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    Home > Research group of associate professor Fan Zhiyong of Hong Kong University of science and technology: using nano photon substrate to greatly improve the efficiency of light extraction to achieve high efficiency perovskite LED

    Research group of associate professor Fan Zhiyong of Hong Kong University of science and technology: using nano photon substrate to greatly improve the efficiency of light extraction to achieve high efficiency perovskite LED

    • Last Update: 2019-03-16
    • Source: Internet
    • Author: User
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    In recent years, perovskite materials have been widely studied and applied in solar cells due to their excellent photoelectric properties At the same time, due to the advantages of perovskite material, such as high internal quantum efficiency and adjustable light-emitting wavelength, perovskite LED is expected to become the basic component of the next generation of high-definition flat panel display after OLED Since the first report in 2014, the external quantum efficiency of perovskite LED has been improved rapidly, and reached a milestone of 20% of the external quantum efficiency of green light and red light in 2018 However, most of the previous studies focused on the optimization of the morphology and properties of the active layer and the transport layer However, considering perovskite as a high refractive index material, the optical extraction index will be the key factor to limit the further improvement of its external quantum efficiency Recently, an efficient LED device based on methylammonium lead bromide (mapbbr 3) has been fabricated on the photonic crystal substrate by the research group of associate professor Fan Zhiyong of Hong Kong University of science and technology 17.5% of the external quantum efficiency (twice the highest record before LED of this material system) and 73% of the theoretical optical extraction efficiency have been obtained The efficient extraction of light comes from the two steps of nano dome and nano wire The former couple the luminescence in the active layer of the device into the photonic crystal composed of nanowire array, and the latter, as an optical antenna, converts the binding energy in the photonic crystal into the transmissible light energy Relevant research results were published in NAT Commin (DOI: 10.1038 / s41467-019-08561-y) under the title of "efficient metal halide perovskite light emitting diodes with signi" and "cantly improved light extraction on nanophotonic substrates" The first author was Zhang qianpeng, a doctoral student Prof fan Zhiyong, associate professor, Department of electronic and computer engineering, Hong Kong University of science and technology In 1998 and 2001, he received his bachelor's degree and master's degree from the Department of physics and electronics of Fudan University He received his Ph.D in materials science from the University of California, Irvine in 2006 From 2007 to 2010, he worked as a postdoctoral researcher at the University of California, Berkeley and Lawrence Berkeley National Laboratory He joined Hong Kong University of science and technology in 2010 and is currently an associate professor in the Department of electronic and computer engineering He was elected member of the Royal Society of chemistry in 2018 In 2018, he was rated as a global high cited scholar by web of Science (clarivate Analytics) At present, he has published more than 150 high-level papers, cited more than 15000 times in total, H factor 59 Served as the editorial board member of NPG scientific reports and Springer nanoscale research letters He is also the reviewer of nature, nature materials, Nature Nanotechnology, nature communications, science advanced, nano letters, ACS Nano, advanced materials, IEEE EDL and other journals At present, the research includes perovskite nanowires, perovskite optoelectronic devices, flexible wearable devices, gas sensors and the interaction between light and matter in nanostructured optoelectronic devices Cutting edge scientific research achievements: the device structure in this work is shown in Figure 1 The device is prepared on the top rather than the inside of the nano photon substrate, so as to minimize the impact of the introduction of nano structure on the electrical performance of the device What's more, the nanophotonic substrate here is based on the porous anodic alumina template (AAM) which is easy to prepare and low cost, and the structure size of the photonic crystal substrate can be accurately controlled Fig 1 LED device based on nano photon substrate (scale bar in Fig B and C is 1 μ m) a) Device structure diagram; b) AAM film; c) device cross section diagram (source: Nat Commun.) by controlling the structure size of AAM, the author prepared three kinds of different devices (Fig 2) including plane comparison devices It is found that only reasonable design of the geometric parameters of the photonic crystal substrate can greatly improve the optical efficiency Figure 2 Device performance a) Current density and brightness; b) external quantum efficiency; c) enhancement coefficient of external quantum efficiency (source: Nat Commun.) in order to further explore the influence of substrate geometry on device performance, the author has made a systematic study on the relationship between optical efficiency and substrate geometry by using the FDTD method (Fig 3) It is found that the optimized structure of this kind of nano photon substrate is based on AAM with 1000 nanometer period and 0.4 diameter / period ratio 。 At the same time, AAM needs to be filled with high refractive index materials, which is to make the nanowires in AAM as the core layer of optical waveguide, so as to form a guided mode, and facilitate the coupling of light from the active layer into the nanowire array Figure 3 Simulation of light extraction rate a) AAM is filled with high refractive index material titanium dioxide; b) AAM is filled with air (source: Nat Commun.) furthermore, the propagation process of light in different geometric size substrates is studied It is found that most of the light energy of the planar devices is bound in the active layer of the device, most of the light of the 500 nm periodic devices is bound in the nanowire array as the guided mode, and the 1000 nm and 1500 nm periodic devices can convert the guided mode into the leaky mode, thus becoming the light radiation energy Figure 4 Evolution of electric field in time domain From top to bottom are planar devices, 500 nanometer periodic devices, 1000 nanometer periodic devices and 1500 nanometer periodic devices (source: Nat Commun.) in order to better compare the light emission effect of different geometric size devices, the far-field distribution of different devices is studied The results further verify that the light energy needs to be coupled into the nanowire array from the active layer of the device to form the guided mode, and then the guided mode is transformed into the leaky mode by the scattering effect of the nanowire array to achieve high-efficiency light extraction Fig 5 Electric field intensity distribution of cross section and far field From top to bottom are planar devices, 100 nanometer periodic devices, 500 nanometer periodic devices, 1000 nanometer periodic devices and 1500 nanometer periodic devices (source: Nat Commun.) however, the difference between 1000 nm periodic device and 1500 nm periodic device is that 1500 nm periodic device can form more guided modes, and the guided modes that can not be converted into leakage mode will eventually be lost According to the study of extinction rate of these two size devices (Fig 6), it is shown that the 1000 nanometer period nanowire array can form scattering resonance at the light-emitting wavelength of 530 nm, and the light-emitting wavelength is in the pass band of the optical antenna; while the 1500 nanometer period nanowire array has no obvious scattering resonance, and the light-emitting wavelength is at the edge of the pass band of the optical antenna This also explains why the device with 1000 nanometer period has better optical extraction performance than the device with 1500 nanometer period Figure 6 Near field distribution and extinction spectrum From top to bottom, there are 500 nanometer periodic devices, 1000 nanometer periodic devices and 1500 nanometer periodic devices (source: Nat Commun.) relevant research results were published in NAT Commun (DOI: 10.1038/s41467-019-08561-y) The first author is Zhang qianpeng, PhD student of HKUST, and the corresponding author is fan Zhiyong, associate professor of HKUST The related work was supported by NSFC, Shenzhen Science and Technology Innovation Committee and Hong Kong research funding Bureau Nowadays, people and scientific research have been paid more and more attention in the economic life China has ushered in the "node of science and technology explosion" Behind the progress of science and technology is the work of countless scientists In the field of chemistry, in the context of the pursuit of innovation driven, international cooperation has been strengthened, the influence of Returned Scholars in the field of R & D has become increasingly prominent, and many excellent research groups have emerged in China For this reason, CBG information adopts the 1 + X reporting mechanism CBG information, chembeangoapp, chembeango official microblog, CBG wechat subscription number and other platforms jointly launch the column of "people and scientific research", approach the domestic representative research group, pay attention to their research, listen to their stories, record their demeanor, and explore their scientific research spirit.
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