Methylammonium-Free Perovskite Photovoltaic Modules.

Abstract

For perovskite photovoltaic industrialization, it is essential to simultaneously achieve high conversion efficiency, long-term stability, and scalable fabrication of modules. Halide perovskites with the ABX₃ structure are composed of A-site monovalent cations, (e.g., formamidinium (FA⁺), methylammonium (MA⁺), and Cs⁺), B-site divalent cations (predominantly Pb²⁺), and X-site halide anions. Though the incorporated MA cations can facilitate the nucleation and growth of perovskite films, their volatility undermines the thermal stability. α-FAPbI₃ exhibits an optimal bandgap, but both it and α-CsPbI₃ are susceptible to converting into the nonphotoactive δ-phase at room temperature. However, their FACsPbI₃ alloy effectively counteracts the imperfections in the tolerance factor, enabling the formation of a room-temperature photoactive phase. Hence, the development of large-area, high-quality, and MA-free perovskite films remains a substantial challenge for efficient photovoltaic modules. This review first discusses the impact of A-site cations on the phase stability of perovskite structures and subsequently examines the film growth mechanism. Then, we summarize the MA-free perovskite photovoltaic modules and highlight advances in the CsPbX₃ (Br^-/I^-), FAPbI₃, and FACsPbX₃ systems. Finally, we propose potential directions and challenges toward perovskite photovoltaic industrialization.