Tuning the Optoelectronics of Mixed-Semiconductors through the interplay of Quantum confinement and Stoichiometry Engineering
All-inorganic cesium lead bromide (CsPbBr3) nanocrystals (NCs) have established themselves as an emerging semiconductor for next-generation optoelectronic technologies due to their unique combination of properties, such as near unity photoluminescence quantum yields, narrow color pure emission, and exceptional defect tolerance. Although size-dependent optical signatures of these NCs are well reported, the complexity of mixed ionic-electronic transport remains largely unexplored. In this study, we provide a comprehensive analysis of size-dependent charge transport by decoupling ionic and electronic transport dynamics through carefully designed transient current and space charge limited current measurements. By employing NCs of different sizes ranging from 5.6 nm to 11.3 nm in thin films, we provide a comprehensive understanding of quantum confinement effects and related synthetic chemistry. Contrary to popular beliefs of quantum confinement and band gap broadening, our results demonstrate that the smallest NCs exhibit the most efficient transport characteristics, evidenced by the lowest activation energy (hole activation energy = 78 meV) for hole transport and the highest barrier for vacancy-mediated ion migration (ion activation energy = 370 meV). This work paves a way forward for perovskite-based efficient quantum devices, by demonstrating that moving into a strong quantum confinement regime, a superior charge transport can be facilitated, when supported by carefully tailored stoichiometry.