Probing Nanoscale\nCharge Transport Mechanisms in Quasi-2D\nHalide Perovskites for Photovoltaic Applications

Quasi-2D layered halide perovskites (quasi-2DLPs) have\nemerged\nas promising materials for photovoltaic (PV) applications owing to\ntheir advantageous bandgap for absorbing visible light and the improved\nstability they enable. Their charge transport mechanism is heavily\ninfluenced by the grain orientation of their crystals as well as their\nnanostructures, such as grain boundaries (GBs) and edge statesthe\nformation of which is inevitable in polycrystalline quasi-2DLP thin\nfilms. Despite their importance, the impact of these features on charge\ntransport remains unexplored. In this study, we conduct a detailed\ninvestigation on polycrystalline quasi-2DLP thin films and devices,\ncarefully analyzing how grain orientation and nanostructures influence\ncharge transport. Employing nondestructive atomic force microscopy\n(AFM) topography, along with transient absorption spectroscopy (TAS)\nand grazing-incidence wide-angle X-ray scattering (GIWAXS), we obtained\nsignificant insights regarding the phase purity, crystallographic\ninformation, and morphologies of these films. Moreover, our systematic\ninvestigation using AFM-based techniques, including Kelvin probe force\nmicroscopy (KPFM) and conductive AFM (c-AFM), elucidates the roles\nplayed by GBs and edge states in shaping charge transport behavior.\nIn particular, the local band structure along the GBs and edge states\nwithin both vertical and parallel grains was found to selectively\nrepel electrons and holes, thus facilitating charge carrier separation.\nThese findings provide perspectives for the development of high-performance\nquasi-2DLP PV devices and highlight potential approaches that can\nleverage the intrinsic properties of quasi-2DLPs to advance the performance\nof perovskite solar cells.