Synergistic effect of the selenophene-containing central core and the regioisomeric monochlorinated terminals on the molecular packing, crystallinity, film morphology, and photovoltaic performance of selenophene-based nonfullerene acceptors

We synthesize a pair of regioisomer-free selenophene-containing non-fullerene acceptors (NFAs) (TSeIC-M-Cl and TSeIC-P-Cl), which have an identical indacenodithieno[3,2-b]selenophene core and two types of monochlorinated (2,3-dihydro-3-oxo-1H-inden-1-ylidene)propanedinitrile (INCN) end groups with chlorine substituents at different positions (meta- orpara-position relative to the dicyanovinylene moiety), respectively. Compared with TSeIC-M-Cl, TSeIC-P-Cl shows slightly blue-shifted absorption spectra and elevated molecular energy levels owing to the weak electron-withdrawing ability of IC-P-Cl. Besides, owing to the multiple and strong intermolecular Cl⋯H/C and Se⋯π interactions in the single crystal, TSeIC-P-Cl displays three-dimensional molecular packing with a rectangle-like interpenetrating network and a higher degree of π-orbital overlap for charge transport, which results in a higher electron mobility in the film of TSeIC-P-Cl than TSeIC-M-Cl with a linear stacked structure. Moreover, the PBT1-C:TSeIC-P-Cl blend film shows better miscibility and forms a nanofibril-like network with suitable phase separation and a preferential face-on orientation. Finally, the PBT1-C:TSeIC-P-Cl devices yield 11.26% efficiency, which far outperforms the PBT1-C:TSeIC-M-Cl devices (9.72%). This work highlights that the combination of fusing the selenophene ring on the end of the central core and adjusting the position of the chlorine atom on INCN is an alternative way to multiply modulate the molecular packing, crystallinity and film morphology for efficient regioisomer-free monohalogenated INCN-based NFAs.