Intermolecular interaction induced spontaneous aggregation enables over 14% efficiency as-cast nonfullerene solar cells

Organic solar cells (OSCs) composed of polymer donors and electron acceptors are facing the challenge to modulate the aggregation-induced morphology in pristine phases and active layers. We herein report our effective chemical modification on thieno [2'(,),3'(,) : 5',6']-s-indaceno[2',1' :4, 5]thieno [3,2-b]thieno[2,3-d]pyrrole cored fused-ring electron acceptors (FREAs). By introducing either para-F, -Cl or -methyl onto meta-hexyloxy phenyl side chain, we can finetune the surface electrostatic potentials and aggregation behaviours of the FREAs (IMOF, IMOCl and IMOM) and their intermolecular interactions with polymer donor (PM6). Consequently, F-substituted acceptor IMOF presents higher crystallinity and induces intensified aggregation in blends with PM6. The PM6:IMOF (1:1.2, w/w) as-cast binary OSCs contribute the highest Power conversion efficiency (PCE) of 13.89% and a fill factor of 73.59%. By adding 10 wt% PC71BM, the as-cast ternary devices exhibit an improved PCE of 14.42%. In contrast, the PM6 based binary OSCs with three reference acceptors deliver the maximum PCE of only 12.61%. Such molecular interactions induced aggregation can be further promoted by device optimization via processing additive and thermal annealing. The sidechain engineering to induce intermolecular interactions of FREAs demonstrates as an effective strategy to regulate the molecular aggregation and phase morphology in active layers for high-performance as-cast OSCs.