Solvent engineering of the Brownian tree-shaped lateral heterogeneity in 2D Ruddlesden–Popper perovskites: Resolving the trade-off between crystallinity and buried interface integrity

Two-dimensional Ruddlesden-Popper perovskites (2D RPPs) are promising light absorbers for stable perovskite solar cells (2D-PSCs). However, the influence of lateral mesoscopic heterogeneity, particularly its correlation with buried-interface defects and photovoltaic performance, remains poorly understood. Here, we employ solvent engineering to tune the crystallization kinetics of 2D RPP films and investigate the evolution of Brownian tree-shaped lateral heterogeneity and its impact on buried-interface integrity and device performance. Increasing the DMSO fraction gradually delays crystallization, leading to improved crystallinity and preferred vertical orientation. Meanwhile, the Brownian tree-shaped domains progressively expand, accompanied by the development of interconnected void networks at the buried interface and reduced charge collection due to compromised buried-interface contact. An intermediate DMF:DMSO ratio of 8:2 achieves the optimal balance between crystalline quality and buried-interface integrity, yielding a champion power conversion efficiency of 17.63%. These findings demonstrate that balancing crystalline quality and buried-interface integrity is essential for achieving high-performance 2D-PSCs and other related optoelectronics.