Two stable iminofullerene isomers, [5,6]-open azafulleroid (open APCBM) and [6,6]-closed aziridinofullerene (closed APCBM) enable us to scrutinize the use of these new acceptors in polymer bulk heterojunction (BHJ) solar cells and compare the effects of open trans- and closed trans-annlar subunits. When we compared the performance of both isomer devices, the poly(3-hexylthiophene)(P3HT):open APCBM device demonstrates an enhancement in photocurrent in comparison with the P3HT:closed APCBM device. From the comparative study, we attribute the enhanced current to the lower degree of symmetry of open APCBM. The alteration of fullerene structure from closed to open breaks its high degree of symmetry and consequently leads to an improved bulk heterojunction with the electron donating conjugated polymer.