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Perovskite light‐emitting diodes (PeLEDs) are advancing because of their superior external quantum efficiencies (EQEs) and color purity. Still, additional work is needed for blue PeLEDs to achieve the same benchmarks as the other visible colors. This study demonstrates an extremely efficient blue PeLED with a 488 nm peak emission, a maximum luminance of 8600 cd m⁻², and a maximum EQE of 12.2% by incorporating the double‐sided ethane‐1,2‐diammonium bromide (EDBr₂) ligand salt along with the long‐chain ligand methylphenylammonium chloride (MeCl). The EDBr₂successfully improves the interaction between 2D perovskite layers by reducing the weak van der Waals interaction and creating a Dion–Jacobson (DJ) structure. Whereas the pristine sample (without EDBr₂) is inhibited by small stacking number (n) 2D phases with nonradiative recombination regions that diminish the PeLED performance, adding EDBr₂successfully enables better energy transfer from smallnphases to largernphases. As evidenced by photoluminescence (PL), scanning electron microscopy (SEM), and atomic force microscopy (AFM) characterization, EDBr₂improves the morphology by reduction of pinholes and passivation of defects, subsequently improving the efficiencies and operational lifetimes of quasi‐2D blue PeLEDs.

Blue electroluminescence is highly desired for emerging light‐emitting devices for display applications and optoelectronics in general. However, saturated, efficient, and stable blue emission has been challenging to achieve, particularly in mixed‐halide perovskites, where intrinsic ion motion and halide segregation compromises spectral purity. Here, CsPbBr_3−xCl_xperovskites, polyelectrolytes, and a salt additive are leveraged to demonstrate pure blue emission from single‐layer light‐emitting electrochemical cells (LECs). The electrolytes transport the ions from salt additives, enhancing charge injection and stabilizing the inherent perovskite emissive lattice for highly pure and sustained blue emission. Substituting Cl into CsPbBr₃tunes the perovskite luminescence from green through blue. Sky blue and saturated blue devices produce International Commission on Illumination coordinates of (0.105, 0.129) and (0.136, 0.068), respectively, with the latter meeting the US National Television Committee standard for the blue primary. Likewise, maximum luminances of 2900 and 1000 cd m⁻², external quantum efficiencies (EQEs) of 4.3% and 3.9%, and luminance half‐lives of 5.7 and 4.9 h are obtained for sky blue and saturated blue devices, respectively. Polymer and LiPF₆inclusion increases photoluminescence efficiency, suppresses halide segregation, induces thin‐film smoothness and uniformity, and reduces crystallite size. Overall, these devices show superior performance among blue perovskite light‐emitting diodes (PeLEDs) and general LECs.

Hybrid perovskites are emerging as highly efficient materials for optoelectronic applications, however, their operational lifetime has remained a limiting factor for their continued progress. In this work, perovskite light emitting electrochemical cells utilizing an optimized fraction of lithium hexafluorophosphate (LiPF₆) salt additive exhibit enhanced stability. At 0.5 wt% LiPF₆, devices exhibit 100 h operation at high brightness in excess of 800 cd m⁻²under constant current driving, achieving a maximum luminance of 3260 cd m⁻²and power efficiency of 9.1 Lm W⁻¹. This performance extrapolates to a 6700 h luminance half‐life from 100 cd m⁻², a 5.6‐fold improvement over devices with no LiPF₆. Analysis under constant voltage driving reveals three current regimes, with lithium addition strongly enhancing current in the second and third regimes. The third regime correlates lower rates of luminance with lowered current flow. These losses are mitigated by LiPF₆addition, an effect postulated to arise from preservation of perovskite structure. Electrochemical impedance spectroscopy with equivalent circuit modeling reveals that electrical double layer widths are minimized at 0.5 wt% LiPF₆and inversely correlated with efficient performance. These results demonstrate that an optimal LiPF₆concentration improves stability and efficiency through improved double layer formation and retention of perovskite structure.

Hybrid organic–inorganic perovskite light‐emitting devices (LEDs) have recently shown the characteristic dynamical behavior of light‐emitting electrochemical cells (LECs), with intrinsic ionic migration creating an electric double layer and internal p‐i‐n structure and by accumulation of ions at interfaces. Therefore, the development of perovskite light‐emitting and photovoltaic devices based on the concepts of LEC operation attracts much attention and clarifies general physical processes in perovskites. Here, new directions that can further improve perovskite optoelectronic devices and extend their functionalities using additive mobile ions are overviewed: 1) enhancing single‐layer LECs with lithium additives for increased efficiency and longer lifetime; 2) facilitating ionic motion in three‐layer perovskite LECs to create dual‐functional devices, operating as both LEC and solar cells; and 3) creating truly ambipolar LEC devices with carbon nanotubes as stable electrodes that leverage ionic doping. Taken together, the use of these approaches provides a strategy to create efficient, stable, and bright LECs, which use advantages of both LED and LEC operation. It is discussed that how the LEC behavior in perovskite LEDs can be further improved to address the long‐term challenges in perovskite optoelectronics, such as stability, through approaches like ionically reconfigurable host/guest systems.