Preparation And Properties Of Flexible Polycrystalline Silicon Film

With the approaching of global energy crisis and energy conflicts, renewable energy especially solar energy, is changing the global energy structure and energy sources. Applied to all kinds of solar photovoltaic cells, because of the characteristics with low consumption, low cost, high stability, and the effect of microelectronic devices, the polycrystalline silicon (Poly-Si) film solar cells are received widespread attention. Traditional Poly-Si film solar cells were mostly prepared on cheap substrates, such as stainless steel, glass, and graphite etc., they must be processed into the hard solar cell panels like plate shape, this malpractice limits the widely uses of Poly-Si film solar cells. Flexible polycrystalline silicon film solar cells are prepared on flexible substrate materials, have important scientific value and application prospect. The flexible Poly-Si film solar cells unbreakable, light weight, and the most important characteristic is can be folded, and curled, is conducive to industrialization. Then, the key to increase the photoelectric conversion efficiency of flexible Poly-Si film solar cells is to prepare high-quality flexible Poly-Si film.In this paper, based on the outstanding characteristics of graphite, and unique feature of flexible graphite paper such as high temperature, similarly thermal expansion coefficient with silicon, and flexible etc., the flexible graphite paper is acted as substrate material of flexible Poly-Si film solar cell. Meanwhile, based on the mismatch of thermal expansion coefficient and lattice constant between flexible graphite paper substrate and Poly-Si film, the formation of poly-Si thin film seed layers have a key role to subsequent poly-Si films, after the crystallization of amorphous silicon thin films on heterogeneous substrates. Meanwhile the poly-Si thin film seed layers can prevent the diffusion of impurities.In this paper, flexible poly-Si films were fabricated on flexible graphite paper substrate by magnetron sputtering (MSC), rapid thermal annealing (RTA), and convection-assisted chemical vapor deposition (CoCVD) technology, and the flexible poly-Si films with the introduction of ZnO transition layer. This paper systematic studied the influence of RTA technology on crystallization condition about flexible poly-Si films; and studied the effects about preferred orientation and crystallization degree of the flexible poly-Si films when introduced the ZnO transition layer. The flexible poly-Si films were analyzed and characterized by Electron Microscope (SEM), X-ray diffraction(XRD), Raman spectra, and Microwave Reflectance Photoconductivity Decay (μ-PCD). The main conclusions were as follows:1. On the flexible graphite paper substrate, MSC and RTA techniques were used to prepare the flexible poly-Si thin film seed layer samples. Firstly, the Si thin film samples were fabricated on flexible graphite paper substrate by MSC. XRD and Raman showed that the directly deposited silicon films were amorphous. After annealed by RTA method, the amorphous silicon samples turned into crystalline state. Meanwhile, the flexible poly-Si thin film seed layers which deposited directly had highly (220) preferred orientation.2. On the poly-Si thin film seed layers, the flexible poly-Si film samples were prepared by CoCVD techniques. SEM, XRD, and Raman indicted that, the flexible poly-Si films had high quality, and had highly (220) preferred orientation. Meanwhile, the mechanisms that the (220) preferred orientation of flexible poly-Si films were analyzed preliminarily.3. In this paper, ZnO transition layer was introduced as impurity diffusion barrier layer between flexible graphite paper substrate and silicon film. First, on the flexible graphite paper substrate, before the prepared of amorphous silicon film, the ZnO transition layer was prepared by MSC, then through the RTA, and CoCVD, the flexible poly-Si film was prepared. SEM, XRD, and Raman showed that, by the introduction of ZnO transition layer, the flexible poly-Si film had highly (400) preferred orientation. The transformation of (400) preferred orientation is convenience to the subsequent production of solar cells. And meanwhile, the mechanisms of flexible poly-Si films with ZnO transition layer which had (400) preferred orientation were analyzed.4. Based on the SEM, XRD, Raman tests, compared with the samples without ZnO transition layer, the flexible poly-Si films with ZnO transition layer could improve the crystal quality of flexible poly-Si films. Meanwhile, μ-PCD spectra showed that the introduced of ZnO transition layer can improve the uniformity of minority carrier lifetime of flexible poly-Si films.