Design and fabrication of multi-functional working electrodes with TiO2/CZTSe/bamboo-charcoal-powder composite particles for use in dye-sensitized solar cells

Abstract

This study developed a multi-functional electrode with composite particles for use in high-efficiency dye-sensitized solar cells (DSSCs). Photoelectron current was enhanced through the inclusion of the visible light absorber Cu2ZnSnSe4 (CZTSe) as well as narrow band gap carbon-doped TiO2 in conjunction with a novel dye absorber, bamboo charcoal powder (BCP). Photoelectron voltage was maintained at a high level through the inclusion of a p–n junction (CZTSe–TiO2). The CZTSe was synthesized using a solvo-thermal process that does not require an autoclave, and BCP was obtained from dehydrated bamboo charcoal. Composites of TiO2 (P-25)/BCP, TiO2 (P-25)/CZTSe, and TiO2 (P-25)/CZTSe/BCP were prepared by wet ball mill grinding prior to the fabrication of DSSC working electrodes. The band gap of the TiO2 (P-25)/CZTSe electrode was shown to decrease with an increase in the quantity of CZTSe; dropping from 2.92 to 2.32eV when the mass ratio of TiO2 to CZTSe changed from 10:0.1 to 10:0.9. Calculations based on density functional theory reveal unintentional substitutions of Cu (to Ti) and Se (to O) atoms contribute to the narrowing of original TiO2 band gap. We also measured the cell performance, including short-circuit photocurrent density (Jsc), open-circuit photovoltage (Voc), and power conversion efficiency (η). The η of DSSCs (6.85%) with a TiO2 (P-25)/CZTSe/BCP electrode (TiO2:CZTSe:BCP=10:0.3:0.6) far exceeded that of conventional DSSCs with a TiO2 (P-25) electrode (3.84%). Of particular note is the fact that the Voc and Jsc of the proposed DSSC exceed those of conventional devices by 9.5% and 100%, respectively. The principles used in the design of the proposed electrode could be extended to all photovoltaic devices.