Multiphysics Modeling and Optimization of High‐Efficiency Lead‐Free CH 3 NH 3 SnBr 3 Perovskite Solar Cells

ABSTRACT Traditional perovskite solar cells (PSCs) based on lead (Pb) halides have achieved high power conversion efficiencies due to their excellent optical and electrical properties. However, their large‐scale application is limited by concerns about lead toxicity and stability. In this work, a comprehensive 3D multiphysics modeling framework is developed for Pb‐free PSCs using methylammonium tin bromide (CH 3 NH 3 SnBr 3 ) as the absorber layer, integrating optical, electrical, and thermal effects, an aspect rarely addressed in existing tin‐based studies. Device performance is analyzed using COMSOL Multiphysics (3D) and SCAPS‐1D by optimizing key parameters, including absorber thickness, doping concentration, defect densities, and resistive losses. Among various configurations, the structure FTO/ZnO/CH 3 NH 3 SnBr 3 /CuI/Au shows optimal performance, delivering a current density of 31.12 mA/cm 2 , an open‐circuit voltage of 1.13 V, a fill factor of 88.86%, and a power conversion efficiency of 31.34% under ideal conditions. Additionally, thermal effects such as non‐radiative recombination and Joule heating are investigated to understand internal heat generation and its influence on device behavior. The proposed approach demonstrates improved performance compared to prior numerical studies and provides deeper physical insight, offering a pathway toward efficient, environmentally friendly tin‐based PSCs, while underscoring the need for experimental validation.