Fullerene derivatives, as novel acceptors, have been successfully applied in bulk heterojunction (BHJ) photovoltaic devices. A new fullerene derivative, PC61B-NHCS, has been recently synthesized as an electron acceptor for improving absorption and power conversion efficiency (PCE) by modifying [C-60]-PCBM. In this work, we analyze the structural and electronic properties of PC61B-NHCS using density functional theory (DFT) calculations by employing a hybrid B3LYP-D3 level of theory. Also, we study the UV Vis absorption spectrum of this compound using time-dependent DFT (TD-DFT) method. The calculated results of energy levels and oscillator strengths are consistent with the available experimental data. Furthermore, we have investigated substituents effect on the LUMO levels and absorption spectra in designing the new acceptors. The results reveal that the methyl group on the para-position of the phenyl ring improves the electrical and optical properties of the complex under evaluation. The strong absorption in the visible region and an increase in the LUMO level of the presented complex can enhance the Jsc and Ifc,c values of BHJ photovoltaic devices and therefore maximize the efficiency of BHJ photovoltaic devices. We hope our studies in the present work can offer a theoretical guideline in designing the fullerene-based acceptors for organic solar cells. (C) 2017 Elsevier B.V. All rights reserved.