Effects of power and hydrogen in the discharge on the photovoltaic properties of sputtered amorphous silicon

The photovoltaic properties of amorphous silicon films produced by reactive sputtering have been investigated as a function of power level and hydrogen concentration in the discharge. We find that raising the power in the discharge leads to films with better bulk properties but poorer surface properties. Increasing the hydrogen concentration in the discharge affects the photovoltaic properties of the films by increasing the optical gap of the film and simultaneously decreasing the density of states in the middle of the gap. Because of this dual role of hydrogen, films with optical gaps of 1.7–1.85 eV are capable of generating the same magnitude of short circuit current in sunlight. However, the large gap material is capable of providing a higher open circuit voltage and therefore results in solar cells with better overall performance.