Conditioning of Silicon substrates by wet chemical etching and oxidation

High efficiency a Si H c Si heterojunction solar cells are composed of thin amorphous silicon a Si H layers deposited on crystalline silicon c Si wafers. The a Si H layer is used to form the p n junction. Therefore, the substrate surface directly becomes part of the electronic interface. In order to improve solar cell efficiencies random pyramid textures are commonly utilized to minimize re flection losses and to increase the absorption probability by light trapping. However, adequate inter face passivation of pyramid textured Si substrates is more difficult to achieve due to the increased effective surface area and a higher number of crystallographic imperfections. As a result of our optimized saw damage removal, surface texturization and wet chemical sur face conditioning by wet chemical oxidation and oxide removal, a Si H c Si solar cells on n type substrates with conversion efficiencies exceeding 20 could be fabricated, as discussed in detail elsewhere [ ]. This values represents a considerable improvement over our previously reported best cell efficiencies for cells with a Si H i buffer layer. It was achieved by thorough optimization of the surface texture and wet chemical conditioning by surface oxidation and oxide removal and the a Si H c Si interface passivation, resulting in improved open circuit voltages and fill factors [18]. Moreover, it was shown, that wet chemical oxidation in ozone containing ultra pure water could be a high quality and low cost alternative to current cleaning processes with RCA and sulphuric acid peroxide solutions. Optimized DIW O3 treatment at ambient temperature can be prospectively utilized for minimizing the energy and chemical consumption and the number of process steps in various cleaning and passivation procedures