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This paper reports the heat dissipation ability of nanocrystalline diamond (NCD) film used as an insulator in interconnection layers. The thermal resistance is used as an evidence for evaluating particular ability. There are two points to measure, that is to say, the temperature in the active Si region and that of the nearest point at the top of the insulating film. We used a thin film Si resistor covered with NCD or silicon dioxide (SiO2) on a silicon on insulator substrate. The NCD film was deposited by microwave-plasma chemical vapor deposition at 400 °C, while the SiO2 film was deposited by plasma-enhanced chemical vapor deposition at 350 °C. The thickness of the NCD film was 600 nm, while that of the SiO2 film was 300 and 500 nm. The aluminium (Al) was deposited by sputtering and patterned on the top of the insulating-film. Heat was applied to the resistor by directly applying electricity to the resistor. The temperature of the Si resistor and Al was determined from the resistance change. It was found that the thermal resistance of NCD film was approximately 14 % less than that of SiO2 film, leading to the reduction of the thin-film Si temperature by 20 °C, even though it was thicker than 100 nm.

Cu 2 ZnSnS 4 (CZTS) thin films were prepared by sulfurizing precursors deposited by electroplating. The precursors (Cu/Sn/Zn stacked layers) were deposited by electroplating sequentially onto Mo-coated glass substrates. Aqueous solutions containing copper sulfate for Cu plating, tin sulfate for Sn plating and zinc sulfate for Zn plating were used as the electrolytes. The precursors were sulfurized by annealing with sulfur at temperatures of 300, 400, 500 and 600 °C in an N 2 gas atmosphere. The X-ray diffraction peaks attributable to CZTS were detected in thin films sulfurized at temperatures above 400 °C. A photovoltaic cell using a CZTS thin film produced by sulfurizing an electroplated Sn-rich precursor at 600 °C exhibited an open-circuit voltage of 262 mV, a short-circuit current of 9.85 mA/cm 2 and an efficiency of 0.98%.

The low cost, environmental harmless Cu 2 ZnSnS 4 (CZTS)-based thin film solar cells are fabricated by using abundant materials. The CZTS film possesses promising characteristic optical properties; band-gap energy of about 1.5 eV and large absorption coefficient in the order of 10 4 cm − 1 . All constituents of this CZTS film, which are abundant in the crust of the earth, are non-toxic. Therefore, if we can use CZTS film practically as the absorber of solar cells, we will be free from both of the resource saving problem and the environmental pollution. In our CZTS project, CZTS absorber films were prepared by two independent techniques. One is three rf sources co-sputtering followed by annealing in sulfurized atmosphere. The latest conversion efficiency of over 6.7% was achieved by this technique. The other is co-evaporation technique. CZTS films were grown on Si (100) by vacuum co-evaporation using elemental Cu, Sn, S and binary ZnS as sources. XRD patterns indicated that the polycrystalline growth was suppressed and the orientational growth was relatively induced in a film grown at higher temperatures. In this presentation, the development of CZTS-based thin film solar cells will be surveyed.

Stacked precursors of Cu, Sn, and Zn were fabricated on glass/Mo substrates by electron beam evaporation. Six kinds of precursors with different stacking sequences were prepared by sequential evaporation of Cu, Sn, and Zn with substrate heating. The precursors were sulfurized at temperatures of 560 °C for 2 h in an atmosphere of N2 + sulfur vapor to fabricate Cu2ZnSnS4 (CZTS) thin films for solar cells. The sulfurized films exhibited X-ray diffraction peaks attributable to CZTS. Solar cells using CZTS thin films prepared from six kinds of precursors were fabricated. As a result, the solar cell using a CZTS thin film produced by sulfurization of the Mo/Zn/Cu/Sn precursor exhibited an open-circuit voltage of 478 mV, a short-circuit current of 9.78 mA/cm2, a fill factor of 0.38, and a conversion efficiency of 1.79%.

Cu(In,Ga)S 2 crystals have been grown from the melt using constituent elementary substances as sources. The chalcopyrite structure was confirmed by powder X-ray diffraction patterns. Lattice parameters a and c changed almost linearly corresponding to the composition ratio between In and Ga. The amplitudes of photo-acoustic signals changed greatly near the band gap energies. This phenomenon is due to the changes of the absorption coefficient. Band gap energies, estimated from the photo-acoustic spectra, also showed continuous change with the composition.

Cu(In,Ga)S 2 films were grown on Si(100) by vacuum evaporation using the constituent elementary substances as sources. It was found from X-ray diffraction studies that orientational growth occurred in a limited temperature region. The chalcopyrite structure was confirmed by studying RHEED patterns. The existence of c -axis growth, two kinds of a -axis growth and four kinds of {112} twins which can be classified as two symmetrical pairs is proposed.

