Strategy to mitigate the dipole interfacial states in (i)a-Si:H/MoO_x passivating contacts solar cells

Abstract

Molybdenum oxide (MoOx) is attractive for applications as hole-selective contact in silicon heterojunction solar cells for its transparency and relatively high work function. However, the integration of MoOx stacked on intrinsic amorphous silicon (i)a-Si:H layer usually exhibits some issues that are still not fully solved resulting in degradation of electrical properties. Here, we propose a novel approach to enhance the electrical properties of (i)a-Si:H/MoOx contact. We manipulate the (i)a-Si:H interface via plasma treatment (PT) before MoOx deposition minimizing the electrical degradation without harming the optical response. Furthermore, by applying the optimized PT, we can reduce the MoOx thickness down to 3.5 nm with both open-circuit voltage and fill factor improvements. Our findings suggest that the PT mitigates the decrease of the effective work function of the MoOx (WFMoOx) thin layer when deposited on (i)a-Si:H. To support our hypothesis, we carry out electrical simulations inserting a dipole at the (i)a-Si:H/MoOx interface accounting the attenuation of WFMoOx caused by both MoOx thickness and dipole. Our calculations confirm the experimental trends and thus provide deep insight in critical transport issues. Temperature-dependent J-V measurements demonstrate that the use of PT improves the energy alignment for an efficient hole transport.