WO2005072947A1 - Solar control films composed of metal oxide heterostructures, and method of making same - Google Patents

Solar control films composed of metal oxide heterostructures, and method of making same Download PDF

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Publication number
WO2005072947A1
WO2005072947A1 PCT/US2004/044081 US2004044081W WO2005072947A1 WO 2005072947 A1 WO2005072947 A1 WO 2005072947A1 US 2004044081 W US2004044081 W US 2004044081W WO 2005072947 A1 WO2005072947 A1 WO 2005072947A1
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energy gap
low energy
solar control
control film
doped
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PCT/US2004/044081
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French (fr)
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Roman David Yuryevich Korotkov
Thomas Dudley Culp
David Alan Russo
Jeffery Lee Stricker
Ryan Christopher Smith
Gary Stephen Silverman
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Arkema Inc.
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Publication of WO2005072947A1 publication Critical patent/WO2005072947A1/en

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    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C17/00—Surface treatment of glass, not in the form of fibres or filaments, by coating
    • C03C17/34—Surface treatment of glass, not in the form of fibres or filaments, by coating with at least two coatings having different compositions
    • C03C17/3411—Surface treatment of glass, not in the form of fibres or filaments, by coating with at least two coatings having different compositions with at least two coatings of inorganic materials
    • C03C17/3417—Surface treatment of glass, not in the form of fibres or filaments, by coating with at least two coatings having different compositions with at least two coatings of inorganic materials all coatings being oxide coatings
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/20—Filters
    • G02B5/208—Filters for use with infrared or ultraviolet radiation, e.g. for separating visible light from infrared and/or ultraviolet radiation
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/20—Filters
    • G02B5/26—Reflecting filters

Definitions

  • This invention relates .to solar control films, and more particularly to transparent conductive oxide (TCO) coatings having improved reflectivity in the near infrared (NIR) spectrum.
  • TCO transparent conductive oxide
  • the improved reflectivity is achieved by forming the TCO coatings with heterostructures having different band gaps to increase the electron concentration beyond the solubility limit of a given dopant, and thereby decrease or blue shift the plasma wavelength of the coatings.
  • the invention also relate to a method of making TCO solar control films having the above-described properties.
  • the purpose of solar control coatings is to maximize transmittance of visible light while reflecting most infrared and near infrared (NIR) light.
  • NIR near infrared
  • the wavelength above which most photons will be reflected is the "plasma wavelength,” and the closer the plasma wavelength to the visible (blue) side of the NIR spectrum, the more NIR light will be reflected.
  • Typical solar control coatings are composed of multiple Ag/metal oxide stacks with high visible transmittance ⁇ 80% and high near IR reflectance (-70%). These films have plasma wavelengths ⁇ p of ⁇ 0.7 ⁇ m. Most photons with wavelength ⁇ > ⁇ p will be reflected due to the negative real part of the dielectric constant in this region.
  • pyrolytic coatings composed of transparent conductive oxides (TCOs) such as ITO and doped SnO 2 have high transmission in the visible but NIR reflective properties that are lower than those of sputtered film because their plasma wavelengths generally lie in the 1.0 to 1.6 ⁇ m range.
  • the plasma wavelength is inversely proportional to the square root of the electron concentration, an increase in electron concentration results in a decrease in the plasma wavelength.
  • the electron concentration is limited by the solubility limit of the dopant, which in turn is limited by the site density where the dopant substitutes.
  • the theoretical limit for plasma wavelength in conventional coatings made of In 2 O 3 :Sn (ITO), which 21 3 has an electron concentration of 10 cm- is 22 22 3
  • the highest free electron concentration at room 20 3 temperature (RT) is 7x10 cm- (see H.L. Ma et al, Thin Solid Films 298, 151 (1997)), and the theoretical plasma wavelength limit is 1.3 ⁇ m.
  • the present invention overcomes these theoretical limits by depositing variable band gap heterostructures (quantum wells) to increase doping efficiencies, and therefore electron concentrations, in TCO films.
