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359 results on '"Zhang, Hanzhuang"'

7. Over 800% Efficiency Enhancement of Solution-Processed All-Inorganic Quantum-Dot Light Emitting Diodes with an Ultrathin Alumina Passivating Layer

Author

Ji, Wenyu, Shen, Huaibin, Zhang, Han, Kang, Zhihui, and Zhang, Hanzhuang

Subjects
Physics - Applied Physics
Abstract

The use of robust, inorganic charge-transport materials is always desired in quantum-dot light emitting diodes (QLEDs) because they are expected to allow higher stability and less cost than that of organic counterparts. Here we report an all-inorganic QLED with excellent efficiency by modifying the solution-processed NiO (s-NiO) surface with an ultrathin Al2O3 passivating layer. The localized electric field induced by nickel oxyhydroxide (NiOOH) is estimated to be ~ 70 MV/cm at a distance of 6 nm from the surface of s-NiO layer. Both transient resolution photoluminescence (TRPL) and X-Ray photoelectron spectroscopy (XPS) measurements demonstrate that the Al2O3 passivating layer can effectively passivate the NiOOH on the s-NiO surface, hence suppressing the exciton quenching. As a result, over 800% efficiency enhancement up to 34.1 cd/A (8.1%) for the current efficiency (external quantum efficiency, EQE) of the QLEDs is achieved. To the best of our knowledge, this is the best-performing all-inorganic QLED so far., Comment: There are some errors in the manuscript

Published
2018

19. Photoluminescence Mechanism of Dual‐State Emission Materials Based on the Sulfone Bridged Distyrylbenzene Derivative.

Author

Li, Yexi, Dai, Jianan, Yang, Song, Sui, Ning, Wang, Chenguang, Meng, Xiangdong, Wang, Kai, Zhang, Hanzhuang, Liu, Xiaomin, Lu, Geyu, and Wang, Yinghui

Subjects
SULFONES, PHOTOLUMINESCENCE, QUANTUM efficiency, LIGHT propagation, MOLECULAR crystals, ANISOTROPY, OPTICAL polarization, CRYSTALS
Abstract

Herein, a novel molecular SO2‐Bri‐DSB based on the sulfone‐bridged distyrylbenzene derivative is synthesized, and its organic crystal is fabricated. It has a very high photoluminescence (PL) quantum efficiency in the solution and crystalline state, i.e., dual‐state emission (DSE), and the corresponding PL mechanism is clarified in detail using the transient absorption and transient PL test. The PL behaviors in the monomolecular state and organic crystal are compared. In addition, the optical anisotropy of the SO2‐Bri‐DSB crystal is thoroughly investigated using various polarization‐dependent spectroscopy techniques. The time evolution of anisotropy is composed of a step behavior caused by the anisotropy of the electronic transition and a slow enhancing process with a lifetime of 4.86 ns, which is governed by the change in emission lifetime due to the anisotropy. The space‐resolved evolution of the optical anisotropy is investigated using the polarization‐dependent light wave‐guiding test and exhibits that the emission anisotropy gradually decreases with length, and it has a longer effective propagation length than the polarization emission signal. The findings provide insight into the intrinsic optical anisotropy of single‐molecular crystals and indicate that these materials have enormous potential in the domains of polarization lighting and display. [ABSTRACT FROM AUTHOR]

Published
2024
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20. Multinary Cu─In─Zn─S‐based Quantum‐Dot Electroluminescence and Implications on Device Designs.

