Alkyl-chain engineering of low-dimensional perovskite seeds for high-efficiency perovskite solar cells†
Abstract
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 (VOC) 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.