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An angular-shaped 4,9-didodecylnaphthodithiophene-based octacyclic ladder-type structure was developed. This new ladder-type donor (LD) was coupled with electron-withdrawing IC and FIC units to form two A-LD-A type non-fullerene acceptor materials, NCIC and NCFIC. NCIC and NCFIC as the n-type acceptors are blended with a p-type donor PBDB-T to form the complementary absorption and suitable energy level alignments. The binary-blend PBDB-T:NCIC and PBDB-T:NCFIC devices achieved an efficiency of 7.3% and 7.5%, respectively. PC 71 BM was incorporated to form D 1:A 1:A 2 ternary blends which further strengthen the absorption at shorter wavelengths. Introduction of PC 71 BM not only efficiently improves the absorption but also provides multiple channels for exciton dissociation and electron transport to dramatically improve J sc . It is interesting to find that the V oc of the ternary-blend devices is reversely in proportional to the added amount of PC 71 BM. The device using the PBDB-T:NCIC:PC 71 BM (1:1:1 in wt %) showed an improved PCE of 8.32%. Moreover, the optimized device using the PBDB-T:NCFIC:PC 71 BM (1:1:1.5 in wt %) blend achieved the highest efficiency of 9.18%.
Cao et al. (2018) studied this question.