Amorphous oxide alloys as interfacial layers with broadly tunable electronic structures for organic photovoltaic cells

Zhou, Nan; Kim, Myung Gil; Loser, Stephen; Smith, Jeremy; Yoshida, Hiroyuki; Guo, Xugang; Song, Charles Kiseok; Jin, Hosub; Chen, Zhihua; Yoon, Seok Min; Freeman, Arthur J; Chang, Robert P. H.; Facchetti, Antonio; Marks, Tobin J.

doi:10.1073/pnas.1508578112

Cited by 43 publications

(36 citation statements)

References 66 publications

(82 reference statements)

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“…Organic photovoltaics, a promising application in next‐generation energy‐harvesting technology, have attracted considerable attention with great advantages of tailored molecular structures, low cost, solution processability, light weight, flexibility, large‐area fabrication techniques, and so on . However, the short exciton‐diffusion length, the small donor–acceptor interface, and the discontinuous carrier‐transport pathways restrain the photovoltaic effect of organic materials.…”

Section: Advanced and Emerging Functionality Of Organic Cocrystalsmentioning

confidence: 99%

Cocrystal Engineering: A Collaborative Strategy toward Functional Materials

et al. 2019

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materials, [9][10][11][12] which are crystalline singlephase materials composed of two or more different compounds generally in a stoichiometric ratio, [13] providing a platform for unveiling the structure-property relationships at a molecular level. [14] The building blocks are assembled via noncovalent interactions, offering the opportunity to achieve noncovalent synthesis of functional molecules. [15] Compared with the traditional covalent synthesis, cocrystal engineering offers numerous advantages, including: 1) avoiding complicated synthesis procedures, and cocrystal assemblies have been successfully fabricated by the vapor methods and solution-processing methods in a facile and low-cost way; 2) manipulating intermolecular interactions through selecting suitable conformers from a plentiful supply of raw materials, resulting in tunable structures, morphologies, and sizes; 3) achieving rare and multifunctional properties through a collaborative strategy in distinct constituent units, which are difficult to realize for individual components. [16][17][18] Cocrystal engineering began to draw much attention since the exploration of the metal conductive tetrathiafulvalene-7,7,8,8-tetracyanoquinodimethane (TTF-TCNQ) cocrystals in 1973. [19] The peculiar conductivity in organic materials makes it possible for cocrystals to serve as organic electrodes, which can effectively lower the contact resistance and further improve device performance. Encouraged by this, cocrystals can serve as a breakthrough and provide an opportunity to discover novel physicochemical properties, which are far beyond the performance of single materials. In this respect, dielectric response [20] and nonlinear optics [21,22] are also realized through rational design of each component, which is absent in their constitute components. Even more, the bottom-up supramolecular assembly provides the opportunity to equip them with the individual properties of the donor or acceptor to create multifunctional materials. [23] Typically, ambipolar charge transport can be generated by coassembling p-type semiconductors and n-type ones, and the charge-carrier mobility is now up to 1.57 cm 2 V −1 s −1 for holes and 0.47 cm 2 V −1 s −1 for electrons. [24] To date, these exciting results accelerate the investigations of organic functional cocrystals, such as room-temperature ferroelectricity, [25][26][27] optical waveguide properties, [28,29] pure organic room-temperature phosphorescent properties, [30][31][32] stimulusresponse (e.g., mechanical stress, [33,34] heat, [35,36] or solvent [37] ) characteristics, photovoltaics, [38] and near-infrared photothermal (PT) conversion and imaging, [39] etc.Cocrystal engineering with a noncovalent assembly feature by simple constituent units has inspired great interest and has emerged as an efficient and versatile route to construct functional materials, especially for the fabrication of novel and multifunctional materials, due to the collaborative strategy in the distinct constituent units. Meanwhile, the precise crystal a...

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Section: Advanced and Emerging Functionality Of Organic Cocrystalsmentioning

confidence: 99%

Cocrystal Engineering: A Collaborative Strategy toward Functional Materials

et al. 2019

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“…Figure illustrates the materials and device structures, along with the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) for each material in the photodiode. Interfacial layers are incorporated to adjust electrode work functions, using zinc oxide with polyethylenimine (PEIE) for the cathode and molybdenum oxide (MoO 3 ) for the anode. As a side note, the molybdenum oxide interface is shown to aid in hole extraction but does not serve as an electron‐blocking layer in organic BHJ cells.…”

Section: Device Structure and Performance Metric Definitionsmentioning

confidence: 99%

Elucidating the Detectivity Limits in Shortwave Infrared Organic Photodiodes

Yao

London

et al. 2018

Adv Funct Materials

107

173

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While only few organic photodiodes have photoresponse past 1 µm, novel shortwave infrared (SWIR) polymers are emerging, and a better understanding of the limiting factors in narrow bandgap devices is critically needed to predict and advance performance. Based on state-of-the-art SWIR bulk heterojunction photodiodes, this work demonstrates a model that accounts for the increasing electric-field dependence of photocurrent in narrow bandgap materials. This physical model offers an expedient method to pinpoint the origins of efficiency losses, by decoupling the exciton dissociation efficiency and charge collection efficiency in photocurrent-voltage measurements. These results from transient photoconductivity measurements indicate that the main loss is due to poor exciton dissociation, particularly significant in photodiodes with low-energy charge-transfer states. Direct measurements of the noise components are analyzed to caution against using assumptions that could lead to an overestimation of detectivity. The devices show a peak detectivity of 5 × 10 10 Jones with a spectral range up to 1.55 µm. The photodiodes are demonstrated to quantify the ethanol-water content in a mixture within 1% accuracy, conveying the potential of organics to enable economical, scalable detectors for SWIR spectroscopy.

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“…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). In this work, we designed transparent amorphous oxide semiconductors for EILs and ETLs because these materials form uniform thin films over large areas around room temperature (RT) with high visible transparency.…”

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.

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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Amorphous oxide alloys as interfacial layers with broadly tunable electronic structures for organic photovoltaic cells

Cited by 43 publications

References 66 publications

Cocrystal Engineering: A Collaborative Strategy toward Functional Materials

Cocrystal Engineering: A Collaborative Strategy toward Functional Materials

Elucidating the Detectivity Limits in Shortwave Infrared Organic Photodiodes

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

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