Transparent Patternable Large-Area Graphene p-n Junctions by Photoinduced Electron Doping.

We present a novel approach to achieve n-type doping in graphene and create graphene p-n junctions through a photoinduced electron doping method using photobase generators (PBGs). The unique properties of PBGs allow us to spatially and temporally control the doping process via light activation. The selective irradiation of specific regions on the graphene film enables switching their doping from p- to n-type, as confirmed by changes in the electromotive force and Seebeck and Hall coefficients.

High-Performance Isotropic Thermo-Electrochemical Cells Using Agar-Gelled Ferricyanide/Ferrocyanide/Guanidinium.

An isotropic thermo-electrochemical cell is introduced with a high Seebeck coefficient ( ) of 3.3 mV K that uses a ferricyanide/ferrocyanide/guanidinium-based agar-gelated electrolyte. A power density of about 20 µW cm is achieved at a temperature difference of about 10 K, regardless of whether the heat source is on the top or bottom section of the cell.

Bicyclic-ring base doping induces n-type conduction in carbon nanotubes with outstanding thermal stability in air.

The preparation of air and thermally stable n-type carbon nanotubes is desirable for their further implementation in electronic and energy devices that rely on both p- and n-type material. Here, a series of guanidine and amidine bases with bicyclic-ring structures are used as n-doping reagents. Aided by their rigid alkyl functionality and stable conjugate acid structure, these organic superbases can easily reduce carbon nanotubes.

Design and synthesis of proton-dopable organic semiconductors.

This paper shows how protonated 3,4-ethylene dioxythiophene moieties can be used as an end group to make organic conductors. An organic semiconductor 2,5-bis(5-(2,3-dihydrothieno[3,4-][1,4]dioxin-5-yl)-3-dodecylthiophen-2-yl)thieno[3,2-]thiophene is designed and synthesized. This molecule could be doped by protonic acid in both solution and solid-state, resulting in a broad absorption in the near-infrared range corresponding to polaron and bipolaron absorption.

Thermoelectrochemical Cells Based on Ferricyanide/Ferrocyanide/Guanidinium: Application and Challenges.

Ferricyanide/ferrocyanide/guanidinium-based thermoelectrochemical cells have been investigated under different loading conditions in this work. Compared with ferricyanide/ferrocyanide-based devices, the device with guanidinium-added electrolytes shows higher power and energy densities. We observed that the enhanced performance is not due to the ionic Seebeck effect of guanidinium but because of the configuration entropy change resulting from the selective binding of Gdm to Fe(CN).

Control of anisotropic conduction of carbon nanotube sheets and their use as planar-type thermoelectric conversion materials.

The large anisotropic thermal conduction of a carbon nanotube (CNT) sheet that originates from the in-plane orientation of one-dimensional CNTs is disadvantageous for thermoelectric conversion using the Seebeck effect since the temperature gradient is difficult to maintain in the current flow direction. To control the orientation of the CNTs, polymer particles are introduced as orientation aligners upon sheet formation by vacuum filtration. The thermal conductivities in the in-plane direction decrease as the number of polymer particles in the sheet increases, while that in the through-plane direction increases.

Outstanding Electrode-Dependent Seebeck Coefficients in Ionic Hydrogels for Thermally Chargeable Supercapacitor near Room Temperature.

Thermoelectric power generation from waste heat is an important component of future sustainable development. Ion-conducting materials are promising candidates because of their high Seebeck coefficients. This study demonstrates that ionic hydrogels based on imidazolium chloride salts exhibit outstanding Seebeck coefficients of up to 10 mV K.

Reversible Protonic Doping in Poly(3,4-Ethylenedioxythiophene).

In this study, poly(3,4-ethylenedioxythiophene), a benchmark-conducting polymer, was doped by protons. The doping and de-doping processes, using protonic acid and a base, were fully reversible. We predicted possible doping sites along the polymer chain using density functional theory (DFT) calculations.

Humidity control in a closed system utilizing conducting polymers.

In this study, we demonstrate that conducting polymers could be ideal materials for continuously managing humidity in a wide range of enclosed spaces. We demonstrate a simple battery-driven humidity control unit to manage the humidity in a closed environment and studied humidity-responsive nanocapsules using Zn-coordinated lipid nanovesicles. This study not only promises new applications for conducting polymers but also provides an easy approach for fabricating chambers with a controlled environment, which are often used by physicists, chemists, and biologists.

Electrical transport and thermoelectric properties of boron carbide nanowires.

The electrical transport and thermoelectric property of boron carbide nanowires synthesized by a carbothermal method are reported. It is demonstrated that the nanowires achieve a higher Seebeck coefficient and power factor than those of the bulk samples. The conduction mechanism of the nanowires at low temperatures below 300 K is different from that of the sintered-polycrystalline and single-crystal bulk samples.

Photoinduced Dedoping of Conducting Polymers: An Approach to Precise Control of the Carrier Concentration and Understanding Transport Properties.

Exploring the various applications of conjugated polymers requires systematic studies of their physical properties as a function of the doping density, which, consequently, calls for precise control of their doping density. In this study, we report a novel solid-state photoinduced charge-transfer reaction that dedopes highly conductive polyelectrolyte complexes such as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate). Varying the UV-irradiation time of this material allows the carrier density inside the film to be precisely controlled over more than 3 orders of magnitude.

Recent Progress on PEDOT-Based Thermoelectric Materials.

The thermoelectric properties of poly(3,4-ethylenedioxythiophene) (PEDOT)-based materials have attracted attention recently because of their remarkable electrical conductivity, power factor, and figure of merit. In this review, we summarize recent efforts toward improving the thermoelectric properties of PEDOT-based materials. We also discuss thermoelectric measurement techniques and several unsolved problems with the PEDOT system such as the effect of water absorption from the air and the anisotropic thermoelectric properties.

Experimental Studies on the Anisotropic Thermoelectric Properties of Conducting Polymer Films.

We reported general methods for studying the thermoelectric properties of a polymer film in both the in-plane and through-plane directions. The bench-mark PEDOT/PSS films have highly anisotropic carrier transport properties and thermal conductivity. The anisotropic carrier transport properties can be explained by the lamellar structure of the PEDOT/PSS films where the PEDOT nanocrystals could be isolated by the insulating PSS in the through-plane direction.

Self-aligned formation of sub 1 nm gaps utilizing electromigration during metal deposition.

We developed a procedure for the fabrication of sub 1 nm gap Au electrodes via electromigration. Self-aligned nanogap formation was achieved by applying a bias voltage, which causes electromigration during metal evaporation. We also demonstrated the application of this method for the formation of nanogaps as small as 1 nm in width, and we found that the gap size can be controlled by changing the magnitude of the applied voltage.

Morphological change and mobility enhancement in PEDOT:PSS by adding co-solvents.

Adding ethylene glycol (EG) to a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solution improves the crystallinity of the PEDOT and the ordering of the PEDOT nanocrystals in solid films. The carrier-mobility enhancement is confirmed by using ion-gel transistors combined with in situ UV-vis-NIR spectroscopy.

Pressure-dependent hydrogen permeability extended for metal membranes not obeying the square-root law.

Hydrogen permeability of metal membranes is generally defined by the square-root law, as the proportional coefficient of permeation flux to the square-root difference of the pressures on both sides of the membrane. However, deviation from the law has been widely reported for palladium, niobium, etc. Although n-th power instead of the square root has often been employed to determine permeability for these membranes, it has no theoretical base.