Graphene oxide (GO) material was synthesized by an improved Hummers method and characterized by FT-IR, XPS, XRD, AFM, SEM, and UV-VIS analyses. The thickness of the GO layer was measured as 1.5 nm. Solution processed bulk heterojunction solar cells comprising poly(3-hexylthiophene) (P3HT) as the electron donor and N,N'-bis-2-(1-hydoxyhexyl)-3,4,9,10-perylenebis(dicarboximide) (HHPER) as the electron acceptor component of the active layer were produced with and without the GO doped PEDOT-PSS hole transport layers. The optical investigations of the active layer were performed by ground state absorption and photoluminescence measurements. Optimized blend w/w was determined as P3HT:HHPER, 3:1. It was found that the presence of GO in PEDOT:PSS by 0.05 w/w reduces the charge transfer resistance and enhances not only the Jsc , but also V oc values. However, it cannot inhibit V oc losses obtained through annealing the active layer at temperatures higher than 120• C.