Papers by Keyword: Photovoltaic Properties

Abstract: Bi_1-xLa_xFeO₃(x=0, 0.3) thin films were deposited on glass/ITO substrates through Sol-Gel Dip-Coating method and rapid annealing process. The structures were detected by X-ray diffraction patterns, Raman spectrometer and scanning electron microscopy. The magnetic, ferroelectric and optical properties of the films were studied by vibrating sample magnetometer, ferroelectric integrate tester and photovoltaic performance testing system, respectively. The experimental results indicate that BiFeO₃ thin film presents rhombohedral perovskite structure and Bi_0.7La_0.3FeO₃ films showed distorted perovskite structure, which were confirmed by XRD patterns and Raman spectrometer. The magnetism and ferroelectric properties of the films were obviously enhanced by La doping. Furthermore, the photocurrent response and photovltaic effect in BLFO thin films were detected.

Abstract: ZnO films were deposited on fluorine doped tin oxide glass substrate and chemically treated by KOH solutions. The films were immersed into 2 M KOH solution with various immersing time of 0-6 min at room temperature, rinsed and thermally treated. Small pore size was observed for treated films by scanning electron microscopy indicated that dense ZnO particles were removed. Eosin-Y sensitizer was loaded into treated photoanode using re-adsorption technique. The photovoltaic characteristics were investigated under standard light illumination (AM1.5). Short circuit current densities are not much changed for 0-4 min treatment. After then, it is rapidly decreased for 6 min treatment. Open-circuit voltage, fill factor and shunt resistance are increased after treatment. In addition, increased charge transfer resistance indicated that recombination is reduced by KOH solution treatment. The reduced recombination contributes efficient electrons transport through external circuit. These improvements resulting efficiency reached maximum value of 0.72% at 4 min treatment, compared with pristine cell efficiency of 0.64%.

Abstract: The Sn-doped ZnO thin films were deposited on glass and ITO by sol gel Spin Coating technique. The Structural and electrical properties of Sn-doped ZnO thin films were studied and discussed. The Sn-doped ZnO thin film particle sizes were decreased whenever the doping concentration increased. Besides that, the resistivity 7.7 x 10² Ω.cm was obtained at 2 at.% Sn-doped thin films and aligned ZnO nanorod arrays with large surface area were grown on 2 at.% Sn-doped ZnO film. Therefore, dye sensitized solar cell at 2.0 at.% Sn-doped ZnO thin films with aligned ZnO Nanorod arrays have improved in the photocurrent density and conversion efficiency.

Abstract: Among the different ways to improve the performances of light harvesting inside solar cells, multilayer configuration can be used. The bandgap of each single layer will contribute to absorption in a well defined wave-lengths range, enhancing the overall performances. Here, we investigate such performances in the case of solar cells made by two layers: a silicon one, and a SiC-based layer, and show the increasing of electrical working by means of computer simulations. These simulations are based on Finite Difference Time Domain (FDTD) for the optical calculations, on one side, and the Finite Element Method (FEM) for the electrical ones, on the other. The main goal is to show the enhancement of the electrical performances in heterostructure solar cells. In this paper, we investigate the influence of each different structure on the optical and electrical response. Our results show the influence of the device structures, in particular, the enhancement of the UV-ligth absorption inside the solar cell. Moreover, the difference structures allow us to show an improvement in the harvesting charge carrier by the heterojunction.

Abstract: Zinc oxide (ZnO) with various morphologies consisting of nanoparticles with a diameter of approximately 20 nm have been successfully prepared by hydrothermal method from zinc nitrate (Zn (NO₃)₂)/carbamide (CO(NH₂)₂) solution. The morphologies and phase structures of the as-prepared ZnO samples were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD). Results show that the morphologies of the as-prepared ZnO are successively present in broom-like, cabbage-like, chinese cabbage-like, honeycomb-like with the increase of the CO(NH₂)₂ concentration from 0.1 M to 1 M. The photovoltaic performances of dye-sensitized solar cells, based on ZnO with various morphologies as the photoelectrodes, are unobvious. With the morphologies of ZnO evolving, the short circuit photocurrent density (J_sc) increases from 2.35 to 3.72 mA/cm², the fill factor (FF) increases from 0.400 to 0.570, and the corresponding conversion efficiency (η) varies from 0.520 % to 1.200 %. The low η may be due to the formation of the Zn²⁺/dye polymers.

