Electronic transport, ionic activation energy and trapping phenomena in a polymer-hybrid halide perovskite composite

Abstract The exploitation of methylammonium lead iodide perovskite-polymer composites is a promising strategy for the preparation of photoactive thin layers for solar cells. The preparation of these composites is a simple fabrication method with improved moisture stability when compared to that of pristine perovskite films. To deepen the understanding of the charge transport properties of these films, we investigated charge carrier mobility, traps, and ion migration. For this purpose, we applied a combinatory measurement approach that proves how such composites can still retain an ambipolar charge transport nature and the same mobility values of the related perovskite. Furthermore, thermally stimulated current measurements revealed that the polymer influenced the creation of additional defects during film formation without affecting charge mobility. Finally, impedance spectroscopy measurements suggested the addition of starch may hinder ion migration, which would require larger activation energies to move ions in composite films. These results pave the way for new strategies of polymer-assisted perovskite film development

Rheological and physical characterization of PEDOT: PSS/graphene oxide nanocomposites for perovskite solar cells

In this work, the influence of graphene oxide (GO) doped Poly(3,4 ethylenedioxythiophene):poly (styrenesulfonate)(PEDOT:PSS) thin nanocomposite on an indium–tin-oxide (ITO) anode, as hole transport layer (HTL) in perovskite solar cells, was investigated. Different concentrations of GO were added into the PEDOT:PSS in order to enhance its conductivity. In particular, the influence of GO content on the rheological and thermal properties of Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/GO nanocomposites was initially examined. The GO filler was prepared by using modified Hummers method and dispersed into PEDOT:PSS in different quantity (ranging from 0.05 to 0.25 %wt/wt). The obtained nanocomposite solutions were analyzed by rheological characterizations in order to evaluate the influence of the GO filler on the viscosity of the PEDOT:PSS matrix. The wettability of solutions was evaluated by Contact Angle (CA) measurements. The quality of GO dispersion into the polymer matrix was studied using Scanning electron microscopy (SEM) and X-ray diffraction (XRD). Thermal characterizations (DSC and TGA) were, finally, applied on nanocomposite films in order to evaluate thermal stability of the films as well as to indirectly comprehend the GO influence on PEDOT:PSS-water links

Effect of surface tension and drying time on inkjet-printed PEDOT:PSS for ITO-free OLED devices

Abstract Highly conductive PEDOT:PSS is one of the most promising materials for indium tin oxide (ITO) substitution in printed electronics. Here, we report the development and optimisation of two PEDOT:PSS ink formulations for the fabrication of inkjet-printed transparent conductive layers. Starting from aqueous commercial solutions, co-solvents and a non-ionic surfactant were employed to modify the surface tension, improve the wetting capability of the ink, and obtain uniform and homogeneous thin films. In particular, the quantities of ethanol and surfactant were systematically adjusted to determine the optimal conditions for inkjet printing. The results demonstrate that a surface tension value between 28 and 40 mN/m and approximately 40 vol.% of a low-boiling-point co-solvent are fundamental to ensure the proper wetting of the glass substrate and a quick-drying process that confers uniformity to the printed thin film. The printed PEDOT:PSS thin films show good morphological, optical, and electrical properties that are similar to those observed for the corresponding spin-coated layers. The organic light-emitting diodes (OLEDs) fabricated with the inkjet-printed PEDOT:PSS electrodes showed a maximum quantum efficiency of 5.5% and maximum current efficiency of 15 cd/A, which is comparable to spin-coated reference devices. These results demonstrate the great potential of polymeric electrodes for the fabrication of high-efficiency printed OLED devices that are compatible with flexible and stretchable substrates

PEDOT:PSS/GO nanocomposites: Determination of the aspect ratio by indirect measurements

Polymer nanocomposites properties significantly depend on the average size of the fillers dispersed into the matrix and on the grade of the dispersion, the latter influenced by the process techniques. In this work, we determined the aspect ratio of graphene oxide (GO) dispersed into Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), starting from the indirect measurement of the rheological behavior of polymer/filler mixtures, as a function of the shear rate and the volumetric composition. PEDOT:PSS+GO nanocomposite films were also realized by spin coating on different substrates and characterized by Scanning electron microscopy (SEM) and X-ray diffraction (XRD), in order to analyze the quality of the dispersion, even by direct measurements

Preparation and Characterization of EG-Chitosan Nanocomposites via Direct Exfoliation: A Green Methodology

