Industrial application of PV/T solar energy systems 2007[edit | edit source]
Abstract: Hybrid photovoltaic/thermal (PV/T) systems consist of PV modules and heat extraction units mounted together. These systems can simultaneously provide electrical and thermal energy, thus achieving a higher energy conversion rate of the absorbed solar radiation than plain photovoltaics. Industries show high demand of energy for both heat and electricity and the hybrid PV/T systems could be used in order to meet this requirement. In this paper the application aspects in the industry of PV/T systems with water heat extraction is presented. The systems are analyzed with TRNSYS program for three locations Nicosia, Athens and Madison that are located at different latitudes. The system comprises 300 m2 of hybrid PV/T collectors producing both electricity and thermal energy and a 10 m3 water storage tank. The work includes the study of an industrial process heat system operated at two load supply temperatures of 60ºC and 80ºC. The results show that the electrical production of the system, employing polycrystalline solar cells, is more than the amorphous ones but the solar thermal contribution is slightly lower. A non-hybrid PV system produces about 25% more electrical energy but the present system covers also, depending on the location, a large percentage of the thermal energy requirement of the industry considered. The economic viability of the systems is proven, as positive life cycle savings are obtained in the case of hybrid systems and the savings are increased for higher load temperature applications. Additionally, although amorphous silicon panels are much less efficient than the polycrystalline ones, better economic figures are obtained due to their lower initial cost, i.e., they have better cost/benefit ratio.
This paper looks at the application of PVT systems in an industrial setting and comparing polycrystalline and amorphous silicon and the result is that the a-Si was better from a cost/benifit analysis stated in the paper.
Industrial application of PV/T solar energy systems. S.A. Kalogiru and Y. Tripanagnostopoulos. Applied Thermal Engineering 27 (2007) 1259–1270
5mjmp 18:05, 16 September 2009 (UTC)
09_09_16_Industrial application of PV-T solar energy systems.pdf
A Comparison of Fill Factor and Recombination Losses in Amorphous Silicon Solar Cells on ZnO and SnO2 2007[edit | edit source]
Written: 2007
It states that hydrogenated amorphous silicion p-i-n thin film most promising material since cheap. However solar degradation is a problem.
Research Topics:
- low cost
- improve the conversion efficiency
- reduce radiation loss
ZnO issues:
- minimize resistance between p-layer and TCO
- plasma resistant
- 96-97% transmission
- Electrical performance poorer
- Tend to have low FF (fill factor) and VOC
- due to changes in the p/i junction recombination not contact
- low v (DC)
- Higher QM and modulated v
SnO2 issues:
- chemically reduced by H or SiH4 plasma which causes a thin film of Sn to form lowering the transmission.
- Only 92-95% internal transmission over the visible spectrum
"Aim of the paper is to optimize the radiation and recombination losses by investigation two types of p-i-n solar cells which have the same a-si recipe and back contact ZnO and SnO2 TCO substrate materials." - paper
Renewable Energy 34 (2009) 1595–1599. A comparison of fill factor and recombination losses in amorphous silicon solar cells on ZnO and SnO2. A. Alkaya, R. Kaplan, H. Canbolat and S.S. Hegedus. http://scholarsportal.info/cgi-bin/sciserv.pl?collection=journals&journal=09601481&issue=v34i0006&article=1595_acoffascozas
5mjmp 15:15, 4 June 2009 (UTC)
Determination of the thickness and optical constants of amorphous silicon 2008[edit | edit source]
Abstract: Over the last 30 years, a large amount of research on PV-Thermal (PVT) collectors has been carried out. An overview of this research is presented, both in terms of an historic overview of research projects and in the form of a thematic overview, addressing the different research issues for PVT.
This paper goes through the equations required to calculated the refractice index, absorbtion coefficient and the thickness of the sample using transmission spectrum data. These equations are simple enough to be used in a programmable calculator.
