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

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.

SUBMITTER: Hinrichsen TF 

PROVIDER: S-EPMC7645751 | biostudies-literature | 2020 Nov

REPOSITORIES: biostudies-literature

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

Hinrichsen Ture F TF   Chan Christopher C S CCS   Ma Chao C   Paleček David D   Gillett Alexander A   Chen Shangshang S   Zou Xinhui X   Zhang Guichuan G   Yip Hin-Lap HL   Wong Kam Sing KS   Friend Richard H RH   Yan He H   Rao Akshay A   Chow Philip C Y PCY  

Nature communications 20201105 1

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 magnit  ...[more]