Chemical Interaction, Space-Charge Layer, and Molecule Charging Energy for a TiO<sub>2</sub>/TCNQ Interface

Martínez, José I.; Ortega, José; Rangan, Sylvie; Ruggieri, Charles; Bartynski, Robert

doi:10.1021/acs.jpcc.5b07045

Cited by 9 publications

(34 citation statements)

References 33 publications

(84 reference statements)

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“…14,15,47 In UPS and XPS, the kinetic energy of electrons ejected from the sample by excitation from monoenergetic photons reflects the density of occupied states in the system. In IPS the photon energy distribution associated with the decay of a monoenergetic beam of electrons directed to the sample reflects the density of unoccupied states.…”

Section: Experiments and Techniquesmentioning

confidence: 99%

“…Core levels were probed using X-ray photoemission spectroscopy excited by Al Kα radiation, and the valence band electrons were examined using He II (40.8 eV) excited ultraviolet photoemission spectroscopy. 14,15 In both cases, electron energy distribution was measured using a cylindrical mirror analyser. IPS was performed using a grating spectrometer with a primary electron energy of 20.3 eV.…”

Section: Experiments and Techniquesmentioning

confidence: 99%

“…For both clean and sensitized surfaces, the secondary electron cut-off was measured on biased samples using He I (21.1 eV) to determine the organic electron affinity and the induced interface dipole. 14,15 In order to study the adsorbate geometry for some of the organic molecule, STM measurements were performed on an Omicron VT-STM at 300 K. In some of the figures presented in this paper, we show the energy level alignment obtained from these experiments.…”

Section: Experiments and Techniquesmentioning

confidence: 99%

“…These interfaces have been studied using a combination of experimental and theoretical techniques in previous publications. [14][15]18 Herein, we review the main results and discuss the similarities and differences found in these different paradigmatic cases, putting these results in a more general perspective. Also, in order to get new insights (and better understand the connection between these different cases), we present a new proof-of-concept analysis in which we apply a "theoretical" bias potential between the organic and the oxide, Δ, and analyse the energy level alignment at these interfaces as a function of Δ.…”

Section: Introductionmentioning

confidence: 97%

“…12 However, effects such as electron charge transfer upon molecular adsorption with possible space charge layer formation in the oxide, as well as the nature of the chemical interaction of the organic on the oxide surface, are important considerations in any attempt to fully understand such interfaces. [13][14][15][16][17][18] In this perspective we analyse the physicochemical mechanisms that control energy level alignment at the interface between a prototypical metal oxide surface, TiO 2 (110), and different organic monolayers with dissimilar properties, PTCDA, 18 Zn-TPP 15 and TCNQ.…”

Section: Introductionmentioning

confidence: 99%

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Unveiling universal trends for the energy level alignment in organic/oxide interfaces

Martínez

Ortega

Rangan

et al. 2017

Phys. Chem. Chem. Phys.

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In this perspective we present a comprehensive analysis of the energy level alignment at the interface between an organic monolayer (organic = perylenetetracarboxylic dianhydride, PTCDA, zinc tetraphenylporphyrin, Zn-TPP, and tetracyanoquinodimethane, TCNQ) and a prototypical oxide surface, TiO 2 (110), looking for universal behaviours. PTCDA shows a physisorbed interaction with TiO 2 and a small interface dipole potential with its highest occupied molecular orbital (HOMO) energy level located in the oxide energy gap and the lowest occupied molecular orbital (LUMO) energy level located above the oxide conduction band minimum, E C . We analyse how the interface barrier depends on an external bias potential between the organic layer and the oxide surface, Δ, and find for this interface that the screening parameter S = d|(E C -HOMO)|dΔ is close to 1. In the second case, the Zn-TPP monolayer shows a moderate chemisorbed interaction with some charge transfer from the molecule to the oxide and a significant interface dipole potential, in such a way that S decreases to around 0.8. In the TCNQ/TiO 2 (110) case, the TCNQ molecules present a strong chemical interaction with the oxide; the LUMO energy level is located in the oxide energy gap in such a way that one electron is transferred from the oxide to the organic molecule; we also find that in this case S ≈ 0.5. All these cases can be integrated within a universal behaviour when (E C -HOMO) is calculated as a function of Δ; that function presents a zig-zag curve with a central part having an S-slope, and two plateaus associated with either the LUMO or the HOMO energy levels crossing the oxide Fermi level. In these plateaus, a Coulomb blockade regime arises and a space charge layer develops in the oxide surface.

