Photoconductance of ITO/Conductive Polymer Junctions in the UV and Visible Ranges

Abstract

Controlling charge transfer at indium-doped tin oxide (ITO)/conductive polymer junctions is of special importance for organic photovoltaic (OPV) devices and organic light emitting diodes (OLEDs), where ITO is often the transparent electrode of choice. Light induced conductance enhancement, i.e., photoconductance, can allow such control. ITO/conductive polymer junctions are shown herein to exhibit photoconductance under UV illumination mostly due to photoinduced decrease of an electron barrier at the ITO–polymer interface by discharging of ITO extrinsic surface states, related to the adsorption of oxygen species. Furthermore, we show that ITO surface modification by photoactive porphyrin adsorption can sensitize the ITO/conductive polymer junctions, extending the photoconductance to the visible range, to which ITO is transparent. This process is ascribed mostly to discharging of ITO adsorbate states by recombination with photogenerated holes in the photoexcited molecules. Such sensitization is highly relevant for organic optoelectronic devices utilizing ITO interfaced with photoactive organic species and operating in the visible range, such as OPV and OLED devices, and might be applicable also to other UV-photoconductive metal oxide electrodes.

Enhancement of electronic effects at a biomolecule–inorganic interface by multivalent interactions

“…13,21 The SPV was measured as the change in CPD upon illumination with a λ = 375 nm laser, at the tail of the super bandgap absorption of the material. 13,42 We note that while the obtained SPV values may not represent quantitatively the surface band banding magnitude because flattening of the bands might not have been achieved, 43 they provide valuable comparative information on differences in the band bending between the different samples. A band bending of 90 mV was found for the pristine sample and increased to 150–170 mV upon functionalization (Fig.…”

“…7 We envisaged that these basic peptides would bind not only titania but also other metal oxides, and more specifically ITO, which is commonly used as a transparent cathode in opto-electronics applications. 27 Indeed, although ITO modification through acidic ligands is more common, 19,28,29 derivatization via basic amine moieties has also been reported. 30,31 Furthermore, since modification with amine containing molecules is known to reduce the surface work function, 13,19,[32][33][34] we hypothesized that the display of multiple basic side chains in the peptide would lead to a reduction of the surface work function.…”

Diazonium-Based Covalent Molecular Wiring of Single-Layer Graphene Leads to Enhanced Unidirectional Photocurrent Generation through the p-doping Effect

“…8 Among them, chemisorption, which ensures the formation of covalent bonds on the substrate, is a promising strategy to achieve a strong and stable attachment of the (photo)electroactive molecules. Depending on the materials, various molecular wiring approaches have been reported with the use of carboxylates, 9 silanes, 10 titanates, 11 phosphonates, 12 thiolates, 13 and diazonium salt, as the most commonly used.…”