Effects of substrate temperature on the properties of transparent conducting AZO thin films and CIGS solar cells

Chalcopyrite CuInGaSe₂ (CIGS) based thin-film solar cells are regarded as most promising candidates for film power modules due to high efficiencies and low cost. Aluminum doped zinc oxide (ZnO:Al, AZO) is a common material for transparent conducting films used as a front contact layer on CIGS solar cells. In this study, AZO thin films were deposited on soda-lime glass (SLG) by conventional RF-magnetron sputtering using a commercial ceramic target. The dependence of the electrical and crystalline properties on the substrate to target position at different substrate temperature was investigated. The result shows that adjusting the substrate temperature could develop better transparent conducting thin films. However, the plasma ion-bombardment producing from the magnetron sputtering method makes significant effects on the distribution of electric conductive uniformity. When the substrate is placed on the appropriate position and the deposition process is carried out at higher substrate temperature, highly conductive AZO films with the average transmittance >90% would be obtained. The transparent conducting AZO films are also utilized as the front contact to fabricate (Cu(In,Ga)Se₂, CIGS) thin-film solar cells at different substrate temperature. The results find that the CIGS solar cells show better efficiencies at lower temperature even if high conductive AZO films are obtained at higher substrate temperature. It shows that the substrate temperature significantly affects the properties of CIGS solar cells.