White organic light-emitting devices (WOLEDs) based on phosphorescent blue and yellow emitters were fabricated, while p-type di-(4-(N,N-ditolyl-amino)-phenyl)cyclohexane (TAPC) and n-type 2,2',2 ''-(1,3,5-benzenetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) were separately utilized as a homogeneous host for both blue and yellow emissive layers (EMLs). Then, various spacers were inserted between the two EMLs for performance characterization. The results showed that for the TAPC-host devices, a device using 4,7-diphenyl-1,10-phenanthroline (Bphen) as the spacer had a maximum current efficiency (CE) of 11.3 cd/A, while stable white light emission with Commission Internationale del'Eclairage (CIE) coordinates of (0.394, 0.435) at a bias of 5 V was observed. Similarly, among the TPBi-host devices, a device using 4,4'-bis(carbazol-9-yl) biphenyl (CBP) as the spacer exhibited a maximum CE of 18.1 cd/A, accompanied by negligible color variation with the CIE coordinates of (0.284,0.333)at 5 V. For the double-EML devices, the improved device efficiency and color stability by introducing proper spacer was attributed to broadened recombination region and efficient energy transfer between the EMLs. (c) 2012 Elsevier B.V. All rights reserved.