Optimization of Porous Donor Matrix by Introducing a Highly Soluble Polymer Additive for High‐Efficient Layer‐by‐Layer Organic Solar Cells

ABSTRACT A green and degradable nonconjugated polymer, polylactic acid (PLA) is applied as a donor additive in fabricating highly efficient layer‐by‐layer organic solar cells (LbL‐OSCs). The additive can assist the deposition of a nano‐porous donor layer due to the significant solubility differences between PLA and donor material in organic solvent, which facilitates the infiltration of acceptor into the bottom porous donor matrix. Moreover, the sizes of the nanopores can be finely tuned by the incorporated amount of the additive, obtaining an ideal and controllable interdigitated vertical morphology at the donor/acceptor (D/A) interface. This novel PLA‐assisted technique integrated with the LbL deposition can construct an active layer with greatly increased D/A interfaces and long‐range, vertical continuous phase, leading to the enhanced exciton dissociation and charge transport in the optimized devices. As a result, with the addition of PLA, the maximum efficiency of the PM6/Y6‐based OSC increased from 15.36% to 17.46%, while for the D18/L8‐BO system, the champion efficiency enhanced from 18.96% to 20.02%. Since our PLA‐assisted deposition technique firstly introduced the morphology control by differences in solubility, inducing remarkable and precise morphology regulation of the active layer, this study expands the application of the additive‐assisted deposition technology in fabricating highly efficient OSCs.