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# Spectral Selective Coatings Literature Review

 This page was developed by the Queen's University Applied Sustainability Research Group.

## 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

$e=mc^2$

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

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

Where:

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

Note: Transmission is T = 1 - R

Absorption of Light

Absorbed light at a distance into the semiconductor

Intensity of light = I

$I = I(x_o) exp( -\alpha (x - x_o))$

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

Note:

• $\lambda = \frac{c}{f}$

Math Equation Help in Wiki

Other Wiki Basics

Direct Band Gap Semiconductor

$hf = E_f - E_i$

$\alpha(hf) = A (hf - E_g)^{1/2}$

Where

• $E_f$ Final energy state
• $E_i$ Initial energy state
• $E_g$ Band Gap Energy
• A is a constant with a value of 2E4 when alpha is expressed in $cm^(-1)$ and hf and $E_g$ is in eV.

Indirect Band Gap Semiconductor

$hf = E_g - E_p$

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

Where

• $E_p$ is energy of an absorbed phonon with the required momentum

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

## Applicable ASTM Standards

Please note, although these standards will be useful in future work, they provide little new insight for the work that is currently being conducted. I still thought it worthwhile to keep them around.

### E 408-71 (Reapproved 2008): Standard Test Methods for Total Normal Emittance of Surfaces Using inspection-Meter Techniques

Provides equation for total normal emittance (the ratio of the normal radiance of a specimen to that of a blackbody at the same temperature; dependent on wavelength and temperature. The rest of the standard goes on how to measure the emittance of large surfaces, in a non-destructive manner using portable devices, neither of which are neither an integrating sphere nor a spectrophotomer. This standard is included here when the time comes to test full-scale spectrally selective panels.

### E-1980-01: Standard Practice for Calculating Solar Reflectance Index of Horizontal and Low-Sloped Opaque Surfaces

Calculation of the Solar Reflectance Index (SRI) of horizontal and low-sloped opaque surfaces at standard conditions (emissivity /0.1). References E 903, Test Method for Solar Absorption, Reflectance and Transmittance of Materials Using Intergrating Spheres (this standard is not accessible through Queen’s resources, it is possible that it has been superseded by something else). Standard definition of thermal emissivity as: the ratio of radiant flux emitted by a surface at a given temperature to that emitted by a blackbody radiator at the same temperature (for temps below 150ºC).

• Gives equation for steady state surface temp of a material exposed to the sun (define solar absorptance as 1-solar reflectance)

### C 1549-04: Standard Test Method for Determination of Solar Reflectance Near Ambient Temperature Using a Portable Solar Reflectometer

Technique for determining the solar reflectance of a flat opaque material in a laboratory or field setting using portable solar reflectometer to evaluate temperatures and heat flows across surfaces exposed to solar radiation. This references E 903 again. It would be great to get that one. Measurements are made when a sample is heated by a tungsten lamp for 2 seconds out of a 10 second measurement cycle. 4 detectors measure the reflection at 20º from the sample surface. Solar energy that is absorbed is defined as Energy absorbed=area*solar flux*(1-solar reflectance), where solar reflectance is a dimensionless quantity. Describes how to perform the measurement, again, not using an integrating sphere.

### E 1175-87 (Re-approved 2009): Standard Test Method for Determining Solar or Photopic Reflectance, Transmittance, and Absorptance of Materials Using a Large Diameter Integrating Sphere

Accurate optical property measurements of spatially nonuniform materials is covered in this standard. For large specimens with specular and diffuse optical properties. Suggests that transmittance is measured by placing sample on top of port, but reflectance is measured by placing sample inside the sphere, this is not what PIKE recommends we do. Large sphere is used to average the disparities in the material (the sample size is large and so is the beam of light hitting it). States again that absorption can be calculated as 1-total solar reflectance in opaque materials. A large sphere is defined as one with a minimum radius of 1 m. Our sphere is definitely not large. Unfortunately, this also isn’t very useful.

## Testing Papers

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

### The challenge of high-performance selective emitters for thermophotovoltaic applications

A. Licciulli, D Diso, G Torsello, S Tundo, A Maffeszzoli, M Lomascolo, and M Mazzer. Semiconductor Science and Technology. 18 (2003) S174-S183

This is a review article on what’s been done in materials science for high temperature application of thermophotovoltaics. Selective emitter is denied as a class of materials equilibrium thermal-radiation emission occurs in a narrower spectral region compared to a black body at the same temperature. This isn’t quite the same kind of selective surface we have been looking for, but it’s a neat article none the less. Operating temperatures for devices in question is 100-1500ºC. Says that detailed microscopic analysis and the basic theory of the mechanisms ruling high temp emission is required.

