[en] 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-VO_x) for effective hole injection interfacial layer (HIL) by using commercial V₂O₅ powders. Atomic force microscopy and X-ray photoelectron spectroscopy measurements show that s-VO_x 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-VO_x-based OLED gives a maximum luminous efficiency of 6.4 cd A^-1 and power efficiency of 4.1 lm W^-1, which are comparable to those (6.1 cd A^-1 and 3.6 lm W^-1) of vacuum thermally deposited VO_x-based counterpart. The current versus voltage characteristics and impedance spectroscopy of hole-only devices elucidate that s-VO_x possesses robust hole injection capacity and thereby promotes the OLED performance. Our results pave an alternative approach for broadening VO_x application with solution process and accelerating OLED development. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)