Role of oxygen incorporation in electronic properties of rubrene films

Song, Xin; Wang, Li; Fan, Qitang; Wu, Yaodong; Wang, Hongming; Liu, Chunmei; Liu, Nian-Hua; Zhu, Junfa; Qi, Dongchen; Gao, Xingyu; Wee, Andrew Thye Shen

doi:10.1063/1.3466914

Cited by 23 publications

(25 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Hence, it can be presumed that the peak appeared at ∼286.3 eV in our case is due to the formation of epoxy (C-O-C) and/or endoperoxide (C-O-O-C) groups as it should have a larger BE compared to hydroxyl groups15,[41][42][43][44] . To estimate the fraction of rubrene molecules that has been oxidized, we have plotted the ratio of reacted to non-reacted carbon intensity with exposure time in figure 6 (a).…”

mentioning

confidence: 93%

“…The researchers have previously reported their works by focusing the change of electronic structure of vacuum deposited π conjugated organic semiconductors by introducing oxygen at various pressures in the chamber [15][16][17][18] . But the concerned issue about the worldwide manufacturing of OTFTs is the degradation with time in ambient operating environments [19][20][21] .…”

Section: ■ Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Oxidation of Rubrene Thin Films: An Electronic Structure Study

et al. 2014

View full text Add to dashboard Cite

The performances of organic semiconductor devices are crucially linked with their stability at the ambient atmosphere. The evolution of electronic structures of 20 nm thick rubrene films exposed to ambient environment with time has been studied by UV and X-ray photoemission spectroscopy (UPS and XPS), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, and density functional theory (DFT). XPS, NEXAFS data, and DFT calculated values suggest the formation of rubrene-epoxide and rubrene-endoperoxide through reaction of tetracene backbone with oxygen of ambient environment. Angle dependent XPS measurement indicates that the entire probed depth of the films reacts with oxygen by spending only about 120 min in ambient environment. The HOMO peak of pristine rubrene films almost disappears by exposure of 120 min to ambient environment. The evolution of the valence band (occupied states) and NEXAFS (unoccupied states) spectra indicates that the films become more insulating with exposure as the HOMO-LUMO gap increases on oxidation. Oxygen induced chemical reaction completely destroys the delocalized nature of the electron distribution in the tetracene backbone of rubrene. The results are relevant to the performance and reliability of rubrene based devices in the environment.

show abstract

mentioning

confidence: 93%

Section: ■ Introductionmentioning

confidence: 99%

Oxidation of Rubrene Thin Films: An Electronic Structure Study

et al. 2014

View full text Add to dashboard Cite

show abstract

“…However, illumination in an oxygen atmosphere with an intense white light (e.g., 2-3 hours at an integrated power density of 85 mW cm À2 ) triggers surface photo-oxidation and long-lasting oxygen diffusion into the bulk that may continue for hours or days, even after the illumination is turned off, resulting in the formation of oxygen-induced traps throughout the crystal. 33,[34][35][36][37] However, there are clear indications that both shallow and deep trap states are formed in this process, 23,38 with their relative fractions depending on whether oxygen forms covalent or van der Waals bonds with the organic molecules, as well as on the prevalence of different oxidative states of the same molecule in the former case. It was unambiguously demonstrated that oxygen incorporation always reduces both dark and photo-conductivity of rubrene, leading to qualitative changes in the photocurrent excitation spectra.…”

mentioning

confidence: 99%

Dynamic character of charge transport parameters in disordered organic semiconductor field-effect transistors

Chen

Lee

et al. 2012

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

In this perspective article, we discuss the dynamic instability of charge carrier transport in a range of popular organic semiconductors. We observe that in many cases field-effect mobility, an important parameter used to characterize the performance of organic field-effect transistors (OFETs), strongly depends on the rate of the gate voltage sweep during the measurement. Some molecular systems are so dynamic that their nominal mobility can vary by more than one order of magnitude, depending on how fast the measurements are performed, making an assignment of a single mobility value to devices meaningless. It appears that dispersive transport in OFETs based on disordered semiconductors, those with a high density of localized trap states distributed over a wide energy range, is responsible for the gate voltage sweep rate dependence of nominal mobility. We compare such rate dependence in different materials and across different device architectures, including pristine and trap-dominated single-crystal OFETs, as well as solution-processed polycrystalline thin-film OFETs. The paramount significance given to a single mobility value in the organic electronics community and the practical importance of OFETs for applications thus suggest that such an issue, previously either overlooked or ignored, is in fact a very important point to consider when engaging in fundamental studies of charge carrier mobility in organic semiconductors or designing applied circuits with organic semiconductors.

