Mixed Domains Enhance Charge Generation and Extraction in Bulk-Heterojunction Solar Cells with Small-Molecule Donors

Obaid Alqahtani; Maxime Babics; Julien Gorenflot; Victoria Savikhin; Thomas Ferron; Ahmed H. Balawi; Andreas Paulke; Zhipeng Kan; Michael Pope; Andrew J. Clulow; Jannic Wolf; Paul L. Burn; Ian R. Gentle; Dieter Neher; Michael F. Toney; Frédéric Laquai; Pierre M. Beaujuge; Brian A. Collins

doi:10.1002/aenm.201702941

Mixed Domains Enhance Charge Generation and Extraction in Bulk-Heterojunction Solar Cells with Small-Molecule Donors

Obaid Alqahtani, Maxime Babics, Julien Gorenflot, Victoria Savikhin, Thomas Ferron, Ahmed H. Balawi, Andreas Paulke, Zhipeng Kan, Michael Pope, Andrew J. Clulow, Jannic Wolf, Paul L. Burn, Ian R. Gentle, Dieter Neher, Michael F. Toney, Frédéric Laquai^*, Pierre M. Beaujuge, Brian A. Collins

^*Corresponding author for this work

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

45 Scopus citations

Abstract

The interplay between nanomorphology and efficiency of polymer-fullerene bulk-heterojunction (BHJ) solar cells has been the subject of intense research, but the generality of these concepts for small-molecule (SM) BHJs remains unclear. Here, the relation between performance; charge generation, recombination, and extraction dynamics; and nanomorphology achievable with two SM donors benzo[1,2-b:4,5-b]dithiophene-pyrido[3,4-b]-pyrazine BDT(PPTh₂)₂, namely SM1 and SM2, differing by their side-chains, are examined as a function of solution additive composition. The results show that the additive 1,8-diiodooctane acts as a plasticizer in the blends, increases domain size, and promotes ordering/crystallinity. Surprisingly, the system with high domain purity (SM1) exhibits both poor exciton harvesting and severe charge trapping, alleviated only slightly with increased crystallinity. In contrast, the system consisting of mixed domains and lower crystallinity (SM2) shows both excellent exciton harvesting and low charge recombination losses. Importantly, the onset of large, pure crystallites in the latter (SM2) system reduces efficiency, pointing to possible differences in the ideal morphologies for SM-based BHJ solar cells compared with polymer-fullerene devices. In polymer-based systems, tie chains between pure polymer crystals establish a continuous charge transport network, whereas SM-based active layers may in some cases require mixed domains that enable both aggregation and charge percolation to the electrodes.

Original language	English (US)
Article number	1702941
Journal	Advanced Energy Materials
Volume	8
Issue number	19
DOIs	https://doi.org/10.1002/aenm.201702941
State	Published - Jul 5 2018

Bibliographical note

Funding Information:
O.A. was supported by Prince Sattam bin Abdulaziz University in Saudi Arabia and the Saudi Arabian Cultural Mission in the United States. T.F. was supported by the Washington State University Seed Grant Program. A.P. and D.N. acknowledge financial support from the German Ministry of Science and Education (project UNVEIL). V.S. acknowledges financial support from the NDSEG fellowship. This research used resources described above of the Advanced Light Source, which is a DOE Office of Science User Facility under Contract No. DE-AC02-05CH11231 and Stanford Synchrotron Radiation Lightsource. P.M.B. acknowledges support by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No. CRG_R2_13_BEAU_KAUST_1 and under KAUST Baseline Research Funding. The authors also wish to acknowledge the Australian Centre for Neutron Scattering (formerly the Bragg Institute at the time of the measurements) and the Australian Nuclear Science and Technology Organisation (ANSTO) for providing the neutron research facilities for the NR experiments. The NR measurements were supported by an Australian Research Council Discovery Program (DP120101372). The authors would like to thank Dr. Andrew Nelson, Dr. Ravi Chandra Raju Nagiri, and Mr. Jake McEwan for their assistance in performing the NR measurements.

Publisher Copyright:
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Keywords

charge transport
domain purity
microscopy
mixed domains
organic solar cells
photovoltaic devices
resonant X-ray scattering
small molecules
transient spectroscopy

ASJC Scopus subject areas

Renewable Energy, Sustainability and the Environment
General Materials Science

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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10.1002/aenm.201702941

Cite this

Alqahtani, O., Babics, M., Gorenflot, J., Savikhin, V., Ferron, T., Balawi, A. H., Paulke, A., Kan, Z., Pope, M., Clulow, A. J., Wolf, J., Burn, P. L., Gentle, I. R., Neher, D., Toney, M. F., Laquai, F., Beaujuge, P. M., & Collins, B. A. (2018). Mixed Domains Enhance Charge Generation and Extraction in Bulk-Heterojunction Solar Cells with Small-Molecule Donors. Advanced Energy Materials, 8(19), Article 1702941. https://doi.org/10.1002/aenm.201702941

