Spectral Selective Coatings Literature Review: Difference between revisions

The Goal

It is desirable to combine solar photovoltaic and solar thermal applications in order to extract the maximum benefit from the sun's energy, creating both electricity and useful heat. To maximize output, high solar absorbtance, and low thermal emissivity are required.

A non selective coating (like black paint) has a high thermal emittance (gives off thermal radiation (heat) to the environment) and a high absorbtance of solar radiation.

Selective coatings can allow us to manipulate the ratio of absorbtance to emittance. Some selective coatings are strong absorbers of solar radiation, but are transparent to thermal radiation, in that case, thermal emittance is determined by the properties of what the coating is applied to.

Things To Keep In Mind

Emittance: Ability of a surface to emit heat by radiation. Emissivity is the ratio of emission of a surface to that of a black body at the same temperature. The duller the material, the higher the emissivity, the more reflective the material, the lower the emissivity. Think of comparing a bright white surface and a dull black surface in the middle of summer. The black surface, is much hotter to touch. Emissivity is a surface property, so surface roughness, temperature and wavelength all have an influence on it.

Reflectance: The percentage of incoming energy reflected off a surface at a given wavelength.

Absorbtance: The fraction of light absorbed by a sample at a given wavelength.

Transmittance: The fraction of light at a given wavelength that passes through a sample.

Fundamentals of Semiconductors/PV

${\displaystyle e=mc^{2}}$

The following equations came from Solar Cells by Martin E. Green

pg 41 Reflection ${\displaystyle R={\frac {({\hat {n}}-1)^{2}+{\hat {k}}^{2}}{({\hat {n}}+1)^{2}+{\hat {k}}^{2}}}}$

Where:

• ${\displaystyle {\hat {n}}}$ is the real part of the index of refraction
• ${\displaystyle {\hat {k}}}$ is the imaginary part of the index of refraction
• Index of Refraction ${\displaystyle {\hat {n_{c}}}={\hat {n}}-i{\hat {k}}}$

Note: Transmission is T = 1 - R

Absorption of Light

Absorbed light at a distance into the semiconductor

Intensity of light = I

${\displaystyle I=I(x_{o})exp(-\alpha (x-x_{o}))}$

• ${\displaystyle \alpha ={\frac {4\pi f{\hat {k}}}{c}}}$

Note:

• ${\displaystyle \lambda ={\frac {c}{f}}}$

Math Equation Help in Wiki

http://en.wikipedia.org/wiki/Help:Displaying_a_formula

Other Wiki Basics

http://www.appropedia.org/Help:Contents

Direct Band Gap Semiconductor

${\displaystyle hf=E_{f}-E_{i}}$

${\displaystyle \alpha (hf)=A(hf-E_{g})^{1/2}}$

Where

• ${\displaystyle E_{f}}$ Final energy state
• ${\displaystyle E_{i}}$ Initial energy state
• ${\displaystyle E_{g}}$ Band Gap Energy
• A is a constant with a value of 2E4 when alpha is expressed in ${\displaystyle cm^{(}-1)}$ and hf and ${\displaystyle E_{g}}$ is in eV.

Indirect Band Gap Semiconductor

${\displaystyle hf=E_{g}-E_{p}}$

${\displaystyle \alpha (hf,T)=\sum _{m=1,2n=1,2}A_{ij}({\frac {(hf-E_{gn}(T)+E_{pm})^{2}}{exp(E_{pm}/kT)-1}}+{\frac {(hf-E_{gn}(T)-E_{pm})^{2}}{1-exp(-E_{pm}/kT)}})+A_{d}(hf-E_{gd}(T))^{1/2}}$

Where

• ${\displaystyle E_{p}}$ is energy of an absorbed phonon with the required momentum

The values can be found in Table 3.1 page 49 for Silicon

Testing Papers

The following papers are to help create a procedure for measuring emmisivity ect.

Mathematical Framework for Predicting Solar Thermal Build-up of Spectrally Selective Coatings at the Earth's Surface

This article talks about the different colour paints and their ability to absorb the spectrum of light. Temperature was also observed and found the black gets the hot while lighter colours remain cooler. It has some interesting graphes to show this.

