Polymer solar cells (PSCs) based on alkyl-substituted thienylenevinylene and phthalimide-based D-A copolymer (PTVPhI-Eh) as a donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC 71 BM) as an acceptor were investigated with the intent of gaining high performance photovoltaic properties. PTVPhI-Eh had a deep highest-occupied molecular orbital (HOMO) level, ~0.3eV lower than rr-P3HT. As a result, PTVPhI-Eh:PC 71 BM devices showed a high open circuit voltage (V oc ) of 0.87V, which is over 0.2V higher compared to that of P3HT:PCBM-based PSCs. The maximum power conversion efficiency (PCE) of PSCs was 4.14% with V oc of 0.87V, short circuit current (J sc ) of 7.32mA/cm 2 , and fill factor (FF) of 65%, under optimized conditions of a 1:1wt/wt ratio and treatment with a 2vol% 1-chloronaphthalene solvent additive. The V oc and consequent photovoltaic performance of this PSC was significantly affected by the concentration of the solvent additive. To determine the relationship between V oc and concentration of solvent additive, PTVPhI-Eh:PC 71 BM devices were investigated with various analyses such as optical spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD).