Effect of charge-transfer state energy on charge generation efficiency via singlet fission in pentacene-fullerene solar cells

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Uittreksel

Singlet fission in pentacene creates two triplet excitons per absorbed photon. In a solar cell, each triplet can generate an electron-hole pair, and hence, external quantum efficiencies exceeding 100% have been reported for pentacene-fullerene solar cells. The energetics of this process are intriguing because the minimum photon energy loss, defined as the energy difference between the (triplet) exciton state and the open-circuit voltage, is less than 0.5 eV and distinctively smaller than that in most organic donor-acceptor solar cells. To investigate the energetics of this process, we analyze the effect of the energy of the lowest unoccupied molecular orbital (LUMO) for different fullerene derivatives. With the LUMO energy becoming less negative, the open-circuit voltage increases and charge generation decreases. For all but one of the fullerenes tested, the charge-transfer state energy is distinctively higher than the pentacene triplet energy, revealing that charge generation via singlet fission is actually endergonic. An elementary Marcus model for the rate of electron transfer provides a qualitative description of the experimental trends, in accordance with an endergonic charge transfer. Considering that charge generation from triplet states is endergonic, involvement of pentacene singlet states, either from direct photoexcitation or via triplet-triplet annihilation, cannot be excluded.

TaalEngels
Pagina's10253-10261
Aantal pagina's9
TijdschriftJournal of Physical Chemistry C
Volume123
Nummer van het tijdschrift16
DOI's
StatusGepubliceerd - 25 apr 2019

Vingerafdruk

Fullerenes
Electron energy levels
fullerenes
fission
Charge transfer
Solar cells
solar cells
charge transfer
Molecular orbitals
Open circuit voltage
Excitons
Photons
open circuit voltage
Electrons
Photoexcitation
Quantum efficiency
molecular orbitals
excitons
energy
Energy dissipation

Citeer dit

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title = "Effect of charge-transfer state energy on charge generation efficiency via singlet fission in pentacene-fullerene solar cells",
abstract = "Singlet fission in pentacene creates two triplet excitons per absorbed photon. In a solar cell, each triplet can generate an electron-hole pair, and hence, external quantum efficiencies exceeding 100{\%} have been reported for pentacene-fullerene solar cells. The energetics of this process are intriguing because the minimum photon energy loss, defined as the energy difference between the (triplet) exciton state and the open-circuit voltage, is less than 0.5 eV and distinctively smaller than that in most organic donor-acceptor solar cells. To investigate the energetics of this process, we analyze the effect of the energy of the lowest unoccupied molecular orbital (LUMO) for different fullerene derivatives. With the LUMO energy becoming less negative, the open-circuit voltage increases and charge generation decreases. For all but one of the fullerenes tested, the charge-transfer state energy is distinctively higher than the pentacene triplet energy, revealing that charge generation via singlet fission is actually endergonic. An elementary Marcus model for the rate of electron transfer provides a qualitative description of the experimental trends, in accordance with an endergonic charge transfer. Considering that charge generation from triplet states is endergonic, involvement of pentacene singlet states, either from direct photoexcitation or via triplet-triplet annihilation, cannot be excluded.",
author = "Willems, {Robin E.M.} and Meskers, {Stefan C.J.} and Wienk, {Martijn M.} and Janssen, {Ren{\'e} A.J.}",
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T1 - Effect of charge-transfer state energy on charge generation efficiency via singlet fission in pentacene-fullerene solar cells

AU - Willems,Robin E.M.

AU - Meskers,Stefan C.J.

AU - Wienk,Martijn M.

AU - Janssen,René A.J.

PY - 2019/4/25

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N2 - Singlet fission in pentacene creates two triplet excitons per absorbed photon. In a solar cell, each triplet can generate an electron-hole pair, and hence, external quantum efficiencies exceeding 100% have been reported for pentacene-fullerene solar cells. The energetics of this process are intriguing because the minimum photon energy loss, defined as the energy difference between the (triplet) exciton state and the open-circuit voltage, is less than 0.5 eV and distinctively smaller than that in most organic donor-acceptor solar cells. To investigate the energetics of this process, we analyze the effect of the energy of the lowest unoccupied molecular orbital (LUMO) for different fullerene derivatives. With the LUMO energy becoming less negative, the open-circuit voltage increases and charge generation decreases. For all but one of the fullerenes tested, the charge-transfer state energy is distinctively higher than the pentacene triplet energy, revealing that charge generation via singlet fission is actually endergonic. An elementary Marcus model for the rate of electron transfer provides a qualitative description of the experimental trends, in accordance with an endergonic charge transfer. Considering that charge generation from triplet states is endergonic, involvement of pentacene singlet states, either from direct photoexcitation or via triplet-triplet annihilation, cannot be excluded.

AB - Singlet fission in pentacene creates two triplet excitons per absorbed photon. In a solar cell, each triplet can generate an electron-hole pair, and hence, external quantum efficiencies exceeding 100% have been reported for pentacene-fullerene solar cells. The energetics of this process are intriguing because the minimum photon energy loss, defined as the energy difference between the (triplet) exciton state and the open-circuit voltage, is less than 0.5 eV and distinctively smaller than that in most organic donor-acceptor solar cells. To investigate the energetics of this process, we analyze the effect of the energy of the lowest unoccupied molecular orbital (LUMO) for different fullerene derivatives. With the LUMO energy becoming less negative, the open-circuit voltage increases and charge generation decreases. For all but one of the fullerenes tested, the charge-transfer state energy is distinctively higher than the pentacene triplet energy, revealing that charge generation via singlet fission is actually endergonic. An elementary Marcus model for the rate of electron transfer provides a qualitative description of the experimental trends, in accordance with an endergonic charge transfer. Considering that charge generation from triplet states is endergonic, involvement of pentacene singlet states, either from direct photoexcitation or via triplet-triplet annihilation, cannot be excluded.

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