Thin-film metal oxides in organic semiconductor devices: their electronic structures, work functions and interfaces

Greiner, Mark; Lu, Zheng‐Hong

doi:10.1038/am.2013.29

Cited by 350 publications

(324 citation statements)

References 224 publications

(200 reference statements)

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“…We attribute this low value to the presence of anionic electrons existing at interstitial positions without belonging to specific orbitals of the structure's ions (27). The work function of a-ZSO (3.5 eV) is significantly lower than that of typical transparent oxide semiconductors (20,28) including ZnO (4.3eV), as is summarized in Fig. 2C.…”

Section: Resultsmentioning

confidence: 91%

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Transparent amorphous oxide semiconductors for organic electronics: Application to inverted OLEDs

Hosono

Kim

Yoshitake

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

114

112

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Efficient electron transfer between a cathode and an active organic layer is one key to realizing high-performance organic devices, which require electron injection/transport materials with very low work functions. We developed two wide-bandgap amorphous (a-) oxide semiconductors, a-calcium aluminate electride (a-C12A7:e) and a-zinc silicate (a-ZSO). A-ZSO exhibits a low work function of 3.5 eV and high electron mobility of 1 cm 2 /(V · s); furthermore, it also forms an ohmic contact with not only conventional cathode materials but also anode materials. A-C12A7:e has an exceptionally low work function of 3.0 eV and is used to enhance the electron injection property from a-ZSO to an emission layer. The inverted electron-only and organic light-emitting diode (OLED) devices fabricated with these two materials exhibit excellent performance compared with the normal type with LiF/Al. This approach provides a solution to the problem of fabricating oxide thin-film transistor-driven OLEDs with both large size and high stability.inverted OLEDs | electron injection | electron transport | amorphous oxide semiconductor | low work function material E lectronic and photonic devices based on organic semiconductors have attracted much attention due to their intrinsic characteristics that are difficult to achieve in inorganic semiconductors, such as flexibility and the capability of precise molecular design of active organic layers (1-3). However, organic devices suffer from the material properties that organic semiconductors in general have: rather high lowest unoccupied molecular orbital (LUMO) levels and low electron mobilities, such as 10 −6 to 10 −3 cm 2 /(V·s). This leads to inefficiency in electron injection/transport between an electrode and an organic active layer and a large energy loss. In other words, the creation of materials suitable for efficient electron injection layers (EILs) and electron transport layers (ETLs), with very low work functions, reasonable chemical stability, and high electron mobility, should lead to organic devices with improved performance.Organic light-emitting diodes (OLEDs) are regarded as nextgeneration flat-panel displays (4). Although small high-resolution OLED displays are used widely for smart phones/tablets, and large televisions are being commercialized, several issues still remain, such as lifetime, image sticking, power consumption, and production cost (5). The recent high-resolution OLED pixels (6) with reduced aperture ratios [areal ratio of thin-film transistor (TFT) to pixel] raise the importance of the top emissiontype structure for practical use. For large OLEDs, it is unrealistic to use low-temperature polycrystalline silicon (LTPS) TFTs for backplanes. Only oxide TFTs, as represented by a-In-Ga-Zn-O (a-IGZO) (7), are practical candidates for the backplane (8, 9). The current small OLEDs use normal-type structures combined with p-channel LTPS TFTs. However, only n-channel TFTs are possible for oxide TFTs in actual applications. Simple substitution of the p-channel LTPS TFTs wi...

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Section: Resultsmentioning

confidence: 91%

“…Metal oxide thin films are attractive as carrier injection/transport layers (20). In particular, transparent amorphous oxide semiconductors are very favorable due to their process compatibility, chemical stability, optical transparency, and wide tunability of various relevant properties (21).…”

Section: Materials Designmentioning

confidence: 99%

Transparent amorphous oxide semiconductors for organic electronics: Application to inverted OLEDs

Hosono

Kim

Yoshitake

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

114

112

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“…Another feature of the studied TMOs is their peculiarly large work function (Φ TMO ) and how it changes as a result of redox environments, contamination by adsorbates and chemical interaction with adjacent interfaces [27]. In this sense, the Φ TMO values after thermal evaporation will be several meV smaller than those of in-situ metal oxidation.…”

Section: Properties Of Transition Metal Oxidesmentioning

confidence: 98%

“…Such n-type semiconductivity generates from intrinsic oxygen vacancies in their atomic structure (i.e. Oxidation state transitions and generation of states within the E gap have been reported as characteristic features of oxygen loss during TMO deposition [27]. In order to identify such vacancy-related effects, the XPS photoemission spectra were analyzed.…”

Section: Properties Of Transition Metal Oxidesmentioning

confidence: 99%

Transition metal oxides as hole-selective contacts in silicon heterojunctions solar cells

Gerling

Mahato

Morales-Vilches

et al. 2016

Solar Energy Materials and Solar Cells

349

281

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This work reports on a comparative study comprising three transition metal oxides, MoO 3 , WO 3 and V 2 O 5 , acting as front p-type emitters for n-type crystalline silicon heterojunction solar cells. Owing to their high work functions (>5 eV) and wide energy band gaps, these oxides act as transparent hole-selective contacts with semiconductive properties that are determined by oxygen-vacancy defects (MoO 3-x ), as confirmed by x-ray photoelectron spectroscopy. In the fabricated hybrid structures, 15 nm thick transition metal oxide layers were deposited by vacuum thermal evaporation. Of all three devices, the V 2 O 5 /n-silicon heterojunction performed the best with a conversion efficiency of 15.7% and an open-circuit voltage of 606 mV, followed by MoO 3 (13.6%) and WO 3 (12.5%). These results bring into view a new silicon heterojunction solar cell concept with advantages such as the absence of toxic dopant gases and a simplified low-temperature fabrication process.

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“…[181,182] Figure 4. a) Silicon heterojunction (SHJ) solar cell structure and b) zoom-in of the front TCO layer indicating the 1. metal/TCO interface, 2. bulk and 3.…”

Section: Progress Reportmentioning

confidence: 99%

Transparent Electrodes for Efficient Optoelectronics

Morales‐Masis

Wolf

Woods‐Robinson

et al. 2017

Adv Elect Materials

348

288

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With the development of new generations of optoelectronic devices that combine high performance and novel functionalities (e.g., flexibility/bendability, adaptability, semi or full transparency), several classes of transparent electrodes have been developed in recent years. These range from optimized transparent conductive oxides (TCOs), which are historically the most commonly used transparent electrodes, to new electrodes made from nano‐ and 2D materials (e.g., metal nanowire networks and graphene), and to hybrid electrodes that integrate TCOs or dielectrics with nanowires, metal grids, or ultrathin metal films. Here, the most relevant transparent electrodes developed to date are introduced, their fundamental properties are described, and their materials are classified according to specific application requirements in high efficiency solar cells and flexible organic light‐emitting diodes (OLEDs). This information serves as a guideline for selecting and developing appropriate transparent electrodes according to intended application requirements and functionality.

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Thin-film metal oxides in organic semiconductor devices: their electronic structures, work functions and interfaces

Cited by 350 publications

References 224 publications

Transparent amorphous oxide semiconductors for organic electronics: Application to inverted OLEDs

Transparent amorphous oxide semiconductors for organic electronics: Application to inverted OLEDs

Transition metal oxides as hole-selective contacts in silicon heterojunctions solar cells

Transparent Electrodes for Efficient Optoelectronics

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