www.afm-journal.de FULL PAPER © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Funct. Mater. 2010, XX, 1–7 1 www.MaterialsViews.com wileyonlinelibrary.com By Bin Hu, Dapeng Li, Okan Ala, Prakash Manandhar, Qinguo Fan, Dayalan Kasilingam, and Paul D. Calvert* 1. Introduction Many types of electro-optic devices depend on having a trans- parent electrical conductor as the front electrode. This group includes liquid-crystal displays (LCDs), organic light emitting diodes (OLEDs), photovoltaic cells, and electroluminescent (EL) displays. The most widely used transparent conductor is indium tin oxide (ITO) coated onto glass, but it has the dis- advantages of being expensive, heavy, and brittle. Present devices also are generally intended for a five year working life and the impermeability of glass to moisture and oxygen is an advantage. [1] There is considerable interest in the development of short-lived, disposable devices that would be printed onto, or attached to, paper or textiles. Yet, to date, there have been only limited reports on textile-based electrodes or devices. [2–4] These devices would require a cheap, flexible, and transparent conductor. ITO or poly(3,4-ethylenedioxythiophene) (PEDOT) coupled with poly(styrene sulfonate) (PSS) (PEDOT:PSS) coated polyethylene terephthalate (PET) films are possible solutions for this application, taking advantaging of the superior transparency, light weight, flex- ibility, and robustness of the polymer films. [5,6] However, there has not been an ideal polymer material available to meet all the requirements. [7] The three main functions required of such conductor material, transparency, conductivity, and flexibility, will involve trade-offs. Thicker films of ITO or conducting polymer can be more conducting, but at the price of lower transparency and a greater ten- dency to crack when flexed or stretched. Devices will differ in the current densities, optical transmis- sion, and toughness required, and therefore a range of mate- rials will probably be required. In recent work, our group has studied inkjet-printed con- ducting polymer strain sensors on textiles, [8,9] inkjet-printed copper and nickel conductors on paper, [10] and inkjet-printed silver–PEDOT composite antennas on textiles. [11] The woven structure of textiles gives great flexibility and many textiles are quite transparent. Therefore, we wanted to explore transparent conductors based on conducting polymer inkjet-printed onto textiles. We speculate that a hybridization of the open structure of woven textiles and a layer of PEDOT:PSS conducting film shall result in a superior textile-based conductor that simulta- neously satisfies the flexibility, transparency, and conductivity requirements. In order to test such multifunctionality of the materials, they were used to construct EL devices. As one kind of light-emitting diodes, EL devices have gained more interest because of their high brightness, uniform light emission, thin architecture, and low power consumption. [12] EL lights can be used for LCD backlighting for cellular phones, personal digital assistants (PDA), and keyboards. They can also be used for architectural and decorative lighting. [13] Flexible powder EL devices can be fabricated with flexible substrates such as ITO-coated PET films. [14] A typical EL device is fabri- cated by sandwiching a phosphor layer between two electrodes and generates light when excited by an alternating current (AC) electric field, i.e., an alternating current powder EL (ACPEL) device. The emission color of an EL device depends on the phosphors and the dopant materials. Printed PEDOT:PSS is the obvious conductor for this application since it is readily available and requires only low processing temperatures. The polymer could be deposited by roll-to-roll printing, dipping, and vapor phase polymeriza- tion [15,16] instead of inkjet printing. In the laboratory context, Textile-Based Flexible Electroluminescent Devices DOI: 10.1002/adfm.201001110 [∗] B. Hu, Dr. D. Li, Prof. Q. Fan, Prof. P. D. Calvert Department of Materials and Textiles University of Massachusetts Dartmouth N. Dartmouth, MA 02747-2300, USA E-mail: pcalvert@umassd.edu O. Ala Department of Mechanical Engineering Texas A&M University College Station, TX 77843-3123, USA P. Manandhar, Prof. D. Kasilingam Department of Electrical and Computer Engineering University of Massachusetts Dartmouth N. Dartmouth, MA 02747-2300, USA Flexible and transparent textile-based conductors are developed by inkjet printing poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) onto polyethylene terephthalate (PET) mesh fabrics. The conductivity–transparency relationship is determined for textile-based conductors with different thicknesses of the printed PEDOT:PSS film. The function of these textile-based conductors is studied in the alternating current powder electroluminescent (ACPEL) devices and compared with indium tin oxide (ITO) glass in an ACPEL device of the same configuration. Textiles coated with conducting polymers are a potential alternative to coated polymer films for flexible, transparent conductors.