  • quantum confinement (QC) effect of increasing doping concentration in III-V semiconductor heterostructures is well-known, it has not heretofore been used to increase electron concentration in TCO films for the purpose of decreasing the plasma wavelength.
  • TCOs transparent conductive oxides
  • second objective of the invention to provide TCO coatings having high visible transmittance and plasma wavelengths of less than 1 ⁇ m.
  • metal oxide film stacks with sufficient band gap energy difference using atmospheric pressure chemical vapor deposition (APCVD), the film stacks being composed of various metal oxides such as F doped SnO 2 (3.8 eVVZnO (3.4 eV)/F:SnO 2 (3.8 eV).
  • APCVD atmospheric pressure chemical vapor deposition
  • deposition techniques such as sputtering, molecular beam epitaxy (MBE), or laser-assisted deposition (LAD) may be used to deposit the stacks.
  • the film thickness and morphology of each layer in the stack is preferably controlled by varying deposition conditions such as precursor concentration, carrier gas, substrate temperature, and coreactants and accelerants, such as water.
  • Fig. 1 is a schematic energy diagram of a finite quantum well.
  • Fig. 2 is a schematic diagram showing an example of a superlattice used in a preferred embodiment of the present invention.
  • Fig. 3 is a schematic energy diagram of a triangular potential well formed at the interface of two semiconductors.
  • Fig. 1 shows a heterostructure formed by sandwiching one oxide layer 1 with a low band gap (E G] ) between two oxide layers with a higher band gap (E G2 ), E G1 ⁇ E G
  • E G low band gap
  • E G2 higher band gap
  • E G1 ⁇ E G
  • SL superlattice
  • materials I and II are n-type doped up to their respective solubility limits, the electrons from material II will decrease their potential energy and move into material I because of the difference in the band gaps.
  • the total free electron concentration and Fermi energy (E p ) of material I will increase leading to electron levels above the normal solubility limits. If certain conditions exist, then the heterostructures will exhibit quantum confinement
  • QC structures are any structures where quantum confinement is achieved in multi-layer semiconductor heterostructures with different energy gaps and with wells of considerably small size. The size of the well is determined by n concerned. 1 1 12 13 14 3
  • n s 10 , 10 , 10 , and 10 cm- , respectively.
  • QC is characterized by the formation of single/multiple quantum levels within the low band gap semiconductor.
  • the density of sates in 2D structures is narrower than that of 3D materials and the number of quantum levels is related to the well length and height.
  • TCO film heterostructures with different band gaps are deposited, whereby the number of free electrons is increased beyond that permitted by doping solubility limits of the TCO films.
  • One method of forming the heterostructures is by the controlled atmospheric pressure chemical vapor deposition (APCVD) of organometallic reagents. This method can be used to form heterostructures in a variety of metal oxides including, but not limited to, F doped SnO 2 (3.8 eV)/ZnO (3.4 eV)/F:SnO 2 (3.8 eV).
  • APCVD is used to form doped heterostructures with different band gaps of variable well and barrier height.
  • the increase of the electron concentration inside the well, which is greater than the values obtained by individual doping of a given material has the effect of blue shifting the plasma wavelength.
  • quantum confinement inside the coating material is achieved with a small band gap or well, which not only increases electron concentration but also increases electron mobility.
  • a small band gap or well which not only increases electron concentration but also increases electron mobility.
  • Any triangular potential well formed at the interface of two semiconductors will also qualify as a QC structure (see Fig. 3).
  • Modulation doping is characterized by the dopant separation between high and low energy gap materials. For example, in a SnO 2 (3.8 eV)/ZnO (3.4 eV)/SnO 2 structure, the doping with donors is performed at the SnO 2 /ZnO interfaces.
