Aqueous Solution-Processed Vanadium Oxide for Efficient Hole Injection Interfacial Layer in Organic Light-Emitting Diode

Solution-processing techniques have effectively promoted low-cost and large-scale manufacturing of organic light-emitting diodes (OLEDs). An ecofriendly process is demonstrated here to obtain aqueous solution-processed vanadium oxide (s-VOx) for effective hole injection interfacial layer (HIL) by using commercial V2O5 powders. Atomic force microscopy and X-ray photoelectron spectroscopy measurements show that s-VOx exhibits superior film morphology and non-stoichiometry with slight oxygen deficiency which account for exceptional electronic properties in tailoring hole injection. With tris(8-hydroxy-quinolinato)aluminum as emitter, s-VOx-based OLED gives a maximum luminous efficiency of 6.4cdA(-1) and power efficiency of 4.1lmW(-1), which are comparable to those (6.1cdA(-1) and 3.6lmW(-1)) of vacuum thermally deposited VOx-based counterpart. The current versus voltage characteristics and impedance spectroscopy of hole-only devices elucidate that s-VOx possesses robust hole injection capacity and thereby promotes the OLED performance. Our results pave an alternative approach for broadening VOx application with solution process and accelerating OLED development.