Silicon-based thin-film solar cells fabricated near the phase boundary by VHF PECVD technique

The light-soaked and annealing behaviors for silicon (Si)-based thin-film single-junction solar cells fabricated near the phase boundary using a very-high-frequency plasma-enhanced chemical vapor deposition (VHF PECVD) technique are investigated. The hydrogen dilution ratio is changed in order to achieve wide band gap hydrogenated amorphous Si (a-Si:H) and narrow band gap hydrogenated microcrystalline Si (μc-Si:H) absorbers. Just below the a-Si:H-to-μc-Si:H transition, highly hydrogen-diluted a-Si:H solar cells with a good stability against light-soaking and fast annealing behavior are obtained. In contrast, the solar cell fabricated at the onset of the μc-Si:H growth is very unstable and its annealing behavior is slow. In the case of μc-Si:H solar cells with the crystal volume fraction of 43–53%, they show the lowest light-induced degradation among the fabricated solar cells. However, it is very difficult to recover the degraded μc-Si:H solar cells via thermal annealing.