  • Electrons from the wider gap semiconductor (doped SnO 2 ) (EG2) will transfer to the narrower band gap (EGl) semiconductor (undoped/doped ZnO). A positive charged will be created at the interface of the wider gap material and free electrons will fill the levels in triangular potential wells formed at the interface.
  • the average well size should be smaller than de Broglie wavelength. A more preferred size is 2.5 to 8 nm.
  • the well can be composed of any undoped/doped metal oxide with a lower band gap than the doped metal oxide layers.
  • the 14 2 14 2 preferred sheet carrier concentration should be between -0.1x10 cm- and -1x10 cm- . Oxides with similar crystal structures and lattice parameters are most preferred.
  • Example 1 A 2.2 mm thick glass substrate (soda lime silica), two inches square, was heated on a hot block to about 650°C. The substrate was positioned about 25 mm under the center section of a vertical concentric tube coating nozzle. A carrier gas of dry air flowing at a rate of 12.5 liters per minute (1pm) was heated to about 160°C and passed through a hot wall vertical vaporizer. A liquid coating solution containing monobutyltin trichloride (MBTC) and either 5 or 10 wt% trifluoroacetic acid (TFA) was fed to the vaporizer via a syringe pump at a volume flow designed to give a 0.5 mol % concentration in the gas composition.
  • MBTC monobutyltin trichloride
  • TSA trifluoroacetic acid
  • Doping of ZnO can be conducted using fluorine or Al dopants.
  • the second gas mixture was formed by mixing two separate gas streams in a manifold just before the coating nozzle. The water vapor and air were introduced at the top of the nozzle to minimize premature reaction with the zinc precursor.
  • the DEED liquid was fed via a syringe pump to the second vaporizer through which a nitrogen carrier gas was flowing at 160°C at about 10 slpm. The volume flow was designed to give a 0.5 mol % concentration in the carrier gas. Water was fed via syringe pump into a third vaporizer through which an air carrier gas was flowing at about 10 1pm. The vapor concentration was about 3 mols per mol of zinc precursor.
  • the bilayer film stack was immediately overcoated with a TOF film in the same manner as previously described.
  • the resulting TOF/ZnO/TOF film stack had a visible transmission greater 20 3 than 70 %, an electron concentration in the range of 7-10 xlO e/cm and a mobility higher than 2
  • Stacks with exactly the same (rutile) crystal structure include film stacks composed of SnO 2 /MO ⁇ /SnO 2 , where M equals Ti (3.0 eV), V, Cr, Mo and Ru, which can be deposited from readily available, volatile precursors. The properties of the film stack would be similar to those described in Example 1.

Abstract

Transparent conductive oxide (TCO) coatings for solar control films having improved reflectivity in the near infrared (NIR) spectrum are formed by depositing heterostructures having different band gaps. The heterostructures increase the electron concentration beyond the solubility limit of a given dopant, and thereby decrease or blue shift the plasma wavelength of the coatings.

Description

SOLAR CONTROL FILMS COMPOSED OF METAL OXIDE HETEROSTRUCTURES, AND METHOD OF MAKING SAME
BACKGROUND OF THE INVENTION
Field of the Invention This invention relates .to solar control films, and more particularly to transparent conductive oxide (TCO) coatings having improved reflectivity in the near infrared (NIR) spectrum. The improved reflectivity is achieved by forming the TCO coatings with heterostructures having different band gaps to increase the electron concentration beyond the solubility limit of a given dopant, and thereby decrease or blue shift the plasma wavelength of the coatings.
The invention also relate to a method of making TCO solar control films having the above-described properties.
Description of Related Art The purpose of solar control coatings, such as might be used on window glass, is to maximize transmittance of visible light while reflecting most infrared and near infrared (NIR) light. The wavelength above which most photons will be reflected is the "plasma wavelength," and the closer the plasma wavelength to the visible (blue) side of the NIR spectrum, the more NIR light will be reflected.
