Steric hindrance induced low exciton binding energy enables low-driving-force organic solar cells

Exciton binding energy(E_(b))has been regarded as a critical parameter in charge separation during photovoltaic conversion.Minimizing the E_(b) of the photovoltaic materials can facilitate the exciton dissociation in low-driving force organic solar cells(OSCs)and thus improve the power conversion efficiency(PCE);nevertheless,diminishing the E_(b) with deliberate design principles remains a significant challenge.Herein,bulky side chain as steric hindrance structure was inserted into Y-series acceptors to minimize the E_(b) by modulating the intra-and intermolecular interaction.Theoretical and experimental results indicate that steric hindrance-induced optimal intra-and intermolecular interaction can enhance molecular polarizability,promote electronic orbital overlap between molecules,and facilitate delocalized charge trans-fer pathways,thereby resulting in a low E_(b).The conspicuously reduced E_(b) obtained in Y-ChC5 with pinpoint steric hindrance modulation can minimize the detrimental effects on exciton dissociation in low-driving-force OSCs,achieving a remarkable PCE of 19.1%with over 95%internal quantum efficiency.Our study provides a new molecular design rationale to reduce the E_(b).

Efcient soluble PTCBI‑type non‑fullerene acceptor materials for organic solar cells

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 coefcient,and one magnitude higher electron mobility.Finally,OSCs based on one soluble PTCBI-type NFA,namely MAS-7,exhibit a champion power conversion efciency(PCE)of 4.34%,which is signifcantly 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.