Performance Optimization Of Planar Perovskite Solar Cells Based On SnO₂ Electron Transport Layer

Organic-inorganic metal halide perovskites have great commercial application potential and scientific research significance in photovoltaic fields owing to their excellent optoelectronic properties,including outstanding optical absorption efficiency,large charge carrier diffusion length,low exciton binding energy,and so on.Currently,the latest solar cells using perovskites as absorber layers have yielded a power conversion efficiency?PCE?of 23.7%,much higher than those of other solar cells.The PCE of perovskite solar cells is crucially limited by the quality of perovskite films and the interficial condition of electron transport layer?ETL?/perovskite and perovskite/hole transport layer?HTL?interfaces.In this paper,two strategies were developed to improve perovskite performance.On one hand,the quality of perovskite films was significantly improved by introducing volatile addtitive into perovskite precursor solutions during the film growth.On the other hand,better interficial condition of SnO₂/perovskite interface was achieved by spin coating a NaCl layer on SnO₂ ETL.The main contents are shown as following:?1?the volatile Lewis base,thioacetaminde?CH₃CSNH₂?,abbreviated as TAA,was used as an additive added into methylammonium lead iodide?MAPbI₃?perovskite precursor solution to slow down perovskite film growth and increase film grain size by forming a MAI·PbI₂·DMSO·TAA adduct.The average grain size of optimal perovskite films with 1.0%TAA reaches as high as¹?m,which greatly reduces grain boundries and enhance carrier lifetime.However,the average gain size drops dramatically to the value of samples without TAA and then it keeps nearly unchanged upon further increasing TAA.This unusual grain size change is attributed to the volatility of additives.A working mechanism is proposed concerning the perovskite growth with the aid of volatile Lewis base.The perovskite solar cells assembled by MAPbI₃ films with 1.0%TAA yield a PCE of 18.9%and retain 88.9%of its initial PCE after 816hours aging in air,exhibiting excellent performance with outstanding stability.?2?NaCl was deposited on SnO₂ via spin-coating to modify the ETL/perovskite interface,which can partially dissolve in the perovskite precursor solution to assist perovskite crystallization and increase perovskite grain size.Also,by interacting with MAPbI₃ perovskite layer and SnO₂ electron transport layer,the NaCl layer enhances the chemical bonding at the interface,reduces defect states,and greatly improve carrier lifetime and transport efficiency.Furthermore,the NaCl layer reduces the work function of ETL,leading to better energy allignment with perovskite absorber layer.The perovskite solar cells assembled by 0.25 mol/L NaCl modification gain a V_OC as high as 1.141 V and achieve a photoelectric conversion efficiency of 19.49%.