Spatially resolved extrinsic photoresponse under additional intrinsic bias photoexcitation of two terminal pentacene devices

Spatially resolved extrinsic photoresponse experiments in pentacene two terminal devices without or under additional intrinsic bias-light excitation are employed. These experiments are used to investigate the microscopic mechanism of the recently observed phenomenon of the photoresponse enhancement under additional bias-light intrinsic excitation and to preclude that this phenomenon arises from contact-related artifacts. It is found that the extrinsic photogeneration near the contacts via electric field-assisted exciton splitting and/or light-induced depletion width-reduction have a negligible contribution to the extrinsic photoresponse. Under additional bias-light intrinsic excitation, a uniform increase of the photogenerated hole density is found to take place across the whole conduction channel, without changes in the electric field distribution and in the interfacial properties of the contacts. The photoresponse enhancement by the blue bias-light becomes stronger upon increasing the red-light intensity. A nearly square root dependence of the photoresponse enhancement on the blue bias-light intensity is found. It is shown that the observed dependence of the photoresponse enhancement on the light intensities of the extrinsic and intrinsic excitation can be explained with the extrinsic photogeneration mechanism based on hole detrapping by triplet exciton dissociation.     

Biomimetic Lamellar Chitosan Scaffold for Soft Gingival Tissue Regeneration

Mucogingival surgery has become a common procedure for soft gingival tissue reparation in dental clinical practice, which mainly relies on autograft or commercial collagen membranes (CM). However, the autograft faces grand challenges in source availability and long-term post-surgery pain management, and the CM is restricted by its poor mechanical properties in an aqueous environment. Here, it is reported that a bio-inspired lamellar chitosan scaffold (LCS) with long range ordered porous structure, manufactured through a bidirectional freezing method, can serve as a promising gingival tissue engineering material. The LCS not only exhibits excellent mechanical properties in the hydrated state but also accelerates vessel formation and soft tissue regeneration in vivo. Most interestingly, the LCS is found to be capable of inducing macrophage differentiation to M2 macrophages, which is thought to play an important role in tissue regeneration. These advantages combined with its easy and low-cost preparation process make the LCS a promising candidate for dental clinical applications.     

Effect of linker used in D–A–π–A metal free dyes with different π-spacers for dye sensitized solar cells

Two novel D–A–π–A metal free dyes with triphenylamine as donor, dithiophene-diketo-pyrrolo-pyrrole as acceptor unit, thiophene and phenyl π-conjugated bridges and a cyanoacetic acid as electron acceptor (TDPP1 and TDPP2 were denoted for thiophene and phenyl π-conjugated bridge, respectively) have been designed and used as sensitizers for DSSCs. Incorporation of dithiophene-diketo-pyrrolo-pyrrole, reduces the band gap significantly. The influence of π-conjugated bridge on optical and electrochemical properties were investigated. Results demonstrated that the absorption band of TDPP with thiophene π-conjugated bridge has red shifted due to the enhancement of electron donating ability of π-conjugated bridge. The DSSC based on TDPP1 shows prominent power conversion efficiency about 4.81%, which is higher that for TDPP2 (3.42%). The electrochemical impedance spectroscopy analysis reveal that the charge recombination resistance at the TiO₂/dye/electrolyte interface for the DSSC based on TDPP1 is higher than that for TDPP2, which improves both J_sc and V_oc. The PCE of the DSSC based on TDPP1 is further improved up to 6.34%, when deoxycholic acid (DCA) was employed as coadsorbant.     

Poly(2,5-Dihydroxy-1,4-Benzoquinonyl Sulfide) As an Efficient Cathode for High-Performance Aqueous Zinc–Organic Batteries

Aqueous rechargeable zinc-ion batteries (ZIBs) have attracted considerable attention as a promising candidate for low-cost and high-safety electrochemical energy storage. However, the advancement of ZIBs is strongly hindered by the sluggish ionic diffusion and structural instability of inorganic metal oxide cathode materials during the Zn²⁺ insertion/extraction. To address these issues, a new organic host material, poly(2,5-dihydroxy-1,4-benzoquinonyl sulfide) (PDBS), has been designed and applied for zinc ion storage due to its elastic structural factors (tunable space and soft lattice). The aqueous Zn-organic batteries based on the PDBS cathode show outstanding cycling stability and rate capability. The coordination moieties (O and S) display the strong electron donor character during the discharging process and can act as the coordination arms to host Zn²⁺. Also, under the electrochemical environment, the malleable polymer structure of PDBS permits the rotation and bending of polymer chains to facilitate the insertion/extraction of Zn²⁺, manifesting the superiority and uniqueness of organic electrode materials in the polyvalent cation storage. Finally, quasi-solid-state batteries based on aqueous gel electrolyte demonstrate highly stable capacity under different bending conditions.     

