Investigations of annealing temperatureand aging time on energy conversion efficiency of Cu2S/CdS solar cells

Different structures of Cu₂S/CdS solar cells under different deposition parameters were prepared using vacuum thermal evaporation technique. The transmittance of CdS thin films was measured for different light wavelengths. The films exhibited high degree of transmittance in the infrared region and sharp falling absorption edge at nearly 500 nm. On the other hand Cu₂S layer has a maximum transmittance at 700 nm wavelength. It was also noticed that the sample exposed to 100°C annealing gave maximum photocurrent (1.5 mA) but lower open circuit voltage (0.365 V). A maximum open circuit voltage (0.4V) and lower short circuit current (1.3 mA) was produced by the sample exposed to 400°C annealing. The variation of V_oc as a function of aging time for the Cu₂S/ CdS films under repeated cycles of illumination and annealing is investigated. The results show clearly that the annealing improves the fabricated V_oc samples and V_oc. increases considerably with time. A technique involving heat treatment, washing and depositing a very thin layer of copper on top of the solar cell has been employed to improve the cell efficiency.