Eco-friendly solvent-processed layer-by-layer ternary all-polymer solar cells exhibiting over 18.5% efficiency

•The LbL APSCs exhibit a PCE of 18.55%, which should be among the highest values for LbL APSC with eco-friendly solvent.•The exciton dissociation in ternary LbL APSCs can be promoted by the formation of alloyed state.•The smaller energy loss of optimized LbL APSCs is conductive to the improvement of VOC. In this work, a series of eco-friendly solvent-processed all-polymer solar cells (APSCs) were fabricated by employing the sequentially spin-coating method. Two polymer donor materials PBQx-TCl and PM6 were deliberately selected due to their similar chemical structure, preferring to form the alloyed state for better exciton dissociation and hole transport in the layer-by-layer (LbL) APSCs. The better exciton dissociation between PBQx-TCl and PM6 can be confirmed from PL spectra of neat and blend films, as well as the short-circuit current densities (JSC) of special cells without acceptor layer. The optimized ternary LbL APSCs with 30 wt% PM6 in donor layer exhibit the power conversion efficiency (PCE) of 18.55 %, originating from the simultaneously improved JSC of 25.16 mA cm−2, open-circuit voltage (VOC) of 0.966 V, and fill factor of 76.33 %. The increased VOC of ternary LbL APSCs is mainly attributed to the decreased energy loss due to the good compatibility of the two polymer donors. The PCE of 18.55 % should be among the highest value for LbL APSCs processed by eco-friendly solvent.