Poor Electron Mobility Research Articles

Donor-acceptor type of triazine-based conjugated organic polymers with excellent charge separation for efficient photocatalytic production of hydrogen peroxide

Hydrogen peroxide (H2O2) was widely utilized as an environmentally friendly and efficient chemical in various fields. The photocatalytic production of H2O2 using conjugated organic polymers as photocatalysts is promising. However, conjugated organic polymers have limited applications due to the high recombination rate of photogenerated carriers, poor electron mobility rate, and long synthesis time. Herein, we rapidly prepared a novel triazine-based conjugated organic polymer (CTP-TT) for efficient photocatalytic production of H2O2 using a facile sonochemical method. The H2O2 photosynthesis rate of CTP-TT reached 3383 μmol · g−1·h−1 in pure water without the addition of sacrificial agents. The experimental and characterization results confirmed that CTP-TT possessed dual H2O2 production pathways of 2e− oxygen reduction reaction (ORR) and 2e− water oxidation reaction, with 2e− ORR dominating. The theoretical calculations indicated that the excellent charge separation efficiency of CTP-TT was due to its unique donor–acceptor structure. This study provides novel design ideas for improving the photocatalytic performance of conjugated organic polymers, which is expected to promote the development of photocatalytic production of H2O2 applications and the rational design and preparation of organic semiconductor photocatalysts.

High Electron Mobility in Si-Doped Two-Dimensional β-Ga2O3 Tuned Using Biaxial Strain.

Two-dimensional (2D) semiconductors have attracted much attention regarding their use in flexible electronic and optoelectronic devices, but the inherent poor electron mobility in conventional 2D materials severely restricts their applications. Using first-principles calculations in conjunction with Boltzmann transport theory, we systematically investigated the Si-doped 2D β-Ga2O3 structure mediated by biaxial strain, where the structural stabilities were determined by formation energy, phonon spectrum, and ab initio molecular dynamic simulation. Initially, the band gap values of Si-doped 2D β-Ga2O3 increased slightly, followed by a rapid decrease from 2.46 eV to 1.38 eV accompanied by strain modulations from -8% compressive to +8% tensile, which can be ascribed to the bigger energy elevation of the σ* anti-bonding in the conduction band minimum than that of the π bonding in the valence band maximum. Additionally, band structure calculations resolved a direct-to-indirect transition under the tensile strains. Furthermore, a significantly high electron mobility up to 4911.18 cm2 V-1 s-1 was discovered in Si-doped 2D β-Ga2O3 as the biaxial tensile strain approached 8%, which originated mainly from the decreased quantum confinement effect on the surface. The electrical conductivity was elevated with the increase in tensile strain and the enhancement of temperature from 300 K to 800 K. Our studies demonstrate the tunable electron mobilities and band structures of Si-doped 2D β-Ga2O3 using biaxial strain and shed light on its great potential in nanoscale electronics.

G-C3N4/Bromocobaloxime nanocomposites as multi-functional electrocatalysts for water splitting and energy storage

The depletion of fossil fuels necessitates the search for alternative sources of energy and energy storage for long-term usage. Recently graphitic carbon nitride (g-C3N4) based materials have gained attention due to their enhanced activity compared to previously tested materials. But the poor electron mobility of g-C3N4 continues to cause a significant energy loss in the electrocatalytic processes. Herein we report the synthesis and characterization of g-C3N4/Bromocobaloxime composites and their electrocatalytic applications towards hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and energy storage. Bromocobaloximes [BrCo(dpgH)2B] (B1-B4) containing diphenylglyoxime [dpgH] as the equatorial ligand and functionalized neutral bases such as Isonicotinic acid (1), Pyridine-3,5-dicarboxylic acid (2), Indole-2-carboxylic acid (3) and p-Aminobenzoic acid (4) were synthesized using the standard procedure. The g-C3N4/Cobaloxime nanocomposites (g-C3N4/B1, g-C3N4/B2, g-C3N4/B3 and g-C3N4/B4) were prepared using g-C3N4 nanosheets by solvothermal method. The prepared nanocomposites were characterized by FT-IR, UV-DRS, XRD, SEM, EDAX, TEM and XPS analysis. The electrochemical HER studies of the synthesized nanocomposites showed low overpotentials in the range of 51 to 228 mV at −10 mAcm−2 and the OER studies exhibited overpotentials in the range of 310 to 460 mV at 10 mAcm−2. Among them nanocomposite g-C3N4/B2 showed a lower Tafel slope of 45 mV/dec for HER and 112 mV/dec for OER. The supercapacitance studies indicated that among the nanocomposites, g-C3N4/B1 showed a good specific capacitance of 302 F/g at 0.5 A/g. The increased electrochemical performance of the synthesized nanocomposites is due to the incorporation of cobaloximes containing carboxylic acid functionalized neutral bases into the g-C3N4 nanosheets, which increases the electron mobility. This will lead to explore the applications of g-C3N4/metal complexes towards energy conversion by tuning the ligands in the metal complexes.

