Perovskite light-emitting diodes (PeLEDs) attract significant attention because of their high photoluminescence quantum yields (PLQYs), tunable light emission and high color purity. Extensive efforts have been keen on improving the device performance of PeLEDs. Very recently, green-, red- and near-infrared-emitting PeLEDs have obtained impressive external quantum efficiencies (EQEs) of exceeding 20%, which represents an important step towards the commercial application. 

However, blue PeLEDs, as one of the most important prerequisites, tremendously impede the progress in commercialization. In general, two approaches have been developed to obtain blue PeLEDs. One relies on incorporating chlorine into bromine-based perovskites to tune the bandgap, and the other depends on modulating the quantum-well structure. Yet, these mixed-halide perovskites exhibit intrinsic phase instabilities especially under electrical potential via using the former way, , which induced by the halide migration. Also, as the consequence of the later, these PeLEDs show extremely low EQEs (less than 0.1%) , broad multiple EL peaks because of the inefficient internal energy transfer. Moreover, Ostwald ripening typically takes place within minutes that leads to EL spectra significantly red-shift. Therefore, device performance and in particular the spectral stabilities of blue PeLEDs remain considerable challenges for the entire PeLED community.

Our research group (Mingjian Yuan, Nankai University) has investigated a Rubidium-Cesium alloyed, quasi-two-dimensional perovskite and demonstrated its great potential for pure-blue PeLED applications. 

In our resent work, we conceive an approach by tuning the ‘A-site’ cation composition of perovskites to develop blue-emitters with good spectral stabilities and use the method of in-situ passivation to further improve the material’s emission property and stabilities. In that case, we fabricate a Rb-Cs alloyed, <n>_Rb0.6 = 3 quasi-2D perovskite and demonstrate its great potential for further pure-blue LED application. As a result, we achieve a prominent film PLQY of around 82% at 476 nm, with excitation density as low as 1.5 mW cm^-2. Encouraged by these findings, we finally achieve a spectra-stable blue PeLED with the peak external quantum efficiency of 1.35% and a half-lifetime of 14.5 min, representing the most efficient and stable pure-blue PeLEDs reported so far. The strategy is also demonstrated to be able to generate efficient perovskite blue emitters and PeLEDs in the whole blue spectral region (from 454 to 492 nm).

The related paper has been published in Nature Communications. Please see details: 

Yuanzhi Jiang^†, Chaochao Qin^†, Minghuan Cui, Tingwei He, Kaikai Liu, Yanmin Huang, Menghui Luo, Li Zhang, Hongyu Xu, Saisai Li, Junli Wei, Zhiyong Liu, Huanhua Wang, Gi-Hwan Kim, Mingjian Yuan* & Jun Chen. Spectra stable blue perovskite light-emitting diodes. Nat. Commun. DOI: 10.1038/s41467-019-09794-7