TY - JOUR
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
N1 - Funding Information:
This study was partly supported by ACT-C, JST Grant JPMJCR12YW, Japan, Electric Technology Research Foundation of Chugoku, Chugoku Regional Innovation Research Centre, and JKA through its promotion funds from KEIRIN RACE (2018 M-184). The GIWAXS experiments were performed at BL46XU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposals 2016A1768 and 2016B1875). We gratefully thank Prof. Itaru Osaka and Dr. Masahiko Saito (Hiroshima University) and Dr. Tomoyuki Koganezawa (JASRI) for the measurement of GIWAXS images, Prof. Koichi Mitsudo and Prof. Seiji Suga (Okayama University) for the CV measurements, Prof. Naoshi Ikeda (Okayama University) for the AFM images, Prof. Yoshi-hiro Kubozono (Okayama University) for the EQE spectra and measurement of thickness, Ms. Megumi Kosaka and Mr. Motonari Kobayashi at the Department of Instrumental Analysis, Advanced Science Research Center, Okayama University, for the measurements of elemental analyses, and the SC-NMR Laboratory of Okayama University for the NMR spectral measurements.
Funding Information:
This study was partly supported by ACT-C, JST Grant JPMJCR12YW, Japan, Electric Technology Research Foundation of Chugoku, Chugoku Regional Innovation Research Centre, and JKA through its promotion funds from KEIRIN RACE (2018 M-184). The GIWAXS experiments were performed at BL46XU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposals 2016A1768 and 2016B1875). We gratefully thank Prof. Itaru Osaka and Dr. Masahiko Saito (Hiroshima University) and Dr. Tomoyuki Koganezawa (JASRI) for the measurement of GIWAXS images, Prof. Koichi Mitsudo and Prof. Seiji Suga (Okayama University) for the CV measurements, Prof. Naoshi Ikeda (Okayama University) for the AFM images, Prof. Yoshihiro Kubozono (Okayama University) for the EQE spectra and measurement of thickness, Ms. Megumi Kosaka and Mr. Motonari Kobayashi at the Department of Instrumental Analysis, Advanced Science Research Center, Okayama University, for the measurements of elemental analyses, and the SC-NMR Laboratory of Okayama University for the NMR spectral measurements.
Publisher Copyright:
© 2018 Wiley Periodicals, Inc.
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 - Phenanthrodithiophene
KW - molecular ordering
KW - open-circuit voltage
KW - organic photovoltaics
KW - polymers
KW - semiconductors
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U2 - 10.1002/pola.29248
DO - 10.1002/pola.29248
M3 - Article
AN - SCOPUS:85055710644
VL - 56
SP - 2646
EP - 2655
JO - Journal of Polymer Science, Part A: Polymer Chemistry
JF - Journal of Polymer Science, Part A: Polymer Chemistry
SN - 0887-624X
IS - 23
ER -