New Strategy to Balance the Miscibility and Phase Separation to Improve Organic Solar Cells Efficiency

Obtaining superior charge separation and charge extraction efficiency through tuning the gradient separation morphology of the active layer has been the goal of preparing high-performance organic solar cells (OSCs). Here, we selected two non-fullerene acceptors,3,9-bis{2-methylene-[3-(1,1-dicyanomethylene)-indanone]}-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno [2,3-d:2',3'-d']-sindaceno[1,2-b:5,6-b']-dithiophene(ITIC)and 3,9-bis (2-methylene-{[3-(1,1-dicyanomethylene)-6,7-fluoro]-indanone})-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno [2,3-d:2',3'-d']-s-indaceno [1,2-b:5,6-b']dithiophene(IT-2F),with different end groups as the third component. The conventional bulk-heterojunction (BHJ) and optimized pseudo-planar-heterojunction (PPHJ) ternary OSC devices were prepared by two active layer construction processes, named one-step deposition (O-SD) and distributed sequential deposition (T-SD), respectively. It was found that the difference in the miscibility of the third component in the bulk-heterojunction films could regulate the phase separation morphology of the films. Among them, the phase separation increased significantly in the ternary films based on IT-2F and its device efficiency decreased to 9.25% compared to 12.02% of the binary device, while the phase separation morphology of the ternary films based on ITIC did not change significantly, the device efficiency increased slightly. It is worth noting that the active layer films with vertical distribution can be obtained by T-SD method, which avoids the effect of miscibility differences on the film morphology, the corresponding PPHJ device achieves an efficiency of over 13%. This work shows that the utilization of miscibility differences and sequential deposition processes to modulate the phase separation morphology of the active layer is an effective strategy for the preparation of high-performance organic solar cells.