Abstract
Organic materials are used in novel optoelectronic devices because of the ease and high compatibility of their fabrication processes. Here, we demonstrate a low-driving-voltage cathodic-controlled organic upconverter with a mapping application that converts near-infrared images to produce images of visible blood vessels. The proposed upconverter has a multilayer structure consisting of a photosensitive charge-generation layer (CGL) and a phosphorescent organic light-emitting diode (OLED) for producing clear images with a high resolution of 600 dots per inch. In this study, temperature-dependent electrical characterization was performed to analyze the interfacial modification of the cathodic-controlled upconverter. The result shows that the upconverter demonstrated a high conversion efficiency of 3.46% because of reduction in the injection barrier height at the interface between the CGL and the OLED.
Highlights
A phosphorescent organic light-emitting diode (OLED) was deposited layer-by-layer in sequence of 1,1-bis(di-4-tolylaminophenyl) cyclohexane (TAPC), 4,4’-Bis(N-carbazolyl)-1,1’-biphenyl (CBP) doped with fac-tris (2-phenylpyridine) iridium (III) [Ir(ppy)3], and 4,7-diphenyl-1,10-phenanthroline (BPhen), all of which were used as a hole-transporting layer (HTL), emitting layer (EML), and electron-transporting layer (ETL), respectively
We demonstrated a charge-generation layer (CGL) that enabled generating electrons and an Electron-injection layers (EILs) that activated electron injection to an OLED for emitting light
When a thin LiF layer was inserted between the ETL of the OLED and the CGL, the turn-on voltage and device performance improved compared with the device without an EIL
Summary
Based on a similar mechanism, a tandem upconverter with a photosensitive charge-generation layer (CGL) can be a new type of upconverter and thereby high conversion efficiency is expected. The applications of upconverters lie in the sequence of deposition processes and carrier-supply types, where upconverters with photosensitive-CGLs are inserted between the cathode and the OLED Such device configuration is defined as cathodic-controlled device, which is still rare reported in this field. To realize a new IR imaging device, in this paper we describe a 3.46% conversion efficiency, cathodic-controlled, and NIR organic upconverter for 3D mapping applications, where our proposed imaging system included several components, i.e. phosphorescent OLED, organic photosensitive CGL, transparent electrode, lens module, and NIR LED, to convert the NIR photon to visible light. To investigate the effect of the electron injection efficiency in the proposed upconverter, a temperature-dependent electrical characterization was performed to determine the energy barrier height between the EIL and the electron-transporting layer (ETL)
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