Alkyl-chain engineering of low-dimensional perovskite seeds for high-efficiency perovskite solar cells

Perovskite solar cells show immense promise for approaching the Shockley-Queisser limit with a theoretical power conversion efficiency (PCE) of more than 30%. However, their practical implementation remains constrained by crystal phase impurities and the suboptimal performance of the perovskite photoactive layer, where uncontrolled crystallization and residual PbI₂ impede charge transport and stability. To address these challenges, we introduce a novel seed-mediated crystallization approach utilizing 1,3-dimethylimidazolium chloride (DMIMCl) and 1-ethyl-3-methylimidazolium chloride (EMIMCl) to convert residual PbI₂ into strain-tolerant low-dimensional (LD) DMIMPbI₃ and LD EMIMPbI₃, respectively. Comparative analysis reveals that EMIMCl, with its longer alkyl chain, enhances crystallization kinetics, suppresses non-radiative recombination, and mitigates interfacial stress, yielding high-quality perovskite films with superior crystallinity and reduced defect densities. Consequently, devices incorporating LD EMIMPbI₃ achieve a remarkable PCE of 24.25% with an open-circuit voltage (V_OC) of 1.143 V and retain 90% of their initial efficiency after 1200 hours under ambient conditions. This work provides a robust strategy for perovskite crystallization control and interfacial engineering, advancing the development of high-efficiency photovoltaics.