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Jiming Bao1 2 Yanan Wang2 1 Chong Wang3 1 Xinghua Su4 1 Viktor Hajdev1 Yizhou Ni1 Shuo Chen1 Zhifeng Ren1 Zhiming Wang2

1, University of Houston, Houston, Texas, United States
2, University of Electronic Science and Technology of China, Chengdu, , China
3, Yunnan University, Kunming, , China
4, Changan University, Xian, , China

CsPb2Br5 is a 2D perovskite where single layer Cs acts as a spacer, monolayer PbBr6 octahedrons are edge shared. Although CsPb2Br5 was synthesized more than 10 years ago[1, 2], only recently it began to draw a lot of attention. Despite extensive research over past two years, its fundamental bandgap and basic electronic and optical properties still remain controversial: is this a wide bandgap indirect semiconductor or a direct bandgap material with strong green luminescence at ~520 nm? Zhang et al. reported that the attachment of CsPb2Br5 dots to CsPbBr3 nanocrystals can enhance external quantum efficiency of CsPbBr3 light-emitting diode (LED) by 50%[3]. Wang et al. later demonstrated a nearly 90% quantum efficiency with CsPb2Br5 nanocrystals. Using ion exchange with I and Cl, they further expended emission wavelength from UV to red[4]. But these claims of high luminescence have met with skeptics. Li et al. observed no photoluminescence, in agreement with their calculation result of indirect wide bandgap semiconductor[5]. Since then, the controversy remains, some group still report strong visible bandgap and strong photoluminescence and even demonstrate lasing action in CsPb2Br5 microplates[6, 7], while others reported the opposite[8]. In this talk, I will discuss the reason for different observations and present our result of the bandgap investigation of CsPb2Br5.

References:
[1] I. Y. Kuznetsova, I. S. Kovaleva, V. A. Fedorov, Russ. J. Inorg. Chem. 2001, 46, 1730.
[2] M. Rodova, J. Brozek, K. Knizek, K. Nitsch, J. Therm. Anal. Calorim. 2003, 71, 667.
[3] X. L. Zhang, B. Xu, J. B. Zhang, Y. Gao, Y. J. Zheng, K. Wang, X. W. Sun, Adv. Funct. Mater. 2016, 26, 4595.
[4] K. H. Wang, L. Wu, L. Li, H. B. Yao, H. S. Qian, S. H. Yu, Angew. Chem.-Int. Edit. 2016, 55, 8328.
[5] G. P. Li, H. Wang, Z. F. Zhu, Y. J. Chang, T. Zhang, Z. H. Song, Y. Jiang, Chem. Commun. 2016, 52, 11296.
[6] X. S. Tang, Z. P. Hu, W. Yuan, W. Hu, H. B. Shao, D. J. Han, J. F. Zheng, J. Y. Hao, Z. G. Zang, J. Du, Y. X. Leng, L. Fang, M. Zhou, Adv. Opt. Mater. 2017, 5.
[7] W. S. Longfei Ruan, Aifei Wang, Aishuang Xiang, Zhengtao Deng, The Journal of Physical Chemistry Letters 2017, DOI: 10.1021/acs.jpclett.7b01657.
[8] M. D. B. Ibrahim Dursun, Bekir Turedi, Badriah, A. S. Alamer, Jun Yin, Issam Gereige,, O. F. M. Ahmed Alsaggaf, Mohamed Eddaoudi,, a. O. M. Bakr, ChemSusChem 2017, ChemSusChem 10.1002/cssc.201701131.

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