High Efficiency Graphene SolarCells by Chemical DopingXiaochang Miao, Sefaattin Tongay, Maureen K. Petterson, KaraBerke, Andrew G. Rinzler, Bill R. Appleton and Arthur F. Hebard*Department of Physics, Department of Material Science andEngineering and Nanoscience Institute for Medical and EngineeringTechnologies, University of Florida, Gainesville, Florida 32611,United States By Tufan GhoshNano Lett. 2012, 12, 2745−2750
Schematic diagram of TFSA doped-graphene/n-SiSchottky junction solar cell
Advantages of graphene-based Schottky junctionsolar cells Tunable work function of graphene can be used to optimized the performance of the device Graphene electrodes are inexpensive and are very convenient to form Schottky junction This technique can be applied on other semiconductors (GaAs, CdSe, etc.) owing the tunability of graphene’s work function Bis(trifluoromethanesulfonyl)amine as a dopant has added advantage of environmental stability due to its hydrophobic nature
Device fabricationFig. 1 (a) Graphene/n-Si. (b) TFSA doped graphene/n-Si Schottky solar cellgeometry. (c) Optical image of a completed TFSA doped graphene/n-Si solar cellshowing contacts and contact leads
Fig. 2 (a) Current density J versus V curves of graphene/n-Si and doped-graphene/n-Si Schottkysolar cells in the dark and after illumination. (b) Data of panel a on expanded scales. (c) J-V plotsof graphene/n-Si and doped-graphene/n-Si junctions under illumination with time. (d) The seriesresistance Rs values extrapolated from dV/dln I vs I curves before and after the doping.
Fig. 3 (a) J-V characteristic in the semilogarithmic scale, (b) Zoomed in J-V characteristic ofgraphene/n-Si diodes, and (c,d) The band diagram at the graphene/n-Si interface before and afterdoping.
Fig. 4 (a) External quantum efficiency (EQE) vs wavelength (λ, nm) and (b) Transientphotovoltage as a function of time for pristine and TFSA-doped graphene/n-Si cells.Fig. 5 Room-temperature inverse square of the capacitance (1/C2) versus reverse bias (VR)plots before and after the TFSA doping.
ConclusionsDoping of graphene with TFSA in a graphene/n-Si Schottkyjunction solar cell can enhance the overall power efficiency from1.9 to 8.6%The increase in PCE are due to the reduction in graphene’s sheetresistance (Rs) and increase in build-up potential (Vbi)The described methods used are practical, simple and scalablesince device fabrication need simple planar thin-film geometries