Improvement of CIGS solar cells with high performance transparent conducting Ti-doped GaZnO thin films

Abstract

This study reports upon the enhancement of the optoelectronic characteristics and crystallite quality of a typical Ga-doped ZnO ternary alloy achieved by using titanium (Ti) doping to form novel Ti-doped GaZnO (GTZO) transparent conductive oxide (TCO) thin films with characteristics of low-cost and indium-free for employment in Cu(In,Ga)Se2 (CIGS) solar cell applications. These thin films are highly favorable for solar power systems. Photoluminescence measurement and X-ray diffraction were employed to assess the GTZO thin films. A high crystal quality was obtained through radio-frequency magnetron sputtering deposition with a sputtering power of 200 W, a thin-film thickness of 750 nm, a substrate temperature of 250 °C, and a growth pressure of 1 mTorr. The thin-film characteristics were a high transmittance of 86.8%, a low thin-film resistivity of 5.1 × 10−4 Ω-cm (carrier mobility of 10.9 cm2 V−1 s−1, and carrier concentration of 1.1 × 1021 cm−3), and a high figure of merit of 32.6 × 10−3 Ω−1; these characteristics established GTZO thin films as an alternative TCO for CIGS solar cell applications.These devices demonstrated the superior optoelectronic properties of GTZO TCO thin films 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 on average, a high external quantum efficiency of 87.1% in the wavelength range from 550 to 1100 nm. The performance of these devices demonstrated in this study indicated that GTZO TCO thin films can be used for developing high-performance CIGS solar cells.