China University of Science and Technology has made significant progress in the field of pure red perovskite light-emitting diodes

Recently, four research groups from the University of Science and Technology of China, namely Yao Hongbin, Fan Fengjia, Lin Yue, and Hu Wei, have collaborated to make significant progress in the field of pure red perovskite light-emitting diodes (LEDs). The team independently invented the Electrical Excitation Transient Spectroscopy (EETA) technology and used it to reveal that hole leakage is the key factor causing the efficiency roll off of pure red three-dimensional perovskite LEDs. They also developed a new type of three-dimensional perovskite heterojunction luminescent layer to reduce hole leakage (Figure 1), successfully preparing high-performance pure red perovskite LEDs. The relevant research results have been published in the journal Nature, marking significant progress in pure red perovskite LED technology.

Figure 1. Three dimensional perovskite heterojunction limits hole leakage suppression in LED

Currently, high-performance pure red perovskite LEDs (with external quantum efficiency exceeding 20%) that have been reported mainly use quasi two-dimensional and small-sized quantum dot perovskites. However, due to their low carrier mobility, it is difficult to improve brightness. Three dimensional mixed halide perovskites (such as CsPbI3 xBrx) have high carrier mobility, but currently, the efficiency of CsPbI3 xBrx three-dimensional perovskite LEDs decreases significantly with increasing brightness. Due to the lack of in situ characterization equipment for LEDs, the underlying mechanism is unclear.

In response to this issue, team members used their independently invented EETA technology to "film" CsPbI3 xBrx based LEDs and found that hole leakage into the electron transport layer is the performance bottleneck of three-dimensional CsPbI3 xBrx based LEDs. The EETA results indicate that better confinement of holes and suppression of their leakage are key to achieving high-performance CsPbI3 xBrx based pure red LEDs. In order to enhance the carrier confinement capability of perovskite, the team proposed a novel three-dimensional perovskite heterojunction design, which contains narrow bandgap emitters and wide bandgap energy barriers for confined carriers within the heterojunction material. The wide bandgap material is achieved by inserting organic molecules with strong interaction and low steric hindrance with the lead halide framework into a portion of the CsPbI3 xBrx lattice, thereby inducing partial lattice expansion (Figure 2a, b). 

Through systematic theoretical calculations and molecular design, we have successfully developed organic molecules that form stable bonds with lead halide frameworks through multifunctional functional groups such as carboxyl, amino, and sulfonyl groups, and achieved precise introduction of wide bandgap phases (Figure 2c). Through this method, the team obtained perovskite materials with heterostructures and continuous three-dimensional skeletons, which can achieve carrier confinement while maintaining high mobility. The obtained three-dimensional perovskite heterostructure was fully validated by high-resolution transmission electron microscopy (Figure 2d-i).

Figure 2. Design and Material Characterization of Three Dimensional CsPbI3 xBrx Perovskite Heterojunction

By constructing a three-dimensional CsPbI3 xBrx heterojunction luminescent layer, the hole leakage of pure red perovskite LED devices was effectively suppressed (Figure 3a, b). The peak external quantum efficiency (EQE) of the corresponding device reaches 24.2%, and the maximum brightness is 24600 cd m-2 (Figure 3c, d). And the device exhibits very low efficiency roll off - even at a brightness of 22670 cd m-2, the device still has an EQE of over 10%, which is better than previously reported results (Figure 3e). The research results of this work demonstrate the enormous potential of three-dimensional perovskite heterojunction material design in developing efficient, bright, and stable perovskite LEDs.

Figure 3. Performance of Three Dimensional Heterojunction CsPbI3 xBrx Based Pure Red LED

Song Yonghui (PhD), Li Bo (postdoctoral fellow), Wang Zijian (PhD student), and Tai Xiaolin (PhD student) from the University of Science and Technology of China are co first authors of this paper. Professors Yao Hongbin, Fan Fengjia, Lin Yue, and Hu Wei from the University of Science and Technology of China are co corresponding authors of this paper. The development of EETA technology has received strong support from Academician Du Jiangfeng. This work has received support from the National Natural Science Foundation of China, the Ministry of Science and Technology, and other funding sources. The Physical and Chemical Science Experimental Center provided support for the development of this project with characterization equipment such as SEM, PL, UV vis, and aberration corrected electron microscopy.

Source: Opticsky