Performance Improvement of Dye-Sensitized Solar Cells Using a Combination of TiO<sub>2</sub> and ZnO as Photoanodes

TiO2 are usually used as photoanode to get high-performance dye-sensitized solar cells (DSSCs). TiO2 has good chemical stability, but still has poor electron mobility so that the DSSC efficiency is low. An alternative semiconductor metal-oxides such as ZnO currently are being explored due to ease of processing, higher electron mobility, interface band energetics, and can be utilized as photoanode also, but the chemical stability is low. Based on these facts, by combining the advantages of TiO2 and ZnO, the TiO2:ZnO composite can be an ideal material as a photoanode in DSSC. In this study, composite of TiO2:ZnO was synthesized using sol-gel method with ratio of TiO2 to ZnO were varied from 80:20, 60:40, 50:50, 40:60, and 20:80 in atomic percent. DSSCs were fabricated by coating the photoanode using screen-printing technique on a FTO-glass substrate. Composite of TiO2:ZnO photoanodes were then sensitized in a solution of N719 dye for several hours. Finally, the DSSCs were assembled and the power conversion efficiency was measured using an I–V measurement system. The highest power conversion efficiency of 2.30% was obtained from the cell fabricated with TiO2:ZnO (50:50) photoanode. This result indicated that the balanced composition allowed to increase Jsc along with reducing recombination process and retaining high dye-loading capability.

Surface crystallinity enhancement in organic solar cells induced by spinodal demixing of acceptors and additives

Surface spinodal demixing of DIO:ITIC leads to poor electron mobility, while the CN:Y6 blend undergoes a binodal demixing process which is similar to that occurs in the bulk liquid layer, contributing to uniform vertical crystallinity distribution.

Fabrication of cobalt doped titania for enhanced oxygen evolution reaction

Due to poor electron mobility, early transition metal oxides typically, are not known to catalyze water electroxidation. Here we report the modulation of electrocatalytic properties of pristine anatase by the doping of an earth-abundant metal (Co). So obtained hybrid materials show enhanced catalytic activity for oxygen evolution reaction (OER). It was noted that the retention of free carbon during the synthesis of such hybrid materials further enhances their OER activity bringing it at par with the benchmark IrO2 catalyst. Evaporation induced self-assembly (EISA) was used to prepare mesoporous titania using a triblock copolymer (P123) as structure directing agent. Nanostructured titania was first impregnated with a cobalt complex followed by thermal treatment at 500, 700 and 900 °C under air, argon and hydrogen atmosphere to obtain a series of catalysts. The effect of metal content and annealing atmosphere was studied on the composition and OER activity of the catalysts. The best OER activity (η: 440mV@10 mA.cm−2), comparable to benchmark IrO2 and decent stability was noted for the material annealed under argon and containing 15 wt % Co. Improved OER activity was attributed to better water adsorption, charge transfer and conductivity of titania upon Co doping and carbon retention.

Facile growth of AgVO3 nanoparticles on Mo-doped BiVO4 film for enhanced photoelectrochemical water oxidation

BiVO4 is largely restricted by its intrinsic poor electron mobility and sluggish surface reaction. Aiming at eliminating the deficiency of BiVO4, we assemble a novel composite photoanode through simultaneous bulk and surface modification. In detail, controllable Mo doping is manipulated through a spin-coating method, and AgVO3 nanoparticles are loaded by successive ionic layer adsorption and reaction (SILAR) process. The as-prepared photoanode boosts the photocurrent density by 7 folds at 1.23 V vs. RHE and moves the onset potential negatively by 387 mV compared to the bare BiVO4. Furthermore, the charge injection efficiency is substantially boosted to 49% at 1.23 VRHE, nearly 5 times as that of pure BiVO4. With detailed physical and electrochemical characterization, we reveal the essential reason for the boosted photoelectrochemical activity. Appropriate Mo doping can simultaneously enhance the carrier density and electron mobility of BiVO4. Specifically, more (0 4 0) facet are exposed for retarding charge recombination and increasing photocatalytic reaction sites. Then the simple SILAR process grows AgVO3 nanoparticles homogeneously with uniform diameter of 3–5 nm on BiVO4, forming p-n heterojunction to accelerate charge separation, and abundant oxygen vacancy emerged on the surface, which has been demonstrated as active sites for water oxidation reaction.

