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Low‐Dimensional Metal Halide Perovskite Photodetectors

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Advanced Materials
Authors:
Hsin-Ping Wang
Hsin-Ping Wang
Siyuan Li
Siyuan Li
Siyuan Li
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Xinya Liu at Fudan University
Xinya Liu
Zhifeng Shi at Zhengzhou University
Zhifeng Shi
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Abstract and Figures

Metal halide perovskites (MHPs) have been a hot research topic due to their facile synthesis, excellent optical and optoelectronic properties, and record‐breaking efficiency of corresponding optoelectronic devices. Nowadays, the development of miniaturized high‐performance photodetectors (PDs) has been fueling the demand for novel photoactive materials, among which low‐dimensional MHPs have attracted burgeoning research interest. In this report, the synthesis, properties, photodetection performance, and stability of low‐dimensional MHPs, including 0D, 1D, 2D layered and nonlayered nanostructures, as well as their heterostructures are reviewed. Recent advances in the synthesis approaches of low‐dimensional MHPs are summarized and the key concepts for understanding the optical and optoelectronic properties related to the PD applications of low‐dimensional MHPs are introduced. More importantly, recent progress in novel PDs based on low‐dimensional MHPs is presented, and strategies for improving the performance and stability of perovskite PDs are highlighted. By discussing recent advances, strategies, and existing challenges, this progress report provides perspectives on low‐dimensional MHP‐based PDs in the future.
Typical low‐dimensional MHP nanostructures synthesized by solution‐based methods. a) Schematic illustration of CsPbBr3 lattice. b,c) typical TEM images of monodisperse CsPbBr3 NCs by hot injection. a–c) Reproduced with permission.[⁵²] Copyright 2015, American Chemical Society. d) Schematic illustration of the emulsion synthesis of MAPbBr3 QDs. e) Optical photographs of MAPbBr3 emulsion and QD colloidal solution. d,e) Reproduced with permission.[⁵⁶] Copyright 2015, American Chemical Society. f) Schematic illustration of the one‐step blade coating method for single‐crystalline 1D MAPbI3 microwire arrays. g) cross‐polarized optical image of the perovskite arrays. f,g) Reproduced with permission.[³²] Copyright 2016, Wiley‐VCH. h) A tilted MAPbI3 serpentine structure prepared by 3D printing (scale bar: 2 µm). Reproduced with permission.[⁶⁹] Copyright 2019, Wiley‐VCH. i) The optical image of CsPbBr3 microflakes on SiO2 by solvent evaporation. The inset shows the schematic illustration of the growth process. Reproduced with permission.[⁷²] Copyright 2017, American Chemical Society. j) The optical image of mechanically exfoliated 2D BA2MA2Pb3I10 on SiO2/Si substrates (scale bar: 20 µm). Reproduced with permission.[⁷⁸] Copyright 2019, American Chemical Society. k) TEM image of face‐to‐face stacked CsPbBr3 nanoplatelets by hot injection. Red and blue areas represent nanoplatelets standing perpendicular to and tilted with the substrate, respectively. Reproduced with permission.[⁸⁴] Copyright 2016, American Chemical Society.
Typical low‐dimensional MHP nanostructures synthesized by solution‐based methods. a) Schematic illustration of CsPbBr3 lattice. b,c) typical TEM images of monodisperse CsPbBr3 NCs by hot injection. a–c) Reproduced with permission.[⁵²] Copyright 2015, American Chemical Society. d) Schematic illustration of the emulsion synthesis of MAPbBr3 QDs. e) Optical photographs of MAPbBr3 emulsion and QD colloidal solution. d,e) Reproduced with permission.[⁵⁶] Copyright 2015, American Chemical Society. f) Schematic illustration of the one‐step blade coating method for single‐crystalline 1D MAPbI3 microwire arrays. g) cross‐polarized optical image of the perovskite arrays. f,g) Reproduced with permission.[³²] Copyright 2016, Wiley‐VCH. h) A tilted MAPbI3 serpentine structure prepared by 3D printing (scale bar: 2 µm). Reproduced with permission.[⁶⁹] Copyright 2019, Wiley‐VCH. i) The optical image of CsPbBr3 microflakes on SiO2 by solvent evaporation. The inset shows the schematic illustration of the growth process. Reproduced with permission.[⁷²] Copyright 2017, American Chemical Society. j) The optical image of mechanically exfoliated 2D BA2MA2Pb3I10 on SiO2/Si substrates (scale bar: 20 µm). Reproduced with permission.[⁷⁸] Copyright 2019, American Chemical Society. k) TEM image of face‐to‐face stacked CsPbBr3 nanoplatelets by hot injection. Red and blue areas represent nanoplatelets standing perpendicular to and tilted with the substrate, respectively. Reproduced with permission.[⁸⁴] Copyright 2016, American Chemical Society.
