Effects of Hydrogen Diluted silane plasma on Amorphous Silicon Solar Cells

Abstract

We systematically studied amorphous silicon (a-Si:H) films and solar cells which were fabricated by H2-diluted SiH4 plasma. The H2 dilution improves the quality of poor materials resulting from non optimized pure SiH4 conditions however this improvement can also be achieved by reducing the RF power under pure SiH4 conditions. The H2 dilution is not always necessary for the optimization of a-Si:H. Higher diluted plasma reduces the optical absorption coefficient of a-Si:H, resulting in a lower short circuit current (Isc), and the H2-dilution conditions could not give higher conversion efficiency (Eff) than the optimized pure SiH4 condition. The H2-diluted plasma at a relatively low pressure (0.2 Torr) causes a lower open circuit voltage (Voc) in spite of wider optical gaps and lower Isc than values estimated from the optical absorption coefficient, probably due to the damage of underlying layers by H ions or radicals. These plasma damages are suppressed by increasing the pressure up to ∼1.0 Torr.