Dysprosium doping in CdTe@CdS type II core/shell and cosensitizing with CdSe for photocurrent and efficiency enhancement in quantum dot sensitized solar cells

Abstract

Quantum dot sensitized solar cells (QDSSCs) based on the II-VI QDs have become a promising and attractive technology due to their unique properties. However, the applications of the II-VI QDs, especially CdTe QDs, have still been restricted. Herein, a CdTe@Dy-doped CdS core/shell QDs cosensitized with CdSe QDs have been developed as a sensitizer in QDSSCs for enhancing the light-harvesting range and efficiency, accelerating charge separation, and suppressing charge recombination. The fabricated QDSSCs using TiO2/CdTe@Dy-doped-CdS/CdSe/ZnS photoanode exhibited the best short-circuit current (JSC = 20.08 mA/cm2) and power conversion efficiency (ƞ=8.26%) in comparison with that of other photoanodes comprising TiO2/CdTe, TiO2/CdTe@CdS, TiO2/CdTe@CdS/ZnS, TiO2/CdTe@CdS/CdSe/ZnS, and TiO2/CdTe@CdS/CdSe/Dy-Doped ZnS. As the obtained results from Diffuse Reflectance Spectroscopy, Photoluminescence, and Electrochemical Impedance Spectroscopy revealed, the CdTe/CdS type-II core/shell structure QDs leads to a wide absorption range, fast electron injection, and slower recombination rate because of the spatially indirect energy gap formation. Moreover, the presence of Dy cations in CdS crystal lattice boosts the charge transferring rate to the conduction band of TiO2. On the other hand, the cosensitizing of CdTe@Dy-doped CdS QDs with CdSe is advantageous not only to the electron injection and transferring but also to the hole-recovery from the valence band of QDs toward the electrolyte.