Maximization of the open circuit voltage for hydrogenated amorphous silicon n–i–p solar cells by incorporation of protocrystalline silicon <i>p</i>-type layers

Abstract

In studies of hydrogenated amorphous silicon (a-Si:H) n–i–p solar cells fabricated by rf plasma-enhanced chemical vapor deposition (PECVD), we have found that the maximum open circuit voltage (Voc) is obtained by incorporating p-type doped Si:H layers that are protocrystalline in nature. Specifically, these optimum p layers are prepared by PECVD in the a-Si:H growth regime using the maximum hydrogen-to-silane flow ratio possible without crossing the thickness-dependent transition into the mixed-phase (amorphous+microcrystalline) growth regime for the ∼200 Å p-layer thickness. The strong dependence of the p-layer phase and solar cell Voc on the underlying i-layer phase also confirms the protocrystalline nature of the optimum Si:H p layer.