A stoichiometric CdS interlayer for the photovoltaic performance enhancement of quantum-dot sensitized solar cells

Abstract

The CdS interlayer plays an important role as the seed layer and energy barrier in photovoltaic performance enhancement of CdSe quantum-dot sensitized solar cells (QDSCs). However, the CdS (CdS-CBD) interlayer is generally synthesized by the chemical bath deposition method (CBD) and suffers from excessive Cd²⁺ due to the poor controllability of interfacial chemical reactions. Here, we employed a sol–gel method to prepare a CdS interlayer (CdS-SG) with a stoichiometric ratio of Cd²⁺ to S²⁻ on a TiO₂ mesoporous photoanode and then fabricated CdSe QDSCs. A power conversion efficiency of 3.37% was obtained in the CdS-SG QDSCs (Cell-SG), which is higher than that of 2.64% in the CdS-CBD QDSCs (Cell-CBD) under AM 1.5G solar illumination of 100 mW cm⁻². Charge extraction measurements showed that the Cell-SG contained fewer trap states than the Cell-CBD. A comprehensive study of the electron dynamics based on open-circuit voltage decay (OCVD), electrochemical impedance spectroscopy (EIS), intensity-modulated voltage spectroscopy (IMVS), and intensity-modulated photocurrent spectroscopy (IMPS) measurements revealed that the stoichiometric CdS-SG interlayer significantly reduced the charge recombination and prolonged the lifetime of photogenerated electrons in contrast to the CdS-CBD interlayer in the QDSCs.