A novel photoelectrochemical cell (PEC) based on graphene/P3OT (poly(3-octyl-thiophene)) nanocomposites was developed for photovoltaic solar energy conversion. Based on the noncovalent functionalizadon with pyrenebutyrate (PB), solution processable graphene was achieved and used to prepare the graphene/P3OT nanocomposites for PEC application. It has been shown that the doping of the graphene in P3OT film significantly improved the photocurrent as well as the photovoltaic conversion efficiency of the PEC cells by over 10 folds. The highest on-off ratio of photocurrent from the graphene/P3OT nanocomposites reached about 100. Moreover, the performances of the photoelectrochemical cells were largely dependent on the graphene content and morphology of the graphene/P3OT nanocomposites, and the highest photovoltaic conversion efficiency was obtained at a graphene content of 5 wt.% in the nanocomposites. The solution-processed graphene/P3OT nanocomposites PEC provides a general platform for next generation solar energy conversion, photoconductivity and photodetectors. (C) 2010 Elsevier B.V. All rights reserved.