Angular-Shaped 4,9-Dialkylnaphthodithiophene-Based Octacyclic Ladder-Type Non-Fullerene Acceptors for High Efficiency Ternary-Blend Organic Photovoltaics

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. PC₇₁BM was incorporated to form D₁:A₁:A₂ ternary blends which further strengthen the absorption at shorter wavelengths. Introduction of PC₇₁BM 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 PC₇₁BM. The device using the PBDB-T:NCIC:PC₇₁BM (1:1:1 in wt %) showed an improved PCE of 8.32%. Moreover, the optimized device using the PBDB-T:NCFIC:PC₇₁BM (1:1:1.5 in wt %) blend achieved the highest efficiency of 9.18%.