Flat-plate PV-Thermal collectors and systems: A review. H.A. Zondag. Renewable and Sustainable Energy Reviews 12 (2008) 891–959
5mjmp 19:03, 16 September 2009 (UTC)
09_09_16_Determination of the thickness and optical constants of amorphous silicon.pdf
Energy metrics analysis of hybrid – photovoltaic (PV) modules 2009[edit | edit source]
Abstract: In this paper, energy metrics (energy pay back time, electricity production factor and life cycle conversion efficiency) of hybrid photovoltaic (PV) modules have been analyzed and presented for the composite climate of New Delhi, India. For this purpose, it is necessary to calculate (1) the energy consumption in making different components of the PV modules and (2) the annual energy (electrical and thermal) available from the hybrid-PV modules. A set of mathematical relations have been reformulated for computation of the energy metrics. The manufacturing energy, material production energy, energy use and distribution energy of the system have been taken into account, to determine the embodied energy for the hybrid-PV modules. The embodied energy and annual energy outputs have been used for evaluation of the energy metrics. For hybrid PV module, it has been observed that the EPBT gets significantly reduced by taking into account the increase in annual energy availability of the thermal energy in addition to the electrical energy. The values of EPF and LCCE of hybrid PV module become higher as expected.
Energy metrics analysis of hybrid – photovoltaic (PV) modules. A. Tiwari, P. Barnwal, G.S. Sandhu and M.S. Sodha. Applied Energy 86 (2009) 2615–2625
5mjmp 17:39, 16 September 2009 (UTC)
09_09_16_Energy metrics analysis of hybrid – photovoltaic (PV) mod.pdf
Analysis of the temperature history of amorphous silicon photovoltaic module outdoors 2009[edit | edit source]
Abstract: Toanalyzetheeffectsofthemoduletemperatureandirradianceonphotovoltaic(PV)modulesoutdoors, contour graphsweremadefortheperformanceratio(PR)ofsingle-crystallineSi(sc-Si)andamorphous Si (a-Si)PVmodules.TheresultshowsthatthePRofthesc-SiPVmoduledecreaseswithincreasein module temperature.Incontrast,thePRofthea-SiPVmoduleshowsuniquetemperaturedependence influencedbytemperaturehistory.DependenceofenvironmentalfactorsofthePRofthea-SiPVmodule wasanalyzedinalmostthesametemperatureseasons,i.e.,SpringandFall.ThePRinFallwashigher than thatinSpring.TheresultshowsthattherecoveredperformanceinsummermaycontinueforFall. The contourgraphofremainderofPRinFallandSpringwasmade.Theenvironmentalconditionthat the PRinFallwashigherwasclarified.
Analysisofthetemperaturehistoryofamorphoussiliconphotovoltaic module outdoors. S. Fukushige, K. Ichida, T. Minemoto and H. Takura. Solar Energy Materials & Solar Cells 93(2009)926–931
5mjmp 19:21, 16 September 2009 (UTC)
09_09_16_Analysis of the temperature history of amorphous silicon photovoltaic module outdoors.pdf
UofT Amorphous Silicon Papers[edit | edit source]
Note: Stefan Zukotynski is a retired professor.
An effective-mass model of hydrogenated amorphous silicon: A tail state analysis 1992[edit | edit source]
Abstract:An effective-mass model of hydrogenated amorphous silicon (a-Si:H) is proposed. This model focuses upon the impact of hydrogen on the electronic structure of the tail states. Tail state density-of-states calculations are performed in the high hydrogen concentration limit, and the results are found to be in general agreement with present experimental data. These results are shown to be quite robust to variations in the modeling parameters.
Stephen K. O'Leary and Stefan Zukotynski, John M. Perz. J. Appl. Phys. 72, 2272 (1992); doi:10.1063/1.351568. An effective-mass model of hydrogenated amorphous silicon: A tail state analysis. http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JAPIAU000072000006002272000001&idtype=cvips&gifs=yes
10_01_19_An effective-mass model of hydrogenated amorphous silicon A tail state analysis
Hydrogen-induced quantum confinement in amorphous silicon 1995[edit | edit source]
Abstract:We study how hydrogen-induced quantum confinement in hydrogenated amorphous silicon influences the distribution of tail states. To do this, the potential structure of this semiconductor is treated as being comprised of an ensemble of potential wells, these wells corresponding to unhydrogenated regions enveloped by hydrogenated regions. To evaluate the distribution of states, we determine the ground state associated with each well, and then average over the distribution of wells. We find that our calculated distribution of tail states exhibits an essentially exponential functional dependence, over several decades, and that this tail of states shifts toward the band edge as the hydrogen content is increased. This shift toward the band edge is suggested to be one of the factors responsible for the observed increase in energy gap with higher hydrogen content.
