Surface Engineering Boosting Al/Zn-Coincorporated Cu–In–Se Quantum Dot-Sensitized Solar Cell Efficiency

High-quality QDs play a crucial role in the fabrication of high-performance quantum dot-sensitized solar cells (QDSCs). Surface defects/traps of QDs commonly act as nonradiative carrier recombination centers and thereby deteriorate the power conversion efficiency of the fabricated QDSCs. Herein a protective ZnSe shell is grown on the surface of Al/Zn coincorporated Cu–In–Se QDs to form (Al/Zn)–Cu–In–Se/ZnSe (AZCISe/ZnSe) core/shell QDs, which are used as light harvesters to fabricate QDSCs. It is found that the PL intensity of AZCISe/ZnSe QDs is significantly improved as the ZnSe shell thickness increases, indicating that the ZnSe shell is beneficial to reduce the surface defects/traps of AZCISe QDs. Moreover, the ZnSe shell thickness can be tailored by controlling the cycles of injected Zn and Se precursors during the synthesis process. Furthermore, electrochemical impedance spectroscopy, open-circuit voltage decay, and time-resolved fluorescence spectroscopy analysis demonstrate that the ZnSe shell layer can effectively reduce the surface defect/trap density of the QDs, suppress the charge recombination at photoanode/electrolyte interfaces, and improve the photovoltaic performance of the constructed QDSCs. Benefiting from the surface engineering of QDs, the average power conversion efficiency increases from 10.15% for pristine AZCISe QDSCs to 10.53% for AZCISe/ZnSe core/shell QDSCs.