Comparison between silver sulfide and cadmium sulfide quantum dots in ZnO and ZnO/ZnFe2O4 photoanode of quantum dots sensitized solar cells

Zinc oxide (ZnO) and Zinc ferrite (ZnFe2O4) have unique electrical and optical characteristics. In this work, ZnO and ZnFe2O4 are the working electrodes used in the quantum dots sensitized solar cells (QDSSCs). ZnFe2O4 is able to enhance light absorption. Its band gap is 2.12 eV. ZnO and ZnFe2O4 nanoparticles were synthesized by way of co-precipitation. ZnO and ZnFe2O4 phase structures have been investigated using X-rays. The crystallite size of ZnO and ZnFe2O4 has been determined using the Williamson-Hall method. The morphologies of ZnO and ZnFe2O4 have been examined via electron microscopies and the optical properties of ZnO and ZnFe2O4 have been studied using absorption spectroscopy in the wavelength range from 200 to 800 nm. The ZnO and ZnFe2O4 band gaps were calculated using the Tauc method. Gel polymer electrolyte (GPE) based on methylcellulose, sulfur, and sodium sulfide has been prepared. The GPE has been characterized using electrochemical impedance microscopy (EIS). The bulk resistance of the electrolyte has been determined from the Nyquist plot and enabled the ionic conductivity to be calculated. Mesoporous thin films of ZnO and ZnFe2O4 have been sensitized with Ag2S and CdS and have been used as photoanodes in QDSSCs. The photovoltaic characteristics of four different QDSSCs were investigated at 100 mW cm−2 light intensity. EIS measurements have also been carried out to investigate the kinetic processes at the interfaces within the QDSSC. The performance of QDSSCs using CdS and Ag2S QDs has been compared. Photoanodes using CdS exhibit lower charge carrier resistance, higher fill factor, and longer electron lifetime resulting in cell efficiency enhancement compared to Ag2S-based photoanodes.