In this study, free-standing expanded graphite chitosan (EG-chitosan) nanocomposite films have been prepared using a novel green and simple preparation method, starting from a commercial expandable graphite (GIC). The in situ exfoliation of GIC by a solvent-free sonication method was monitored as a function of the process parameters using X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS) and UV-visible transmittance (UV-VIS) analyses. The optimal process parameters were selected in order to obtain an efficient dispersion of EG in chitosan solutions. The effective EG amount after the in situ exfoliation was also determined by thermogravimetric analyses

Biodegradable extruded thermoplastic maize starch for outdoor applications

In the recent years, great progress was achieved in the development of biodegradable products based on agricultural raw materials. Among them, one of the most promising and diffused biomaterials is represented by starch. For this reason, different approaches have already been explored to use starch as a natural source for the production of biodegradable thermoplastic polymers. However, there is still a lack of a controlled, easy and cheap procedure to process maize native starch in order to obtain a highly performing thermoplastic polymer. The purpose of this paper is the development of a simple and reproducible method able to produce a thermoplastic starch that can be easily transformed into extruded objects, suitable for several potential applications. To reach this aim, a proper plasticizer was added to a commercial maize starch at different concentrations corresponding to mass fraction from 50 to 70% (in the following text %). The effect of the different amounts of the plasticizer on the processability of the starch powder was assessed by varying the parameters during the extrusion process. The interaction of the structure of starch with the plasticizer, firstly, and the final thermal and physical–mechanical properties of the extruded thermoplastic starch samples, secondly, were analysed by using several techniques: differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, UV transmittance, moisture absorption, colorimetric and mechanical tests. The samples containing 50% of plasticizer, in possess of the best physical and thermal performances, were further characterized in terms of durability, in order to predict their lifetime in outdoor conditions, by using artificial ageing tests, such as moisture absorption and QUV accelerated weathering tests

Cure reaction of epoxy resins catalyzed by graphite-based nanofiller

A significant effort was directed to the synthesis of graphene stacks/epoxy nanocomposites and to the analysis of the effect of a graphene precursor on cure reaction of a model epoxy matrix. A comparative thermal analysis of epoxy resins filled with an exfoliated graphite oxide eGO were conducted. The main aim was to understand the molecular origin of the influence of eGO on the Tg of epoxy resins. The higher Tg values previously observed for low curing temperatures, for epoxy resins with graphite-based nanofillers, were easily rationalized by a catalytic activity of graphitic layers on the reaction between the epoxy and amine groups of the resin, which leads to higher crosslinking density in milder conditions. A kinetic analysis of the cure mechanism of the epoxy resin associated to the catalytical activity of the graphite based filler was performed by isothermal DSC measurements. The DSC results showed that the addition of graphite based filler greatly increased the enthalpy of epoxy reaction and the reaction rate, confirming the presence of a catalytic activity of graphitic layers on the crosslinking reaction between the epoxy resin components (epoxide oligomer and di-amine). A kinetic modelling analysis, arising from an auto-catalyzed reaction mechanism, was finally applied to isothermal DSC data, in order to predict the cure mechanism of the epoxy resin in presence of the graphite based nanofiller

GO/glucose/PEDOT:PSS ternary nanocomposites for flexible supercapacitors

Poly(3,4 ethylenedioxythiophene)polystyrene sulfonate (PEDOT:PSS), among the most used conductive polymers, shows properties easily modulating by adding fillers as Graphene Oxide (GO). Recently, PEDOT-based polymers have been used with encouraging results as electrodes for flexible supercapacitors. We have already developed a green ternary nanocomposite based on PEDOT:PSS doped with GO and glucose (GGO-PEDOT) with a specific capacitance of 16 F/g, indicating how this nanocomposite is potentially suitable to be used as an electrode material for a supercapacitor. In this work, a free-standing nanocomposite film was realized by drop casting the solution in a proper silicone mould, followed by peeling and thermal annealing. Specific analyses, such as thermogravimetric, colorimetric and contact angle measurements, have been performed aiming at assessing the stability of the thermal and of the surface properties, even in severe moisture and UV aging conditions. Finally, The capacitive performance of PEDOT:PSS and of GGO-PEDOT was investigated by means of cyclic voltammetry (CV), in the pristine conditions and under UV aging. The deposited GGO-PEDOT film showed a good conductive behaviour and stability under UV treatment of 4 hours