Crystallographic analysis of high quality poly-Si thin films deposited by atmospheric pressure chemical vapor deposition

Crystallinity of thin film polycrystalline silicon (poly-Si) grown by atmospheric pressure chemical vapor deposition has been investigated by X-ray diffraction measurement and Raman spectroscopy. Poly-Si films deposited at high temperatures of 850–1050°C preferred to 2 2 0 direction. By Raman spectroscopy, the broad peak of around 480–500 cm⁻¹ belonged to microcrystalline Si (μc-Si) phase was observed even for the poly-Si deposited at 950°C. After high-temperature annealing (1050°C) 3 3 1 direction of poly-Si increased. This result indicates that the μc-Si phase at grain boundary became poly-Si phase preferred to 3 3 1 direction by high-temperature annealing. Effective diffusion length of poly-Si films deposited at 1000°C was estimated to be 11.9–13.5 μm and 10.2–12.9 μm before and after annealing, respectively.     

A model for distribution of oxygen in multicrystalline silicon ingot grown by directional solidification

A model, including segregation from silicon melt to silicon crystal as well as evaporation from silicon melt to Ar atmosphere, was established for simulating the oxygen distribution in multicrystalline silicon (mc-si) ingot, which shows good agreement with the experimental results. According to this model, the oxygen distribution in the bottom of ingot is mainly determined by the evaporation of oxygen, whereas that in the top of ingot is dominated by the segregation of oxygen. Furthermore, it could be found that the O_i profiles in growth direction of ingots become more and more steeper with the increase of the exponent X.     

Comparative study of performance degradation in poly- and mono-crystalline-Si solar PV modules deployed in different applications

Data on long-term performance and degradation of field-aged solar photovoltaic modules is widely recognized as necessary for continued technological improvement and market confidence. It is also important that such research should cover various geographical regions of the globe. This paper presents a study on twenty-nine (29) crystalline silicon modules deployed in grid-connected, battery-charging and water-pumping applications. The modules, installed at six different locations in Ghana were aged between 6 and 32 years. Peak power (P_max) losses ranged from 0.8%/year – 6.5%/year. The P_max losses were dominated by losses in fill factor (FF) and short-circuit current (I_sc). Visually observable defects are also reported.     

High stability of oxidation of methanol catalyzed by Pt supported by oxygen-incorporated bamboo-shaped CNTs grown directly on carbon cloth

Bamboo-shaped CNTs in which oxygen was incorporated were directly grown on carbon cloth (O-BCNT-CC) by microwave plasma-enhanced chemical vapor deposition. Mixed precursors CH₄/H₂/N₂/O₂ were introduced during the growth process. For comparison, bamboo-shaped CNTs without incorporated oxygen were prepared herein (BCNT-CC). Then, platinum catalysts were prepared on the as-grown O-BCNT-CC (Pt/O-BCNT-CC) and the as-grown BCNT-CC (Pt/BCNT-CC). According to TEM-EELS oxygen mapping, O atoms were uniformly distributed on the O-BCNT surface. Methanol oxidation was performed using Pt/O-BCNT-CC and Pt/BCNT-CC in 1 M methanol and 1 M sulfuric acid by cyclic voltammetry. In the initial cycle, the peak current density of Pt/O-BCNT-CC was almost equal to that of Pt/BCNT, indicating that both had nearly equal activities in the beginning. After 300 cycles, the peak current of Pt/BCNT-CC was reduced to half of the initial peak current owing to platinum-poisoning; however, the peak current of Pt/O-BCNT-CC decayed less. In Pt/O-BCNT-CC, the oxygen-containing functional groups affect the orientation index of crystalline Pt, providing a means of oxidizing methanol and stabilizing Pt catalysts for the long-term.