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Regulating Charge and Exciton Distribution in High-Performance Hybrid White Organic Light-Emitting Diodes with n-Type Interlayer Switch

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Nano-Micro Letters 2017年第4期9卷 3-10页

作者： Dongxiang Luo Yanfeng Yang Ye Xiao Yu Zhao Yibin Yang Baiquan Liu School of Materials and Energy Guangdong University of Technology Institute of Polymer Optoelectronic Materials and Devices State Key Laboratory of Luminescent Materials and DevicesSouth China University of Technology luminous Center of Excellence for Semiconductor Lighting and Displays School of Electrical and Electronic Engineering Nanyang Technological University

The interlayer(IL) plays a vital role in hybrid white organic light-emitting diodes(WOLEDs); however,only a negligible amount of attention has been given to n-type ILs. Herein, the n-type IL, for the first time,has been demonstrated to achieve a high efficiency, high color rendering index(CRI), and low voltage *** device exhibits a maximum total efficiency of 41.5 lm W^(-1), the highest among hybrid WOLEDs with n-type ILs. In addition, high CRIs(80–88) at practical luminances(C1000 cd m^(-2)) have been obtained, satisfying the demand for indoor lighting. Remarkably, a CRI of 88 is the highest among hybrid WOLEDs. Moreover, the device exhibits low voltages, with a turn-on voltage of only 2.5 V([1 cd m^(-2)), which is the lowest among hybrid WOLEDs. The intrinsic working mechanism of the device has also been explored; in particular, the role of n-type ILs in regulating the distribution of charges and excitons has been unveiled. The findings demonstrate that the introduction of n-type ILs is effective in developing high-performance hybrid WOLEDs.

关键词： White light Hybrid Interlayer Color rendering index Organic light-emitting diodes

Regeneration of adhesive tail pad scales in the New Zealand gecko (Hoplodactylus maculatus) (Reptilia, Squamata; Lacertilia) can serve as an experimental model to analyze setal formation in lizards generally

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Zoological Research 2017年第4期38卷 191-197页

作者： Lorenzo Alibardi Benno Meyer-Rochow Comparative Histolab and Department of Bigea Dipartimento di Biologia University of Bologna Bologna 40126 Italy Research Institute of luminous Organisms Tokyo 100-1623 Japan Department of Genetics and Physiology Oulu University Oulu FIN 90140 Finland

During the regeneration of the tail in the arboreal New Zealand gecko （Hoplodactylus maculatus） a new set of tail scales, modified into pads bearing setae 5-20 μm long, is also regenerated. Stages of the formation of these specialized scales from epidermal pegs that invaginate the dermis of the regenerating tail are described on the basis of light and electron microscopic images. Within the pegs a differentiating clear layer interfaces with the spinulae and setae of the Oberh^utchen according to a process similar to that described for the digital pads. A layer of clear cytoplasm surrounds the growing tiny setae and eventually comities around them and their spatular ends, later leaving the new setae free- standing on the epidermal surface. The fresh adhesive pads help the gecko to maintain the prehensile function of its regenerated tail as together with the axial skeleton （made of a cylinder of elastic cartilage） the pads allow the regenerated tail to curl around twigs and small branches just like the original tail. The regeneration of caudal adhesive pads represents an ideal system to study the cellular processes that determine setal formation under normal or experimental manipulation as the progressive phases of the formation of the setae can be sequentially analyzed.

关键词： Gecko lizard Regeneration Epidermis Tail pad scales Adhesion Prehensile function Ultrastructure

New observations-with older ones reviewed-on mass migrations in millipedes based on a recent outbreak on Hachijojima(Izu Islands) of the polydesmid diplopod(Chamberlinius hualienensis,Wang 1956):Nothing appears to make much sense

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Zoological Research 2015年第3期36卷 119-132页

作者： Victor Benno MEYER-ROCHOW Research Institute of luminous Organisms Department of Biology (El?inmuseo) University of Oulu

Mass aggregations and migrations of millipedes despite numerous attempts to find causes for their occurrences are still an enigma. They have been reported from both southern and northern hemisphere countries, from highlands and lowlands of both tropical and temperate regions and they can involve species belonging to the orders Julida and Spirobolida, Polydesmida and Glomerida. According to the main suggestions put forward in the past, mass occurrences in Diplopoda occur：（1） because of a lack of food and a population increase beyond sustainable levels;（2） for the purpose of reproduction and in order to locate suitable oviposition sites;（3） to find overwintering or aestivation sites;（4） because of habitat disruption and changes in the local environment;（5） as a consequence of weather conditions the year（or winter and spring） before. A recent outbreak（November 2014） of a mass migration of the polydesmid Chamberlinius hualienensis Wang 1956 on the Japanese Izu Island of Hachijojima 300 km to the south of Tokyo gave this author an opportunity to review the existing literature on millipede mass migrations and to carry out additional observations on the phenomenon in the field as well as the laboratory. Hitherto unreported heavy infestations with phoretic deutonymphs of the mite Histiostoma sp. as well as dense populations of internal rhabditid nematodes（Oscheius cf. necromena and an unidentified species of the genus Fictor）, suggest that infestations of this kind could be necromenic and either have been a contributing factor for the mass migration or been a consequence of so manyindividuals occurring together at close proximity. It is concluded that mass migrations and aggregations in millipedes do not have one common cause, but represent phenomena that often are seasonally recurring events and appear identical in their outcome, but which have evolved as responses to different causes in different millipede taxa and therefore need to be examined on a case-to-case basis.

