Abstract

Copper Indium Gallium Selenide (CIGS) based solar cells are receiving worldwide attention for solar power generation. They are efficient thin film solar cells that have achieved 22.8% efficiency comparable to crystalline silicon (c-Si) wafer based solar cells. Thin films of Gallium Selenide (GaSe) were deposited on glass substrate at room temperature by Chemical Bath Deposition (CBD) Technique. The sources of Ga and Se were respectively GaSO4 and Na2SeSO3 while NaOH was employed as completing agent. The deposited sample slides were annealed in an oven at temperatures of 200 °C, 300 °C, 400 °C, 500 °C and 600 °C. The samples were characterized for optical band gap using Spectrophotometer (GENESYS 10S UV-VIS Model) by measuring the optical absorption and transmission and photo conductivity by using the two point probe method in which silver paint was used for attaching two copper wires (as electrodes) on the sample. The estimated band gaps are 2.9eV, 2.97eV, 3.06eV and 3.03eV for the as deposited and the annealed thin films at temperatures of 200 °C , 300 °C, 400 °C, 500 °C and 600 °C respectively. Annealing increases band gap energy slightly as substrate temperature increases from 200 °C to 600 °C which indicate blue shifts from the normal bulk value, while the photo and dark currents of the sample annealed at different temperature were observed to increase linearly with the applied electric field, but the former being large and the latter is less, which is an indication of positive photoconductivity.

Keywords:Optoelectronic properties; Thin film; Solar cells; Chemical bath deposition