Alleviation of Precursor Degradation Induced by DMF/DMSO Mixture for Enhanced Performance of Perovskite Solar Cells

The precursor quality critically determines the morphology, grain size, crystallinity, and trap state density of the perovskite films. A long shelf life of the perovskite precursor could greatly benefit the reliable upscaling of perovskite solar cells (PSCs). Herein, we suggest that the most commonly used N, N-Dimethylformamide/Dimethyl sulfoxide (DMF/DMSO) mixed solvent exhibits more severe degradation compared to its corresponding single solvents, due to the complex interplay of reactions, including hydrolysis, oxidation, and deprotonation of precursor species in the solution. 2-thiouracil (Th) was thus introduced into the precursor to inhibit these side reaction chains and effectively alleviate the detrimental degradation of cations and iodide ions (I⁻). The synergistic effects of Th allow it to bind with undercoordinated Pb²⁺, modulating the crystallization process and thereby achieving high-quality films with a low defect density. Consequently, Th-based precursor demonstrates enhanced shelf life, retaining 94.78% of the initial efficiency (25.13%) of the device prepared from fresh solution after 30 days of aging, compared to 64.22% for the control sample. The target device also exhibits remarkable stability, maintaining 87.8% of its initial efficiency after 1000 h of maximum power point tracking.