Ultrafast Charge Transfer Dynamics at the Origin of Photoconductivity in Doped Organic Solids

Tsokkou, Dimitra; Cheng, Chiao-Yu; Krainova, Nina; Mukhopadhyay, Sukrit; Giebink, Noel C.; Banerji, Natalie (2021). Ultrafast Charge Transfer Dynamics at the Origin of Photoconductivity in Doped Organic Solids. Journal of physical chemistry. C, 125(13), pp. 7086-7096. American Chemical Society 10.1021/acs.jpcc.1c01990

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In spite of their growing importance for optoelectronic devices, the fundamental properties and photophysics of molecularly doped organic solids remain poorly understood. Such doping typically leads to a small fraction of free conductive charges, with most electronic carriers remaining Coulombically bound to the ionized dopant. Recently, we have reported photocurrent for devices containing vacuum-deposited TAPC (1,1-bis(4-bis(4-methylphenyl)aminophenyl)cyclohexane) doped with MoO3, showing that photoexcitation of charged TAPC molecules increases the concentration of free holes that contribute to conduction. Here, we elucidate the excited-state dynamics of such doped TAPC films to unravel the key mechanisms responsible for this effect. We demonstrate that excitation of different electronic transitions in charged and neutral TAPC molecules allows bound holes to overcome the Coulombic attraction to their MoO3 counterions, resulting in an enhanced yield of long-lived free carriers. This is caused by ultrafast back-and-forth shuffling of charges and excitation energy between adjacent cations and neutral molecules, competing with relatively slow nonradiative decay from higher excited states of TAPC•+. The light-induced generation of conductive carriers requires the coexistence of cationic and neutral TAPC, a favorable energy level alignment, and intermolecular interactions in the solid state.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Department of Chemistry, Biochemistry and Pharmaceutical Sciences (DCBP)

UniBE Contributor:

Tsokkou, Dimitra and Banerji, Natalie

Subjects:

500 Science > 540 Chemistry

ISSN:

1932-7447

Publisher:

American Chemical Society

Funders:

[18] European Research Council ; [4] Swiss National Science Foundation ; [UNSPECIFIED] University of Bern

Language:

English

Submitter:

Olivier Nicolas Ludovic Bardagot

Date Deposited:

07 Jun 2021 16:14

Last Modified:

08 Aug 2022 08:16

Publisher DOI:

10.1021/acs.jpcc.1c01990

Related URLs:

PubMed ID:

33859770

Additional Information:

The authors thank the funders:
- ERC-STG, Acronym: OSIRIS, Grant number: 714586
["European Union (EU)" and "Horizon 2020"]
- Swiss National Science Foundation
Type: Project Funding, Grant number: 200020_184819
- University of Bern

BORIS DOI:

10.48350/156690

URI:

https://boris.unibe.ch/id/eprint/156690

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