Introduction of Co atoms into CdS thin films for improving photovoltaic properties

Abstract

This paper represents a systematic work on the fabrication of chemical bath-grown CdS films with and without Co atoms and their photovoltaic performances in hybrid solar cells. Structural properties showed 1% Co-doping promoted crystal quality of CdS films. However, a poor crystal quality was developed above 3% Co concentrations. A reduction in sphere size of CdS samples was observed for 1% Co-doping which was ascribed to slow growth of film. Optical examination demonstrated CdS films with 1% Co-doping displayed the highest transparency of 85% in the visible and near-infrared regions, which were explained by the improvement of crystal quality. A maximum band gap of 2.43eV was found for 1% Co-doped CdS films, whereas an increase in Co concentration to 7% led to a decline in the band gap of CdS that was attributed to sp-d exchange interaction. Photoluminescence data showed Co-doped CdS films had lower PL peak intensity than that of CdS, demonstrating a decrease in the number of intrinsic defects. Photovoltaic measurements displayed that the best efficiency of 0.488% was achieved for CdS-based device including 1% Co atoms, which were almost a seven-fold boost in overall efficiency compared to bare CdS-based device. The enhancement in power conversion efficiency originated from an increase in short-circuit current density of 1% Co-doped CdS-based photovoltaic cell.