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

Abstract 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.