Apcvd of doped titanium oxide and the coated article made thereby

Related application The present application claims the benefits of US Patent Provisional Application No. 61 / 512,651 filed on July 28, 2011 under US Patent Law 111 (b) under US Patent Law 119 (e). To do. The provisional application is incorporated herein by reference in its entirety.

Field of invention The present invention relates to a method of depositing a conductive titanium oxide coating on a glass substrate, a coated article comprising a conductive titanium oxide coating, and a solar cell comprising such a coated article.

The demand for increased efficiency in photovoltaic devices such as solar cells has led to the consideration of strategies for obtaining more electrical energy from known types of solar cells, such as amorphous silicon and cadmium telluride (Cd-Te) devices. ing. One region where improvement may be beneficial is the interface of transparent conductive oxide (TCO) layers, and so-called active layers, such as amorphous silicon or Cd-Te. Since the most commonly used TCO for solar cells is tin oxide doped, the addition of a chemically stable conductive layer between the TCO and the active layer, eg titanium oxide, is such. There are many reasons why the conversion efficiency of a built solar cell can be increased.

TiO_２Improvements in various properties of the thin film of are also reported in the following patent documents, for example.

Patent Document 1 describes a thin semiconductor electrode made of a single crystal, polycrystalline or amorphous material. A preferred n-type anode material is "properly doped TiO._２It can be said that it includes.

Patent Document 2 is a partial continuation application of Patent Document 1.

Patent Document 3 describes two TiOs._２TIO by screen printing multilayers on the substrate, including layers_２Describes how to manufacture a thick film photoanode. The resulting structure is then processed to deliberately reduce the electrical resistivity of the printed film.

Patent Document 4 describes a dopant in the sol-gel process, eg, niobdo-doped TiO._２A conductive metal oxide fine particle film whose electrical conductivity is increased due to the use of a ceramic film is described.

Patent Document 5 describes a series of TiOs._２Described is a solar cell with a light-transmitting conductive layer deposited on a layered glass plate or transparent polymer sheet. Such a TiO_２One or more of the layers may be doped with divalent or trivalent metal ions.

Patent Document 6 discloses the application of a niobium-doped tin oxide coating onto a glass substrate to produce low emissivity glass. This coating can be optionally doped with both niobium and other dopants such as fluorine.

Patent Document 7 describes the doped TIO._２A compound and a method for producing a compound formed by the compound are described. This process is basically TiO_２And M (an element having an octagonal coordination structure) oxide and TIO_２The mixture was heated at a time and temperature sufficient to cause the reaction of the oxides of and M to dope the TIO._２And this doped TiO_２Includes providing a reducing atmosphere.

Patent Document 8 is a TiO composed of porous particles in a specific size range and having a relatively high bulk density in combination with a high surface area._２A photovoltaic cell containing a powdered semiconductor layer is described.

Patent Document 9 describes an alkaline battery containing an electrolyte to which an n-type metal oxide is added, which improves the electrochemical ability. The n-type metal oxide additive is either a doped metal oxide or a reduced metal oxide.

Patent Document 10 describes a niobium-titanium film, a laminate of one or more such niobium-titanium films, and a substrate containing such a film.

Patent Document 11 describes a photocatalyst having first and second semiconductors, wherein the first semiconductor is, for example, nitrogen-doped or carbon-doped TiO._２The second semiconductor may be a metal-doped TIO, each of which has an increase in oxidation or reduction potential when irradiated with visible light._２It may be.

Patent Document 12 is TIO._２And other suitable deficient equivalents of metal oxides are disclosed, including multilayer film laminates containing a light transmission optimized intermediate layer having a refractive index of 2.3-3.5.

Patent Document 13 describes, for example, transparent conductors to be used in LCDs, solar cells and electroluminescent electrodes. The transparent conductor contains an M: TiC> type 2 metal oxide having an anatase-type crystal structure. It is said that the transparent conductor can increase the electric conductivity while maintaining its transparency by substituting the Ti atom with another metal atom such as Nb, Ta, Mo, As, Sb, W. ..

<p><patcit num="1"><text>U.S. Pat. No. 4,011,149</text></patcit><patcit num="2"><text>U.S. Pat. No. 4,090,933</text></patcit><patcit num="3"><text>U.S. Pat. No. 4,524,091</text></patcit><patcit num="4"><text>U.S. Pat. No. 5,028,568</text></patcit><patcit num="5"><text>U.S. Pat. No. 5,350,644</text></patcit><patcit num="6"><text>U.S. Pat. No. 6,524,647</text></patcit><patcit num="7"><text>U.S. Pat. No. 6,524,750</text></patcit><patcit num="8"><text>U.S. Pat. No. 6,720,202</text></patcit><patcit num="9"><text>U.S. Pat. No. 6,818,347</text></patcit><patcit num="10"><text>U.S. Pat. No. 7,037,589</text></patcit><patcit num="11"><text>U.S. Pat. No. 7,169,733</text></patcit><patcit num="12"><text>International Publication No. 2007/027498</text></patcit><patcit num="13"><text>European Patent No. 1796107</text></patcit></p>

