Meng Cao

Substrate temperature and thickness dependence of properties of boron and gallium co-doped ZnO films

Transparent conducting oxide films of boron and gallium co-doped ZnO (BGZO) were prepared on glass substrates by radio frequency magnetron sputtering at room temperature and 200°C, respectively. The dependence of structural, electrical and optical properties on the thickness and substrate temperature were investigated. All films demonstrated c-axis preferred orientation and showed highly transparent in the visible wavelength region. With the increase thickness and substrate temperature, the grain size of BGZO films increased and the full width at half maximum decreased, the carrier mobility increased and resistivity decreased, which indicated that the crystallinity and conductivity of films were improved. The research also found that the optical band gap (Eg) of BGZO thin films decreased with increased substrate temperature and thickness.

Preparation of Graphene Films and their Applications in Dye-Sensitized Solar Cells

A facile and rapid deposition process is developed for the fabrication of large-area graphene films by scalpel technology using graphene nanopartical as material. Graphite oxide (GO) was synthesized using modified Hummers method. Graphene nanopartical was fabricated by a reducing process in which GO was well reduced by hydrazine hydrate. The crystal structure and photoelectric properties of graphene and graphene films were investigated by X-ray diffraction. The composition of production (GO and graphene) is investigated by Fourier Transform Infrared Spectroscopy (FTIR) and Raman spectroscopy technology. Surface morphology of graphene layers were observed by SEM. Then, the semitransparent conductive films were applied to backside illumination DSSC. As a result, the maximum power conversion efficiency (PCE) is as high as 0.2558% and the fill factor is 30.97%.

Preparation of graphene/polymer composite photocathode for QDSSC

Graphene (rGO) was fabricated by modified Hummers method and a reducing process. Conductive polymer/graphene films were obtained by scalpel technology and used as photocathode in CdS quantum dot-sensitized solar cell (QDSSC). Polymers used in this paper were ethyl cellulose (EC), polyphenyl vinyl (PPV) and polyvinyl butyral (PVB), respectively. The obtained composite films were investigated by X-ray diffraction, Raman spectroscopy technology and scanning electron microscope (SEM). The photoelectric properties of QDSSCs were tested under AM 1.5 irradiation. Test results show that the film performance of the EC/rGO and PPV/rGO photocathode have been improved effectively. Power conversion efficiency (PCE) of the relative QDSSCs under AM 1.5 irradiation were 0.81% and 0.86%, respectively.

Sol-modified ZnO photoanode for dye-sensitized solar cells

Sol-modified ZnO (SM-ZnO) photoanodes for high-efficient dye-sensitized solar cells (DSSCs) were prepared. The influence of sol on the crystallinity and morphology of ZnO films was investigated by x-ray diffraction and scanning electron microscopy (SEM). Compared with unmodified ZnO-based DSSCs, the conversion efficiency of SM-ZnO-based DSSCs increased from 2.03% to 2.83%, which may be attributed to forming a uniformly distributed ZnO nanocrystalline photoanode and exhibiting a more efficient charge-transfer process, as evidenced from SEM and electrochemical impedance spectroscopy. The conversion efficiency was further increased to 3.13% by constructing an SM-ZnO/compact ZnO two-layer photoanode.

Influence of ion-doping on the photoelectric properties of mesoporous ZnO thin films

Sn, Al, Y-doped mesoporous ZnO(doping with 5 at.%) thin films (M-ZnO-5%X, X= (Sn, Al, Y))with regular mesoporous structures were successfully prepared through sol-gel and spin-coating methods, as evidenced from small angle X-ray diffraction (SAXRD) and scanning electron microscopy (SEM). The diameter/d value is about 8 nm calculated by Bragg equation. Influences of ion-doping on the photoluminescence spectra of mesoporous ZnO thin films were investigated. The energy gaps of Y, Al, Sn-doped mesoporous ZnO increase from 3.0 eV (the energy gap of undoped ZnO thin film) to 3.05, 3.08 and 3.15 eV, respectively. Dye-sensitized solar cells (DSSCs) based on Sn, Al, Y-doped ZnO photoelectrodes were structured and the properties of the cells were studied. Compared with undoped ZnO film, M-ZnO-5%Sn film showed higher solar-to-electric conversion efficiency, which may come from the broader absorbance.

