Efficient inverted planar formamidinium lead iodide perovskite solar cells via a post improved perovskite layer

Abstract

Formamidinium lead iodide (FAPbI₃) is a more promising broader absorption material than methylammonium lead iodide (MAPbI₃) for perovskite solar cells (PSCs). However, in most cases the power conversion efficiencies (PCE) of FAPbI₃ based inverted planar PSCs are still lower than those of MAPbI₃ ones due to the inferior morphology of FAPbI₃ film. In this paper, we demonstrate an optimised formamidinium iodide/isopropyl alcohol (FAI/IPA) modification procedure to improve the photoactive layer for efficient inverted planar FAPbI₃ PSCs. The results show that there is an obvious improvement in open circuit voltage, short current density (J_SC), and fill factor (FF). Finally, the best PCE of 14.00% with a J_SC of 21.75 mA cm⁻² and a FF of 0.78 was achieved in low-temperature solution-processed PSCs, which represents a more than 40% enhancement in PCE over that of the PSCs without surface modification. Moreover, the devices exhibit good reproducibility and excellent stability. The simple FAI/IPA modification on the photoactive layer can greatly improve planar FAPbI₃ based device performance, which can be a good choice for practical applications.