Using the Ti-doped GaZnO transparent conductive oxide films for the development of CIGS photovoltaics

In this paper, Ti-doped GaZnO (GTZO) quaternary alloys were used as the transparent conductive oxides (TCOs) for Cu(In,Ga)Se-2 (CIGS) solar cell application. These thin films are highly favorable for solar power systems. Photoluminescence measurement and X-ray diffraction were employed to investigate the GTZO thin films. Advantageous crystal quality was produced by radio-frequency magnetron sputtering deposition with a sputtering power of 200 W, a thin-film thickness of 750 nm, a substrate temperature of 250 degrees C, and a growth pressure of 1 mtorr. The results indicated that GTZO thin films showed a high transmittance of 86.8%, and a low thin-film resistivity of 5.14x10(-4) Omega-cm. Two sets of CIGS solar cells were made with GTZO and indium-tin-oxide (ITO) TCO layers. Observations of these devices demonstrated the superior optoelectronic properties of GTZO TCO thin film and the effectiveness of Ti-doping in GaZnO. The CIGS solar cells with high-performance GTZO TCOs exhibited a superior conversion efficiency of 9.1% and an average high external quantum efficiency of 87.1% in the wavelength range from 550 to 1100 nm whereas the ITO-based control solar cells showed an efficiency of 5.9% and an external quantum efficiency of 58.9%. The device performance levels in this study demonstrated that GTZO TCO thin films can be used for developing high-performance CIGS solar cells.