Mild Coordination Enabled by Steric Hindrance Facilitates Fabrication of Large‐Area Perovskite Solar Modules

ABSTRACT The scalable fabrication of high‐efficiency perovskite solar modules is critically challenged by the difficulty in controlling crystallization homogeneity and mitigating buried interfacial defects across large‐area substrates. The commonly used dimethyl sulfoxide (DMSO) can induce heterogeneous nucleation and is prone to remain trapped within the films. Herein, diethyl sulfoxide (DESO) is introduced, a volatile Lewis acid‐base additive that leverages steric hindrance effects from its branched‐chain structure to achieve mild coordination with PbI 2 . This structural feature reduces the binding energy between DESO and PbI 2 , which avoid the formation of complex metastable intermediate phases. Moreover, the low binding energy of DESO enables its complete removal during vacuum quenching via rapid evaporation, effectively suppressing void formation at the buried interfaces during the subsequent annealing. The resultant perovskite films yield perovskite solar modules (PSMs) with power conversion efficiencies (PCEs) of 22.9% (11.2 cm 2 , aperture area) and 20.8% (692 cm 2 , aperture area) via scalable processes. These devices exhibit operational stability, retaining >96% of their initial PCE after 2000 h under continuous 1‐sun illumination and >95% PCE following 2000 h damp‐heat testing (85°C/85% RH).