Cobalt–phosphate-modified Mo:BiVO4 mesoporous photoelectrodes for enhanced photoelectrochemical water splitting

Bismuth vanadate as photoanode with suitable bandgap and appropriate valence band positions is generally very stable in aqueous solution and cheap, but the photochemical activity is usually limited by poor electron mobility and low oxygen evolution kinetics. Herein, we exhibit that the above-mentioned problems can be solved by introducing a foreign dopant (Mo6+) into the BiVO4 film to create a distributed n+-n heterojunction and combining the BiVO4 photoanode with cobalt–phosphate water oxidation catalyst to improve the oxygen evolution kinetic. We systematically study the relationship between the higher photoelectrochemical performance and Mo-doping and cobalt–phosphate (CoPi) modification by XRD, Raman, SEM, TEM, LSV, EIS, I–t, and Mott–Schottky measurements, and the CoPi-Mo:BiVO4 heterojunction photoanode shows a current density of 3.27 times higher than that of pristine BiVO4 photoanode. Then, we concentrate our attention on a novel perspective for understanding the photoelectrochemical mechanism of interfacial charge transfer with the Mo-doping and CoPi modification on the BiVO4 photoanodes. This work provides new insights into the rational design of novel photoanodes from various improvement strategies with high photoelectrochemical performance and further utilization for environmental practical applications.

Cu Doped Crystalline Carbon-Conjugated g-C3N4, a Promising Oxygen Reduction Catalyst by Theoretical Study

The single atom supported by carbon nitride (g-C3N4) materials, as efficient substitutes for platinum catalysts, recently have attracted extensive attention. Owing to poor electron mobility, g-C3N4 suffers from unavoidable energy loss, while g-C3N4 with crystalline carbons (g-C3N4/C) can enhance electron transfer. In this study, single Cu atom doped g-C3N4 (Cu/g-C3N4) and g-C3N4/C (Cu/g-C3N4/C) are investigated by using the density functional method. Our study indicated that they are stable thermodynamically. ORR intermediates have weakened adsorption energies in Cu/g-C3N4/C compared with Cu/g-C3N4. For Cu/g-C3N4, the rate-determining step is O2 hydrogenation to form OOH with an energy barrier of 0.40 eV, similar to 0.39 eV for Pd/g-C3N4. Compared with Cu/g-C3N4, Cu/g-C3N4/C shows higher catalytic activity. For Cu/g-C3N4/C, the energy barrier at the rate-determining step is 0.15 eV, smaller than 0.40 eV for Cu/g-C3N4, and much smaller than 0.80 eV for Pt (111). Meanwhile, the predicted working potential is 0.57 V for Cu/g-C3N4/C, also larger than 0.22 V for Cu/g-C3N4. Thus, the introduced crystalline carbons on Cu/C3N4/C enhances not only electron conduction but also catalytic activity.

Electrochemcial Synthesis of Nanoporous Hematite (α-Fe2O3) and Their Applications Towards Photocatalytic Water Oxidation

