ABSTRACT
Conducting polymers are critically important materials in organic electronic platforms relevant to sustainability (organic photovoltaics and organic light-emitting diodes) and wearable electronics (organic electrochemical transistors). However, most chemistry students do not receive formal training in the fundamental properties and extensive characterization of these fascinating materials. Described here are four scaffolded learning modules adapted from the primary literature and designed to build the fundamental understanding and practical skills necessary for productive contribution to emerging research in the field of conducting polymers and conducting polymer modified electrodes (CPMEs). These activities were performed by first-year chemistry graduate students and have been used in the lab to orient and equip new student researchers with the electrochemical, spectroscopic, and spectroelectrochemical skillsets central to working in CPMEs. First year master's students and undergraduate student researchers worked individually to complete data collection, analysis, and interpretation over three 4 h periods with additional time for sample preparation and imaging. Alternatively, one or more of these modules can be adapted and performed by pairs or groups of three over two 4 h lab periods as part of an undergraduate course such as instrumental analysis, polymers, and macromolecules, or as a capstone experience; instructions for these and other modifications are as described herein. If lab equipment and/or available time are limiting factors, sufficient sample data are provided for use as dry laboratories. Through completion of these modules, student researchers learn how to build chemically rational explanations for the electrochemical and spectroscopic signals, to collectively examine data from multiple complementary characterization techniques, and to extract enabling structure-property relationships, all while coming to see themselves as researchers and members of a worldwide scientific community.
ABSTRACT
We use electroabsorption spectroscopy to measure the change in built-in potential (VBI) across the polymer photoactive layer in diodes where indium tin oxide electrodes are systematically modified using dipolar phosphonic acid self-assembled monolayers (SAMs) with various dipole moments. We find that VBI scales linearly with the work function (Φ) of the SAM-modified electrode over a wide range when using a solution-coated poly(p-phenylenevinylene) derivative as the active layer. However, we measure an interfacial parameter of S = eΔVBI/ΔΦ < 1, suggesting that these ITO/SAM/polymer interfaces deviate from the Schottky-Mott limit, in contrast to what has previously been reported for a number of ambient-processed organic-on-electrode systems. Our results suggest that the energetics at these ITO/SAM/polymer interfaces behave more like metal/organic interfaces previously studied in UHV despite being processed from solution.
ABSTRACT
Poly(3-methylthiophene) (P3MT) was synthesized directly from indium tin oxide (ITO) electrodes modified with a phosphonic acid initiator, using Kumada catalyst transfer polymerization (KCTP). This work represents the first time that polymer thickness has been controlled in a surface initiated KCTP reaction, highlighting the utility of KCTP in achieving controlled polymerizations. Polymer film thicknesses were regulated by the variation of the solution monomer concentration and ranged from 30 to 265 nm. Electrochemical oxidative doping of these films was used to manipulate their near surface composition and effective work function. Doped states of the P3MT film are maintained even after the sample is removed from solution and potential control confirming the robustness of the films. Such materials with controllable thicknesses and electronic properties have the potential to be useful as interlayer materials for organic electronic applications.
