Semi-transparent Schottky junction solar cell based on evaporated CdSe thin films: Influence of post-deposition air-annealing

FTO/CdSe/Al semi-transparent Schottky junction solar cells were fabricated by evaporating 300 nm CdSe thin films onto the FTO electrode and forming the Schottky junction by evaporation the aluminum onto the absorber layer. The performance of the samples was optimized by air-annealing the absorber layer prior to the evaporating of the top electrode. Also, the structural, optical and electrical properties of thermally evaporated CdSe thin films were investigated as a function of post-deposition air-annealing temperature. The surface morphology of the specimens was studied using field emission scanning electron microscope (FE-SEM) analysis. X-ray diffraction (XRD) analysis revealed the hexagonal structure of the samples. The crystallite size, micro-strain and dislocation density of CdSe thin films were evaluated using XRD patterns. The transmittance spectra in the wavelength range of 400 - 2500 nm were measured and then used to study other optical parameters. The optical energy band gap was decreased with air-annealing from 2.17 eV to 1.69 eV. It is observed that complex refractive index, relative density, complex dielectric constant and electrical polarizability of specimens were increased by air-annealing. Electrical conductivity and the photovoltaic efficiency of FTO/CdSe/Al Schottky barrier devices were improved by thermal annealing and annealed sample at 300 degrees C shows the best performance (eta = 1.53 %). Obtained results show that CdSe thin films are a promising candidate to use as an absorber layer in semi-transparent solar cells and colorful photovoltaic windows.