TY  - JOUR
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.
TI  - The role of exciton lifetime for charge generation in organic solar cells at negligible energy-level offsets
JO  - Nature energy
VL  - 5
IS  - 9
SN  - 2058-7546
CY  - London
PB  - Nature Publishing Group
M1  - FZJ-2021-00671
SP  - 711 - 719
PY  - 2020
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.
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000564493100001
DO  - DOI:10.1038/s41560-020-00684-7
UR  - https://juser.fz-juelich.de/record/890081
ER  -