Proton Radiation Studies on Conjugated Polymer Thin Films

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Proton Radiation Studies on Conjugated Polymer Thin Films Harold O. Lee III1, Muhammed Hasib1, and Sam-Shajing Sun1,2* 1

Center for Materials Research, Ph.D. Program in Materials Science and Engineering,

Norfolk State University, Norfolk, VA 23504, USA 2

Department of Chemistry, Norfolk State University, Norfolk, VA 23504, USA

ABSTRACT Polymeric thin film based electronic and optoelectronic materials and devices are attractive for potential space and certain radiation related applications due to their inherent features such as being light weight, flexible, biocompatible and environmental friendly, etc. Proton radiation is a major form of ionizing radiation in space, yet very few literature and data are available on proton radiation effects on conjugated polymer systems. In this study, UV-Vis absorption spectra of several conjugated polymers and/or their composite thin films were measured and compared right before and after a 200 MeV proton beam irradiation at different dosages, and the results revealed that proton radiation has very little or negligible impact up to 800 Rads on the optoelectronic properties of several polymers and their composite thin films. INTRODUCTION Durability of conjugated polymers in certain high energy radiations are essential for potential polymer-based devices in radiation related or space applications. Proton radiation is one of a few key ionizing radiations (others including gamma, beta, X-rays) prevalent in space, particularly in the so-called ‘inner Van-Allen belt’ region where most near-earth satellites are orbiting [1-2]. While classic inorganic semiconductor based optoelectronic devices outperform the current polymer-based devices with regards to efficiency and stability, polymeric optoelectronic devices exhibit the inherent advantages of being lightweight, flexible, biocompatible, environmental friendly, cost effective, and less energy consumption in large scale manufacturing. A key property of all materials used in space applications is their durability under typical space ionizing radiations. Proton radiation is particularly important due to their high abundance in space, especially in the so-called ‘Inner Van Allen belt’ [1-2], which is a spherical belt shaped space region from the surface of the earth where most near-earth satellites maintain their orbit. Conjugated polymers are the main components of polymer-based electronic and optoelectronic devices. There are a few reports covering the radiation effects on conjugated polymers in beta rays [3], X-rays [4], and gamma rays [5]. The proton radiation studies have been reported on a polyphenylenevinylene (PPV) polymer system, where the photoluminescence PL emission spectra of PPV was found to exhibit smaller decrease at higher proton energies up to 3 MeV [6]. However, PPV has been known to be a relatively less stable conjugated polymer as compared to more stable conjugated polymers such as poly-3-hexyl-thiophene (P3HT). In addition, space crafts and satellites are also exposed to occasionally solar events such as extremely in

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