Detailed transient current response characteristics under pulsed voltage in MoO3-based organic light-emitting diodes (OLEDs) are first investigated. The transient current can be divided into three parts: positive current spike (IP), steady-state current (IS), and negative current spike (IN). It is found that IS is the operating current of OLED devices. IP and IN show a linear relationship with pulsed voltage amplitude. Higher IN than IP is induced by the difference of anode Fermi level and highest occupied molecular orbital (HOMO) of NPB. We also derive an expression for duty ratio with space charges. Results show that IP and IN correspond to the charging and discharging processes of space charge, respectively. The current spikes and threshold duty ratio are found only to be affected by the injection barrier and independent of internal device structure.

In this work, an organic–inorganic hybrid optical upconverter that can convert irradiated 980 nm IR light to 510 nm green phosphorescence sensitively was fabricated and studied. fac-Tris(2-phenylpyridine) iridium (Ir(ppy)3) doped 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) was used as emitting layer in the phosphorescent organic light-emitting diode (OLED) unit. The upconverter using a phosphorescent OLED as display unit can achieve a higher upconversion efficiency and a low power consumption when compared with the one using fluorescent. An upconversion efficiency of 4.8% can be achieved for phosphorescent device at 15 V, much higher than that of fluorescent one (2.0%). The upconverter’s transient optical and electric response to IR pulse were also investigated for the first time. The response time was found to be influenced by IR intensity and applied voltage. It has a response time as short as 60 μs. The rapid response property of the upconverter makes it feasible to be applied to high-speed IR imaging systems.Keywords: fast response; infrared photo detector; OLED; optical upconverter; organic−inorganic hybrid device; phosphorescentKeywords: 42.79.Pw; 85.60.Bt; 85.60.Jb