CIGS Absorbers Prepared By Magnetron Sputtering And Their Photoelectric Properties

The impending exhaustion of fossil fuels and serious environmental pollution problems are placing increasing demand on clean and sustainable energy for human society. Energy harvested from sunlight is an ideal energy utilization manner due to its inexhaustible and clean nature. Among all the sunlight utilizations, photovoltaic devices can convert sunlight to electricity, which is the most direct and efficient manner for energy harvest. In recent years, there is a growing interest shifts towards thin-film solar cells due to their low cost, low transportation costs and high production rate. Among all the thin film solar cells, polycrystalline CIGS absorber materials have been considered as one of the most promising candidates for the manufacturing of low-cost thin film photovoltaics. As we know, CIGS was developed based on CIS. When In substituted by an appropriate amount of Ga, polycrystalline CuIn_1-xGa_xSe₂ absorbers can be prepared and its band gap can be adjusted by changing the ratio of In and Ga.Various methods are employed to prepare CIGS absorbers, such as evaproation, magnetron sputtering, electrodeposition, selenization of metal pre-layer, spray pyrolysis and molecular beam epitaxy. Among them, new record power conversion efficiency?PCE? has been achieved on the laboratory scale by using the classic three-stage co-evaporation. During the evaporation, the film composition can be controlled effectively. However, the evaporation technique is relatively complicate and can not ensure the reproducibility of the film quality. On the other hand, it seems unsuitable for mass production and due to its low reaction rate and difficulity in large-scale preparation. In the industrial and commercial view, it is more practical and significant to develop new technique to fabricate low-cost and high efficient CIGS thin film solar cells.Aimed to explore the process for the fabrication of a low-cost and high-performance CIGS thin film materials, CIGS thin film photovoltaic material was prepared by magnetron sputtering in this work. The growth mechanism of thin films, defects control mechanism and the relationship between microstructure and the photovoltaic performance were investigated systematically. Stoichiometric Cu-In-Ga alloy material was deposited by co-sputtering of Cu_0.8Ga_0.2 and In targets simultaneously to form a dense and compact alloy prefabricated layer, then the homogeneous surface morphology and better crystallinity CIGS thin-film photovoltaic material was obtained by the rapid thermal vacuum selenization process. This process avoids the usage of highly toxic H₂Se, which is simple and easy to control. Through which, high quality CIGS absorber layer with exact stoichiometry can be obtained. Mainly, four parts of research works were carried out in this paper.?1? Preparation of Cu-In-Ga metallic preformed layer.The Cu/In/Ga precursor films were deposited on the soda lime glass?SLG? substrate by two independent direct current?DC? sputtering sources employed for the co-sputtering of Cu_0.8Ga_0.2 and In targets simultaneously, while the base pressure of the deposition chamber was4×10^-4 Pa and the work pressure was kept at 0.5Pa. High-purity argon?99.999%? was used as the working gas. Prefabricated metal layer with appropriate composition and better combined surface was obtained by adjusting the working pressure and the relative sputtering powers of CuGa target and In target. The thickness of the alloy precursor layer is about 600nm when the DC sputtering power was Cu_0.8Ga_0.2 40W-In 80 W, co-sputtering time was 50min.?2? The post-selenization of the co-sputtered Cu/In/Ga precursor film.A rapid thermal process?RTP?, selenium powder and a sealed stone cartridges were performed for the post-selenization of the co-sputtered Cu/In/Ga precursor film under 60 mtorr vacuum pressure, then the samples were rapidly heated to 600 oC within 40 seconds and kept at that temperature for 30 min. Finally, the absorbing layer with good crystallinity and absorption properties was obtained, and the thickness of the absorbing layer is about 1.6 ?m.?3? The structural and optical properties of CIGS abosrbers.The surface morphologies, cross-sectional morphologies and Raman spectroscopy?Raman? analysis, XRD, UV-visible absorption analysis of the samples were investigated, the results show that the absorbing layer thin-film we prepared is of good crystallinity, with good absorption characteristics in the visible range, and does not have the copper selenide, indium selenide miscellaneous binary phase, only pure CIGS chalcopyrite phase structure exists.?4? The performances of CIGS thin film solar cells.On the basis of preliminary research analysis, we applied the CIGS absorbing layer prepared by co-sputtering technique and vacuum post-selenization method to thin film solar cell device. Efficiency of the of the solar cell device reaches 9.62%, as the open circuit voltage is 427.3mV, the maximum current density is 38.90mA, and the fill factor FF is equal to 57.87%. The results showed that the prepared CIGS absorber layer has good photoelectric propertie.