Selective Surface Passivation in Semiconductor Nanocrystals: Implications on Hot Carrier Relaxation Dynamics

Abstract Lead‐free double‐perovskites offer high photo‐thermal stability, enhanced conductivity, and suitable bandgap‐tuning, making them excellent light absorbers for photovoltaic applications. However, abundant surface trap states in this promising family of materials drastically reduce the photovoltaic efficiencies, posing a significant bottleneck for their commercial applications to be used as active materials in devices. The use of capping ligands during synthesis has long been a widely‐acknowledged strategy for minimizing surface defect states. However, insights into the molecular‐level mechanism, particularly whether these ligands are more effective in sweeping out electron or hole trap states, remain elusive. To address this, oleylamine is employed as a surface capping ligand when synthesizing Cs 4 CuSb 2 Cl 12 (CCSC) nanocrystals. Based on structural and spectral characterization, femtosecond transient absorption spectroscopy, and electronic structure calculations, our in‐depth study demonstrates that oleylamine modifies structural, electronic, and optical properties of CCSC nanocrystals by exclusively passivating electron trap states, which significantly impacts hot carrier relaxation dynamics, and underscores the significance of defect passivation strategies in managing hot carrier cooling in CCSC nanocrystals, thereby offering a framework for developing high‐performance and durable perovskite optoelectronic devices. The concept of selective surface passivation paves the way to explore similar phenomena within broader classes of materials.