关键词： Myriapoda Spawning migration Aggregation behaviour Diplopod commensals and parasites

Exciton dynamics in luminescent carbon nanodots： Electron-hole exchange interaction

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Nano Research 2016年第2期9卷 549-559页

作者： Bo Peng Xin Lu Shi Chen Cheng Hon Alfred Huan Qihua Xiong Evren Mutlugun Hilmi Volkan Demir Siu Fung Yu Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University Singapore 637371 Singapore NOVITAS Nanoelectronics Centre of Excellence School of Electrical and Electronic Engineering Nanyang Technological UniversitySingapore 639798 Singapore luminous Centre of Excellence for Semiconductor Lighting and Displays School of Electrical and Electronic Engineering NanyangTechnological University Singapore 639798 Singapore Department of Applied Physics the Hong Kong Polytechnic University Hong Hum Hong Kong SAR China

The electron-hole exchange interaction significantly influences the optical properties of excitons and radiative decay. However, exciton dynamics in luminescent carbon dots （Cdots） is still not clear. In this study, we have developed a simple and efficient one-step strategy to synthesize luminescent Cdots using the pyrolysis of oleylamine. The sp^2 clusters of a few aromatic rings are responsible for the observed blue photoluminescence. The size of these clusters can be tuned by controlling the reaction time, and the energy gap between the π-π＊ states of the sp^2 domains decreases as the sp^2 cluster size increases. More importantly, the strong electron-hole exchange interaction results in the splitting of the exciton states of the sp^2 clusters into the singlet-bright and triplet-dark states with an energy difference ΔE, which decreases with increasing sp^2 cluster size owing to the reduction of the confinement energy and the suppression of the electron-hole exchange interaction.

关键词： carbon dots photoluminescence pyrolysis electron-hole exchange interaction energy splitting

Organic semiconductor heterojunctions: electrode-independent charge injectors for high-performance organic light-emitting diodes

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Light(Science & Applications) 2016年第1期5卷 570-576页

作者： Yong-Hua Chen Dong-Ge Ma Heng-Da Sun Jiang-Shan Chen Qing-Xun Guo Qiang Wang Yong-Biao Zhao State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied ChemistryChinese Academy of SciencesChangchun 130022China Department of Macromolecular Science and Engineering School of EngineeringCase Western Reserve UniversityClevelandOH 44106USA School of Materials Science and Engineering Shaanxi Normal UniversityXi’an 710062China luminous Center of Excellence for Semiconductor Lighting and DisplaysSchool of Electrical and Electronic EngineeringNanyang Technological UniversitySingapore 639798Singapore

Organic light-emitting diodes(OLEDs)are driven by injected charges from an anode and a *** low and high work function metals are necessary for the effective injection of electrons and holes,***,we introduce a fully novel design concept using organic semiconductor heterojunctions(OSHJs)as the charge injectors for achieving highly efficient OLEDs,regardless of the work functions of the *** contrast to traditional injected charges from the electrodes,the injected charges originate from the *** device performance was shown to be significantly improved in efficiency and stability compared to conventional ***,the OLEDs based on OSHJs as charge injectors still exhibited an impressive performance when the low work function Al was replaced by air-and chemistry-stable high work function metals,such as Au,Ag,and Cu,as the cathode contact,which has been suggested to be difficult in conventional *** concept challenges the conventional design approach for the injection of charges and allows for the realization of practical applications of OLEDs with respect to high efficiency,selectable electrodes,and a long lifetime.

