Revealing the Role of Donor/Acceptor Interfaces in Nonfullerene-Acceptor Based Organic Solar Cells: Charge Separation versus Recombination

Abstract

Organic solar cells (OSCs) based on nonfullereneacceptors (NFAs) have achieved rapid development, while the role of donor/acceptor (D/A) interfaces in NFA based heterosystems has not been fully addressed. Here, we clarify that the photoinduced spontaneous charge separation efficiency in typical NFA heterosystems can reach up to 67%, and the charge separation efficiency contributed by the D/A interface is only 25%. The more important role of D/A interfaces is reducing the charge recombination rate, especially optimizing the competition between radiative and nonradiative charge recombination, thus reducing the nonradiative voltage loss. Systematical simulations demonstrate that there exists an optimal interfacial distance for a fixed energy offset, at which the D/A interface can reduce the nonradiative voltage loss by a maximum value of 0.12 V. Hence, we propose that optimizing the interfacial distance combined with the actual interfacial energy offset of a given heterosystem is important to develop its best photovoltaic performance.

From light to hydrogen: the complete life cycle of free charges in photocatalytic nanoparticles

“…44,49,60 Recent reports have suggested that due to the rapid dissociation of most excitons in Y6, the intermediate state in this polaron-formation process is free polarons in Y6 domains, rather the formation of interfacial CT states. 43,45,46…”

“…45 A recent computational study suggests that charge generation occurs primarily in the acceptor domain for typical NFAs such as Y6, and the role of the donor–acceptor interface is primarily to reduce polaron recombination rather than to promote charge generation. 46 Two mechanisms for free polaron generation when PM6 is excited have been reported: the conventional mechanism in which the exciton migrates to a PM6–Y6 interface and forms a charge-transfer (CT) state, which then dissociates; or Förster resonance energy transfer (FRET) to Y6 followed by back hole transfer. 44,47–51 FRET from PM6 to other NFAs has also been observed.…”