Carbon particulate matter derived from combustion consists of a variety of organic compounds, which often present features similar to polymers and molecules used as photoactive layers in the most common organic solar cells (Zhu et al. 2009). This consideration has recently provided the inspiration to check out the possible applications of these products in the optoelectronic application such as the photovoltaic technology. At the current state of knowledge the flame-formed carbon particulate matter mainly contain two different classes of materials: soot and nanoparticle of organic carbon (NOC) (D'Anna 2009). These two classes of particles present substantial differences on their sizes, optical properties and chemical features. In this study, combustion-formed carbonaceous materials were collected from various fuel-rich laminar premixed flames of ethylene and air, in order to characterize both the optical and the electrical properties. UV-visible absorption spectroscopy analysis has been used to measure the optical band-gaps of the materials by reporting the optical spectra in the Tauc plot (Tauc et al. 1966). The I-V characteristics, i.e. current vs. voltage plots, have been measured in order to estimate the electrical conductivity. Three different sampling procedures have been developed. A quartz substrate was rapidly inserted in flame, to collect by thermophoresis the carbon particulate matter, containing two main different classes of materials: soot and nanoparticles of organic carbon (NOC). The first class showed a bandgap ranging between 0.1 eV and 0.8 eV and a fair electrical conductivity, while the second class was characterized by a larger optical band-gap ranging between 1.9 eV and 3 eV and a low electrical conductivity. The optical band-gap was investigated under a varying of flame conditions (C/O ratio and height above the burner) and residence time of the substrate in the flame. A second particles collecting approach was realized by using a tube probe, positioned inside the flame, with a 0.8 mm orifice, followed by a particles impactor. This method was used to collect selected classis of particles. A third method was a chemical procedure based on Soluble organic fraction (SOF) which was chemically extracted from the sampled particulate. In this later case the electrical characterization of the collected material showed an unusual presence of a hysteresis in the I quadrant of the I-V characteristic of SOF. Finally by using the theoretical model proposed by Bruschi and Nannini 1991, the phenomenon of electrical conduction through a soot particles layer was simulated via tunnelling and percolative effect, which include both microscopic and macroscopic phenomena relative the charge transfer. Zhu H., Wei J., Wang K. Wu D. (2009), Application of carbon materials in photovoltaic solar cells, Sol. Energy Mater. Sol. Cells 93: 1461-1470. D'Anna A. (2009), Combustion-formed nanoparticles, Proc. Comb. Inst. 32: 593-613. Tauc J., Grigorovici R. Vancu A. (1966), Optical properties and electronic structure of amorphous germanium, Phys. Stat. Sol. 15: 627-637. Bruschi P., Nannini A., (1991), Current vs voltage characteristics of ion-beam-grown polymer-metal granular thin films, Thin solid films 201: 29-38.
Electrical Properties of Carbonaceous Particles Collected from Laminar Premixed Flames
G De Falco;M Commodo;GP Pepe;P Minutolo;
2012
Abstract
Carbon particulate matter derived from combustion consists of a variety of organic compounds, which often present features similar to polymers and molecules used as photoactive layers in the most common organic solar cells (Zhu et al. 2009). This consideration has recently provided the inspiration to check out the possible applications of these products in the optoelectronic application such as the photovoltaic technology. At the current state of knowledge the flame-formed carbon particulate matter mainly contain two different classes of materials: soot and nanoparticle of organic carbon (NOC) (D'Anna 2009). These two classes of particles present substantial differences on their sizes, optical properties and chemical features. In this study, combustion-formed carbonaceous materials were collected from various fuel-rich laminar premixed flames of ethylene and air, in order to characterize both the optical and the electrical properties. UV-visible absorption spectroscopy analysis has been used to measure the optical band-gaps of the materials by reporting the optical spectra in the Tauc plot (Tauc et al. 1966). The I-V characteristics, i.e. current vs. voltage plots, have been measured in order to estimate the electrical conductivity. Three different sampling procedures have been developed. A quartz substrate was rapidly inserted in flame, to collect by thermophoresis the carbon particulate matter, containing two main different classes of materials: soot and nanoparticles of organic carbon (NOC). The first class showed a bandgap ranging between 0.1 eV and 0.8 eV and a fair electrical conductivity, while the second class was characterized by a larger optical band-gap ranging between 1.9 eV and 3 eV and a low electrical conductivity. The optical band-gap was investigated under a varying of flame conditions (C/O ratio and height above the burner) and residence time of the substrate in the flame. A second particles collecting approach was realized by using a tube probe, positioned inside the flame, with a 0.8 mm orifice, followed by a particles impactor. This method was used to collect selected classis of particles. A third method was a chemical procedure based on Soluble organic fraction (SOF) which was chemically extracted from the sampled particulate. In this later case the electrical characterization of the collected material showed an unusual presence of a hysteresis in the I quadrant of the I-V characteristic of SOF. Finally by using the theoretical model proposed by Bruschi and Nannini 1991, the phenomenon of electrical conduction through a soot particles layer was simulated via tunnelling and percolative effect, which include both microscopic and macroscopic phenomena relative the charge transfer. Zhu H., Wei J., Wang K. Wu D. (2009), Application of carbon materials in photovoltaic solar cells, Sol. Energy Mater. Sol. Cells 93: 1461-1470. D'Anna A. (2009), Combustion-formed nanoparticles, Proc. Comb. Inst. 32: 593-613. Tauc J., Grigorovici R. Vancu A. (1966), Optical properties and electronic structure of amorphous germanium, Phys. Stat. Sol. 15: 627-637. Bruschi P., Nannini A., (1991), Current vs voltage characteristics of ion-beam-grown polymer-metal granular thin films, Thin solid films 201: 29-38.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
