Optimizing performance parameters of graphene-silicon and thin transparent graphite-silicon heterojunction solar cells

We investigated heterojunctions of Si with large-area high-quality monolayer and multi-layer graphene, as well as thin transparent graphite. We show that by controlling the transmittance and sheet resistance of large-area graphitic electrodes, it is possible to obtain solar cells with power conversion efficiency (PCE) exceeding 3% without any doping requirements. Our calculations indicate that such junctions can form extremely robust interfaces with near-100% internal quantum efficiency. Under optimized doping conditions, power conversion efficiencies increase almost universally by a factor of 2.5. Optimized conditions for reproducibly obtaining cells with PCE > 5% are presented, with the best PCE obtained ∼7.5% with short-circuit current density exceeding 24 mA/cm2.