Electrical and optical properties of low pressure chemical vapor deposited Al-doped ZnO transparent conductive oxide for thin film solar cell

Al-doped ZnO (AZO) is a representative transparent conductive oxide (TCO) to replace indium tin oxide. The advantages of AZO include low resistivity, high transmittance, and low cost. Typically, for solar cell applications, the surface of TCO is textured by a chemical treatment to improve the light adsorption of surface. In this study we adopted a simple process, the chemical vapor deposition method, to form a rough surface without an additional process. In order to reduce the resistivity, aluminum was doped using a trimethylaluminum (TMA) source. The incorporated Al contents decreased at high TMA pressure due to Al solubility limitation. The introduction of TMA showed strong influence on resistivity and diffusion of light in a wide wavelength range. The film resistivity is found to strongly depend on the electron carrier concentration, which is correlated with the donor level creations with Al content in the film as evaluated by photoluminescent measurement. A high haze factor up to 43 at 600 nm was achieved without an additional surface texturing process. The application of low pressure chemical vapor deposition AZO as a TCO for p-i-n a-Si:H thin film solar cells resulted in high energy conversion efficiency up to 7.7, which was comparable to commercially available fluorine doped tin oxide (SnO₂:F) TCO.