They published their work on May. 15 in Energy Material Advances.
"With lead-halide perovskites reaching a mature research stage approaching product marketing, concerns remain about the materials' stability and the toxicity of lead-based salts." said paper author Hongwei Song, professor at College of Electronic Science and Engineering, Jilin University. Double perovskites with Cs2AgInCl6 composition, often doped with various elements, have been in the spotlight owing to their intriguing optical properties, namely, self-trapped exciton (STEs) emission and dopant-induced photoluminescence. This interest has sparked different synthesis approaches towards both crystals and nanocrystals, and the exploration of many alloy compositions with mono- and trivalent cations other than Ag+ and In3+.
Song explained that, in the development of lead-free perovskite materials, people's first thought is to replace Pb element with non-toxic element. In order to replace Pb in halide perovskite, researchers chose several low-toxic cations in the same period closest to it, such as Sn, Ge, Bi, Sb, In, etc., because they have similar inactive shell s orbital. This is the key to the unique photoelectric properties of perovskite materials. The emergence of double perovskite just solved the above problems, lead-based perovskite materials have attracted great attentions in solid-state lighting area due to their high efficiency, high color rendering and tunable luminescence performance. This is both an opportunity and a challenge for the overall development of the photoelectric industry.
"Since the pioneering work on Cs2AgInCl6 in 2017 reported by Giustino et al. and Zhou et al. nearly simultaneously, many efforts have been devoted to its synthesis, modification of its composition, study of its electronic structure, optoelectronic properties, and applications. Recently, a record of white light emission with 86 % PLQY was achieved by Luo et al. via simultaneous alloying of Ag+ with Na+ and Bi3+ doping, marking an important milestone in the development of Cs2AgInCl6 related materials.” Song said. "Despite several advantages, major issues with these lead halide perovskites remain their poor stability and toxicity. In order to solve such problems, various attempts have been made to reduce the toxicity of perovskites while still maintaining their efficient optical properties."
The existence of Bi3+ ions decrease the excitation (absorption) energy, provides a new absorption channel and increases the energy transfer rate to Eu3+ ions. Through adjusting the Bi3+ and Eu3+ concentrations, a maximum photoluminescence efficiency (PLQY) of 80.1% is obtained in 6% Eu3+ and 0.5% Bi3+ co-doped Cs2AgInCl6 DPs.
"The energy transfer efficiency can be fitted with the decay rates under different Bi3+ doping concentrations. It can be seen that the energy transfer rate improves as a whole with the increase of the doping concentration of Bi3+, and the optimum energy transfer rate corresponding to the Bi3+ concentration is 0.5%. Next, we conducted PLQY test on the materials. For the undoped Cs2AgInCl6 DPs, PLQY is only 0.5%, which dramatically increases to 20.1% after the addition of Bi3+. After co-doped with Eu3+ and Bi3+ ions, PLQY continues to increase, and reaches the maximum of 80.1% when the Eu concentration reaches 6%. Here, we propose a possible mechanism to describe Eu3+ emission in Bi/Eu3+: Cs2AgInCl6. Cs2AgInCl6 DP is a direct bandgap semiconductor. Bi3+ doping provides a new absorption channel for the material, which may be caused by the contribution of the Bi3+ orbital in the band edge, breaking the STE-state compatibility ban transition, generating a new light absorption channel at a lower energy, and promoting the PLQY emitted by STE. For the Eu3+emission, we think there are two pathways. First, the energy transfer from STE to Eu3+ ions is possible as we have observed the Eu3+ emission in the Eu3+ doped Cs2AgInCl6 DPs. Second, the Eu3+ emission may mainly come from the energy transfer from Bi3+ ions to Eu3+ ions. The Bi3+ ions absorb the excitation light and transfer the energy from 1P1, 3P2, 3P1, 3P0 levels of Bi3+ ions to 5D3, 5D2, 5D1 and 5D0 levels of Eu3+ ions. The characteristic emission of Eu3+ ions is then formed through 5D0→7Fj(j=0,1,2,3) transitions." Song said.
"Finally, we prepared the white light emitting diodes based on Bi3+ and Eu3+ codoped Cs2AgInCl6 DPs were fabricated with the optimum color rendering index of 89, the optimal luminous efficiency of 88.1 lm/W and a half-lifetime of 1493 h. This strategy of imparting optical functions to metal halide DPs may lead to future applications, such as optical fiber communications, daily lighting, military industry, displays, and other fields."Song said.
