In order to determine the suitable source temperatures to deposit CuInSe2 thin films for solar cells, absorption coefficient α and energy gap Eg of this compound were evaluated. The films were grown by vacuum free CSVT technique for 3 h. The source temperatures of deposition ranged from 400 to 600°C. Absorption coefficient and energy gap were determined from transmittance (T) and reflectance (R) of obtained films. Transmittance (T) and reflectance (R) were characterized using a spectrophotometer with wavelength γ range 1-2.5 µm. Curves (α) and (hvα)2 versus photon energy (hv) were analysed. At source temperatures of 450-500°C, the value of α was found to be about 104 cmG1. At source temperature higher than 500°C, α dropped to lower values of 104 cmG1. CuInSe2 thin films were found to have a direct allowed transition and the best Eg value was estimated between 0.94-0.96 eV at source temperatures of 450-500°C. A decrease in Eg value was observed when the source temperature became higher than 500°C. In view of these results, the source temperature range of 450-500°C was found to be more appropriate to grow CuInSe2 films for solar cells. Indeed, α and Eg values can be increased by introducing Gallium into ternary CuInSe2 for a better alignment with the solar spectrum, e.g., a CuIn1-xGaxSe2 heterojunction device.
K. Konan, J.K. Saraka , P. Gbaha , K.D. Konan and B. Hadjoudja , 2007. Absorption Coefficient and Energy Gap of Vacuum Free CSVT Deposited CuInSe2 Thin Films. Journal of Applied Sciences, 7: 2646-2650.