Unraveling the Impact of Interface Modification on Perovskite Microstructure and Photovoltaic Efficiency.

Understanding the microstructural evolution of perovskite films is crucial for optimizing the performance of perovskite solar cells (PSCs). In this study, we systematically investigated the impact of interface modification on perovskite crystallization using high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED). While maintaining identical perovskite deposition conditions, the planar structure PSC device exhibited disordered grain orientations and irregular lattice fringes, whereas the mesoscopic structure device demonstrated a well-ordered crystal lattice extending from the TiO2 interface to the perovskite surface. Dark field TEM (DF-TEM) further confirmed that this structural continuity persisted throughout the entire perovskite film in the mesoscopic structure, in contrast to the planar structure where coherent crystal domains were confined to isolated regions near the compact TiO2 interface. SAED analysis revealed that adjacent grains in the mesoscopic structure share a consistent crystal orientation, whereas the planar structure exhibited largely uncorrelated diffraction patterns between grains. These structural differences, undetectable by conventional XRD or surface SEM, directly correlate with the improved photovoltaic performance as high as 20.8% photoconversion efficiency in the conventional CH3NH3PbI3 device without additional doping or passivation treatment. These findings highlight the critical role of interface engineering in directing perovskite crystallization, providing insights into improving efficiency through microstructural control.