Impact of epitaxial growth at the heterointerface of a-Si:H∕c-Si solar cells

The authors have demonstrated that interface structures of heterojunction solar cells consisting of hydrogenated amorphous silicon $(a\text{-}\mathrm{Si}:\mathrm{H})$ and crystalline silicon $\left(c\text{-}\mathrm{Si}\right)$ have quite large impact on the solar cell performance. In particular, unintentional epitaxial growth was found to occur during an intended $a\text{-}\mathrm{Si}:\mathrm{H}$ $i$ -layer growth on $c\text{-}\mathrm{Si}$ in plasma-enhanced chemical vapor deposition (PECVD). By the formation of the epitaxial layer at the interface, the solar cell efficiency decreases significantly. Their result shows that the epitaxial layer is formed rather easily in PECVD, even without the presence of ${\mathrm{H}}_2$ gas, and may have affected many previous studies on $a\text{-}\mathrm{Si}:\mathrm{H}∕c\text{-}\mathrm{Si}$ solar cells seriously.