The role of exciton lifetime for charge generation in organic solar cells at negligible energy-level offsets

Classen A, Chochos CL, Lüer L, Gregoriou VG, Wortmann J, Osvet A, Forberich K, McCulloch I, Heumüller T, Brabec C (2020)


Publication Type: Journal article

Publication year: 2020

Journal

DOI: 10.1038/s41560-020-00684-7

Abstract

Organic solar cells utilize an energy-level offset to generate free charge carriers. Although a very small energy-level offset increases the open-circuit voltage, it remains unclear how exactly charge generation is affected. Here we investigate organic solar cell blends with highest occupied molecular orbital energy-level offsets (∆EHOMO) between the donor and acceptor that range from 0 to 300 meV. We demonstrate that exciton quenching at a negligible ∆EHOMO takes place on timescales that approach the exciton lifetime of the pristine materials, which drastically limits the external quantum efficiency. We quantitatively describe this finding via the Boltzmann stationary-state equilibrium between charge-transfer states and excitons and further reveal a long exciton lifetime to be decisive in maintaining an efficient charge generation at a negligible ∆EHOMO. Moreover, the Boltzmann equilibrium quantitatively describes the major reduction in non-radiative voltage losses at a very small ∆EHOMO. Ultimately, highly luminescent near-infrared emitters with very long exciton lifetimes are suggested to enable highly efficient organic solar cells.

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APA:

Classen, A., Chochos, C.L., Lüer, L., Gregoriou, V.G., Wortmann, J., Osvet, A.,... Brabec, C. (2020). The role of exciton lifetime for charge generation in organic solar cells at negligible energy-level offsets. Nature Energy. https://doi.org/10.1038/s41560-020-00684-7

MLA:

Classen, Andrej, et al. "The role of exciton lifetime for charge generation in organic solar cells at negligible energy-level offsets." Nature Energy (2020).

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