Origin of High Ionic Conductivity of Sc-Doped Sodium-Rich NASICON Solid-State Electrolytes

Substitution of liquid electrolyte with solid-state electrolytes (SSEs) has emerged as a very urgent and challenging research area of rechargeable batteries. NASICON (Na₃Zr₂Si₂PO₁₂) is one of the most potential SSEs for Na-ion batteries due to its high ionic conductivity and low thermal expansion. It is proven that the ionic conductivity of NASICON can be improved to 10⁻³ S cm⁻¹ by Sc-doping, of which the mechanism, however, has not been fully understood. Herein, a series of Na_3+xSc_xZr_2−xSi₂PO₁₂ (0 ≤ x  ≤  0.5) SSEs are prepared. To gain a deep insight into the ion transportation mechanism, synchrotron-based X-ray absorption spectroscopy (XAS) is employed to characterize the electronic structure, and solid-state nuclear magnetic resonance (SS-NMR) is used to analyze the dynamics. In this study, Sc is successfully doped into Na₃Zr₂Si₂PO₁₂ to substitute Zr atoms. The redistribution of sodium ions at certain specific sites is proven to be critical for sodium ion movement. For x ≤ 0.3, the promotion of sodium ion movement is attributed to sodium ion concentration increase at the Na2 sites and decrease at the Na1 and Na3 sites. For x > 0.3, the inhibition of sodium ion movement is due to the phase change from monoclinic to rhombohedral and an increasing impurity content.     

3D Graphene Films Enable Simultaneously High Sensitivity and Large Stretchability for Strain Sensors

Integration of 2D membranes into 3D macroscopic structures is essential to overcome the intrinsically low stretchability of graphene for the applications in flexible and wearable electronics. Herein, the synthesis of 3D graphene films (3D‐GFs) using chemical vapor deposition (CVD) is reported, in which a porous copper foil (PCF) is chosen as a template in the atmospheric‐pressure CVD preparation. When the 3D‐GF prepared at 1000 °C (noted as 3D‐GF‐1000) is transferred onto a polydimethylsiloxane (PDMS) membrane, the obtained 3D‐GF‐1000/PDMS hybrid film shows an electrical conductivity of 11.6 S cm^?1 with good flexibility, indicated by small relative resistance changes (ΔR/R₀) of 2.67 and 0.36 under a tensile strain of 50% and a bending radius of 1.6 mm, respectively. When the CVD temperature is reduced to 900 °C (generating a sample noted as 3D‐GF‐900), the 3D‐GF‐900/PDMS hybrid film exhibits an excellent strain‐sensing performance with a workable strain range of up to 187% and simultaneously a gauge factor of up to ≈1500. The 3D‐GF‐900/PDMS also shows a remarkable durability in resistance in repeated 5000 stretching‐releasing cycles. Kinetics studies show that the response of ΔR/R₀ upon strain is related to the graphitization and conductivity of 3D‐GF which are sensitive to the CVD preparation temperature.     

Monitoring the Channel Formation in Organic Field‐Effect Transistors via Photoinduced Charge Transfer

Conducting channel formation in organic field‐effect transistors (OFETs) is considered to happen in the organic semiconductor layer very close to the interface with the gate dielectric. In the gradual channel approximation, the local density of accumulated charge carriers varies as a result of applied gate bias, with the majority of the charge carriers being localized in the first few semiconductor monolayers close to the dielectric interface. In this report, a new concept is employed which enables the accumulation of charge carriers in the channel by photoinduced charge transfer. An OFET employing C₆₀ as a semiconductor and divinyltetramethyldisiloxane‐bis(benzocyclobutene) as the gate dielectric is modified by a very thin noncontinuous layer of zinc‐phthalocyanine (ZnPc) at the semiconductor/dielectric interface. With this device geometry, it is possible to excite the phthalocyanine selectively and photogenerate charges directly at the semiconductor/dielectric interface via photoinduced electron transfer from ZnPc onto C₆₀. Thus the formation of a gate induced and a photoinduced channel in the same device can be correlated.     

