Bulk Heterojunction or Layer‐by‐Layer Structure PM6:L8‐BO Based Polymer Solar Cells Exhibiting an Efficiency of 17.84 % or 18.43 %

Abstract Two kinds of polymer solar cells (PSCs) were fabricated with polymer donor PM6 and small molecule non‐fullerene acceptor L8‐BO as accepted based on bulk heterojunction (BHJ) or layer‐by‐layer (LbL) structure. The power conversion efficiency (PCE) of 18.43 % and 17.84 % can be achieved from the PSCs based on BHJ and LbL structure, respectively. Two kinds of PSCs exhibit the same open circuit voltage ( V OC ) of 0.88 V, which can be well explained from the same donor and acceptor materials and the same electrodes. The LbL based PSCs exhibit a relatively large short circuit current density ( J SC ) of 26.97 mA cm −2 and fill factor (FF) of 77.64 % in comparison with J SC of 26.64 mA cm −2 and FF of 76.07 % for BHJ based PSCs. The relatively high PCE of LbL based PSCs should be attributed to the sufficient exciton dissociation and charge collection efficiency, as well as the more balanced charge transport, which can be confirmed from the photogenerated current density dependence on the effective bias. This work demonstrates that layer‐by‐layer structure may have great potential in preparing highly efficient PSCs.