Potentials of mixed-phase doped layers in p-type Si heterojunction solar cells with ZnO:Al

We present and discuss advances in the development of p-type Si heterojunction solar cells with Al-doped ZnO (AZO) on both front and rear side, by means of mixed-phase Si- and SiOx-based doped layers. We demonstrate that while rear AZO can be deleterious when using p-type amorphous silicon (a-Si:H), p-type microcrystalline silicon (μc-Si:H) allows for: (1) suppression of the p-layer/AZO Schottky-like barrier, (2) relevant Voc increase, and (3) improved transport and extraction of carriers. In contrast, Voc reduction and increased low-injection recombination is observed with n-type μc-Si:H in conjunction with AZO, likely due to the low defect density of the material which entails severe depletion effects. These issues are avoided with the more defective mixed-phase n-SiOx, which additionally provides for reduced parasitic absorption losses and is thus established as the optimal emitter choice. •p-type SHJ solar cells with AZO and mixed-phase doped layers are investigated.•Voc increase and improved transport are achieved with use of p-μc-Si:H vs. p-a-Si:H.•The impact of mismatched TCO with variation of emitter defectiveness is highlighted.•n-μc-SiOx:H is established as optimal emitter, in electrical and optical perspective.