Stephen K. O'Leary and Stefan Zukotynski, John M. Perz. Hydrogen-induced quantum confinement in amorphous silicon. J. Appl. Phys. 78, 4282 (1995); doi:10.1063/1.359828. http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JAPIAU000078000006004282000001&idtype=cvips&gifs=yes
10_01_19_Hydrogen-induced quantum confinement in amorphous silicon
Optical absorption in amorphous semiconductors 1995[edit | edit source]
Abstract:We use the joint density-of-states function to study the optical-absorption spectrum of amorphous semiconductors. To determine the overall joint density of states, we average a local joint density of states over spatially correlated Gaussian distributions of conduction-band and valence-band potential fluctuations. Our results span the transition from below to above the energy gap and both analytical and numerical results are obtained. Spatial correlations are found to play a dramatic role in influencing the shape of the optical-absorption spectrum. We apply this formalism to the case of hydrogenated amorphous silicon and several other amorphous semiconductors of interest, and find that our results are consistent with those of experiment.
Stephen K. O'Leary and Stefan Zukotynski, John M. Perz. Phys. Rev. B 52, 7795–7797 http://prb.aps.org/abstract/PRB/v52/i11/p7795_1
10_01_19_Optical absorption in amorphous semiconductors.pdf
Semiclassical density-of-states and optical-absorption analysis of amorphous semiconductors 1995[edit | edit source]
Abstract:A semiclassical analysis of amorphous semiconductors is presented. This analysis, cast within an effective-mass setting, provides for the overall density-of-states by averaging a local density-of-states over a distribution of potential fluctuations. Our density-of-states results span the transition from the tail states to the band states, and both analytical and numerical results are obtained. We then determine the functional form of the optical-absorption coefficient, and show that both subgap and Tauc absorption edges are captured within this analytical framework. Finally, we apply this formalism to the case of hydrogenated amorphous silicon, and find that our results are consistent with those of experiment.
Stephen K. O'Leary and Stefan Zukotynski,John M. Perz. Phys. Rev. B 51, 4143–4149. http://prb.aps.org/abstract/PRB/v51/i7/p4143_1
10_01_19_Semiclassical density-of-states and optical-absorption analysis of amorphous semiconductors.pdf
RECOMBINATION IN TRITIATED AMORPHOUS SILICON 2000[edit | edit source]
Abstract:Tritiated amorphous silicon was used for the intrinsic layer of a p-i-n hydrogenated amorphous silicon diode. Current versus voltage measurements were carried out on the diode over time under dark and illuminated conditions. There was a decrease in the forward characteristic of the diode when measured under dark conditions and there was a decrease in photovoltaic power. These changes can be explained by the creation of dangling bonds when bonded tritium atoms decay. By annealing the diode at 125 °C, most of its photovoltaic properties could be recovered. It was also found that luminescence could be recovered in tritiated amorphous silicon by thermal annealing.
http://web.archive.org/web/20120106124824/http://www.ecf.utoronto.ca/~kherani/articles/r4.pdf
Tome Kosteski, Franco Gaspari, David Hum, Stefan Costea, Stefan Zukotynski, Nazir P. Kherani, and Walter T. Shmayda. Mat. Res. Soc. Symp. Proc. Vol. 609 © 2000 Materials Research Society.
10_01_14_RECOMBINATION IN TRITIATED AMORPHOUS SILICON.pdf
1/f noise in p-type amorphous silicon 2000[edit | edit source]
Abstract:We have measured conductance fluctuations in four samples of p-type hydrogenated amorphous silicon, two doped at 10–4 and the other two at 5×10–2, at temperatures between 22 and 200 °C. The noise power density varies for the most part as 1/f in the frequency range 2 Hz to 1 kHz, although deviations from a strict power law are observed. In all samples, the magnitude of the noise trends higher with temperature typically increasing by a factor of 5 over the temperature range. also increases with temperature from near unity to over 1.4. The magnitude of the noise decreases as the Fermi level moves toward the valence band with increased doping. The dependence on doping and temperature is inconsistent with generation-recombination noise. Above 180 °C for the 10–4 doped samples, the noise fails to scale as the square of the bias current at low frequencies.
