Development of a phenanthrodithiophene-difluorobenzoxadiazole copolymer exhibiting high open-circuit voltage in organic solar cells

Hiroki Mori, Ryosuke Takahashi, Yasushi Nishihara

Research output: Contribution to journalArticle

Abstract

A phenanthrodithiophene (PDT)-difluorobenzoxadiazole (DFBO) copolymer, P-PDT-DFBO, was synthesized and characterized. Replacing a thiadiazole with an oxadiazole ring gives the synthesized polymer a highest occupied molecular orbital (HOMO) about 0.1 V lower, and lowest unoccupied molecular orbital energy levels lower than those of its benzothiadiazole (BT) counterpart, due to the more electron-deficient oxadiazole. Furthermore, since oxadiazole has a larger dipole moment than BT, P-PDT-DFBO exhibits greater aggregation strength than previously reported for P-PDT-DFBT. The low-lying HOMO level of P-PDT-DFBO gave about 0.1 V higher open-circuit voltage (Voc), yielding over 0.9 V in a fabricated solar cell. From grazing incidence wide-angle X-ray diffraction analysis, P-PDT-DFBO formed a favorable face-on orientation in both neat and blended films, indicating that the incorporation of an oxadiazole moiety can enhance Voc without any orientation change in the solid state. However, a P-PDT-DFBO-based cell exhibited significantly lower Jsc and FF, and thus less power conversion efficiency, not >4.43%, due to its lower hole mobility than P-PDT-DFBT. One possible reason for poor performance may be the low crystallinity of P-PDT-DFBO in blended film. This may be caused by its strong aggregation tendency, leading to fast crystallization into a semiamorphous structure or to interference with the construction of long-range ordered structure.

Original languageEnglish
Pages (from-to)2646-2655
Number of pages10
JournalJournal of Polymer Science, Part A: Polymer Chemistry
Volume56
Issue number23
DOIs
Publication statusPublished - Dec 1 2018

Fingerprint

Oxadiazoles
Molecular orbitals
Open circuit voltage
Copolymers
Agglomeration
Hole mobility
Dipole moment
Thiadiazoles
X ray diffraction analysis
Electron energy levels
Conversion efficiency
Solar cells
Crystallization
Polymers
Electrons
Organic solar cells
benzo-1,2,3-thiadiazole

Keywords

  • Benzoxadiazole
  • Energy conversion
  • molecular ordering
  • open-circuit voltage
  • organic photovoltaics
  • Phenanthrodithiophene
  • polymers
  • semiconductors

ASJC Scopus subject areas

  • Polymers and Plastics
  • Organic Chemistry
  • Materials Chemistry

Cite this

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title = "Development of a phenanthrodithiophene-difluorobenzoxadiazole copolymer exhibiting high open-circuit voltage in organic solar cells",
abstract = "A phenanthrodithiophene (PDT)-difluorobenzoxadiazole (DFBO) copolymer, P-PDT-DFBO, was synthesized and characterized. Replacing a thiadiazole with an oxadiazole ring gives the synthesized polymer a highest occupied molecular orbital (HOMO) about 0.1 V lower, and lowest unoccupied molecular orbital energy levels lower than those of its benzothiadiazole (BT) counterpart, due to the more electron-deficient oxadiazole. Furthermore, since oxadiazole has a larger dipole moment than BT, P-PDT-DFBO exhibits greater aggregation strength than previously reported for P-PDT-DFBT. The low-lying HOMO level of P-PDT-DFBO gave about 0.1 V higher open-circuit voltage (Voc), yielding over 0.9 V in a fabricated solar cell. From grazing incidence wide-angle X-ray diffraction analysis, P-PDT-DFBO formed a favorable face-on orientation in both neat and blended films, indicating that the incorporation of an oxadiazole moiety can enhance Voc without any orientation change in the solid state. However, a P-PDT-DFBO-based cell exhibited significantly lower Jsc and FF, and thus less power conversion efficiency, not >4.43{\%}, due to its lower hole mobility than P-PDT-DFBT. One possible reason for poor performance may be the low crystallinity of P-PDT-DFBO in blended film. This may be caused by its strong aggregation tendency, leading to fast crystallization into a semiamorphous structure or to interference with the construction of long-range ordered structure.",
keywords = "Benzoxadiazole, Energy conversion, molecular ordering, open-circuit voltage, organic photovoltaics, Phenanthrodithiophene, polymers, semiconductors",
author = "Hiroki Mori and Ryosuke Takahashi and Yasushi Nishihara",
year = "2018",
month = "12",
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doi = "10.1002/pola.29248",
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T1 - Development of a phenanthrodithiophene-difluorobenzoxadiazole copolymer exhibiting high open-circuit voltage in organic solar cells

