Layer‐by‐Layer Processed PM6:Y6‐Based Stable Ternary Polymer Solar Cells with Improved Efficiency over 18% by Incorporating an Asymmetric Thieno[3,2‐b]indole‐Based Acceptor

Abstract

AbstractAlthough much research on device engineering have brought about significant improvements in PM6:Y6‐based polymer solar cell (PSCs) performance, there is still a lack of relevant research to solve the problems caused by the over‐aggregation of Y6 and the long‐term stability of the device morphology. Herein, a newly designed and synthesized low‐bandgap asymmetric small molecule acceptor TIT‐2Cl based on thieno[3,2‐b]indole core is elaborately introduced into PM6:Y6‐based PSCs to suppress the over‐aggregation of Y6 molecules with significantly increased efficiency from 15.78% to 17.00%. Moreover, the addition of TIT‐2Cl contributes to improved light harvesting, the lowest unoccupied molecular orbital level of Y6:TIT‐2Cl, charge separation, transport, and extraction. Simultaneously, the PSCs are further prepared by using the progressive spin‐coating method of layer‐by‐layer (LBL). Due to the formation of vertical phase distribution and the improvement of carrier transport performance, the champion efficiency of LBL‐type ternary PSCs reaches 18.18%, which is the highest efficiency reported for PM6:Y6‐based PSCs, along with superior stability and compositional insensitivity. Therefore, the results show that the combination of ternary strategy by incorporating appropriate asymmetric molecules and the LBL method is an effective means to fabricate highly efficient stable PSCs.