Isomer‐Dependent Modulation of Perovskite Crystallization by Methoxythioanisole for High‐Performance Inverted Solar Cells

Abstract Energy losses derived from inferior film crystalline and severe trap‐assisted non‐radiative recombination in the light‐absorber limit the further development of high‐performance perovskite solar cells (PSCs). Herein, volatile positional isomers— ortho ‐, meta ‐, and para ‐methoxythioanisole ( o ‐/ m ‐/ p ‐MTA)—are strategically tailored to regulate the crystallization kinetics of perovskites. Among them, m ‐MTA optimally balances dipole moment, configuration, and multiple active sites, enabling S atoms and methoxy groups to interact with both the under‐coordinated Pb 2+ and FAI. This interaction modulates intermediate chemistry and crystallization kinetics, promoting homogeneous nucleation and extending crystallization time, thereby affording high‐quality perovskites with no MTA residue in the resulting film. Consequently, target devices with m ‐MTA treatment deliver a champion power conversion efficiency (PCE) of 26.46% (aperture 0.09 cm 2 ) with a minimal non‐radiative voltage loss of 72 mV, and scale to a 1 cm 2 device with 24.75% PCE. Unencapsulated devices demonstrate great durability, retaining over 86% and 90% of their initial PCEs after 672 h at 85 °C and 1440 h of maximum power point tracking under 1‐sun illumination (white LED array), respectively. The study reveals a pronounced positional isomerism effect in additive engineering and establishes volatile, multi‐active‐site molecules as an effective strategy for simultaneously directing crystallization, mitigating defects, and achieving efficient PSCs.