Enhancement of Open Circuit Voltage via Light soaking in Amorphous Silicon Solar Cells

Abstract

The increase in open-circuit voltage (Voc) due to light soaking was investigated in amorphous silicon solar cells. The light-induced increase in Voc appears when i-layers are prepared in H2-diluted plasma (H2/SiH4>10). It is necessary that more than two-thirds of the i-layer thickness be formed under such hydrogen dilution. This phenomenon is not related to p/i interface effects but reflects the bulk properties of the dilution layer. The increase in Voc is caused by the voltage shift of dark I–V characteristics. The change of Voc is determined by the balance between the shift of dark current and the reduction of photocurrent due to the light-induced defects. The voltage shift suggests an increase in the diode barrier height of the pin junction; however, the increase in built-in potential in the active layers (i-layers) is not observed in our experiments. The advantage of this effect is seen with sufficiently thin i-layers, because conventional light-induced degradation is negligible. The increase in Voc improves conversion efficiency by 2% after light soaking in the case of 500 Å i-layers.