Research Article www.acsami.org
Laser-Scanned Programmable Color Temperature of Electroluminescence from White Light-Emitting Electrochemical Cells Hsiao-Chin Lee,† Chien-Ming Fan Chiang,‡ Po-Yi Wu,† Yung-Chi Yao,§ Monima Sarma,∥ Zu-Po Yang,*,‡ Hai-Ching Su,*,† Ya-Ju Lee,§ and Ken-Tsung Wong∥ †
Institute of Lighting and Energy Photonics and ‡Institute of Photonic Systems, National Chiao-Tung University, Tainan 71150, Taiwan § Institute of Electro-Optical Science and Technology, National Taiwan Normal University, 88, Sec.4, Ting-Chou Road, Taipei 116, Taiwan ∥ Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan S Supporting Information *
ABSTRACT: Recently, the control of correlated color temperature (CCT) of artificial solid-state white-light sources starts to attract more attention since CTs affect human physiology and health profoundly. In this work, we proposed and demonstrated a method that can widely tune the CCTs of electroluminescence (EL) from white-light-emitting electrochemical cells (LECs) by employing plasmonic filters. These integrated on-chip plasmonic filters are composed of semicontinuous thin Ag film or Ag nanoparticles (NPs) both included in the indium tin oxide anode contact, which have different characteristics of plasmonic resonant absorptions that can tune the EL spectra of white LECs. The CCTs of EL from white LECs integrated with semicontinuous thin Ag film and randomly distributed Ag NPs are 5778 and 2350 K, respectively. A commercially available laser scanning system was used to locally thermal anneal the semicontinuous thin Ag film to form the randomly distributed Ag NPs on the scanned areas. Hence, these two kinds of filters can be integrated on the same chip of white LEC, giving more freedom to control the CCTs of white EL and more potential applications. In addition, the laser scanning system used here is quite often used in display manufactures so that our proposed method can be immediately adopted by the light-emitting diode industry. KEYWORDS: light-emitting electrochemical cells, color temperature, nanoparticles, plasmonic filter, white light
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INTRODUCTION Much effort has been used in researching solid-state white-lightemitting diodes (LEDs), including inorganic and organic emissive materials, as replacements for conventional incandescent or fluorescent lamps because of their many advantages, such as high efficiency, compact size, and flexibility.1−3 Comparing with inorganic LEDs, organic LEDs (OLEDs) have much simpler fabrication processes and flexibility, so many applications have been proposed, for example, flexible display panels and flexible lighting devices.4 However, the fabrications of conventional OLEDs have to satisfy many requirements, including careful design of multilayer structure and intentional choosing of electrode metals, to achieve balance of injection carrier. This issue can be avoided by employing alternative emissive materials, that is, organic light-emitting electrochemical cells (LECs).5 For solid-state LECs, only a single emissive layer is generally required, which is solutionprocessable, and the constraints on the selection of electrode metals are not as strong because electrochemically doped regions can be formed spontaneously near the contacts under © 2016 American Chemical Society
an applied bias, resulting in relatively easier achievement of balanced injection carrier, lower operation voltage, and higher power efficiency. Several works on solid-state white LECs have been reported.6−16 In general, the solid-state white LECs are fabricated by the so-called host−guest method,6−13 in which dual emission spectra are emitted from red-emitting guest material with low doping concentration ( 5%) (Table 1). With the highly efficient complexes, such device performance was sufficient for commercial applications, especially for consumer electronics, since they can be fabricated in a simple and cost-effective way.
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CONCLUSIONS In summary, we proposed and demonstrated a method that can widely tune the CCTs of white LEC by different plasmonic filters embedded in ITO. These plasmonic filters are composed of semicontinuous thin Ag film or randomly distributed Ag NPs, which can be fabricated easily by metal evaporation (e.g., sputtering) and local thermal annealing using a laser scanning system. The fabricated thin Ag film plasmonic filter and Ag NPs plasmonic filter have different absorption spectra due to having different sizes, shapes, and distributions of Ag NPs. Therefore, for the white LECs with CCT of 3820 K, the thin Ag film plasmonic filter and Ag NPs plasmonic filter both embedded in ITO can tune the CCT of white LECs to 5778 and 2350 K, respectively. Moreover, we demonstrated that the integration of different kinds of plasmonic filters together on the same piece of substrate (which showed multiple transmission areas) by using a laser scanning system to perform local thermal annealing, which cannot be realized by conventional thermal annealing methods (e.g., RTA). Therefore, multiple plasmonic filters could be integrated in a single-chip white LECs, giving more freedom to control the CCTs of white LECs and more potential applications. The laser scanning system we used here is typically used in display manufacturing so that our proposed method can be immediately adopted by the light-emitting diode industry. 31804
DOI: 10.1021/acsami.6b10619 ACS Appl. Mater. Interfaces 2016, 8, 31799−31805
Research Article
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DOI: 10.1021/acsami.6b10619 ACS Appl. Mater. Interfaces 2016, 8, 31799−31805
