Publications by authors named "Zhishan Fang"

11 Publications

  • Page 1 of 1

Efficient light-emitting diodes based on oriented perovskite nanoplatelets.

Sci Adv 2021 Oct 8;7(41):eabg8458. Epub 2021 Oct 8.

Zhejiang Key Laboratory for Excited-State Materials, State Key Laboratory of Silicon Materials, Department of Chemistry, Zhejiang University, Hangzhou 310027, China.

Solution-processed planar perovskite light-emitting diodes (LEDs) promise high-performance and cost-effective electroluminescent devices ideal for large-area display and lighting applications. Exploiting emission layers with high ratios of horizontal transition dipole moments (TDMs) is expected to boost the photon outcoupling of planar LEDs. However, LEDs based on anisotropic perovskite nanoemitters remain to be inefficient (external quantum efficiency, EQE <5%) due to the difficulties of simultaneously controlling the orientations of TDMs, achieving high photoluminescence quantum yields (PLQYs) and realizing charge balance in the films of assembled nanostructures. Here, we demonstrate efficient electroluminescence from an in situ grown perovskite film composed of a monolayer of face-on oriented nanoplatelets. The ratio of horizontal TDMs of the perovskite nanoplatelet film is ~84%, which leads to a light-outcoupling efficiency of ~31%, substantially higher than that of isotropic emitters (~23%). In consequence, LEDs with a peak EQE of 23.6% are achieved, representing highly efficient planar perovskite LEDs.
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http://dx.doi.org/10.1126/sciadv.abg8458DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8500509PMC
October 2021

Near-Unity-Efficiency Energy Transfer from Perovskite to Monolayer Semiconductor through Long-Range Migration and Asymmetric Interfacial Transfer.

ACS Appl Mater Interfaces 2021 Sep 25;13(35):41895-41903. Epub 2021 Aug 25.

State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou 310027, Zhejiang, China.

van der Waals heterostructures combining perovskites of strong light absorption with atomically thin two-dimensional (2D) transition-metal dichalcogenides (TMDs) hold great potential for light-harvesting and optoelectronic applications. However, current research studies integrating TMDs with low-dimensional perovskite nanomaterials generally suffer from poor carrier/energy transport and harnessing, stemming from poor interfacial interaction due to the nanostructured nature and ligands on surface/interface. To overcome the limitations, here, we report prototypical three-dimensional (3D)/2D perovskite/TMD heterostructures by combing highly smooth and ligand-free CsPbBr film with a WSe monolayer. We show that the energy transfer at interface occurs through asymmetric two-step charge-transfer process, with ultrafast hole transfer in ∼200 fs and subsequent electron transfer in ∼10 ps, driven by the asymmetric type I band alignment. The energy migration and transfer from CsPbBr film to WSe can be well described by a one-dimensional diffusion model with a carrier diffusion length of ∼500 nm in CsPbBr film. Thanks to the long-range carrier migration and ultrafast interfacial transfer, highly efficient (>90%) energy transfer to WSe can be achieved with CsPbBr film as thick as ∼180 nm, which can capture most of the light above its band gap. The efficient light and energy harvesting in perovskite/TMD 3D/2D heterostructures suggest great promise in optoelectronic and photonic devices.
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http://dx.doi.org/10.1021/acsami.1c11753DOI Listing
September 2021

Mixed Halide Perovskite Films by Vapor Anion Exchange for Spectrally Stable Blue Stimulated Emission.

Small 2021 Oct 21;17(39):e2103169. Epub 2021 Aug 21.

State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou, 310027, P. R. China.

Solution-processed all-inorganic CsPbX perovskites exhibit outstanding optoelectronic properties and are being considered as a promising optical gain medium, with impressive performance in the green and red region. However, the development of CsPbX for blue emission is still lagging far behind, owing to difficulties in thin films synthesis and spectral instability subject to light irradiation. Here, a facile vapor anion exchange (VAE) method that enables preparation of blue-emitting perovskite films with both excellent surface morphology and good photo-stability is reported. The mixed-Br/Cl quasi-2D perovskite films show spectrally stable pure blue emission (471 nm) under continuous-wave laser irradiation with power density as high as 81 W cm . Furthermore, optically pumped blue amplified spontaneous emission (ASE) is realized based on the mixed-Br/Cl perovskite films. By changing the duration of VAE treatment, the ASE peak can be tuned from 537 nm down to 475 nm. This work not only presents a facile method to prepare high quality mixed halide Cs-based perovskite films, but also pave the way for further exploration of stable blue perovskite lasing.
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http://dx.doi.org/10.1002/smll.202103169DOI Listing
October 2021

Coexistence of light-induced photoluminescence enhancement and quenching in CHNHPbBr perovskite films.

RSC Adv 2020 Mar 17;10(19):11054-11059. Epub 2020 Mar 17.