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Typical low‐dimensional MHP nanostructures synthesized by vapor‐based methods. a) Schematic illustration of CsPbI3 NWs prepared by chemical vapor diffusion of CsI using an AAO template. b) The top view SEM image of CsPbI3 NWs coming out of AAO. a,b) Reproduced with permission.[⁹⁰] Copyright 2017, American Chemical Society. c) The optical image of CsPbX3 nanowire arrays prepared by vapor‐phase epitaxy on mica substrate. Reproduced with permission.[⁹¹] Copyright 2016, American Chemical Society. The optical images of the as‐grown d) CsSnI3 and e) CsSnBrI2 NW arrays by solid‐source CVD method (scale bars: 100 µm). d,e) Reproduced with permission.[⁹³] Copyright 2019, American Chemical Society. f) The images and thickness of PbI2 templates (above data line) and CH3NH3PbI3 nanoplatelets after being thermally intercalated by methyl ammonium halides (below data line). Reproduced with permission.[⁹⁴] Copyright 2014, Wiley‐VCH. g) The SEM image of CH3NH3PbI3 microplate arrays fabricated by the intercalation of lithographically patterned PbI2 precursor microplates (scale bar: 20 µm). The inset shows the schematic illustration of vapor‐phase intercalation. Reproduced with permission.[⁹⁶] Copyright 2015, AAAS. h) The optical image of CsPbBr3/MoS2 van der Waals heterostructure and the corresponding schematic diagram. Reproduced with permission.[¹⁰⁰] Copyright 2018, Wiley‐VCH.
Typical low‐dimensional MHP nanostructures synthesized by vapor‐based methods. a) Schematic illustration of CsPbI3 NWs prepared by chemical vapor diffusion of CsI using an AAO template. b) The top view SEM image of CsPbI3 NWs coming out of AAO. a,b) Reproduced with permission.[⁹⁰] Copyright 2017, American Chemical Society. c) The optical image of CsPbX3 nanowire arrays prepared by vapor‐phase epitaxy on mica substrate. Reproduced with permission.[⁹¹] Copyright 2016, American Chemical Society. The optical images of the as‐grown d) CsSnI3 and e) CsSnBrI2 NW arrays by solid‐source CVD method (scale bars: 100 µm). d,e) Reproduced with permission.[⁹³] Copyright 2019, American Chemical Society. f) The images and thickness of PbI2 templates (above data line) and CH3NH3PbI3 nanoplatelets after being thermally intercalated by methyl ammonium halides (below data line). Reproduced with permission.[⁹⁴] Copyright 2014, Wiley‐VCH. g) The SEM image of CH3NH3PbI3 microplate arrays fabricated by the intercalation of lithographically patterned PbI2 precursor microplates (scale bar: 20 µm). The inset shows the schematic illustration of vapor‐phase intercalation. Reproduced with permission.[⁹⁶] Copyright 2015, AAAS. h) The optical image of CsPbBr3/MoS2 van der Waals heterostructure and the corresponding schematic diagram. Reproduced with permission.[¹⁰⁰] Copyright 2018, Wiley‐VCH.