Robert E. Johanson and S. O. Kasap, Franco Gaspari, Davit Yeghikyan, and Stefan Zukotynski. J. Vac. Sci. Technol. A Volume 18, Issue 2, pp. 661-664. 1/f noise in p-type amorphous silicon. http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JVTAD6000018000002000661000001&idtype=cvips&gifs=yes
10_01_19_1 over f noise in p-type amorphous silicon
Tritiated Amorphous Silicon Films and Devices 2001[edit | edit source]
It's a Thesis.
https://tspace.library.utoronto.ca/bitstream/1807/15626/1/NQ63643.pdf
10_01_14_Tritiated Amorphous Silicon Films and Devices THESIS
PROMOTING GRID-TIED SOLAR ELECTRICITY ON BUILDINGS IN CANADA 2003[edit | edit source]
Abstract:A recent study by the Photovoltaics and Hybrid Systems Program at CANMET Energy Technology Centre-Varennes examined the benefits of on-site generation of electricity using grid-tied photovoltaic technology on buildings in Canada. The study focused on the grid-connect segment of the PV market, which has been experiencing the strongest growth. It showed that while costs of PV worldwide have been falling at about 5% per year in real terms over the past twenty years following a well-established learning curve, there remain several barriers to be addressed before greater inroads can be made in this sector of photovoltaics in Canada. There are many challenges to grid-tied PV in Canada. CETC-Varennes has been addressing these challenges through their RD&D programactivities. These activities range from removing interconnection barriers to the grid, providing assistance to Canadian industry by championing climate change TEAM projects, accelerating the development of adequate policies, and providing quality information to Canadians. The outcomes of these efforts are elucidated in this paper. CETC-Varennes is committed to continuing building alliances with the private sector and with other federal, provincial and municipal levels of government to mainstream grid-tied PV in Canada. It will continue to seek out technology investment opportunities, such as those provided by TEAM, in order to share the RD&D risk and to demonstrate the benefits of linking private sector business strategies and technology capabilities with global business opportunities. PV projects show how GHG reduction and economic benefits can be achieved together, along with environmental and social co-benefits.
J. Ayoub, L. Dignard-Bailey, and W. Richardson. SESCI 2003 CONFERENCE. Queen's University. Kingston, Ontario, Canada. August 18 to 20, 2003
10_01_14_PROMOTING GRID-TIED SOLAR ELECTRICITY ON BUILDINGS IN CANADA.pdf
MODELING OF DC SADDLE FIELD PECVD USING THE DIRECT MONTE CARLO METHOD 2004[edit | edit source]
Abstract:Enhancements in rates of ionization, dissociation, and current in the DC saddle field (DCSF) glow discharge are studied using the direct Monte Carlo method (DMCM). The DCSF consists of a planar semitransparent anode positioned between two planar cathodes, producing a symmetric electric field that serves to lengthen the path of electrons. Simulations of current versus anode transparency of a N2 discharge agree very well with experimental results reported previously. Numerical results of the DCSF SiH4 discharge are also presented. At typical operating conditions (600V, 5cm cathode-anode spacing, anode transparency of 0.8), DMCM predicts a significant increase in the dissociation rate at pressures below 100mTorr in comparison to the DC diode. In consideration of its use for plasma enhanced chemical vapour deposition, the efficiency with which the DCSF operates at low pressures makes it attractive for the production of thin films whose qualities are sensitive to gas phase reactions.
http://www.solarbuildings.ca/c/sbn/file_db/Modelling%20of%20DC%20saddle%20field%20PECVD.pdf
Johnson Wong, Nazir P. Kherani, Stefan Zukotynski. Canadian Solar Buildings Conference. Montreal, August 20-24, 2004. Refereed Paper.
10_01_14_MODELING OF DC SADDLE FIELD PECVD USING
Density of states in tritiated amorphous silicon obtained with the constant photocurrent method 2005[edit | edit source]
Abstract: The constant photocurrent method was implemented to determine the density of states in tritiated hydrogenated amorphous silicon below the Fermi level. The tritiated hydrogenated amorphous silicon samples were grown using a mixture of silane and tritium gases in the dc saddle-field deposition system. Over time the tritium incorporated in the amorphous silicon undergoes beta decay and transmutation into helium. The transmutation leads to an increase in the density of states in the energy gap of the material. These states are linked to silicon dangling-bond defects. Given its well-characterized decay process, tritium can be used as an experimental tool to study the behavior of hydrogenated amorphous silicon thin films as a function of their defect state density. The density-of-states information in this work indicates a dominant peak of doubly occupied dangling bonds (D–) positioned 1.24 eV below the conduction band. The defect density was monitored in time showing an increase of more than two orders of magnitude over a period of 20 days and a decrease of similar magnitude upon thermal annealing.
