Highly efficient blue organic light emitting device using indium-free

Highly efficient blue organic light emitting device using indium-free

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Highly efFcient blue organic light emitting device using indium-free transparent anode Ga:ZnO with scalability for large area coating Liang Wang, 1 Dean W. Matson, 1 Evgueni Polikarpov, 1 James S. Swensen, 1 Charles C. Bonham, 1 Lelia Cosimbescu, 1 Joseph J. Berry, 2 David S. Ginley, 2 Daniel J. Gaspar, 1 and Asanga B. Padmaperuma 1, a ! 1 Energy and Environment Directorate, Pacifc Northwest National Laboratory, Richland, Washington 99352, USA 2 National Center For Photovoltaics, National Renewable Energy Laboratory, Golden, Colorado 80401, USA s Received 28 September 2009; accepted 30 November 2009; published online 19 February 2010 d Organic light emitting devices have been achieved with an indium-free transparent anode, Ga doped ZnO s GZO d . A large area coating technique was used s RF magnetron sputtering d to deposit the GZO ±lms onto glass. The respective organic light emitting devices exhibited an operational voltage of 3.7 V, an external quantum ef±ciency of 17%, and a power ef±ciency of 39 lm/W at a current density of 1 mA / cm 2 . These parameters are well within acceptable standards for blue OLEDs to generate a white light with high enough brightness for general lighting applications. It is expected that high-ef±ciency, long-lifetime, large area, and cost-effective white OLEDs can be made with these indium-free anode materials. © 2010 American Institute oF Physics . f doi: 10.1063/1.3282526 g I. INTRODUCTION The availability of economically produced and environ- mentally stable transparent conductive oxide s TCO d coatings is critical for the development of a variety of electronic de- vices requiring transparent electrodes. Such devices include liquid crystal displays organic light emitting devices s OLEDs d , 1 , 2 solar cells, 3 , 4 low-emissivity and electrochromic windows, 5 , 6 and electrically heated windows. 7 , 8 The materi- als ful±lling these requirements are usually wide band gap inorganic TCOs such as indium tin oxide and ²uorine doped tin oxide. 9 Tin-doped indium oxide s ITO d has traditionally been used for optoelectronic TCO applications because of its low resistivity, high work function, and transparency over 80% in the visible. Due to the high cost of indium, problems with processing ITO ±lms, and the tendency of indium to migrate into the device, there has been an increased research interest in developing indium-free TCO materials. A number of alternative metal oxides and doped oxides have been evaluated as TCO materials with varying degrees of success. 10 , 11 Among these alternatives to ITO, gallium-doped zinc oxide 2 , 12 s GZO d and aluminum-doped zinc oxide 13 , 14 s AZO d have drawn particular attention. These materials have demonstrated resistivities and transparencies approaching those of the best ITO, along with low toxicity and much lower materials cost s 1/5 to 1/10 that of ITO d . Although AZO is attractive as a TCO electrode material, GZO provides the advantage of having a greater resistance to oxidation as a result of gallium’s greater electronegativity compared to alu- minum and a broader range of doping concentrations.
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This note was uploaded on 03/27/2011 for the course CHEM 2211L taught by Professor T.a. during the Spring '08 term at UGA.

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Highly efficient blue organic light emitting device using indium-free

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