Materials Science Forum Vol. 685

Abstract: Hierarchical porous carbons (HPC) were synthesized by a combination of self-assembly and chemical activation method. A mesoporous carbon with large-size pore was used as raw materials. N₂ sorption measurement indicated that plenty of micropores generated within the mesopore wall in the mesoporous carbon during KOH activation. Electrochemical impedance spectroscopy measurement demonstrated a high electrocatalytic activity of HPC electrode for triiodide reduction. The overall conversion efficiency of dye-sensitized solar cells with HPC counter electrode was 6.48%, which is similar to that of the device with conventional Pt counter electrode.

Abstract: Pristine and Al-doped zinc oxide nanopowders were synthesized via a surfactant-assisted complex sol-gel method, possessing a pure ZnO phase structure and controllable grain size which was characterized by X-ray diffraction and scanning electron microscopy. Using these nanopowders, the pristine and Al-doped ZnO magnetron sputtering targets were prepared following a mold-press, cold isostatical-press and schedule sintering temperature procedure. The relative density of these as-prepared targets was tested by Archimedes’ method on densitometer. All of the results were above 95 theory density percents, and the resistivity was tested on four-probe system at a magnitude of 10^-2 Ω cm. Related pristine ZnO thin films and Al-doped ZnO thin films were fabricated by magnetron sputtering method, respectively. The pristine and Al-doped ZnO films deposited on the quartz glass by dc sputtering owned a (002) orientation with a thickness of 350 nm at a deposition power of 100 W for two hours under an argon plasma. A good optical transparency above 80% and low resistivity of 1.60×10^-3 Ω cm were obtained with a deposition temperature of 573 K. The optical energy bandgap could be tailored by Al doping at 4 at.% Al.

Abstract: Many studies reported that dye-sensitized solar cells have more significant capacitance characteristics than the silicon solar cell. In this study, it was found the capacitance characteristics of dye-sensitized solar cell changes with the imposed bias voltage. The bias voltage is indispensable in the standard measurement for the conversion efficiency of dye-sensitized solar cell. The influence of changed capacitance during the measurement on the conversion efficiency of dye-sensitized solar cells was investigated. The analysis on the EIS spectra and equivalent circuit shows that the capacitance of dye-sensitized solar cells is small and the deviation cell I-V characteristics from the steady-state value is minor when the applied bias is small; while under a condition with a large applied bias, the capacitance characteristics of dye-sensitized solar cell grew rapidly and the I-V characteristics deviated from the steady-state value significantly increased. This phenomenon is helpful for the accurate measurement of the quantum conversion efficiency and photoelectric conversion efficiency of dye-sensitized solar cells.

Abstract: The Macroporous Nanocrystalline TiO₂ Thin Film Was Prepared by Dipping-Coating Method. Polystyrene (PS) Microspheres Template Was Used as Pore-Forming Assistant and TiO₂ Sol Was Used as Precursor. the Photoelectric Characteristics of the Samples Were Studied Using Surface Photovoltage (SPV) and Photoacoustic (PA) Techniques. the Presence of a Small Amount of Residual Template Damages the Integrity of the Porous TiO₂ Film with Inverse Opal Structure, and TiO₂ May Be Restricted in Certain Application Fields as Photonic Crystals. a Small Amount of Residual Template Changes the Surface Photovoltaic Properties of the Porous TiO₂ Film, Resulting Mainly in the Broadened Scope and the Increased Intensity of SPV Response.

Abstract: Texturing for mono-crystalline silicon solar cell by chemical anisotropic etching is one of the most important techniques in photovoltaic industry. In recent years, tetramethylammonium hydroxide (TMAH) solution or a mixture of TMAH solution with IPA was reported to be used for random pyramids texturization on silicon surface due to its non-volatile, nontoxic, good anisotropic etching characteristics and uncontaminated metal ions. However, most of the studies were reported about the etching processes by using high TMAH concentration solutions. In this study, a simple and cost-effective approach for texturing mono-crystalline silicon wafers in low TMAH concentration solutions was proposed. Etching was performed on (100) silicon wafers using silicon-dissolved tetramethylammonium hydroxide (TMAH) solutions (0.5~1 %) without addition of surfactant. The surface phenomena, surface morphology and surface reflectance have been analyzed. A textured surface with smaller and smooth pyramids can be realized by using 1 % silicon-dissolved TMAH solutions.

Abstract: Texturization of mono-crystalline by chemical anisotropic etching is one of the most important technologies for modern silicon photovoltaic. IPA is usually added to the alkaline etchants to improve the uniformity of the random pyramid texture due to remove hydrogen bubbles sticking on the silicon wafer by improving the wettability of wafer surface. In this investigation, we carried out a systematic study on the influence of IPA concentrations on the textured surface. The etching experiments were performed on (100) silicon wafer in a mixture of 20 vol. % commercial TMAH solutions (10 wt.%) and IPA (rang from 0~12 vol. %) for etching time ranging from 10 to 70 min at 80°C. The etching mechanism in the TMAH solutions with IPA addition was explained basing on the experimental results and the theoretical considerations.

Abstract: The effects of composition on the performance of hybrid photovoltaic cells based on PbSe nanocrystal quantum dot(NQD)/ poly(3-hexylthiophene) nanocomposites were studied. The device performance and the absorption property strongly depended on the loading of PbSe. To improve the device performance, a pure light-absorbing P3HT film was inserted underneath the blended layer of P3HT and PbSe nanocrystal quantum dots in the active region. Such a design allowed for the employment of a thinner bulk heterojunction for more efficient carrier collection without an excessive reduction of the overall light absorption by the photovoltaic cell. The measured device performance showed a significant improvement over previously reported hybrid cells containing bulk heterojunctions of P3HT and Pb(S,Se) nanocrystal quantum dots.

Abstract: Mesoporous carbon (MC) materials with surface area of 400 m²g^-1 were prepared and incorporated into the polymer gel electrolyte comprising of polyvinylidene fluoride and 1-methyl-3-hexylimidazolium iodide to fabricate the composite gel electrolytes. The photovoltaic performance of the quasi-solid-state dye-sensitized solar cells was improved through incorporating MC into electrolyte. The dye-sensitized solar cell with composite gel electrolyte containing 3 wt% MC achieved the best photovoltaic performance, and the corresponding open-circuit voltage, short-circuit current density, fill factor and overall conversion efficiency were 0.59V, 13.22 mAcm^-2, 0.66 and 5.15%, respectively. The stability of dye-sensitized solar cells with composite gel electrolyte was far superior to the cell with organic liquid electrolyte.

Abstract: A novel method to grow silicon dioxide layers for passivating the silicon surface is given more attention. SiO₂ was grown by applying a positive voltage across silicon wafers in a nitric acid solution at low temperature. After annealing in N₂ media at 900°C for 20min, excellent surface passivation was achieved. The maximum effective lifetime of the silicon arrived at 29.8μs and 29.75μs, which was three times the value of silicon without passivation. The effective lifetime of other types of silicon could be ten times the initial value without the silicon dioxide. A comparison study of the effect of the FGA, annealing at low temperature and annealing in N₂ or O₂ containing medium at high temperature were investigated.