Ternary Organic Solar Cells with > 11% Efficiency Incorporating Thick Photoactive Layer and Nonfullerene Small Molecule Acceptor

Currently, constructing ternary organic solar cells (OSCs) and developing nonfullerene small molecule acceptors (n-SMAs) are two pivotal avenues to enhance the device performance. However, introducing n-SMAs into the ternary OSCs to construct thick layer device is still a challenge due to their inferior charge transport property and unclear aggregation mechanism. In this work, a novel wide band gap copolymer 4,8-bis(4,5-dioctylthiophen-2-yl) benzo[1,2-b:4,5-b]dithiophene-2,6-diyl-alt-N-(2-hexyldecyl)-5,5-bis(thiophen-2-yl)-2,2-bithiophene-3,3-dicarboximide (PDOT) is designed and blend of PDOT:PC71BM achieves a power conversion efficiency (PCE) of 9.5% with active layer thickness over 200 nm. The rationally selected n-SMA based on a bulky seven-ring fused core (indacenodithieno[3,2-b]thiophene) end-capped with 2-(3-oxo-2,3-dihydroinden-1-ylidene) malononitrile groups (ITIC) is introduced into the host binary PDOT:PC71BM system to extend the absorption range and reduce the photo energy loss. After fully investigating the morphology evolution of the ternary blends, the different aggregation behavior of n-SMAs with respect to their fullerene counterpart is revealed and the adverse effect of introducing n-SMAs on charge transport is successfully avoided. The ternary OSC delivers a PCE of 11.2% with a 230 nm thick active layer, which is among the highest efficiencies of thick layer OSCs. The results demonstrate the feasibility of using n-SMAs to construct a thick layer ternary device for the first time, which will greatly promote the efficiency of thick layer ternary devices.