Cu2ZnSnS4 (CZTS) thin films were prepared by sulfurization of electrodeposited Cu-Zn-Sn precursors. The Cu-Zn-Sn precursors were deposited on Mo-coated glass substrates in a one-step process from an electrolyte containing copper (II) sulfate pentahydrate, zinc sulfate heptahydrate, tin (II) chloride dehydrate and tri-sodium citrate dehydrate. The precursors were sulfurized by annealing with sulfur at temperatures of 580 °C and 600 °C in an N2 atmosphere. X-ray diffraction peaks attributable to CZTS were detected in the sulfurized films. Photovoltaic cells with the structure glass/Mo/CZTS/ CdS/ZnO:Al/Al were fabricated using the CZTS films by sulfurizing the electrodeposited precursors. The best photovoltaic cell performance was obtained with Zn-rich samples. An open-circuit voltage of 540 mV, a short-circuit current of 12.6 mA/cm2 and an efficiency of 3.16% were achieved. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The development of environment friendly type thin film solar cell Cu2ZnSnS4 (say CZTS-type) fabricated using abundant materials is introduced in this paper. Three RF sources co-sputtering continued with vapor phase sulfurization method (inline-type vacuum apparatus) is utilized. Those processes were sequentially done in different apparatus in our previous work. In this study, an inline-type vacuum apparatus is firstly introduced to acquire higher quality of CZTS films. Inductively Coupled Plasma Spectroscopy (ICPS) is used to analyze the minute material composition of CZTS thin film solar cell. By optimizing the material composition, 5.74% of conversion efficiency is obtained. It is the best data for CZTS-type thin film solar cells at present.

CuGaS 2 films have been grown on (1 0 0) GaAs and GaP wafers by the vacuum evaporation technique using constituent elementary substances as sources. RHEED patterns of the films that use 〈0 1 1〉 azimuths in a substrate show two different patterns in mutually orthogonal directions. In one direction, the observed pattern is a single pattern which illustrates that CuGaS 2 grows in the [0 0 1] orientation direction (the c -axis growth). In another direction, however, additional patterns appeared. This phenomenon indicates that one pair of the 180 rotated {1 1 2} twins exists in addition to c -axis growth in a film, and it also indicates that additional orientations except for c -axis growth are reduced in films grown on compound substrates as compared with ones on (1 0 0) Si.

AgGaS 2 thin films have been prepared by the vacuum evaporation method on GaAs(100). Elemental silver, gallium and sulfur have been used as the source materials. The X-ray diffraction and the RHEED analysis show that the good epitaxial films with the c -axis normal to the GaAs(100) substrate are grown for the stoichiometric composition. The non-stoichiometric films show that the two different orientational types coexist in a film. One type is that the c -axis is normal to the substrate. The other type is that the c -axis is parallel to the two a -axes of GaAs.

The vacuum evaporation technique, using constituent elementary substances as sources, has been examined in growing CuGaS2 on (100) Si wafers. The RHEED patterns of the grown films show that two different orientational types coexist in the film, i.e., the type with the c-axis of CuGaS2 along the two a-axes of the Si substrate and the type with the c-axis normal to the substrate surface. Additional spots are observed in the RHEED patterns, which propose that the {112} twin 180° rotated about 〈221〉 also exists in the film.

Cu2ZnSnS4 (CZTS) thin films were fabricated by using three RF co-sputtering continued with sulfurization method. The new type of thin film solar cells using CZTS as an absorber consists of buffer-layer and window-layer on CZTS films that were fabricated on a Mo-coated Soda Lime Glass (SLG) substrate. It was confirmed that CZTS solar cells with high conversion efficiency existed in a relatively narrow composition region. In this paper, the fabrication method of CZTS-based thin film solar cells in our laboratory was stated briefly and the influence of the composition ratio on the photovoltaic properties were presented. Furthermore, the properties of a genuine non-toxic solar cell using a Cd-free buffer-layer were introduced.

The improvement in the quality of ZnO:Al films grown on glass substrates was investigated using a sputtered buffer layer inserted between a glass substrate and a ZnO:Al CVD film. ZnO:Al layers were grown at 773 K using dimethylzinc (DMZn), trimethylaluminum (TMAl), and high-temperature H2O generated by a catalytic reaction as zinc, aluminum, and oxygen sources, respectively. The electron mobility increased by approximately 20 cm2 V−1 s−1 with the use of a buffer layer with a thickness of approximately 40 nm. In addition, the optical transmittance in the wavelength range of 380–600 nm increased with the insertion of the buffer layer. For the growth of ZnO films on a sputtered buffer layer, the average surface roughness was reduced, and as a result the fluctuation in crystal orientation along the c-axis became smaller than that of the film grown directly on the glass substrate by the proposed CVD. This resulted in improvements in the optical transmittance and electron mobility of the ZnO:Al films.