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Calculation and Improvement on external quantum efficiency of OLEDs

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Semiconductor Photonics and Technology 2006年第1期12卷 1-4页

作者： LI Chuan-nan XIE Wen-fa LIU Shi-yong College of Electronics Science and Engineering State Key Laboratory of Integrated Optoelectronics Jilin University Changchun 130012 CHN

The calculation of the external quantum efficiency(η_ ext ) of organic light-emitting devices(OLEDs) is presented theoretically. The basic idea is to obtain η_ ext by calculating the fraction of the generated light that can escape through the top surface and the average transmittance over the escape cone. During the calculation, the effects of the interference, absorption and multiple reflections are neglected. Then a result of a typical 8-tris-hydroxyquinoline aluminum(Alq_ 3 )-based OLEDs on a planar glass substrate is obtained. And a twice increase in η_ ext can be achieved by using a high-index-glass substrate with an antireflection coating(SiO_ 2 ) on substrate surface.

关键词： external quantum efficiency OLEDs Average transmittance Antireflection coating

Influence of Disassociation Probability on external quantum efficiency in Organic Electrophosphorescent Devices

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Semiconductor Photonics and Technology 2007年第3期13卷 181-185页

作者： ZHANG Jian-hua OU YANG Jun LI Xue-yong LI Hong-jian Department of Physics Xiangnan University Chenzhou 423000 CHN College of Physics Science and Technology Central South University Changsha 410083 CHN

An analytical model is presented to calculate the disassociation probability and the external quantum efficiency at high field in doped organic electrophosphorescence(EPH) devices. The charge recombination process and the triplet(T)-triplet(T) annihilation processes are taken into account in this model. The influences of applied voltage and the thickness of the device on the disassociation probability, and of current density and the thickness of the device on the external quantum efficiency are studied thoroughly by including and ignoring the disassociation of excitons. It is found that the dissociation probability of excitons will come close to 1 at high electric field, and the external EPH quantum efficiency is almost the same at low electric field. There is a large discrepancy of the external EPH quantum efficiency at high electric field for including or ignoring the disassociation of excitons.

关键词： electrophosphorescence disassociation probability triplet external quantum efficiency

Chiral multiple-resonance thermally activated delayed fluorescence materials based on chiral spiro-axis skeleton for efficient circularly polarized electroluminescence

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Science China Chemistry 2024年第7期67卷 2257-2264页

作者： Shi-Quan Song Xiao Han Zhong-Zhong Huo Ching-Fai Yip Xian-Fang Hong Meng-Ning Ding You-Xuan Zheng State Key Laboratory of Coordination Chemistry Jiangsu Key Laboratory of Advanced Organic MaterialsSchool of Chemistry and Chemical EngineeringNanjing UniversityNanjing 210023China Key Laboratory of Mesoscopic Chemistry of Ministry of Education School of Chemistry and Chemical EngineeringNanjing UniversityNanjing 210023China

Chiral luminescence materials have potential applications in the field of three-dimensional displays due to their circularly polarized luminescence(CPL)***,the further development of circularly polarized organic light-emitting diodes(CP-OLEDs)needs to meet the requirements of high efficiency,high color purity,low cost,and high dissymmetry factor(gPLor gEL),chiral multiple resonance thermally activated delayed fluorescence(MR-TADF)materials are considered as candidates in these ***,based on a pair of chiral spirofluorene precursors,two pairs of high-performance chiral MR-TADF emitters((R/S)-p-Spiro-DtBuCzB and(R/S)-m-Spiro-DtBuCzB)are developed,which exhibit strong emissions peaking at 491 and 502 nm in toluene with full-width at half-maximum values of 25 and 33 nm,*** addition,small singlet–triplet energy gaps of 0.15 and 0.10 eV with high absolute photoluminescence efficiencies of 95.0%and 96.7%are observed for p-Spiro-DtBuCzB and m-Spiro-DtBuCzB molecules,*** based on p-Spiro-DtBuCzB and m-Spiro-DtBuCzB display high maximum external quantum efficiencies of 29.6%and 33.8%,*** importantly,CP-OLEDs present symmetric circularly polarized electroluminescence spectra with|gEL|factors of 3.36×10^(-4)and 7.66×10^(-4)for devices based on(R/S)-p-Spiro-DtBuCzB and(R/S)-m-Spiro-DtBuCzB enantiomers,respectively.

