Xiangfei Qi
University of Michigan
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Featured researches published by Xiangfei Qi.
Journal of Applied Physics | 2010
Xiangfei Qi; Ning Li; Stephen R. Forrest
We study electron and hole injection in MoO3 charge generation layers (CGLs) commonly used for establishing balanced injection in multilayer stacked organic light-emitting diodes (SOLEDs). A compound CGL consisting of 100-A-thick MoO3 and Li-doped 4,7-diphenyl-1,10-phenanthroline in a 1:1 molar ratio is demonstrated to have a high electron generation efficiency. Charge injection from the compound CGL is modeled based on a two-step process consisting of tunneling-assisted thermionic emission over an injection barrier of (1.2±0.2) eV and a trap level due to oxygen vacancies at (0.06±0.01) eV above the MoO3 valence band edge. Peak external quantum efficiencies (EQEs) of (10.5±0.2)%, (10.1±0.2)%, (8.6±0.2)%, and (8.9±0.2)% are obtained for tris-(phenylpyridine)iridium-based electrophosphorescent OLEDs with indium tin oxide (ITO) anode/CGL cathode, CGL anode/CGL cathode, CGL anode/Al cathode, and ITO anode/Al cathode contacts, respectively. Based on our analysis, a three-element green emitting electrophosphore...
Applied Physics Letters | 2008
Xiangfei Qi; Michael Slootsky; Stephen R. Forrest
We demonstrate a white organic light-emitting device where individual red, green, and blue (R, G, and B) phosphorescent organic light-emitting devices are vertically stacked and electrically interconnected by a compound MoO3/Li-doped charge generation layer. For the order of B, G, and R cells positioned relative to the indium tin oxide anode, the device yields a peak total external quantum efficiency (EQE) and power efficiency (PE) of ηext=(36±2)% at a current density of J=82 μA/cm2 and ηp=21±1 lm/W at J=17 μA/cm2, respectively. The EQE and PE of the device roll off to (32±2)% and 13±1 lm/W at 1000 cd/m2, corresponding to J=2 mA/cm2. At this luminance, the device shows Commission Internationale de L’Eclairage chromaticity coordinates of (0.45, 0.36) and a color rendering index of 63.
Journal of Applied Physics | 2011
Xiangfei Qi; Stephen R. Forrest
We use a general transmission matrix formalism to determine the thermal response of organic light-emitting diodes (OLEDs) under high currents normally encountered in ultra-bright illumination conditions. This approach, based on Laplace transforms, facilitates the calculation of transient coupled heat transfer in a multi-layer composite characteristic of OLEDs. Model calculations are compared with experimental data on 5 cm × 5 cm green and red-emitting electrophosphorescent OLEDs under various current drive conditions. This model can be extended to study other complex optoelectronic structures under a wide variety of conditions that include heat removal via conduction, radiation, and convection. We apply the model to understand the effects of using high-thermal- conductivity substrates, and the transient thermal response under pulsed-current operation.
Journal of Photonics for Energy | 2012
Peter Levermore; Alexey Borisovich Dyatkin; Zeinab Elshenawy; Huiqing Pang; Jeffrey Silvernail; Emory Krall; Raymond Kwong; Ruiqing Ma; Michael S. Weaver; Julie J. Brown; Xiangfei Qi; Stephen R. Forrest
We report data for a pair of singlestack all-phosphorescent 15 × 15 cm 2 organic light emitting-diode (OLED) light panels with high efficacy, long lifetime, and very low operating temperature: Panel 1 has 62 lm∕W efficacy, CRI ¼ 81 and lifetime to LT70 ¼ 18;000 h at 1000 cd∕m 2 , while Panel 2 has 58 lm∕W efficacy, CRI ¼ 82 and lifetime to LT70 ¼ 30;000 h at 1000 cd∕m 2 . Operating at a higher luminance of 3000 cd∕m 2 , Panel 2 has 49 lm∕W efficacy with lifetime to LT70 ¼ 4000 h. Excellent panel lifetime is enabled by a stable light blue phosphorescent materials system. Panel temperatures are within 10°C of ambient temperature at 3000 cd∕m 2 . Panel 2 was further used as a building block to demonstrate an all-phosphorescent OLED luminaire for under-cabinet lighting applications. Operating at approximately 3000 cd∕m 2 , theluminairedelivers570lmwith52 lm∕Wtotalsystemefficacy,CRI ¼ 86andCCT ¼ 2940 K.© 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). (DOI: 10.1117/1.JPE.2.021205)
lasers and electro-optics society meeting | 2007
Xin Xu; Xiangfei Qi; Marcelo Davanco; Stephen R. Forrest
We demonstrate a new approach to print organic photodetector arrays on 3D transparent plastic substrates. A 15x15 matrix with a feature size of 500 mum is fabricated, with dark current density is 3.1 muA/cm at -IV.
Organic Electronics | 2008
Xin Xu; Marcelo Davanco; Xiangfei Qi; Stephen R. Forrest
Archive | 2009
Stephen R. Forrest; Xiangfei Qi; Michael Slootsky
Archive | 2009
Stephen R. Forrest; Xiangfei Qi; Michael Slootsky
Archive | 2008
Stephen R. Forrest; Xiangfei Qi; Marcelo Davanco; Xin Xu
Archive | 2008
Stephen R. Forrest; Xiangfei Qi; Marcelo Davanco; Xin Xu