Doping of Monolayer Graphene for Silicon based Schottky Junction Solar Cells

Abstract

Silicon-based hybrid solar cells have garnered extensive attentions in the photovoltaics industry due to easy processing attributes and high optical absorption and outstanding carrier mobility of silicon. Among all, indium tin oxide (ITO)/silicon solar cells have achieved a power conversion efficiency of 13% due to excellent conductivity, transmittance and applicable surface potential of ITO. However, the cost of ITO has risen significantly recently due to the deficiency of indium. Therefore, graphene has been an inexpensive alternative to ITO. For solar cell applications, graphene plays an important role as transparent electrodes (TE) with tunable work functions for efficient carrier collection. Therefore, graphene-based Schottky junction solar cells (SJSC) on crystalline silicon thin films hold great promises for low-cost photovoltaics owing to potentials for high efficiency and rapid production on flexible substrates. According to previous reports, the key factors to achieve a highly efficient SJSC include excellent transparence and conductance, as well as tunable work functions. Herein, we demonstrate a single layer graphene/n-Si Schottky junction solar cell that exhibits a power conversion efficiency (PCE) of 1.2 % under one-sun AM 1.5G illumination, and an integrated short-circuit photocurrent of 18.3 mA/cm(2) from the external quantum efficiency measurement. The transmittance of the monolayer graphene in this device is over 97 % and the sheet resistance is around 800 to 1200 Omega/square. Furthermore, we investigate a doping method involving bis(trifluoromethanesulfonyl)-amid (TFSA) for the monolayer graphene to improve the separation and collection of photogenerated carriers in the SJSC. The preliminary data show that the sheet resistance is decreased rapidly from 1200 to 300 Omega/square. and the surface potential is also adjusted by the chemical doping. Currently, device fabrication with doped monolayer graphene is still in process and complete characterization data will be presented.