researchers have used a series of strategies such as component engineering,additive engineering,dimensional control,interface modification,and transport layer optimization to make the power conversion efficiency（PCE）increased from the initial 3.8%to the certified 25.5%.Although considerable progress has been made in optimizing the PCE,there are still many problems with the stability of PSCs,a large part of which is caused by the thermal instability of methylammonium（MA）molecules in the commonly used perovskite active layer materials.Recently,MA-free PSCs have attracted attention due to their better band gap and excellent stability.However,due to the large energy loss caused by defects,the development of its PCE in MA-free PSCs has been lagging behind that of MA-based PSCs.Based on this,in order to simultaneously improve the PCE and stability of MA-free PSCs,this thesis conducts research from the following two aspects:component engineering and surface reconstruction.By adjusting the concentration of components in the precursor through component engineering to optimize device efficiency.First,based on the passivation effect of excessive lead iodide（Pb I₂）on the grain boundary,this thesis adjusted the composition of the Pb I₂ concentration to obtain an optimized concentration（1.3 mol/L）,and obtained a PCE of 18.31%.On this basis,by adding formamidine hydrochloride（FACl）additives to the precursor to improve the crystallization and surface morphology of the perovskite film,increase the grain size,successfully prepare high-quality perovskite films,and further enhance the photovoltaic performance of MA-free PSCs with a PCE of 19.2%.By depositing hydrophobic ammonium salt N-hexyl trimethylammonium bromide（HTAB）on the surface of the perovskite film,2D particles are formed and uniformly distributed on the surface of the methylammonium-free perovskite film.The 2D particles coated on the surface of the perovskite significantly smooth the surface potential and suppress the carrier loss caused by defects,thereby improving the charge collection efficiency at the interface.Therefore,the PCE of the device after HTAB surface modification get increased from 18.85%to 20.36%.In addition,these 2D particles structure help to increase the hydrophobicity of perovskite films and improve the long-term stability of devices.The device still maintains more than 95%of the original PCE after aging for 500 hours in a humidity environment of 35%-40%RH.In addition,the device showed better operation stability after 100 hours of continuous sunlight exposure,still maintaining 70% of the initial PCE.