Recently, an international research team revealed the mechanism that leads to low luminescence efficiency of a type of quasi two-dimensional perovskite, and proposed a solution to develop high-efficiency green LED beads based on this type of material.

Organic inorganic hybrid perovskites have attracted widespread attention in the field of optoelectronic research due to their low cost, easy processing, and excellent optoelectronic properties. LED beads based on this type of material also have great potential to become the next generation of lighting and display components. Among them, three-dimensional perovskite is formed by the alternating combination of organic and inorganic components in three-dimensional space, two-dimensional perovskite is a layered structure formed by the alternating combination of two components, and quasi two-dimensional perovskite is a mixed structure of two types of perovskites, that is, a large-sized shell layer enveloping three-dimensional perovskites of different sizes. Due to the naturally formed quantum well structure of quasi two-dimensional perovskites, they have a larger exciton binding energy compared to traditional three-dimensional perovskites, which is more conducive to luminescence. Although some quasi two-dimensional perovskite LED beads have achieved high electro-optic conversion efficiency, the reason for the low efficiency of some green light devices when using different organic components is still unknown. In this research, researchers provided answers to this question through a large amount of relevant experimental data obtained through international cooperation. The first author and co corresponding contact person of the paper, Qin Chuanjiang, said, "Currently, most researchers believe that this type of perovskite exhibits more characteristics of traditional inorganic semiconductors. However, we have demonstrated that quasi two-dimensional perovskites have many properties of organic semiconductors, so it is necessary to consider exciton behavior with different energies."

Unlike typical inorganic semiconductors, organic semiconductors first form excitonic states during the electroluminescence process and then relax to emit light. Due to the spin properties of electrons, two different types of excitons, singlet and triplet, will be formed. Although regulating singlet and triplet excitons is the foundation for designing and developing efficient organic LED beads, it has not yet been considered in the research of perovskite LED beads. In this study, researchers compared two types of perovskite luminescent materials with similar crystal properties but different organic components, and found that the triplet excitons disappeared in one type of perovskite material. Through analysis, it is found that organic components with low triplet energy levels are used in this type of perovskite, and the poor luminescence performance may be due to the transfer of triplet excitons to lower energy organic parts, resulting in non radiative energy loss. When using organic components with high triplet energy levels, triplet excitons will remain in the perovskite luminescent host, thereby achieving high luminescence efficiency. In addition, researchers further found that in specific quasi two-dimensional perovskites, dark triplet excitons can also be upconverted into radiative singlet excitons, making it possible to achieve full exciton utilization in quasi two-dimensional perovskite devices.