Advantages of using amorphous IZO films for the transparent conducting oxide layer in Cu(In, Ga)Se2 solar cells

The advantages of using indium zinc oxide (IZO) films instead of conventional Ga-doped zinc oxide (ZnO:Ga) films for Cu(In, Ga)Se₂ (CIGS) solar cells are described. The electrical properties of IZO are independent of film thickness. IZO films have higher mobility (30-40 cm²/Vs) and lower resistivity (4-5 × 10^-4 Ω cm) compared to ZnO:Ga films deposited without intentional heating, because the number of grain boundaries in amorphous IZO films is small. In addition, transmittance greater than 80% was obtained in the wavelength range of 400-1200 nm. The properties of a CIGS solar cell using IZO at the window layer were better than those obtained using a conventional ZnO:Ga at the window layer; moreover, the properties tended to be independent of thickness. These results indicate that use of IZO as a transparent conducting oxide (TCO) layer is expected to increase the efficiency of CIGS solar cells.