Roles of MACl in Sequentially Deposited Bromine-Free Perovskite Absorbers for Efficient Solar Cells

So far, the combination of methylammonium bromide/methylammonium chloride (MABr/MACl) or methylammonium iodide (MAI)/MACl is the most frequently used additives to stabilize formamidinium lead iodide (FAPbI(3)) fabricated by the sequential deposition method. However, the enlarged bandgap due to the addition of bromide and the ambiguous functions of these additives in lead iodide (PbI2) transformation are still worth considering. Herein, the roles of MACl in sequentially deposited Br-free FA-based perovskites are systematically investigated. It is found that MACl can finely regulate the PbI2/FAI reaction, tune the phase transition at room temperature, and adjust intermediate-related perovskite crystallization and decomposition during thermal annealing. Compared to FAPbI(3), the perovskite with MACl exhibits larger grain, longer carrier lifetime, and reduced trap density. The resultant solar cell therefore achieves a champion power conversion efficiency (PCE) of 23.1% under reverse scan with a stabilized power output of 23.0%. In addition, it shows much improved photostability under 100 mW cm(-2) white illumination (xenon lamp) in nitrogen atmosphere without encapsulation.

Automated summary

This study systematically investigated the role of MACl in sequentially deposited Br-free FA-based perovskites, revealing that MACl can regulate the reaction, phase transition, and crystallization. Compared to traditional FAPbI(3), perovskites with MACl exhibit superior performance in terms of grain size, carrier lifetime, and trap density.