The non-fullerene-based flexible solar cells were subjected to the previously-described underwater cyclic bending tests. FIG. 26 and Table 4 show decreasing tendencies in PCE of the pristine and the surface IT-M removed solar cells as the bending cycles increase. From both groups, the PCE decreased more rapidly compared to the P3HT:PCBM solar cells. Yet even in this non-fullerene system, the PCE slope for the surface IT-M removed group is relatively less gradual compared to that for the pristine group. As the bending cycle increases, the gap in the PCE between the pristine and the surface IT-M removed groups widens by 17 times, from 9% to 155%. After 1000 bending cycles, the surface IT-M removed solar cell group maintains about 80% of its initial PCE, whereas for the pristine solar cell group, more than half of the initial PCE is lost under the same conditions. FIG. 27A and FIG. 27B are the representative J-V characteristic curves for the pristine and surface IT-M removed solar cells, which show that the significant PCE decrease in the pristine solar cell is attributed to the reduced current and fill factor with increased series resistance. The poor durability of the pristine PBDB-T:IT-M solar cells can be attributed to the presence of the IT-M in the pristine PBDB-T:IT-M film surface, which weakens the electrode adhesion and causes exfoliation and disconnection. This finding can be further supported by the fact that the peel strength between IT-M and the top electrode (14.8 N/m) is much weaker than that between PBDB-T and top electrode (>1258 N/m) (FIG. 28 and FIG. 29). Further, ultrasonic fatigue tests in the water bath reveal that the surface IT-M removed solar cell has higher electrode adhesion durability than the pristine solar cell (FIG. 30).