High-efficiency red, green and blue phosphorescent homojunction organic light-emitting diodes based on bipolar host materials

摘要

In this paper, we demonstrate red, green and blue (RGB) phosphorescent p-i-n homojunction devices by using a series of bipolar host materials, including 2,6-bis(3-(carbazol-9-yl)phenyl) pyridine (26DCzPPy), 3,5-bis(3-(carbazol-9-yl)phenyl) pyridine (35DCzPPy) and 4,6-bis(3-(carbazol-9-yl)phenyl) pyrimidine (46DCzPPm). Homojunction devices comprise a MoO_3-doped host as a hole transport layer, and a Cs_2CO_3-doped host as an electron transport layer. Emission layer consists of a host doped with iridium(IH) bis(4,6-(di-fluoro-phenyl)pyridinato-N,C~(2')) picolinate (FIrpic) for blue, fac-tris(2-phenylpyridine) iridium (Ir(ppy)_3) for green, and tris(l-phenylisoquinolinolato-C~2,N)iridium(HI) (Ir(piq)_3) for red devices. External quantum efficiencies of 12.9% for the 35DCzPPy-based blue, 9.5% for the 46DCzPPm-based green, and 8.5% for the 46DCzPPm-based red devices were achieved at 100 cd m~(-2). By systematically investigating carrier balance in these homojunction devices, well-balanced charge carrier injection and transport in emission layers are found to be critical factors for constructing efficient homojunction devices.