Author

Zheng, Xiankun, Wang, Lijin, Bai, Jialin, Zhang, Han, Zhang, Hanzhuang, Tang, Aiwei, and Ji, Wenyu

Subjects
QUANTUM dots, FRONTIER orbitals, ELECTROLUMINESCENCE, LIGHT emitting diodes, VALENCE bands, QUANTUM dot LEDs
Abstract

Currently, the performance of quantum‐dot light‐emitting diodes (QLEDs) based on environmental‐friendly Cu─In─Zn─S quantum dots (QDs) still lags far behind that of Cd‐QDs‐based devices. Here it is demonstrated that the unique trap‐related recombination in Cu─In─Zn─S QDs is mainly responsible for the low device efficiency. The luminous efficiency of Cu─In─Zn─S‐based QLEDs is rather sensitive to the temperature and hole‐transporting layers (HTLs) due to the susceptible thermal‐related trappingdetrapping processes of holes in radiative Cu‐related traps. The holes in Cu‐related traps can be quenched by escaping to the valence band of the QDs or/and transferring to the adjacent HTLs. An HTL with low highest occupied molecular orbitals is desired to enhance the hole injection and hinder the aforementioned hole transfer. As a result, a high device efficiency of 6.0 cd A−1 is achieved at room temperature, which is attributed to suppressed HTL‐induced emission quenching and efficient valence‐band‐dominated hole injection from HTL to the QDs. The device efficiency is further increased to 13.2 cd A−1 at 150K by suppressing thermal‐induced quenching. [ABSTRACT FROM AUTHOR]

Published
2024
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43. On the Electroluminescence Turn‐On Mechanism of Blue Quantum‐Dot Light‐Emitting Diodes.

Author

Zhang, Huimin, Bai, Jialin, Zhu, Xiaoxiang, Xue, Xulan, Zhang, Hanzhuang, Zhou, Mi, and Ji, Wenyu

Subjects
QUANTUM dots, LIGHT emitting diodes, ELECTROLUMINESCENCE, CHARGE injection, STRUCTURAL engineering, QUANTUM dot LEDs, FIELD emission
Abstract

A clear understanding on the fundamental working mechanisms of quantum‐dot light emitting diodes (QLEDs), especially the blue devices, is always sought after. Here the electroluminescence (EL) turn‐on mechanism of blue QLEDs is unraveled by structure engineering of the hole‐transport layers (HTLs). It is demonstrated that the EL turn‐on in blue QLEDs is highly dependent on the charge‐transport polarity of the HTLs. Energy transfer between HTLs and the blue quantum dots (QDs) occurs for the QLEDs based on bipolar HTLs, and, in contrast, charge injection is responsible for EL turn‐on of the blue devices consisting of unipolar HTLs. In addition, large hole‐injection barrier results in serious accumulation of holes at the interface of HTLs/QDs, then inducing serious electrons leakage into the HTLs, thereby leading to poor device efficiency under low driving current. It is suggested here that confining the carriers to the quantum dots and reducing the hole‐injection barrier remain two critical aspects to optimize the performance of blue QLEDs. [ABSTRACT FROM AUTHOR]

Published
2023
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45. Optoelectronic Properties of Polyvinylidene Fluoride Films Embedded with FAPbBr3Nanocrystals Affected by Carrier Kinetics

Author

Li, Yexi, Fan, Dongniu, Sui, Ning, Li, Liang, Li, Fangfei, Chi, Xiaochun, Kang, Zhihui, Zhou, Qiang, Zhang, Hanzhuang, Cui, Cuili, and Wang, Yinghui

Abstract

Polyvinylidene fluoride (PVDF) films embedded with perovskite nanocrystals (NCs) can maintain their stability for a long time under extreme water, oxygen, and acid-alkali environments. In this study, PVDF films embedded with different FAPbBr3(FA = formamidinium) NCs are synthesized by employing a fast and direct method, and prototypes of photodetectors utilizing these films are fabricated. The relationships between the optoelectronic performance and the carrier kinetics in the composite film affected by the synthesis temperature are analyzed in detail by employing transient absorption and temperature-dependent spectroscopy. A primitive fixable light-sensitive detector is fabricated so as to broaden the application of PVDF films embedded with different FAPbBr3NCs in the optoelectronics field. Our results suggest that PVDF films embedded with perovskite NCs can be applied in many semiconductor devices.

Published
2023
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