Thin films of electron donor–acceptor complexes: characterisation of mixed-crystalline phases and implications for electrical doping

Opitz, Andreas; Duva, Giuliano; Gebhardt, Marius; Kim, Hongwon; Meister, Eduard; Meisel, Tino; Beyer, Paul; Belova, Valentina; Kasper, Christian; Pflaum, Jens; Pithan, Linus; Hinderhofer, Alexander; Schreiber, Frank; Brütting, Wolfgang

doi:10.1039/d1ma00578b

Cited by 3 publications

(6 citation statements)

References 99 publications

(204 reference statements)

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“…The functionality of virtually all organic and hybrid (opto-)electronic devices depends on interface energetics, and a thorough understanding of energy-level alignment mechanisms at organic-metal and organic-organic interfaces is indispensable for further efficiency improvements [1][2][3][4][5]. For example, the energy-level offset at the donor-acceptor interface in organic photovoltaic devices is crucial for exciton dissociation [6][7][8]; chemisorbed molecular monolayers on metals can tune the substrate work functions by an interfacial charge transfer [9,10] and allow, consequently, to lower charge injection barriers into electrodes [11,12]. The number of organic materials used for optoelectronic applications is virtually unlimited [13,14] and energy-level diagrams (ELDs) are frequently used to choose the best material for a given purpose [4,15].…”

Section: Introductionmentioning

confidence: 99%

Advanced characterization of organic–metal and organic–organic interfaces: from photoelectron spectroscopy data to energy-level diagrams

et al. 2022

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Organic-metal and organic-organic interfaces account for the functionality of virtually all organic optoelectronic applications and the energy-level alignment is of particular importance for device performance. Often the energy-level alignment is simply estimated by metal work functions and ionization energies and electron affinities of the organic materials. However, various interfacial effects such as push back, mirror forces (also known as screening), electronic polarization or charge transfer affect the energy-level alignment. We perform X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) measurements on copper-hexadecafluorophthalocyanine (F16CuPc) and titanyl-phthalocyanine (TiOPc) thin films on Ag(111) and use TiOPc bilayers to decouple F16CuPc layers from the metal substrate. Even for our structurally well-characterized model interfaces and by stepwise preparation of vacuum-sublimed samples, a precise assignment of vacuum-level and energy-level shifts remains challenging. Nevertheless, our results provide guidelines for the interpretation of XPS and UPS data of organic-metal and organic-organic interfaces.

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Section: Introductionmentioning

confidence: 99%

Advanced characterization of organic–metal and organic–organic interfaces: from photoelectron spectroscopy data to energy-level diagrams

et al. 2022

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“…The most significant observation is, however, the emergence of a new peak at q z = 0.33 Å –1 for 11 mol % concentration that becomes prominent for the largest dopant ratio studied and corresponds to an associated interlayer spacing of ∼1.90 nm. This peak is absent in the single-component films of either C 8 -BTBT or F 6 TCNNQ. , In analogy to the cocrystal structure reported for C 8 -BTBT-F 4 TCNQ , and C 10 -BTBT/F 4 TCNQ, the new peak is labeled (001) C , being attributed to the formation of cocrystals consisting of an alternated stacking C 8 -BTBT-F 6 TCNNQ. The 1:1 mixed structure is driven by the interaction of the respective conjugated cores of the acceptor and OSC.…”

Section: Resultsmentioning

confidence: 54%

“…This peak is absent in the single-component films of either C 8 -BTBT or F 6 TCNNQ. 26,33 In analogy to the cocrystal structure reported for C 8 -BTBT-F 4 TCNQ 34,35 and C 10 -BTBT/F 4 TCNQ, 25 the new peak is labeled (001) C , being attributed to the formation of cocrystals consisting of an alternated stacking C 8 -BTBT-F 6 TCNNQ. The 1:1 mixed structure is driven by the interaction of the respective conjugated cores of the acceptor and OSC.…”