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Section: Experiments and Techniquesmentioning

confidence: 99%

Section: Experiments and Techniquesmentioning

confidence: 99%

Section: Experiments and Techniquesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Unveiling universal trends for the energy level alignment in organic/oxide interfaces

Martínez

Ortega

Rangan

et al. 2017

Phys. Chem. Chem. Phys.

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Molecule‐Doped Nickel Oxide: Verified Charge Transfer and Planar Inverted Mixed Cation Perovskite Solar Cell

et al. 2018

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Both conductivity and mobility are essential to charge transfer by carrier transport layers (CTLs) in perovskite solar cells (PSCs). The defects derived from generally used ionic doping method lead to the degradation of carrier mobility and parasite recombinations. In this work, a novel molecular doping of NiO hole transport layer (HTL) is realized successfully by 2,2'-(perfluoronaphthalene-2,6-diylidene)dimalononitrile (F6TCNNQ). Determined by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy, the Fermi level (E ) of NiO HTLs is increased from -4.63 to -5.07 eV and valence band maximum (VBM)-E declines from 0.58 to 0.29 eV after F6TCNNQ doping. The energy level offset between the VBMs of NiO and perovskites declines from 0.18 to 0.04 eV. Combining with first-principle calculations, electrostatic force microscopy is applied for the first time to verify direct electron transfer from NiO to F6TCNNQ. The average power conversion efficiency of CsFAMA mixed cation PSCs is boosted by ≈8% depending on F6TCNNQ-doped NiOx HTLs. Strikingly, the champion cell conversion efficiency of CsFAMA mixed cations and MAPbI -based devices gets to 20.86% and 19.75%, respectively. Different from passivation effect, the results offer an extremely promising molecular doping method for inorganic CTLs in PSCs. This methodology definitely paves a novel way to modulate the doping in hybrid electronics more than perovskite and organic solar cells.

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Novel Molecular Doping Mechanism for n‐Doping of SnO₂ via Triphenylphosphine Oxide and Its Effect on Perovskite Solar Cells

et al. 2019

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Molecular doping of inorganic semiconductors is a rising topic in the field of organic/inorganic hybrid electronics. However, it is difficult to find dopant molecules which simultaneously exhibit strong reducibility and stability in ambient atmosphere, which are needed for n‐type doping of oxide semiconductors. Herein, successful n‐type doping of SnO2 is demonstrated by a simple, air‐robust, and cost‐effective triphenylphosphine oxide molecule. Strikingly, it is discovered that electrons are transferred from the R3P+O−σ‐bond to the peripheral tin atoms other than the directly interacted ones at the surface. That means those electrons are delocalized. The course is verified by multi‐photophysical characterizations. This doping effect accounts for the enhancement of conductivity and the decline of work function of SnO2, which enlarges the built‐in field from 0.01 to 0.07 eV and decreases the energy barrier from 0.55 to 0.39 eV at the SnO2/perovskite interface enabling an increase in the conversion efficiency of perovskite solar cells from 19.01% to 20.69%.

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Chemical Interaction, Space-Charge Layer, and Molecule Charging Energy for a TiO₂/TCNQ Interface

Cited by 9 publications

References 33 publications

Unveiling universal trends for the energy level alignment in organic/oxide interfaces

Unveiling universal trends for the energy level alignment in organic/oxide interfaces

Molecule‐Doped Nickel Oxide: Verified Charge Transfer and Planar Inverted Mixed Cation Perovskite Solar Cell

Novel Molecular Doping Mechanism for n‐Doping of SnO₂ via Triphenylphosphine Oxide and Its Effect on Perovskite Solar Cells

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Chemical Interaction, Space-Charge Layer, and Molecule Charging Energy for a TiO2/TCNQ Interface

Cited by 9 publications

References 33 publications

Unveiling universal trends for the energy level alignment in organic/oxide interfaces

Unveiling universal trends for the energy level alignment in organic/oxide interfaces

Molecule‐Doped Nickel Oxide: Verified Charge Transfer and Planar Inverted Mixed Cation Perovskite Solar Cell

Novel Molecular Doping Mechanism for n‐Doping of SnO2 via Triphenylphosphine Oxide and Its Effect on Perovskite Solar Cells

Contact Info

Product

Resources

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Chemical Interaction, Space-Charge Layer, and Molecule Charging Energy for a TiO₂/TCNQ Interface

Novel Molecular Doping Mechanism for n‐Doping of SnO₂ via Triphenylphosphine Oxide and Its Effect on Perovskite Solar Cells