Overlapping fasten packing enables efficient dual-donor ternary organic solar cells with super stretchability

The flexibility and stability of organic solar cells (OSCs) have becoming a hotspot research for their practical applicaitons. Molecular arrangement and network morphology of active layer are important factors affecting the flexibility and stability of OSCs. Herein, two polymer donors (PBB1-Cl and PBB2-Cl) with different sidechains were investigated as the third component to finely regulate morphology and molecular accumulation of the active layer to improve the performance of OSCs. Both third components show complementary absorption spectra and good compatibility. The good planarity of PBB1-Cl and PBB2-Cl significantly increases intermolecular overlap to promote the charge transfer in active layer. In addition, the steric hindrance of the one-dimensional side chain of PBB1-Cl enhanced the intermolecular close packing and entanglement of the active layer. As a result, the tensile endurance of PM6:PBB1-Cl:Y6-BO-4Cl ternary blend film reached 4.6 times (26.86%) of the PM6:Y6-BO-4Cl binary blend film. Furthermore, the power conversion efficiency (PCE) increased from 15.83% for PM6:Y6-BO-4Cl based binary OSCs to 17.36% for PBB1-Cl based rigid ternary OSCs, and the flexible OSCs increased from 13.44% to 14.96%, respectively. 17.36% efficiency of PBB1-Cl based ternary OSCs is the highest value in OSCs with elongation at break of active layer exceeding 25% so far. What’ more, the PCEs of PBB1-Cl based flexible ternary OSCs still remain above 74% within 500 cycles of bending with diameter of 10 mm or annealing at 100 oC for 24 hours, which is mainly attributed to the smaller surface energy difference between PBB1-Cl based ternary blend film and transport layers, higher glass transition temperature and larger elongation at break of active layer. All results suggest that enhancing intermolecular overlapping fasten packing in active layer has great potential in improving the photovoltaic performance, mechanical and thermal stability of OSCs.