State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University Hangzhou 310027 China

Lead halide perovskites are promising semiconductors for various optoelectronic devices working in a wide photo-excitation density regime. However, photo-induced instability, attributed to illumination-activated mobile ions, has been an obstacle to their application. Herein, we use the time evolution of photoluminescence (PL) to investigate the light illumination effects of CHNHPbBr perovskite films under relatively high excitation (up to 4.5 W cm). We demonstrate that continuous illumination can lead to both PL enhancement and PL quenching simultaneously, with their weight ratios depending on the excitation density. The experimental data can be well described and interpreted by considering the coexistence of and competition between the photo-induced annihilation and the formation of long-living filled trap states. Our study may provide in-depth insight into the photo-induced instability of perovskite films and help to improve the performance of perovskite-based optoelectronic devices.
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http://dx.doi.org/10.1039/d0ra00605jDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC9050461PMC
March 2020

Achieving long carrier lifetime and high optical gain in all-inorganic CsPbBr perovskite films via top and bottom surface modification.

Phys Chem Chem Phys 2019 Oct;21(39):21996-22001

State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, People's Republic of China.

Solution-processed all-inorganic CsPbX3(X = Br, I, and Cl) perovskites are proven to be promising materials for various optoelectronic applications. However, CsPbX3 films as optical gain media were confronted with unsatisfactory surface coverage and inferior photoluminescence performance when compared with their colloidal nanocrystal counterparts. Herein, we demonstrate a strategy for improving the optical properties via modification of both top and bottom surfaces of CsPbBr3 films. The treated perovskite films show ultra-smooth morphology and a carrier lifetime of 44 ns, more than one order of magnitude longer than the untreated one. Meanwhile, a mixed polymer layer on the top of the perovskite film could combine surface passivation with symmetric waveguide effects, leading to an outstanding net gain coefficient of 694 cm-1. These merits predict the great potential of all-inorganic perovskite films to support high efficiency charge transport or stimulated emission.
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http://dx.doi.org/10.1039/c9cp04033aDOI Listing
October 2019

R-phycoerythrin [email protected] composite thin films for mercury ion detection.

Analyst 2019 Jun 23;144(12):3892-3897. Epub 2019 May 23.

State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China.

Mercury, as one of the most prevalent toxic metals released by various natural and anthropogenic processes, causes severe pollution of soil and groundwater. In this work, R-phycoerythrin (R-PE) proteins encapsulated into ZIF-8 composite thin films were prepared via a solid-confinement conversion process and applied as fluorescent sensors for mercury ion detection. The R-PE proteins encapsulated into ZIF-8 exhibit dual color emissions including green (518 nm) and red (602, 650 nm) fluorescence, while the original orange emission (578 nm) of pure R-PE is significantly suppressed. [email protected] presents excellent selectivity and sensitivity for mercury detection in a large pH range without buffer solution. Under the optimal conditions, there is a good linear relationship between the fluorescence quenching efficiencies of [email protected] and logarithmic concentrations of mercury ions in the range of 0.001-50 μM with the detection limit (LOD) of 6.7 nM much lower than the guideline value given by the World Health Organization. Furthermore, multi-peak detection of [email protected] improves the detection accuracy of Hg concentration.
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http://dx.doi.org/10.1039/c9an00449aDOI Listing
June 2019

Embedded Two-Dimensional Perovskite Nanoplatelets with Air-Stable Luminescence.

ACS Appl Mater Interfaces 2019 Feb 13;11(8):8436-8442. Epub 2019 Feb 13.

Key Laboratory of Atomic and Molecular Physics & Functional Materials of Gansu Province, College of Physics and Electronic Engineering , Northwest Normal University , Lanzhou 730070 , China.

Two-dimensional (2D) perovskites represent a class of promising nanostructures for optoelectronic applications owing to their giant oscillator strength transition of excitons and high luminescence. However, major challenges lie in the surface ligand engineering and ambient stability. Here, we show that air-stable quasi-2D CsPbBr nanoplatelets can be formed in the matrix of CsPbBr nanosheets by reducing the thickness of CsPbBr to ∼7.6 nm, the scale comparable to the exciton Bohr radius of CsPbBr. The 2D behavior of excitons is evidenced by the linear increase of the radiative lifetime with increasing temperature. Moreover, the wide-bandgap CsPbBr plays roles of surface passivation and protection, which leads to good photoluminescence properties without the photobleaching effect and with ambient stability for over 1 month. Our work demonstrates a unique quasi-2D heterostructure of perovskite nanomaterials, which may either serve as a workbench for studying the exciton recombination dynamics or find application in high-performance optoelectronic devices.
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http://dx.doi.org/10.1021/acsami.8b21396DOI Listing
February 2019

Understanding the Role of Lithium Doping in Reducing Nonradiative Loss in Lead Halide Perovskites.

Adv Sci (Weinh) 2018 Dec 23;5(12):1800736. Epub 2018 Oct 23.

State Key Laboratory of Silicon Materials School of Materials Science and Engineering Zhejiang University Hangzhou 310027 China.

