Nanocrystalline Silicon Oxide in Silicon Heterojunction Solar Cells

To advance the contribution of photovoltaic (PV) systems in a transition towards fully sustainable energy generation, the costs of the associated systems need to decrease. In particular, a constant evolution of their solar energy conversion efficiency ($\eta$) is an effective way to reduce the overall costs of the energy production of a solar cell. In the recent decade high $\eta$ have been achieved by the silicon heterojunction (SHJ) solar cell technology, which allows for a very high open circuit voltage (Voc). However, the parasitic absorptance (A$_{paras}$) within the doped hydrogenated amorphous silicon (a-Si:H) layers still causes a significant reduction in the short circuit current density (J$_{sc}$) of a SHJ solar cell. In contrast, thin films of hydrogenated nanocrystalline silicon oxide (nc-SiO$_{x}$:H) are significantly more transparent. This is related to their advantageous microstructure, in which a conductive network of crystalline silicon (c-Si) is combined with a silicon dioxide (SiO$_{2}$)-like matrix at the nanoscale. Nevertheless, a trade-off between a high conductivity and a high transparency has to be considered due to the conflicting properties of the two phases. Accordingly, the aim of this thesis was to develop doped nc-SiO$_{x}$:H films at an increased deposition frequency (very high frequency (VHF)) to improve the optoelectronic trade-off of the films. Furthermore, these layers were applied in SHJ solar cells to achieve a low Aparas and, thereby, an enhanced J$_{sc}$. Additionally, a continuous enhancement of $\eta$ was accomplished by changes in the design of the solar cells. In detail, films of nc-SiO$_{x}$:H were optimized at VHF using plasma enhanced chemical vapor deposition (PECVD). By exploiting the increased atomic H density at VHF, an improved phase separation was achieved in comparison to films deposited at radio frequency (RF) within the same deposition system and the [...