Characterization for Organic Solid Solution and Formation of Organic Electronics

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Characterization for Organic Solid Solution and Formation of Organic Electronics Yan Shao, Yang Yang * Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095, USA Recent two decades have seen the rapid development of organic electronics and much attention has been paid to carrier transport behavior. However, other characteristics, such as material compatibility, may be overlooked. We propose a new doping method taking advantage of fused organic solid solution, which is prepared by high-pressure and high temperature processing. In this method, the stable material systems can be selected and high performance organic light-emitting diodes with different colors have been demonstrated. KEYWORD: organic solid solution, organic light-emitting diodes, organic electronics

1. Introduction Organic compounds have been extensively investigated in the fabrication of various electronic and photonic devices in recent two decades 1-4). There are currently two general technologies to enhance device performance. One is adoption of multi-layer device structure; the other is introduction of small amount of dopants. Organic lightemitting diodes (OLEDs) are very good examples for these two characteristics and the device performance has been improved dramatically by doping technology and proper multi-layer structure 5-7). In recent decade, a new trend in OLED structure utilizes a graded mixed-layer as the active layer to replace the heterojunction, such that relatively high efficiencies and lifetimes are obtained and higher performance OLEDs have been demonstrated 8,9). However, device fabrication is becoming more complicated, due to necessary control of the dopant(s) and host(s) simultaneously 8). In this paper, we propose a new material system, the fused organic solid solution (FOSS), which homogeneously blends dopant and host organics through a high-temperature fusion process to form a multi-component system, and high performance OLEDs have been demonstrated after stable doping system have been obtained. This material system might also be utilized to analyze and understand the compound aging behavior under heating or device long-time working status. Currently, the most common technology for preparing doped organic thin films are co-evaporation under ultra-high vacuum and spin-coating from solution, which are very different from doping process in inorganic semiconductors. Dopant concentration plays an important role in device performance; however, a precise control of dopants over large area is still a challenging task in manufacturing. This process is further complicated if more than one dopant(s) is involved in a graded mixed-layer or other mixed layers 10,11). Another important issue for doped organic thin films is proper selection of the host-dopant system 12,13). In OLEDs and other organic material system, the common criteria for material selection are often control of carrier transport and their recombination or dissociation process, in which much attention has been paid to molecu