Angermann, H.; Kegel, J.; Stürzebecher, U.; Grün, A.; Stegemann, B.: Conditioning of Silicon substrates by wet-chemical etching and oxidation. In: Proceedings of 8th solid state surfaces and interfaces, 2013, Smolenice Castle, Slovak Republic, 2013. - ISBN 978-80-223-3501-0
Abstract:
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.