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Reference
Authors: TIANYUAN WANG, DONGLEI ZHOU , ZHONGZHENG YU, TINGTING ZHOU, RUI SUN, YUQI WANG, XIAOMEI SUN, YUE WANG, YONGZHI SHAO, AND HONGWEI SONG
Title of original paper: Eu3+-Bi3+ Codoping Double Perovskites for Single-Component White-Light-Emitting Diodes
Journal: Energy Material Advances
DOI: 10.34133/energymatadv.0024
Affiliations:
1State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun, 130012, China.
2Cavendish Laboratory, University of Cambridge, Cambridge, CB3 0HE, UK.
About the authors:
Song Hongwei (1967-) is professor and doctoral supervisor of State Key Joint Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University; BR Program of Chinese Academy of Sciences (2000), winner of the National Outstanding Youth Fund (2009), the third batch of senior experts of Provincial Management of Jilin Province (2011), the "Micro and Nano Information materials and Devices Innovation Team" led by the National Key field Innovation Team (2017), the fourth batch of National 10,000 Thousand Plan Leading Talents (2018). Currently, he serves as deputy Director of Luminescence Committee of Chinese Granular Society, member of Luminescence Branch of Chinese Physical Society, member of Luminescence Committee of Chinese Rare Earth Society. He is the editorial board member of Nanomaterials, Journal of Nanosciences and Reports, Scientific Report, Current Chinese Science, Journal of Luminescence and other academic journals. As well as universities outstanding scientific research achievement award, National Natural Science Award evaluation experts. Mainly engaged in rare earth luminescent materials, optoelectronic materials and devices research; Representative achievements: The doping of rare earth ions in perovskite nanocrystals was achieved for the first time, and a quantum cutting luminescent material with a quantum efficiency of nearly 200% was obtained. The material was used as a fluorescence conversion layer in crystalline silicon cells, which improved the photoelectric conversion efficiency of the cells by 3-4 percentage points and the efficiency of the reference devices by 20%. Has been described as one of the most exciting jobs in recent years.
Zhou Donglei (1990-), PhD, Associate professor, postgraduate supervisor, "Tang Aoqing Scholar" of Jilin University, selected in Jilin Province Youth Science and Technology Talent Promotion Project. From 2018 to 2020, he worked as a postdoctoral researcher in Nanyang Technological University, Singapore. In 2020, he was appointed as an associate professor in Jilin University, mainly engaged in the application research of new rare earth nanoluminescent materials and optoelectronic energy devices. In Advanced Materials, ACS Nano, Nano Letters, Light: More than 80 SCI papers have been published in Science & Applications, Advanced Energy Materials, Advanced Functional Materials, ACS Energy Letters and other international academic journals. He has been cited more than 3,500 times and published a chapter in English (Taylor & Francis). She has undertaken projects of National Natural Science Foundation, Youth projects of National Natural Science Foundation, and Natural Science Foundation of Jilin Province, etc. As a participant, she won the first prize of Natural Science of Jilin Province in 2019, and was invited to give invitation reports at international and domestic conferences for more than 10 times. He is the young editorial board member of Journal of Luminescence and guest editor of Nanomaterials, Frontiers in Chemistry and other journals. The main research achievements are as follows: 1. A new type of rare earth doped perovskite nanocrystalline with wide spectral band and strong absorption was developed to obtain high efficiency quantum clipper luminescence, which was applied to improve the photoelectric conversion efficiency of crystalline silicon cells, which was evaluated as "one of the most exciting work in recent years" by Science magazine; 2. Based on a new rare earth doped perovskite material, a single component of white electroluminescent LED device was developed, and a near infrared electroluminescent LED based on Er was obtained. 3. A rare earth photodetector with ultraviolet and infrared biband response was developed, and the internal mechanism of rare earth to maintain efficient luminescence under the high-pressure limit environment was discovered, and a visual detection array system was constructed. The high efficiency perovskite solar cells sensitized by rare earth quantum dots and natural materials were developed, and the key principles of rare earth ions to improve the device efficiency were summarized.
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