Crystal phase and band edge modulation of MA- and Br-free CsFA-based perovskites for efficient inverted solar cells and minimodules

The non-radiative voltage loss associated with traps (V^non-rad_loss) is the crucial factor limiting the performance of inverted perovskite solar cells (PSCs). In this study, we manipulate the crystal growth and spectral response of MA-/Br-free CsFA-based perovskites to minimize the V^non-rad_loss by rationally introducing methyl(methylsulfinyl)methyl sulfide (MMS) into the precursor. MMS effectively inhibits the oxidation of halides and reduces the formation of δ-phase perovskites during phase-transformation, resulting in the formation of a high-quality perovskite film with fewer defects and reduced non-radiative recombination. Notably, a 5 nm red-shift in the band edge of the perovskite is achieved, providing an additional integrated current density of 0.24 mA cm⁻². Consequently, a certified efficiency of 26.01% from the reverse scan, along with a quasi-steady-state output efficiency of 25.30%, is obtained for the 0.09-cm² inverted PSC, marking the highest values for inverted PSCs based on MA-/Br-free CsFA double-cation perovskites to date. The champion device exhibits a minimal V^non-rad_loss of 67 mV. The present strategy is also extended to a minimodule with an active area of 12.96 cm² by delivering an efficiency of 22.67% from the reverse scan. Moreover, the target devices demonstrate great thermal and operational stability. This study offers a versatile Lewis base for regulating the crystal growth and spectral response of perovskite films and emphasizes the significance of minimizing the V^non-rad_loss for high-performance inverted PSCs.