• Equation for spectral radiance of at black body in terms of wavelength and temp that might be useful
• Equation for emissivity of a surface as a function of temperature
• Suggest measuring temp of samples using a thermocouple, but cautions that conduction will occur and remove heat from that area of the sample more quickly, non invasive temperature measurement techniques may include IR radiation thermometers, one study referenced knew the emissivity based on the power of the furnace they assumed the sample to be in equilibrium with.

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

G. Hass, J.B. Ramsey, J.B. Heaney, and J.J. Trilo. Applied Optics. Volume 8, Issue 2. February 1969. pp275-282

This is an old article, but I thought it might be helpful because we’re working with aluminum too. Confirms what we already know that aluminum can be coated with surface films to produce a surface that is non absorbing in the visible region, but strongly absorbing in the IR region. Describe the effects of varying the size of an electron beam used in SiO2 deposition has on absorptance in UV region (wide beam = no absorption in far UV to near IR). They used highly polished samples to measure reflectance, this isn’t possible for us since it seems to mess up the integrating sphere even more, and we want to test the aluminum in the condition we’re going to use it in. Solar reflectance was measured using a modified Beckman DU instrument with a Perkin-Elmer model 350 double beam spectrophotometer. (reflectance measurements were absolute). Absorption and emission were evaluated graphically from charts with distorted λ scales and integration by means of planimeter.

• Used a thermocouple (copper-constantan ) to measure the temperature of the sample. Equation to calculate emissivity as sample cools:ϵ=WCP3σAt(τ2-τ1)1T23-1T13 , corrected because of heat losses from attached thermocouples
• Some reflectance and emissivity graphs, might be helpful to see if ours are anything close to right.

### Spectral selectivity of high-temperature solar absorbers

D.M. Trotter, Jr., and A. J. Sievers. Applied Optics. Vol. 19, No. 5. March 1980 pp 711-728

The first paragraph in this is really helpful. There should be a cutoff wavelength in spectral selective materials at which point the spectral absorptance abruptly drops to zero. This position is weakly a function of operating temperature (verifying that we should be checking this) and the solar flux concentration (this value is fixed by the sun, but in our experiments we should try to use the same) They suggest the cut off frequency should be less than or equal to 2x3.14xc/2.

• equations for thermal emittance and solar absorption in terms of area, operating temperature, energy flux, the solar spectrum and Plancks law spectral distribution
• Use models consisting of models with selectively absorbing coatings
• Values of emissivity determined by the overlap between the blackbody absorptivity and what the material produces at a given temp
• lots of math in this paper, I don’t think its exactly what we want, deals a lot with material thickness
• Graph of a thermally broadened and blackbody emissivity appears to show aluminum having the same emissivity with temperature as an aluminum black body?
• emissivity is also strongly correlated to incidence angle

### Integrating Sphere for Mid- and Near-infrared Reflection Spectroscopy

Leonard M. Hanssen, and Keith A. Snail. Handbook of Vibrational Spectroscopy. John Wiley & Sons Ltd. 2002

This is a literature review article on integrating spheres, it does an excellent job summarizing what’s been done in the past and some of the nuances associated with operating spheres. Here are some highlights…Integrating spheres are the primary analysis tool for quantitative characterization of reflectance and absorptance for materials that are highly scattering.

