Conversion of amorphous TiO2 coatings into their crystalline form using a novel microwave plasma treatment

Crystalline titanium dioxide (TiO₂) coatings have been widely used in photo-electrochemical solar cell applications. In this study, TiO₂ and carbon-doped TiO₂ coatings were deposited onto unheated titanium and silicon wafer substrates using a DC closed-field magnetron sputtering system. The resultant coatings had an amorphous structure and a post-deposition heat treatment is required to convert this amorphous structure into the photoactive crystalline phase(s) of TiO₂. This study investigates the use of a microwave plasma heat treatment as a means of achieving this crystalline conversion. The treatment involved placing the sputtered coatings into a 2.45 GHz microwave-induced nitrogen plasma where they were heated to approximately 550 °C. It was observed that for treatment times as short as 1 min, the 0.25-μm thick coatings were converted into the anatase crystalline phase of TiO₂. The coatings were further transformed into the rutile crystalline phase after treatments at higher temperatures. The doping of TiO₂ with carbon was found to result in a reduction in this phase transformation temperature, with higher level of doping (up to 5.8% in this study) leading to lower anatase-to-rutile transition temperature. The photoactivity performance of both doped and un-doped coatings heat-treated using both furnace and microwave plasma was compared. The carbon-doped TiO₂ exhibited a 29% increase in photocurrent density compared to that observed for the un-doped coating. Comparing carbon-doped coatings heat-treated using the furnace and microwave plasma, it was observed that the latter yielded a 19% increase in photocurrent density. This enhanced performance may be correlated to the differences in the coatings' surface morphology and band gap energy, both of which influence the coatings' photoabsorption efficiency.     

微波烧结技术在超硬材料制品中的应用探讨

介绍了微波烧结技术的原理及特点,简要概括了目前制备特种陶瓷的研究现状,并对微波烧结陶瓷材料、硬质合金(WC-Co)、微波烧结金刚石烧结体等问题进行了分析讨论,初步探讨了微波烧结技术在超硬材料制品中广泛应用的可能性。     

Synthesis and characterization of triphenylamine-based organic dyes for dye-sensitized solar cells

We synthesized three organic dyes (DYE 1, DYE 2, and DYE 3) containing triphenylamine (TPA) moieties as electron donors and cyanoacrylic acid moieties as electron acceptors, designed at the molecular level, and developed them for use in dye-sensitized solar cells (DSSCs). Among all the dyes, DYE 2 exhibited the highest overall solar-energy-to-electricity conversion efficiency of 4.06% with a short-circuit photocurrent density of 11.15 mA cm^?2, an open-circuit voltage of 0.64 V, and a fill factor of 0.57 under AM 1.5 irradiation with 100 mW cm^?2 simulated sunlight. The results indicate that the organic dyes are promising in the development of DSSC.     

碳纳米复合对电极染料敏化太阳能电池的电化学性能

在染料敏化太阳能电池(DSCs)碳对电极中添加多壁碳纳米管,制作碳纳米复合对电极。通过循环伏安法研究复合电极中碳纳米管对I3?/I?氧化还原行为的影响。采用电化学阻抗谱表征,比较纳米炭黑、石墨鳞片、碳纳米管、纳米炭黑-纳米碳管复合材料对碳电极/电解质界面的影响。结果表明:添加纳米碳管后,电极的催化还原电位降低,电流密度增大;碳纳米管的加入使电极表面催化活性点增多,碳电极与电解液的界面电势差减少。光伏性能测试表明,添加10%(质量分数)的碳纳米管的DSCs的开路电压提高了17.9%,短路电流提高了24.1%,填充因子提高了14.4%。     

Using a molten organic conducting material to infiltrate a nanoporous semiconductor film and its use in solid-state dye-sensitized solar cells

We describe a method to fill thin films of nanoporous TiO₂ with solid organic hole-conducting materials and demonstrate the procedure specifically for use in the preparation of dye-sensitized solar cells. Cross-sections of the films were investigated by scanning electron microscopy and it was observed that a hot molten organic material fills pores that are 10 μm below the surface of the film. We characterized the incident photon to current conversion efficiency properties of the solid TiO₂/organic dye/organic hole-conductor heterojunctions and the spectra show that the dye is still active after the melting process.     

A novel microwave absorption and dielectric spectrum detection technology in photoelectron dynamic study for solar cells

The photoelectron property is directly related to the light-energy conversion efficiency of solar cells. In this paper, the photoelectron dynamic of semiconductor was analyzed. The diffusion of electrons has influence on the dielectric function of the solar cell material. And the amplitude variance of the imaginary andreal part of the dielectric function is in direct proportion to the dynamic process of free and shallow-trapped electrons. Based on the untouched detection technique, the method is present to detect the amplitude change of the microwave signal which is passing through the material whose dielectric function changes after exposure. A35GHz oscillator was used as a microwave source. The absorptionand dispersion microwave signals, which contain the dynamic information of free and shallow-trapped electron signal, are split respectively with phase-sensitive instrument. The photoelectron character of n-type Si(100) thin film was investigated by the novel equipment, and the lifetime of different kinds of electronswith the resolution of 1 ns was obtained. The equipment can be directly used inthe study of the optoelectronic conversion mechanism of solar cells.     

