VHF A-SI-H SOLAR-CELLS - A SYSTEMATIC MATERIAL AND CELL STUDY

A systematic study of material quality has been performed for intrinsi c a-Si:H layers deposited by plasma enhanced chemical vapor deposition at excitation frequencies between 30 and 80 MHz (VHF). The process co nditions were optimized not only for ''device quality'' opto-electroni c properties but also for a uniformity in layer thickness better than 5% over the 10 cm X: 10 cm substrate area. We found optimized homogene ities at different pressures depending on the excitation frequency. Th e effect of frequency at these optimum conditions on the material qual ity is small. VHF-intrinsic layers have been used in a-Si:H p(+)-i-n() solar cells, in which both the p(+) and n(+) layer were made using 1 3.56 MHz, There is a clear correlation between material quality and so lar cell parameters. Material deposited at low power densities is of s o-called ''device quality,'' which is confirmed by demonstrating an in itial efficiency of 10% for cells deposited at 65 MHz using a low powe r density. The deposition rate still is 2-3 times higher than the one at 13.56 MHz. Light-soaking of the cell leads to stabilization at 6% f or the best cells, which compares well to conventional 13.56 MHz cells .