Title: Stable Blue Perovskite Light-Emitting Diodes Achieved by Optimization of Crystal Dimension through Zinc Bromide Addition

Zhen-Li Yan, Jean-Sebastien Benas, Chu-Chen Chueh, Wei-Cheng Chen, Fang-Cheng Liang, Zhi-Xuan Zhang, Bi-Hsuan Lin, Chun-Jen Su, Takayuki Chiba,* Junji Kido*, and Chi-Ching Kuo*

https://www.sciencedirect.com/science/article/pii/S1385894721003715#!

Abstract
Low-dimensional perovskites have been widely studied as a promising candidate for realizing stable light-emitting diodes (LEDs). However, blue-light-emitting devices generally possess low stability associated with gradually red-shifted emission. To overcome this issue, the effect of zinc bromide (ZnBr2) addition on the regulation of the crystal structures of phenethylammonium and bromine-chlorine mixed inorganic perovskites (PEA-CsPbBrxCl3-x) is investigated. With the ZnBr2 addition, low-dimensional perovskite structures undergo morphological changes, such as thickening of their crystal structures and higher degree of crystal arrangement. Stoichiometric selective characterization reveals that perovskite bonding forces changed from Van der Waals with PEA to ionic with ZnBr2. Meanwhile, ZnBr2 can effectively address the ion defect filling and dimensional structure property switching. Consequently, the optimized ZnBr2-assisted PEA-CsPbBrxCl3-x LED is shown to deliver a high luminance of 1245 cd/m2 along with a high external quantum efficiency of 1.30%. Furthermore, this blue LED exhibits excellent spectral stability, for which only 3-nm red-shift on external excitation (0.1 to 5.0 mA) is observed. Our result clearly shows that ZnBr2 addition effectively improves the stability of blue light-emitting perovskites.