Section: ■ Experimental Methodsmentioning

confidence: 75%

“…The conductivity was observed to increase with the dopant ratio, achieving a maximum value for a dopant concentration of 5 mol % and decreasing beyond this value. Other articles 22,26 have reported differences in the dependence of the conductivity on dopant concentration. 5,7,27 Although current studies highlight the potential offered by CTC for electrical doping in small-molecule OSCs, they also reveal the difficulty in tailoring the microstructure resulting from mixing the two molecular materials, that is, the fraction, order, and spatial distribution of the cocrystalline regions within the OSC film.…”

Section: ■ Introductionmentioning

confidence: 92%

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Charge-Transfer Complexes in Organic Field-Effect Transistors: Superior Suitability for Surface Doping

Babuji

Cazorla

Solano

et al. 2022

ACS Appl. Mater. Interfaces

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We demonstrate the key role of charge-transfer complexes in surface doping as a successful methodology for improving channel field-effect mobility and reducing the threshold voltage in organic field-effect transistors (OFETs), as well as raising the film conductivity. Demonstrated here for 2,7doping by sequential deposition is consistently rationalized by the development of a cocrystalline structure that forms and evolves from the surface of the organic semiconductor film without trading the thin-film structure integrity. This scenario brings higher benefits for the device operation than doping by codeposition, where a decrease in the field-effect mobility of the device, even for a dopant content of only 1 mol %, makes codeposition less suitable. Insight into the structural and electronic properties of the interface satisfactorily explains the improved performance of OFETs upon the incorporation of the dopant and provides an understanding of the mechanism of doping in this system.

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“…38,39 These changes enable a series of electronic transitions in SY, giving rise to a new spectral feature at 545 nm. 40,41 Upon biasing the HC-OLEFETs, electrons and holes will transport and accumulate at the SY interface (Figure 1d). These accumulated electrons have low mobility and long transit time, leading to enhanced capture efficiency in SY.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Achieving Bright Organic Light-Emitting Field-Effect Transistors with Sustained Efficiency through Hybrid Contact Design

Chiu

Hsu

Ying

et al. 2023

ACS Appl. Mater. Interfaces

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Organic light-emitting field-effect transistors (OLEFETs) with bilayer structures have been widely studied due to their potential to integrate high-mobility organic transistors and efficient organic light-emitting diodes. However, these devices face a major challenge of imbalance charge transport, leading to a severe efficiency roll-off at high brightness. Here, we propose a solution to this challenge by introducing a transparent organic/inorganic hybrid contact with specially designed electronic structures. Our design aims to steadily accumulate the electrons injected into the emissive polymer, allowing the light-emitting interface to effectively capture more holes even when the hole current increases. Our numerical simulations show that the capture efficiency of these steady electrons will dominate charge recombination and lead to a sustained external quantum efficiency of 0.23% over 3 orders of magnitude of brightness (4 to 7700 cd/m2) and current density (1.2 to 2700 mA/cm2) from −4 to −100 V. The same enhancement is retained even after increasing the external quantum efficiency (EQE) to 0.51%. The high and tunable brightness with stable efficiency offered by hybrid-contact OLEFETs makes them ideal light-emitting devices for various applications. These devices have the potential to revolutionize the field of organic electronics by overcoming the fundamental challenge of imbalance charge transport.

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Thin films of electron donor–acceptor complexes: characterisation of mixed-crystalline phases and implications for electrical doping

Abstract: For electron donor–acceptor complexes a link will be established between optical, structural and vibrational properties of EDA complexes as well as the electrical doping by them.

Cited by 3 publications

References 99 publications

Advanced characterization of organic–metal and organic–organic interfaces: from photoelectron spectroscopy data to energy-level diagrams

Advanced characterization of organic–metal and organic–organic interfaces: from photoelectron spectroscopy data to energy-level diagrams

Charge-Transfer Complexes in Organic Field-Effect Transistors: Superior Suitability for Surface Doping

Achieving Bright Organic Light-Emitting Field-Effect Transistors with Sustained Efficiency through Hybrid Contact Design

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