Achieving 15.81% and 15.29% efficiency of all-polymer solar cells based on layer-by-layer and bulk heterojunction structures

Wide bandgap polymer donor PM6 and narrow bandgap polymer acceptor PY-IT were selected to construct all-polymer solar cells (all-PSCs) with a layer-by-layer (LbL) or bulk heterojunction (BHJ) structure. The solvent additive 1-chloronaphthalene (CN) plays a vital role in improving the performance of all-PSCs. The power conversion efficiency (PCE) of LbL all-PSCs is improved to 15.81% from 13.67% by incorporating 1 vol% CN in PY-IT solution, benefiting from the simultaneously enhanced short circuit current density (J_SC) of 22.61 mA cm⁻² and fill factor (FF) of 73.62%. A similar phenomenon is also observed in BHJ all-PSCs whose PCE increased from 13.29% to 15.29% by incorporating 1 vol% CN in PM6:PY-IT blend solution, originating from the optimized phase separation for better exciton dissociation and charge transport in the BHJ active layers. Over 15% PCE improvement can be obtained in the BHJ and LbL all-PSCs by incorporating appropriate additive CN as a morphology regulator. It should be noticed that the PCEs of LbL all-PSCs with CN are higher than those of other all-PSCs, indicating that the LbL processing method combined with the additive should be a prospective strategy to fabricate highly efficient all-PSCs.