Improved photovoltaic performance and stability of quantum dot sensitized solar cells using Mn–ZnSe shell structure with enhanced light absorption and recombination control

Abstract

To make quantum-dot-sensitized solar cells (QDSSCs) competitive, photovoltaic parameters comparable to those of other emerging solar cell technologies are necessary. In the present study, ZnSe was used as an alternative to ZnS, one of the most widely used passivation materials in QDSSCs. ZnSe was deposited on a TiO₂–CdS–CdSe photoanode to form a core–shell structure, which was more efficient in terms of reducing the electron recombination in QDSSCs. The development of an efficient passivation layer is a requirement for preventing recombination processes in order to attain high-performance and stable QDSSCs. A layer of inorganic Mn–ZnSe was applied to a QD-sensitized photoanode to enhance the adsorption and strongly inhibit interfacial recombination processes in QDSSCs, which greatly improved the power conversion efficiency. Impedance spectroscopy revealed that the combined Mn doping with ZnSe treatment reduces interfacial recombination and increases charge collection efficiency compared with Mn–ZnS, ZnS, and ZnSe. A solar cell based on the CdS–CdSe–Mn–ZnSe photoanode yielded excellent performance with a solar power conversion efficiency of 5.67%, V_oc of 0.584 V, and J_sc of 17.59 mA cm⁻². Enhanced electron transport and reduced electron recombination are responsible for the improved J_sc and V_oc of the QDSSCs. The effective electron lifetime of the device with Mn–ZnSe was higher than those with Mn–ZnS, ZnSe, and ZnS, leading to more efficient electron–hole separation and slower electron recombination.