Symmetric-breaking strategy has broadly applied in organic photovoltaic material design while a comprehensive understanding of the effects of two dimension (2D) asymmetric side chains in all-small-molecule organic solar cells (ASM-OSCs)...

Hybrid cycloalkyl-alkyl side chains are considered a unique composite side-chain system for the construction of novel organic semiconductor materials. However, there is a lack of fundamental understanding of the variations in the single-crystal structures as well as the optoelectronic and energetic properties generated by the introduction of hybrid side chains in electron acceptors. Herein, symmetric/asymmetric acceptors (Y-C10ch and A-C10ch) bearing bilateral and unilateral 10-cyclohexyldecyl are designed, synthesized, and compared with the symmetric acceptor 2,2′-((2Z,2′Z)-((12,13-bis(2-butyloctyl)-3,9 bis(ethylhexyl)-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3″′:4′,5′]thieno[2′,3′:4,5] pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1diylidene))dimalononitrile (L8-BO). The stepwise introduction of 10-cyclohexyldecyl side chains decreases the optical bandgap, deepens the energy level, and enables the acceptor molecules to pack closely in a regular manner. Crystallographic analysis demonstrates that the 10-cyclohexyldecyl chain endows the acceptor with a more planar skeleton and enforces more compact 3D network packing, resulting in an active layer with higher domain purity. Moreover, the 10-cyclohexyldecyl chain affects the donor/acceptor interfacial energetics and accelerates exciton dissociation, enabling a power conversion efficiency (PCE) of >18% in the 2,2′-((2Z,2′Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl12,13-dihydro-[1,2,5]thiadiazolo[3,4e]thieno[2″,3″′:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1Hindene-2,1-diylidene))dimalononitrile (Y6) (PM6):A-C10ch-based organic solar cells (OSCs). Importantly, the incorporation of Y-C10ch as the third component of the PM6:L8-BO blend results in a higher PCE of 19.1%. The superior molecular packing behavior of the 10-cyclohexyldecyl side chain is highlighted here for the fabrication of high-performance OSCs.

All small molecule organic solar cells (ASM-OSCs) have numerous advantages but lower power conversion efficiencies (PCEs) than their polymer equivalents, which is largely due to the suboptimal nanoscale network structure in a bulk heterojunction (BHJ). Herein, new small molecule donors with symmetric/asymmetric hybrid cyclopentyl-hexyl side chains are designed, accounting for manipulated intermolecular interactions and BHJ morphology. Theoretical and experimental results reveal that the asymmetric cyclopentylhexyl side chains modification has a significant influence on potential energy surface and intermolecular interaction that can ensure preferable molecular assembly and regulate the D/A interfacial energetics, thus boosting the exciton dissociation and charge transport when pairing with a wide-used acceptor L8-BO. Concurrently, a nanoscale bicontinuous interpenetrating network with optimal domain size can be fully evolved in the BHJ layer. As a consequence, the As-TCp-based binary device achieves a superior PCE of 16.46% in comparison to that of the controlled symmetric counterparts S-BF (14.92%) and A-TCp (15.77%), and ranks one of best performance among ASM-OSCs. This study demonstrates that precise manipulation of the cyclo-alkyl chain in combination with the asymmetric 2D side chain strategy is an effective synergistic approach to control intermolecular interaction and nanoscale bicontinuous phase separation for achieving high-performance ASM-OSCs.

Single perylene diimide (PDI) used as a non-fullerene acceptor (NFA) in organic solar cells (OSCs) is enticing because of its low cost and excellent stability. To improve the photovoltaic performance, it is vital to narrow the bandgap and regulate the stacking behavior. To address this challenge, we synthesize soluble perylenetetracarboxylic bisbenzimidazole (PTCBI) molecules with a bulky side chain at the bay region, by replacing the widely used “swallow tail” type alkyl chains at the imide position of PDI molecules with a planar benzimidazole structure. Compared with PDI molecules, PTCBI molecules exhibit red-shifted UV–vis absorption spectra with larger extinction coefficient, and one magnitude higher electron mobility. Finally, OSCs based on one soluble PTCBI-type NFA, namely MAS-7, exhibit a champion power conversion efficiency (PCE) of 4.34%, which is significantly higher than that of the corresponding PDI-based OSCs and is the highest PCE of PTCBI-based OSCs reported. These results highlight the potential of soluble PTCBI derivatives as NFAs in OSCs. Graphical abstract