@article{c82092944c4f484bbb7f4f890c2ca78e,

title = "Mixed Domains Enhance Charge Generation and Extraction in Bulk-Heterojunction Solar Cells with Small-Molecule Donors",

abstract = "The interplay between nanomorphology and efficiency of polymer-fullerene bulk-heterojunction (BHJ) solar cells has been the subject of intense research, but the generality of these concepts for small-molecule (SM) BHJs remains unclear. Here, the relation between performance; charge generation, recombination, and extraction dynamics; and nanomorphology achievable with two SM donors benzo[1,2-b:4,5-b]dithiophene-pyrido[3,4-b]-pyrazine BDT(PPTh2)2, namely SM1 and SM2, differing by their side-chains, are examined as a function of solution additive composition. The results show that the additive 1,8-diiodooctane acts as a plasticizer in the blends, increases domain size, and promotes ordering/crystallinity. Surprisingly, the system with high domain purity (SM1) exhibits both poor exciton harvesting and severe charge trapping, alleviated only slightly with increased crystallinity. In contrast, the system consisting of mixed domains and lower crystallinity (SM2) shows both excellent exciton harvesting and low charge recombination losses. Importantly, the onset of large, pure crystallites in the latter (SM2) system reduces efficiency, pointing to possible differences in the ideal morphologies for SM-based BHJ solar cells compared with polymer-fullerene devices. In polymer-based systems, tie chains between pure polymer crystals establish a continuous charge transport network, whereas SM-based active layers may in some cases require mixed domains that enable both aggregation and charge percolation to the electrodes.",

keywords = "charge transport, domain purity, microscopy, mixed domains, organic solar cells, photovoltaic devices, resonant X-ray scattering, small molecules, transient spectroscopy",

author = "Obaid Alqahtani and Maxime Babics and Julien Gorenflot and Victoria Savikhin and Thomas Ferron and Balawi, {Ahmed H.} and Andreas Paulke and Zhipeng Kan and Michael Pope and Clulow, {Andrew J.} and Jannic Wolf and Burn, {Paul L.} and Gentle, {Ian R.} and Dieter Neher and Toney, {Michael F.} and Fr{\'e}d{\'e}ric Laquai and Beaujuge, {Pierre M.} and Collins, {Brian A.}",

note = "Funding Information: O.A. was supported by Prince Sattam bin Abdulaziz University in Saudi Arabia and the Saudi Arabian Cultural Mission in the United States. T.F. was supported by the Washington State University Seed Grant Program. A.P. and D.N. acknowledge financial support from the German Ministry of Science and Education (project UNVEIL). V.S. acknowledges financial support from the NDSEG fellowship. This research used resources described above of the Advanced Light Source, which is a DOE Office of Science User Facility under Contract No. DE-AC02-05CH11231 and Stanford Synchrotron Radiation Lightsource. P.M.B. acknowledges support by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No. CRG_R2_13_BEAU_KAUST_1 and under KAUST Baseline Research Funding. The authors also wish to acknowledge the Australian Centre for Neutron Scattering (formerly the Bragg Institute at the time of the measurements) and the Australian Nuclear Science and Technology Organisation (ANSTO) for providing the neutron research facilities for the NR experiments. The NR measurements were supported by an Australian Research Council Discovery Program (DP120101372). The authors would like to thank Dr. Andrew Nelson, Dr. Ravi Chandra Raju Nagiri, and Mr. Jake McEwan for their assistance in performing the NR measurements. Publisher Copyright: {\textcopyright} 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim",

year = "2018",

month = jul,

day = "5",

doi = "10.1002/aenm.201702941",

language = "English (US)",

volume = "8",

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Alqahtani, O, Babics, M, Gorenflot, J, Savikhin, V, Ferron, T, Balawi, AH, Paulke, A, Kan, Z, Pope, M, Clulow, AJ, Wolf, J, Burn, PL, Gentle, IR, Neher, D, Toney, MF, Laquai, F, Beaujuge, PM & Collins, BA 2018, 'Mixed Domains Enhance Charge Generation and Extraction in Bulk-Heterojunction Solar Cells with Small-Molecule Donors', Advanced Energy Materials, vol. 8, no. 19, 1702941. https://doi.org/10.1002/aenm.201702941

TY - JOUR

T1 - Mixed Domains Enhance Charge Generation and Extraction in Bulk-Heterojunction Solar Cells with Small-Molecule Donors

AU - Alqahtani, Obaid

AU - Babics, Maxime

AU - Gorenflot, Julien

AU - Savikhin, Victoria

AU - Ferron, Thomas

AU - Balawi, Ahmed H.

AU - Paulke, Andreas

AU - Kan, Zhipeng

AU - Pope, Michael

AU - Clulow, Andrew J.

AU - Wolf, Jannic

AU - Burn, Paul L.

AU - Gentle, Ian R.