AU - Mori, Hiroki

AU - Takahashi, Ryosuke

AU - Nishihara, Yasushi

PY - 2018/12/1

Y1 - 2018/12/1

N2 - A phenanthrodithiophene (PDT)-difluorobenzoxadiazole (DFBO) copolymer, P-PDT-DFBO, was synthesized and characterized. Replacing a thiadiazole with an oxadiazole ring gives the synthesized polymer a highest occupied molecular orbital (HOMO) about 0.1 V lower, and lowest unoccupied molecular orbital energy levels lower than those of its benzothiadiazole (BT) counterpart, due to the more electron-deficient oxadiazole. Furthermore, since oxadiazole has a larger dipole moment than BT, P-PDT-DFBO exhibits greater aggregation strength than previously reported for P-PDT-DFBT. The low-lying HOMO level of P-PDT-DFBO gave about 0.1 V higher open-circuit voltage (Voc), yielding over 0.9 V in a fabricated solar cell. From grazing incidence wide-angle X-ray diffraction analysis, P-PDT-DFBO formed a favorable face-on orientation in both neat and blended films, indicating that the incorporation of an oxadiazole moiety can enhance Voc without any orientation change in the solid state. However, a P-PDT-DFBO-based cell exhibited significantly lower Jsc and FF, and thus less power conversion efficiency, not >4.43%, due to its lower hole mobility than P-PDT-DFBT. One possible reason for poor performance may be the low crystallinity of P-PDT-DFBO in blended film. This may be caused by its strong aggregation tendency, leading to fast crystallization into a semiamorphous structure or to interference with the construction of long-range ordered structure.

AB - A phenanthrodithiophene (PDT)-difluorobenzoxadiazole (DFBO) copolymer, P-PDT-DFBO, was synthesized and characterized. Replacing a thiadiazole with an oxadiazole ring gives the synthesized polymer a highest occupied molecular orbital (HOMO) about 0.1 V lower, and lowest unoccupied molecular orbital energy levels lower than those of its benzothiadiazole (BT) counterpart, due to the more electron-deficient oxadiazole. Furthermore, since oxadiazole has a larger dipole moment than BT, P-PDT-DFBO exhibits greater aggregation strength than previously reported for P-PDT-DFBT. The low-lying HOMO level of P-PDT-DFBO gave about 0.1 V higher open-circuit voltage (Voc), yielding over 0.9 V in a fabricated solar cell. From grazing incidence wide-angle X-ray diffraction analysis, P-PDT-DFBO formed a favorable face-on orientation in both neat and blended films, indicating that the incorporation of an oxadiazole moiety can enhance Voc without any orientation change in the solid state. However, a P-PDT-DFBO-based cell exhibited significantly lower Jsc and FF, and thus less power conversion efficiency, not >4.43%, due to its lower hole mobility than P-PDT-DFBT. One possible reason for poor performance may be the low crystallinity of P-PDT-DFBO in blended film. This may be caused by its strong aggregation tendency, leading to fast crystallization into a semiamorphous structure or to interference with the construction of long-range ordered structure.

KW - Benzoxadiazole

KW - Energy conversion

KW - molecular ordering

KW - open-circuit voltage

KW - organic photovoltaics

KW - Phenanthrodithiophene

KW - polymers

KW - semiconductors

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DO - 10.1002/pola.29248

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VL - 56

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JO - Journal of Polymer Science, Part A: Polymer Chemistry

JF - Journal of Polymer Science, Part A: Polymer Chemistry

SN - 0887-624X

IS - 23

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