Long-lived and disorder-free charge transfer states enable endothermic charge separation in efficient non-fullerene organic solar cells

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Hinrichsen, Ture F.  ORCID logo  https://orcid.org/0000-0001-7599-2436
Chan, Christopher C. S.  ORCID logo  https://orcid.org/0000-0001-6725-6463
Ma, Chao 
Paleček, David 

Abstract: Organic solar cells based on non-fullerene acceptors can show high charge generation yields despite near-zero donor–acceptor energy offsets to drive charge separation and overcome the mutual Coulomb attraction between electron and hole. Here, we use time-resolved optical spectroscopy to show that free charges in these systems are generated by thermally activated dissociation of interfacial charge-transfer states that occurs over hundreds of picoseconds at room temperature, three orders of magnitude slower than comparable fullerene-based systems. Upon free electron–hole encounters at later times, both charge-transfer states and emissive excitons are regenerated, thus setting up an equilibrium between excitons, charge-transfer states and free charges. Our results suggest that the formation of long-lived and disorder-free charge-transfer states in these systems enables them to operate closely to quasi-thermodynamic conditions with no requirement for energy offsets to drive interfacial charge separation and achieve suppressed non-radiative recombination.


Funder: HKU | University Research Committee, University of Hong Kong (HKU Research Committee); doi: https://doi.org/10.13039/501100003802

Article, /639/638/439/946, /639/301/119/998, /140/125, /128, article
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Nature Communications
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Nature Publishing Group UK