Papers by Keyword: Polycrystalline Silicon

Abstract: This research uses a transmission electron microscopy (TEM) approach to analyze the deterioration of the crystallinity of poly-Si placed on the textured substrate. On the textured substrate, we created a poly-Si photovoltaic film with a RMS roughness, σ of 64 nm. Based on TEM findings, we discovered that growth collisions are present in the poly-Si photovoltaic layer that was deposited on the textured substrate with an RMS roughness, σ of 64 nm. The growth direction of the columnar-like grains tends to be perpendicular to the slant slope of the textured substrate. The diagonally oriented columnar growth collisions may be seen clearly at V-shaped formations in the textured substrate. There are also cavities and fissures that were created by the collisions. There are also cavities and fissures that were created by the collisions. The crystallinity of poly-Si grown above the V-shape structure has worsened, as compared to poly-Si grown above the Λ-shape structure, according to the TEM and SAED pictures.

Abstract: Desert locations are of great interest for photovoltaic applications due to their high solar availability. However, in these regions, harsh climatic conditions can have a significant impact on the performance and reliability of photovoltaic panels. In the present study, the effect of temperature on the performance of the two PV technologies, Polycrystalline Silicon (pc-Si) and thin film Cadmium Telluride (CdTe), in a hot desert climate was investigated. To accomplish this, one module from each technology was installed in Benguerir city and exposed to outdoor conditions during the hot season of the year (May to October). Results indicate that although pc-Si exhibits higher module efficiency than CdTe, the latter was less temperature-sensitive under high ambient temperature values. In fact, during the monitoring period, CdTe technology demonstrated lower module temperatures than pc-Si, with a daily average temperature deviation of 1.75°C. In addition, the performance ratio and conversion efficiency for pc-Si were reduced by 8.7% and 1.35%, respectively, when the daily average ambient temperature increased from 25°C to 40°C. While with the thin film CdTe technology, the decline in these performance parameters did not exceed 6.8% and 1.05%, respectively.

Abstract: We investigate the characteristics of polycrystalline Silicon (poly-Si) thin films for solar cells produced by very high frequency (VHF) plasma enhanced chemical vapor deposition using a conductive scanning probe microscope (SPM). We measure the surface morphology and local current images are simultaneously of the poly-Si layers with a thickness, d=2 mm, formed on textured Ag/SnO₂/glass in the range of RMS based-textured substrate (a) s=85nm, (b) s=42nm and (c) s=2nm respectively. Influences of the substrate texture on the crystal growth as well as the local current flow are discussed. Where we found that the average of local current proportional with crystallinity, where the poly-Si layer that has rich crystallinity indicated low conductivity that yield high local current.

Abstract: We demonstrated efficient crystallization of amorphous Si films induced by their direct irradiation with near-IR femtosecond laser pulses coming at sub-MHz repetition rate. Comprehensive analysis of morphology and composition of the laser-annealed film by atomic-force microscopy, Fourier-transform IR, Raman and energy dispersive X-ray spectroscopy as well as numerical modeling of optical spectra confirmed efficient crystallization of amorphous Si and high-quality of the obtained films opening pathway for applications in thin-film solar cells, transistors and displays.

Abstract: To integrate circuits into the organic light emitting diode displays, it is necessary to fabricate polycrystalline silicon (poly-Si) based thin-film transistors (TFTs) on the glass substrates. In this work we investigated the correlation between the electrical characteristics and the poly-Si morphology of the excimer laser annealed (ELA) TFTs in ultralow oxygen concentrations (~ ppm). The main feature of ELA poly-Si films is the protrusion at grain boundaries that makes the film surface rough. The surface roughness increases with an increasing oxygen concentration during the laser annealing and degrades the TFT characteristics in the on-state as well as the breakdown voltage of the gate insulator, while the off current is independent of process conditions. This result is attributed to the increased oxygen incorporation in the film in the case of an ELA process. Since oxygen increased the defect density in the polysilicon bandgap, controlling the oxygen concentrations in the process chamber helped to improve the performance of the ELA poly-Si TFTs. Based on these results, we discuss the relationship between performance of active matrix organic light emitting display panels and oxygen concentrations during ELA.