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a) The image of needle‐shaped bulk C4N2H14PbBr4 crystals under ambient light. b) The crystals in (a) show strong bluish white‐light emission under 365 nm UV light. c) The absorption (dash lines) and emission (solid lines) spectra of the needle‐shaped bulk and 1D microscale C4N2H14PbBr4 crystals. a–c) Reproduced under the terms of the CC‐BY 4.0 license.[¹²⁸] Copyright 2017, the Authors, published by Springer Nature. d) The schematic illustration of interparticle anion exchange among CsPbX3 perovskite NCs. e) The absorption and PL spectra of CsPb(Br1−xClx)3 and CsPb(Br1−xIx)3 NCs prepared by interparticle anion exchange. d,e) Reproduced with permission.[¹³²] Copyright 2015, American Chemical Society. f) CIE color coordinates and g) photograph of a deep‐blue LED based on 2D (PEA)2PbBr4 nanoplates. Reproduced with permission.[¹³¹] Copyright 2019, Wiley‐VCH. h) The illustration of the dominant exciton dissociation pathway via tunneling when interparticle distance is short and the coupling energy is high. When coupling energy decreases, the resonant energy transfer becomes dominant. Reproduced with permission.[¹⁴²] Copyright 2010, American Chemical Society. i) The illustration of increased CsPbBr3 inter‐NS coupling resulting from ligands rearrangement by annealing. Reproduced with permission.[¹³⁸] Copyright 2018, Wiley‐VCH. j) Schematic illustration of tuning the bandgap of perovskites by dimensionality engineering. Reproduced with permission.[¹⁸²] Copyright 2018, Wiley‐VCH. k) PL intensity image shows the carrier diffusion in an individual single‐crystalline MAPbI3 NW (scale bar: 5 µm). Reproduced with permission.[¹⁵⁶] Copyright 2015, American Chemical Society.
a) The image of needle‐shaped bulk C4N2H14PbBr4 crystals under ambient light. b) The crystals in (a) show strong bluish white‐light emission under 365 nm UV light. c) The absorption (dash lines) and emission (solid lines) spectra of the needle‐shaped bulk and 1D microscale C4N2H14PbBr4 crystals. a–c) Reproduced under the terms of the CC‐BY 4.0 license.[¹²⁸] Copyright 2017, the Authors, published by Springer Nature. d) The schematic illustration of interparticle anion exchange among CsPbX3 perovskite NCs. e) The absorption and PL spectra of CsPb(Br1−xClx)3 and CsPb(Br1−xIx)3 NCs prepared by interparticle anion exchange. d,e) Reproduced with permission.[¹³²] Copyright 2015, American Chemical Society. f) CIE color coordinates and g) photograph of a deep‐blue LED based on 2D (PEA)2PbBr4 nanoplates. Reproduced with permission.[¹³¹] Copyright 2019, Wiley‐VCH. h) The illustration of the dominant exciton dissociation pathway via tunneling when interparticle distance is short and the coupling energy is high. When coupling energy decreases, the resonant energy transfer becomes dominant. Reproduced with permission.[¹⁴²] Copyright 2010, American Chemical Society. i) The illustration of increased CsPbBr3 inter‐NS coupling resulting from ligands rearrangement by annealing. Reproduced with permission.[¹³⁸] Copyright 2018, Wiley‐VCH. j) Schematic illustration of tuning the bandgap of perovskites by dimensionality engineering. Reproduced with permission.[¹⁸²] Copyright 2018, Wiley‐VCH. k) PL intensity image shows the carrier diffusion in an individual single‐crystalline MAPbI3 NW (scale bar: 5 µm). Reproduced with permission.[¹⁵⁶] Copyright 2015, American Chemical Society.
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Strategies to improve 0D MHP PDs. a) Schematics of the surface engineering process by replacing weak‐interaction OA, OLA, and ODE ligands with strong‐interaction MPA ligands on CsPbCl3 NCs. Reproduced with permission.[²⁰⁸] Copyright 2019, American Chemical Society. b) TEM images of different shapes of CsPbBr3 NCs. c) SEM images of the pristine CsPbBr3 NC thin film, and the films treated with 1, 2, and 5 times of film modification. All the scale bars are 5 µm and the insets are graphs of corresponding samples. b,c) Reproduced with permission.[²¹⁶] Copyright 2016, Wiley‐VCH. d) Schematics of NC films before and after centrifugal casting treatment. e) Examples of 0D MHP‐based hybrid structures.
