Effects of Side-Chain Length and Functionality on Polar Poly(dioxythiophene)s for Saline-Based Organic Electrochemical Transistors.

Understanding the impact of side chains on the aqueous redox properties of conjugated polymers is crucial to unlocking their potential in bioelectrochemical devices, such as organic electrochemical transistors (OECTs). Here, we report a series of polar propylenedioxythiophene-based copolymers functionalized with glyme side chains of varying lengths as well as an analogue with short hydroxyl side chains. We show that long polar side chains are not required for achieving high volumetric capacitance (C*), as short hydroxy substituents can afford facile doping and high C* in saline-based electrolytes. Furthermore, we demonstrate that varying the length of the polar glyme chains leads to subtle changes in material properties. Increasing the length of glyme side chain is generally associated with an enhancement in OECT performance, doping kinetics, and stability, with the polymer bearing the longest side chains exhibiting the highest performance ([µC*]OECT = 200 ± 8 F cm-1 V-1 s-1). The origin of this performance enhancement is investigated in different device configurations using in situ techniques (e.g., time-resolved spectroelectrochemistry and chronoamperometry). These studies suggest that the performance improvement is not due to significant changes in C* but rather due to variations in the inferred mobility. Through a thorough comparison of two different architectures, we demonstrate that device geometry can obfuscate the benchmarking of OECT active channel materials, likely due to contact resistance effects. By complementing all electrochemical and spectroscopic experiments with in situ measurements performed within a planar OECT device configuration, this work seeks to unambiguously assign material design principles to fine-tune the properties of poly(dioxythiophene)s relevant for application in OECTs.

Self assembled films of porphyrins with amine groups at different positions: influence of their orientation on the corrosion inhibition and the electrocatalytic activity.

Self-assembled molecular films of two cobalt porphyrins with amine groups at different positions-(5,10,15,20-tetrakis-(2-aminophenyl) porphyrin-cobalt(II), [Co(II) (T(o-NH(2))PP)] and (5,10,15,20-tetrakis-(4-aminophenyl) porphyrin-cobalt(II), [Co(II)(T(p-NH(2))PP)]-were formed on a gold substrate. The functionalized surfaces were characterized using Raman spectroscopy, atomic force microscopy and electrochemical methods. Both modified gold surfaces completely mask the charge transfer of a [Fe(CN)(6)](3-/4-) redox couple in solution, indicating the layer is highly resistive in behavior. Electrochemical impedance spectroscopy analyses revealed that the porphyrin film with amine groups at ortho positions shows a higher charge-transfer resistance with a better protective behavior compared to the para position modified surface. Raman, AFM and EIS data suggests that an ortho amine positioned molecule forms a more compact layer compared to the para-positioned molecule. This can be explained in terms of their orientation on the gold surface. [Co(II)(T(o-NH(2))PP)] adopted a saddle shape orientation whereas [Co(II)(T(p-NH(2))PP)] adopted a flat orientation on the gold surface. The porphyrin modified gold electrode catalyzes the oxygen reduction at lower potentials compared to the bare gold electrode. The shift in the overvoltage was higher in case of molecules with flat orientation compared to the saddle shaped oriented porphyrin molecules on the surface.

Rationalizing energy level alignment by characterizing Lewis acid/base and ionic interactions at printable semiconductor/ionic liquid interfaces.

Charge transfer and energy conversion processes at semiconductor/electrolyte interfaces are controlled by local electric field distributions, which can be especially challenging to measure. Herein we leverage the low vapor pressure and vacuum compatibility of ionic liquid electrolytes to undertake a layer-by-layer, ultra-high vacuum deposition of a prototypical ionic liquid EMIM+ (1-ethyl-3-methylimidazolium) and TFSI- (bis(trifluoromethylsulfonyl)-imide) on the surfaces of different electronic materials. We consider a case-by-case study between a standard metal (Au) and four printed electronic materials, where interfaces are characterized by a combination of X-ray and ultraviolet photoemission spectroscopies (XPS/UPS). For template-stripped gold surfaces, we observe through XPS a preferential orientation of the TFSI anion at the gold surface, enabling large electric fields (∼108 eV m-1) within the first two monolayers detected by a large surface vacuum level shift (0.7 eV) in UPS. Conversely, we observe a much more random orientation on four printable semiconductor surfaces: methyl ammonium lead triiodide (MAPbI3), regioregular poly(3-hexylthiophene-2,5-diyl (P3HT)), sol-gel nickel oxide (NiOx), and PbIx-capped PbS quantum dots. For the semiconductors considered, the ionization energy (IE) of the ionic liquid at 3 ML coverage is highly substrate dependent, indicating that underlying chemical reactions are dominating interface level alignment (electronic equilibration) prior to reaching bulk electronic structure. This indicates there is no universal rule for energy level alignment, but that relative strengths of Lewis acid/base sites and ion-molecular interactions should be considered. Specifically, for P3HT, interactions are found to be relatively weak and occurring through the π-bonding structure in the thiophene ring. Alternatively, for NiOx, PbS/PbIx quantum dots, and MAPbI3, our XPS data suggest a combination of ionic bonding and Lewis acid/base reactions between the semiconductor and IL, with MAPbI3 being the most reactive surface. Collectively, our results point towards new directions in interface engineering, where strategically chosen ionic liquid-based anions and cations can be used to preferentially passivate and/or titrate surface defects of heterogeneous surfaces while simultaneously providing highly localized electric fields. These opportunities are expected to be translatable to opto-electronic and electrochemical devices, including energy conversion and storage and biosensing applications.