Simone Pisana,Stefan Costea, Tome Kosteski, Walter T. Shmayda,Nazir P. Kherani, and Stefan Zukotynski. JOURNAL OF APPLIED PHYSICS 98, 093705 2005
10_01_14_Density of states in tritiated amorphous silicon obtained with the constant photocurrent method.pdf
Tritiation of amorphous and crystalline silicon using T2 gas 2006[edit | edit source]
Abstract:Incorporation of tritium in hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) at 250 °C using tritium (T2) gas at pressures of up to 120 atm is reported. The tritium is stored in a surface layer which is approximately 150 and 10 nm for a-Si:H and c-Si, respectively. The concentration of tritium occluded in planar and textured c-Si is linearly dependent on the total surface area. The tritium is stable and the dominant tritium evolution occurs at temperatures above 300 °C. The concentration of tritium locked in a-Si:H and c-Si was 20 and 4 at. %, respectively. Self-catalysis appears to be important in the tritiation process.
Baojun Liu and Kevin P. Chena,Nazir P. Kherani, Tome Kosteski, Stefan Costea, and Stefan Zukotynski, Armando B. Antoniazzi. APPLIED PHYSICS LETTERS 89, 044104 2006
10_01_14_Tritiation of amorphous and crystalline silicon using T2 gas
Raman scattering characterization of SF-PECVD-grown hydrogenated microcrystalline silicon thin films using growth surface electrical bias 2006[edit | edit source]
Abstract:A series of hydrogenated microcrystalline films were grown by a novel thin film deposition method using the Saddle Field Plasma Enhanced Chemical Vapour Deposition system. We show that the surface potential during growth strongly affects the microcrystalline character of the films, as quantified by Raman scattering. This effect can be reproduced on both conductive and non-conductive substrates. Films grown close to the threshold for microcrystalline growth exhibit laser-induced crystallization at low laser intensities.
Erik V. Johnson Æ Nazir P. Kherani, Stefan Zukotynski. J Mater Sci: Mater Electron (2006) 17:801–813.
10_01_14_Raman scattering characterization of SF-PECVD-grown hydrogenated microcrystalline silicon thin films using growth surface electrical bias.pdf
Density of States in Tritiated Amorphous Silicon Measured Using CPM[edit | edit source]
Abstract: The constant photocurrent method has been used to obtain the density of occupied electronic states of tritiated amorphous silicon thin films. The analyses showed a peak of defects located
- 24 eV below the conduction band edge, suggesting that the main type of defect present in the
films was a doubly occupied dangling bond. The concentration of defect states increases as a result of tritium decay by about two orders of magnitude over a period of 500 hours. The defect density in the tritiated amorphous silicon samples could be reduced by thermal annealing, after which it increased once more.
http://web.archive.org/web/20120106124711/http://www.ecf.utoronto.ca/~kherani/articles/r10.pdf
Simone Pisana†, Stefan Costea, Tome Kosteski, Nazir P. Kherani, Stefan Zukotynski and Walter T. Shmayda
10_01_14_Density of States in Tritiated Amorphous Silicon Measured Using CPM
Use of Tritium in the Study of Defects in Amorphous Silicon 2006[edit | edit source]
Abstract:Hydrogen is known to strongly affect the physical properties of amorphous semiconductors. Indeed hydrogen is introduced during the growth of amorphous silicon films, used in active matrix displays and solar cells, to passivate silicon dangling bonds and to relax the lattice thereby reducing the density of states in the energy gap by several orders of magnitude and giving rise to device grade material. Ideally, hydrogenated amorphous silicon (a-Si:H) is a continuous covalently bonded random network of silicon-silicon and silicon-hydrogen atoms, with the predominant nearest neighbour environment similar to that of crystalline silicon. a-Si:H typically contains about 10 atomic percent hydrogen.Tritium can readily substitute for hydrogen in a-Si:H without altering the physicochemical properties of the material. Tritium decay leads to a change in the local bond structure of the material as helium detaches from bonds leaving behind dangling bonds. The decay rate of tritium and therefore the rate of dangling bond formation is determined by the half-life of tritium. Hence, tritium provides a unique avenue to dynamically study the effect of dangling bonds on the density of states in the energy gap and therefore on the optoelectronic properties of a-Si:H. Tritiated hydrogenated amorphous silicon (a-Si:H:T) was deposited using mixtures of tritium and silane gases in a dc saddle-field glow-discharge deposition system. The amount of tritium in the films was controlled by adjusting the relative flow of tritium and silane gases into the deposition chamber.Photoluminescence, isothermal capacitive transient spectroscopy and constant photocurrent spectroscopy were used to measure defect concentration as a function of time in the films. The defect concentration was found to increase between 1 and 2 orders of magnitude, in about 300 hours. Thermal annealing decreased the defect concentration. It was found that tritium permits a study of the change in the density of defect states due to dangling bond formation in a-Si:H without the uncertainties introduced by the use of multiple samples.