Strategies to improve 0D MHP PDs. a) Schematics of the surface engineering process by replacing weak‐interaction OA, OLA, and ODE ligands with strong‐interaction MPA ligands on CsPbCl3 NCs. Reproduced with permission.[²⁰⁸] Copyright 2019, American Chemical Society. b) TEM images of different shapes of CsPbBr3 NCs. c) SEM images of the pristine CsPbBr3 NC thin film, and the films treated with 1, 2, and 5 times of film modification. All the scale bars are 5 µm and the insets are graphs of corresponding samples. b,c) Reproduced with permission.[²¹⁶] Copyright 2016, Wiley‐VCH. d) Schematics of NC films before and after centrifugal casting treatment. e) Examples of 0D MHP‐based hybrid structures.
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Optical microscopy image of a) the MAPbI3 NWs and b) NWs crossing the Pt source–drain contacts. a,b) Reproduced with permission.[⁶⁵] Copyright 2014, American Chemical Society. c,d1) SEM images of MAPbI3 NWs and networks synthesized by controlling the crystallization. d2) XRD patterns of MAPbI3 thin film, NWs, and networks deposited on PET. The peaks of OTP and PET substrates are marked as red and blue marks, respectively. d3) Photocurrent statistical boxplots of PD arrays made by MAPbI3 thin film, NWs, and networks. c,d1–d3) Reproduced with permission.[³³] Copyright 2015, American Chemical Society. e1) Schematic of working mechanism of a biomimetic eye with a hemispherical MHP NW array retina. Reproduced with permission.[²³¹] Copyright 2020, Springer Nature. e2) Normalized photocurrent of a MAPbI3 NW‐based PD as a function of the polarization angle θ; the unity corresponds to the photocurrent when θ = 90° or 270°. Reproduced with permission.[³⁶] Copyright 2016, American Chemical Society.
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Optical microscopy image of a) the MAPbI3 NWs and b) NWs crossing the Pt source–drain contacts. a,b) Reproduced with permission.[⁶⁵] Copyright 2014, American Chemical Society. c,d1) SEM images of MAPbI3 NWs and networks synthesized by controlling the crystallization. d2) XRD patterns of MAPbI3 thin film, NWs, and networks deposited on PET. The peaks of OTP and PET substrates are marked as red and blue marks, respectively. d3) Photocurrent statistical boxplots of PD arrays made by MAPbI3 thin film, NWs, and networks. c,d1–d3) Reproduced with permission.[³³] Copyright 2015, American Chemical Society. e1) Schematic of working mechanism of a biomimetic eye with a hemispherical MHP NW array retina. Reproduced with permission.[²³¹] Copyright 2020, Springer Nature. e2) Normalized photocurrent of a MAPbI3 NW‐based PD as a function of the polarization angle θ; the unity corresponds to the photocurrent when θ = 90° or 270°. Reproduced with permission.[³⁶] Copyright 2016, American Chemical Society.
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Review
Low-Dimensional Metal Halide Perovskite Photodetectors
Hsin-Ping Wang, Siyuan Li, Xinya Liu, Zhifeng Shi, Xiaosheng Fang,* and Jr-Hau He*
Dr. H.-P. Wang, Prof. J.-H. He
Department of Materials Science and Engineering
City University of Hong Kong
Tat Chee Avenue, Kowloon, Hong Kong
E-mail: jrhauhe@cityu.edu.hk
S. Y. Li, X. Y. Liu, Prof. X. S. Fang
Department of Materials Science
Fudan University
Shanghai 200433, P. R. China
E-mail: xshfang@fudan.edu.cn
Prof. Z. F. Shi
Key Laboratory of Materials Physics of Ministry of Education
School of Physics and Microelectronics
Zhengzhou University
Daxue Road 75, Zhengzhou 450052, P. R. China
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adma.202003309.
DOI: 10.1002/adma.202003309
charge carrier collection. Nowadays,
PDs detecting in the UV–visible to near-
infrared (NIR) spectrum range are mainly
based on crystalline inorganic elemental
semiconductors, such as Si, III–V and
II–VI semiconductors, and their hetero-
junctions.[5,6] These PDs have been fully
investigated and mature, but they usually
have complicated structures and require
high-temperature and complex fabrication
processes, such as metal-organic chemical
vapor deposition (MOCVD) and molec-
ular-beam epitaxy (MBE), leading to high
cost. Moreover, the mechanical inflexibility
of materials limits their broader applica-
tions for large-area and flexible PDs.
