An asymmetric small-molecule donor enables over 18% efficiency in ternary organic solar cells

An asymmetric small molecule donor, TTBT-R, incorporated with 4,5-di(2-ethylhexyl)oxybenzo[2,1-b:3,4-b ']dithiophene as the core, was exploited for high-performance ternary organic solar cells (OSCs), and possesses a complementary absorption band and cascaded energy levels with PM6 and Y6. The ternary blend film (PM6:TTBT-R:Y6 = 0.9 : 0.1 : 1) attains the most optimized morphology with a nanofiber-like structure and small domain size as well as strong face-on molecular packing, which leads to the most balanced charge transport, highest charge mobilities and lowest charge recombination in its device. In addition, TTBT-R possesses a lower-lying HOMO energy level than PM6, which brings about higher V-oc in ternary OSCs. Accordingly, the ternary OSC with 10 wt% TTBT-R achieved a PCE of 18.07% due to the comprehensively improved V-oc (0.863 V), J(sc) (27.38 mA cm(-2)), and FF (76.46%) values compared with the PM6:Y6 binary OSC. This work provides not only a small molecule with 4,5-dialkyloxybenzo[2,1-b:3,4-b ']dithiophene as the core but also an asymmetric strategy with a non-fused structure to tune the molecular packing, energy levels and absorption spectrum of small molecules for constructing high-performance ternary OSCs.

Automated summary

In this study, an asymmetric small molecule donor, TTBT-R, was used to fabricate high-performance ternary organic solar cells (OSCs). The optimized morphology of the ternary blend film resulted in balanced charge transport and improved power conversion efficiency through tuning molecule packing, energy levels, and absorption spectrum.