关键词： charge injection OLEDs organic semiconductor heterojunctions

All-optical control of exciton flow in a colloidal quantum well complex

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Light(Science & Applications) 2020年第1期9卷 1749-1756页

作者： Junhong Yu Manoj Sharma Ashma Sharma Savas Delikanli Hilmi Volkan Demir Cuong Dang luminous Centre of Excellence for Semiconductor Lighting and DisplaysSchool of Electrical and Electronic EngineeringThe Photonics Institute(TPI)Nanyang Technological University50 Nanyang Avenue639798 SingaporeSingapore Department of Electrical and Electronics Engineering and Department of Physics UNAM-Institute of Materials Science and NanotechnologyBilkent UniversityBilkent06800 AnkaraTurkey School of Physical and Mathematical Sciences Division of Physics and Applied PhysicsNanyang Technological University639798 SingaporeSingapore CINTRA UMI CNRS/NTU/THALES 3288 Research Techno Plaza50 Nanyang DriveBorder X BlockLevel 6637553 SingaporeSingapore

Excitonics,an alternative to romising for processing information since semiconductor electronics is rapidly approaching the end of Moore’s ***,the development of excitonic devices,where exciton flow is controlled,is mainly focused on electric-field modulation or exciton polaritons in high-Q ***,we show an alloptical strategy to manipulate the exciton flow in a binary colloidal quantum well complex through mediation of the Förster resonance energy transfer(FRET)by stimulated *** the spontaneous emission regime,FRET naturally occurs between a donor and an *** contrast,upon stronger excitation,the ultrafast consumption of excitons by stimulated emission effectively engineers the excitonic flow from the donors to the ***,the acceptors’stimulated emission significantly accelerates the exciton flow,while the donors’stimulated emission almost stops this *** this basis,a FRET-coupled rate equation model is derived to understand the controllable exciton flow using the density of the excited donors and the unexcited *** results will provide an effective alloptical route for realizing excitonic devices under room temperature operation.

关键词： process flow quantum

High-efficiency CdTe/CdS core/shell nanocrystals in water enabled by photo-induced colloidal hetero-epitaxy of CdS shelling at room temperature

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Nano Research 2015年第7期8卷 2317-2328页

作者： Hakimeh Zare Maziar Marandi Somayeh Fardindoost Vijay Kumar Sharma Aydan Yeltik Omid Akhavan Hilmi Volkan Demir Nima Taghavinia Institute for Nanoscience and Nanotechnology Shafif University of Technology Tehran 14588 Iran Department of Physics Faculty of Sciences Arak University Arak 38156-8-8349 Iran Department of Physics Department of Electrical and Electronics Engineering and UNAM-Institute of Materials Science and Nanotechnology Bilkent University Ankara Turkey luminous Center of Excellence for Semiconductor Lighting and Displays Microelectronics Division School of Electrical and Electronics Engineering and Physics and Applied Physics Division School of Physical and Mathematical Sciences Nanyang Technological University Singapore 639798 Singapore Physics Department ShafifUniversity of Technology Tehran 14588 Iran

We report high-efficiency CdTe/CdS core/shell nanocrystals synthesized in water by epitaxially growing CdS shells on aqueous CdTe cores at room temperature, enabled by the controlled release of S species under low-intensity ultraviolet （UV） light illumination. The resulting photo-induced dissociation of S2O2- ions conveniently triggers the formation of critical two-dimensional CdS epitaxy on the CdTe surface at room temperature, as opposed to initiating the growth of individual CdS core-only nanocrystals. This controlled colloidal hetero-epitaxy leads to a substantial increase in the photoluminescence （PL） quantum yield （QY） of the shelled nanocrystals in water （reaching 64%）. With a systematic set of studies, the maximum PL QY is found to be almost independent of the illuminating UV intensity, while the shell formation kinetics required for reaching the maximum QY linearly depends on the illuminating UV intensity. A stability study of the QD films in air at various temperatures shows highly improved thermal stability of the shelled QDs （up to 120 ℃ in ambient air）. These results indicate that the proposed aqueous CdTe/CdS core/shell nanocrystals hold great promise for applications requiring efficiency and stability.

关键词： CdTe/CDs,core/shell nanocrystal thermal stability photochemical

Mechanosynthesis of polymer-stabilized lead bromide perovskites:Insight into the formation and phase conversion of nanoparticles

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Nano Research 2021年第4期14卷 1078-1086页

作者： Guocan Jiang Onur Erdem Rene Hubner Maximilian Georgi Wei Wei Xuelin Fan Jin Wang Hilmi Volkan Demir Nikolai Gaponik Physical Chemistry Technische Universitat DresdenZellescher Weg 1901069 DresdenGermany Department of Physics Department of Electrical and Electronics Engineeringand UN A M-Institute of Materials Science and NanotechnologyBilkent University06800 AnkaraTurkey luminous Center of Excellence for Semiconductor Lighting and DisplaysSchool of Electrical and Electronic EngineeringSchool of Mathematical and Physical SciencesSchool of Materials Science and EngineeringNanyang Technological UniversityNanyang AvenueSingapore 639798Singapore Helmholtz-Zentrum Dresden-Rossendorf Institute of Ion Beam Physics and Materials ResearchBautzner Landstrasse 40001328 DresdenGermany Key Laboratory of the Ministry of Education for Advanced Catalysis Materials Zhejiang Normal UniversityJinhua 321004China

