Very high open-circuit voltage in dual-gate graphene/silicon heterojunction solar cells

Abstract

Two dimensional (2D) layered materials and their heterojunctions with other materials are attracted because of their remarkable electrical and optical properties. In particular, graphene/semiconductor Schottky heterojunction is used for high performance solar cells. Here, we demonstrated very high open circuit voltage (Voc) in graphene/silicon heterojunction solar cell by dual-gate electric field application. The low density of states near Dirac point in graphene allows large modulation of graphene Fermi-level and corresponding Schottky barrier in a graphene/silicon junction. The top and bottom gate electric fields independently adjust the built-in potentials of respective upper and lower silicon energy band to induce higher band bending (1.22 eV) than the bandgap (1.12 eV). As a result, a maximum Voc of 0.94 V is achieved at the − 8 V of top-gate voltage and 10 V of bottom-gate voltage, exceeding highest known Voc for previous graphene/silicon solar cell (Voc = 0.61 V) and the S-Q Limit (0.84 V) of conventional silicon solar cell – a thermodynamic limit for the energy conversion efficiency of solar cells with a single band gap energy. The ratio of output power gain to input gate power (ΔPG/ΔPC) is approximately 1012–1014 with negligible power consumption in the gate (PC = 1 fW/cm2–10 pW/cm2), resulting in the significant advances in the power generation (PG = 40 mW/cm2).