Improving the aggregation of layer-by-layer processed all-polymer solar cells with an additive during the film deposition and thermal annealing

Abstract

Optimizing the vertical component distribution, aggregation and molecular stacking of the donor and acceptor is an effective strategy to boost the power conversion efficiency (PCE) of all-polymer solar cells (all-PSCs). Conflict frequently arises between the crystallization and phase separation of the donor and the acceptor. This study introduces a two-stage optimization approach for aggregation in layer-by-layer (LbL) processed films. The aggregation of the donor is enhanced by optimizing the film formation kinetics with an additive, followed by thermal annealing to regulate the aggregation of the acceptor. We select 2-methoxynaphthalene (2-MN) as the solid additive because 2-MN has good molecular miscibility with both donors and acceptors to regulate molecular aggregation. During the LbL deposition, the aggregation time of the donor is prolonged with the addition of 2-MN. With the further thermal annealing process, 2-MN volatilizes, thereby creating a substantial amount of free space for the acceptor to aggregate. The coherence lengths and π–π stacking of active layers have notably enhanced. The optimal morphology increases exciton dissociation efficiency, improves charge transport and suppresses charge recombination losses. The additive-assisted LbL PM6/PY-IT (2-MN) exhibits enhanced short-circuit current and fill factor, showing a PCE of 17.57%, surpassing 14.92% of PM6/PY-IT and 16.79% of PM6:PY-IT (2-MN).