Abstract: TiO₂-ZrO₂ fine binary oxide was firstly prepared by mechanochemical milling process to be homogeneous binary oxide powder. TiO₂-ZrO₂ paste was deposited onto microscopic glass slide by rolling. It was immersed in the Rose solution at different pH levels and annealed at 100°C for 2h. Carbon catalyst obtained from soot and HCl was coated onto another glass slide and it was used as counter electrode. Two glass slides were offset and two binder clips were used to hold the electrodes together. Photovoltaic properties of TiO₂-ZrO₂ cells were measured at different pH levels and it was expected to utilize the dye sensitized solar cells application. The highest efficiency (0.23%) of the dye sensitize solar cell was found to be rose extract at pH level 4.1. The cell exhibited the potential to be a low-cost photovoltaic option.

Abstract: Hexagonal boron nitride (HBN), which has the same crystal structure as graphite, has been used as catalytic material for a counter electrode in dye-sensitized solar cells (DSCs) to investigate its potential application. X-ray diffraction (XRD) has been used to confirm the crystal structure of HBN, scanning electron microscopy (SEM) has been used to characterize the morphology of HBN film on counter electrode, and electrochemical workstation has been employed to obtain the electrochemical impedance spectroscopy (EIS) and corresponding impedance parameters. Results show that the HBN film has rough surface and porous structure with pore size of less than 1 μm. When employed the HBN counter electrode to DSCs, the conversion efficiency (η) is only about a tenth of that of graphite based DSCs. Low efficiency of HBN based DSCs is induced by high charge transfer resistance (Rct) of HBN counter electrode, which means that HBN can hardly provide catalytic activity for the reduction of the triiodide ion. Therefore, the crystal structure is not a crucial factor to select the catalytic material for a counter electrode in DSCs. Moreover, the short circuit photocurrent density (Jsc) and the open circuit voltage (Voc) of device also evidently depend on the characteristics of catalytic material.

Abstract: Fabrication and characterization of fullerene (C₆₀) / dibenzotetrathiafulvalene (DBTTF) solar cells were carried out. Photovoltaic and optical properties of the organic solar cells were investigated. Transmission electron microscopy, x-ray and electron diffraction confirmed that the bulk heterojunction thin films had microstructure of C₆₀ crystal phase in DBTTF amorphous phase. The photovoltaic performance of the bulk heterojunction solar cell would be originated in the extent of electron diffusion across interface around the microstructure. Photovoltaic mechanism was discussed on the basis of experimental results.

Abstract: By applying phosphoric acid in dispersion of fullerene in the fabrication of polypyrrolefullerene photovoltaic cells we present laminated active structure of polypyrrole and subsequent fullerene layers, with two other reference methods to incorporate fullerene: (i) in a physically blended monolayer; and (ii) in a blend from chemical reaction. I-V characteristics show that a blend monolayer cell can display photosensitive effect however without photovoltaics; a bilayer cell displays photovoltaics either in dark or in illumination, with its VOC up to1V and its JSC up to12.5 μA cm-2 under AM1 105 mW cm-2 condition. The results demonstrate that phosphoric acid is effective in dispersion of fullerene as well as combining it with polypyrrole layer in a photovoltaic cell. The effects of phosphoric acid in fabricating a bilayered photovoltaic cell are discussed mainly in terms of H-bonding.

Abstract: For the purpose of developing novel photovoltaic materials and organic photovoltaic devices with good performance characteristics, 5-cyano-2,2′:5′,2″-terthiophene (3T-CN) and 5-cyano -2,2′:5′,2″:5″,2″′-tetrathiophene (4T-CN) were synthesized. The 3T-CN and 4T-CN was donor-acceeptor type oligothiophene derivatives with liquid crystal properties. The rigid and flexible photovoltaic devices were fabricated using 3T-CN, 4T-CN and 3,4,9,10-perylenetertracarboxylic dianhydride (PTCDA). Comparision of the rigid device based on 4T showed that both rigid device glass-ITO/4T-CN/PTCDA/Al and flexible device PET-ITO/4T-CN/PTCDA/Al had higher short circuit current density (Isc) and power conversion efficiency (PCE) than that of glass-ITO/4T /PTCDA/Al. The -CN group played an important role in increasing Isc and PCE. It is due to that the mesogenic properties of 4T-CN, which enhances the efficiency by promoting forward interfacial electron transfer.