Extremely Stable Luminescent Crosslinked Perovskite Nanoparticles under Harsh Environments over 1.5 Years

© 2020 Wiley-VCH GmbHOrganic–inorganic hybrid perovskite nanoparticles (NPs) are a very strong candidate emitter that can meet the high luminescence efficiency and high color standard of Rec.2020. However, the instability of perovskite NPs is the most critical unsolved problem that limits their practical application. Here, an extremely stable crosslinked perovskite NP (CPN) is reported that maintains high photoluminescence quantum yield for 1.5 years (>600 d) in air and in harsher liquid environments (e.g., in water, acid, or base solutions, and in various polar solvents), and for more than 100 d under 85 °C and 85% relative humidity without additional encapsulation. Unsaturated hydrocarbons in both the acid and base ligands of NPs are chemically crosslinked with a methacrylate-functionalized matrix, which prevents decomposition of the perovskite crystals. Counterintuitively, water vapor permeating through the crosslinked matrix chemically passivates surface defects in the NPs and reduces nonradiative recombination. Green-emitting and white-emitting flexible large-area displays are demonstrated, which are stable for >400 d in air and in water. The high stability of the CPN in water enables biocompatible cell proliferation which is usually impossible when toxic Pb elements are present. The stable materials design strategies provide a breakthrough toward commercialization of perovskite NPs in displays and bio-related applications.

Conductivity Enhancement of Nickel Oxide by Copper Cation Codoping for Hybrid Organic-Inorganic Light-Emitting Diodes

We demonstrate a Cu­(I) and Cu­(II) codoped nickel­(II) oxide (NiO_<i>x</i>) hole injection layer (HIL) for solution-processed hybrid organic-inorganic light-emitting diodes (HyLEDs). Codoped NiO_<i>x</i> films show no degradation on optical properties in the visible range (400–700 nm) but have enhanced electrical properties compared to those of conventional Cu­(II)-only doped NiO_<i>x</i> film. Codoped NiO_<i>x</i> film shows an over four times increased vertical current in comparison with that of NiO_<i>x</i> in conductive atomic force microscopy (c-AFM) configuration. Moreover, the hole injection ability of codoped NiO_<i>x</i> is also improved, which has ionization energy of 5.45 eV, 0.14 eV higher than the value of NiO_<i>x</i> film. These improvements are a consequence of surface chemical composition change in NiO_<i>x</i> due to Cu cation codoping. More off-stoichiometric NiO_<i>x</i> formed by codoping includes a large amount of Ni vacancies, which lead to better electrical properties. Density functional theory calculations also show that Cu doped NiO model structure with Ni vacancy contains diverse oxidation states of Ni based on both density of states and partial atomic charge analysis. Finally, HyLEDs of Cu codoped NiO_<i>x</i> HIL have higher performance comparing with those of pristine NiO_<i>x</i>. The current efficiency of devices with NiO_<i>x</i> and codoped NiO_<i>x</i> HIL are 11.2 and 15.4 cd/A, respectively. Therefore, codoped NiO_<i>x</i> is applicable to various optoelectronic devices due to simple sol–gel process and enhanced doping efficiency