New Technique Boosts QLED Efficiency

A research team from Nanjing University of Science and Technology, in collaboration with international partners, has developed a pressure-assisted thermal annealing (PTA) technique to modify inkjet-printed quantum dot light-emitting diodes (QLEDs). The study demonstrates that PTA enables the formation of highly ordered quantum dot films.

QLEDs are a key component of next-generation display technology, offering high color stability and purity. However, conventional spin-coating techniques used in QLED fabrication present scalability limitations and increased production costs, restricting broader adoption.

While inkjet printing presents a more cost-effective alternative, challenges such as poor film uniformity and reduced device performance have limited its potential.

To address these issues, the research team developed a pressure-assisted thermal annealing (PTA) technique to enhance the quality of inkjet-printed quantum dot (QD) films. By precisely controlling solvent evaporation in a vacuum-assisted environment, the PTA method improved QD alignment and surface uniformity. The resulting films achieved a root-mean-square roughness of 0.54 nm, significantly surpassing conventional annealing techniques in uniformity.

This improved morphology enhanced charge transport and minimized defects, leading to a record-breaking external quantum efficiency (EQE) of 23.08 % for red QLEDs and 22.43 % for green QLEDs. The devices also demonstrated extended operational lifetimes, with red QLEDs exceeding 343,342 hours and green QLEDs surpassing 1,500,463 hours at a brightness of 100 cd/m². Additionally, the PTA technique proved scalable, ensuring uniformity across large-scale films.

This approach offers a viable pathway for cost-effective, high-performance QLED production, addressing key limitations in inkjet-printed displays.

This breakthrough demonstrates the transformative potential of the PTA strategy in surmounting the challenges associated with inkjet-printed QLEDs. Attaining such remarkable efficiency and stability underscores the precision and scalability inherent in our approach, heralding a new era for display technology.

Dr. Haibo Zeng, Study Lead Researcher and Professor, Nanjing University of Science and Technology

The PTA process provides a scalable and cost-effective production solution for high-performance QLEDs, with applications extending beyond screens to include lighting and optoelectronics. By cutting production costs and greatly increasing device longevity, this breakthrough hastens the transition of QLEDs from research to market, with important implications for the consumer electronics and lighting industries.

The study was supported by the National Natural Science Foundation of China (NSFC) (Nos. 62261160392, 52131304, 61725402, U1605244, 22279059), the Fundamental Research Funds for the Central Universities (Nos. 30921011106, 30919012107), the Research Innovation Program of Nanjing Overseas Returnees (No. AD411025), and start-up funding from the Nanjing University of Science and Technology. Additional support was provided by the Jiangsu Funding Program for Excellent Postdoctoral Talent (No. 2023ZB844) and the China Postdoctoral Science Foundation (No. 2023M731687).

The authors also acknowledge the Vacuum Interconnect Nano X Research Facility (NANO-X) at the Suzhou Institute of Nano-Tech and Nano-Bionics, CAS, and the NJUST Big Instrument Equipment Open Fund for their contributions.

Journal Reference:

Wei, C., et al. (2024) Highly ordered inkjet-printed quantum-dot thin films enable efficient and stable QLEDs with EQE exceeding 23%. eScience. doi.org/10.1016/j.esci.2023.100227.