Existing solar control coatings can be divided into two major classes: a. sputtered and b. pyrolytic. Typical sputtered coatings are composed of multiple Ag/metal oxide stacks with high visible transmittance ~80% and high near IR reflectance (-70%). These films have plasma wavelengths λp of ~0.7 μm. Most photons with wavelength λ > λp will be reflected due to the negative real part of the dielectric constant in this region. On the other hand, pyrolytic coatings composed of transparent conductive oxides (TCOs) such as ITO and doped SnO2 have high transmission in the visible but NIR reflective properties that are lower than those of sputtered film because their plasma wavelengths generally lie in the 1.0 to 1.6 μm range.
Since the plasma wavelength is inversely proportional to the square root of the electron concentration, an increase in electron concentration results in a decrease in the plasma wavelength. However, the electron concentration is limited by the solubility limit of the dopant, which in turn is limited by the site density where the dopant substitutes. As a result, the theoretical limit for plasma wavelength in conventional coatings made of In2O3:Sn (ITO), which 21 3 has an electron concentration of 10 cm- (see, R.G. Gordon, MRS Bulletin 25, 52 (2000)), is 22 22 3
775 nm. For SnO2:F, which has oxygen and tin site densities of 2.8x10 and 5.6x10 cm- and
3.6 and 7.2 % doping efficiencies respectively, the highest free electron concentration at room 20 3 temperature (RT) is 7x10 cm- (see H.L. Ma et al, Thin Solid Films 298, 151 (1997)), and the theoretical plasma wavelength limit is 1.3 μm. The present invention overcomes these theoretical limits by depositing variable band gap heterostructures (quantum wells) to increase doping efficiencies, and therefore electron concentrations, in TCO films. Although the quantum confinement (QC) effect of increasing doping concentration in III-V semiconductor heterostructures is well-known, it has not heretofore been used to increase electron concentration in TCO films for the purpose of decreasing the plasma wavelength.
U.S. Patent Publication Nos. 2002158572 (2002) and 20021031 (2002) describe application of the QC effect to LEDs, European Patent Publication EP 98-101278 (1998) describes application of the effect to HEMT devices, and R. Apetz et al, Solid State Electronics, 37, 957 (1994) describes application of the effect to modulation doped structures. In addition, Bennett et al, Appl. Phys. Lett., 72, 1193 (1998) suggests that modulation doping can be effectively used to decrease the sheet resistance of an InAs/AlSb quantum well by a factor of 3 to 6 for signal and double sided modulation doping. None of these references suggests use of wide band gap oxide heterostructures to increase doping for the purpose of improving near infrared (NIR) reflection properties of solar control TCO coatings.
SUMMARY OF THE INVENTION
It is accordingly a first objective of the invention to provide coatings composed of transparent conductive oxides (TCOs) having high visible transmission and improved NIR reflective properties. It is a second objective of the invention to provide TCO coatings having high visible transmittance and plasma wavelengths of less than 1 μm. It is a third objective of the invention to provide TCO coatings having plasma wavelengths approaching - 0.7 μm, rather than the 1.0 -1.6 μm range for current pyrolytic TCO coatings. These objectives are achieved by redistributing carriers through the use of doped heterostructures with different band gaps, thereby exploiting the quantum well effect on doping efficiency to increase the concentration of free electrons beyond theoretical limits resulting from doping solubility limits in semiconductor/oxide materials. This may be achieved by depositing metal oxide film stacks with sufficient band gap energy difference using atmospheric pressure chemical vapor deposition (APCVD), the film stacks being composed of various metal oxides such as F doped SnO2 (3.8 eVVZnO (3.4 eV)/F:SnO2 (3.8 eV). Alternatively, deposition techniques such as sputtering, molecular beam epitaxy (MBE), or laser-assisted deposition (LAD) may be used to deposit the stacks. The film thickness and morphology of each layer in the stack is preferably controlled by varying deposition conditions such as precursor concentration, carrier gas, substrate temperature, and coreactants and accelerants, such as water.
BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic energy diagram of a finite quantum well.
