Ž . Synthetic Metals 111–112 2000 125–128 www.elsevier.comrlocatersynmet A novel RGB multicolor light-emitting polymer display Hidekazu Kobayashi a, ) , Sadao Kanbe a , Shunichi Seki a , Hiroshi Kigchi a , Mutsumi Kimura a , Ichio Yudasaka a , Satoru Miyashita a , Tatsuya Shimoda a , Carl R. Towns b , Jeremy H. Burroughes b , Richard H. Friend b a Base Technology Research Center, Seiko Epson, 3-3-5 Owa, Suwa, Nagano 392-8502, Japan b Cambridge Display Technology, 181a Huntingdon Road, Cambridge CB3 0DJ, UK Abstract Ž . Ž .Ž . We have developed a system for depositing the light-emitting polymers LEP poly para-phenylene vinylene PPV for a green or a Ž .Ž . red emitter with a conventional ink jet head followed by spin-coating of poly di-octyl fluorene F8 for an electron-transferring layer or a Ž . Ž . blue emitter. Using this system, we have succeeded in patterning electroluminescent EL layers on a thin film transistor TFT substrate using the inkjet process and displaying a multicolor image using the TFT–LEP display. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Light-emitting diode; Ink jet; Patterning 1. Introduction The patterning of light-emitting layers is the most im- portant process in all manufacturing processes of multi- Ž . color organic electroluminescent EL displays. The mask-patterning method has been developed for low wx molecular type organic EL multicolor displays 1 . On the other hand, the ink jet patterning method has been devel- Ž . oped for light-emitting polymer LEP multicolor displays due to the good matching between polymer solution and w x the ink jet patterning method 2,3 . Therefore, we have developed a multicolor LEP display using ink jet pattern- ing process. 2. Methods We have developed an ink jet machine with a conven- tional ink jet head for patterning an EL layer. The head has 32 = 2 = RGB nozzles, and the diameter of an ink droplet is about 30 mm. The ink jet machine has a total resolution of "30 mm, and it can pattern EL layers on a 30 = 30 cm 2 substrate. The head is made of metal plates and a plastic resin which is damaged by aromatic solvents, be- cause our conventional ink jet head is designed for water- ) Corresponding author. Fax: q 81-266-52-7409. Ž . E-mail address: kobayashi.hidekazu@exc.epson.co.jp H. Kobayashi . based ink. Therefore, the EL materials are limited to the materials that are soluble in water or alcohol. A Ž .Ž . poly para-phenylene vinylene PPV precursor is soluble in methanol. Therefore, we selected PPV for green emitter and PPV with Rhodamine 101 additive for red emitter. However, we have no good blue EL material which or whose precursor can be soluble in water or alcohol. There- Ž .Ž . fore, we used poly di-octyl fluorene F8 for the blue emitter and formed the layer by spin-coating a xylene solution. In this process, the F8 solution gives no damage to the PPV and RPPV layers. 3. Experimental Fig. 1 shows the multicolor device structure that is suitable for our ink jet process. We formed banks between each pixel on a glass substrate with thin film transistor Ž . wx TFT array 4 . After a treatment by CF plasma on the 4 surface of the substrate, PEDTrPSS solution was spin- coated on the substrate to form a hole-injecting layer. As the result, the PEDTrPSS was not coated on the banks, but coated on the pixels due to the hydrophobicity of the bank surfaces. After that, an ink jet head on the red pixels discharged the RPPV ink. After drying the RPPV ink, the PPV ink was discharged on the green pixels. During the ink jet process, the banks treated by CF plasma prevented the EL 4 0379-6779r00r$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. Ž . PII: S0379-6779 99 00322-7