%0 Journal Article
%A Classen, Andrej
%A Chochos, Christos L.
%A Lüer, Larry
%A Gregoriou, Vasilis G.
%A Wortmann, Jonas
%A Osvet, Andres
%A Forberich, Karen
%A McCulloch, Iain
%A Heumüller, Thomas
%A Brabec, Christoph J.
%T The role of exciton lifetime for charge generation in organic solar cells at negligible energy-level offsets
%J Nature energy
%V 5
%N 9
%@ 2058-7546
%C London
%I Nature Publishing Group
%M FZJ-2021-00671
%P 711 - 719
%D 2020
%X 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.
%F PUB:(DE-HGF)16
%9 Journal Article
%U <Go to ISI:>//WOS:000564493100001
%R 10.1038/s41560-020-00684-7
%U https://juser.fz-juelich.de/record/890081