The capture and storage of solar energy in the molecular bonds of chemical fuels provides a promising route to overcoming the current global energy dependence on fossil fuels. Solar assisted water splitting, the process usually known as artificial photosynthesis, is a favourable means of converting solar energy into transportable and end user chemical fuels. The system requires optimisation in terms of cost and performance on a scale commensurate with the global energy demand. However, most abundant semiconductors suffer from the undesirable photoelectron-hole recombination within the semiconductor due to their short diffusion path lengths and lifetimes, which results in fewer than 10% of the incident photons being used for water splitting. Hematite (α-Fe2O3), one of the few naturally occurring n-type metal oxides, is the most promising candidate for an efficient photoanode because of its high earth abundance (4th most abundant element in the earth’s crust) and visible light active band gap of 2.1 eV, a scalable CMOS compatible synthesis technique, excellent photostability and favourable energy band position capable to drive off the water oxidation reactions without of any external bias. Despite having those advantages, hematite has several inherent drawbacks such as poor electron mobility (~ 10-1 cm2 V-1 s-1)[1], short excited carrier lifetime (about 10 ps)[2] and short carrier (hole) diffusion length (2−4 nm)[3]. Hence, most of the photogenerated charge carriers (electron-hole) cannot be extracted to the semiconductor-electrolyte interface before they quickly recombine inside of the materials and dissipate as heat energy. Nanoscale design of hematite such as nanowires[4], cauliflowers[5] or core-shell nanostructures synthesised via solution based hydrothermal growth and expensive chemical vapour deposition or atomic layer deposition[6] along with surface modification with oxygen evolution catalysts[5] have led to circumvent their drawbacks and made the nanostructured hematite a promising photoanode. In this work, electrochemical deposition of nanoporous α-Fe2O3 and surface modification with cobalt (Co) catalyst is described. The method involves the electrodeposition of iron (Fe) nanoporous film followed by thermal annealing in air (Fig. 1a). The kinetics of the photoelectrochemical (PEC) reactions was improved by modifying the hematite surface with oxygen evolution catalysts. The PEC activity of the optimised nanoporous α-Fe2O3/Co has been correlated with the morphology, thickness and Co loading under standard operational conditions (Am 1.5 G, 100 mW/cm2, 1 mol/L KOH). This presentation will also discuss our current research to develop cheap and efficient photocatalysts towards fabrication of tandem PEC water splitting device. Figure. SEM images of the electrodeposited nanoporous hematite (α-Fe2O3) in (a) low and (b) high magnified view. Acknowledgements: Authors acknowledge Marie Curie Actions co-funded Irish Research Council Elevate fellowship ELEVATEPD/2014/15.

Enhancing Electron Transfer and Electrocatalytic Activity on Crystalline Carbon-Conjugated g-C3N4

Carbon nitride (g-C3N4) materials are electro-activated for oxygen reduction (ORR) and oxygen evolution (OER) reactions when they are supported by conductive carbons. However, the electrocatalytic process on semiconductor-based heterostructures such as carbon-supported g-C3N4 still suffers from a huge energy loss because of poor electron mobility. Here, we demonstrated a concept that the conjugation of g-C3N4 with crystalline carbon can improve the in-plane electron mobility and make interior triazine units more electro-active for ORR and OER. As a result, the Co metal coordinated g-C3N4 with crystalline carbons (Co–C3N4/C) showed a remarkable electrocatalytic performance toward both ORR and OER. For example, it displayed an onset potential of 0.95 V for ORR and an overpotential of 1.65 V for OER at 10 mA cm–2, which are comparable and even better than those of benchmark Pt, RuO2, and other carbon nitride-based electrocatalysts. As a proof-of-concept application, we employed this catalyst as an air electr...

(Keynote) Interface Control for High Performance N-Channel Ge FETs

The demonstration of high electron mobility Ge n-MOSFETs was not an easy task. To overcome such big challenge, three carrier scattering mechanisms in Ge MOS inversion layer such as Coulomb scattering, phonon scattering, and surface roughness scattering were carefully investigated. The first step was to improve the peak electron mobility by reducing the interface states density (Dit ). We succeeded in the reduction of Dit (<1011 eV-1cm-2) at Ge/GeO2 interface by employing the high-pressure O2 (HPO) oxidation [1]. This is quite reasonable thermodynamically [2]. However, there still remained two critical challenges. One was how to suppress the significant degradation of high-Ns electron mobility. The other one was how to keep electron mobility high in thin EOT region [3]. It is generally considered that high-Ns electron mobility is dominated by the interface roughness scattering. Since we demonstrated that Ge(111) was the best surface orientation for electrons to achieve the highest peak electron mobility, we challenged to realize the atomically flat Ge(111) surface by using H2 annealing [4]. Then, MOSFETs on Ge(111) with and without atomically flat surface were fabricated with HPO. N-channel MOSFETs fabricated by HPO on atomically flat Ge(111) exhibited greatly improved high-Ns electron mobility [5]. EOT reduction was also challenging because HPO should naturally form thicker GeO2. This fact was a big hurdle on Ge FET technology. Meanwhile, it was interestingly found that the low-temperature HPO (LT-HPO) reduced the oxidation rate [6]. This fact enabled us to achieve ~2 nm EOT GeO2 on Ge with superior interface and bulk GeO2. Another way to reduce EOT is obviously to replace HPO-GeO2 with other high-k oxides which are appropriate for Ge. We have fortunately found that Y2O3 is very friendly with Ge [7]. Furthermore, in our recent experiments Y2O3-doped GeO2 (YGO) is much better than pure Y2O3 on Ge. Significantly improved electron mobility in n-channel Ge FETs in a wide range of electron density has been achieved, when YGO in addition to H2 annealing has been used for the interfacial layer in gate stacks [8]. Poor electron mobility in n-channel Ge FETs is not true now. We can engineer the Ge interface through understanding of thermodynamics in gate stack formation and of kinetics of both surface planarization and oxidation. Thus, we can safely conclude that Ge is very promising not only for p-channel but also for n-channel FETs.

