Role of Interfacial Engineering of "Giant" Core–Shell Quantum Dots

Structural engineering of the shell layer in "giant" core–shell quantum dots (QDs) offers precise control over the spatial carrier separation and other optoelectronic properties by forming a quasi-type-II band alignment. We report the synthesis of highly stable "giant" CdSe–CdS QDs with different CdS shell thicknesses (2.2–4.8 nm) and alloyed PbxCd1–xS interfacial layers at the CdSe–CdS interface. The "giant" core–shell QDs with alloyed interfacial layers show a broader absorption spectrum, faster carrier transfer rate, and higher hole leakage into the shell region, compared to CdSe–CdS QDs with similar size, as confirmed by optical, transient photoluminescence decay measurements and theoretical simulations. As a proof of concept, the as-synthesized "giant" core-alloyed shell QD (denoted as CdSe@CPS-13)-sensitized solar cells (QDSCs) yield a power conversion efficiency (PCE) of 4.15%, which is 77% higher than the PCE of QDSCs based on "giant" CdSe–CdS QDs with comparable size and shell thickness. These results show that interfacial engineering is an effective methodology to tailor the optical and electronic properties of core–shell QDs with great potential to enhance the performance of photovoltaic and other solar-energy-driven devices.