Fig. 2 is a schematic diagram showing an example of a superlattice used in a preferred embodiment of the present invention.
Fig. 3 is a schematic energy diagram of a triangular potential well formed at the interface of two semiconductors.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 shows a heterostructure formed by sandwiching one oxide layer 1 with a low band gap (EG]) between two oxide layers with a higher band gap (EG2), EG1 < EG An example of this would be a superlattice (SL), where two materials I and II of different gaps are deposited one after the other, as illustrated in Fig. 2. If materials I and II are n-type doped up to their respective solubility limits, the electrons from material II will decrease their potential energy and move into material I because of the difference in the band gaps. As a result, the total free electron concentration and Fermi energy (Ep) of material I will increase leading to electron levels above the normal solubility limits. If certain conditions exist, then the heterostructures will exhibit quantum confinement
(QC). These conditions are that the carrier motion is confined to a layer with a thickness of the de Broglie wavelength (for a single well) λp = [2π/ns] , where ng is the sheet carrier density.
Furthermore, atomically smooth interfaces and small size wells (L < 50 run) in material I are imperative for the formation of quantum confined layers. QC structures are any structures where quantum confinement is achieved in multi-layer semiconductor heterostructures with different energy gaps and with wells of considerably small size. The size of the well is determined by n„. 1 1 12 13 14 3
For example, for L = 79, 25, 8, and 2.5 nm, ns = 10 , 10 , 10 , and 10 cm- , respectively. QC is characterized by the formation of single/multiple quantum levels within the low band gap semiconductor. The density of sates in 2D structures is narrower than that of 3D materials and the number of quantum levels is related to the well length and height.
This property is exploited in the preferred embodiments of the invention to obtain TCO films having blue-shifted plasma wavelengths. In order to decrease the plasma wavelength, TCO film heterostructures with different band gaps are deposited, whereby the number of free electrons is increased beyond that permitted by doping solubility limits of the TCO films. One method of forming the heterostructures is by the controlled atmospheric pressure chemical vapor deposition (APCVD) of organometallic reagents. This method can be used to form heterostructures in a variety of metal oxides including, but not limited to, F doped SnO2 (3.8 eV)/ZnO (3.4 eV)/F:SnO2 (3.8 eV).
In accordance with a first preferred embodiment of the invention, APCVD is used to form doped heterostructures with different band gaps of variable well and barrier height. The increase of the electron concentration inside the well, which is greater than the values obtained by individual doping of a given material has the effect of blue shifting the plasma wavelength.
Alternatively, in accordance with a second preferred embodiment of the invention, quantum confinement inside the coating material is achieved with a small band gap or well, which not only increases electron concentration but also increases electron mobility. As a result, not only is the plasma wavelength blue shifted, but a sharper rise for the reflection edge can be observed due to the improved electron mobility. Any triangular potential well formed at the interface of two semiconductors will also qualify as a QC structure (see Fig. 3). Modulation doping is characterized by the dopant separation between high and low energy gap materials. For example, in a SnO2 (3.8 eV)/ZnO (3.4 eV)/SnO2 structure, the doping with donors is performed at the SnO2/ZnO interfaces. Electrons from the wider gap semiconductor (doped SnO2) (EG2) will transfer to the narrower band gap (EGl) semiconductor (undoped/doped ZnO). A positive charged will be created at the interface of the wider gap material and free electrons will fill the levels in triangular potential wells formed at the interface.
If material I, with lower band gap, is undoped and doping is conducted only in material II, which is the barrier, higher than bulk mobilities are expected due to decreased scattering. The electron liquid formation is expected under certain conditions (see M. Dyakov, M. Shur, Phys.
Rev. Lett. 71, 2465 (1993)). To achieve 2D confinement the average well size should be smaller than de Broglie wavelength. A more preferred size is 2.5 to 8 nm. The well can be composed of any undoped/doped metal oxide with a lower band gap than the doped metal oxide layers. The 14 2 14 2 preferred sheet carrier concentration should be between -0.1x10 cm- and -1x10 cm- . Oxides with similar crystal structures and lattice parameters are most preferred.
