On March 5th, a collaborative team from the Key Laboratory of Advanced Display and System Applications (Ministry of Education) at Shanghai University, led by Prof. Xuyong Yang and Prof. Jianhua Zhang, and Prof. Jiaqi Zhang's team at Jilin University, published an important research achievement in the international top academic journal Nature titled "Homogeneous ZnSeTeS Quantum Dots for Efficient and Stable Pure Blue LEDs".  

Paper link: https://www.nature.com/articles/s41586-025-08645-4  

Research Background and Challenges  

Heavy-metal-free blue quantum dot light-emitting diodes (QLEDs) have gained significant attention for their environmental advantages, yet their electroluminescence performance remains notably inferior to cadmium-based devices. ZnSeTe quantum dots (QDs), as a promising alternative, face two critical challenges:  

1. Compositional Inhomogeneity: Tellurium (Te) aggregation forms isoelectronic centers, leading to broadened emission spectra, color impurity (e.g., low-energy tail emissions), and structural instability.  

2. Stability Deficiencies: The high reactivity and oxygen sensitivity of Te induce lattice defects and non-radiative recombination, reducing device longevity.  

Key Technology: Isoelectronic Control Strategy  

This study introduces an isoelectronic control strategy using sulfur (S)-coordinated triphenyl phosphite (TPP-S) to fabricate homogeneous quaternary alloy ZnSeTeS QDs. The mechanisms are as follows:  

1. Reactivity Balance: TPP-S balances the reactivity of anionic precursors (Se, Te, S) by weakening phosphorus-chalcogen bonds, suppressing Te-rich domain formation and ensuring compositional uniformity.  

2. Suppression of Hole Localization: Electronegative S disrupts carrier distribution around Te, reducing  isoelectronic centers and enhancing color purity (the low-energy peak intensity ratio in PL spectra decreased from 0.79 to 0.46).  

3. Structural Stability Enhancement: S incorporation increases configurational entropy, eliminates stacking faults and oxygen defects (e.g., disappearance of TeO signals in QD-2), and improves thermal stability (PL intensity retained >97% after 64 hours at 150°C).  

Characterization and Performance of Quantum Dots  

1. Luminescence Efficiency: ZnSeTeS QDs (QD-2) exhibit near-unity photoluminescence quantum yield (PLQY), pure blue emission at 460 nm with a narrow full-width at half-maximum (FWHM) of 14 nm, and CIE coordinates (0.14, 0.06) meeting the Rec. 2020 color gamut standard.  

2. Homogeneity Verification: X-ray photoelectron spectroscopy depth profiling confirms uniform radial distribution of Te and S in QD-2, whereas QD-1 (S-free) shows Te aggregation at the core.  

3. Single-QD Analysis: QD-2 demonstrates a low standard deviation (σFWHM) of 10.65 meV in single-dot PL spectra, far lower than QD-1’s 20.57 meV, validating compositional uniformity.  

Device Structure and Performance  

• Device Architecture: The ITO/PEDOT:PSS/PF8Cz/QDs/ZnMgO/Al structure is adopted, where PF8Cz (poly(9,9-dioctylfluorenyl-2,7-diyl)-alt-(9-(2-ethylhexyl)-carbazole-3,6-diyl)) serves as the hole transport layer. Its energy level matching (HOMO ~ -5.4 eV) efficiently facilitates hole transfer from PEDOT:PSS to the QD layer while balancing electron-hole injection to reduce carrier recombination loss.  

• Electroluminescence Performance:  

1. Efficiency: The external quantum efficiency (EQE) reaches 24.7%, among the highest for heavy-metal-free blue QLEDs and surpassing most cadmium-based QLEDs and perovskite LEDs.  

2. Stability: The operational half-lifetime (T50) is 112.6 hours at an initial luminance of 2000 cd/m2, equivalent to ~30,000 hours at 100 cd/m2, significantly outperforming the control device (QD-1).  

3. Large-Area Uniformity: A 2×1 cm2 device exhibits uniform luminance (1297±11 cd/m2), confirming process reliability.  

Conclusion and Significance  

This study achieves compositional homogeneity and structural stabilization of ZnSeTeS QDs via the TPP-S coordination strategy, combined with energy level regulation by the PF8Cz hole transport layer, to fabricate efficient and stable pure blue QLEDs. This work establishes a new paradigm for heavy-metal-free luminescent materials, advancing environmentally friendly display technology toward high color gamut and long lifetime.  

Role of PF8Cz: As the hole transport layer, PF8Cz promotes hole transport through energy level matching, balances carrier injection, and enhances device efficiency and stability, serving as a critical component for achieving high EQE and long operational lifetime.