Photoreflectance characteristics and photovoltaic performance of CBD-CdS/Cu(In, Ga)Se2 thin-film solar cells

We have investigated the photoreflectance characteristics and the photovoltaic performance of Cu(In, Ga)Se₂ (CIGS) thin-film solar cells that have CdS layers prepared by chemical bath deposition (CBD). The CdS was deposited on CIGS by three different conditions. (I) CdSO₄ 0.014 M, thiourea 0.014 M, NH₄OH(30%) 60 ml, (II) CdSO₄ 0.0015 M, thiourea 0.074 M, NH₄OH(30%) 56 ml, and (III) CdSO₄ 0.0015 M, thiourea 0.05 M, NH₄OH(30%) 80 ml. The efficiencies of the solar cells fabricated in processes I, II, and III were 12.17 %, 14.47 %, and 14.97 %, respectively. Quantum efficiency spectra of the solar cells in the region of the CdS band gap showed consistent results with photoreflectance observations. The photoreflectance spectra of the solar cells indicate that different states were formed in CdS depending on the conditions of CBD processes.