Multiple Charge Transfer States in Donor–Acceptor Heterojunctions with Large Frontier Orbital Energy Offsets

Saeed-Uz-Zaman Khan, Giacomo Londi, Xiao Liu, Michael A. Fusella, Gabriele D’Avino, Luca Muccioli, Alyssa N. Brigeman, Bjoern Niesen, Terry Chien-Jen Yang, Yoann Olivier, Jordan T. Dull, Noel C. Giebink, David Beljonne, Barry P. Rand

Research output: Contribution to journalArticle

Abstract

In this work, we demonstrate several organic amorphous donor-acceptor systems that exhibit sub-bandgap features over a more than 2 eV spectral range. An in-depth study of one of these systems, NPB:HAT-CN (NPB is N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine and HAT-CN is 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile), reveals that the broad sub-bandgap features are attributed to multiple electronic charge transfer (CT) state transitions, broadened by energetic disorder sourcing from the fluctuations of intramolecular conformations and by the disordered intermolecular environment. These unique CT features originate from an unconventional donor and acceptor selection that reveals new insight about photocurrent generation and nonradiative recombination. Unlike materials employed in high performing organic solar cells, the materials studied here feature large optical energy gaps with very large frontier orbital energy level offsets, creating high bandgap devices with low open-circuit voltage. In addition to multiple electronic CT levels, we reveal that the internal quantum efficiency of these multiple CT transitions is not constant but photon energy dependent and with photoluminescence that originates primarily from the second lowest electronic CT state implying slow (relative to radiative and nonradiative rates) internal conversion within the CT manifold. Overall, this class of donor-acceptor pairs provides an opportunity to probe CT states in unique ways to potentially unravel their role in carrier generation-recombination and energy loss mechanisms.

Original languageEnglish
Pages (from-to)6808-6817
Number of pages10
JournalChemistry of Materials
Volume31
Issue number17
DOIs
Publication statusPublished - 10 Sep 2019

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Heterojunctions
Charge transfer
Energy gap
Diamines
Open circuit voltage
Electron transitions
Photocurrents
Quantum efficiency
Electron energy levels
Conformations
Energy dissipation
Photoluminescence
Photons

Cite this

Khan, S-U-Z., Londi, G., Liu, X., Fusella, M. A., D’Avino, G., Muccioli, L., ... Rand, B. P. (2019). Multiple Charge Transfer States in Donor–Acceptor Heterojunctions with Large Frontier Orbital Energy Offsets. Chemistry of Materials, 31(17), 6808-6817. https://doi.org/10.1021/acs.chemmater.9b01279
Khan, Saeed-Uz-Zaman ; Londi, Giacomo ; Liu, Xiao ; Fusella, Michael A. ; D’Avino, Gabriele ; Muccioli, Luca ; Brigeman, Alyssa N. ; Niesen, Bjoern ; Yang, Terry Chien-Jen ; Olivier, Yoann ; Dull, Jordan T. ; Giebink, Noel C. ; Beljonne, David ; Rand, Barry P. / Multiple Charge Transfer States in Donor–Acceptor Heterojunctions with Large Frontier Orbital Energy Offsets. In: Chemistry of Materials. 2019 ; Vol. 31, No. 17. pp. 6808-6817.
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abstract = "In this work, we demonstrate several organic amorphous donor-acceptor systems that exhibit sub-bandgap features over a more than 2 eV spectral range. An in-depth study of one of these systems, NPB:HAT-CN (NPB is N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine and HAT-CN is 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile), reveals that the broad sub-bandgap features are attributed to multiple electronic charge transfer (CT) state transitions, broadened by energetic disorder sourcing from the fluctuations of intramolecular conformations and by the disordered intermolecular environment. These unique CT features originate from an unconventional donor and acceptor selection that reveals new insight about photocurrent generation and nonradiative recombination. Unlike materials employed in high performing organic solar cells, the materials studied here feature large optical energy gaps with very large frontier orbital energy level offsets, creating high bandgap devices with low open-circuit voltage. In addition to multiple electronic CT levels, we reveal that the internal quantum efficiency of these multiple CT transitions is not constant but photon energy dependent and with photoluminescence that originates primarily from the second lowest electronic CT state implying slow (relative to radiative and nonradiative rates) internal conversion within the CT manifold. Overall, this class of donor-acceptor pairs provides an opportunity to probe CT states in unique ways to potentially unravel their role in carrier generation-recombination and energy loss mechanisms.",
author = "Saeed-Uz-Zaman Khan and Giacomo Londi and Xiao Liu and Fusella, {Michael A.} and Gabriele D’Avino and Luca Muccioli and Brigeman, {Alyssa N.} and Bjoern Niesen and Yang, {Terry Chien-Jen} and Yoann Olivier and Dull, {Jordan T.} and Giebink, {Noel C.} and David Beljonne and Rand, {Barry P.}",
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Khan, S-U-Z, Londi, G, Liu, X, Fusella, MA, D’Avino, G, Muccioli, L, Brigeman, AN, Niesen, B, Yang, TC-J, Olivier, Y, Dull, JT, Giebink, NC, Beljonne, D & Rand, BP 2019, 'Multiple Charge Transfer States in Donor–Acceptor Heterojunctions with Large Frontier Orbital Energy Offsets', Chemistry of Materials, vol. 31, no. 17, pp. 6808-6817. https://doi.org/10.1021/acs.chemmater.9b01279

