The PCE of 18.43 % and 17.84 % are achieved in LbL and BHJ PSCs with polymer donor PM6 and small acceptor L8-BO. Over 3 % PCE improvement can be obtained in LbL PSC, benefiting from the enhanced exciton dissociation, charge collection efficiency and charge transport in LbL active layer.

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.