High-efficiency amorphous silicon solar cells: Impact of deposition rate on metastability

Hydrogenated amorphous silicon (a-Si:H) films, used for light absorbers of p-i-n solar cells, were deposited at various deposition rates (R-d) ranging over two orders of magnitude (R-d similar to 2 x 10(-3)-3 x 10(-1) nm/s) by using diode and triode plasma-enhanced chemical vapor deposition (PECVD). The impact of varying R-d on the light-soaking stability of the solar cells has been investigated. Although a reduction of R-d mitigates the light-induced degradation in the typical range of R-d (>10(-1) nm/s), it remains present even in the very low R-d (<10(-2) nm/s), indicating that the metastable effect persists in a-Si:H regardless of R-d. The best performing cell, whose a-Si:H absorber is characterized by low amount of metastable defect and high bandgap, can be obtained at R-d of similar to 1-3 x 10(-2) nm/s by triode PECVD. By applying such a-Si:H in the improved p-i-n devices, we demonstrate two record independently confirmed stabilized efficiencies of 10.22% for single-junction and 12.69% for a-Si:H/hydrogenated microcrystalline silicon (mu c-Si:H) tandem solar cells. (C) 2015 AIP Publishing LLC.