The relationship between the device performance and hole mobility of host materials in mixed host system for deep blue phosphorescent organic light emitting devices

We report on the systematic investigation of the relationship between hole mobility of host materials and device performance to maximize the power efficiency. Three different materials with different hole mobility were used as host materials of iridium(III)[bis(4,6-difluorophenyl)pyridinato-N,C-2']tetrakis(1-pyrazolyl)borate (FIr6) based deep blue phosphorescent organic light-emitting device (PHOELD). Host material, tris(4-(N-carbazolyl)phenyl)methylsilane (MCBP), with higher hole mobility (1.1 x 10(-3) cm(2) V-1 s(-1)), can accommodate more electron current carried by an n-type host, bis(4-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)phenyl)dimethylsilane (SiTAZ), than the other p-type hosts with lower hole mobility, maintaining the charge balance between hole and electron current. As a result, the optimized device shows high external quantum efficiency (EQE) of 19.0%, high power efficiency of 23.5 lm/W, low efficiency roll off, and deep blue color coordinates of (0.15, 0.23). (C) 2011 Elsevier B. V. All rights reserved.