Abstract: MWCNTs were synthesized by chemical vapor deposition from Sesamum indicum oil, functionalized, cut into short lengths and used as additives in organic photovoltaic solar cells (OPVs) using poly (3-octylthiophene) (P3OT) as a photoactive molecule and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) as an exciton dissociation agent. Results indicate that the addition of the MWCNTs and the functionalized and cut MWCNTs increases the power conversion efficiency of the OPVs by 22% and 40%, respectively. MWCNTs improve the collection and transportation of holes from the P3OT after exciton dissociation owing to their high hole mobility. The functionalization and cutting of MWCNTs improves their dispersion in P3OT and PCBM, which further increases the power conversion efficiency.