Surface passivation and band engineering: a way toward high efficiency graphene–planar Si solar cells

Graphene–Si Schottky junction solar cells are promising candidates for high-efficiency, low-cost photovoltaic applications. However, their performance enhancement is restricted by strong carrier recombination and relative low barrier height. Here, we demonstrated the successful construction of high-efficiency graphene–planar Si solar cells via modification of the Si surface with a molecule monolayer as well as tuning the interface band alignment with an organic electron blocking layer. Methylated Si showed the capability to effectively suppress the surface carrier recombination, leading to a remarkable improvement of device efficiency. The recombination was further reduced by inserting a thin P3HT organic layer; the unique band alignment could prevent electron transfer from n-Si to the graphene anode so as to minimize the current leakage. These methods, along with careful control of the graphene doping level and layer number, gave rise to a power conversion efficiency (PCE) as high as 10.56%. The scalability of the devices was further investigated by studying the device area dependent photovoltaic performance.