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We present a detailed optimization of a hole selective rear contact for p –type crystalline silicon solar cells which relies on full-area processes and provides full-area passivation. The passivating hole-contact is based on a layer stack comprising a chemically grown thin silicon oxide, an intrinsic silicon interlayer, and an in-situ boron-doped non-stoichiometric silicon-rich silicon-carbide layer on top. After deposition, the structure is annealed at 775–900 °C to diffuse dopant impurities to the c-Si wafer and a hydrogenation step is carried out. It is shown that hydrogenation is essential to obtain high quality surface passivation. In particular, we compare the effect of annealing in forming gas and annealing with a silicon-nitride overlayer as hydrogen source. We present a systematic optimization of the hole-selective contact, for which we varied the doping concentration, annealing parameters and report the implied open circuit voltage ( iV oc ) and combined specific contact resistivity ( ρ c ). It is observed that for highly doped layers the optimum annealing temperature for high quality surface passivation is 800 °C while for lowly doped layers the optimum annealing condition shifts to 850 °C. Excellent surface passivation and efficient current transport is evidenced by an iV oc value of 718 mV which corresponds to a saturation current density ( J 0 ) of 11.5 fA/cm 2 and a ρ c of 17 mΩcm 2 on p −type wafers. Moreover, the evolution of the boron diffusion profiles with different annealing conditions is investigated. Finally, we demonstrate proof-of-concept p −type hybrid solar cells employing the full-area hole-selective rear contact presented here and standard heterojunction front electron contact. The excellent efficiency potential of our passivating rear contact is highlighted by conversion efficiencies up to of 21.9%, enabling V oc of 708 mV, FF of 79.9% and J sc of 38.7 mA/cm 2 . [ABSTRACT FROM AUTHOR]

We present a novel passivating contact structure based on a nanostructured silicon-based layer. Traditional poly-Si junctions feature excellent junction characteristics but their optical absorption induces current losses when applied to the solar cell front side. Targeting enhanced transparency, the poly-Si layer is replaced with a mixed-phase silicon oxide/silicon layer. This mixed-phase layer consists of an amorphous SiO x matrix with incorporated Si filaments connecting one side of the layer to the other, and is referred to as nanocrystalline silicon oxide (nc-SiO x ) layer. We investigate passivation quality, measured as saturation current density, and nanostructural changes, characterized by Raman spectroscopy and transmission electron microscopy, carefully studying the influence of annealing dwell temperature. Excellent surface passivation on n-type and also p-type wafers is shown. An optimum annealing temperature of 950 °C is found, resulting in a saturation current density of 8.8 fA cm −2 and 11.0 fA cm −2 for n-type and p-type wafers, respectively. Even before forming gas annealing, emitter saturation current densities of 27.9 fA cm −2 (n+/n junction) and 32.0 fA cm −2 (n+/p junction) are reached. Efficient current extraction is presented with specific contact resistivities of 86 mΩ cm 2 on n-type wafer and 19 mΩ cm 2 on p-type wafers, respectively. High-resolution transmission electron microscopy reveals that the layer stack consists of intermixed SiO x and Si phases with the Si phases being partly crystalline already in the as-deposited state. Thermal annealing at temperatures ≥850 °C further promotes crystallization of the Si-rich regions. The addition of the SiO x phase enhances the thermal stability of the contact and should allow to tune the refractive index and improve transparency, while still providing efficient electrical transport through the crystalline Si phase, which extends throughout almost the entire contact. [ABSTRACT FROM AUTHOR]