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Layer‐by‐layer all‐polymer solar cells (LbL all‐PSCs) are prepared with PM6 and PY‐IT by using sequential spin coating method. The exciton dissociation efficiency in acceptor layer near electrode is rather low due to the limited exciton diffuse distance and impossible energy transfer from narrow bandgap acceptor to wide bandgap donor. In this study, less PM6 is incorporated into PY‐IT layer to enhance exciton dissociation in PY‐IT layer near electrode. A power conversion efficiency (PCE) of 17.45% is achieved in the LbL all‐PSCs incorporating 10 wt% PM6 into PY‐IT layer, which is much larger than 16.04% PCE of PM6/PY‐IT‐based LbL all‐PSCs. Over 8% PCE enhancement can be realized by incorporating 10 wt% PM6 into PY‐IT layer, which is attributed to the enhanced exciton utilization efficiency in PY‐IT layers near electrode. The enhanced exciton utilization efficiency in PY‐IT layer can be confirmed from the quenched photoluminescence (PL) emission in PY‐IT:PM6 films. Meanwhile, charge transport in acceptor layers can be optimized by incorporating less PM6, as confirmed from the optimized molecular arrangement. This study indicates that the strategy of incorporating less donor into acceptor layer has great potential in fabricating efficient LbL all‐PSCs by improving exciton utilization efficiency in acceptor layer near electrode. [ABSTRACT FROM AUTHOR]

Filter‐free narrowband photomultiplication‐type planar heterojunction (PHJ) organic photodetectors (PM‐PHOPDs) are first realized by employing a thick front donor layer and an ultrathin PC71BM layer. The thick front donor layer is employed as an optical field adjusting (OFA) layer. The sequentially coated PC71BM will diffuse slightly into OFA layer, which works as interfacial electron traps to capture photogenerated electrons for assisting hole tunneling injection. The P3HT/PC71BM‐based PM‐PHOPDs exhibit narrowband response with full‐width of half‐maximum of 32 nm and external quantum efficiency (EQE) of 1700% at 650 nm under −20 V bias. Due to the enhanced hole transport and reduced charge recombination in PHJ compared to those in bulk heterojunction (BHJ), the EQE of P3HT/PC71BM‐based narrowband PM‐PHOPDs is twice as P3HT:PC71BM BHJ‐based narrowband PM‐OPDs under the same bias. The response peak of PM‐PHOPDs is adjusted from 650 to 695 or 745 nm by incorporating SMPV1 or DRCN5T in OFA layers due to the red‐shifted absorption edge. The EQEs of 3600% at 695 nm and 870% at 745 nm are obtained for P3HT:SMPV1 and P3HT:DRCN5T‐based PM‐PHOPDs under −20 V bias, respectively. This work provides a smart strategy to achieve narrowband PM‐OPDs by designing different OFA layers. [ABSTRACT FROM AUTHOR]