High performance and reduced charge recombination of CdSe/CdS quantum dot-sensitized solar cells

Abstract

CdSe and CdSe/CdS quantum dots (QDs) with narrow size distribution are attached onto TiO₂ electrodes by linker-assisted chemical bath deposition (LACBD). Preparation is carried out at 60 °C or 160 °C, which results in the formation of CdSe or CdSe/CdS QDs onto the TiO₂ nanoparticles connected by thioglycolic acid (TGA). The solar cell based on a CdSe/CdS QD-sensitized TiO₂ photoelectrode shows higher J_SC, V_OC and power conversion efficiency comparing to single CdSe QD-sensitized TiO₂, which can be ascribed to superior light absorption, faster electron transport and slower charge recombination for the former. Furthermore, the effects of a ZnS passivation layer and thermal annealing on the photovoltaic performance have been investigated by UV-vis spectra, incident photo-to-current conversion efficiency (IPCE) and electrochemical impedance spectra (EIS). As a result, a quantum dot-sensitized solar cell (QDSSC) based on a TiO₂–CdSe/CdS–ZnS photoanode (400 °C, 300 s calcination), polysulfide electrolyte and Cu₂S counter electrode achieves a power conversion efficiency of 4.21% under AM 1.5 G one sun illumination.