Recently, a joint research team formed by the Changchun Institute of Applied Chemistry (hereinafter referred to as Changchun Institute of Applied Chemistry) of the Chinese Academy of Sciences and Kyushu University in Japan revealed the mechanism leading to a class of quasi-two-dimensional perovskite with low luminous efficiency, and then developed a material based on this class The high-efficiency green light-emitting diodes, related results were published online in "Nature-Photonics".
Organic-inorganic hybrid perovskites have received widespread attention in the field of optoelectronics due to their low cost, ease of processing, and excellent optoelectronic properties. Light-emitting diodes based on such materials also have great potential to become the next generation of lighting and display components. Among them, three-dimensional perovskite is formed by alternating combination of organic and inorganic components in three-dimensional space, two-dimensional perovskite is a lamellar structure formed by alternating two components, and quasi-two-dimensional perovskite is two types The mixed structure of perovskite, that is, a three-dimensional perovskite of different sizes is surrounded by a large-sized organic shell layer.
"Since the quasi-two-dimensional perovskite has a naturally formed quantum well structure, it has a larger exciton binding energy than the traditional three-dimensional perovskite, which is more conducive to luminescence." Changchun Yinghua Institute Researcher Qin Chuanjiang pointed out, "Although some quasi-two-dimensional perovskite light-emitting diodes have achieved high electro-optical conversion efficiency, when using different organic components, the efficiency of some green light devices is very low, the reason is still unknown."
A large number of relevant experimental data obtained by the joint research team through international cooperation answered this question. Qin Chuanjiang introduced to China Science News: "At present, most researchers believe that this type of perovskite exhibits more characteristics of traditional inorganic semiconductors. However, we have proved that quasi-two-dimensional perovskites have many properties of organic semiconductors, so they need to Consider the behavior of excitons with different energies. "
Unlike typical inorganic semiconductors, organic semiconductors first form exciton states during electroluminescence and then relax to emit light. Due to the spin characteristics of electrons, two different properties of singlet and triplet excitons will be formed. Although the regulation of singlet and triplet excitons is the basis for the design and development of high-efficiency organic light-emitting diodes, it has not been considered in the study of perovskite light-emitting diodes.
The joint research team compared two types of perovskite luminescent materials with similar crystal properties and containing different organic components, and found that the triplet excitons in one type of perovskite materials disappeared. Through analysis, organic components with low triplet energy levels are used in this type of perovskite. The reason for its poor luminescent performance should be the transfer of triplet excitons to the organic part with lower energy, resulting in non-radiative energy loss. When an organic component with a high triplet energy level is used, the triplet excitons will remain in the perovskite luminescence host, thereby obtaining higher luminescence efficiency.
In addition, the joint research team also found that in specific quasi-two-dimensional perovskites, the dark triplet excitons can also be converted into radiant singlet excitons, making all quasi-two-dimensional perovskite devices to achieve all excitons Sub-use becomes possible.
Based on the above findings, the joint research team prepared a quasi-two-dimensional perovskite light-emitting diode capable of efficiently capturing triplet excitons by selecting appropriate organic components, and obtained an electro-optic conversion efficiency of 12.4%. "We not only explained the experimental phenomena observed before, but some new discoveries also provided guidance for the development of high-efficiency perovskite optoelectronic devices, such as light-emitting diodes, lasers, and solar cells." Anda Chiba, a professor at Kyushu University in Japan who led the study Say. (Reporter Shen Chunlei)
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