The role of H/sub 2/ dilution in the deposition of a-Si:H films and its effect on the solar cell degradation

The role of H/sub 2/ dilution in the mercury-sensitized photochemical vapor deposition of a-Si:H film solar cells has been investigated by using D/sub 2/ as a diluent instead of H/sub 2/. The increase in the D content in the a-Si:H,D film with the D/sub 2//SiH/sub 4/ dilution ratio indicated that the H/sub 2/ dilution could increase the atomic hydrogen concentration near the growth surface. In addition, the numerical model has been used to estimate the change in the dangling bonds density and energy level in the H/sub 2/-diluted film by comparing with the temperature dependency of dark conductivity in initial and light-soaked states. It was found that the center level of the dangling bonds shifted toward the valence band edge as the bandgap of the film widened due to the H/sub 2/ dilution. This shift in the dangling bonds level in the i layer resulted in the increase of open circuit voltage of a-Si:H solar cell with the light soaking time as confirmed by simulation and experimental results.