The Roles of Organic Spacer Molecular Structures in Modulating Crystallization Toward High-Performance Quasi-2D Perovskite Solar Cells

Organic spacers play a crucial role in governing the optoelectronic properties of quasi-2D perovskites; however, a limited understanding of their structure-performance relationships hampers progress in enhancing device efficiency. Here, we systematically explore how the chlorine substituent position on commonly used benzylamine organic spacer affects quasi-2D perovskite solar cell performance. Combining experimental and theoretical calculations results, we demonstrate that the structure of the organic spacer influences both the formation energy of low-dimensional perovskites and the interactions between the organic spacer and the 3D perovskite framework. Our findings reveal that the introduction of a meta-chlorine substitution into benzylamine results in a higher formation energy for 2D perovskites and improved interaction with 3D perovskites, leading to the formation of a well-structured film with reduced defects. Correspondingly, the optimized meta-chlorine benzylamine device achieves a peak efficiency exceeding 20% and exhibits significantly improved long-term light, heat and humidity stability.