Structural and optical properties of Ti and Cu co‐doped ZnO thin films for photovoltaic applications of dye sensitized solar cells

Abstract

ZnO, 1% Ti doped ZnO and 1% Ti and (0.5%, 1%, and 1.5%) Cu co-doped ZnO thin films are deposited on fluorine doped tin oxide glass substrates using sol-gel technique. The impact of Ti and Cu co-doping on optical, structural, and photovoltaic properties of ZnO thin films have been analyzed. X-ray diffraction also confirms the hexagonal wurtzite crystal structure of the film. The 1% Ti and 1% Cu co-doping percentage has an astonishing impact on the structural properties of the doped film, such as large grain size (19 nm), d-spacing (2.48 Å), small dislocation line density (2.96 × 1015 m−2), lattice parameters (a = b = 3.2 Å, c = 5.2 Å), bond length (1.9 Å) and positional parameter (3.7 × 10−1) of the ZnO thin film. Optical parameters like reflectance, absorbance, transmittance, refractive index, and dielectric constants are calculated in the range of spectral from (250-750) nm by using an ultraviolet - visible spectrophotometer. In the visible region, all the films have approximately 85% transmittance, which is excellent for solar cells. The ZnO film prepared at the co-doping percentage of 1% Ti and 1% Cu has high absorbance, high refractive index (2.09) and small band gap energy (3.37 eV) as compared to other doped films. The dye-sensitized solar cells of these films as a Photoanode have been fabricated and studied the efficiency variation of films. It is found that the performance of the dye-sensitized solar cell (DSSC) using a Ti-Cu co-doped film is much better than a pure ZnO film. The highest efficiency of DSSC 2.38% is achieved in the dye-sensitized solar cell by using a 1% Ti and 1% Cu co-doped ZnO thin film. When Ti is doped in ZnO then the surface area and pore size of the ZnO increased, which increase the dye loading ability. Cu reduces the recombination rate and enhances the electron injection efficiency rate from the dye to the conduction band of ZnO. Therefore, it is suggested that the thin films prepared by co-doping of Cu and Ti into ZnO will upgrade the efficiency of cell.