Multiple Charge Transfer States in Donor–Acceptor Heterojunctions with Large Frontier Orbital Energy Offsets. / Khan, Saeed-Uz-Zaman; Londi, Giacomo; Liu, Xiao; Fusella, Michael A.; D’Avino, Gabriele; Muccioli, Luca; Brigeman, Alyssa N.; Niesen, Bjoern; Yang, Terry Chien-Jen; Olivier, Yoann; Dull, Jordan T.; Giebink, Noel C.; Beljonne, David; Rand, Barry P.

In: Chemistry of Materials, Vol. 31, No. 17, 10.09.2019, p. 6808-6817.

Research output: Contribution to journalArticle

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T1 - Multiple Charge Transfer States in Donor–Acceptor Heterojunctions with Large Frontier Orbital Energy Offsets

AU - Khan, Saeed-Uz-Zaman

AU - Londi, Giacomo

AU - Liu, Xiao

AU - Fusella, Michael A.

AU - D’Avino, Gabriele

AU - Muccioli, Luca

AU - Brigeman, Alyssa N.

AU - Niesen, Bjoern

AU - Yang, Terry Chien-Jen

AU - Olivier, Yoann

AU - Dull, Jordan T.

AU - Giebink, Noel C.

AU - Beljonne, David

AU - Rand, Barry P.

PY - 2019/9/10

Y1 - 2019/9/10

N2 - In this work, we demonstrate several organic amorphous donor-acceptor systems that exhibit sub-bandgap features over a more than 2 eV spectral range. An in-depth study of one of these systems, NPB:HAT-CN (NPB is N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine and HAT-CN is 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile), reveals that the broad sub-bandgap features are attributed to multiple electronic charge transfer (CT) state transitions, broadened by energetic disorder sourcing from the fluctuations of intramolecular conformations and by the disordered intermolecular environment. These unique CT features originate from an unconventional donor and acceptor selection that reveals new insight about photocurrent generation and nonradiative recombination. Unlike materials employed in high performing organic solar cells, the materials studied here feature large optical energy gaps with very large frontier orbital energy level offsets, creating high bandgap devices with low open-circuit voltage. In addition to multiple electronic CT levels, we reveal that the internal quantum efficiency of these multiple CT transitions is not constant but photon energy dependent and with photoluminescence that originates primarily from the second lowest electronic CT state implying slow (relative to radiative and nonradiative rates) internal conversion within the CT manifold. Overall, this class of donor-acceptor pairs provides an opportunity to probe CT states in unique ways to potentially unravel their role in carrier generation-recombination and energy loss mechanisms.

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