Journal Name: Fusion Science and Technology; Journal Volume: 48; Journal Issue: 1; Other Information: Copyright (c) 2006 American Nuclear Society (ANS), United States, All rights reserved. http://epubs.ans.org/; Country of input: International Atomic Energy Agency (IAEA)
http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=20854245
Time evolution of charged defect states in tritiated amorphous silicon 2007[edit | edit source]
Abstract:Tritiated hydrogenated amorphous silicon (a-Si:H:T) thin films were deposited on crystalline silicon and high resistivity glass substrates. The time evolution of the density of defect states in these films was studied using the constant photocurrent method (CPM) and isothermal capacitance transient spectroscopy (ICTS). The density of defect states was found to change with time and to recover upon thermal annealing. The ICTS results revealed that, following thermal annealing, in a sample with approximately 1 at. % tritium, the concentration of positively charged dangling bonds (D+) decreased by more than an order of magnitude over a period of 300 h. The CPM results showed that, over the same period of time, the concentration of negatively charged dangling bonds (D−) increased by over two orders of magnitude. The D+ and D− concentrations followed exponential functions of time, but the rate was different than that of tritium decay. At the same time, the Urbach energy was found to decrease with time to about 1/2 of its postanneal value. The change in the D+ and D− concentrations is primarily the result of capture of the beta particle generated electrons in dangling bonds and weak bonds, with steady state achieved through the development of a balance between carrier generation and carrier capture processes. The role of excess carriers was confirmed by CPM experiments under electrical bias.
Stefan Costea, Nazir P. Kherani,and Stefan Zukotynski. JOURNAL OF APPLIED PHYSICS 102, 103715 2007.
10_01_14_Time evolution of charged defect states in tritiated amorphous silicon
Photocarrier Radiometric Lifetime Measurements of Intrinsic Amorphous-Crystalline Silicon Heterostructure[edit | edit source]
Abstract: Intrinsic hydrogenated amorphous silicon films were deposited by the DC saddle field system on crystalline silicon wafers. The substrate temperature of the amorphous film, crystalline silicon surface cleaning schemes, and the native oxide etchant were varied. The transport parameters of the amorphous-crystalline silicon heterostructures were evaluated by Photocarrier Radiometric (PCR) lifetime measurements. PCR bulk lifetime estimates were obtained using the quinhydrone in methanol solution to passivate the crystalline silicon surface. We present the effectiveness of the PCR system in evaluating different surface passivation schemes
http://www.mrs.org/s_mrs/sec_subscribe.asp?CID=6472&DID=175208&action=detail
costs money...
HYDROGENATED AMORPHOUS CARBON AS A SPECTRALLY SELECTIVE COATING FOR PHOTOVOLTAIC-THERMAL PANELS *[edit | edit source]
Abstract:Photovoltaic (PV) panels utilize only a small fraction of incident solar radiation. Typical PV panels convert only about 10-20% of incident solar radiation into electricity, while approximately 10% is reflected, and the remaining 70-80% is dissipated as thermal energy. In photovoltaic-thermal (PV/T) panels, the thermal energy is stored and utilized as a water or air heating source. Thus PV/T panels are able to make use of a much higher percentage of incident solar radiation. While there is a clear advantage for the use of PV/T, key technical challenges have yet to be overcome. One of the primary obstacles with PV/T is the fact that due to the high emissivity of the PV cells, PV/T panels have a lower thermal yield than stand-alone solar thermal collectors. In this paper, spectrally selective, low-emissive, hydrogenated amorphous carbon (a-C:H) coatings are investigated for application to PV/T panels. These coatings have the properties of being highly transparent in the solar region (300nm-900nm) and reflective in the mid-infrared (5μm-25μm). An evaluation of these a- C:H coatings and how they relate to the current stateof- the-art in spectrally selective coatings will be given. In addition, a discussion of the application of these a- C:H coatings to thin-film hydrogenated amorphous silicon (a-Si:H) PV/T cells will be presented.
