Daiki Ichida

Improvement on the Electron Transfer of Dye-Sensitized Solar Cell Using Vanadium Doped TiO2

In dye-sensitized solar cells, nanoporous structure of TiO2 is very important for efficient cell because lots of dye molecules are adsorbable and they are the source of the photocurrent. However, the internal impedance of TiO2 is relatively large and it limits the performance. For better performance, vanadium was doped into TiO2 in this work. Doping different material generally improves the characteristics and functions of original materials. Vanadium doping has some advantages such as the reduction of internal resistance, the improvement of chemical stability and high absorption. Especially, reduced internal resistance is so helpful for better electron transfer in TiO2 network. Various amounts of vanadium were applied and photovoltaic performance, internal impedance and absorbance were measured in order to verify the effect of vanadium doping. As a result, vanadium doping improved the overall performance from 6.01 to 6.81% with decreased internal resistance although adsorbed dye amount was reduced by decreased surface area and open circuit voltage was also decreased by the change of band-gap energy.

Characteristics of crystalline silicon/Si quantum dot/poly(3,4- ethylenedioxythiophene) hybrid solar cells

Here, we report the characteristics of a novel organic/inorganic hybrid photovoltaic device using a Si quantum dot (QD) layer synthesized by multi-hollow discharge plasma chemical vapor deposition. The hybrid device has a p–i–n structure, which consists of a crystalline Si (c-Si) substrate, a Si QD layer, and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). We have examined the absorption coefficient and photoconductivity of Si QD layers, and confirmed electricity generation from Si QD layers. We have measured the current–voltage characteristics and incident photon-to-current conversion efficiency (IPCE) of c-Si/Si QD/poly(3,4-ethylenedioxythiophene) (PEDOT) hybrid solar cells. This hybrid device shows an energy conversion efficiency of 2.84%, a short-circuit current of 6.84 mA/cm2, an open-circuit voltage of 0.73 V, and a fill factor of 0.58. A high IPCE value of 82.8% is obtained at a short wavelength of 460 nm.

Performance dependence of Si quantum dot-sensitized solar cells on counter electrode

Au counter electrode is generally used with polysulfide electrolyte for quantum dot-sensitized solar cells (QDSCs) due to degradation of QD by iodine electrolyte and strong interaction between Pt counter electrode and S2− ions in polysulfide electrolyte. In this work, the effects of the thickness and morphology of Au counter electrode on the performance of Si QDSC were investigated. Au film thickness was linearly controlled from 5 to 500 nm by deposition time. Cyclic voltammetry and impedance analysis clarified the catalytic activity of counter electrode, surface resistance of transparent conductive oxide (TCO), and the charge transportation at the counter electrode. The increase of Au film thickness reduced the surface resistance of TCO with increased conductivity. No significant difference in the redox reaction from electrolyte to Si QDs was observed for Au film thickness from 20 to 500 nm. Catalytic reaction of counter electrode was activated with the increase of Au film thickness up to 200 nm. The impedance of charge transportation at the counter electrode was also decreased with Au deposition. Their surface resistance, catalytic activity and internal resistance were reflected in overall performance. Consequently, Si QDSC with 200-nm-thick Au counter electrode had the best performance.

Photovoltaic application of Si nanoparticles fabricated by multihollow plasma discharge CVD: Dye and Si co-sensitized solar cells

Dye-sensitized solar cells (DSCs) still need wider absorption range despite their stable and good performance. This work proposed the co-sensitization of Si quantum dot (QD) and N749 dye for better photo-generation. Si QD was chemically stable with regard to all DSC components and its stability enabled to co-sensitize with dye. Si QDs were fabricated by multihollow discharge plasma chemical vapor deposition and applied for the co-sensitization. Si and dye co-sensitization led to the increase of incident photon to current conversion efficiency and decrease of internal impedance as compared with a standard DSC. As a result, short-circuit current density was increased over 1 mA/cm2 and the performance was enhanced with co-sensitization from 4.36 to 5.10%. Si and dye co-sensitization was very effective because the enhancement was much larger than the performance of Si QDSC without dye sensitization.

Preparation of Si nanoparticles by laser ablation in liquid and their application as photovoltaic material in quantum dot sensitized solar cell

Quantum dot sensitized solar cell was fabricated using silicon nanoparticles prepared by laser ablation in liquid. The obtained particles are spherical and have an average size of 6 nm. These particles were utilized as photosensitizing material in solar cell with polysulfide as an electrolyte. The conversion efficiency of solar cell with silicon nanoparticles was 5.3 times higher than the one with only TiO2 particles. Electrical impedance spectroscopy also revealed the decrease in resistance in the former case led to higher current density than the latter one.

Effects of H 2 Gas Addition on Structure of Ge Nanoparticle Films Deposited by High-pressure RF Magnetron Sputtering Method

Graduate School of Information Science and Electrical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan Center of Plasma Nano-interface Engineering, Kyushu University, 744 Motooka, Fukuoka, 819-0395, Japan Fuculty of Arts and Science, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan PRESTO, Japan Science and Technology Agency, Gobancho, Chiyoda-ku, Tokyo 102-0076, Japan

Combinatorial Plasma CVD of Si Nanoparticle Composite Films for Band Gap Control

Graduate School of Information Science and Electrical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan Center of Plasma Nano-interface Engineering, Kyushu University, 744 Motooka, Fukuoka, 819-0395, Japan Faculty of Arts and Science, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan Presto, Japan Science and Technology Agency, Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan

Nanostructure Control of Si and Ge Quantum Dots Based Solar Cells Using Plasma Processes

We report characteristics of quantum dot (QD) sensitized solar cells using Si nanoparticles and Ge nanoparticles. Si nanoparticles were synthesized by multi-hollow discharge plasma chemical vapor deposition, whereas Ge nanoparticles were done by a radio frequency magnetron sputtering using Ar+H2 under high pressure conditions. The electrical power generation from Si QDs and Ge QDs was confirmed. Si QD sensitized solar cells show an efficiency of 0.024%, fill factor of 0.32, short-circuit current of 0.75 mA/cm2 and open-circuit voltage of 0.10 V, while Ge QD sensitized solar cells show an efficiency of 0.036%, fill factor of 0.38, short-circuit current of 0.64 mA/cm2 and open-circuit voltage of 0.15 V.

Deposition of crystalline Ge nanoparticle films by high-pressure RF magnetron sputtering method

We report here deposition of crystalline Ge nanoparticle films using a radio frequency magnetron sputtering method in argon and hydrogen gas mixture under a high pressure condition. The size of Ge nanoparticles is deduced to be 6.3-6.4 nm from the peak frequency shift of Raman spectra. Raman and X-ray diffraction spectra show that the films are crystalline. The film crystallinity strongly depends on substrate temperature (Ts). Highly crystalline Ge nanoparticle films are successfully fabricated at Ts = 180?C.