| Energy supply problem and ecological consideration have taken over as main driving forces in promoting alternative energy sources, in particular, PV solar energy. The cost reduction and efficiency improvement are very essential to push the application of solar cell. Hydrogenated microcrystalline silicon (μc-Si:H) has been confirmed as a promising PV absorber material, owing to its low cost, high convension efficiency and good stablility. Flexibleμc-Si:H thin film solar cell (FMTFSC) can be manufactured in large scale through roll-to-roll process with low cost, and it is more convenient and widely used. However, there are still some disadvantages such as low absorption coefficient, interface interdiffusion, bad structural homogeneity, which restrict the developement and application of FMTFSC to some extent. The scope of this paper is to solve the problems mentioned above.Firstly, the study on the preparation of Al back electrode with texture surface was carried out on PI substrate. The mechanism of the formation of texture surface was discussed. Secondly, the AINi alloy was firstly used as the barrier layer in FMTFSC and the results showed that it had a good barrier effect on the interdiffusion of Al and Si film. Thirdly, a new two-step method was proposed, which can effectively improve the uniformity ofμc-Si:H thin film. At last, the optimism deposition parameters of tramsparent ZnO:Al were obtained and the variation mechanism of film structure and the influence of this variation on the properties were discussed. These studies provide abundant experimental and theoritical fundations to the solution of those problems in FMTFSC. The results of this paper are showed below:1. Study on the growth of texture surface of Al electrode and its mechanismAl electrode with texure suface was prepared at room temperature by r. f sputtering. The film deposited under high power (300-450W) had high depositon rate, low resistivity and high diffuse reflectivity. The average diffuse reflectivity of the film can be as high as 70%. The effect of deposition parameters on the shape and size of three-dimensional surface islands was discussed. High deposition rate, low working pressure and oblique incident can promote the particle kinetic energy and mobility on the film surface, which is favorable for the aggregation and growing up of surface islands. The columnar morphology of the surface is mostly ralated to the oblique incident and the release of strain energy during depositon. It is easy to prepare texture surface with this method and avoids the influence of high temperatur on plastic substrate, which illustrates a good prospect of application. 2. Study on the AlxNiy alloys as the diffusion barriers between Al and SiAlxNiy thin films were prepared using r. f. magnetron co-sputtering technology. The chemical compositions of the films were controlled through adjusting the sputtering powers on Al and Ni targets. When the ratio of Al and Ni were 1:1 and 2:3, the structures of films were polycrystalline. Compared to Ni, AlxNiy alloys had the merits of good oxidation resistance and chemical stability. Among them, the AlNi film had the minimum sheet resistance, the best barrier performance to the interdiffusion between Al and Si, and the lowest contact potential with Si film. Thus, the AlNi film was more suitable in using as the barrier layer of flexible Si based thin film solar cells.3. Study on the uniformity ofμc-Si:H thin filmsBase on the ECR-PECVD technology, a new two-step growth method was proposed to deposite theμc-Si:H thin film without incubation layer. A very thin film in thickness of～15 nm was firstly deposited using ECR-PECVD and then it was treated with H2 plasma to get the seed layer, after that, normal parameters were used to depositμc-Si:H film on it. The uniformity in the longitudinal direction of theμc-Si:H thin film can be improved using this new two-step growth method, and the crystalline volume fraction of the films would be increased from 24.3% to 50.7%.. The mechanism of hydrogen-induced crystallization of amorphous silicon was discribed according to experimental results. And the growth model of the two-step growth method was proposed in this work.4. Preparation and structure analysis of ZnO:Al thin filmsAl-doped ZnO (ZnO:Al) thin films with high c-axis preferred grain orientation were deposited by radio frequency magnetron sputtering. The variation of structure were discussed, and were correlated to the electical properties of ZnO:Al films. The film, deposited at sputtering power of 100 W, working pressure of 0.3 Pa and substrate temperature of 250℃performs high crystalline quality and good properties. The film exhibits a transmittance of about 90% in the visible region and a resistivity of 3.1×10-3Ω·cm. The further studies on structure were performed through GID-XRD and HRTEM. The results show that the interplanar spacings are enlarged in other directions besides the direction perpendicular to the substrate, Apart from the film stress, the doping concentration and the doping site of Al play an important role in the variation of lattice parameters. When the doping content of Al is 2 wt. %, the redundant Al atoms are incorporated into the interstitial position, which leads to the increase of crystal lattice. This viewpoint is also proved by first-principle calculations. |
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