This article states that a-C:H is amenable to a-Si:H for a highly transparent low-E coating. It deals with some of the basic physics to explain what one would want to create a perfect PVT system. It also talks about a Transparent Heat Mirror which is created by placing a thin metallic layer between a dielectric stack, usually silver. However, adding one of these (or more) adds complexity to manufacturing the PVT and therefore makes it more expensive. However, the THM talked about in this paper were designed at room temperature...
Pratish Mahtani, Nazir P. Kherani, and Stefan Zukotynski
10_01_14_HYDROGENATED AMORPHOUS CARBON AS A SPECTRALLY.pdf
THE USE OF AMORPHOUS SILICON IN FABRICATING A PHOTOVOLTAIC-THERMAL SYSTEM 2007[edit | edit source]
Abstract: In this paper, a PV/T system based on directly depositing hydrogenated amorphous silicon photovoltaic devices on the surface of a heat exchanger will be presented. This system has the potential of overcoming the drawbacks of current PV/T systems. A background on amorphous silicon related to its application to PV/T systems will be given. In addition, an overview of current experimental work as well as future research goals will discussed.
This paper deals with my my thesis is about and hopefully I will be working with them.
"There are three major road blocks that are preventing PV/T systems from penetrating the commercial market:
- lower PV efficiency due to high temperature operation of the thermal system;
- lower thermal performance due to high emissivity of PV module; and
- PV/T systems do not provide any manufacturing cost savings over separately manufacturing PV and STC modules.
As temperature is increased, there are two major effects in typical PV cell operation. First, the dark saturation current of the PV cell increases which leads to a decrease in open circuit voltage. Second, the bandgap of the photovoltaic material decreases which leads to an increase in photocurrent. The first effect is more dominant than the second effect and thus there is a net decrease in the solar conversion efficiency with increasing temperature [Nelson, 2003]. Nelson, J. 2003. The Physics of Solar Cells (Properties of Semiconductor Materials), London: Imperial College Press
The positive temperature coefficient of a-Si:H was demonstrated in a module by Hof et. al, showing that after several months an a-Si:H PV module kept at an average temperature of 60ºC during daylight hours produces 20% more power than when the same module is kept at an average temperature of 35 ºC during daylight hours [Hof et al, 1996]. Hof, C., Ludii, M., Goetz, M., Fischer, D., Shah, A., 1996. "Long term behaviour of passively heated or cooled a-Si:H modules", Proceedings of 25th Photovoltaic Specialists Conference, pp. 1057.
Future Work Following the investigation into diffusion barriers and demonstration of an integrated PV/T system using a-Si:H, research on optical coatings amenable to maximizing absorption and minimizing IR emissivity will be pursued. In addition, an investigation into integrating thermally conductive and electrically insulative materials such as Al2O3 will be performed. These materials will be necessary in order to monolithically interconnect the a-Si:H PV cells in series. Also, the potential of using tandem cells such as a-SiGe/a-Si:H and nc-Si/a-Si:H in order to increase the combined electrical-thermal efficiency of the system will be carried out." - paper
2nd Canadian Solar Buildings Conference Calgary, June 10 - 14, 2007. THE USE OF AMORPHOUS SILICON IN FABRICATING A PHOTOVOLTAIC-THERMAL SYSTEM. Pratish Mahtani, Davit Yeghikyan, Nazir P. Kherani and Stefan Zukotynski. http://www.solarbuildings.ca/c/sbn/file_db/The%20use%20of%20amorphous%20silicon%20in%20fabricating%20a%20photovoltaic.pdf
5mjmp 18:38, 16 September 2009 (UTC)
09_09_16_The use of amorphous silicon in fabricating a PVT system.pdf
A comparison between defects created by light soaking and tritium decay in amorphous silicon 2007[edit | edit source]
Abstract:We compare two ways to create defects in a-Si:H, namely decay of bonded tritium and irradiation with visible light. Tritium decays to He^3, emitting a beta particle and an antineutrino. In tritium doped a-Si:H samples each beta decay of tritium bonded to silicon will create a defect by converting a bonded tritium to an interstitial helium, leaving behind a silicon dangling bond. We track these defects using electron spin resonance (ESR). We have kept the sample in liquid nitrogen for two years. After two years the defect density increases without saturation to a value of 7x10^19/cm^3. In the second experiment, we have kept the sample in liquid nitrogen irradiated with white light of intensity about 100mW/cm^2. After about 6 months, the spin density increased to about 9x10^17/cm^3 with no evidence of saturation. In the tritiated sample the increase in the defect density is proportional to the time, t, while in the light-soaked sample the increase is approximately proportional to t^1/3. This difference in behavior will be discussed.
