The binary-blend bulk heterojunction (D073:PC71BM) demonstrates increased performance by the addition of a highly crystalline conjugated polymer poly[(2,5-bis(2-hexyldecyloxy)-phenylene)-alt-(5,6-difl uoro-4,7-di(thiophen-2-yl)benzo[c] [1,2,5]-thiadiazole)] (PPDT2FBT). The power conversion efficiency (PCE) of the D073-based OPV was improved from 4.62 % to 5.36 % by the addition of 5 vol % PPDT2FBT to the photoactive layer, which was composed of D073 and a fullerene derivative. This increased power conversion efficiency (PCE) is achieved due to improvements in Voc, Jsc, and FF.
Furthermore, the addition of PPDT2FBT enhanced the photo-stability of the D073-based OPV by decreasing the burn-in loss. The binary-blend bulk heterojunction (D073:PC71BM) maintains 17% of the initial efficiency, while the ternary-blend bulk heterojunction (D073:PPDT2FBT:PC71BM) maintains 76% of the initial efficiency after 1500 hours under a light soaking intensity of 1 sun. The most noticeable difference between binary and ternary-blend bulk heterojunction is Voc and FF. The binary-blend shows rapid Voc drop and it finally maintains 41% , 47% of initial Voc and FF respectively, while ternary-blend maintains initial Voc and 80% of initial FF. The huge decrease in Voc and FF may be due to charge recombination in photo-active film.
In order to explain changes in the blend after 1500 hours light soaking test, we performed GIWAXS, AFM, and various electrical characterizations were conducted.