Due to their excellent luminous efficiency and low cost, perovskite materials have shown broad application prospects in solar cells, light-emitting diodes (LEDs) and detectors in recent years. However, the electrons and holes in traditional perovskite materials are often difficult to recombine efficiently, which limits their luminescence properties. To this end, researchers generally adopt the strategy of strong confinement to improve the luminous efficiency. In addition, how to further enhance the brightness of perovskite LEDs (PeLEDs) and prolong their working life has become a key research direction in this field.
Recently, the journal Nature published the latest research results of Professor Xiao Zhengguo's team at the University of Science and Technology of China, Chinese Academy of Sciences. The team proposed a novel weak confinement strategy to construct a new type of perovskite film using large-grained, all-inorganic perovskite crystals, which significantly improved the brightness and thermal stability of PeLEDs. With this approach, the researchers succeeded in increasing the maximum brightness of PeLEDs to 1.16 million nits and extending their theoretical lifetime to more than 180,000 hours.
At the heart of this strategy lies in the breakthrough of the material preparation process. Additives such as hypophosphorous acid and ammonium chloride were introduced into the perovskite precursor, and annealed at high temperatures to form large grain structures in the films, significantly reducing crystal defects.
High-temperature annealing is a heat treatment process widely used in the field of materials science and engineering, which mainly improves the microstructure, mechanical properties and processing properties of materials by heating, holding and cooling them.
Figure: USTC develops a new type of inorganic perovskite LED
The main purpose and function of high-temperature annealing
Relief of internal stress:
Residual internal stresses can occur during casting, forging, welding, cold working (e.g., rolling, cutting), etc., which can lead to deformation, cracking, or unstable performance. High-temperature annealing can relax stress by atomic diffusion.
For example, welded metal components are often deformed due to internal stress, and the stress is significantly reduced after annealing.
Improved mechanical properties:
Softened material: reduce hardness, improve plasticity and toughness, and facilitate subsequent processing (e.g. cutting, stamping). For example, cold-rolled steel plate has a reduced hardness after annealing and is easier to form.
Homogeneous properties: Eliminate tissue inhomogeneity and make all parts of the material perform consistently.
On the one hand, the high-temperature annealing process effectively inhibits the non-radiative recombination (i.e., the process of energy dissipation but does not produce light), and greatly reduces the ion migration phenomenon. On the other hand, it avoids the defect problem caused by too small grains in the traditional method, and comprehensively improves the luminous intensity and structural stability of the device.
The new PeLEDs have reached more than 22% in luminous efficiency, which is close to the level of existing commercial display products. Its peak brightness is as high as 1.16 million nits, far exceeding the upper limit of a few kits of brightness for current mainstream commercial LED screens. Even more prominently, at conventional brightness (100 nits), the device has a theoretical lifetime of more than 180,000 hours, which is fully compliant with the lifetime standards of commercial LEDs.
This innovative fabrication strategy not only achieves an important breakthrough in the efficiency and stability of PeLEDs, but also opens up a new situation for practical applications such as high-end displays and ultra-high brightness lighting, showing promising industrialization potential.