Adding alkali metal into lead halide perovskites has recently been demonstrated as an effective strategy for reducing nonradiative loss. However, the suggested role of the alkali metal is usually limited to surface passivation, and the semiconductor doping effect is rarely discussed. Here, the mechanism of lithium doping in the photocarrier recombination in solution-processed methylammonium lead halide films is investigated by photoluminescence and photoelectron spectroscopies. It is demonstrated that lithium doping weakens the electron-phonon coupling and acts as donor in perovskites, which provide solid evidence that lithium enters the lattice rather than just in the surface region. The n-type doping creates free electrons to fill the trap states in both the bulk and surface regions, leading to suppressed trapping of photocarriers and reduces nonradiative recombination.
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http://dx.doi.org/10.1002/advs.201800736DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6299680PMC
December 2018

Bright Tail States in Blue-Emitting Ultrasmall Perovskite Quantum Dots.

J Phys Chem Lett 2017 Dec 4;8(24):6002-6008. Epub 2017 Dec 4.

State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University , Hangzhou 310027, China.

All-inorganic lead halide perovskite quantum dots (CsPbBr QDs) are attracting significant research interests because of their highly efficient light-emitting performance combined with tunable emission wavelength facilely realized by ion exchange. However, blue emission from perovskite QDs with strong quantum confinement is rarely reported and suffers from lower luminescence efficiency. Here we report blue-emitting ultrasmall (∼3 nm) CsPbBr QDs with photoluminescence (PL) quantum yield as high as 68%. Using time-resolved and steady-state PL spectroscopy, we elucidate the mechanism of the highly efficient PL as recombination of excitons localized in radiative band tail states. Through analyzing the spectral-dependent PL lifetime and the PL line shape, we obtain a large band tail width of ∼80 meV and a high density of state of ∼10 cm. The relaxation of photocarriers into the radiative tail states suppresses the capture by nonradiative centers. Our results provide solid evidence for the positive role of band tail states in the optical properties of lead halide perovskites, which can be further tailored for high-performance optoelectronic devices.
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http://dx.doi.org/10.1021/acs.jpclett.7b02786DOI Listing
December 2017

Effects of Organic Cation Length on Exciton Recombination in Two-Dimensional Layered Lead Iodide Hybrid Perovskite Crystals.

J Phys Chem Lett 2017 Oct 9;8(20):5177-5183. Epub 2017 Oct 9.

State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University , Hangzhou 310027, People's Republic of China.

In recent years, 2D layered organic-inorganic lead halide perovskites have attracted considerable attention due to the distinctive quantum confinement effects as well as prominent excitonic luminescence. Herein, we show that the recombination dynamics and photoluminescence (PL) of the 2D layered perovskites can be tuned by the organic cation length. 2D lead iodide perovskite crystals with increased length of the organic chains reveal blue-shifted PL as well as enhanced relative internal quantum efficiency. Furthermore, we provide experimental evidence that the formation of face-sharing [PbI] octahedron in perovskites with long alkyls induces additional confinement for the excitons, leading to 1D-like recombination. As a result, the PL spectra show enhanced inhomogeneous broadening at low temperature. Our work provides physical understanding of the role of organic cation in the optical properties of 2D layered perovskites, and would benefit the improvement of luminescence efficiency of such materials.
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http://dx.doi.org/10.1021/acs.jpclett.7b02083DOI Listing
October 2017

Development of a Liquid Chip Technique to Simultaneously Detect Spring Viremia of Carp Virus, Infectious Hematopoietic Necrosis Virus, and Viral Hemorrhagic Septicemia of Salmonids.

J AOAC Int 2017 Jan;100(1):159-164

Guangxi Academy of Fishery Science, Nanning 530021, China.

A liquid chip technique was developed to detect spring viremia of carp virus (SVCV), infectious hematopoietic necrosis virus (IHNV), and viral hemorrhagic septicemia virus (VHSV) of salmonids simultaneously. Sequences of the G gene of SVCV, N gene of IHNV, and G gene of VHSV were used to design SVCV-, IHNV-, and VHSV-specific primers, which were labeled with biotin and subjected to amination modification. They were then coupled with fluorescence-coded microspheres and used for hybridization with reverse-transcription PCR products of SVCV, IHNV, and VHSV. A BD FACSArray was used to detect fluorescence signal in the reaction system. This assay system had a high sensitivity to SVCV, VHSV, and IHNV, with LODs of 10, 10, and 100 pg/μL, respectively. Moreover, the assay was specific for the detection of SVCV, IHNV, and VHSV and was not susceptible to cross-detection of other viruses, including pike fry rhabdovirus, hirame rhabdovirus, infectious pancreatic necrosis virus, viral nervous necrosis virus, yellowtail ascites virus, grass carp reovirus, red sea bream iridovirus, and koi herpesvirus. The liquid chip assay technique established in this study provides a novel, convenient, and rapid approach for the detection of SVCV, IHNV, and VHSV.
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http://dx.doi.org/10.5740/jaoacint.16-0066DOI Listing
January 2017
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