Physical Science International Journal

We numerically study how the rear n⁺-a-Si:H Back-Surface-Field (BSF) thickness and doping co-determine the performance of a-Si:H(n⁺)/c-Si(n)/a-Si:H(p⁺) silicon heterojunction (SHJ) solar cells. Using a two-diode formalism coupled to TCAD SILVACO-ATLAS drift–diffusion under AM1.5G and , we sweep a thin BSF window ( ) and its doping ( ) while keeping the optical stack and interface-defect sets fixed to isolate the electrical role of the rear contact. A thin, highly doped BSF reduces rear-surface recombination and strengthens carrier selectivity, yielding a small but systematic Voc increase (  in our setup), a modest  improvement consistent with lower effective series/recombination losses ( ), and a broadly stable . The resulting efficiency  peaks when combining a thin BSF with high doping; by contrast, too-thin layers under-passivate and too-thick layers introduce resistive and potential optical penalties. Modeling includes SRH and Auger recombination with fixed trap sets, standard mobility/bandgap temperature dependences, and constant front/back optical conditions, thereby attributing observed performance changes specifically to BSF thickness/doping. For clarity and design use, we report baseline vs. near-optimum KPIs ( ), indicating an absolute η gain of  percentage points under AM1.5G, 25 °C. A brief sensitivity note (series resistance; rear interface traps) explains how further increases in resistive or defect-related losses would primarily round the  knee (lowering ) and slightly reduce Voc, consistent with our trends. Overall, these results provide practical guidance for rear-contact engineering in SHJ cells and align with recent literature on passivating selective contacts, while deliberately keeping other surface-property variations outside the present scope.