Solvent mixture formulation for orthogonal inkjet processing and uniform pixel patterning of quantum dot light-emitting diode

Abstract

Quantum dot light-emitting diode (QLED) can be directly patterned for pixel array by solution processing, while the limitation of resolution and device stability exists unless a proper solvent system and multilayer design are established. With a small-sized nozzle inkjet printing process, solvent formulation effects on the morphology and precision of printing for the quantum dot layer were investigated. Drop formation as well as ink spreading and wetting behavior on the non-crosslinked organic hole-transporting polymer were optimized with a non-erosive solvent formulation composed of octane and cyclohexane. While the ink composition formed low-contact angle droplet on the surface and was not completely ideal for the defectless pixelating process of high-resolution inkjet, its controllability of wetting at a small-scale nozzle, uniform drying, and orthogonal characteristics with an effective hole transport layer resulted in a high-performance green inkjet QLED with 6.13 cd/A at 19,550 nits highly bright region. This amounted to about 50% of efficiency performance compared to an identical device prepared with spin-coating, but one of the best green inkjet QLED properties reported with less than 120-μm sub-pixel pitch.