This paper describes analysis of dropcast nanocrystalline and electrochemically deposited films of NiO and α-Fe 2 O 3 as model metal oxide semiconductors immersed in redox-inactive organic electrolyte solutions using electrochemical impedance spectroscopy (EIS). Although the data reported here fit a circuit commonly used to model EIS data of metal oxide electrodes, which comprises an RC circuit nested inside a second RC circuit that is in series with a resistor, our interpretation of the physical meaning of these circuit elements differs from that applied to EIS measurements of metal oxide electrodes immersed in redox-active media. The data presented here are most consistent with an interpretation in which the nested RC circuit represents charge transfer between the metal oxide film and the underlying metal electrode, and the non-nested RC circuit represents the resistance and capacitance associated with formation of a charge-compensating double-layer at the exposed interface between the metal electrode and electrolyte solution. Applying this interpretation to analysis of EIS data collected for metal oxide films in organic media enables the impact of film morphology on electrochemical behavior to be distinguished from the effects of the intrinsic electronic structure of the metal oxide. This distinction is crucial to the evaluation of nanostructured metal oxide electrodes for electrochemical energy storage and electrocatalysis applications.
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Fungi-Derived Pigments for Sustainable Organic (Opto)Electronics
ABSTRACT We present on the optical and electronic properties of a fungi-derived pigment xylindein for potential use in (opto)electronic applications. Optical absorption spectra in solutions of various concentrations and in film are compared and are consistent with aggregate formation in concentrated solutions and films. In order to improve film morphology obtained by solution deposition techniques, an amorphous polymer PMMA was introduced to xylindein to form xylindein:PMMA blends. Current-voltage characteristics and hole mobilities extracted from space-charge limited currents were found to be comparable between pristine xylindein and xylindein:PMMA films. Side by side comparison of the photoresponse of pristine xylindein and xylindein:PMMA films at 633 nm revealed an increase in the photosensitivity in xylindein:PMMA films due to the improved morphology favouring enhanced charge generation.
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- Award ID(s):
- 1705099
- NSF-PAR ID:
- 10059637
- Date Published:
- Journal Name:
- MRS Advances
- ISSN:
- 2059-8521
- Page Range / eLocation ID:
- 1 to 6
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The morphology of semiconducting polymer thin films is known to have a profound effect on their opto-electronic properties. Although considerable efforts have been made to control and understand the processes which influence the structures of these systems, it remains largely unclear what physical factors determine the arrangement of polymer chains in spin-cast films. Here, we investigate the role that the liquid–vapor interfaces in chlorobenzene solutions of poly(3-hexylthiophene) [P3HT] play in the conformational geometries adopted by the polymers. Using all-atom molecular dynamics (MD), and supported by toy-model simulations, we demonstrate that, with increasing concentration, P3HT oligomers in solution exhibit a strong propensity for the liquid–vapor interface. Due to the differential solubility of the backbone and side chains of the oligomers, in the vicinity of this interface, hexyl chains and the thiophene rings, have a clear orientational preference with respect to the liquid surface. At high concentrations, we additionally establish a substantial degree of inter-oligomer alignment and thiophene ring stacking near the interface. Our results broadly concur with the limited existing experimental evidence and we suggest that the interfacial structure can act as a template for film structure. We argue that the differences in solvent affinity of the side chain and backbone moieties are the driving force for the anisotropic orientations of the polymers near the interface. This finer grained description contrasts with the usual monolithic characterization of polymer units. Since this phenomenon can be controlled by concurrent chemical design and the choice of solvents, this work establishes a fabrication principle which may be useful to develop more highly functional polymer films.more » « less
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ABSTRACT The properties of phosphonium polyelectrolytes (PELs) were evaluated in an effort to assess the influence of both side chain and main chain composition. The influence of side chain was examined by comparing properties of a series of PELs having hydrophobic octyloxy side chains to those of structural analogues lacking the side chains. The influence exerted by backbone flexibility/length of spacer between charges was revealed by comparing properties of two series of polymers with a variable number of methylene units between phosphonium charge‐bearing sites. Side chain composition and spacing between phosphonium units lead to noteworthy influence on thermal stability, glass transition, and crystallinity. The molecular structure of PELs also correlates with trends in film morphology and critical surface energy of PEL dip‐cast films. Sensitivity of morphology to humidity or water in the casting solvent was observed. Supramolecular assembly of films via layer‐by‐layer deposition of PELs alternating with anionic polythiophene derivative layers was also undertaken. The linearity of film growth, amount of material deposited in each bilayer, polycation:polyanion ratio, and film roughness all show noteworthy trends that depend on both the presence/absence of side chains and on spacing between ionic centers. The relationship between side chain and spacer on bactericidal activity against
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Semiconducting conjugated polymers (CPs) have shown great potential in organic solar cells and organic field-effect transistors (OFETs), due to their tunable electronic and optical properties. In this study, we compare computational predictions of electronic and optical properties of ensembles of cis-polyacetylene (cis-PA) multiple oligomers in two different forms (a) undoped cis-PA and (b) cis- PA doped by phosphorous fluoride (PF6−) via density functional theory (DFT) with hybrid functionals. The comparison of undoped cis-PA under the constraint of injected charge carrier and cis-PA doped by PF6− shows that either doping or injection provides very similar features in electronic structure and optical properties. Doped and injected are similar to each other and different from the pristine, undoped PA. Computed results also indicate that the injection of charge carriers and adding p-type doping into the semiconducting CP model both greatly affect the conductivity. These observations provide a better understanding and practical use of the properties of polyacetylene films for flexible electronic applications.more » « less
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Abstract Hybrid halide 2D perovskites deserve special attention because they exhibit superior environmental stability compared with their 3D analogs. The closer interlayer distance discovered in 2D Dion–Jacobson (DJ) type of halide perovskites relative to 2D Ruddlesden–Popper (RP) perovskites implies better carrier charge transport and superior performance in solar cells. Here, the structure and properties of 2D DJ perovskites employing 3‐(aminomethyl)piperidinium (3AMP2+) as the spacing cation and a mixture of methylammonium (MA+) and formamidinium (FA+) cations in the perovskite cages are presented. Using single‐crystal X‐ray crystallography, it is found that the mixed‐cation (3AMP)(MA0.75FA0.25)3Pb4I13perovskite has a narrower bandgap, less distorted inorganic framework, and larger PbIPb angles than the single‐cation (3AMP)(MA)3Pb4I13. Furthermore, the (3AMP)(MA0.75FA0.25)3Pb4I13films made by a solvent‐engineering method with a small amount of hydriodic acid have a much better film morphology and crystalline quality and more preferred perpendicular orientation. As a result, the (3AMP)(MA0.75FA0.25)3Pb4I13‐based solar cells exhibit a champion power conversion efficiency of 12.04% with a high fill factor of 81.04% and a 50% average efficiency improvement compared to the pristine (3AMP)(MA)3Pb4I13cells. Most importantly, the 2D DJ 3AMP‐based perovskite films and devices show better air and light stability than the 2D RP butylammonium‐based perovskites and their 3D analogs.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1557/adv.2018.446
