Electrochemical deposition of patterning and highly luminescent organic films

This paper describes a simple electrochemical deposition (ED) technique to prepare luminescent and patterned films for light-emitting devices (LEDs). The luminescent films are deposited directly on the patterned ITO (indium tin oxide) electrodes through an oxidation coupling reaction of an electroactive and luminescent precursor. The ED films deposited on the ITO strips (width of 200 μm) exhibit smooth surface morphology (roughness of morphology surface of 3.1 nm), small roughness in electrode edge of 1–2 μm and high fluorescence quantum efficiency (>60%). The LEDs with structure ITO/ED film/Ba/Al show pure blue emission (CIE coordinates of (0.16, 0.07)), high brightness of 3080 cd m−2 and the maximum external quantum efficiency of 0.60%. (Some figures in this article are in colour only in the electronic version) Since organic light-emitting devices (OLEDs) with high efficiency were reported by Tang and Van Slyke [1], many works have been done to deeply understand the basic processes in OLEDs and to commercialize these new display devices. One of the key components in OLED devices is the emitting layer, which is generally prepared by vacuum evaporation and spin-coating. For OLED displays, the patterning of emitting layers with size from ten to a few hundred of μm is the basic requirement. Ink-jet printing [2, 3] and shadow masks [4, 5] are the most common candidates for the active technique in patterning OLEDs. However, these methods do not take advantage of pre-patterned electrodes to pattern the emission colour and require additional steps such as the precise positioning of shadow masks. The high cost is a major problem besides technical problems. There has been great interest recently in the development of patterning technology for display such as lift-off [6, 7], laser ablation [8], micromoulding in capillary (MIMIC) [9–11] and maskless dye diffusion technique [12]. Although a small, monochrome, flatpanel display based on these methods has been demonstrated, all of these techniques are still immature for patterning of LEDs. Electrochemical deposition (ED) is considered to be a very promising technique for the production of thin polymer films on a conductive substrate. In this technique, the luminescent films can be deposited directly on the patterned ITO (indium tin oxide) electrodes through an oxidation coupling reaction of the electroactive and luminescent precursor. Generally ED films have a very low luminescence efficiency due to structural defects and doped counterions present in the ED films [13–19], which strongly quench the fluorescence. Recently, through a structural design of precursor for ED and accurate control over ED quality, we have designed a compound TCPC with high luminescence efficiency (see figure 1) and have resolved the issue of quenching of fluorescence in ED films. In this paper, we report the preparation of micropatterning and the acquirement of highly luminescent film by utilizing the ED method and its electroluminescent properties. As shown in figure 2(a), ED was performed using a BAS100W electroanalytical system with a homemade threeelectrode arrangement [20, 21], equipped with a titanium counter electrode, an Ag/Ag+ reference electrode and a patterned ITO glass working electrode (the patterned ITO was made by photolithography). The patterned ITO glass has an 0268-1242/07/080855+04$30.00 © 2007 IOP Publishing Ltd Printed in the UK 855