Amorphous silicon

About: Amorphous silicon is a research topic. Over the lifetime, 26777 publications have been published within this topic receiving 423234 citations.

Light-enhanced hydrogen motion in a-Si:H.

Abstract: We report the first direct observation of light-enhanced hydrogen motion in hydrogenated amorphous silicon. Diffusion enhancement increases with illumination intensity in undoped material and is suppressed in doped and in compensated material. The enhancement is attributed to an increased release rate of hydrogen from silicon-hydrogen bonds in the presence of photogenerated carriers. The implications of the effect for metastable defect formation are discussed.

A high capacity silicon–graphite composite as anode for lithium-ion batteries using low content amorphous silicon and compatible binders

Abstract: In this study, silicon–graphite composites were prepared and investigated as anode materials for Li-ion batteries with small amounts of silicon and different binders. The silicon powders were prepared by ball-milling crystalline silicon for 100 h and 200 h. After 200 h, an average silicon particle size of 0.73 μm was obtained and XRD measurements confirmed the formation of an amorphous powder embedded within nanocrystalline regions. XPS analysis of the silicon samples showed that silicon particles were covered with a native silicon oxide layer that grows during ball-milling. Battery cycling of the silicon powders in half cells showed that the powder ball milled for 200 h gave the lowest first-cycle irreversible capacity and the highest reversible capacity reaching over 500 mA h g−1 after 50 cycles at C/12. Composites were made using graphite and only 5 wt% silicon powders. The silicon was found to be uniformly dispersed into the composites as evidenced by X-ray mapping and SEM. When tested in half cells using different binders, it was found that the polyetherimide binder showed the highest capacity reaching 514 mA h g−1 after 350 cycles at C/12, which is 1.6 times greater than commercial graphite anode. High rate cycling showed good capacity retention reaching half the capacity at 5 C.

Evaluation and Validation of Equivalent Circuit Photovoltaic Solar Cell Performance Models

Abstract: The "five-parameter model" is a performance model for photovoltaic solar cells that predicts the voltage and current output by representing the cells as an equivalent electrical circuit with radiation and temperature-dependent components. An important feature of the five-parameter model is that its parameters can be determined using data commonly provided by module manufacturers on their published datasheets. This paper documents the predictive capability of the five-parameter model and proposes modifications to improve its performance using approximately 30 days of field-measured meteorological and module data from a wide range of cell technologies, including monocrystalline, polycrystalline, amorphous silicon, and copper indium diselenide (CIS). The standard five-parameter model is capable of predicting the performance of monocrystalline and polycrystalline silicon modules within approximately 6% RMS but is slightly less accurate for a thin-film CIS and an amorphous silicon array. Errors for the amorphous technology are reduced to approximately 5% RMS by using input data obtained after the module underwent an initial degradation in output due to aging. The robustness and possible improvements to the five-parameter model were also evaluated. A sensitivity analysis of the five-parameter model shows that all model inputs that are difficult to determine and not provided by manufacturer datasheets such as the glazing material properties, the semiconductor band gap energy, and the ground reflectance may be represented by approximate values independent of the PV technology. Modifications to the five-parameter model tested during this research did not appreciably improve the overall model performance. Additional dependence introduced by a seven-parameter model had a less than 1% RMS effect on maximum power predictions for the amorphous technology and increased the modeling errors for this array 4% RMS at open-circuit conditions. Adding a current sink to the equivalent circuit to better model recombination currents had little effect on the model behavior.

Composition and Structure of Ceramic Fibers Prepared from Polymer Precursors

Abstract: Ceramics fibers in the system Si-C-N-O prepared by pyrolysis of melt-spun, cured, amorphous organosilicon polymers have a predominantly amorphous chemical structure, consisting of carbon, nitrogen, and oxygen bonds to silicon. These amorphous silicon oxycarbonitrides have chemical bonding approach a random distribution: i.e. individual silicon atoms are simultaneously bonded to C, N, and O in a random fashion. Such structures have not been characterized previously. Excess C, present in all compositions studied, appears to be present as very small polyaromatic crystallites ({approx} 4 nm domain size in the aromatic plane) resembling pyrolytic carbon in structure. This carbon is highly resistant to oxidation. The amorphous, random structure of these ceramics is a consequence of small-scale elemental homogeneity in the amorphous polymer precursor and of insufficient thermal energy during pyrolysis to promote crystallization.