Geometry-based, n-type-enhanced p-type polymer/metal oxide nanocomposites for high-efficiency, high-specificity conducti
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Geometry-based, n-type-enhanced p-type polymer/metal oxide nanocomposites for highefficiency, high-specificity conductive systems Riccardo Raccis1, Laura Wortmann1, Shaista Ilyas1, Johannes Schläfer1, Andreas Mettenbörger1, Sanjay Mathur1 1 Universität zu Köln, Institut für Anorganische Chemie, Greinstrasse 6, 50939 Cologne, Germany
ABSTRACT Hematite (α-Fe2O3) nanoparticles were diffused of two different shapes (spherical and cubical) in PEDOT:PSS matrices below the percolation threshold. Increases in conductivity within a distinct range in concentration were observed in the dark and under simulated solar illumination. The effect was ascribed to a generalized Poole-Frenkel effect in conjunction with basic properties of heterojunctions and electrostatic dipoles, and verified through data fitting. A difference in behaviour between sphere- and cube-based nanocomposites was also observed. INTRODUCTION Conjugated polymer systems as a research subject are continuing to receive major interest for their applications in a variety of fields including photovoltaics,1,2,3 electronics,4,5,6 sensing,7,8,9 and electroluminescence2,10. The reported work addresses two aspects of conjugated polymer-metal oxide heterojunctions: on the interface front, the influence was studied of the shape of the junction; on the conductivity enhancement front, a model is proposed for the enhancement of p-type system through contact with an n-type phase, a reported phenomenon for which agreement is generally lacking on an explanation2,11. The study was conducted on nanocomposites in which an n-type phase (α-Fe2O3) was dispersed in a p-type phase (PEDOT:PSS) below the percolation threshold. The two phases were chosen for their similar, low band gaps, their wide use in semiconductor research,12,13 and their easy availability. The α-Fe2O3 phase was present as monodispersed, monocrystalline nanoparticles (NPs) of lateral size 40 nm, while PEDOT:PSS was present as a disordered, uncrosslinked bulk phase where NPs were diffused. The study was performed as a function of three variables: 1) NP weight fraction (c) in the polymer, ranging between 0 and 7 % (0 - 2 % volume range); 2) NP shape, the considered c range being investigated once for spherical NPs, and once for cubical NPs; and 3) all specimens were studied both in the dark and under simulated solar illumination. EXPERIMENT NPs were synthesized in-house. For NP preparation, reagents were purchased from Sigma Aldrich and used as received. Ferric nitrate (Fe(NO3)3), N,N-dimethylformamide (DMF), poly(N-vinyl-2-pyrrolidone) (PVP), and ethylene glycol (C2H6O2) were employed. Cubic α-Fe2O3 NPs were prepared by a modified one-step solvothermal reduction pathway in DMF, in the presence of PVP. The reaction solution was prepared by dissolving 0.4 g
of hydrated Fe(NO3)3 and 0.8 g PVP in 30 mL DMF; after stirring for 30 min, the solution was transferred into a Teflon-lined stainless autoclave and heated at 180 °C for 30 hours to obtain monodispersed cubic α-Fe2O3 NPs. Spherical α-Fe2O3 NPs were synthesized usin
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