N.P. Lavery. Mathematical Framework for Predicting Solar Thermal Build-up of Spectrally Selective Coatings at the Earth's Surface. Applied Mathematical Modelling 31 (2007) 1635–1651

5mjmp 20:16, 22 September 2009 (UTC)

Stainless steel/tin/glass coating as spectrally selective material for passive radiative cooling applications

T. Mouhib, A. Mouhsen, E.M. Oualim, M. Harmouchi, J.P. Vigneron, P. Defrance. Stainless steel/tin/glass coating as spectrally selective material for passive radiative cooling applications. Optical Materials 31 (2009) 673–677

Spectral selectivity of composite enamel coatings on 321 stainless steel

H. J. Brown-Shaklee, W. Carty and D. D. Edwards. Spectral selectivity of composite enamel coatings on 321 stainless steel. Solar Energy Materials & Solar Cells 93(2009)1404–1410

Structure and optical properties of pulsed sputter deposited CrxOy/Cr/Cr2O3 solar selective coatings

H. C. Barshilia, N. Selvakumar and K.S. Rajam. Structure and optical properties of pulsed sputter deposited CrxOy/Cr/Cr2O3 solar selective coatings. JOURNAL OF APPLIED PHYSICS 103, 023507 (2008)

MODELS FOR THE ANGLE-DEPENDENT OPTICAL PROPERTIES OF COATED GLAZING MATERIALS

M. Rubin, R. Powles and K. Von Rottkay. MODELS FOR THE ANGLE-DEPENDENT OPTICAL PROPERTIES OF COATED GLAZING MATERIALS. Solar Energy Vol. 66, No. 4, pp. 267–276, 1999

Optical Characterization of Industrially sputtered nickel-nickel oxide solar selective surface M. Adsten, R. Joerger, K. Jarrendahl and E. Wackelgard. Solar Energy Vol. 68, No. 4, pp. 325–328, (2000)

Their goal was to find if the optical constants of their materials were close to the ideal ones, and learn enough about the materials to improve them if they weren't. Commecial absorber in question had a solar absorptance of 0.94-0.96, and a thermal emittance of 0.13-0.15. Tools employed:

• Rutherford backscattering to determine atomic composition
• Xray photo electron spectroscopy for surface composition
• Non-standard spectrophotometer with an integrating sphere to measure absolute reflectance and transmittance (in this case sample is loaded on a ring and sphere 4mm large acts as the detector and is rotated all around the sample

Although graphs in paper show different temperatures (0ºC and 55ºC) measurements for reflectance, no mention is made of how they did this in the paper

Laboratory Testing of the Reflectance Properties of Roofing Materials Parker, D S, J E R McIlvaine, S F Barkaszi, D J Beal and M T Anello (2000). FSEC-CR670-00. Florida Solar Energy Center, Cocoa, FL

Although this article is focused on testing samples with a high reflectivity, high infrared emittance in order to reduce residential cooling loads, some of their measurement techniques could be used by us, as they tested similar materials. They suggest two ASTM standards:

• ASTM Standard Test Method E903-88 Hemispherical spectral reflectance of the samples oer the solar bandwidth from 300 to 2500nm. This one used an integrating sphere
• ASTM E480-71 Long-wave infrared reflectance of samples allowing calculation of reflectance

They also used an infrared camera to show different heat emission levels

The development and testing of emissivity enhancement coatings for thermophotovoltaic (TPV) radiator applications B.V. Cockeram, D.P. Measures, A.J. Mueller. (1999) Thin Solid Films 355-356, pp 17-25

TPV radiator requires that high temperature photons are emitted to TPV cells for converstion to electricity, and it is desirable to enhance emissivity. They've tried to do this with coatings and surface roughness. Characterization equipment used:

• Scanning electron microscopy
• X-ray diffraction
• Assumed no transmittance (e=1-R) and measured spectral reflectance . Assume that optical properties are independent of temperature. Equation given for total hemispherical emittance at a given temperature from the spectral emittance data and the black body distribution function at the temperature of interest