The application of polymers to replace oleylamine(OLA)and oleic acid(OA)as ligands for perovskite nanocrystals is an effective strategy to improve their stability and durability especially for the solution-based ***,we report a mechanosynthesis of lead bromide perovskite nanoparticles(NPs)stabilized by partially hydrolyzed poly(methyl methacrylate)(h-PMMA)and highmolecular-weight highly-branched poly(ethylenimine)(PEI-25K).The as-synthesized NP solutions exhibited green emission centered at 516 nm,possessing a narrow full-width at half-maximum of 17 nm and as high photoluminescence quantum yield(PL QY)as 85%,while showing excellent durability and resistance to polar solvents,e.g.,*** colloids of polymer-stabilized NPs were directly processable toform stable and strongly-emitting thin films and solids,making them attractive as gain ***,the roles of h-PMMA and PEI-25K in the grinding process were studied in *** h-PMMA can form micelles in the grinding solvent of dichloromethane to act as size-regulating templates for the growth of *** PEI-25K with large amounts of amino groups induced significant enrichment of PbBr_(2)in the reaction mixture,which in turn caused the formation of CsPb_(2)Br_(5)-mPbBr_(2)and CsPbBr_(3)-Cs_(4)PbBr_(6)-nCsBr *** presence of CsPbBr_(3)-Cs_(4)PbBr_(6)-nCsBr NPs was responsible for the high PL QY,as the Cs_(4)PbBr_(6)phase with a wide energy bandgap can passivate the surface defects of the CsPbBr_(3)*** work describes a direct and facile mechanosynthesis of polymer-coordinated perovskite NPs and promotes in-depth understanding of the formation and phase conversion for perovskite NPs in the grinding process.

关键词： lead bromide perovskites mechanosynthesis polymer ligands polymer micelles poly(ethyleneimine)-induced phase conversion

Interfacial charge and energy transfer in van der Waals heterojunctions

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InfoMat 2022年第3期4卷 64-84页

作者： Zehua Hu Xue Liu Pedro Ludwig Hernandez-Martínez Shishu Zhang Peng Gu Wei Du Weigao Xu Hilmi Volkan Demir Haiyun Liu Qihua Xiong Division of Physics and Applied Physics School of Physical and Mathematical SciencesNanyang Technological UniversitySingaporeSingapore Institutes of Physical Science and Information Technology Anhui UniversityHefeiP.R.China luminous Center of Excellence for Semiconductor Lighting and DisplaySchool of Electrical and Electronics EngineeringNanyang Technological UniversitySingaporeSingapore State Key Laboratory of Low-Dimensional Quantum Physics Department of PhysicsTsinghua UniversityBeijingP.R.China Beijing Academy of Quantum Information Sciences BeijingP.R.China Institute of Functional Nano and Soft Materials(FUNSOM) Soochow UniversitySuzhouP.R.China Key Laboratory of Mesoscopic Chemistry of MOE School of Chemistry and Chemical EngineeringNanjing UniversityNanjingP.R.China Department of Physics Department of Electrical and Electronics EngineeringUNAM-National Nanotechnology Research Center and Institute of Materials Science and NanotechnologyBilkent UniversityAnkaraTurkey Beijing Innovation Center for Future Chips Tsinghua UniversityBeijingP.R.China

Van der Waals heterojunctions are fast-emerging quantum structures fabricated by the controlled stacking of two-dimensional(2D)*** to the atomically thin thickness,their carrier properties are not only determined by the host material itself,but also defined by the interlayer interactions,including dielectric environment,charge trapping centers,and stacking *** abundant constituents without the limitation of lattice constant matching enable fascinating electrical,optical,and magnetic properties in van der Waals heterojunctions toward next-generation devices in photonics,optoelectronics,and information *** review focuses on the charge and energy transfer processes and their dynamics in transition metal dichalcogenides(TMDCs),a family of quantum materials with strong excitonic effects and unique valley properties,and other related 2D materials such as graphene and hexagonalboron *** the first part,we summarize the ultrafast charge transfer processes in van der Waals heterojunctions,including its experimental evidence and theoretical understanding,the interlayer excitons at the TMDC interfaces,and the hot carrier injection at the graphene/TMDCs *** the second part,the energy transfer,including both Förster and Dexter types,are reviewed from both experimental and theoretical ***,we highlight the typical charge and energy transfer applications in photodetectors and summarize the challenges and opportunities for future development in this field.

关键词： 2-dimensional semiconductors carrier dynamics charge and energy transfer optical spectroscopy optoelectronics