Impact of Hole-Transport Layer and Interface Passivation on Halide Segregation in Mixed-Halide Perovskites

摘要

Mixed-halide perovskites offer ideal bandgaps for tandem solar cells, but photoinducedhalide segregation compromises photovoltaic device performance.This study explores the influence of a hole-transport layer, necessary for a fulldevice, by monitoring halide segregation through in situ, concurrent X-ray diffractionand photoluminescence measurements to disentangle compositionaland optoelectronic changes. This work demonstrates that top coatingFA_(0.83)Cs_(0.17)Pb(Br_(0.4)I_(0.6))_3 perovskite films with a poly(triaryl)amine (PTAA)hole-extraction layer surprisingly leads to suppression of halide segregationbecause photogenerated charge carriers are rapidly trapped at interfacialdefects that do not drive halide segregation. However, the generation ofiodide-enriched regions near the perovskite/PTAA interface enhances holeback-transfer from the PTAA layer through improved energy level offsets,increasing radiative recombination losses. It is further found that whilepassivation with a piperidinium salt slows halide segregation in perovskitefilms, the addition of a PTAA top-coating accelerates such effects, elucidatingthe specific nature of trap types that are able to drive the halide segregationprocess. This work highlights the importance of selective passivationtechniques for achieving efficient and stable wide-bandgap perovskitephotovoltaic devices.