关键词： chiral spiro-axis skeleton-based material multiple resonance thermally activated delayed fluorescence circularly polarized electroluminescence dissymmetry factor external quantum efficiency

Organic-inorganic hybrid Sn-based perovskite photodetectors with high external quantum efficiencies and wide spectral responses from 300 to 1000 nm

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Science China Materials 2019年第6期62卷 790-796页

作者： Yukun Wang Dezhi Yang Dongge Ma Dong Ha Kim Tansir Ahamad Saad M. Alshehri Agafbnv Vadim Institute of Polymer Optoelectronic Materials and Devices State Key Laboratory of Luminescent Materials and DevicesSouth China University of Technology Department of Chemistry and Nano Science Ewha Womans University Department of Chemistry College of ScienceKing Saud University Moscow Institute of Physics and Technology Dolgoprudny

Organic-inorganic hybrid perovskites are ideal materials for photodetection owing to their high charge carrier mobility, long charge carrier diffusion length, low dark current density and sharp absorption edge. However, a relatively small band gap(1.6 e V) limits their photonharvesting efficiency in the near-infrared region. In the present work, we demonstrate a hybrid methylamine iodide and Pb-Sn binary perovskite as the light absorption layer in photodetectors. Experimentally, the wavelength of photoresponse onset for the photodetectors can be extended to as great as 1,000 nm when the Sn content of the hybrid perovskite is increased to 30 mol%. In addition, the photodetectors exhibit a photoresponsivity of 0.39 A W^-1, a specific detectivity of 7×10^12 Jones, a fast photoresponse with rise and decay time constants and an external quantum efficiency greater than 50% in the wavelength range of350–900 nm, with a maximum value of about 80% at 550 nm.

关键词： organic-inorganic hybrid perovskite photodetector external quantum efficiency spectral response specific detectivity

Improving performance of thermally activated delayed fluorescence emitter by extending its LUMO distribution

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Science China Materials 2019年第5期62卷 719-728页

作者： Ke Ke Jia-Xiong Chen Ming Zhang Kai Wang Yi-Zhong Shi Hui Lin Cai-Jun Zheng Si-Lu Tao Xiao-Hong Zhang School of Optoelectronic Science and Engineering University of Electronic Science and Technology of China Functional Nano and Soft Materials Laboratory (FUNSOM) and Collaborative Innovation Center of Suzhou Nano Science and Technology Soochow University

An optimized compound 9-(9,9-dimethylacridin-10(9 H)-yl)-6 H-benzo[c]ch-romen-6-one(MAB) was designed and synthesized based on our previously reported TADF emitter 6-(9,9-dimethylacridin-10(9 H)-yl)-3-methyl-1 H-isochromen-1-one(MAC) to further improve the performance of thermally activated delayed fluorescence(TADF)emitters. With the additional phenyl in coumarin-contained plane, MAB possesses an extended distribution of the lowest unoccupied molecular orbitals(LUMO), and thus realizes reduced electron exchange between the frontier molecular orbitals and a stretched molecular dipole moment compared with MAC. MAB based organic light-emitting diode(OLED)exhibits a remarkable maximum external quantum efficiency(EQE) of 21.7%, which is much better than the maximum EQE of MAC-based OLED with a value of 12.8%. Our work proves that extending the distribution of LUMO is a simple but effective method to improve the efficiency of TADF emitter.

关键词： organic light-emitting diode thermally activated delayed fluorescence lumo distribution external quantum efficiency

Infrared light-emitting diodes based on colloidal Pb Se/Pb S core/shell nanocrystals

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Chinese Physics B 2020年第1期29卷 482-488页

作者： Byung-Ryool Hyun Mikita Marus Huaying Zhong Depeng Li Haochen Liu Yue Xie Weon-kyu Koh Bing Xu Yanjun Liu Xiao Wei Sun Guangdong University Key Laboratory for Advanced quantum Dot Displays and Lighting Shenzhen Key Laboratory for Advanced Quantum Dot Displays and LightingDepartment of Electrical&Electronic EngineeringSouthern University of Science and TechnologyShenzhen 518055China School of Electrical and Electronic Engineering Nanyang Technological UniversitySingapore Shenzhen Planck Innovation Technologies Co.Ltd Shenzhen 518112China

Colloidal Pb Se nanocrystals(NCs)have gained considerable attention due to their efficient carrier multiplication and emissions across near-infrared and short-wavelength infrared spectral ***,the fast degradation of colloidal Pb Se NCs in ambient conditions hampers their widespread applications in infrared *** is well-known that the inorganic thick-shell over core improves the stability of ***,we present the synthesis of Pb Se/Pb S core/shell NCs showing wide spectral tunability,in which the molar ratio of lead(Pb)and sulfur(S)precursors,and the concentration of sulfur and Pb Se NCs in solvent have a significant effect on the efficient Pb S shell *** infrared light-emitting diodes(IR-LEDs)fabricated with the Pb Se/Pb S core/shell NCs exhibit an external quantum efficiency(EQE)of 1.3%at 1280 *** ligand exchange to optimize the distance between NCs and chloride treatment are important processes for achieving high performance on Pb Se/Pb S *** results provide evidence for the promising potential of Pb Se/Pb S NCs over the wide range of infrared optoelectronic applications.