show abstract

“…X. Song et al [ 7 ] used photoemission and X-ray absorption spectroscopies to show that the HOMO of oxidized rubrene is ≈ 1 eV deeper than that of pure rubrene and hence can not account for formation of acceptor-like states within the bandgap. Therefore, in this contribution, we set out to answer the following questions: What triggers oxygen incorporation in molecular crystals?…”

mentioning

confidence: 99%

Photon‐Assisted Oxygen Diffusion and Oxygen‐Related Traps in Organic Semiconductors

et al. 2011

View full text Add to dashboard Cite

Organic molecular crystals represent an excellent platform for fundamental studies of optoelectronic properties of organic semiconductors. [ 1 ] Rubrene, in particular, has attracted significant attention due to a very low density of charge traps, recordhigh charge carrier mobility, and a very large micrometer-scale exciton diffusion length. [ 2 , 3 ] In this study, using rubrene as a model compound questions related to the interaction of crystalline organic semiconductors with oxygen are addressed. Although the chemistry of photo-oxidation of rubrene in solution and gas phases is understood based on self-sensitized photo-oxidation (see for example, Ref. [ 4 ] ), the mechanism of oxygen incorporation and its effect on the photophysical properties of crystalline rubrene still remain controversial. Mitrofanov et al. [ 5 ] identifi ed an oxygen-related in-gap band in photooxidized rubrene by means of a two-photon photoluminescence excitation spectroscopy and showed that oxygen is concentrated near the surface of the crystals. Krellner et al. [ 6 ] revealed that an oxygen-related impurity forms an acceptor-like in-gap state in rubrene with an energy ≈ 0.28 eV above the highest occupied molecular orbital (HOMO). X. Song et al. [ 7 ] used photoemission and X-ray absorption spectroscopies to show that the HOMO of oxidized rubrene is ≈ 1 eV deeper than that of pure rubrene and hence can not account for formation of acceptor-like states within the bandgap. Therefore, in this contribution, we set out to answer the following questions: What triggers oxygen incorporation in molecular crystals? What is its effect on the conductivity of these materials? What dictates the depth distribution of oxygen defects?In this paper, a highly sensitive trap characterization technique based on wavelength-and polarization-resolved photocurrent excitation spectroscopy of single crystalline organic semiconductors is developed and applied for the fi rst time. The method reveals that even a brief illumination of organic molecular crystals in an oxygen atmosphere triggers a long-term oxygen diffusion that continues in the dark and results in formation of oxygen-related traps in the crystal at the length scale ≈ α − 1 , where α is the light absorption coeffi cient. For example, in rubrene, no oxygen diffusion occurs in the dark without an initial photoexcitation, even if the samples are stored in pure oxygen. Our studies show that oxygen incorporation reduces both the dark-and photoconductivity of rubrene and leads to qualitative changes in the photocurrent excitation spectra that can be used for the characterization of traps in molecular crystals.We take advantage of the anisotropic molecular packing of rubrene which results in an optical absorption coeffi cient, α ( λ , θ ), that is both wavelength, λ , and polarization angle, θ , dependent, as is the case in many molecular crystals. [ 8 ] Here, θ is defi ned as an angle between the polarization of linearly polarized light and the a -axis of rubrene (light is always at normal incidence to the...

show abstract

Role of oxygen incorporation in electronic properties of rubrene films

Cited by 23 publications

References 22 publications

Oxidation of Rubrene Thin Films: An Electronic Structure Study

Oxidation of Rubrene Thin Films: An Electronic Structure Study

Dynamic character of charge transport parameters in disordered organic semiconductor field-effect transistors

Photon‐Assisted Oxygen Diffusion and Oxygen‐Related Traps in Organic Semiconductors

Contact Info

Product

Resources

About