Boosting Electrochemical Activity of Porous Transparent Conductive Oxides Electrodes Prepared by Sequential Infiltration Synthesis

Sequential infiltration synthesis (SIS) is an emerging technique for producing inorganic-organic hybrid materials and templated inorganic nanomaterials. The application space for SIS is expanding rapidly in areas such as lithography, filtration, photovoltaics, antireflection, and triboelectricity, but not in the field of electrochemistry. This study performs SIS for the fabrication of porous, transparent, and electrically conductive films of indium zinc oxide (IZO) to evaluate their potential as an electrode for electrochemistry. The electrochemical activity of IZO-coated electrodes is evaluated when their surfaces are modified with ferrocenecarboxylic acid (FcCOOH), a model redox molecule. Results show a 25-fold enhancement in peak current densities mediated by an Fc/Fc⁺ redox couple for an IZO-coated electrode in comparison with bare electrodes; this is afforded by the porous morphology of the IZO film and the enhanced binding efficiency of FcCOOH on the IZO film. The results confirm the potential of SIS for the preparation of porous transparent conducting oxide electrodes, which will enable the application of SIS-derived materials in various electrochemical fields.

Highly piezoelectric BaTiO3 nanorod bundle arrays using epitaxially grown TiO2 nanomaterials

Low-dimensional piezoelectric nanostructures such as nanoparticles, nanotubes, nanowires, nanoribbons and nanosheets have been developed for potential applications as energy harvesters, tunable sensors, functional transducers and low-power actuators. In this study, lead-free BaTiO ₃ nanorod bundle arrays (NBA) with highly piezoelectric properties were successfully synthesized on fluorine-doped tin oxide (FTO) substrate via a two-step process consisting of TiO₂ epitaxial growth and BaTiO₃ conversion. Through the TiO₂ epitaxial growth on FTO substrate, (001) oriented TiO₂ nanostructures formed vertically-aligned NBA with a bundle diameter of 80 nm and an aspect ratio of six. In particular, chemical etching of the TiO₂ NBA was conducted to enlarge the surface area for effective Ba²⁺ ion diffusion during the perovskite conversion process from TiO₂ to BaTiO₃. The final structure of perovskite BaTiO₃ NBA was found to exhibit a feasible piezoelectric response of 3.56 nm with a clear phase change of 180° from the single BaTiO₃ bundle, by point piezoelectric forced microscopy (PFM) analysis. Consequently, highly piezoelectric NBA could be a promising nanostructure for various nanoscale electronic devices.

Optical-Electrical-Chemical Engineering of PEDOT:PSS by Incorporation of Hydrophobic Nafion for Efficient and Stable Perovskite Solar Cells

In PIN-type perovskite solar cells (PSCs), the hydroscopicity and acidity of the poly(3,4-ethylenedioxythiophene)-poly(styrene-sulfonate) (PEDOT:PSS) hole transport layer (HTL) have critical influences on the device stability. To eliminate these problems, Nafion, the hydrophobic perfluorosulfonic copolymer, is incorporated into PEDOT:PSS by a simple spin-coating process. For the modified film, Nafion/PSSH (poly(styrene sulfonate) acid) acts as an electron-blocking layer on the surface and the PEDOT-rich domain tends to gather into larger particles with better interchain charge transfer inside the film. Consequently, the modified PEDOT:PSS HTL shows enhanced conductivity and light transmittance as well as more favorable work function, ending up with the increased short-circuit current density (J_sc) and open-circuit voltage (V_oc) of the device. Finally, PSCs with Nafion-modified HTLs achieve the best power conversion efficiency of 16.72%, with 23.76% improvement compared with PEDOT:PSS-only devices (13.51%). Most importantly, the device stability is obviously enhanced because of the hydrophobicity and chemical and mechanical stability of the Nafion polymer that is enriched on the surface of the PEDOT:PSS film.

Electrodeposition of SnO2 on FTO and its Application in Planar Heterojunction Perovskite Solar Cells as an Electron Transport Layer

We report the performance of perovskite solar cells (PSCs) with an electron transport layer (ETL) consisting of a SnO₂ thin film obtained by electrochemical deposition. The surface morphology and thickness of the electrodeposited SnO₂ films were closely related to electrochemical process conditions, i.e., the applied voltage, bath temperature, and deposition time. We investigated the performance of PSCs based on the SnO₂ films. Remarkably, the experimental factors that are closely associated with the photovoltaic performance were strongly affected by the SnO₂ ETLs. Finally, to enhance the photovoltaic performance, the surfaces of the SnO₂ films were modified slightly by TiCl₄ hydrolysis. This process improves charge extraction and suppresses charge recombination.

Efficient perovskite/fullerene planar heterojunction solar cells with enhanced charge extraction and suppressed charge recombination

Alcohol soluble titanium chelate TIPD (titanium (diisopropoxide) bis(2,4-pentanedionate)) was used as an electron transporting layer to form an ohmic contact with the negative electrode, aiming to enhance the charge extraction and suppress the charge recombination for high performance CH3NH3PbI3/PCBM-based PHJ perovskite solar cells. The TIPD layer shows excellent suitability to CH3NH3PbI3 perovskite synthesized by different methods. For one-step synthesized CH3NH3PbI3, the power conversion efficiency (PCE) of the device with the TIPD buffer reaches 8.75%, with a nearly 33% increase in comparison with the device without the buffer layer (6.58%). For two-step synthesized CH3NH3PbI3, an open-circuit voltage (Voc) of 0.89 V, a short-circuit current density (Jsc) of 22.57 mA cm(-2), and a fill factor (FF) of 64.5%, corresponding to a PCE of 12.95% for the device with a TIPD buffer layer were achieved, which is among the best performances reported in the literature for CH3NH3PbI3/PCBM-based PHJ perovskite solar cells.

Transparent conducting aerogels of antimony-doped tin oxide

Bulk antimony-doped tin oxide aerogels are prepared by epoxide-initiated sol-gel processing. Tin and antimony precursors are dissolved in ethanol and water, respectively, and propylene oxide is added to cause rapid gelation of the sol, which is then dried supercritically. The Sb:Sn precursor mole ratio is varied from 0 to 30% to optimize the material conductivity and absorbance. The materials are characterized by electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), nitrogen physisorption analysis, a four-point probe resistivity measurement, and UV-vis diffuse reflectance spectroscopy. The samples possess morphology typical of aerogels without significant change with the amount of doping. Calcination at 450 °C produces a cassiterite crystal structure in all aerogel samples. Introduction of Sb at 15% in the precursor (7.6% Sb by XPS) yields a resistivity more than 3 orders of magnitude lower than an undoped SnO2 aerogel. Calcination at 800 °C reduces the resistivity by an additional 2 orders of magnitude to 30 Ω·cm, but results in a significant decrease in surface area and pore volume.