关键词： Pb Se/Pb S core/shell nanocrystal ligand exchange infrared light-emitting diodes external quantum efficiency

Green light-emitting diodes based on hybrid perovskite films with mixed cesium and methylammonium cations

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Nano Research 2017年第4期10卷 1329-1335页

作者： Junjie Si Yang Liu Nana Wang Meng Xu Jing Li Haiping He Jianpu Wang Yizheng Jin State Key Laboratory of Silicon Materials Center for Chemistry of High-Performance & Novel Materials School of Materials Science and Engineering Zhejiang University Hangzhou 310027 China Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM) Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM) Nanjing Tech University (NanjingTech) 30 South Puzhu Road Nanjing 211816 China State Key Laboratory of Silicon Materials School of Materials Science and Engineering Zhejiang University Hangzhou 310027 China Center for Chemistry of High-Performance & Novel Materials State Key Laboratory of Silicon Materials Department of ChemistryZhejiang University Hangzhou 310027 China

We report the formation of high-quality Cs0.4MA0.6PbBr3 thin films with nearly full surface coverage and good emission properties upon the introduction of Cs^＋ into perovskite crystals. The Cs0.4MA0.6PbBr3 thin films were applied as emissive layers in light-emitting diodes. A maximum external quantum efficiency of -2.0% was achieved for these green-emitting devices.

关键词： perovskite light-emitting diodes cesium emission properties external quantum efficiency

Effects of polarization and p-type GaN resistivity on the spectral response of InGaN/GaN multiple quantum well solar cells

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Chinese Physics B 2014年第6期23卷 629-634页

作者：杨静赵德刚江德生刘宗顺陈平李亮吴亮亮乐伶聪李晓静何晓光王辉朱建军张书明张宝顺杨辉 State Key Laboratory on Integrated Optoelectronics Institute of Semiconductors Chinese Academy of Sciences Suzhou Institute of Nano-Tech and Nano-Bionics Chinese Academy of Sciences

Effects of polarization and p-type GaN resistivity on the spectral response of InGaN/GaN multiple quantum well （MQW） solar cells are investigated. It is found that due to the reduction of piezoelectric polarization and the enhancement of tunneling transport of photo-generated carriers in MQWs, the external quantum efficiency （EQE） of the solar cells increases in a low energy spectral range （λ 〉 370 nm） when the barrier thickness value decreases from 15 nm to 7.5 nm. But the EQE decreases abruptly when the barrier thickness value decreases down to 3.75 nm. The reasons for these experimental results are analyzed. We are aware that the reduction of depletion width in MQW region, caused by the high resistivity of the p-type GaN layer may be the main reason for the abnormally low EQE value at long wavelengths （λ 〉 370 nm）.

关键词： nitride materials external quantum efficiency polarization p-type GaN resistivity

Light-emitting field-effect transistors with EQE over 20%enabled by a dielectric-quantum dots-dielectric sandwich structure

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Science Bulletin 2022年第5期67卷 529-536,M0004页

作者： Lingmei Kong Jialong Wu Yunguo Li Fan Cao Feijiu Wang Qianqian Wu Piaoyang Shen Chengxi Zhang Yun Luo Lin Wang Lyudmila Turyanska Xingwei Ding Jianhua Zhang Yongbiao Zhao Xuyong Yang Key Laboratory of Advanced Display and System Applications of Ministry of Education Shanghai UniversityShanghai 200072China CAS Key Laboratory of Crust-Mantle Materials and Environments School of Earth and Space SciencesUniversity of Science and Technology of ChinaHefei 230026China Henan Key Laboratory of Photovoltaic Materials Henan UniversityKaifeng 475004China Faculty of Engineering University of NottinghamNottingham NG72RDUK Center for Optoelectronic Engineering Research Department of PhysicsSchool of Physics and AstronomyYunnan UniversityKunming 650091China

Emerging quantum dots(QDs)based light-emitting field-effect transistors(QLEFETs)could generate light emission with high color purity and provide facile route to tune optoelectronic properties at a low fabrication *** efforts have been devoted to designing device structure and to understanding the underlying physics,yet the overall performance of QLEFETs remains low due to the charge/exciton loss at the interface and the large band offset of a QD layer with respect to the adjacent carrier transport ***,we report highly efficient QLEFETs with an external quantum efficiency(EQE)of over 20%by employing a dielectric-QDs-dielectric(DQD)sandwich *** DQD structure is used to control the carrier behavior by modulating energy band alignment,thus shifting the exciton recombination zone into the emissive ***,enhanced radiative recombination is achieved by preventing the exciton loss due to presence of surface traps and the luminescence quenching induced by interfacial charge *** DQD sandwiched design presents a new concept to improve the electroluminescence performance of QLEFETs,which can be transferred to other material systems and hence can facilitate exploitation of QDs in a new type of optoelectronic devices.

关键词： Light-emitting field-effect transistors quantum dots Electroluminescence external quantum efficiency