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| TITLE | Counterion Control and the Spectral Signatures of Polarons, Coupled Polarons, and Bipolarons in Doped P3HT Films |
|---|---|
| AUTHOR | Eric C. Wu, Charlene Z. Salamat, Omar León Ruiz, Thomas Qu, Alexis Kim, Sarah H. Tolbert, Benjamin J. Schwartz |
| YEAR | 2023 |
| JOURNAL | Advanced Functional Materials |
| ABSTRACT | When an electron is removed from a conjugated polymer, such as poly(3-hexylthiophene-2,5-diyl) (P3HT), the remaining hole and associated change in the polymer backbone structure from aromatic to quinoidal are referred to as a polaron. Bipolarons are created by removing the unpaired electron from an already-oxidized polymer segment. In electrochemically-doped P3HT films, polarons, and bipolarons are readily observed, but in chemically-doped P3HT films, bipolarons rarely form. This is explained by studying the effects of counterion position on the formation of polarons, strongly coupled polarons, and bipolarons using both spectroscopic and X-ray diffraction experiments and time-dependent density functional theory calculations. The counterion positions control whether two polarons spin-pair to form a bipolaron or whether they strongly couple without spin-pairing are found. When two counterions lie close to the same polymer segment, bipolarons can form, with an absorption spectrum that is blueshifted from that of a single polaron. Otherwise, polarons at high concentrations do not spin-pair, but instead J-couple, leading to a redshifted absorption spectrum. The counterion location needed for bipolaron formation is accompanied by a loss of polymer crystallinity. These results explain the observed formation order of single polarons, coupled single polarons, and singlet bipolarons in electrochemically- and chemically-doped conjugated polymers. |
| FULL ARTICLE | https://onlinelibrary.wiley.com/doi/full/10.1002/adfm.202213652 |
| INSTRUMENT | FTIR-420 |
| KEYWORDS | bipolarons, chemical doping, counterions, electrochemical doping, polarons, semiconducting polymers |
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