Here, researchers from Los Alamos Laboratories and other units in the United States have proved that perovskite nanocrystals stabilized in metal-organic framework (MOF) films can produce bright and stable LEDs. Perovskite nanocrystals in MOF films can maintain photoluminescence and electroluminescence under continuous ultraviolet irradiation, thermal stress and electrical stress. Optical and X-ray spectra show that the strong emission comes from local carrier recombination. The maximum external quantum efficiency of perovskite-type MOF nanocrystalline light-emitting diodes exceeds 15% and the high brightness of105cmd2. In the process of LED operation, nanocrystals can be well protected by MOF matrix, without ion migration and crystal merger, and can have stable performance for more than 50 hours. The related paper was published in the journal Nature Photonics of 202 1, entitled "Bright and stable light-emitting diodes made of stable perovskite nanocrystals in metal-organic framework".
Paper link:
/articles/s 4 1566-02 1-00857-0
Metal halide perovskite nanocrystals are emerging optical emitters with adjustable optical band gap, improved color purity and high photoluminescence quantum yield (PLQY). These characteristics are attributed to confinement effect, electron-hole pair binding energy and charge localization in nanostructures. Thin films can be prepared by solution method, which makes perovskite nanocrystals attractive candidates for light emitting diodes, lasers and radiation scintillators. Impressively, the LED based on perovskite nanocrystals has reached a record external quantum efficiency (EQE) of more than 20%. Despite these advantages, stabilizing perovskite nanocrystals remains a challenge. The results show that under environmental conditions, CsPbBr 3 nanocrystals can be merged into bulk phase, which can quench the emission characteristics ten times. It has also been suggested that nanocrystals can be decomposed back to their precursors under continuous ultraviolet (UV) irradiation in humid environment, which is a key problem when used in displays.
In order to solve these problems, people have made great efforts to design stronger ligands, add additives and introduce crosslinking agents to protect nanocrystals from the surrounding environment. In order to solve these bottlenecks, some interesting concepts recently skillfully use metal-organic framework (MOF) as the matrix, which contains perovskite nanocrystals. This system shows significantly improved material stability, and the PLQY value exceeds 50%. The combination of the porosity of MOF and the photoelectric properties of perovskite-type nanocrystals makes this material have great application prospects in photoelectrochemistry and catalysis. However, most of these studies focus on the use of powder, and perovskite MOF(PeMOF) structure has never been used as an emission layer in LED applications. This is mainly due to the challenge of depositing uniform thin films required for high-quality diodes. In addition, in order to realize effective charge injection, it is necessary to consider the trade-off of conductivity by adding a large number of insulating components. (Text: Aisingiorro Star)
Figure1| Formation and characterization of PEM thin films.
Fig. 2 | PEMA image analysis of PEMA film.
Figure 3 | Analysis of performance characteristics of LED devices.