• reflectance is defined as the ratio of flux reflected from a surface to that incident on the same surface
• integrating sphere throughput is the efficiency of the integrating sphere system related to the incident flux of the detector over the input flux
• First recording spectrophotomer made in 1928 at MIT, 1916 Taylor and Rosa develop a technique for measuring absolute reflectance using an integrating sphere
• National Institute of Standards and Technology is developing a standard for the integrating sphere using roughened gold, another is used by the National Physics Laboratory (UK) based on flame-sprayed aluminum.
• Key aspects of sphere design are shape and Lambertian inner coating that allows light to be reflected off all surfaces equally in all directions – the detector should receive a flux directly proportional to the light on the sphere. If the sphere isn’t perfect, the high surface reflectance ensures that the light bounces around several times before it hits the detector
• Several methods for solving for sphere efficiency (throughput), conservation of energy, integral equation of sphere irradiance, solving a matrix equation determined by the number of distinct regions in the sphere (all methods are consistant)
• Absolute reflectance sphere are used to calibrate standards for reflectance instruments
• Describe some spheres where the sample goes on the inside of the sphere, and others where it goes on top. For some methods of collection (which we obviously wont use) the sample has to be the same material as the sphere
• Relative reflectance measurements are fine for the vast majority of applications
• We have a substitution type sphere (the reference and the sample can’t be on the detector at the same time). This is the simplest design and doesn’t require any moving parts which would suggest we should be keeping our mirror in the sample position when making measurements
• Some losses because our sample is flat, may not direct light everywhere

### Inverse estimation of temperature dependent emissivity of solid metals

J. Zueco and F. Alhama. Journal of quantitative spectroscopy & radiative transfer [0022-4073] Zueco yr.2006 vol.101 iss.1 pg.73-86 [1]

Super mathy review. They figure out what temp the sample was at without actually measuring it. They say that total emissivity depends on temperature, but experimental methods (2 referenced) are complicated and time consuming – their approach lets you measure for a smaller amount of time, figure out and equation that governs temp. Check references from this paper, they might have something more useful

### Temperature-dependent emissivity of silicon-related materials and structures

Ravindra, N.M.; Abedrabbo, S.; Wei Chen; Tong, F.M.; Nanda, A.K.; Speranza, A.C.;Semiconductor Manufacturing, IEEE Transactions on Volume 11, Issue 1, Feb. 1998 Page(s):30 – 39 [2]

Might be able to use this paper for the math in it, but they used very specific equipment that allowed them to measure everything over a huge temperature range. Emissivity is an important parameter in radiation thermometry.It is defined as the ratio of the radiance of a given object to that of a blackbody at the same temperature and for the same spectral and directional conditions. It is a function of wavelength and temperature. In this experiment transmittance and reflectance were measured and equations are provided that link the observed to the true values. A spectral emissometer (one of three in the USA) allowed measurement of radiance, reflectance, transmittance, and temperature simultaneously. They got % emittance, % transmittance, and % reflectance as a function of temperature across wave lengths.

### Optical Characterization of Industrially Sputtered Nickel-Nickel Oxide Solar Selective Surface

M Adsten, R. Joerger, K. Jarrendahl, E. Wackelgard. Solar Energy Volume 68. No.4 pp 325-328. Year 2000. [3]

Their goal was to see if the optical constants of the materials and manipulated materials they were testing were close to the ideal ones. They measured absolute spectral specular reflectance and transmittance using a non-standard spectrophotometer with a small (4mm) integrating sphere as a detector. Their sample didn’t go on the sphere, but on a different surface and they spun the sphere all over the place because they were concerned about angles. Also used Co Variable Angles of incidence Spectroscopic ellipsometry (VASE). No temperature series.

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

N.P. Lavery, Applied Mathematical Modelling 31 (2007) 1635-1651 [4]

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 graphs to show this. 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. Optical Materials 31 (2009) 673–677[5]

The authors are studying spectrally selective surfaces in a radiative cooling application. They assume that heat transfer occurs only by radiation and ignore the effects of conduction and convection. They state that at equilibrium the energy emitted is balanced by the energy that is absorbed.Absorptance is defined as 1-(Rsol+Tsol), where are Rsol is the solar reflectance (estimated as the average spectral reflectance over the entire solar spectrum). Measured reflectance, transmittance and absorptance using a spectroradiometer and a monochromator. Have graphs of Reflectance vs wavelength

### Spectral selectivity of composite enamel coatings on 321 stainless steel

H. J. Brown-Shaklee, W. Carty and D. D. Edwards. Solar Energy Materials & Solar Cells 93(2009)1404–1410[6] This article examines porcelain enamel coatings on stainless steel that do not normally exhibit spectrally selective properties unless coated with a low emissivity coating. If they did work though, they'd be ideal for high temp, harsh environments. Shows lots of %A graphs at different temperatures