Controlled Growth of Porous α‐Fe2O3 Branches on β‐MnO2 Nanorods for Excellent Performance in Lithium‐Ion Batteries

Hierarchical nanocomposites rationally designed in component and structure, are highly desirable for the development of lithium‐ion batteries, because they can take full advantages of different components and various structures to achieve superior electrochemical properties. Here, the branched nanocomposite with β‐MnO₂ nanorods as the back‐bone and porous α‐Fe₂O₃ nanorods as the branches are synthesized by a high‐temperature annealing of FeOOH epitaxially grown on the β‐MnO₂ nanorods. Since the β‐MnO₂ nanorods grow along the four‐fold axis, the as‐produced branches of FeOOH and α‐Fe₂O₃ are aligned on their side in a nearly four‐fold symmetry. This synthetic process for the branched nanorods built by β‐MnO₂/α‐Fe₂O₃ is characterized. The branched nanorods of β‐MnO₂/α‐Fe₂O₃ present an excellent lithium‐storage performance. They exhibit a reversible specific capacity of 1028 mAh g^?1 at a current density of 1000 mA g^?1 up to 200 cycles, much higher than the building blocks alone. Even at 4000 mA g^?1, the reversible capacity of the branched nanorods could be kept at 881 mAh g^?1. The outstanding performances of the branched nanorods are attributed to the synergistic effect of different components and the hierarchical structure of the composite. The disclosure of the correlation between the electrochemical properties and the structure/component of the nanocomposites, would greatly benefit the rational design of the high‐performance nanocomposites for lithium ion batteries, in the future.     

Residual strain and electrical resistivity dependence of molybdenum films on DC plasma magnetron sputtering conditions

Sputter deposited molybdenum (Mo) thin films are used as back contact layer for Cu(In_1−xGa_x)(Se_1−yS_y)₂ based thin film solar cells. Desirable properties of Mo films include chemical and mechanical inertness during the deposition process, high conductivity, appropriate thermal expansion coefficient with contact layers and a low contact resistance with the absorber layer. Mo films were deposited over soda-lime glass substrates using DC-plasma magnetron sputtering technique. A 2³ full factorial design was made to investigate the effect of applied power, chamber pressure, and substrate temperature on structural, morphological, and electrical properties of the films. All the films were of submicron thickness with growth rates in the range of 34–82 nm/min and either voided columnar or dense growth morphology. Atomic force microscope studies revealed very smooth surface topography with average surface roughness values of upto 17 nm. X-ray diffraction studies indicated, all the films to be monocrystalline with (001) orientation and crystallite size in the range of 4.6–21 nm. The films exhibited varying degrees of compressive or tensile residual stresses when produced at low or high chamber pressure. Low pressure synthesis resulted in film buckling and cracking due to poor interfacial strength as characterized by failure during the tape test. Measurement of electrical resistivity for all the films yielded a minimum _value of 42 μΩ cm for Mo films deposited at 200 W DC power.     

Effect of preincubation of sorghum flour with enzymes on the digestibility of sorghum gruel

A low-tannin sorghum cultivar M-35-1 was used in this study. Sorghum was germinated for 6 days and protease and amylase activities were measured every 24 h. Results showed that the 5th day germinated sorghum had a higher protease activity and a lower amylase activity. Sorghum flour was incubated for 30 min with the extract from germinated sorghum or with 0.01, 0.05 or 0.1 mg ml⁻¹ papain or trypsin prior to cooking in water. Results showed increase in in vitro protein digestibility (IVPD) with the 5th day germination extract. Pretreatment of sorghum flour with small amounts of papain or trypsin (0.01 mg ml⁻¹) improved the IVPD without affecting the paste viscosity, whereas the germinated sorghum extract led to very low paste viscosity. ©