The development of efficient charge transport layers is a key requirement for the fabrication of efficient and stable organic solar cells. A graphene-based derivative with planar resistivity exceeding 105 Ω/□ and work function of 4.9 eV is here produced by finely tuning the parameters of the chemical vapor deposition process on copper. After the growth, the film is transferred to glass/indium tin oxide and used as hole transport layer in organic solar cells based on a PBDTTT-C-T:[70]PCBM blend. The cells attained a maximum power conversion efficiency of 5%, matching reference cells made with state-of-the-art PEDOT:PSS as the hole transport layer. Our results indicate that functionalized graphene could represent an effective alternative to PEDOT:PSS as hole transport/electron blocking layer in solution-processed organic photovoltaics.