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

Andrej Classen; Christos L. Chochos; Larry Lüer; Vasilis G. Gregoriou; Jonas Wortmann; Andres Osvet; Karen Forberich; Iain McCulloch; Thomas Heumüller; Christoph J. Brabec

doi:10.1038/s41560-020-00684-7

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

Andrej Classen
, Christos L. Chochos
, Larry Lüer
, Vasilis G. Gregoriou
, Jonas Wortmann
, Andres Osvet
, Karen Forberich
, Iain McCulloch
, Thomas Heumüller
, Christoph J. Brabec

Research output: Contribution to journal › Article › peer-review

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 (∆E_HOMO) between the donor and acceptor that range from 0 to 300 meV. We demonstrate that exciton quenching at a negligible ∆E_HOMO 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 ∆E_HOMO. Moreover, the Boltzmann equilibrium quantitatively describes the major reduction in non-radiative voltage losses at a very small ∆E_HOMO. Ultimately, highly luminescent near-infrared emitters with very long exciton lifetimes are suggested to enable highly efficient organic solar cells.

Original language	American English
Pages (from-to)	711-719
Number of pages	9
Journal	Nature Energy
Volume	5
Issue number	9
DOIs	https://doi.org/10.1038/s41560-020-00684-7
State	Published - Sep 1 2020
Externally published	Yes

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials
Renewable Energy, Sustainability and the Environment
Fuel Technology
Energy Engineering and Power Technology

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@article{eb643762ec4f496cbf0a49b869c16fc5,

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

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.",

author = "Andrej Classen and Chochos, \{Christos L.\} and Larry L{\"u}er and Gregoriou, \{Vasilis G.\} and Jonas Wortmann and Andres Osvet and Karen Forberich and Iain McCulloch and Thomas Heum{\"u}ller and Brabec, \{Christoph J.\}",

note = "Publisher Copyright: {\textcopyright} 2020, The Author(s), under exclusive licence to Springer Nature Limited.",

year = "2020",

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doi = "10.1038/s41560-020-00684-7",

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T1 - The role of exciton lifetime for charge generation in organic solar cells at negligible energy-level offsets

AU - Classen, Andrej

AU - Chochos, Christos L.

AU - Lüer, Larry

AU - Gregoriou, Vasilis G.

AU - Wortmann, Jonas

AU - Osvet, Andres

AU - Forberich, Karen

AU - McCulloch, Iain

AU - Heumüller, Thomas

AU - Brabec, Christoph J.

PY - 2020/9/1

Y1 - 2020/9/1

N2 - 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.

AB - 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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DO - 10.1038/s41560-020-00684-7

M3 - Article

SN - 2058-7546

VL - 5

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EP - 719

JO - Nature Energy

JF - Nature Energy

IS - 9

ER -

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

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