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Mansour AE, Valencia AM, Lungwitz D, Wegner B, Tanaka N, Shoji Y, Fukushima T, Opitz A, Cocchi C, Koch N. Understanding the evolution of the Raman spectra of molecularly p-doped poly(3-hexylthiophene-2,5-diyl): signatures of polarons and bipolarons. Phys Chem Chem Phys 2022; 24:3109-3118. [PMID: 35040854 DOI: 10.1039/d1cp04985b] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Molecular doping is a key process to increase the density of charge carriers in organic semiconductors. Doping-induced charges in polymer semiconductors result in the formation of polarons and/or bipolarons due to the strong electron-vibron coupling in conjugated organic materials. Identifying the nature of charge carriers in doped polymers is essential to optimize the doping process for applications. In this work, we use Raman spectroscopy to investigate the formation of charge carriers in molecularly doped poly(3-hexylthiophene-2,5-diyl) (P3HT) for increasing dopant concentration, with the organic salt dimesityl borinium tetrakis(penta-fluorophenyl)borate (Mes2B+ [B(C6F5)4]-) and the Lewis acid tris(pentafluorophenyl)borane [B(C6F5)3]. While the Raman signatures of neutral P3HT and singly charged P3HT segments (polarons) are known, the Raman spectra of doubly charged P3HT segments (bipolarons) are not yet sufficiently understood. Combining Raman spectroscopy measurements on doped P3HT thin films with first-principles calculations on oligomer models, we explain the evolution of the Raman spectra from neutral P3HT to increasingly doped P3HT featuring polarons and eventually bipolarons at high doping levels. We identify and explain the origin of the spectral features related to bipolarons by tracing the Raman signature of the symmetric collective vibrations along the polymer backbone, which - compared to neutral P3HT - redshifts for polarons and blueshifts for bipolarons. This is explained by a planarization of the singly charged P3HT segments with polarons and rather high order in thin films, while the doubly charged segments with bipolarons are located in comparably disordered regions of the P3HT film due to the high dopant concentration. Furthermore, we identify additional Raman peaks associated with vibrations in the quinoid doubly charged segments of the polymer. Our results offer the opportunity for readily identifying the nature of charge carriers in molecularly doped P3HT while taking advantage of the simplicity, versatility, and non-destructive nature of Raman spectroscopy.
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Affiliation(s)
- Ahmed E Mansour
- Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, 12489 Berlin, Germany. .,Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin, Germany
| | - Ana M Valencia
- Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, 12489 Berlin, Germany. .,Carl von Ossietzky Universität Oldenburg, Institute of Physics, 26129 Oldenburg, Germany
| | - Dominique Lungwitz
- Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
| | - Berthold Wegner
- Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, 12489 Berlin, Germany. .,Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin, Germany
| | - Naoki Tanaka
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503, Japan
| | - Yoshiaki Shoji
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503, Japan
| | - Takanori Fukushima
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503, Japan
| | - Andreas Opitz
- Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
| | - Caterina Cocchi
- Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, 12489 Berlin, Germany. .,Carl von Ossietzky Universität Oldenburg, Institute of Physics, 26129 Oldenburg, Germany
| | - Norbert Koch
- Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, 12489 Berlin, Germany. .,Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin, Germany
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Kalbáč M, Kavan L, Gorantla S, Gemming T, Dunsch L. Sexithiophene Encapsulated in a Single-Walled Carbon Nanotube: An In Situ Raman Spectroelectrochemical Study of a Peapod Structure. Chemistry 2010; 16:11753-9. [DOI: 10.1002/chem.201001417] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2010] [Indexed: 11/11/2022]
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Affiliation(s)
- Juzo Nakayama
- a Department of Chemistry , Saitama University , Sakura-ku, Saitama, Saitama, 338-8570, Japan
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Tanaka M, Hatta K, Edura T, Tsutsui K, Wada Y, Nishide H. Conductive characteristics of radical-bearing polythiophenes using a microcomb-shaped electrode. POLYM ADVAN TECHNOL 2007. [DOI: 10.1002/pat.933] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Casado J, Hernández V, Hotta S, López Navarrete JT. Vibrational spectra of charged defects in a series of α,α′-dimethyl end-capped oligothiophenes induced by chemical doping with iodine. J Chem Phys 1998. [DOI: 10.1063/1.477697] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Hernandez V, Hotta S, Lopez Navarrete JT. Vibrational spectroscopic study of 5,5″-bis(dicyanomethylene)-5,5″-dihydro-Δ2,2′:5′,2″-terthiophene bearing a heteroquinonoid structure as a model of doped polythiophene. J Chem Phys 1998. [DOI: 10.1063/1.476855] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Ramı́rez FJ, Aranda MAG, Hernández V, Casado J, Hotta S, López Navarrete JT. Temperature-dependent infrared spectroscopic and crystallographic study of α,α′-dimethyl oligothiophenes in neutral form. J Chem Phys 1998. [DOI: 10.1063/1.476769] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Cuff L, Kertesz M. Evidence of quinonoid structures in the vibrational spectra of thiophene based conducting polymers: Poly(thiophene), poly(thieno[3,4-b]benzene), and poly(thieno[3,4-b]pyrazine). J Chem Phys 1997. [DOI: 10.1063/1.473576] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Furukawa Y. Electronic Absorption and Vibrational Spectroscopies of Conjugated Conducting Polymers. ACTA ACUST UNITED AC 1996. [DOI: 10.1021/jp960608n] [Citation(s) in RCA: 282] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Yukio Furukawa
- Department of Chemistry, School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan
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Yokonuma N, Furukawa Y, Tasumi M, Kuroda M, Nakayama J. Electronic absorption and Raman studies of BF4−-doped polythiophene based on the spectra of the radical cation and dication of α-sexithiophene. Chem Phys Lett 1996. [DOI: 10.1016/0009-2614(96)00383-1] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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