Simple Interface Modification of Electroactive Polymer Film Electrodes.

Understanding the role of interface properties is crucial in the search for alternative design strategies to optimize the efficiency, performance, and lifetime of both solid-state and redox active organic semiconductor devices. Recent advances have focused on controlling and tailoring interfacial effects on the morphology and molecular structure of the active film in multilayer devices triggering new developments in the area of interface engineering. Here, we demonstrate that an inorganic electrode/organic semiconductor interface modification using PEDOT:PSS as an interfacial material influences the charge and ion transport, capacitive, morphological, and color switching properties of a solution processed purple-to-clear switching electrochromic PProDOT-(CH2OEtHx)2 polymer film. We find that the barrier to charge transport from electrode to active material is lowered when adding this PEDOT:PSS film, allowing us to present a fully roll-to-roll compatible, simple, and versatile battery-type electrochromic device (ECD) design without the need for oxidizing the charge storage film, in combination with improved processing reproducibility. In addition to producing ECDs with minimal color differences compared to devices prepared in the more traditional and complicated manner, this new ECD design strategy provides competitive performance showing a consistent optical contrast of 50-55% and switching times of 2-4 s.

All Polymer Solution Processed Electrochromic Devices: A Future without Indium Tin Oxide?

The growing range of applications for optoelectronic and electrochromic devices (ECDs) encourages the search for materials combining high electrical conductivity with optical transparency. Next generation transparent conducting electrodes (TCEs) are required to be inexpensive, lightweight, scalable, and compatible with flexible substrates to trigger innovations towards supporting sustainable living and reducing energy consumption. Here we show that PEDOT:PSS can be solution processed using blade coating and subsequently post-treated with nitric and acetic acid to raise its conductivity above 2000 S cm-1 with a film transparency of ∼95%. A combined grazing-incidence wide angle X-ray scattering, atomic force microscopy, and thickness analysis of the film indicates that the removal of excess insulating PSS- inducing reordering is the critical parameter for the claimed conductivity increase. We then investigate the impact of replacing indium tin oxide electrodes with PEDOT:PSS in ECDs. While electrochromic contrast and optical memory are comparable for devices constructed with both electrode materials, differences in switching kinetics are explored by comparing internal resistances, ion diffusion, and charging effects in the polymer films extracted by electrochemical impedance spectroscopy. While all these ideas are described based on a battery-type ECD configuration, these concepts are easily transferable to other types of redox-active devices.

Transparent Wood Smart Windows: Polymer Electrochromic Devices Based on Poly(3,4-Ethylenedioxythiophene):Poly(Styrene Sulfonate) Electrodes.

Transparent wood composites, with their high strength and toughness, thermal insulation, and excellent transmissivity, offer a route to replace glass for diffusely transmitting windows. Here, conjugated-polymer-based electrochromic devices (ECDs) that switch on-demand are demonstrated using transparent wood coated with poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a transparent conducting electrode. These ECDs exhibit a vibrant magenta-to-clear color change that results from a remarkably colorless bleached state. Furthermore, they require low energy and power inputs of 3 mWh m-2 at 2 W m-2 to switch due to a high coloration efficiency (590 cm2 C-1 ) and low driving voltage (0.8 V). Each device component is processed with high-throughput methods, which highlights the opportunity to apply this approach to fabricate mechanically robust, energy-efficient smart windows on a large scale.

A highly sensitive electrochemical biosensor based on AuNP-modified gold electrodes for selective determination of serum levels of crosslaps.

This article explains a step-wise protocol to develop an electrochemical sensor to quantify serum levels of C-telopeptide (CTX) crosslinks also known as crosslaps in a matter of minutes and with high level of accuracy. The technique needs only one-step (incubation) and can thus be used for point of care screening. Due to the excellent electrical properties of the as-prepared immunosensor, CTX levels were successfully measured from 1 to 1000 pg/mL. This is while the normal reference of the marker is 50-450 pg/mL, suggesting that the sensor can acceptably detect CTX. The results also showed a good correlation with ECLIA in measuring serum levels of CTX.

SR-XRD in situ monitoring of copper-IUD corrosion in simulated uterine fluid using a portable spectroelectrochemical cell.

The objective of this work is to study the initial corrosion of copper in the presence of gold when placed in simulated uterine fluid in order to better understand the evolution of active components of copper-IUDs. In order to carry out this study, a portable cell was designed to partially simulate the uterine environment and provide a way of tracking the chemical changes occurring in the samples in situ within a controlled environment over a long period of time using synchrotron spectroelectrochemistry. The dynamically forming crystalline corrosion products are determined in situ for a range of copper-gold surface ratios over the course of a 10-day experiment in the cell. It is concluded that the insoluble deposits forming over this time are not the origin of the anticonception mechanism.

In-situ spectroelectrochemical characterization of the electrochemical growth and breakdown of a lead dodecanoate coating on a lead substrate.

This paper concerns a time lapse spectroelectrochemical study of the growth of lead dodecanoate layers on a lead substrate in an aqueous solution using cyclic voltammetry. In-situ synchrotron radiation X-ray diffraction measurements were carried out on station BM26A (DUBBLE) at the European Synchrotron Radiation Facility (ESRF) in France. The diffraction pattern images were taken using a two-dimensional Mar CCD camera. After deposition of the coating, a spectroelectrochemical study of a linear sweep voltammetry experiment using an acetic acid electrolyte, simulating 'active' lead corrosion, was carried out on both a bare and lead dodecanoate coated sample. The results show that the coating inhibits the formation of new lead corrosion products.