Abstract: A simple theoretical model and resistor fabrication for calculating the resistance of a polycrystalline silicon thin film is presented. The resistance value for poly-resistor is perfomed in terms of polysilicon thickness and its total area. The KrF excimer laser micromachine is used in assisting the resistor formation for a low pressure chemical vapor deposition (LPCVD) based polysilicon. Laser micromachine with three main parameters is used to aid the fabrication of the poly-resistor; namely as the pulse rate (i.e. number of laser pulses per second), laser beam size and laser energy. These parameters have been investigated to create the isolation between materials and also to achieve the desired poly-resistor shape. Preliminary results show that the 35 um beam size and 15 mJ of energy level is the most effective parameter to produce the pattern. Poly-resistor formation with 12 and 21 number of squares shows the total average resistance of 303.52 Ω and 210.14 Ω respectively. The laser micromachine process also significantly reduce the total time and number of process steps that are required for resistor fabrication.

Abstract: Directional solidification is a main method of mc-Si production for solar cells. The main impurities in MS-Si are oxygen and carbon. In this paper, an improved furnace was designed to reduce the carbon and oxygen impurity in MS-Si at unidirectional solidification process. Simulation results showed that the flow pattern of impurity gas at the top of the silicon melt significantly improved under the small cover conditions and the impurity gas eddy currents was also avoided. Experimental results show that the carbon and oxygen content inside the ingot were both significantly reduced when the eddy currents inside the crucible was suppressed and the average minority carrier’s lifetime of silicon block was significantly increased under the conditions of small cover plate. Meantime, the average cell efficiency of ingot was more than 17% under small cover condition which is significantly higher than that of the ordinary ingot.

Abstract: The tribo-electrochemical performance of polycrystalline silicon was studied by Tafel polarization curves and electrochemical impedance spectroscopy (EIS), based on which the electrochemical mechanical planarization (ECMP) simulating test was done to investigate the effects of applied potentials on friction and material removal rate (MRR) with an ECMP simulating tester. According to the research, a suitable anode polarization potential is advantageous to promote the forming of passivation film with better corrosion inhibition in alkaline CeO₂ polishing liquid, and forming of passivation film on silicon surface can increase both the friction between polishing pad and specimen and the MRR of silicon. This result provides theoretical supports and experimental bases for ECMP of silicon wafer to increase its polishing efficiency.

Abstract: Polycrystalline silicon-photovoltaic industry belongs to high-and-new technology industry, but it produces massive by-products (silicon tetrachloride and so on), even partial chloro-silicane and hydrogen chloride exude into the exhaust in its production process. As a consequence, it not only increases the exhaust processing cost in the polycrystalline silicon-photovoltaic industry, but also increases pollutant discharge of the enterprise. At present, Chinese polycrystalline silicon-photovoltaic enterprises cannot solve technical difficult problems in large-scale production due to lack of coordination of chemical industry. Moreover, polycrystalline silicon has high request of purity that needs quite advanced technology to achieve. This article introduces influences upon production cost and energy consumption with the use of improved Siemens method, and proposes that polytrophic-photovoltaic industry needs to be systematized, normalized and standardized for its healthy development.

Abstract: As non-uniform color and complex texture exist on the polycrystalline silicon solar cell, manual surface inspection adopted by most domestic factories suffers from low efficiency and poor repetitive detection ability. To overcome the shortcomings of manual inspection, based on machine vision and SVM, an automatic silicon wafer surface defect detection and classification system has been developed in this paper: through feature extraction of color images and defect areas, a series of wafer classifiers are trained and used to separate the defective products from qualified ones. Experiments on samples and actual application in the enterprise show that the system has achieved high accuracy and fast run-time performance, indicating that machine vision is an effective and promising method for polycrystalline silicon solar cell inspection.