Low-Temperature CVD-Grown Graphene Thin Films as Transparent Electrode for Organic Photovoltaics
Alaa Y. Ali, Natalie P. Holmes, Mohsen Ameri, Krishna Feron, Mahir N. Thameel, Matthew G. Barr, Adam Fahy, John Holdsworth, Warwick J. Belcher, Paul C. Dastoor, Xiaojing Zhou
Abstract
Good conductivity, suitable transparency and uniform layers of graphene thin film can be produced by chemical vapour deposition (CVD) at low temperature and utilised as a transparent electrode in organic photovoltaics. Using chlorobenzene trapped in poly(methyl methacrylate) (PMMA) polymer as the carbon source, growth temperature (Tgrowth) of 600 °C at hydrogen (H2) flow of 75 standard cubic centimetres per minute (sccm) was used to prepare graphene by CVD catalytically on copper (Cu) foil substrates. Through the Tgrowth of 600 °C, we observed and identified the quality of the graphene films, as characterised by Raman spectroscopy. Finally, P3HT (poly (3-hexylthiophene-2, 5-diyl)): PCBM (phenyl-C61-butyric acid methyl ester) bulk heterojunction solar cells were fabricated on graphene-based window electrodes and compared with indium tin oxide (ITO)-based devices. It is interesting to observe that the OPV performance is improved more than 5 fold with increasing illuminated areas, hinting that high resistance between graphene domains can be alleviated by photo generated charges.