Spectrally Stable Deep-Blue Perovskite Light-Emitting Diodes Enabled by a Deep Eutectic Solvent

Full-color LED display requires Commission Internationale de l'Eclairage (CIE) 1931 coordinates of (0.14, 0.08), based on the National Television Standards Committee (NTSC) blue standard. However, such deep-blue perovskite light-emitting diodes (PeLEDs) still lag far behind in terms of device efficiency. Moreover, spectral stability remains a big challenge. To settle these issues, a kind of deep eutectic solvent (DES) is introduced as the perovskite precursor solvent additive, which is formed from a hydrogen bond acceptor (HBA) choline chloride and a hydrogen bond donor (HBD) urea via the hydrogen bond interaction. The incorporation of DES has multiple advantages, shown as follows: 1) improves the solubility of CsCl to yield dense perovskite morphology, 2) inhibits the growth of the perovskite crystal to achieve low-n phases with narrow distribution, and 3) stabilizes the halide anions in the lattice to ensure stable electroluminescence (EL) spectra. As a result, the as-prepared PeLED shows the maximum external quantum efficiency (EQE(max)) of 2.71% with a CIE coordinate of (0.134, 0.055). With the increase in the DES concentration, the spectra stability is also obviously enhanced.