Combinatorial Fabrication and Screening of Organic Light-Emitting Device Arrays
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Combinatorial Fabrication and Screening of Organic Light-Emitting Device Arrays Joseph Shinar1 and Ruth Shinar2 1 Ames Laboratory – USDOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 2 Microelectronics Research Center, Iowa State University, Ames, Iowa 50011 ABSTRACT Studies of combinatorial fabrication and screening of organic light-emitting devices (OLEDs) are reviewed. These studies include screening of luminescent materials, electron and hole transport layers, lower-gap emitting guest dopants in small molecular emitters, and electronically doped polymeric anodes. The review focuses on screening of 2-dimensional (2-d) small molecular UV/violet arrays, 1-d blue-to-red arrays, and 1-d intense white OLED libraries, and briefly describes arrays fabricated to study Förster energy transfer in guest-host OLEDs. It demonstrates that combinatorial fabrication of OLEDs has become a powerful tool for screening OLED materials and configurations, and for studying their basic properties. INTRODUCTION Combinatorial approaches for discovery and optimization of new materials have emerged as a powerful tool in fields such as catalysis, optoelectronics, and luminescence.1 The multiplicity of parameters that affect device performance renders combinatorial approaches attractive for device development as well. Indeed, in recent years such approaches have proven useful in fabrication, optimization, and basic studies of organic light-emitting devices (OLEDs).2-10 This chapter reviews these studies, with emphasis on studies conducted by J. Shinar and coworkers, which include 2-dimensional (2-d) combinatorial arrays of UV-violet OLEDs,5,11 1-d arrays of red-to-blue OLEDs,7 and 1-d combinatorial screening of white OLEDs.8 1-d arrays fabricated to study Förster energy transfer in doped OLEDs9 are also reviewed briefly. The performance of small molecular and polymer red-to-blue and white OLEDs has improved dramatically over the past decade.12,13 However, OLED performance depends on many variables, e.g., layer thickness, composition, device configuration, electrode material, and interfaces. Therefore, determining the optimal parameters in the complex, multilayer structures using conventional fabrication of one device at a time, varying only one parameter, is tedious and introduces both systematic errors and random variations from batch to batch. In contrast, combinatorial screening using, e.g., a sliding shutter and substrate rotation technique, which allows variations in parameters such as layer thickness or doping, removes these errors and random variations.2,3,5 It enables fabrication of 2-d arrays of OLEDs in which two parameters are varied systematically across the array while other fabrication conditions remain essentially identical for all the pixels, enabling a far more reliable and efficient optimization procedure. COMBINATORIAL SCREENING OF LUMINESCENT MATERIALS Combinatorial processes were used to accelerate the search for luminescent materials such as refractive oxides doped with
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