Modification on the Indacenodithieno[3,2-b]thiophene Core to Achieve Higher Current and Reduced Energy Loss for Nonfullerene Solar Cells

Modification on the indacenodithieno[3,2-b]thiophene (IT) core was used in the central phenyl moiety to explore efficient fused-ring acceptors (FRAs). By replacing two free H atoms with weak and small electron-donating methyl or methoxy groups, two novel IT-4F series FRAs named IM-4F and IOM-4F have been designed. The systematical study is conducted to reveal the impact of core modification on the photovoltaic performance of the resultant FRAs. Both FRAs show red-shifted absorption and upshifted frontier energy levels compared to IT-4F. Their crystallinity and miscibility were slightly improved from IT-4F to IM-4F and to IOM-4F. Importantly, IM-4F- and IOM-4F-based solar cells exhibit better performance (14.01 +/- 0.14 and 13.20 +/- 0.17%), respectively) with higher short-circuit current density (J(SC)) and open-circuit voltage (V-OC). Furthermore, the energy loss originated from radiative and non-radiative recombination loss can be reduced via tuning the substituent on the IT core. Our results demonstrate that modification on the IT core not only modulates the optoelectronic properties of FRAs but also effectively suppresses recombination loss of the relevant device, which may open a new avenue to develop high-efficiency 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITIC)-derived FRAs. It can also broaden the horizon on reducing the energy loss through the design of nonfullerene acceptors.