Reflectance, Solar Absorptivity, and Thermal Emissivity of SiO2-Coated Aluminum

http://www.opticsinfobase.org/DirectPDFAccess/E75F6CB1-BDB9-137E-CF0BBAB1124D8A11_15646.pdf?da=1&id=15646&seq=0

G. Hass, J. B. Ramsey, J. B. Heaney, and J. J. Triolo. Reflectance, Solar Absorptivity, and Thermal Emissivity of SiO2-Coated Aluminum. February 1969 / Vol. 8, No. 2 / APPLIED OPTICS

5mjmp 14:53, 23 September 2009 (UTC)

Determination of global absorptivity and emissivity of some opaque bulk materials using an integrating sphere calorimeter without ports

http://www.iop.org/EJ/article/0957-0233/18/8/043/mst7_8_043.pdf?request-id=5a363ede-ec3c-4a8b-b3fa-c4fd75d6f9f8

Reccab M Ochieng, Frederick N Onyango and Albert J Owino. Determination of global absorptivity and emissivity of some opaque bulk materials using an integrating sphere calorimeter without ports. Meas. Sci. Technol. 18 (2007) 2667–2672

5mjmp 14:57, 23 September 2009 (UTC)

Monte Carlo method in optical radiometry

http://www.iop.org/EJ/article/0026-1394/35/4/44/me8444.pdf?request-id=15db0a6c-a299-4c86-ac18-879458afd6af

A. V. Prokhorov. Monte Carlo method in optical radiometry.Metrologia, 1998, 35, 465-471

5mjmp 14:39, 24 September 2009 (UTC)

MEASUREMENT OF THE TEMPERATURE OF A SURFACE IRRADIATED BY CONCENTRATED LIGHT

http://www.springerlink.com/content/j0w9036437418411/fulltext.pdf

V. V. Kan, T. T. Riskiev and T. P. Salikhov. MEASUREMENT OF THE TEMPERATURE OF A SURFACE IRRADIATED BY CONCENTRATED LIGHT. 0022-0841/91/6104-1284512.50 1992 Plenum Publishing Corporation

5mjmp 14:56, 24 September 2009 (UTC)

Applications for the Integrating Sphere in the Near-Infrared Spectral Region

http://www.piketech.com/technical/application-pdfs/Integrating-Sphere-NIR-Spectral-Region.pdf#search="integrating sphere"

Gabor Kemeny. Applications for the Integrating Sphere in the Near-Infrared Spectral Region. PIKE Technologies.

Although we are using a Mid-Infrared Integrating Sphere, this might spark some ideas...

5mjmp 15:17, 24 September 2009 (UTC)

Mid-IR IntegratIR – Integrating Sphere

http://www.piketech.com/products/product-documentation-pdfs/MidIRIntegratIR_PDS.pdf#search="integrating sphere"

Pike Technologies. Mid-IR IntegratIR – Integrating Sphere. ©2008 PIKE Technologies. All rights reserved. All trademarks are the property of PIKE Technologies.

This is Pike Technologies spec sheet for our integrating sphere... Wish there was more... sigh...

5mjmp 15:22, 24 September 2009 (UTC)

Helpful Papers

[1] Limits to the Efficiency of Silicon Multilayer Thin Film Solar CellsS.R. Wenham, M.A. Green, S. Edmiston, P. Campbell, L. Koschier, C.B. Honsberg, A.B. Sproul, D. Thorpe, Z. Shi and G. Heiser. Solar Energy Materials and Solar Cells. Volumes 41-42, June 1996, Pages 3-17

This article is a detailed report on silicon multilayer multijunction thin film (MMTF) solar cells. The article talks about the performance of multilayer solar cells, quantum efficiencies, resistive losses, open circuit voltage, tolerance to grain boundaries, junction recombination and limits to efficiency. By injecting carriers between parallel layers the MMTF are ablilty to minise lateral resistance losses. It was found through testing that the efficiency was about 15%.

