Growth of ZnO:Al films by RF sputtering at room temperature for solar cell applications

Aluminum-doped ZnO (ZnO:Al) films were prepared at room temperature in pure argon ambient on glass substrates by RF magnetron sputtering. The influence of sputtering power, deposition pressure and film thickness on the film properties was investigated. The deposited ZnO:Al films were characterized to examine the electrical, optical, and structural properties for the application of thin copper indium gallium selenide (CIGS) solar cells. The deposition parameters of ZnO:Al films were optimized. The optimized ZnO:AI films showed a strong and sharp (0 0 2) X-ray diffraction peak. The 600-800 nm thick ZnO-Al films showed a high transparency above 85% in the visible range and a sheet resistance low to 10 Omega/square. CIGS solar cells with 1.2 mu m thick absorbers were fabricated using bi-layer ZnO films (low resistive and thick ZnO:Al/high resistive and transparent thin i-ZnO) as front contacts. The thin absorber layers were prepared by the low cost technique involving co-sputtering of Cu-Ga alloy and In targets and selenization with Se powders. Efficiencies of the order of 6-7% were achieved for the manufactured thin CIGS solar cells without antireflective films. The results demonstrated that RF sputtered ZnO:Al films are suitable for application in low cost and thin CIGS solar cells as transparent conductive electrode layers. (C) 2009 Elsevier Ltd. All rights reserved.