PDs made by solution-processed semi-
conductors have recently emerged as a
potential candidate for next-generation
light sensors.[3,7–9] Among them, metal
halide perovskites (MHPs) have been
sparking wide interest for optoelectronic
devices because they hold several advan-
tages over traditional materials such as the simplicity of their
processing (e.g., solution deposition), high absorption coef-
ficient, weakly bound excitons, long carrier lifetime >1ms in
polycrystalline films, and tunable bandgap between 1.48 and
2.23eV.[10–14] Ballif’s group found a high absorption coecient
of MAPbI3 (MA = methylammonium) perovskite with particu-
larly sharp onset and discussed the relation between sharp
optical absorption edge and its photovoltaic performance.[15]
MHPs exhibit a much higher absorption coecient than
crystalline Si and show an exponential trend over more than
four decades with an Urbach energy of 15 meV for MAPbI3
and as low as 13 meV for MAPbBr3, which is comparable to
III–V materials (e.g., Urbach energy of GaAs is 7 meV).[12,15]
The low value of Urbach energy indicates a very low degree
of structural disorder and high crystallinity of MHP crystals.
The purely exponential optical absorption edge strongly sug-
gests no apparent presence of deep states within the bandgap,
which is likely a key factor why MHPs can feature such great
optoelectronic performance compared to other materials.[12,16]
In brief, MHPs have attracted considerable attention because
of such superb optoelectronic properties comparable to III–V
materials but much cost-eective fabrication processes. These
advantages make researchers believe perovskites could also
be a good candidate for future PDs. Encouragingly, polycrys-
talline MHP PDs exhibit comparable or even better perfor-
mance than those traditional single-crystalline semiconductors
(Si, Ge, etc.) and high-temperature epitaxial semiconductor
PDs (InGaAs, HgCdTe, etc.) due to their great optoelectronic
Metal halide perovskites (MHPs) have been a hot research topic due to their
facile synthesis, excellent optical and optoelectronic properties, and record-
breaking eciency of corresponding optoelectronic devices. Nowadays, the
development of miniaturized high-performance photodetectors (PDs) has been
fueling the demand for novel photoactive materials, among which low-dimen-
sional MHPs have attracted burgeoning research interest. In this report, the
synthesis, properties, photodetection performance, and stability of low-dimen-
sional MHPs, including 0D, 1D, 2D layered and nonlayered nanostructures, as
well as their heterostructures are reviewed. Recent advances in the synthesis
approaches of low-dimensional MHPs are summarized and the key concepts
for understanding the optical and optoelectronic properties related to the PD
applications of low-dimensional MHPs are introduced. More importantly,
recent progress in novel PDs based on low-dimensional MHPs is presented,
and strategies for improving the performance and stability of perovskite PDs
are highlighted. By discussing recent advances, strategies, and existing chal-
lenges, this progress report provides perspectives on low-dimensional MHP-
based PDs in the future.
1. Introduction
Photodetectors (PDs), which convert optical signals to electrical
signals, have wide applications in many fields, such as optical
communication, image sensing, environmental monitoring,
and sensing in the Internet of Things (IoT).[1–4] An ecient
PD requires high responsivity (R), high detectivity (D*), on/o
ratio, and fast response speed. To realize these characteristics,
the active layers in PDs must have a high absorption coecient,
low trap-state density (ntrap), high carrier mobility, and ecient
Adv. Mater. 2021, 33, 2003309
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  • May 2020
  • NATURE
Human eyes possess exceptional image-sensing characteristics such as an extremely wide field of view, high resolution and sensitivity with low aberration1. Biomimetic eyes with such characteristics are highly desirable, especially in robotics and visual prostheses. However, the spherical shape and the retina of the biological eye pose an enormous fabrication challenge for biomimetic devices2,3. Here we present an electrochemical eye with a hemispherical retina made of a high-density array of nanowires mimicking the photoreceptors on a human retina. The device design has a high degree of structural similarity to a human eye with the potential to achieve high imaging resolution when individual nanowires are electrically addressed. Additionally, we demonstrate the image-sensing function of our biomimetic device by reconstructing the optical patterns projected onto the device. This work may lead to biomimetic photosensing devices that could find use in a wide spectrum of technological applications. A biomimetic electrochemical eye is presented that has a hemispherical retina made from a high-density array of perovskite nanowires that are sensitive to light, mimicking the photoreceptors of a biological retina.
