The fabrication of electronic devices based on organic materials, known as 'printed electronics', is an emerging technology due to its unprecedented advantages involving fl exibility, light weight, and portability, which will ultimately lead to future ubiquitous applications. [ 1 ] The solution processability of semiconducting and metallic polymers enables the cost-effective fabrication of optoelectronic devices via high-throughput printing techniques. [ 2 ] These techniques require high-performance fl exible and transparent electrodes (FTEs) fabricated on plastic substrates, but currently, they depend on indium tin oxide (ITO) coated on plastic substrates. However, its intrinsic mechanical brittleness and inferior physical properties arising from lowtemperature ( T ) processing below the melting T of the plastic substrates (i.e., typically below 150 °C) have increased the demand for alternative FTE materials. [ 3 ] Conducting polymers (CPs) have been considered a promising candidate for FTEs due to their mechanical fl exibility and solution processability. The high transparency of CPs originates from the charge carrier density ( n ) of approximately 10 21 cm −3 because both the refl ectance and absorption are confi ned in the IR region below the plasma frequency ( ω P , ω P 2 = 4 π e 2 n / m * where m * is the effective mass of the charge carrier) at approximately hω P ≈ 1 eV. [ 2 ] A complex of poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(4-styrenesulfonate) (PSS), in which PSS acts as both a counter-ion and a soluble template for PEDOT, is a successful CP due to its high electrical conductivity ( σ dc ) and excellent transparency in the visible range. [ 4 ] The conducting fi lms, which were coated from PEDOT:PSS solution in an aqueous dispersion, consist of hydrophobic and conducting PEDOT-rich grains encapsulated by hydrophilic and insulating PSS-rich shells. [ 5 ] These morphological features involve an excess amount of PSS as well as low chain alignment, resulting in a low σ dc of approximately 1 S cm −1 . Over the past decade, pre-and/or post-treatment with various organic solvents, surfactants, salts, and acids have been found to enhance the σ dc of PEDOT:PSS by two to three orders of magnitude. [6][7][8] Recently, the high σ dc (≈3065 S cm −1 ) was achieved using a treatment of dropping a 1.0 M H 2 SO 4 solution onto the PEDOT:PSS fi lms. [ 8 ] Although numerous studies suggested that the σ dc enhancement could be attributed to morphological changes in the PEDOT:PSS complex, such as grain growth, polymer chain expansion, and phase separation, a clear understanding of the mechanism of the σ dc enhancement is still required for both the basic material studies on CPs and developing high-performance FTEs. [6][7][8] Herein, we report the solution-processed crystalline formation in PEDOT:PSS via H 2 SO 4 post-treatment. By rigorously controlling the post-treatment conditions (i.e., the H 2 SO 4 concentration, treatment T , and processing details), we obtained insight into how the H 2 SO 4 solution proce...

A precise control of the size, density, and distribution of metal nanoparticles dispersed on functional oxide supports is critical for promoting catalytic activity and stability in renewable energy and catalysis devices. Here, we measure the growth kinetics of individual Co particles ex-solved on SrTi0.75Co0.25O3‑δ polycrystalline thin films under a high vacuum, and at various temperatures and grain sizes using in situ transmission electron microscopy. The ex-solution preferentially occurs at grain boundaries and corners which appear essential for controlling particle density and distribution, and enabling low temperature ex-solution. The particle reaches a saturated size after a few minutes, and the size depends on temperature. Quantitative measurements with a kinetic model determine the rate limiting step, vacancy formation enthalpy, ex-solution enthalpy, and activation energy for particle growth. The ex-solved particles are tightly socketed, preventing interactions among them over 800 °C. Furthermore, we obtain the first direct clarification of the active reaction site for CO oxidationthe Co-oxide interface, agreeing well with density functional theory calculations.

Tuning of the cation–oxygen bond strength effectively promotes B-site ex-solution in a perovskite, thereby boosting the catalytic activity of CO oxidation.

Organic semiconductors (OSCs) are highly susceptible to the formation of metastable polymorphs that are often transformed by external stimuli. However, thermally reversible transformations in OSCs with stability have not been achieved due to weak van der Waals forces, and poor phase homogeneity and crystallinity. Here, a polymorph of a single crystalline 2,7‐dioctyl[1] benzothieno[3,2‐b][1]benzothio‐phene rod on a low molecular weight poly(methyl methacrylate) (≈120k) that limits crystal coarsening during solvent vapor annealing is fabricated. Molecules in the polymorph lie down slightly toward the substrate compared to the equilibrium state, inducing an order of greater resistivity. During thermal cycling, the polymorph exhibits a reversible change in resistivity by 5.5 orders with hysteresis; this transition is stable toward bias and thermal cycling. Remarkably, varying cycling temperatures leads to diverse resistivities near room temperature, important for nonvolatile multivalue memories. These trends persist in the carrier mobility and on/off ratio of the polymorph field‐effect transistor. A combination of in situ grazing incident wide angle X‐ray scattering analyses, visualization for electronic and structural analysis simulations, and density functional theory calculations reveals that molecular tilt governs the charge transport characteristics; the polymorph transforms as molecules tilt, and thereby, only a homogeneous single‐crystalline phase appears at each temperature.