Low bandgap a-Si:H film with better stability prepared by RF PECVD method using helium dilution

Low bandgap a-Si:H films have been prepared by RF PECVD method (13.56 MHz) using helium as diluent to silane gas. Helium dilution and chamber pressure play an important role in reducing the optical gap at substrate temperature /spl sim/210/spl deg/C. This highly photosensitive low bandgap material shows less light induced degradation compared to that for normal bandgap a-Si:H material. Single junction solar cells having efficiency 7.2% (1 cm/sup 2/ area) and spectral response upto 850 nm have been fabricated using 1.6 eV a-Si:H film.