Reducing Hole Trap Density in Sn–Pb Perovskite Solar Cells via Molecular Phenylhydrazine

Narrow-bandgap Sn–Pb-alloyed perovskite is potential for a bottom cell in perovskite tandem solar cells. However, Sn-contained perovskites tend to be readily oxidized in air atmosphere, which has ill influence on stability and photovoltaic performance. Herein, a method to suppress oxidation of divalent tin via post-treatment of perovskite film with phenylhydrazine is reported. Phenylhydrazine-treated FA_0.5MA_0.5Pb_0.5Sn_0.5I₃ perovskite films effectively reduce the hole traps caused by the oxidation of Sn²⁺ on the perovskite surfaces. In addition, surface energetics are well aligned by post-treatment, which is beneficial for voltage gain and charge transport. As a result, power conversion efficiency (PCE) is increased from 18.16% to 20.67% after post-treatment due mainly to the significant improvement of open-circuit voltage from 0.75 to 0.83 V. Furthermore, the device stability is improved, where 91.67% of initial PCE is maintained after 1000 h.