SOI Based Solar Cell Preparation And Performance Enhancements

Solar energy is an environmentally friendly, clean, and renewable energy. Solar photovoltaic cells convert light energy directly into electricity energy, and its development is of great significance to improve the ecological environment and promote the development of low-carbon economy as well as the production of human life. In this thesis, we discussed the current status of the solar cells, and proposed a new type of SOI-based thin-film solar cells. We explored its fabrication process and its absorption enhancement which shed some lights for developing next generation solar cell technology.Firstly, the traditional solar cell structure was theoretically analyzed from two aspects: the optical loss and electrical loss. For optical loss, light trapping structures can be used, such as wet-etched pyramid, by which incident light is scattered in a wide range of angles obtaining multiple reflections inside the cells to extend the effective optical path, thereby increasing light absorption. On the other hand, in order to avoid the cell electrodes blocking the incident light, both electrodes are put at the back of the cells.For electrical loss, analysis of doping concentration influences on conversion efficiency and open-circuit voltage is required so as to design new back-contact electrode structures.Secondly, we explored the wet-etching process to open the cell window. We used KOH solution for deep silicon etching and analyzed the etching rate at different temperatures and at different concentrations, resulting in optimal processing conditions.We also compared silicon surface morphologies at different etching times, obtaining the rules to obtain pyramid light trapping structures.Thirdly, SOI(Silicon-On-Insulator, silicon on insulator substrate) based thin film solar cells were fabricated. We explored the semiconductor processing technology for solar cell fabrication, such as high-temperature oxidation, thermal diffusion,photolithography, ion implantation, deposition(evaporation coating) and etching. All the processing parameters were optimized and consequently all back contact solar cell were successfully prepared.Finally, the absorption enhancement experiments were conducted among flat solar cells, the solar cells with anti-reflective coating and the solar cells with pyramid surfacetextures. It was found the solar cells with anti-reflective coating or pyramid textures showed superior to flat solar cells. The Silicon Nitride coating on solar cells leads to30% absorption enhancement, and pyramid textures produces absorption increase by about 15%.