Unravelling Alkali‐Metal‐Assisted Domain Distribution of Quasi‐2D Perovskites for Cascade Energy Transfer toward Efficient Blue Light‐Emitting Diodes

Abstract

Solution processable quasi‐2D (Q‐2D) perovskite materials are emerging as a promising candidate for blue light source in full‐color display applications due to their good color saturation property, high brightness, and spectral tunability. Herein, an efficient energy cascade channel is developed by introducing sodium bromide (NaBr) in phenyl‐butylammonium (PBA)‐containing mixed‐halide Q‐2D perovskites for a blue perovskite light‐emitting diode (PeLED). The incorporation of alkali metal contributes to the nucleation and growth of Q‐2D perovskites into graded distribution of domains with different layer number <n>. The study of excitation dynamics by transient absorption (TA) spectroscopy confirms that NaBr induces more Q‐2D perovskite phases with small n number, providing a graded energy cascade pathway to facilitate more efficient energy transfer processes. In addition, the nonradiative recombination within the Q‐2D perovskites is significantly suppressed upon Na+ incorporation, as validated by the trap density estimation. Consequently, the optimized blue PeLEDs manifest a peak external quantum efficiency (EQE) of 7.0% emitting at 486 nm with a maximum luminance of 1699 cd m−2. It is anticipated that these findings will improve the understanding of alkali‐metal‐assisted optimization of Q‐2D perovskites and pave the way toward high‐performance blue PeLEDs.

Suppressed Energy Transfer Loss of Dion–Jacobson Perovskite Enabled by DMSO Vapor Treatment for Efficient Sky-Blue Light-Emitting Diodes

“…Undoubtedly, the passivation effect could effectively suppress the defect-related nonradiative recombination in the quasi-2D phases, which would further enhance the interphase energy transfer. 34,35 As expected, the rearranged phase distribution of the perovskite films shows an efficient energy transfer from the small-n phases, as deduced from the femtosecond transient absorption spectroscopy (TAS) measurement results shown in Figure 3 and Figure S6. For the perovskite films of R 40 , the photobleaching peaks of the middle-n phases are not distinguishable and the energy transfer occurs from the n = 1 phase to the n = 2 phase and then to the light emission phase, as presented in Figure 3b, which again confirms that the energy transfer gap is really formed.…”

“…This is consistent with the in situ GIWAXS measurement results that DMSO vapor can significantly facilitate the ligand migration and delay the crystallization of ligands, which not only results in the suppressed ligand aggregation effect but also contributes to the passivation effect. Undoubtedly, the passivation effect could effectively suppress the defect-related nonradiative recombination in the quasi-2D phases, which would further enhance the interphase energy transfer. , …”

Review on the promising roles of alkali metals toward highly efficient perovskite light-emitting diodes

“…Several articles have reported that smaller-sized alkali metals improved the efficiency of blue PeLEDs without destroying the original emission spectrum. Cai et al 76 studied the role of NaBr doping in a mixed halide quasi-2D perovskite containing PBA for blue light emission. The NaBr works as the spacer ligand to provide extra modulation of the distribution of quasi-2D perovskite.…”

Composition and structure regulation of Ruddlesden–Popper perovskite for light-emitting diodes applications

“…Additives are usually used for phase composition and defect passivation, thus efficiently improving the performance of PeLEDs. 8,[33][34][35][36][37][38][39][40][41] Organics, such as ethoxylated trimethylolpropane triacrylate (ETPTA) containing CQO functional groups, can passivate defects both on the surface and within the perovskites. These materials are, therefore, great candidates for additives.…”