The Research Of Hydrogenated Nanocrystalline-Amorphous Silicon Thin-Film Solar Cells

Environment pollution and energy source shortage are becoming serious for the current society and sustainable developement, and the exploitation of clean power and renewable energy resources becomes the urgent problem. As an inexhaustibility and green energy, solar energy provides a promising prospect.Solar electricity is the technology of converting sunlight directly into electricity. At present, most solar cells in commercial are bulk crystalline silicon solar cells and amorphous silicon solar cells. The cost of bulk crystalline silicon solar cells is very high. The amorphous silicon solar cells has S-W effect. The challenge problems for these solar cells and other compound thin film solar cells are the life span, stable and environmental protection in the processes of the solar cell fabrication and the material itself. The most promising activity in the thin-film field appears to be occurring with a new wave of silicon-based films in their amorphous, microcrystalline and polycrystalline phases.Hydrogenated nanocrystalline amorphous silicon (na-Si:H) thin film is a two phases mixed material, which composes of nano-scaled silicon grains embedded in Si:H amorphous tissues. Because of its super optoelectronic properties, more and more people begin to study na-Si:H thin film. The na-Si:H thin film is also an super material for solar cell because it has no S-W effect compared with the a-Si:H solar cell. The optical band gap(Egopt) of na-Si:H can be tuned by the crystallization ratio(Xc) and the nanocrystalline grain size(D), so we prepared the na-Si:H solar cells according to the requirement of optical energy band.The thesis investigated the electronic properties of na-Si:H thin films by HQD, and the stress induced by lattice aberrance with phonon confine model. We prepared na-Si:H thin films by RFS and PECVD. The samples were tested by infrared absorption (IR), atomic force microscopy (AFM), X-ray diffraction (XRD), spectroscopic ellipsometry (SE) and Raman measurements. We studied the relationships between the Egopt with the crystallization ratio(Xc) and the Egopt with the nanocrystalline grain size(D) in na-Si:H thin films. In addition, na-Si:H solar cells with the graded band gap(GBG)was prepared in the various processing parameters. The conversion efficiencies are 11.43%(active area 75.4mm2, AM1.5,1000W/m2, 25℃) and 9.82%( active area 121.2mm2, AM1.5,1000W/m2, 25℃) respectively, and prepared na-Si:H/c-Si hetero-junction solar cells, its conversion efficiency is 13.80% and 13.50% (aperture area 800mm2,AM1.5,1000W/m2, 25℃). It is obvious that na-Si:H is a promising material for the next generation of stable, mass production and high efficiency thin film soalr cell. The na-Si:H solar cells are very potential compared with the crystalline silicon cells.In Chapter 1 and Chapter 2, we discussed the importance of developing solar electricity, and introduced the structure, photo-electric characteristic of na-Si thin films, preparation methods and the mechanism of electrical conduction, then analysed the difference between computation and experiments of na-Si:H solar cells.In chapter 3, we simulated na-Si:H pin solar cells by AMPS1D software, and gave the optimal thickness of i layer for na-Si:H pin solar cells, and provided the base for preparing na-Si:H pin solar cells in the Lab.In Chapter 4, we analysised the structural characteristic and optoelectronic properties of na-Si:H thin films prepared by RFS. The samples were tested by IR, AFM, XRD, SEM, SE and Raman measurements. The results revealed that the H2 plays a key role in the grain size of na-Si:H thin films. At last, we discussed the relationship between the stress of na-Si thin films and H2 ratio.In Chapter 5, we introduced and analysised the structural characteristic and optoelectronic properties of na-Si:H thin films prepared by PECVD. The samples were tested by HRTEM, Raman measurements XRD, Hall. The na-Si/c-Si hetero-junction solar cells prepared by PECVD were fabricated, and investigated its reverse I-V characteristic, and relationship between performance with temperature and light.In Chapter 6, na-Si:H solar cells with the graded band gap have been designed and prepared successfully, and built the energy band model of this solar cells. The spectral response curve of the na-Si:H solar cells with the graded band gap shows that it is superior to amorphous tandem silicon solar cells.In Chapter 7, the creative work in this thesis was summarized, simultaneously, The research direction of na-Si:H cells was also given in the future.