UV-Vis. Spectroelectrochemical Study on Electron Blocking and Trapping Behaviors in Conducting Polymer Bilayers with Dip
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1212-S08-23
UV-Vis. Spectroelectrochemical Study on Electron Blocking and Trapping Behaviors in Conducting Polymer Bilayers with Diphenylamine End Groups Yunfeng Li1, Chin-Che Tin2 and Vince Cammarata1* Department of Chemistry and Biochemistry, Auburn University, Auburn, AL, 36849, USA. 2 Department of Physics, Auburn University, Auburn, AL, 36849, USA. *corresponding author, [email protected]
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ABSTRACT Spectroelectrochemistry was used to study the electron trapping and rectifying behavior in several diphenylamine endgroup polymeric bilayers. Various combinations of the following monomers were pairwise sequentially electropolymerized onto ITO transparent electrodes: FD, DNTD, DPTD and Cl4DPTD. Poly(FD) is a p-type material while poly(DNTD), poly(DPTD) and poly(Cl4DPTD) are bipolar materials being both n-type and p-type. Bilayers of ITO|poly(FD)|poly (DNTD) or ITO|poly (FD)|poly (DPTD), block electrons from reducing the outer layer even at -1.0 V vs Ag/AgCl, yet holes effectively oxidize both layers. The LUMO differences between poly(DNTD) and poly(Cl4DPTD) or poly(DPTD) and poly(Cl4DPTD) provide a large enough electronic barrier that electron trapping can occur between these n-type materials. The visible spectra results imply that these polymers, poly(DPTD) or poly(Cl4DPTD) can be used as photovoltaic materials. INTRODUCTION Mixed conductor polymeric materials are rarely used for rectifying devices [1, 2]. By virtue of their bipolar nature, dominance by electron transport or hole transport depends on the connecting electrode material and the applied potential. When these materials are in contact with a unipolar material, the potential for rectification exists depending on the charge state of all the materials. The coupling of electrochemical and spectroscopic techniques is intensively used in the characterization of electroactive films[3, 4]. Spectroelectrochemistry (SEC) has been a powerful technique in following the spectral changes of conducting polymer films during their electrochemical growth and doping/dedoping processes for determining energy levels since the late 1960s[5]. Several spectroscopic techniques such as UV-Visible and near-infrared absorption (UV-Vis-NIR) or reflection spectroscopy, infrared spectroscopy (IR), Raman spectroscopy and X-ray absorption or scattering, have been combined with electrochemical methods for study of redox processes that occur on electrode surfaces and in thin solution layers[6]. Over the years, a series of monomers with a structural motif R-X-R have been synthesized in our lab[7-10]. Here R is the diphenylamine (DPA) endgroup and X is an electroactive functional unit. Polymeric films on electrode surfaces can be obtained by electrochemical polymerization of monomers resulting in an alternating polymer of diphenylbenzidine (two para- linked diphenylamine groups) and the X unit. These materials show unusual electrical and optical properties, and depending on the X unit, are promising as electrochromic materials, organic diodes and materials for organic photovoltaic cells
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