Enhancing Silicon Compound Heterojunction Solar Cells with Vanadium-Doped MoO_X as Hole Transport Layers

Crystalline silicon (c-Si) solar cells dominate the global market, and the development of eco-friendly and cost-effective c-Si compound solar cells with carrier-selective passivated contacts has attracted increasing attention. This work investigated the impact of oxygen vacancies (V_O) and vanadium (V) doping on molybdenum trioxide (MoO_X), using a combination of first-principles calculations and device simulations. These V_O defects accumulated from bulk to surface with lower energy barrier of 1.7 eV, compared to 3.4 eV on surface and 3.8 eV from surface to bulk. The surface V_O significantly decreased MoO_X work function from 6.1 eV to 4.8 eV，considering alteration in surface charges from +4 µC cm^-2 to -8 µC cm^-2. Vanadium doping increased V_O transport barrier by 0.1 eV, suppressing defect migration. Meanwhile, it raised work function by 0.26 eV and widened the bandgap by 0.6 eV. As hole transport layer, V-doped MoO_X on illuminated side of c-Si solar cells boosted absolute efficiency by 1.0%, compared to MoO_X on rear side; of this increase, 0.2% was attributed to higher work function and 0.8% was due to reduced optical losses. These findings emphasize V-doped MoO_X in enhancing c-Si compound solar cell performance and in promoting the development of efficient photovoltaic technologies.