Pure-red perovskite light-emitting diodes (PeLEDs), which are crucial for vivid displays and lighting, have long faced a trade-off between efficiency and brightness. While three-dimensional (3D) mixed-halide perovskites like CsPbI_3-xBr_x offer excellent charge transport, their efficiency plummets under high current due to unresolved carrier leakage.

In a study published in Nature on May 7, a team led by Prof. YAO Hongbin, FAN Fengjia, LIN Yue, and HU Wei from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences has resolved a critical challenge in PeLEDs by identifying and addressing the root cause of efficiency loss at high brightness, and enabled record-breaking device performance by introducing a novel material design.

Using a self-developed diagnostic tool called electrically excited transient absorption (EETA) spectroscopy, the researchers captured real-time carrier dynamics in operating devices. They found that the hole leakage into the electron transport layer—previously undetected due to a lack of in situ characterization methods—is the primary culprit behind efficiency roll-off.

To enhance the carrier confinement capability of perovskites, the researchers engineered a 3D intragrain heterostructure within the perovskite emitter, which embeds narrow-bandgap light-emitting regions within a continuous [PbX₆]^4- framework, separated by wide-bandgap barriers that confine carriers. 

The key to this strategy is the molecule p-Toluenesulfonyl-L-arginine (PTLA) which bonds strongly to the perovskite lattice via multiple functional groups (guanidino, carboxyl, amino, and sulfonyl). PTLA expanded the lattice locally, creating wide-bandgap phases without disrupting structural continuity. High-resolution transmission electron microscopy and ultrafast spectroscopy confirmed the seamless carrier transfer between the heterostructure's phases and suppressed hole leakage.

The optimized PeLEDs exhibited unprecedented performance, and achieved a peak external quantum efficiency (EQE) of 24.2% and a maximum luminance of 24,600 cd m^-2—the brightest pure-red PeLED reported to date. Stability tests revealed a half-lifetime of 127 hours at 100 cd m^-2, with minimal spectral shift during operation.

This work bridges a critical gap in perovskite optoelectronics, combining advanced diagnostics with innovative material engineering. Reviewers hailed the study as "a landmark in perovskite LED research," emphasizing its methodological rigor and transformative results.