Conductivity-enhanced thick hole-transporting layers via doping-crosslink synergy for efficient and stable NIR QLEDs

Area of Science:

• Materials Science
• Optoelectronics
• Nanotechnology

Background:

• Scalable manufacturing of quantum-dot light-emitting diodes (QLEDs) faces challenges due to non-uniform charge-transporting layers on rough indium tin oxide substrates, causing leakage currents and low yields.
• Existing methods struggle to create thick, uniform hole-transporting layers (HTLs) that effectively suppress shunting paths without compromising device performance.

Purpose of the Study:

• To develop a scalable method for fabricating uniform and thick HTLs for high-performance near-infrared (NIR) QLEDs.
• To enhance charge transport in thick HTLs by introducing a doped polymer matrix.
• To improve surface coverage and suppress leakage currents in QLEDs manufactured on uneven substrates.

Main Methods:

• Employed a UV/thermally crosslinkable material, 4,4'-bis(3-vinyl-9H-carbazol-9-yl)1,1'-biphenyl (CBP-V), to create thick HTLs (∼100 nm).
• Introduced a doped HTL design by embedding a high-mobility small molecule, 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), into the crosslinked CBP-V matrix.
• Fabricated FAPbI3-based NIR QLEDs using the TAPC-doped CBP-V HTLs and evaluated their performance and stability.

Main Results:

• The TAPC-doped CBP-V HTLs provided smooth morphology, excellent solvent resistance, and improved surface coverage, effectively suppressing shunting paths.
• The doped HTLs facilitated hole transport through the thick polymer layer via auxiliary hopping pathways created by dispersed TAPC molecules.
• Achieved a peak external quantum efficiency of 17.3% and a T50 lifetime of 262 min for NIR QLEDs, significantly outperforming devices with thin or undoped HTLs.
• Demonstrated uniform emission in large-area blade-coated devices, compensating for substrate roughness.

Conclusions:

• The TAPC-doped thick HTL approach offers a scalable and reliable route toward high-performance NIR QLEDs.
• This strategy effectively addresses substrate roughness and enables uniform device fabrication.
• The combination of a crosslinked polymer matrix and embedded small molecules provides a viable solution for overcoming limitations in QLED manufacturing.