CdTe films were deposited by sputtering technique and were then carried out by CdCl2 treatment. The SEM micrographs show that the grain sizes of the as-deposited CdTe film were normally ranged from 50 nm to 100 nm, and they were recrystallized after CdCl2 treatment to obtain the grain sizes in the range of 1~3 £gm. A new device structure for CdTe thin-film solar cells has been proposed to exceed the cell efficiency of current record. The superstrate structure with the layer sequence of Glass/AZO/ZnO/CdS/CdTe/CI(G)S/Mo compared with the conventional device structure of Glass/FTO/CdS/CdTe/metal contact would have the following advantages:(1) a highly conductive AZO layer combined with a thin undoped ZnO layer will have higher optical transmission than that of FTO; (2) the use of p-type CIS under the CdTe layer with the same conductivity type can extend the light absorption to longer wavelength range (the band gaps of CdTe and CIS are 1.45eV and 1.04eV, respectively); (3) the proper addition of Ga to CIS may form CIGS quaternary compounds with a bandgap gradient which produce an electric field in the neutral region of a p-n junction to reduce the carrier recombination; (4) the use of Mo contact to CI(G)S is quite stable as compared with the metal contact normally used for p-CdTe. AMPS-1D simulation had been applied to evaluate the newly designed device structure and the results indicated a great improvement in device performance, i.e. the cell efficiency could exceed 20%. The I-V curve of a CdTe solar cell using the new device structure showed a nearly linear characteristic indicating the failure to form a p-n junction. We speculated that Cu might diffuse through the CdTe layer to the depletion region of the p-n junction formed at the CdS/CdTe interface. This would cause the junction failure. Based on the calculation on the Cu diffusion during the deposition of CIS layer at different temperatures even as low as 150˚C, it always had the chance to diffuse through the CdTe layer. An alternate device fabrication process was the use of the substrate structure for preparing CdTe solar cells, i.e. Glass/Mo/CIS/CdTe/CdS/ZnO/AZO/Al. However, the desired diode behavior was not observed until the thickness of CdTe layer was cut down to 10 nm. The electrical properties of that particular solar cell is the following:Voc=0.36V, Isc=4.991mA/cm2, F.F.=25.3%, efficiency=0.472%. It is probably that the lattice mismatch between CIS and CdTe is large that may cause the formation of interfacial defects and the reduction of photo excited carriers through the recombination processes. The annealing processes had been conducted in order to promote the interdiffusion between CdTe and CIS and minimize the lattice mismatch. However, the films peered off after annealing. Further experiments should be done to solve this problem.

In the present work, deformation behavior, texture and microstructure evolution of commercially pure titanium (CP Ti) are investigated by electron backscattered diffraction (EBSD) after compression tests at elevated temperatures. By analysing work hardening rate vs. flow stress, the deformation behaviour can be divided into three groups, viz. three-stage work hardening, two-stage work hardening and flow softening. A new deformation condition map is presented, dividing the deformation behavior of CP Ti into three distinct zones which can be separated by two distinct values of the Zener-Hollomon parameter. The deformed microstructures reveal that dynamic recovery is the dominant deformation mechanism for CP Ti during hot working. It is the first time that the Schmid factor and pole figures are used to analyse how the individual slip systems activate and how their activities evolve under various deformation conditions. Two constitutive equations are proposed in this work, one is for single peak dynamic recrystallization (DRX), the other is specially for CP Ti deformed during hot working. After the hot compression tests, some stress-strain curves show a single peak, leading to the motivation of setting up a DRX model. However, the examinations of EBSD maps and metallography evidently show that the deformation mechanism is dynamic recovery rather than DRX. Then, the second model is set up. The influence of the deformation conditions on grain size, texture and deformation twinning is systematically investigated. The results show that {10-12} twinning only occurs at the early stage of deformation. As the strain increases, the {10-12} twinning is suppressed while {10- 11} twinning appears. Three peaks are found in the misorientation frequency-distribution corresponding to basal fiber texture, {10-11} and {10-12} twinning, respectively. A logZ-value of 13 is found to be critical for both the onset of {10-11} compressive twinning and the break point for the subgrain size. The presence of {10-11} twinning is the key factor for effectively reducing the deformed grain size. The percentage of low angle grain boundaries decreases with increasing Z-parameter, falling into a region separated by two parallel lines with a common slope and 10% displacement. After deformation, three texture components can be found, one close to the compression direction, CD, one 10~30° to CD and another 45° to CD. / QC 20100819