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Intricacies and Mechanism of p-Doping Spiro-MeOTAD Using Cu(TFSI)₂

DOI zum Zitieren der Version auf EPub Bayreuth: https://doi.org/10.15495/EPub_UBT_00006678
URN to cite this document: urn:nbn:de:bvb:703-epub-6678-6

Title data

Hochgesang, Adrian ; Biberger, Simon ; Grüne, Jeannine ; Mohanraj, John ; Kahle, Frank-Julian ; Dyakonov, Vladimir ; Köhler, Anna ; Thelakkat, Mukundan:
Intricacies and Mechanism of p-Doping Spiro-MeOTAD Using Cu(TFSI)₂.
In: Advanced Electronic Materials. Vol. 8 (2022) Issue 10 . - No. 2200113.
ISSN 2199-160X
DOI der Verlagsversion: https://doi.org/10.1002/aelm.202200113

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Abstract

Abstract Copper salts are a popular choice as p-dopants for organic semiconductors, particularly in N2,N2,N2′,N2′,N7,N7,N7′,N7′-octakis(4-methoxyphenyl)-9,9′-spirobi9H-fluoren-2,2′,7,7′-tetramine (Spiro-MeOTAD) hole transport material for solar cells. While being exceptionally effective, no scientific consensus about their doping mechanism has been established so far. This study describes the thermodynamic equilibria of involved species in copper(II) bis(trifluoromethanesulfonyl)imide (Cu(TFSI)2) doped, co-evaporated Spiro-MeOTAD. A temperature-independent formation of charge transfer states is found, followed by an endothermic release of free charge carriers. Impedance and electron paramagnetic resonance spectroscopy unravel low activation energies for hole release and hopping transport. As a result, (52.0 ± 6.4)\% of the total Cu(TFSI)2 molecules form free, dissociated holes at 10 mol\% and room temperature. CuI species arising out of doping are stabilized by formation of a CuI(TFSI)2- cuprate, inhibiting elemental copper formation. This CuI species presents a potent hole trap reducing their mobility, which can be averted by simple addition of a bathocuproine complexing agent. A nonlinear temperature-dependent conductivity and mobility that contradicts current charge transport models is observed. This is attributed to a combination of trap- and charge transfer state freeze-out. These insights may be adapted to other metal salts, providing guidelines for designing next-generation ultra-high efficiency dopants.

Further data

Item Type: Article in a journal
Keywords: copper; doping; electron transfer; reaction mechanisms; semiconductors
DDC Subjects: 500 Science > 530 Physics
Institutions of the University: Faculties > Faculty of Mathematics, Physics und Computer Science > Department of Physics
Faculties > Faculty of Mathematics, Physics und Computer Science > Department of Physics > Chair Experimental Physics II - Optoelectronics of Soft Matter
Faculties > Faculty of Mathematics, Physics und Computer Science > Department of Physics > Chair Experimental Physics II - Optoelectronics of Soft Matter > Chair Experimental Physics II - Optoelectronics of Soft Matter - Univ.-Prof. Dr. Anna Köhler
Faculties
Faculties > Faculty of Mathematics, Physics und Computer Science
Language: English
Originates at UBT: Yes
URN: urn:nbn:de:bvb:703-epub-6678-6
Date Deposited: 29 Sep 2022 08:45
Last Modified: 13 Oct 2022 07:49
URI: https://epub.uni-bayreuth.de/id/eprint/6678

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