Natural dye -sensitized mesoporous ZnO solar cell

Natural dye-sensitized solar cells (N-DSSCs) were assembled using chlorophyll sensitized mesoporous ZnO (based on FTO) as the photoanode and platinum plate as the cathode. The natural dyes (chlorophyll) were extracted from spinach by simple procedure. The absorption spectrum and fluorescence spectrum of chlorophyll were studied. Mesoporous ZnO (m-ZnO) applied to the N-DSSCs was synthesized through hydrothermal method. The structures and morphologies were characterized by X-ray Diffraction (XRD) and diffuse reflection. The results indicated that the samples had an average pore size of 17 nm and the m-ZnO was hexagonal wurtzite structure. The performances of the N-DSSCs were investigated under AM 1.5G illumination. The Voc of the N-DSSCs was about 480mv, and the Isc was about 470μA. The performance of the N-DSSCs could be further improved by adjusting its structure.

Preparation and properties of low-cost graphene counter electrodes for dye-sensitized solar cells

With the advantages of excellent electrical properties, high catalytic activity and low-cost preparation, Graphene is one of the most expected carbon materials to replace the expensive Pt as counter electrodes for dye-sensitized solar cells (DSSCs). In this paper, graphene counter electrodes were obtained by simple doctor-blade coating method on fluorine tin oxides (FTOs). The samples were investigated by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscope (SEM). Then the low-cost graphene electrodes were applied in typical sandwich-type DSSCs with TiO2 or ZnO as photoanodes, and their photoelectric conversion efficiency (η) were about 4.34% and 2.28%, respectively, which were a little lower than those of Pt electrodes but much higher than those of graphite electrodes. This law was consistent with the test results of electrochemical impedance spectroscopy (EIS). Low-cost graphene electrodes can be applied in DSSCs by process optimization.

1Effects of sputter power, gas pressure and substrate temperature on the structure and optical properties of CdS thin films

CdS is deposited on transparent conductive oxide (TCO)-coated glass substrate by radio frequency (r.f.) magnetron sputtering method. The X-ray diffraction (XRD) measurements revealed that CdS films were polycrystalline with the hexagonal wurtzite structure present only. The same conclusions as described below are arrived at from the photoluminescence (PL) and UV-vis absorption spectra measurements. When the power increases or the gas pressure decreases, the grain size and the film thickness increases, and then lead to the increase of stress in films which results in the decrease of energy band gap. The substrate temperature also has an effect on the strain in the films.

Preparation and photoelectric properties of poly(phenylethanone)- manganese phthalocyanine derivative for polymer photovoltaic cells

A novel soluble poly(phenylethanone) derivative grafted with tetra-acyl-chlorich manganese phthalocyanine (TACMnPc) was synthesized via esterification and characterized by electronic absorption spectrum and fluorescence spectra. The derivative (PPE-MnPc) exhibits high solubility and excellent film-forming property. Electronic absorption spectrum of the polymer exhibits a Q-band peak positioned at about 736 nm, which is obviously red shifted compared with 2, 9, 16, 23-tetra-carboxyl manganese(II) phthalocyanine (TCMnPc). PPE-MnPc films were prepared by dip-coating technology. Photoconductivity of PPE-MnPc films was characterized by current-voltage measurement. At bias voltage of 20 V, photoconductivity of the film was 6.8×10-9 S and dark conductivity was 7.5 ×10-10 S. The electrical conductivity of PPE-MnPc films under irradiation was nine times higher than that in the dark, which indicated that PPE-MnPc had a good photovoltaic response.