Collaborative regulation of rheological property and crystallization kinetics by conjugation-extension strategy enables green-processed organic photovoltaics with outstanding efficiency, stability and flexibility

Enabling green-printed organic solar cells (OSCs) with high efficiency, stability and flexibility is significant to industrialization. In the green-printed process, the slow film-forming process always induces adverse crystallization kinetics with over-size aggregation. Besides, the unfavorable rheological property always leads to severe Marangoni effect and non-uniform morphology. Nowadays, optimization of rheological properties and crystallinity kinetics relies on external methods, but lacks an in-depth understanding of the relationship between the green-printed process and intrinsic material characteristics. Herein, we employ a conjugation-extension strategy to realize the collaborative regulation of the rheological property and crystallization kinetics in green processing. The spin-coated device based on the new tetramer 4BTPOD (BTPOD:2,2′-((2Z,2′Z)-((12,13-bis(2-octyldodecyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno [2′,3′:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methaneylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)) dimalononitrile) achieves an outstanding efficiency of 18.49% for binary OSC and a top-level efficiency of 19.43% for ternary OSC. Furthermore, the rational conjugation extension strengthens the interchain interaction and prevents molecular rapid migration, thereby suppressing the over-size aggregation and Marangoni effect during the green-printed process. The resultant homogeneous film enables the first tetramer-based green-printed OSC with an outstanding efficiency of 17.57%. Moreover, the enhanced interchain entanglement endows OSCs with excellent photothermal stability and flexibility. This work provides a deep insight from intrinsic molecular characteristics into the optimization of rheological properties and crystallization kinetics for green-printed OSCs with high efficiency, stability and flexibility.