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

Abstract

Molybdenum oxide (MoO_x) 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 MoO_x 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/MoO_x contact. We manipulate the (i)a-Si:H interface via plasma treatment (PT) before MoO_x deposition minimizing the electrical degradation without harming the optical response. Furthermore, by applying the optimized PT, we can reduce the MoO_x 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 MoO_x (WF_MoOx) 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/MoO_x interface accounting the attenuation of WF_MoOx caused by both MoO_x 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.