AU - Neher, Dieter

AU - Toney, Michael F.

AU - Laquai, Frédéric

AU - Beaujuge, Pierre M.

AU - Collins, Brian A.

N1 - Funding Information: O.A. was supported by Prince Sattam bin Abdulaziz University in Saudi Arabia and the Saudi Arabian Cultural Mission in the United States. T.F. was supported by the Washington State University Seed Grant Program. A.P. and D.N. acknowledge financial support from the German Ministry of Science and Education (project UNVEIL). V.S. acknowledges financial support from the NDSEG fellowship. This research used resources described above of the Advanced Light Source, which is a DOE Office of Science User Facility under Contract No. DE-AC02-05CH11231 and Stanford Synchrotron Radiation Lightsource. P.M.B. acknowledges support by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No. CRG_R2_13_BEAU_KAUST_1 and under KAUST Baseline Research Funding. The authors also wish to acknowledge the Australian Centre for Neutron Scattering (formerly the Bragg Institute at the time of the measurements) and the Australian Nuclear Science and Technology Organisation (ANSTO) for providing the neutron research facilities for the NR experiments. The NR measurements were supported by an Australian Research Council Discovery Program (DP120101372). The authors would like to thank Dr. Andrew Nelson, Dr. Ravi Chandra Raju Nagiri, and Mr. Jake McEwan for their assistance in performing the NR measurements. Publisher Copyright: © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

PY - 2018/7/5

Y1 - 2018/7/5

N2 - The interplay between nanomorphology and efficiency of polymer-fullerene bulk-heterojunction (BHJ) solar cells has been the subject of intense research, but the generality of these concepts for small-molecule (SM) BHJs remains unclear. Here, the relation between performance; charge generation, recombination, and extraction dynamics; and nanomorphology achievable with two SM donors benzo[1,2-b:4,5-b]dithiophene-pyrido[3,4-b]-pyrazine BDT(PPTh2)2, namely SM1 and SM2, differing by their side-chains, are examined as a function of solution additive composition. The results show that the additive 1,8-diiodooctane acts as a plasticizer in the blends, increases domain size, and promotes ordering/crystallinity. Surprisingly, the system with high domain purity (SM1) exhibits both poor exciton harvesting and severe charge trapping, alleviated only slightly with increased crystallinity. In contrast, the system consisting of mixed domains and lower crystallinity (SM2) shows both excellent exciton harvesting and low charge recombination losses. Importantly, the onset of large, pure crystallites in the latter (SM2) system reduces efficiency, pointing to possible differences in the ideal morphologies for SM-based BHJ solar cells compared with polymer-fullerene devices. In polymer-based systems, tie chains between pure polymer crystals establish a continuous charge transport network, whereas SM-based active layers may in some cases require mixed domains that enable both aggregation and charge percolation to the electrodes.

AB - The interplay between nanomorphology and efficiency of polymer-fullerene bulk-heterojunction (BHJ) solar cells has been the subject of intense research, but the generality of these concepts for small-molecule (SM) BHJs remains unclear. Here, the relation between performance; charge generation, recombination, and extraction dynamics; and nanomorphology achievable with two SM donors benzo[1,2-b:4,5-b]dithiophene-pyrido[3,4-b]-pyrazine BDT(PPTh2)2, namely SM1 and SM2, differing by their side-chains, are examined as a function of solution additive composition. The results show that the additive 1,8-diiodooctane acts as a plasticizer in the blends, increases domain size, and promotes ordering/crystallinity. Surprisingly, the system with high domain purity (SM1) exhibits both poor exciton harvesting and severe charge trapping, alleviated only slightly with increased crystallinity. In contrast, the system consisting of mixed domains and lower crystallinity (SM2) shows both excellent exciton harvesting and low charge recombination losses. Importantly, the onset of large, pure crystallites in the latter (SM2) system reduces efficiency, pointing to possible differences in the ideal morphologies for SM-based BHJ solar cells compared with polymer-fullerene devices. In polymer-based systems, tie chains between pure polymer crystals establish a continuous charge transport network, whereas SM-based active layers may in some cases require mixed domains that enable both aggregation and charge percolation to the electrodes.

KW - charge transport

KW - domain purity

KW - microscopy

KW - mixed domains

KW - organic solar cells

KW - photovoltaic devices

KW - resonant X-ray scattering

KW - small molecules

KW - transient spectroscopy

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U2 - 10.1002/aenm.201702941

DO - 10.1002/aenm.201702941

M3 - Article

AN - SCOPUS:85044339010

SN - 1614-6832

VL - 8

JO - Advanced Energy Materials

JF - Advanced Energy Materials

IS - 19

M1 - 1702941

ER -

Mixed Domains Enhance Charge Generation and Extraction in Bulk-Heterojunction Solar Cells with Small-Molecule Donors

Abstract

Bibliographical note

Keywords

ASJC Scopus subject areas

UN SDGs

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