• Measured refractive index using Becke line method
• solar absorptance and thermal emittance found from total reflectance measurements assuming that Kirchoff's law applies
• 200-2,500nm diffuse reflectance using UV-vis-NIR spectrometer
• 2,500-25,000 FT-IR spectrometer with a cold coated integrating sphere with a mercury-cadmium-telluride detector
• Thermal emittance determined using a weighted integration over the Planck distribution for a specific temperature

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

H. C. Barshilia, N. Selvakumar and K.S. Rajam. Journal of Applied Physics 103, 023507 (2008)[ [7]

• Black chrome coatings used for domestic hot water applications. This study designed a dielectric/metalic/dielectric coating of Cr2O3 resulting in high absorptance in the visible region and low emittance in the IR region. 3 layers deposited on copper substrate by chemical vapour deposition.
• Notes that info on thermal stability, microstructure and optical properties are lacking
• Used XRD, x-ray photo-electron spectroscopy (XPS), atomic force microscopy (AFM), micro-Raman spectroscopy, solar spectrum relectometer and emissometer and a phase modulated spectroscopic ellispometry
• Operating temperature of solar thermal collector listed between 80 and 85ºC, tested thermal stability between 200ºC and 400ºC
• Report average from emissivity and absorption measurements made at four different positions
• Heated emissometer to desired temperature so that sample wouldn't have to be heated (we probably can't do this because our integrating sphere need to be cooled)

### Models for the Angle-Depenedent Optical Properties of Coated Glazing Materials

M. Rubin, R. Powles and K. Von Rottkay. Solar Energy Vol. 66, No. 4, pp. 267–276, (1999) [8]

Not terribly useful for thermal dependence of coatings, however might be good to keep around when trying to model the angle-dependent optics. They used a Perkin-Elmer Lambda 19 Spectrophotometer to measure the transmittance and reflectance. This paper really focuses on transmittance at different angles

### 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) [9]

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. Commercial 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 [10]

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 [11]

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

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

N.P. Lavery, Applied Mathematical Modelling 31 (2007) 1635-1651 [12]

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. 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. Optical Materials 31 (2009) 673–677 [13]

The authors are studying spectrally selective surfaces in a radiative cooling application. They assume that heat transfer occurs only by radiation and ignore the effects of conduction and convection. They state that at equilibrium the energy emitted is balanced by the energy that is absorbed.Absorptance is defined as 1-(Rsol+Tsol), where are Rsol is the solar reflectance (estimated as the average spectral reflectance over the entire solar spectrum). Measured reflectance, transmittance and absorptance using a spectroradiometer and a monochromator. Have graphs of Reflectance vs wavelength

### Spectral selectivity of composite enamel coatings on 321 stainless steel

H. J. Brown-Shaklee, W. Carty and D. D. Edwards. Solar Energy Materials & Solar Cells 93(2009)1404–1410 [14]

This article examines porcelain enamel coatings on stainless steel that do not normally exhibit spectrally selective properties unless coated with a low emissivity coating. If they did work though, they'd be ideal for high temp, harsh environments. Shows lots of %A graphs at different temperatures

• Measured refractive index using Becke line method
• solar absorptance and thermal emittance found from total reflectance measurements assuming that Kirchoff's law applies
• 200-2,500nm diffuse reflectance using UV-vis-NIR spectrometer
• 2,500-25,000 FT-IR spectrometer with a cold coated integrating sphere with a mercury-cadmium-telluride detector
• Thermal emittance determined using a weighted integration over the Planck distribution for a specific temperature

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

H. C. Barshilia, N. Selvakumar and K.S. Rajam. Journal of Applied Physics 103, 023507 (2008)[15]

• Black chrome coatings used for domestic hot water applications. This study designed a dielectric/metalic/dielectric coating of Cr2O3 resulting in high absorptance in the visible region and low emittance in the IR region. 3 layers deposited on copper substrate by chemical vapour deposition.
• Notes that info on thermal stability, microstructure and optical properties are lacking
• Used XRD, x-ray photo-electron spectroscopy (XPS), atomic force microscopy (AFM), micro-Raman spectroscopy, solar spectrum relectometer and emissometer and a phase modulated spectroscopic ellispometry
• Operating temperature of solar thermal collector listed between 80 and 85ºC, tested thermal stability between 200ºC and 400ºC
• Report average from emissivity and absorption measurements made at four different positions
• Heated emissometer to desired temperature so that sample wouldn't have to be heated (we probably can't do this because our integrating sphere need to be cooled)