Recent Advances in the BiVO4 Photocatalyst for Sun-Driven Water Oxidation: Top-Performing Photoanodes and Scale-Up Challenges

Photoelectrochemical (PEC) water splitting, which is a type of artificial photosynthesis, is a sustainable way of converting solar energy into chemical energy. The water oxidation half-reaction has always represented the bottleneck of this process because of the thermodynamic and kinetic challenges that are involved. Several materials have been explored and studied to address the issues pertaining to solar water oxidation. Significant advances have recently been made in the use of stable and relatively cheap metal oxides, i.e., semiconducting photocatalysts. The use of BiVO4 for this purpose can be considered advantageous because this catalyst is able to absorb a substantial portion of the solar spectrum and has favourable conduction and valence band edge positions. However, BiVO4 is also associated with poor electron mobility and slow water oxidation kinetics and these are the problems that are currently being investigated in the ongoing research in this field. This review focuses on the most recent advances in the best-performing BiVO4-based photoanodes to date. It summarizes the critical parameters that contribute to the performance of these photoanodes, and highlights so far unresolved critical features related to the scale-up of a BiVO4-based PEC water-splitting device.

OG-FET: An In-Situ ${O}$ xide, ${G}$ aN Interlayer-Based Vertical Trench MOSFET

In this letter, a novel device design to achieve both low ON-resistance and enhancement mode operation in a vertical GaN FET is demonstrated. In the traditional trench MOSFET structure, a dielectric is deposited on an n-p-n trenched structure and the channel forms via p-GaN inversion at the dielectric/p-GaN interface. However, this results in a relatively high ON-resistance due to poor electron mobility in the channel. By changing the structure to include a metal-organic chemical vapor deposition (MOCVD)-regrown Un-intentionally Doped (UID)-GaN interlayer followed by an in-situ dielectric (MOCVD Al2O3) cap on the n-p-n trenched structure, a pathway (channel) for enhanced electron mobility is created, resulting in reduced ON-resistance. Preliminary results for this device design demonstrated almost 60% reduction in the ON-resistance and similar breakdown voltage compared with a traditional trench MOSFET structure while maintaining normally off operation with a threshold voltage of 2 V.

Graphitic-C3N4 hybridized N-doped La2Ti2O7 two-dimensional layered composites as efficient visible-light-driven photocatalyst

Perovskite-type La2Ti2O7 (LTO), having a layered structure and the separated H2 and O2 evolution sites, is attractive as an efficient photocatalyst. However, the photocatalytic activity is often limited by the poor electron mobility. This problem can be conquered by hybridization with materials having efficient properties for the visible light absorption and charge carrier transport. Here, we report a two-dimensional (2D) layered composite hybridized by approximately 2nm thick graphitic C3N4 nanosheets (g-C3N4) and 7nm thick nitrogen doped LTO nanosheets (NLTO) (g-C3N4/NLTO), in which g-C3N4 and NLTO act as hole receptor and electron conductor, respectively. g-C3N4/NLTO exhibited high photocatalytic activities for H2 production via water splitting and dye degradation under the UV and visible light irradiation, due to the interfacial charge transfer between g-C3N4 and NLTO. The electrochemical measurement showed the type II band alignment with favorable charge transfer from g-C3N4 to NLTO. The 2D architecture with a maximized interfacial area allows efficient charge separation with a short interfacial distance. This efficient interfacial charge transfer is further elucidated from monitoring of charge separation and trapping processes using the femtosecond time-resolved diffused reflectance (TDR) measurement.

