The photovoltaic performance of poly(3-hexylthiophene) (P3HT) has been improved greatly by using indene-C60 bisadduct (ICBA) as acceptor instead of phenyl-C61-butyric acid methyl ester (PCBM). However, the solvent of dichlorobenzene (DCB) used in fabricating polymer solar cells (PSCs) limited the application of the PSCs, because of the environmental problem caused by the harmful halogenated solvent. In this work, we fabricated the PSCs based on P3HT/ICBA processed with four low-harmful non-halogenated solvents of toluene, o-xylene, m-xylene, and p-xylene. The PSCs based on P3HT/ICBA (1:1, w/w) with toluene as the solvent exhibit the optimized power conversion efficiency (PCE) of 4.5% with open-circuit voltage (Voc) of 0.84 V, short circuit current density (Jsc) of 7.2 mA/cm(2), and fill factor (FF) of 71%, under the illumination of AM 1.5G at 100 mW/cm(2). Upon using 1% N-methyl pyrrolidone (NMP) as a solvent additive in the toluene solvent, the PCE of the PSCs was greatly improved to 6.6% with a higher Jsc of 10.3 mA/cm(2) and a high FF of 75%, which is even higher than that of the devices fabricated with halogenated DCB solvent. The X-ray diffraction (XRD) measurement shows that the crystallinity of P3HT increased with the NMP additive. The investigations on morphology of the active layers by atomic force microscopy (AFM) and transmission electron microscopy (TEM) indicate that the NMP additive promotes effective phase separation and formation of nanoscaled interpenetrating network structure of the active layer, which is beneficial to the improvement of Jsc and PCE for the PSCs fabricated with toluene as the solvent.