Improving Charge Injection via Blade Coating Molybdenum Oxide Layer: toward High Performance Large-area Quantum Dot Light-emitting Diodes.

A solution-processed molybdenum oxide (MoOx) as the hole injection layer by doctor-blade coating was developed to improve the efficiency and lifetime of red emitting quantum-dot light emitting diodes (QD-LEDs). It has been demonstrated that by adding isopropyl alcohol into the MoOx precursor during doctor-blade coating process, the morphology, composition, and the surface electronic structure of MoOx hole injection layer could be tailored. High quality MoOx film with optimized charge injection was obtained, based on which all-solution-processed highly efficient red emitting QD-LEDs were realized by using low-cost doctor-blade coating technique at ambient conditions. The red QD-LEDs exhibited the maximum current efficiency and external quantum efficiency of 16 cd/A and 15.1 %, respectively. Moreover, the lifetime of red devices initializing at 100 cd/m2 was 3236 hours under ambient conditions, which is about twice as long as those with conventional poly(3,4-ethylenedioxythiophene)-poly (styrenesulfonate) hole injection layer. Large area QD-LEDs with 4 inches emitting areas were fabricated with blade-coating as well, which exhibit high efficiency of 12.1 cd/A for red emissions. Our work paves a new way to the realization of efficient large area QD-LEDs, and the processing and findings from this work can be expanded into next generation lighting and flat-panel displays.