Reduction of the interface defect density on crystalline silicon solar cell substrates by wet-chemical preparation of ultrathin SiOx passivation layers

Ultrathin SiO_x tunneling layers can be implemented in a wide range of solar cell applications, like for the passivation of the heterojunction interface in a-Si:H/c-Si solar cells. Here we present the successful preparation of ultrathin SiO_x layers by wet-chemical oxidation in HCl:H₂O. Applying m surface photovoltage (SPV) and spectral ellipsometry (SE) measurements during the initial phase of oxidation, the influence of substrate morphology, the oxidation parameters and the preceding process steps on the resulting interface state density was systematically investigated. With respect to the standard RCA process, optimized sequences of smoothing, oxide removal and oxidation of textured Si wafers allow for a distinct reduction of the density of interface states both on hydrophilic and hydrophobic substrate surfaces, as required for different subsequent layer depositions (e.g contact layers, passivation layers) or solar cell fabrication.