Lowering the driving voltage and improving the luminance of blue fluorescent organic light-emitting devices by thermal annealing a hole injection layer of pentacene

We chose pentacene as a hole injection layer（HIL） to fabricate the high performance blue fluorescent organic lightemitting devices（OLEDs）. We found that the carrier mobility of the pentacene thin films could be efficiently improved after a critical annealing at temperature 120℃. Then we performed the tests of scanning electron microscopy, atomic force microscopy, and Kelvin probe to explore the effect of annealing on the pentacene films. The pentacene film exhibited a more crystalline form with better continuities and smoothness after annealing. The optimal device with 120℃ annealed pentacene film and n-doped electron transport layer（ETL） presents a low turn-on voltage of 2.6 V and a highest luminance of 134800 cd/m^2 at 12 V, which are reduced by 26% and improved by 50% compared with those of the control device.