Role of Residual PbI2in Two-step Vapor Processed Perovskite Solar Cells with Methylamine Treatment

Methylamine (MA) treatment of vapor-processed perovskite films is used to improve performance of perovskite solar cells (PSC) by a significant increase in open-circuit voltage. In sequential processing of PSCs, the presence of residual PbI2 in the film impacts device performance. This study aims to understand the role of residual PbI2 after MA treatment and its effect on PSCs. We characterize properties of MA-treated PbI2 films and MA-treated perovskite films with different amounts of PbI2 from two-step vapor processing. Our findings suggest that MA interacts with PbI2 and changes its optical properties. However, the role of excess PbI2 in MA-treated and as-deposited PSCs does not change, with Voc improvement after MA treatment depending on the amount of PbI2 in the as-deposited film. An optimized MA-treatment gives approximately a 10% increase in VOC compared to untreated PSC devices.