Investigation of Alkylamine-Free MACl Substitute Additives for Stable α-FAPBI3 Perovskite Solar Cells

Abstract

Perovskite solar cells, or PSCs, especially those based on a formamidinium lead iodide (FAPbI3) chemistry, have emerged as a promising technology for next-generation photovoltaics, achieving record power conversion efficiencies exceeding 25%1, 2. However, the standard use of methylammonium chloride (MACl) as a processing additive presents significant challenges, including irreversible reactions with formamidinium (FA), production of volatile byproducts, and limited long-term stability under operational conditions3. This study aims to address these issues by systematically investigating alternative additives to replace MACl in FAPbI3-based perovskite solar cells. The research explores a series of ammonia-based, sulfur-based, and organic acid-based additives, including but not limited to NH4Cl, NH4F, iPACl, thiourea, and NH4SCN, focusing on their reactivity with FA, impact on perovskite formation, and potential to improve or replicate FAPBI3 film uniformity and stability. Through in-solution testing and evaluation of the additives' effects on crystallization, film morphology, and optical properties, this study seeks to identify possible optimal additives or combinations to replace MACl and gain an improved understanding of additive-perovskite interactions. The research employs X-ray diffraction to gain insight into crystallization dynamics, optical microscopy for morphological analysis, and UV-Vis spectroscopy to assess optical properties across various lengths of sample aging. Through structural, optical, and morphological characterization, we demonstrate potential combinations of NH4Cl, NH4PF6, and thiourea, as well as pre-aged equimolar combination substitutes of FACl and thiourea as promising substitutes with band gap, morphology, phase stability, and performance characteristics similar to that of and exceeding MACl-based FAPbI3 films and devices.