Pure Blue Electroluminescence by Differentiated Ion Motion in a Single Layer Perovskite Device

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_x perovskites, 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 CsPbBr₃ tunes 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 LiPF₆ inclusion 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.