Tuning Molecular Interactions for Highly Reproducible and Efficient Formamidinium Perovskite Solar Cells via Adduct Approach

TLDR

The Lewis acid–base adduct approach has been widely used to form uniform perovskite films, but its incompatibility with formamidinium (FA)-based perovskites has limited photovoltaic performance and stability. The study presents a reproducible method for fabricating uniform FAPbI3 films using the adduct approach and proposes criteria for selecting Lewis bases based on molecular interactions. The method replaces DMSO with NMP to form a stable FAI·PbI2·NMP adduct that converts into a uniform, pinhole‑free FAPbI3 film, and the authors propose criteria for Lewis base selection based on these interactions. Infrared and computational analyses show that NMP interacts more strongly with the FA cation than DMSO, enabling a stable adduct that yields high‑quality films, and the resulting solar cells achieve a peak PCE over 20% with a stabilized PCE of 19.34% and an average of 18.83 ± 0.73%.

Abstract

The Lewis acid–base adduct approach has been widely used to form uniform perovskite films, which has provided a methodological base for the development of high-performance perovskite solar cells. However, its incompatibility with formamidinium (FA)-based perovskites has impeded further enhancement of photovoltaic performance and stability. Here, we report an efficient and reproducible method to fabricate highly uniform FAPbI3 films via the adduct approach. Replacement of the typical Lewis base dimethyl sulfoxide (DMSO) with N-methyl-2-pyrrolidone (NMP) enabled the formation of a stable intermediate adduct phase, which can be converted into a uniform and pinhole-free FAPbI3 film. Infrared and computational analyses revealed a stronger interaction between NMP with the FA cation than DMSO, which facilitates the formation of a stable FAI·PbI2·NMP adduct. On the basis of the molecular interactions with different Lewis bases, we proposed criteria for selecting the Lewis bases. Owed to the high film quality, perovskite solar cells with the highest PCE over 20% (stabilized PCE of 19.34%) and average PCE of 18.83 ± 0.73% were demonstrated.