A series of top-emitting organic light-emitting devices with different thicknesses of carrier transporting layers (N,N'-di(1-naphtyl)-N,N'-diphenylbenzidine, tris(8-hyroxyquinloine) aluminum (Alq(3))) and emitting layer (EML, 10-(2-Benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-11H,5H,11H-(1)-benzopyropyrano (6,7-8-ij)quinolizin-11-one (C545T)-doped Alq(3)) were fabricated. C545T-doped Alq(3) was found to bring about double recombination peaks in EML As the distance between EML and reflective anode was increased, the outcoupling efficiency greatly deviated from optically-simulated values due to charge imbalance in EML and optical loss at the EML/Alq(3) interface. The device with 30 nm of EML exhibited maximized outcoupling efficiency and further increase of EML thickness brought about decrease in efficiency due to decrease in hole electron recombination at the EML/Alq(3) interface. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.