A-DA'D-A Type Pentacyclic Small Molecule Acceptors to Exceed 16.5% Efficiency by Heteroatom Effect at the Outer Side Chain

In this work, we adopt a "heteroatom side-chains" modification strategy to modify the thiophene units in A-DA'D-A (acceptor-donor-acceptor'-donor-acceptor) type pentacyclic SMAs (small molecule acceptors), that is, introducing branched alkyl chain at the beta-position of thiophene instead of straight alkyl chain, and then introducing oxygen atom at the third-position on the basis of branched chain. Two new pentacyclic SMAs (BZ4F-EH and BZ4F-OEH) were synthesized, and the influence of the heteroatom side-chains on photoelectric properties of A-DA'D-A type pentacyclic SMAs was systematically studied. Compared with our previously reported BZ4F (Y26), BZ4F-EH shows slightly blue-shifted absorption, while BZ4F-OEH has obvious red-shifted absorption. As a result, BZ4F-OEH-based binary device achieved a high power conversion efficiency (PCE) of 16.56% with a fill factor (FF) of 79.3%, which is the highest efficiency of pentacyclic SMAs to date. The results indicated that the modification of hetero-atomization on the beta-position of thiophene is a simple and efficient way to improve the PCE of A-DA'D-A type SMAs, and this work provides an important guideline for future molecular design.