Investigation of emission location in top-emitting green organic light-emitting devices by optical analysis

摘要

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-1H,5H,11H-(1)-benzopyropyrano (6,7-8-i,j)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.