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Facet‐Dependent, Fast Response, and Broadband Photodetector Based on Highly Stable All‐Inorganic CsCu 2 I 3 Single Crystal with 1D Electronic Structure
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Low‐dimensional metal halides at molecular level, which feature strong quantum confinement effects from intrinsic structure, are emerging as ideal candidates in optoelectronic fields. However, developing stable and nontoxic metal halides still remains a great challenge. Herein, for the first time, high‐crystalline and highly stable CsCu2I3 single crystal, which is acquired by a low‐cost antisolvent vapor assisted method, is successfully developed to construct high‐speed (trise/tdecay = 0.19 ms/14.7 ms) and UV‐to‐visible broadband (300–700 nm) photodetector, outperforming most reported photodetectors based on individual all‐inorganic lead‐free metal halides. Intriguingly, facet‐dependent photoresponse is observed for CsCu2I3 single crystal, whose morphology consists of {010}, {110}, and {021} crystal planes. The on–off ratio of {010} crystal plane is higher than that of {110} crystal plane, mainly owing to lower dark current. Furthermore, photogenerated electrons are localized in twofold chains created by [CuI4] tetrahedra, leading to relatively small effective mass and fast transport mobility along the 1D transport pathway. Anisotropic carrier transport characteristic is related to stronger confinement and higher electron density for {110} crystal planes. This work not only demonstrates the great potential of CsCu2I3 single crystal in high‐performance optoelectronics, but also gives insights into 1D electronic structure associated with fast photoresponse and high anisotropy.
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Micro-light-emitting diodes with quantum dots in display technology
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  • May 2020
Micro-light-emitting diodes (μ-LEDs) are regarded as the cornerstone of next-generation display technology to meet the personalised demands of advanced applications, such as mobile phones, wearable watches, virtual/augmented reality, micro-projectors and ultrahigh-definition TVs. However, as the LED chip size shrinks to below 20 μm, conventional phosphor colour conversion cannot present sufficient luminance and yield to support high-resolution displays due to the low absorption cross-section. The emergence of quantum dot (QD) materials is expected to fill this gap due to their remarkable photoluminescence, narrow bandwidth emission, colour tuneability, high quantum yield and nanoscale size, providing a powerful full-colour solution for μ-LED displays. Here, we comprehensively review the latest progress concerning the implementation of μ-LEDs and QDs in display technology, including μ-LED design and fabrication, large-scale μ-LED transfer and QD full-colour strategy. Outlooks on QD stability, patterning and deposition and challenges of μ-LED displays are also provided. Finally, we discuss the advanced applications of QD-based μ-LED displays, showing the bright future of this technology.
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Flexible and Self-Powered Lateral Photodetector Based on Inorganic Perovskite CsPbI 3 -CsPbBr 3 Heterojunction Nanowire Array
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Self‐powered perovskite photodetectors mainly adopt the vertical heterojunction structure composed of active layer, electron–hole transfer layers, and electrodes, which results in the loss of incident light and interfacial accumulation of defects. To address these issues, a self‐powered lateral photodetector based on CsPbI3–CsPbBr3 heterojunction nanowire arrays is designed on both a rigid glass and a flexible polyethylene naphthalate substrate using an in situ conversion and mask‐assisted electrode fabrication method. Through adding the polyvinyl pyrrolidone and optimizing the concentration of precursors under the pressure‐assisted moulding process, both the crystallinity and stability of perovskite nanowire array are improved. The nanowire array–based lateral device shows a high responsivity of 125 mA W⁻¹ and a fast rise and decay time of 0.7 and 0.8 ms under a self‐powered operation condition. This work provides a new strategy to fabricate perovskite heterojunction nanoarrays towards self‐powered photodetection.