### Models for the angle-dependent optical properties of coated glazing materials

M. Rubin, R. Powles and K. Von Rottkay. Solar Energy Vol. 66, No. 4, pp. 267–276, (1999) [16]

Not terribly useful for thermal dependence of coatings, however might be good to keep around when trying to model the angle-dependent optics. They used a Perkin-Elmer Lambda 19 Spectrophotometer to measure the transmittance and reflectance. This paper really focuses on transmittance at different angles

### 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)[17]

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. Commercial 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[18]

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 [19]

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 G. Hass, J. B. Ramsey, J. B. Heaney, and J. J. Triolo. 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

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

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

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

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

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

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

#### Integrating Spheres for Mid- and Near-infrared Reflection Spectroscopy

Introduction:Integrating sphere instrumentation has historically been the primary analysis tool for accurate quantitative characterization of reflectance and absorptance of samples and materials that exhibit a high degree of scattering. The four most widely used types of instruments for performing reflectance measurements of diffusing surfaces are biconical mirror systems, gonio-reflectometers, 2p conic mirror reflectometers, and integrating spheres. Spectrophotometer accessories of biconical design (e.g. “praying mantis” type devices) are the most commonly used for semiquantitatively characterizing the diffuse reflectance of powdered samples. However, because of the restricted angular range of measurement, a fraction of the reflected light that is dependent on the specific directional scattering properties of each sample will be lost. This limits the degree of accuracy for these devices. For quantitative measurements of hemispherical diffuse reflectance, methods based on the 90C years of accumulated knowledge on integrating spheres are preferred. Two comprehensive reviews of absolute methods for integrating sphere-based reflectance measurements were published in the 1970s by Budde1 and the International Commission on Illumination (CIE).2 Since that time, integrating spheres for the mid-infrared have become commonplace, and major advances have occurred in the areas of computational optics modeling of integrating spheres, coupling detectors to spheres with nonimaging concentrators, and the development of new nearly Lambertian reflectors. A single article must necessarily be focused on specific aspects of integrating sphere reflectance spectroscopy. In this article we will describe the integrating sphere instrumentation that is used in diffuse reflection spectroscopy: how sphere systems function, what the various designs and methods for reflectance and transmittance measurement are, both absolute and relative, what the sources of measurement error are, and why sphere systems are used in preference to other techniques. We begin by defining the specialized terms associated with diffuse reflectance measurement in Section 2, followed by a short historical review of the important developments in the use of integrating spheres for reflectance in Section 3. The most important characteristic parameter of an integrating sphere, its throughput (efficiency), is discussed in Section 4. This provides an introduction to a detailed description and comparison of both absolute and relative methods that are used in sphere systems in Section 5. Sources of error and measurement uncertainty are addressed in Section 6. A sampling of current commercial sphere reflectometer systems is described in Section 7, followed by a summary in Section 8.

L. M. Hanssen1 and K. A. Snail. Integrating Spheres for Mid- and Near-infrared Reflection Spectroscopy. Handbook of Vibrational Spectroscopy. (c) John Wiley & Sons Ltd, Chichester, 2002

5mjmp 13:28, 28 September 2009 (UTC)

#### Integrating Sphere for Imperfectly Diffuse Samples

Abstract:An integrating sphere for determining spectral reflectance and transmittance as a function of angle of incidence and wavelength in the 0.33- to 2.5-,u region is described. Geometrical arrangement of sample, entrance port, and detector as well as directional characteristics of detector and sphere wall coating permit absolute or relative measurements to be made for a sample with an arbitrary reflection-distribution function.

D. K. EDWARDS, J. T. GIER, K. E. NELSON, and R. D. RODDICK, "Integrating Sphere for Imperfectly Diffuse Samples," J. Opt. Soc. Am. 51, 1279-1288 (1961) http://www.opticsinfobase.org/abstract.cfm?URI=josa-51-11-1279

5mjmp 18:39, 28 September 2009 (UTC)

#### Comparison of four analytic methods for the calculation of irradiance in integrating spheres

Abstract: The relative merits of four methods—energy balance, summation of reflections, inversion of the irradiancetransfer matrix, and solution of the integral equation—are compared by using each to determine irradiance in a multizone true sphere and in a sphere with a flat port; in the process several new solutions are presented. Although limited in applicability, the energy-balance method is by far the most direct. For the flat-port configuration the relationships among various published expressions are established; furthermore, the curvedsurface interreflection irradiance is shown to be nonuniform when the initial irradiance is restricted to a part of the curved surface.