can't get the article http://adsabs.harvard.edu/abs/2007APS..MARY31014J
Infrared Ellipsometry Investigation of Hydrogenated Amorphous Silicon[edit | edit source]
Abstract:Hydrogenated amorphous silicon (a-Si:H) has been extensively investigated experimentally in the infrared spectral region via techniques such as Fourier Transform Infrared (FTIR) and Raman spectroscopy. Although spectroscopic ellipsometry has been proven to be an important tool for the determination of several parameters of a-Si:H films, including dielectric constant, surface roughness, doping concentration and layer thickness, the spectral range used in these studies has rarely covered the infrared region below 0.6 eV, and never over the complete spectral region of interest (0.04 – 0.3 eV). We have measured for the first time the dielectric function of a-Si:H films grown by the saddle field glow discharge technique by spectroscopic ellipsometry in the energy range from 0.04 eV to 6.5 eV, thus extending the analysis into the far infrared region. The a-Si:H films were deposited on germanium substrates for the ellipsometry studies, and on crystalline silicon substrates for the comparative FTIR analysis. Preparation parameters were chosen to obtain films with different hydrogen content. In this paper, we present the results of the ellipsometry analysis, evaluate different fitting techniques, and compare the results with the corresponding FTIR spectra. The similarities and differences between the spectra are discussed in terms of the a-Si:H properties.
http://www.mrs.org/s_mrs/sec_subscribe.asp?CID=18437&DID=247265&action=detail
Have to buy it...
Metastable defects in tritiated amorphous silicon 2007[edit | edit source]
Abstract:We have observed the growth of defects caused by tritium decay in tritiated a-Si: H instead of inducing defects optically. We kept the samples in liquid nitrogen for two years. After two years the ESR signal reached ～1019 cm-3 with no evidence of saturation. However, the density is still less than the density of tritium that has decayed. We step-wise annealed (isochronally annealed) one sample up to 200 ºC, where all of the defects were annealed out. Another sample was isothermally annealed at 300 K for several months. At this temperature, the defects anneal slowly.
http://web.archive.org/web/20120106124811/http://www.ecf.utoronto.ca/~kherani/articles/r14.pdf
T. Jua, J. Whitakerb, S. Zukotynskic N. Kheranic, P.C. Taylord, P. Stradinse. Mater.Res.Soc.Symp.Proc. (2007). Article 0989-A02-04
10_01_14_Metastable defects in tritiated amorphous silicon
Electrical properties of a-Si:H thin films as a function of bonding configuration 2008[edit | edit source]
Abstract: Hydrogenated amorphous silicon (a-Si:H) thin films were fabricated by Radio Frequency (RF) magnetron sputtering. For solar-cell applications, a-Si:H layers are required to show low dark conductivity and high photoconductivity and, thus, high photosensitivity. Hydrogen flow ratio and working pressure were mainly adjusted to control bonding configurations and hydrogen concentration in the films. At a high working pressure of 12 mTorr, all of the prepared amorphous and microcrystalline silicon films showed a dominant IR absorption peak at 2100 cm−1, which indicates a Si–H2 stretching mode, grain boundaries and microvoids. When the working pressure was decreased to as low as 3 mTorr with a hydrogen flow ratio of 0.1, the bonding configuration of the films was mainly Si–H as determined by the dominant IR absorption peak at 2000 cm−1, and the photosensitivity of the films was maximized to 760.
Do Yun Kim,In Soo Kim,Se Young Choi. 0927-0248/$-see front matter & 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2008.10.003
10_01_14_Electrical properties of a-Si-H thin films as a function of bonding configuration
