Phase diagrams that characterize plasma-enhanced chemical vapor deposition of Si thin films at low substrate temperature (200 C) have been established using real time spectroscopic ellipsometry as a probe of thin film microstructural evolution and optical properties. These deposition phase diagrams describe the regimes over which predominantly amorphous and microcrystalline Si phases are obtained as a function of the accumulated film thickness and the hydrogen-to-silane gas flow ratio R=[H2]/...
We have developed a Kramers–Kronig consistent analytical expression to fit the measured optical functions of hydrogenated amorphous silicon (a-Si:H) based alloys, i.e., the real and imaginary parts of the dielectric function (ϵ1,ϵ2) (or the index of refraction n and absorption coefficient α) versus photon energy E for the alloys. The alloys of interest include amorphous silicon–germanium (a-Si1−xGex:H) and silicon–carbon (a-Si1−xCx:H), with band gaps ranging continuously from ∼...
The ability to characterize the phase of the intrinsic (i) layers incorporated into amorphous silicon [a-Si:H] and microcrystalline silicon [μc-Si:H] thin film solar cells is critically important for cell optimization. In this research, a new method has been developed to extract the thickness evolution of the μc-Si:H volume fraction in mixed phase amorphous + microcrystalline silicon [(a+μc)-Si:H] i-layers. This method is based on real time spectroscopic ellipsometry measurements performed...
Insights into the growth processes and microstructural evolution for intrinsic (i) hydrogenated silicon (Si: H) films obtained from real-time spectroscopic ellipsometry (RTSE) are extended to the characterization of the optoelectronic properties of the corresponding solar cells. Numerical modeling of the J–V characteristics and their temperature dependences support the RTSE results and provide new information about the optoelectronic properties of the i-layer materials.
Thin Solid Films, Jan 1, 2004 The effects of microstructure on the gap states of hydrogen diluted and undiluted hydrogenated amorphous silicon (a-Si:H) thin film materials and their solar cells have been investigated. In characterizing the films the commonly used methodology of relating just the magnitudes of photocurrents and subgap absorption, α(E), was expanded to take into account states other than those due to dangling bond defects. The electron mobility-lifetime products were character...
Real time spectroscopic ellipsometry has been applied to develop deposition phase diagrams for p-type hydrogenated silicon (Si: H) films prepared at low temperature (200° C) by rf plasma-enhanced chemical vapor deposition using gas mixtures of SiH4, H2, and BF3.
In order to obtain more insight into the nature of the recovery in the light induced changes at room temperature in hydrogenated amorphous silicon (a-Si:H) solar cells the relaxation of the photocurrents in the light induced changes in protocrystalline a-Si:H thin films were investigated. Immediately upon the removal of 1 sun illumination recoveries in the photocurrents are found like those present in the currents in the dark current- voltage characteristics in corresponding p-i-n solar cells...
Generally the dark forward bias current voltage (JD-V) characteristics of a-Si:H solar cells are analyzed without clearly separating their contributions due to carrier recombination in the bulk from that at the p/i interface regions nor those imposed by carrier injection from the p and n contacts. Furthermore their exponential regimes are interpreted and fitted with constant diode quality factor n with modeling which is based on many fitting parameters that have not been reliably established....
Real time spectroscopic ellipsometry has been applied to develop deposition phase diagrams that can guide the fabrication of hydrogenated silicon (Si: H) thin films at low temperatures (< 300° C) for highest performance electronic devices such as solar cells. The simplest phase diagrams incorporate a single transition from the amorphous growth regime to the mixed-phase (amorphous+ microcrystalline) growth regime versus accumulated film thickness [the a→(a+ μc) transition].
Indium gallium nitride films with nanocolumnar microstructure were deposited with varying indium content and substrate temperatures using plasma-enhanced evaporation on amorphous SiO2 substrates. FESEM and XRD results are presented, showing that more crystalline nanocolumnar microstructures can be engineered at lower indium compositions. Nanocolumn diameter and packing factor (void fraction) was found to be highly dependent on substrate temperature, with thinner and more closely packed nanoco...
This paper presents the preliminary results of optical characterization using spectroscopic ellipsometry of wurtzite indium gallium nitride (InxGa1-xN) thin films with medium indium content (0.38
There is a renewed interest in photovoltaic solar thermal (PVT) hybrid systems, which harvest solar energy for heat and electricity. Typically, a main focus of a PVT system is to cool the photovoltaic (PV) cells to improve the electrical performance, however, this causes the thermal component to under-perform compared to a solar thermal collector. The low temperature coefficients of amorphous silicon (a-Si:H) allow for the PV cells to be operated at higher temperatures and are a potential can...
Solar water disinfection (SODIS) has proven to be effective at reducing diarrheal incidence in epidemiological intervention studies. However, the SODIS method is limited to waters of low turbidity (
RESUMEN La eficiencia cuántica de materiales fotovoltaicos depende de la longitud de onda de la radiación incidente, el espectro solar influye en la producción de energía producida por estos sistemas. En el presente trabajo, se diseñó y construyó un prototipo funcional de un sistema de medición de radiación solar (global y difusa) basado en un espectrómetro de amplio espectro para el monitoreo solar en Cochabamba, Bolivia, conjuntamente con un sistema similar instalado en Kingston, Ontario.
Historically, the design of hybrid solar photovoltaic thermal (PVT) systems has focused on cooling crystalline silicon (c-Si)-based photovoltaic (PV) devices to avoid temperature-related losses. This approach neglects the associated performance losses in the thermal system and leads to a decrease in the overall exergy of the system. Consequently, this paper explores the use of hydrogenated amorphous silicon (a-Si:H) as an absorber material for PVT in an effort to maintain higher and more favo...