Synthesis and characterization of a novel fullerene derivative containing carbazole group for use in organic solar cells

A novel carbazole-group-containing fullerene derivative (CBZ-C₆₀) with good solubility in common organic solvents was synthesized. This derivative was analyzed by using many techniques such as NMR, FAB-MS, FTIR and UV–vis absorption spectroscopy. Further, bulk heterojunction photovoltaic devices were fabricated. Since the LUMO energy level of CBZ-C₆₀ was higher than that of fullerene, the open-circuit voltage (V_oc) of devices based on CBZ-C₆₀ was higher than that of devices based on fullerene. The power-conversion efficiency was highest for devices with composite thin films that have P3HT/CBZ-C₆₀ composition ratios of 1:1 and were annealed at 150 °C for 10 min. The maximum V_oc, short-circuit current density, and PCE of the best device were 0.64 V, 2.32 mA/cm², and 0.48%, respectively.     

Solvothermal growth of Zn2SnO4 for efficient dye-sensitized solar cells

Zn2SnO4 plates,particles and spheres are suc-cessfully prepared via a facile synthesis way by carefully adjusting the solvothermal conditions,which are further ...     

CNT/PEDOT core/shell nanostructures as a counter electrode for dye-sensitized solar cells

CNT/PEDOT nanostructures composed of carbon nanotube (CNT) cores and poly(3,4-ethylenedioxythiophene) (PEDOT) shells were synthesized by chemical oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) using FeCl₃ and dodecylbenzene sulfonic acid (DBSA) as the oxidant and surfactant, respectively. The resulting CNT/PEDOT nanostructures had a PEDOT layer thickness of 2–5 nm that exhibited not only higher polymerization yield but also enhanced thermal stability and electrical conductivity relative to pure PEDOT. N-Methyl-2-pyrrolidone (NMP)-based CNT/PEDOT paste containing polyvinylidene fluoride (PVDF) as a binder was painted directly onto fluorine-doped tin oxide (FTO) glass for use as a counter electrode (CE) material in dye-sensitized solar cells (DSSCs). While DSSCs made of pure CNT and PEDOT CE exhibited power conversion efficiencies of ～3.88% and 4.32% under standard AM 1.5 sunlight illumination, respectively, the cell efficiency was enhanced to ～4.62% with the CNT/PEDOT CE. This enhancement was due to the improved fill factor of the CNT/PEDOT-based DSSC realized by the increased electrical conductivity of the CNT/PEDOT composite.     

Novel bilayer structure ZnO based photoanode for enhancing conversion efficiency in dye-sensitized solar cells

ZnO film with a novel bilayer structure, which consists of ZnO nanowire (ZnO NW) arrays as underlayer and polydisperse ZnO nanocrystallite aggregates (ZnO NCAs) as overlayer, is fabricated and studied as dye-sensitized solar-cell (DSSC) photoanode. Results indicate that such a configuration of the ZnO nanocrystallite aggregates on the ZnO nanowire arrays (ZnO-(NCAs/NWs)) can significantly improve the efficiency of the DSSC due to its fast electron transport, relatively high surface area and enhanced light-scattering capability. The short-circuit current density (J_sc) and the energy-conversion efficiency (η) of the DSSC based on the ZnO-(NCAs/NWs) photoanode are estimated and the values are 9.19 mA cm⁻² and 3.02%, respectively, which are much better than those of the cells formed only by the ZnO NWs (J_sc = 4.02 mA cm⁻², η = 1.04%) or the ZnO NCAs (J_sc = 7.14 mA cm⁻², η = 2.56%) photoanode. Moreover, the electron transport properties of the DSSC based on the ZnO-(NCAs/NWs) photoanode are also discussed.     

Effects of anchoring groups in multi-anchoring organic dyes with thiophene bridge for dye-sensitized solar cells

Organic photo-sensitizers were designed and synthesized based on a phenothiazine framework containing single- and double-electron acceptors that were bridged with thiophene for the dye sensitized solar cells (DSSCs). The optimized geometries were determined with density functional theory (DFT) calculations to estimate the photovoltaic properties of the dyes in the design stage. The organic dye with the double electron acceptors exhibited a better light absorption at long wavelength and an effective electron extraction pathway from the electron donor to the TiO₂ surface, leading to an improved short-circuit current (11.6 mA cm^?2), compared with that of the dye with the single electron acceptor (10.2 mA cm^?2) and the conventional N3 Ru-dye (10.4 mA cm^?2). Contrarily, the open-circuit voltage of the organic dye with the double electron acceptors decreased because the additional protonated carboxylic groups caused a positive shift in the Fermi level of TiO₂.     

