Journal Article

FZJ-2021-00671

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png The role of exciton lifetime for charge generation in organic solar cells at negligible energy-level offsets

Classen, A. ; Chochos, C. L. ; Lüer, L. ; Gregoriou, V. G. ; Wortmann, J. ; Osvet, A. ; Forberich, K.FZJ* ; McCulloch, I. ; Heumüller, T.FZJ* ; Brabec, C. J. (Corresponding author)FZJ*

2020
Nature Publishing Group London

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Please use a persistent id in citations: http://hdl.handle.net/2128/27279  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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Contributing Institute(s):

1. Helmholtz-Institut Erlangen-Nürnberg Erneuerbare Energien (IEK-11)

Research Program(s):

1. 121 - Solar cells of the next generation (POF3-121) (POF3-121)

Appears in the scientific report 2021

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Database coverage:
; ; Clarivate Analytics Master Journal List ; Current Contents - Engineering, Computing and Technology ; Essential Science Indicators ; IF >= 50 ; JCR ; SCOPUS ; Science Citation Index Expanded ; Web of Science Core Collection

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