Recently, a groundbreaking study led by Professor Fan Fengjia from the Spin Magnetic Resonance Laboratory at the University of Science and Technology of China (USTC), in collaboration with Professor Shen Huaibin, Professor Zeng Zaiping, and Associate Professor Wang Lei from Henan University, has achieved a significant milestone in the realm of quantum dot directional light emission. The team discovered that by deliberately introducing stacking faults into zinc blende quantum dots, they can effectively break the crystal symmetry, paving the way for efficient directional light emission from these quasi-spherical structures—a feat that has traditionally been challenging to accomplish.

The related findings were published in the prestigious international academic journal Nature Photonics.

Quantum dot light-emitting diodes (QD-LEDs) are widely regarded as a promising avenue for next-generation display technologies, thanks to their exceptional attributes, including a broad color gamut, solution processability, high brightness, and high efficiency at low driving voltages. However, a significant drawback of quantum dot light emission is its tendency to radiate uniformly in all directions, causing a substantial portion of the light to become trapped within the device. This insufficient light extraction efficiency has emerged as a critical bottleneck in enhancing their external quantum efficiency.

Through meticulous theoretical analysis and density functional theory calculations, the research team revealed that stacking faults can effectively reduce the crystal symmetry of zinc blende quantum dots from the tetrahedral (Td) to the trigonal pyramidal (C3v) point group. This transformation alters the symmetry of their electronic states, inducing strong in-plane polarized light emission characteristics in the quantum dots.

Experimental results corroborated these findings, demonstrating that quantum dots containing stacking faults exhibited in-plane dipole ratios as high as 81.0% (in the CdZnSe system) and 73.9% (in the InP system) within self-assembled films. Both values surpassed the 66.7% threshold for isotropic emission. Building on this strategy, the team successfully fabricated green QD-LEDs with external quantum efficiencies reaching 34.3% (for CdZnSe-based devices) and 31.0% (for InP-based devices), surpassing the efficiency limits predicted by traditional models while maintaining excellent device stability.

This study marks the first instance of achieving efficient directional light emission from quasi-spherical zinc blende quantum dots, shedding light on the pivotal role of stacking faults in regulating the fine structure of quantum dot excitons and the directionality of light emission. It offers novel material design insights for developing higher-efficiency quantum dot light-emitting diodes and holds significant potential for extending to other quantum dot optoelectronic device applications.