Large bipolaron density at organic semiconductor/electrode interfaces.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 29269880.
- Also identified by DOI 10.1038/s41467-017-02459-3 and PMC identifier 5740113.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Bipolaron states, in which two electrons or two holes occupy a single molecule or conjugated polymer segment, are typically considered to be negligible in organic semiconductor devices due to Coulomb repulsion between the two charges. Here we use charge modulation spectroscopy to reveal a bipolaron sheet density >10<sup>10</sup> cm<sup>-2</sup> at the interface between an indium tin oxide anode and the common small molecule organic semiconductor N,N'-Bis(3-methylphenyl)-N,N'-diphenylbenzidine. We find that the magnetocurrent response of hole-only devices correlates closely with changes in the bipolaron concentration, supporting the bipolaron model of unipolar organic magnetoresistance and suggesting that it may be more of an interface than a bulk phenomenon. These results are understood on the basis of a quantitative interface energy level alignment model, which indicates that bipolarons are generally expected to be significant near contacts in the Fermi level pinning regime and thus may be more prevalent in organic electronic devices than previously thought.