Highly efficient phosphorescent white organic light-emitting devices (WOLEDs) have been fabricated by using two complementary blue and yellow emitting layers, in which the blue guest iridium(III) bis[(4,6-difluorophenyl)-pyridinato-N,C2′] picolinate (Firpic) was doped in a novel blue phosphorescent host. The efficiencies and spectra of WOLEDs can be easily tuned by inserting an ultrathin interlayer between the two emitters and adjusting the thickness of the yellow emitting layer (Y-EML). The device with 1nm thick interlayer and 3nm thick (Y-EML) obtains very high efficiencies of 42.4cd/A and 47.6lm/W and a luminance of 1144cd/m2 was realized at a low voltage of 3.6V. In addition, another device with 2nm thick interlayer and 5nm thick Y-EML exhibited nearly voltage-independent electroluminescent (EL) spectra. Commission International de L’Eclairage (CIE) coordinates of this device only changes from (0.333, 0.436) at a luminance of 100cd/m2 to (0.330, 0.434) at that of 10,000cd/m2, nearly independent of the driving voltage.