Wide Bandgap Molecular Acceptors with a Truxene Core for Efficient Nonfullerene Polymer Solar Cells: Linkage Position on Molecular Configuration and Photovoltaic Properties

Two wide bandgap star-shaped small molecular acceptors, para-TrBRCN and meta-TrBRCN, are synthesized for efficient nonfullerene polymer solar cells (PSCs). The tiny structural variation by just changing the linkage positions affects largely the inherent properties of the resulting molecules. Both molecules have a nonplanar 3D structure, which can prevent the excessively aggregation to realize the optimized morphology and ideal domain size in their active blends. Compared to para-TrBRCN, meta-TrBRCN exhibits the smaller distortions between the truxene skeleton and the benzothiadiazole units, which would also lead to the enhanced - stacking and charge transfer. When blending with PTB7-Th, high power conversion efficiencies (PCEs) of 10.15% and 8.28% are obtained for meta-TrBRCN and para-TrBRCN devices, respectively. To make up the weak absorption of above binary active blend in the longer wavelength region and increase the whole device performance further, low bandgap 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylthienyl)-dithieno[2,3-d:2,3-d]-s-indaceno[1,2-b:5,6-b]-dithiophene (ITIC-Th) is added as the second acceptor material to fabricate ternary blend PSCs. After adding 20wt% of ITIC-Th, the resulting devices exhibit the well-balanced optical absorption and fine-tuned morphology, giving rise to the significantly improved PCE of 11.40% with much higher J(sc) of 18.25mAcm(-2) and fill factor of 70.2%.