Photoelectrochemical Properties of TiO2 Nanowire Arrays: A Study of the Dependence on Length and Atomic Layer Deposition Coating

We report that the length and surface properties of TiO(2) nanowires can have a dramatic effect on their photoelectrochemical properties. To study the length dependence, rutile TiO(2) nanowires (0.28-1.8 μm) were grown on FTO substrates with different reaction times (50-180 min) using a hydrothermal method. Nanowires show an increase in photocurrent with length, and a maximum photocurrent of 0.73 mA/cm(2) was measured (1.5 V vs RHE) for 1.8 μm long nanowires under AM 1.5G simulated sunlight illumination. While the incident photon to current conversion efficiency (IPCE) increases linearly with photon absorptance (1-10(-α×length)) with near band gap illumination (λ = 410 nm), it decreases severely at shorter wavelengths of light for longer nanowires due to poor electron mobility. Atomic layer deposition (ALD) was used to deposit an epitaxial rutile TiO(2) shell on nanowire electrodes which enhanced the photocatalytic activity by 1.5 times (1.5 V vs RHE) with 1.8 μm long nanowires, reaching a current density of 1.1 mA/cm(2) (61% of the maximum photocurrent for rutile TiO(2)). Additionally, by fixing the epitaxial rutile shell thickness and studying photoelectrochemical (PEC) properties of different nanowire lengths (0.28-1.8 μm), we found that the enhancement of current increases with length. These results demonstrate that ALD coating improves the charge collection efficiency from TiO(2) nanowires due to the passivation of surface states and an increase in surface area. Therefore, we propose that epitaxial coating on materials is a viable approach to improving their energy conversion efficiency.

Effect of oxyfluorinated multi-walled carbon nanotube additives on positive temperature coefficient/negative temperature coefficient behavior in high-density polyethylene polymeric switches

Multi-walled carbon nanotubes (MWCNTs) were embedded into high-density polyethylene (HDPE) to improve the electrical properties of HDPE polymeric switches. The MWCNT surfaces were modified by oxyfluorination to improve their positive temperature coefficient (PTC) and negative temperature coefficient (NTC) behaviors in HDPE polymeric switches. HDPE polymeric switches exhibit poor electron mobility between MWCNT particles when the number of oxygen functional groups is increased by oxyfluorination. Thus, the PTC intensity of HDPE polymeric switches was increased by the destruction of the electrical conductivity network. The oxyfluorination of MWCNTs also leads to weak NTC behavior in the MWCNT-filled HDPE polymeric switches. This result is attributed to the reduction of the mutual attraction between the MWCNT particles at the melting temperature of HDPE, which results from a decrease in the surface free energy of the C–F bond in MWCNT particles.

Identification of a major cause of endemically poor mobilities in SiC/SiO2 structures

Poor electron mobility at SiC/SiO2 interfaces has long held up the development of SiC-based power devices. The mobility degradation has been attributed to defects at the interface and the oxide as in the case of the Si/SiO2 system, but a decade of research has led only to limited improvement. Here we examine theoretical results and available experimental evidence and show that thermal oxidation generates immobile carbon di-interstitial defects inside the semiconductor substrate and that they are a major cause of the poor mobility in SiC/SiO2 structures.

A Photoelectrochemical Device with a Nanostructured SnO2 Electrode Modified with Composite Clusters of Porphyrin-Modified Silica Nanoparticle and Fullerene

A silica nanoparticle has been successfully employed as a nanoscaffold to self-organize porphyrin and C60 molecules on a nanostructured SnO2 electrode. The quenching of the porphyrin excited singlet state on the silica nanoparticle is suppressed significantly, showing that silica nanoparticles are promising scaffolds for organizing photoactive molecules three-dimensionally in nanometer scale. Marked enhancement of the photocurrent generation was achieved in the present system compared with the reference system, where a gold core was employed as a scaffold of porphyrins instead of a silica nanoparticle. The rather small incident photon-to-current efficiency relative to a similar photoelectrochemical device using a silica microparticle may result from poor electron and hole mobility in the composite film due to poor connection between the composite clusters of a porphyrin-modified silica nanoparticle and C60 in micrometer scale.

Improved electroluminescence from oligothiophenes

Low quantum efficiency of electroluminescence (EL) from solid state evaporated thin films of α-sexithiophene (α-6T) was accounted for by quenching due to inter-chain interaction. The substitution of α-6T by voluminous substituants at the end of the chains led to an increase of the fluorescence in the solid state with a concomitant decrease in conductivity down to 10 −11 S cm −1 due to the increase in spacing between molecules. A bilayer device α-6T/DPS6T improved hole blocking in the recombination region between organic layers leading to creation of excitons away from the Al electrode. By dispersing the molecules in a highly conducting hole transporting host matrix of PVK the efficiency was further improved. Transient EL response of devices indicate that poor electron injection and mobility limits output efficiencies.