A power conversion efficiency of 6.48% was achieved for polymer solar cells based on poly(3-hexylthiophene) (P3HT) as donor and indene-C-60 bisadduct (ICBA) as acceptor with an open-circuit voltage of 0.84 V, a short-circuit current of 10.61 mA/cm(2), and a fill factor of 72.7% under irradiation at AM1.5G, 100 mW/cm(2) at the optimized conditions of P3HT:ICBA = 1:1 (w/w), solvent annealing and pre-thermal annealing at 150 degrees C for 10 minutes.