A systematic study has been carried out to quantify the effect of microcrystallite nucleation in the intrinsic layer of protocrystalline Si:H p-i-n solar cells prepared by rf plasma enhanced chemical vapor deposition (PECVD). Real-time spectroscopic ellipsometry (RTSE) results that have previously identified the transitions from amorphous to microcrystalline phase were confirmed with atomic force microscopy (AFM) images. The effects of the phase transitions in the bulk intrinsic layer, as wel...
Insights into the growth processes and evolution of microstructure in intrinsic 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. To assess the effects of transition regions from the amorphous to mixed microcrystalline phases, cell structures with and without such regions at different depths in the i-layer from the p-contact have been investigated. ...
As the negative environmental effects of the current use of non-renewable energy sources have become apparent, hydrogenated amorphous silicon (a-Si:H) solar cell technology has advanced to provide a means of powering a future sustainable society. Over the last 25 years, a-Si:H solar cell technology has matured to a stage where there is currently a production of 30 MWpeak/year; and this production capacity continues to increase. The progress is due to the continuous advances made in new materi...
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.
By applying the interdisciplinary approach of Science, Technology & Society, students can solve often-neglected research problems of shifting society’s operation towards a sustainable state. A recent Penn State University student research report entitled “The Mueller Report: Moving from Sustainability Indicators to Sustainability Action”, contained a detailed ecological analysis of one campus building and addressed methods to optimize its ecological performance in terms of sustainabilit...
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].
Many people in less developed countries drink water with microbial contamination, which leads to the annual death of 5 million children. Although some people currently boil water, all microbes that cause disease in humans do not survive at temperatures >65oC, which solar water pasteurizers can easily produce. These pasteurizers are similar to box solar cookers, and typically have a small rectangular reflector. The objective of this work is to calculate the increase in output due to compound p...
Appropriate technologies, those able to be easily and economically constructed from readily available materials by local craftspeople, have a central role in the alleviation of poverty in the developing world. Research and development of these technologies are, however, generally apportioned relatively modest support by the developed world’s institutions in part because the operation of many of these appropriate technologies is dependent on relatively well-understood science accessible even...