Example 1 A 2.2 mm thick glass substrate (soda lime silica), two inches square, was heated on a hot block to about 650°C. The substrate was positioned about 25 mm under the center section of a vertical concentric tube coating nozzle. A carrier gas of dry air flowing at a rate of 12.5 liters per minute (1pm) was heated to about 160°C and passed through a hot wall vertical vaporizer. A liquid coating solution containing monobutyltin trichloride (MBTC) and either 5 or 10 wt% trifluoroacetic acid (TFA) was fed to the vaporizer via a syringe pump at a volume flow designed to give a 0.5 mol % concentration in the gas composition. Water was fed to the same vaporizer via a syringe pump at a volume flow designed to give a 1.5 mol % concentration in the gas composition. The gas mixture was allowed to impinge on the glass substrate for about 3-6 seconds whereby a rutile fluorine doped tin oxide film (TOF) -165-300 nm was deposited. Immediately following, a second gas mixture composed of a diethylzinc tetraethylethylenediamine complex (DEED), a nitrogen carrier gas, water vapor and air impinged on the metal oxide coated surface for about 2-14 seconds. A hexagonal zinc oxide film having a thickness of about 10-50 nm resulted. Doping of ZnO can be conducted using fluorine or Al dopants. The second gas mixture was formed by mixing two separate gas streams in a manifold just before the coating nozzle. The water vapor and air were introduced at the top of the nozzle to minimize premature reaction with the zinc precursor. The DEED liquid was fed via a syringe pump to the second vaporizer through which a nitrogen carrier gas was flowing at 160°C at about 10 slpm. The volume flow was designed to give a 0.5 mol % concentration in the carrier gas. Water was fed via syringe pump into a third vaporizer through which an air carrier gas was flowing at about 10 1pm. The vapor concentration was about 3 mols per mol of zinc precursor. The bilayer film stack was immediately overcoated with a TOF film in the same manner as previously described. The resulting TOF/ZnO/TOF film stack had a visible transmission greater 20 3 than 70 %, an electron concentration in the range of 7-10 xlO e/cm and a mobility higher than 2
50 cm /v-sec as measured by the Hall effect.
Predictive Example 1 In a similar manner as described above, a film stack of SnO2 (3.8 eV)/WO3(2.8 eV)/SnO2
(3.8eV) may be formed using the same tin oxide precursors along with the tungsten precursors tungsten hexafluoride or hexacarbonyl. The tungsten precursors are then placed in stainless steel bubblers and either the nitrogen carrier gas conducts the saturated vapors to the second vaporizer or the bubbler is heated to the desired temperature. The properties of the film stack should be similar to those described in Example 1.
To avoid carrier scattering and trapping at the interfaces, atomically smooth (RMS < 1 nm) interfaces between wells and barriers are most preferred. Therefore, stacks with similar crystal structure would be preferable over those with dissimilar structures. Stacks with exactly the same (rutile) crystal structure include film stacks composed of SnO2/MOχ/SnO2, where M equals Ti (3.0 eV), V, Cr, Mo and Ru, which can be deposited from readily available, volatile precursors. The properties of the film stack would be similar to those described in Example 1.
Having thus described various preferred embodiments of the invention in sufficient detail to enable those skilled in the art to make and use the invention, it will nevertheless be appreciated that numerous variations and modifications of the illustrated embodiment may be made without departing from the spirit of the invention, and it is intended that the invention not be limited by the above description or accompanying drawings, but that it be defined solely in accordance with the appended claims.

Claims

We claim: 1. A solar control film, comprising a transparent conductive oxide (TCO) layer made up of alternating layers of materials having relatively high energy gaps and low energy gaps to form heterostructures with different band gaps, wherein said heterostructures increase electron concentration beyond dopant solubility limits in the low energy gap layers and thereby decrease the plasma wavelength of the conductive oxide layer.
