image: a. The transmission electron microscopy images and schematic diagram of InP/ZnSexS1-x/ZnS QDs. b, The photoluminescence (PL) spectra of InP/ZnSexS1-x/ZnS QDs with various Se/S ratios. With the increasing ratio of Se element, the PL peak redshifts and the full width at half maximum (FWHM) decreases. The best quality InP/ZnSe0.7S0.3/ZnS QDs acquires the highest PLQY of 97% and the narrowest FWHM of 35 nm. c The structure and the electroluminescence spectrum of InP/ZnSe0.7S0.3/ZnS QLEDs. view more
Credit: by Peng Yu, Sheng Cao, Yuliang Shan, Yuhe Bi, Yaqi Hu, Ruosheng Zeng, Bingsuo Zou, Yunjun Wang, and Jialong Zhao
Quantum dot light-emitting diodes (QLEDs) have received considerable attention during these years. Considering that about 15 percent of the global electricity was used on lighting, these advantages made QLEDs become the most promising substitute of traditional light-emitting diodes and organic light-emitting diodes for efficient lighting and display. However, the conventional QLEDs involved toxic elements such as cadmium (Cd) inhibit their application according to the restriction of hazardous substances directive. Hence, they are not suitable for the further development of environmentally friendly lighting and display.
In a new paper published in Light Science & Application, a team of scientists, led by Professor Jialong Zhao from Guangxi University, China, and co-workers have developed a facile strategy to obtain highly efficient pure green-emitting InP-based QLED and the external efficiency (EQE) of as-fabricated InP-based QLEDs reach 15.2% which almost transcend the previous record in the pure green-emitting region. More interestingly, the performance of InP-based QDs and QLEDs can be facilely optimized the components of inner alloyed ZnSexS1-x shell. The reported method and technique will facilitate the development and application of InP-based QLEDs both in academia and industry.
The inner alloyed ZnSexS1-x shell is a buffer layer between the InP core and outer ZnS shell and the components of inner alloyed ZnSexS1-x shell can be facilely regulated by tunning the ratio of TOP-S and TOP-Se precursor. These scientists summarize the mechanism about how the ZnSexS1-x shell influences the performance of InP-based QDs and QLEDs:
“We design a ZnSexS1-x shell between InP core and ZnS outer shell for three purposes in one: (1) to confine the electrons of InP core, (2) to reduce the lattice mismatch between InP core and ZnS outer shell and suppress the auger recombination, and (3) to tailor the energy level of QDs and balance the carrier injection.”
“Since the lattice mismatch has been reduced, the ZnSexS1-x layer can homogeneously and epitaxially grow on InP core and feature a standard spherical shape thus restrain the generation of surface defect.” they added.
“Through regulating the components of the ZnSexS1-x layer, the full width at half maximum is reduced and the photoluminescence quantum yield is increased. This strategy offers a facile method that can improve the color purity and the luminous efficiency of QDs and QLEDs. We believed that the present strategy could promote the further development and the application of green-emitting InP-based QDs and QLEDs and give reliable guidance for the designing of the other highly efficient QDs and QLEDs.” the scientists forecast.
Journal
Light Science & Applications