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To date, almost all reported graphene nanowalls (GNWs)/Si solar cells are fabricated through the direct deposition of GNWs on the silicon wafer. In this work, we report a polymer-free transfer method of GNWs grown on the copper foil for the fabrication of GNWs/Si solar cells. This allows us to further improve the photovoltaic performance of the solar cells by means of interface engineering. An optimized photovoltaic conversion efficiency (PCE) of the as-fabricated GNWs/Si solar cell can reach up to 4.99%. Furthermore, the PCE of the device is further improved by introducing the spiro-OMeTAD thin film as an interface layer, which serves as an electron-blocking and hole-transporting layer through tuning the band structure of the solar cells. Without any chemical doping and anti-reflecting coating, the maximum PCE of 8.27% has been achieved for the GNWs/spiro-OMeTAD/Si solar cell through optimizing the dopant content and the thickness of the spiro-OMeTAD thin film. We believe that our study indicates a new route for the fabrication of high-efficiency, low-cost GNWs/Si Schottky heterojunction solar cells without the need for chemical doping of the GNWs.

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