Bulk Passivation via Surface Engineering with Low‐Dimensional Inorganic Perovskites

Surface treatment of perovskite thin films with additives is a widely adopted strategy to improve photovoltaic performance in metal halide perovskite solar cells (PSCs), enhancing charge transfer at the perovskite–transport layer interface. However, understanding performance enhancement through surface passivation requires examining not only interfacial charge transfer but also bulk charge carrier dynamics. Here, CsPbBr3 nanowires (NWs) and quantum dots (QDs) are utilized owing to their wide bandgap, defect‐passivation ability, and favorable optoelectronic properties. Charge carrier dynamics are examined using photoluminescence (PL) and time‐resolved PL (TRPL) under illumination from both the film and glass sides. QD‐treated films exhibit only surface region passivation without bulk improvements, whereas NW‐treated films demonstrate improved charge carrier dynamics, not only surface region but also bulk carrier dynamics. Therefore, the NW‐treated films exhibit consistent trends in PL intensity and TRPL lifetime as a function of NW concentration under both film‐side and glass‐side illumination. This observation confirms that the enhanced interfacial and bulk carrier extraction leads to simultaneous improvements in JSC and VOC, thereby increasing the device efficiency from 19.0% to 20.3%. These results clarify the function of surface modification in defect passivation and carrier dynamics, thereby providing a practical approach for achieving highly efficient perovskite solar cells.