John F. Clare, "Comparison of four analytic methods for the calculation of irradiance in integrating spheres," J. Opt. Soc. Am. A 15, 3086-3096 (1998) http://www.opticsinfobase.org/abstract.cfm?URI=josaa-15-12-3086

5mjmp 18:39, 28 September 2009 (UTC)

#### Matrix method for integrating-sphere calculations

Abstract:Aplicable to any sphere configuration, including those with flat areas, specular samples, and baffles, and is especially effective when used in computer simulations of sphere irradiance. The formalism can accommodate the angular sensitivity of any detector or the bidirectional-reflectance distribution function of any sample. Examples of simple analytical solutions are presented, and computer simulation is demonstrated with calculations of the irradiance inhomogeneities caused by underfilling a flat sample. In particular, the simulation shows that, when the input beam does not completely fill a flat sample, the sample is surrounded by a band of reduced irradiance. Outside this dark band, the irradiance is increased slightly. The width of the dark band, but not its depth, increases as the beam size decreases relative to the sample size. The depth depends on sample size and reflectance. Outside the dark-band region, the irradiance shifts due to sample underfilling are much smaller than the easily avoidable, first-order errors caused by neglecting the flat-sample effects.

Herbert L. Tardy, "Matrix method for integrating-sphere calculations," J. Opt. Soc. Am. A 8, 1411-1418 (1991) http://www.opticsinfobase.org/abstract.cfm?URI=josaa-8-9-1411

5mjmp 18:41, 28 September 2009 (UTC)

#### Evaluation of correction factors for transmittance measurements in single-beam integrating spheres

Abstract:An integrating sphere for transmittance measurements at normal and oblique angles of incidence has been constructed. The sphere is a single-beam instrument that uses a small-area silicon diode as the detector. The entry port is only 0.37% of the total wall area and has an oblong shape to permit measurements at high angles of incidence for scattering samples. A small beam size has been made possible by using a low-noise preamplifier system for the detector circuit. The oblong port shape and a small beam size make it possible to perform simulated double-beam measurements at near-normal incidence. Modified correction factors for the sample reflectance have been derived. Special attention has been paid to the separation into a diffuse and a specular component of the transmitted light. Results have been compared with the results of measurements on a double-beam instrument, and the correction factors for specular and diffuse samples have been experimentally verified. The importance of using the right correction factors for different types of samples has been evaluated together with the influence of the sphere parameters.

K. Grandin and A. Roos, "Evaluation of correction factors for transmittance measurements in single-beam integrating spheres," Appl. Opt. 33, 6098-6104 (1994) http://www.opticsinfobase.org/abstract.cfm?URI=ao-33-25-6098

5mjmp 18:44, 28 September 2009 (UTC)

#### Reflection and transmission measurements with an integrating sphere and Fourier-transform infrared spectrometer

Abstract:A method of measuring the total reflection and transmission spectra of scattering materials with an integrating sphere and a Fourier-transform infrared spectrometer is studied. The reflectance measurement system is considered in a specific case where the incident beam overfills the back side port of the sphere, and the correction functions for measured spectra are derived for this case. Correction formulas are based on the energy balance between incident radiation and absorbed or escaped radiation in the system. The absorption spectrum of the material is calculated from the corrected spectra. The optical properties of paper samples and radiating surfaces of infrared dryers in the 0.4-20-pum wavelength range are determined. The correction formulas are compared with previous work presented in the literature.

Kari T. Ojala, Esa Koski, and Markku J. Lampinen, "Reflection and transmission measurements with an integrating sphere and Fourier-transform infrared spectrometer," Appl. Opt. 31, 4582-4589 (1992) http://www.opticsinfobase.org/abstract.cfm?URI=ao-31-22-4582

5mjmp 18:46, 28 September 2009 (UTC)

#### Stray-light corrections in integrating-sphere measurements on low-scattering samples

Abstract:A method for correcting integrating-sphere signals that considers differences in the angular distribution of scattered light is extended to sources of errors that are due to stray light from imperfect optical components. We show that it is possible to measure low levels of scattering, below 1%, by using a standard integrating sphere, provided that the various contributions to stray light are taken into account properly. For low-scattering samples these corrections are more important than those from the angular distribution of the scattering. A procedure for the experimental determination of stray-light components is suggested. Simple, easy to use, compact equations for the diffuse and specular reflectance and transmittance values of the sample as functions of the recorded signals are presented.

