Effect of Charge Localization on the Effective Hyperfine Interaction in Organic Semiconducting Polymers

Rugang Geng; Ram C. Subedi; Hoang M. Luong; Minh T. Pham; Weichuan Huang; Xiaoguang Li; Kunlun Hong; Ming Shao; Kai Xiao; Lawrence A. Hornak; Tho D. Nguyen

doi:10.1103/PhysRevLett.120.086602

Effect of Charge Localization on the Effective Hyperfine Interaction in Organic Semiconducting Polymers

Rugang Geng, Ram C. Subedi, Hoang M. Luong, Minh T. Pham, Weichuan Huang, Xiaoguang Li, Kunlun Hong, Ming Shao, Kai Xiao, Lawrence A. Hornak, Tho D. Nguyen

Functional Hybrid Nanomaterials

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Abstract

Hyperfine interaction (HFI), originating from the coupling between spins of charge carriers and nuclei, has been demonstrated to strongly influence the spin dynamics of localized charges in organic semiconductors. Nevertheless, the role of charge localization on the HFI strength in organic thin films has not yet been experimentally investigated. In this study, the statistical relation hypothesis that the effective HFI of holes in regioregular poly(3-hexylthiophene) (P3HT) is proportional to 1/N0.5 has been examined, where N is the number of the random nuclear spins within the envelope of the hole wave function. First, by studying magnetoconductance in hole-only devices made by isotope-labeled P3HT we verify that HFI is indeed the dominant spin interaction in P3HT. Second, assuming that holes delocalize fully over the P3HT polycrystalline domain, the strength of HFI is experimentally demonstrated to be proportional to 1/N0.52 in excellent agreement with the statistical relation. Third, the HFI of electrons in P3HT is about 3 times stronger than that of holes due to the stronger localization of the electrons. Finally, the effective HFI in organic light emitting diodes is found to be a superposition of effective electron and hole HFI. Such a statistical relation may be generally applied to other semiconducting polymers. This Letter may provide great benefits for organic optoelectronics, chemical reaction kinetics, and magnetoreception in biology.

Original language	English
Article number	086602
Journal	Physical Review Letters
Volume	120
Issue number	8
DOIs	https://doi.org/10.1103/PhysRevLett.120.086602
State	Published - Feb 22 2018

Funding

We acknowledge the useful discussion with Professor Valy Vardeny, Professor Eitan Ehrenfreund, Professor Manh-Huong Phan, and Dr. Andreas Sperlich. We thank Professor Yiping Zhao group for helping us with the XRD measurement. Synthesis of the isotope-labeled P3HT and the corresponding Raman and XRD measurement were conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. This work was supported by the University of Georgia (UGA) startup funds and Faculty Research Grant (T. D. N.), startup funds provided by the UGA College of Engineering (L. A. H), NSFC, and National Key Research and Development Program of China (Contracts No. 2016YFA0300103 and No. 2015CB921201, X. L.).

Funders	Funder number
UGA College of Engineering
University of Georgia
National Natural Science Foundation of China	2016YFA0300103, 2015CB921201
National Key Research and Development Program of China

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title = "Effect of Charge Localization on the Effective Hyperfine Interaction in Organic Semiconducting Polymers",

abstract = "Hyperfine interaction (HFI), originating from the coupling between spins of charge carriers and nuclei, has been demonstrated to strongly influence the spin dynamics of localized charges in organic semiconductors. Nevertheless, the role of charge localization on the HFI strength in organic thin films has not yet been experimentally investigated. In this study, the statistical relation hypothesis that the effective HFI of holes in regioregular poly(3-hexylthiophene) (P3HT) is proportional to 1/N0.5 has been examined, where N is the number of the random nuclear spins within the envelope of the hole wave function. First, by studying magnetoconductance in hole-only devices made by isotope-labeled P3HT we verify that HFI is indeed the dominant spin interaction in P3HT. Second, assuming that holes delocalize fully over the P3HT polycrystalline domain, the strength of HFI is experimentally demonstrated to be proportional to 1/N0.52 in excellent agreement with the statistical relation. Third, the HFI of electrons in P3HT is about 3 times stronger than that of holes due to the stronger localization of the electrons. Finally, the effective HFI in organic light emitting diodes is found to be a superposition of effective electron and hole HFI. Such a statistical relation may be generally applied to other semiconducting polymers. This Letter may provide great benefits for organic optoelectronics, chemical reaction kinetics, and magnetoreception in biology.",

author = "Rugang Geng and Subedi, {Ram C.} and Luong, {Hoang M.} and Pham, {Minh T.} and Weichuan Huang and Xiaoguang Li and Kunlun Hong and Ming Shao and Kai Xiao and Hornak, {Lawrence A.} and Nguyen, {Tho D.}",

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AU - Subedi, Ram C.

AU - Luong, Hoang M.

AU - Pham, Minh T.

AU - Huang, Weichuan

AU - Li, Xiaoguang

AU - Hong, Kunlun

AU - Shao, Ming

AU - Xiao, Kai

AU - Hornak, Lawrence A.

AU - Nguyen, Tho D.

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AB - Hyperfine interaction (HFI), originating from the coupling between spins of charge carriers and nuclei, has been demonstrated to strongly influence the spin dynamics of localized charges in organic semiconductors. Nevertheless, the role of charge localization on the HFI strength in organic thin films has not yet been experimentally investigated. In this study, the statistical relation hypothesis that the effective HFI of holes in regioregular poly(3-hexylthiophene) (P3HT) is proportional to 1/N0.5 has been examined, where N is the number of the random nuclear spins within the envelope of the hole wave function. First, by studying magnetoconductance in hole-only devices made by isotope-labeled P3HT we verify that HFI is indeed the dominant spin interaction in P3HT. Second, assuming that holes delocalize fully over the P3HT polycrystalline domain, the strength of HFI is experimentally demonstrated to be proportional to 1/N0.52 in excellent agreement with the statistical relation. Third, the HFI of electrons in P3HT is about 3 times stronger than that of holes due to the stronger localization of the electrons. Finally, the effective HFI in organic light emitting diodes is found to be a superposition of effective electron and hole HFI. Such a statistical relation may be generally applied to other semiconducting polymers. This Letter may provide great benefits for organic optoelectronics, chemical reaction kinetics, and magnetoreception in biology.

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Effect of Charge Localization on the Effective Hyperfine Interaction in Organic Semiconducting Polymers

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