Improved electrical and optical characteristics of transparent graphene thin films produced by acid and doping treatments

New thermal and chemical schemes, which include (i) a modified thermal treatment, (ii) acid treatment in a HNO3 bath and (iii) doping by immersing in a SOBr2 solution, are developed to treat graphene films to improve the electrical conductivity and transparency. It is shown that a longer thermal treatment at 1100 degrees C as well as additional acid and doping treatments reduce the sheet resistance by about 20-50% with improved transmittance. The final product has a sheet resistance of 1600 Omega/sq and a transparency of 82%, which is quite sufficient to replace the transparent conducting films made from indium tin oxide for many existing applications in photovoltaic cells and optoelectronics. The transmittance and sheet resistance measured after 3 months of exposure to air confirms the stability of the improved characteristics after the additional treatments. (C) 2011 Elsevier Ltd. All rights reserved.