Effects of surface-modified photoelectrode on the power conversion efficiency of dye-sensitized solar cells

The effects of Na₂SO₄ as a surface modification material on the performance of dye-sensitized solar cells (DSSCs) were studied. The surfaces of TiO₂ films were firstly modified with aqueous Na₂SO₄ solution by a dip coating process, and then the resulting electrode was applied to the photoelectrode of a DSSC. The DSSC with the Na₂SO₄-modified photoelectrode had a power conversion efficiency of 9.01% compared with that (7.97%) of the reference cell, which corresponds to an increase of about 13.0% in the efficiency due to an enhancement in short-circuit current (J _sc ) and open-circuit voltage (V _oc ). A series of measurements such as UV-visible absorption, electrochemical impedance, incident photon to current conversion (IPCE) efficiency and dark current revealed that incorporation of Na₂SO₄ onto the TiO₂ film led to an increase of dye adsorption and a longer lifetime of electrons injected from dyes to the TiO₂ electrodes, resulting in the improvement in both J _sc and V _oc , compared to those of a reference device without surface modification.     

Gel electrolytes containing several kinds of particles used in quasi-solid-state dye-sensitized solar cells

Composite gel electrolytes containing several kinds of particles used as the quasi-solid-state electrolytes in dye-sensitized solar cells (DSSCs) were reported. Mesoporous particles (MCM-41) with unique structures composed of ordered nanochannels were served as a new kind of gelator for quasi-solid-state electrolytes. MCM-41, hydrophobic fumed silica Aerosil R972 and TiO2 nanopatricles P25 were dispersed into gel electrolytes respectively. The solar energy-to-electricity conversion efficiency of these cells is 4.65%, 6.85% and 5.05% respectively under 30 mW·cm-2 illumination. The preparation methods and the particles sizes exert an influence on the performance of corresponding solar cells. Owing to unique pore structures and high specific BET surface area, mesoporous silica MCM-41 was expected to have the potential to afford conducting nanochannels for redox couple diffusion.     

Synthesis and photovoltaic performance of new diketopyrrolopyrrole (DPP) dyes for dye-sensitized solar cells

Two new metal-free organic dyes (DPP-I and DPP-II) with diketopyrrolopyrrole (DPP) core were designed and synthesized, in which triphenylamine or N,N-bis(4-methoxyphenyl)benzenamine moieties was used as the electron donor, DPP units as the π-conjugated bridge, and carboxylic acid group as the electron acceptor. Photophysical and electrochemical properties of two dyes were investigated by UV–vis spectrometry and cyclic voltammetry. Electrochemical measurement data indicate that the tuning of the HOMO and LUMO energy levels can be conveniently accomplished by alternating the donor moiety. The DSSC based on dye DPP-I showed better photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 80.6% corresponding to an overall conversion efficiency of 2.68%. Although the power conversion efficiencies are not so high, this work explores new donor–π-accepter–π-donor models and the effects of molecular design on optical properties.     

Application of plasma spraying to tubular-type solid oxide fuel cells production

Solid oxide fuel cells (SOFCs) feature the highest energy conversion efficiency of any type of fuel cell yet developed. This article describes SOFC production by means of plasma spraying and presents the resulting SOFC performance. The application of plasma spraying to tubular SOFC production has realized good performance on the order of 40 W or greater in terms of electricity generation per cell stack under standard conditions of 200 mA/cm².     

正偏压对微波等离子体CVD法制备金刚石薄膜的影响

线形同轴耦合式微波等离子体CVD法是在硬质合金微型钻头(微钻)表面沉积金刚石涂层的最佳方法之一.本文首先研究了酸碱两步预处理后微钻表面的形貌和成分,然后研究了微钻工作表面金刚石的沉积情况,最后重点研究了正偏压对微钻不同位置金刚石生长的影响.结果表明,在微钻上施加50 V正偏压时,金刚石薄膜具有最佳的形貌和较好的均匀性.     

Effect of polyethyleneimine on the growth of ZnO nanorod arrays and their application in dye-sensitized solar cells

A series of oriented hexagonal wurtzite ZnO nanorod-array films were grown on fluorine-doped tin oxide (FTO) coated glass substrates by chemical process. The effect of polyethyleneimine (PEI) on the structure and micro-morphology of ZnO nanorod array films, as well as the photoelectric conversion properties in dye-sensitized solar cells (DSSCs) was analyzed. It was found that with the addition of PEI in growth solution, the ZnO nanorods became smaller in diameter and longer in length and hence the dye absorption and the photovoltaic performance of DSSCs were improved. A power conversion efficiency of 2.30% had been achieved on a DSSC based on a 7.9 μm-long nanorod array film prepared by a growth solution containing the PEI.