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Giant Optical Anisotropy of Perovskite Nanowire Array Films
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Polarizers play a key role in generating polarized light for display, imaging, and data communication, but adoption often suffers from high optical loss. Recently, due to superior optoelectronic properties, halide perovskites have been widely developed for lighting applications; however, highly polarized emission (polarization degree >0.8) has not yet been realized with perovskites. Herein, by incorporating inkjet printing and an anodic aluminum oxide (AAO) confinement strategy, highly ordered perovskite nanowire (NW) arrays are demonstrated for anisotropic optical applications. The optical device based on perovskite NW arrays reveals a high photoluminescence external quantum efficiency of 21.6% and emits highly polarized light with polarization degree up to 0.84. The highly polarized emission from perovskite NW arrays has potential to considerably reduce the optical loss of polarizers, which may attract great interest in developing polarized light sources for next‐generation optoelectronic applications.
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Pressure Effects on the Electronic and Optical Properties in Low-Dimensional Metal Halide Perovskites
Article
  • May 2020
Metal halide perovskites have shown enormous application potential in perovskite solar cells and light-emitting diodes, and made unprecedented progress in the past decade. Pressure engineering as an effective mean can systematically modify the electronic structures and physical properties of functional materials. Low-dimensional metal halide perovskites (0D, 1D and 2D) with a variety of compositions have soft lattices, therefore allow pressure effects to drastically modulate their structures and properties. High pressure investigations on metal halide perovskites have been widely carried out and obtained a comprehensive understanding of their structure-property relationships. Simultaneously, discoveries of novel pressure-driven properties, such as metallization and partially retained band gap narrowing not accessible by conventional chemical methods have contributed significantly to the further development of such materials. In this Perspective, we mainly highlight pressure response on the properties and structures of low-dimensional metal halide perovskites, which are essential for designing new perovskite materials and advancing applications.
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Designed growth and patterning of perovskite nanowires for lasing and wide color gamut phosphors with long-term stability
Article
  • Apr 2020
Hybrid halide perovskites are proposed for next-generation photovoltaics and lighting technologies due to their remarkable optoelectronic properties. In this study, we demonstrate printed perovskite nanowires (NWs) for lasing and wide-gamut phosphor using a combination of inkjet printing and nanoporous anodic aluminum oxide (AAO). The random lasing behaviors of the resulting perovskite NWs are analyzed and discussed. Moreover, by varying the composition of Cl⁻, Br⁻, and I⁻ anions, we demonstrate tunable emission wavelengths of the perovskite NWs from 439 to 760 nm, with a large red-green-blue color space that extends to 117% of the color standard defined by the National Television Systems Committee (NTSC). Furthermore, we demonstrate passivation of the perovskite NWs against moisture due to their compact spatial confinement within the AAO template combined with a poly(methyl methacrylate) sealing process, resulting in highly stable emission intensity that degrades only 19% after continuous 250 h of 30 mW/cm² UV excitation and degrades 30% after three months when stored in air at 50% humidity. This inkjet printing fabrication strategy involving AAO-confined perovskite NWs enables highly stable, large-area direct patterning and mass production of perovskite NWs, which is promising for modern lighting applications.
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Machine-Learning-Accelerated Perovskite Crystallization
Article
  • Mar 2020
Perovskites have seen significant research interest in the last decade. As ternary and quaternary compounds, their chemical space is exceptionally large, yet perovskite development has been limited to a restricted set of chemical constituents often discovered through trial and error. Here, we report a high-throughput experimental framework for the discovery of new perovskite single crystals. We use machine learning (ML) to guide the sequence of ever-improved robotic synthetic trials. We perform high-throughput syntheses of perovskite single crystals with a protein crystallization robot and characterize the outcomes with the aid of convolutional neural network-based image recognition. We then use an ML model to predict the optimal conditions for the synthesis of a new perovskite single crystal, enabling us to report the first synthesis of (3-PLA)2PbCl4.This material exhibits strong blue emission, illustrating the applicability of the method in identifying new optoelectronic materials.
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