Daniel Rönnow and Arne Roos, "Stray-light corrections in integrating-sphere measurements on low-scattering samples," Appl. Opt. 33, 6092-6097 (1994) http://www.opticsinfobase.org/abstract.cfm?URI=ao-33-25-6092

5mjmp 18:48, 28 September 2009 (UTC)

#### Explicit solution of the spectral radiance in integrating spheres with application to the Earth Radiation Budget Experiment ground calibration

Abstract:An explicit solution of the spectral radiance leaving an arbitrary point on the wall of a spherical cavity with diffuse reflectivity is obtained. The solution is applicable to spheres with an arbitrary number of openings of any size and shape, an arbitrary number of light sources with possibly nondiffuse characteristics, a nonuniform sphere-wall temperature distribution, nonuniform and nondiffuse sphere-wall emissivity, and nonuniform but diffuse spherewall spectral reflectivity. A general measurement equation is obtained that describes the output of a sensor measuring the sphere output within a given field of view and with specified angular and spectral responses measuring the sphere output. The results are applied to the Earth Radiation Budget Experiment (ERBE) integrating sphere. The sphere-wall radiance uniformity, loading effects, and nonuniform wall temperature effects are investigated. It is shown that by using appropriate interpretation and processing, a high-accuracy shortwave calibration of the ERBE sensors can be achieved.

Nesim Halyo and Deborah B. Taylor, "Explicit solution of the spectral radiance in integrating spheres with application to the Earth Radiation Budget Experiment ground calibration," J. Opt. Soc. Am. A 5, 520-534 (1988) http://www.opticsinfobase.org/abstract.cfm?URI=josaa-5-4-520

5mjmp 18:54, 28 September 2009 (UTC)

#### Interpretation of integrating sphere signal output for non-Lambertian samples

Abstract:A new formalism is derived for the analysis of signal output from double-beam integrating spheres. The analysis explicitly considers the effects of port losses and a non-Lambertian sample surface and introduces a separation of the diffusely reflected light into two parts: one which should be analyzed as a specular component and one which is fully diffuse. An experimental procedure to determine the two parameters in the formalism is described for two cases, a brushed copper and a rolled aluminum surface, and it is experimentally verified that the formalism eliminates spurious structure from the barium sulfate reference. A criterion is also given for the selection of barium sulfate or polytetrafluorethylene powder as a reference material.

Arne Roos and Carl G. Ribbing, "Interpretation of integrating sphere signal output for non-Lambertian samples," Appl. Opt. 27, 3833-3837 (1988) http://www.opticsinfobase.org/abstract.cfm?URI=ao-27-18-3833

5mjmp 19:24, 28 September 2009 (UTC)

#### Effects of non-Lambertian surfaces on integrating sphere measurements

Abstract:The effects of non-Lambertian scattering of the interior wall of an integrating sphere are examined through a sphere simulation model. The model employs Monte Carlo techniques. A sphere used for measurement of directional–hemispherical reflectance is modeled. The simulation allows sphere wall scattering to vary from perfectly Lambertian to perfectly specular in steps. The results demonstrate that significant measurement error can result as the scattering deviates from the Lambertian ideal. The error is found to be a strong function of the wall reflectance value as well: it is minimized for reflectances approaching 1.0 and increases as the reflectance value decreases to the minimum value examined of 0.5. The magnitudes of the errors associated with non-Lambertian scattering are also shown to be relatively independent of the specific field of view of the detector used in the measurement.

L. M. Hanssen, "Effects of non-Lambertian surfaces on integrating sphere measurements," Appl. Opt. 35, 3597-3606 (1996) http://www.opticsinfobase.org/abstract.cfm?URI=ao-35-19-3597

5mjmp 19:29, 28 September 2009 (UTC)

[20] 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%.

[21]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.

[22]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

[23]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

[24]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

[25]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

[26]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

[27]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

[28] 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

[29]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

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

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

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

[33]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

[34]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.