2. A solar control film as claimed in Claim 1, wherein said heterostructures with different band gaps have well and barrier heights selected to increase electron concentration inside the wells beyond the values obtained by separate doping of individual materials.
3. A solar control film as claimed in claim 1, wherein quantum confinement inside said transparent conductive oxide layer is achieved with a small band gap or well, thereby not only increasing electron concentration but also electron mobility in order to obtain a sharper reflection edge.
4. A solar control film as claimed in claim 1, wherein said high energy gap material is doped, and said low energy gap material is not intentionally doped.
5. A solar control film as claimed in claim 1, wherein said high energy gap material is doped SnO2.
6. A solar control film as claimed in claim 5, wherein said low energy gap material is undoped or doped ZnO.
A solar control film as claimed in claim 5, wherein said low energy gap material is undoped or doped WOy
8. A solar control film as claimed in claim 5, wherein said low energy gap material is MO , where M is selected from the group consisting of Ti, V, Cr, Mo, and Ru.
9. A solar control film as claimed in claim 1, wherein said low energy gap material is undoped or doped ZnO.
10. A solar control film as claimed in claim 1, wherein said low energy gap material is undoped or doped WOy
11. A solar control film as claimed in claim 1, wherein said low energy gap material is MO , where M is selected from the group consisting of Ti, V, Cr, Mo, and Ru.
12. A solar control film as claimed in claim 1, wherein said transparent conductive oxide layer is deposited on a glass substrate.
13. A solar control film as claimed in claim 1, wherein said high and low energy gap materials have similar crystal structures.
14. A solar control film as claimed in claim 1, wherein said high and low energy gap materials have identical crystal structures.
15. A method of forming a solar control film, comprising the step of depositing a transparent conductive oxide layer made up of alternating layers of materials having relatively high energy gaps and low energy gaps to form heterostructures with different band gaps, wherein said heterostructures increase electron concentration beyond dopant solubility limits in the low energy gap layers and thereby decrease the plasma wavelength of the conductive oxide layer.
16. A method as claimed in claim 15, further comprising the step of selecting well and barrier heights of said heterostructures with different band gaps to increase electron concentration inside the wells beyond the values obtained by separate doping of a given material.
17. A method as claimed in claim 15, further comprising the step of achieving quantum confinement inside said transparent conductive oxide layer is achieved with a small band gap or well, thereby not only increasing electron concentration but also electron mobility in order to obtain a sharper reflection edge.
18. A method as claimed in claim 15, wherein said high energy gap material is doped, and said low energy gap material is not intentionally doped.
19. A method as claimed in claim 15, wherein said high energy gap material is doped SnO2.
20. A method as claimed in claim 19, wherein said low energy gap material is undoped or doped ZnO.
21. A method as claimed in claim 19, wherein said low energy gap material is undoped or doped WO3.
22. A method as claimed in claim 19, wherein said low energy gap material is MO , where M is selected from the group consisting of Ti, V, Cr, Mo, and Ru.
23. A method as claimed in claim 15 wherein said low energy gap material is undoped or doped ZnO.
24. A method as claimed in claim 15, wherein said low energy gap material is undoped or doped WO3.
25. A method as claimed in claim 15, wherein said transparent conductive oxide layer is deposited on a glass substrate.
26. A method as claimed in claim 15, wherein said transparent conductive oxide layer is deposited by atmospheric pressure chemical vapor deposition (APCVD) of organometallic reagents.
27. A method as claimed in claim 15, wherein said transparent conductive oxide layer is deposited by a method selected from the group consisting of sputtering, molecular beam epitaxy, and laser-assisted deposition.
28. A coated substrate comprising a substrate having directly deposited thereon the solar control film of claim 1.
PCT/US2004/044081 2004-01-23 2004-12-31 Solar control films composed of metal oxide heterostructures, and method of making same WO2005072947A1 (en)

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