[2]Solar Collector Overheating Protection M. Slaman and R. Griessen. Solar Energy. Volume 83, Issue 7, Pages 982-987 The article is about reducing the about of light interacting with the PV panel to reduce the amount of heat generated by the PV panel. They use a primatic structure to reduce the incoming light. Several different experiments were complete; the light was shawn directly at the panel with the primatric cover, the panel was tilted to mimic the earth's rotation and two layers of the primatic structure were used. The conclusion was that it did help reduce the amount of light and therefore some of the temperature. Further publications will use the light reducing properties of pyramids and cones.

[3]Solar@anu

This paper just talks about the resarch being completed at the Australian National University. They are studying the effects of impurities on semiconductors such as iron impurities. They mainly work on multicrystalline silicon cells which usually have thin films applied ot thier surfaces. Furthermore, they are looking at ways to get the maximum benift from thin films such as amorphous silicon and silicon nitride.

Sliver cells are highly efficient thin single crystalline solar cells which have reached an effiency greater than 20%.

They are also looking at Fluorescent Organic Dyes which have several interesting properties such as they emit one wavelength but emit a longer one and the emission is random. If this dye were applied to glaze the effiency of the PV would increase since the glaze would reflect less light and therefore more light would make contact with the PV cells.

They have also looked at PVTs and residential scale thermal systems.

Email at: solar@anu.edu.au

[4]TCO and Light Trapping in Silicon Thin Film Solar CellsJoachim Müller, Bernd Rech, Jiri Springer and Milan Vanecek. Solar Energy. Volume 77, Issue 6, December 2004, Pages 917-930

[5]Fabrication and optimisation of highly efficient cermet-based spectrally selective coatings for high operating temperature S. Esposito, A. Antonaia, M.L. Addonizio, and S. Aprea. Thin Solid Films, 517 (2009) 6000–6006

[6]Photoreflectance study of Si delta-doped low-temerature GaAs grown by molecular beam epitaxy. T.M. Cheng and C.Y. Chang. Journal of Applied Physics. Vol. 77, No. 5

[7]Optical constants and film density of TiNxOy solar selective absorbers. M. Lazarov, P.Raths, H. Metzger, and W.Spirkl. Journal of Applied Physics, Vol. 77, No. 5

[8]Performance improvement of organic solar cells with moth eye anti-reflection coating. K. Forberich, G. Dennler, M. Scharber, K. Hingerl, T. Fromherz, and C. Brabec. Thin Solid Films. Vol. 516. No 20. 30, August 2008. P.7167-7170

[9] Mg-Ti-H thin films for smart solar collectors. D.M Borsa, A Baldi, M. Pasturel, H. Schreuders, B. Dam, and R. Griessen. Applied Physics Letters. Vol. 88 June 14, 2006

[10]On the development, optical properties and thermal performance of cool coloured coatings for the urban environment. A Synnefa, M. Santamouris, and K. Apostolakis. Solar Energy. Vol. 81, No. 4. April 2007, Pages 488-497

[11]Nanostructured black cobalt coatings for solar absorbers. Z. Hamid, A. Aal, and P. Schmuki. Surface and Interface Analysis. October 10, 2008

[12]Structure and optical properties of pulsed sputter deposited Cr_xO_y/Cr/Cr₂O₃ solar selective coatings. H Barshilia, N. Selvakumar, and K. S. Rajam. Journal of Applied Physics. Vol. 103 (2008)

[13]Solar selective absorber coating for high service temperatures, produced by plasma sputtering. M. Lanxner, Z. Elgat. Proc. SPIE Vol. 1272. February 15, 2005

[14]Solar selective coatings based on Nickel Oxide obtained via spray pyrolysis. M. Voinea, E. Ienei, C. Bogatu, A. Duta. Journal of Nanoscience and Nanotechnology. Vol. 9 No. 7, July 2009. Pages 4279-4284

[15]TiAlN/TiAlON/Si₃N₄ tandem absorber for high temperature solar selective applications. D.V. Sridhara Rao and K. Muraleedharan. Applied Physics Letters. Vol 89. November 8 2006.