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.

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[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.