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The charge-transfer (CT) state arising as a hybrid electronic state at the interface between charge donor and charge acceptor molecular units is important to a wide variety of physical processes in organic semiconductor devices. The exact nature of this state depends heavily on the nature and co-facial overlap between the donor and acceptor; however, altering this overlap is usually accompanied by extensive confounding variations in properties due to extrinsic factors, such as microstructure. As a consequence, establishing reliable relationships between donor/acceptor molecular structures, their molecular overlap, degree of charge transfer and physical properties, is challenging. Herein, we examine the electronic structure of a polymorphic system based on the donor dibenzotetrathiafulvalene (DBTTF) and the acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) in the form of high-quality single crystals varying in the donor–acceptor overlap. Using angle-resolved photoemission spectroscopy, we resolve the highest occupied molecular orbital states of the CT crystals. Analysis based on field-effect transistors allows us to probe the sub-gap states impacting hole and electron transport. Our results expand the understanding on the impact of donor and acceptor interactions on electronic structure and charge transport.
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Charge Transport in Ternary Charge‐Transfer Solid Solution Single Crystals
Abstract The electronic effects of structural defects introduced through chemical doping are challenging to characterize in organic semiconductors, especially when measured in thin film devices where the performance is sensitive to structural heterogeneity. Here, a simple approach is presented to probe the roles of indirect and direct electronic coupling on charge transport in a series of compositionally varied charge‐transfer single crystals. In this system, carbazole (CBZ) is controllably substituted withN‐methylcarbazole (NMCBZ) in the cocrystal formed between CBZ and 1,3,4,5,7,8‐hexafluoro‐11,11,12,12‐tetracyano‐2,6‐naphthoquinodimethane (F6TNAP), producing a series of single crystals with compositions that range between 0 – 50% CBZ replacement and preserve the structure type of the parent cocrystal. Gas‐phase electronic structure calculations predict that substitutional replacement of CBZ with NMCBZ introduces two competing effects: (i) strengthening of indirect coupling by increasing the average degree of charge transfer and (ii) weakening of direct exchange by increasing the distance between adjacent charge‐transfer π‐stacks. Charge transport measurements reveal an initial decrease in the mobility upon substitution of CBZ with NMCBZ, rationalized by a combination of hole‐trapping and weakened direct coupling with increasing NMCBZ content. Critically, these results demonstrate the potential for solid solutions to offer insight into charge transport mechanisms and their chemical tunability in molecular electronic materials.
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- PAR ID:
- 10660181
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Advanced Functional Materials
- ISSN:
- 1616-301X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/adfm.202523425
