Degradation mechanism of P3HT:PCBM based bulk heterojunction solar cells.

Abstract

We have studied the degradation mechanism in P3HT:PCBM based bulk heterojunction solar cells by developing the structure ITO/PEDOT:PSS/P3HT:PCBM/Al comprising of different acceptor materials namely PC60BM and PC70BM. Both devices have nearly same photo conversion efficiency (PCE) 3.8% immediately after fabrication. The PCE is observed to decrease in both the devices with passage of time. While the degradation rate is found to be higher in PC60BM based devices but its value is found to saturate after 100 minutes at a constant value of 2%. For PC70BM based cells the devices depict a sudden change in degradation rate from low to high as the time progresses beyond 170 minutes. The PCE in these devices fell to very low value after 250 minutes. This rapid fall in PCE is attributed to the formation of trap states in the energy levels of PC70BM molecules owing to their non-spherical stricture.