<p num="0019"> The present invention relates to a method of making a doped titanium oxide coating by atmospheric chemical vapor deposition during a float glass manufacturing process, and a coated glass article comprising such a doped titanium oxide coating. In a further aspect, the invention includes a solar cell that includes such a coated glass article. Such a doped titanium oxide coating is preferably conductive.</p><p num="0020"> More specifically, the method for making a dope titanium oxide coating is mainly composed of a halogenated inorganic titanium compound, an oxygen-containing organic compound, a halogenated inorganic niobium or tantalum compound, and one or more inert carrier gases. Contains the formation of a homogeneous precursor gas mixture, including the various components. This halogenated inorganic niobium or tantalum compound is intended to function only as a dopant in the precursor mixture and thus contains no more than 0.3 mol% thereof.</p><p num="0021"> This precursor gas mixture is filmed in close proximity to the heated glass ribbon in the float glass manufacturing process. This heated glass ribbon has a substantially higher temperature than the precursor gas mixture, and the heat input from the glass ribbon allows the precursor gas mixture to be deposited at a commercially feasible deposition rate in excess of 35 A / sec. Then, it is chemically reacted so as to form a thermally decomposable doped titanium oxide coating on the glass ribbon. This doped titanium oxide film is preferably 1 × 10.^−３It shows an electrical conductivity exceeding S / cm.</p><p num="0022"> The coated glass article according to the present invention had a titanium oxide coating doped with a halogenated niobium or tantalum compound having a film thickness of 500A to 1500A deposited therein.</p><p num="0023"> The solar cell according to the present invention includes such a coated glass article as a component thereof.</p>

The present invention relates to a method of making a doped titanium oxide coating by atmospheric chemical vapor deposition during a float glass manufacturing process. This titanium oxide coating is preferably imparted by doping with a titanium compound, as described in more detail herein. Conductive titanium oxide coatings are considered to be particularly useful in photovoltaic devices, more specifically solar cells, although they have other uses.

As described above in the present specification, in a typical solar cell, the transparent conductive oxide (TCO) is often laminated with a so-called "active layer" of the solar cell, for example, a layer of amorphous silicon. Providing a layer of material with certain desired properties at the interface between the TCO and the active layer appears to be a means that can cost-effectively increase the efficiency of converting solar radiation into electrical energy. Conductive TiO_２Is suggested as a good candidate for such an interface layer for several reasons. The reasons for this are (1) TiO._２However, it is chemically and thermally stable enough that the active layer can be deposited directly on it, and (2) its index of refraction (2.5-3.5) combined with the index of refraction of the adjacent layer causes reflection. The amount of light loss due to the above is low, and (3) it can help protect the TCO from deterioration during the deposition of the active layer, particularly the active layer of amorphous silicon.

TiO_２The layer does not have to be highly conductive, but it is also important that it is at least conductive as an active layer so as not to form a barrier to current between the TCO and the active layer.

Conductive TiO_２To realize the benefits of interfacial layers, it is possible to produce such conductive coatings in large volumes and at a sufficiently low cost to make them commercially feasible in large-scale solar cell manufacturing processes. Must. Applicants believe that the present invention meets these and other requirements expected by those skilled in the art in an unexpected manner.

First, a combination of gaseous reactants, namely halogenated inorganic titanium compounds and oxygen-containing organic compounds, may be provided. Suitable inorganic titanium compounds include: TiCl_４, TiBr_４And Til_４.. Suitable oxygen-containing organic compounds include ethyl acetate, n-butyl acetate, butyl isoacetate, sec-butyl acetate, propyl acetate and other esters and ethers. One or more inert carrier gases, such as nitrogen, hydrogen, helium, or mixtures thereof, may be utilized as components of the gaseous mixture.

Advocated TiO_２Gaseous halogenated inorganic niobium dopant compounds are preferred to make the layers conductive, but tantalum compounds can also be considered. Suitable halogenated inorganic dopant compounds include: NbCl_５, NbF_５, TaCl_５And TaF_５.. Applicants are sufficient to obtain the desired level of electrical conductivity by adding a niobium or tantalum dopant compound to the gaseous precursor mixture at a level of 0.3 mol% or less. I found. The correlation of the Nb or Ta doping efficiency of the titanium oxide coating with respect to the electrical conductivity of the coating is an aspect of the present invention.

In niobium, the Nb atom is TIO_２Be of the right size to fit in the matrix, and Nb^＋５Because of its normal valence state, TiO_２Was found to be a particularly suitable dopant for. The use of Nb compounds with valence states other than +5 may be possible in connection with the present invention. Applicant is 1x10^−３TIO in the online production of thermally decomposable thin films by APCVD as described herein with electrical conductivity greater than Siemens / cm._２We found that it could be guided inside.

Doped TIO_２The film can be deposited directly on a hot glass substrate by APCVD, but is preferably deposited as part of a multilayer film laminate for solar cell purposes. For example, the doped TiO of the subject_２The coating is SnO doped on a thin layer of silica._２And non-doped SnO_２It may be deposited on an existing membrane laminate containing. Glass coated with such an existing film laminate is available from Pilkington North America, Inc. Is sold as a product of the TEC (trademark) line.

Doped TIO as described above_２The layer reduces the reflection of solar radiation when used at the interface between the TCO and the active layer. It has been found that such loss of solar radiation due to reflection is reduced by 0.5% to 2.0%.

Doped TIO in solar cells_２Considering the various advantages of the interface layer, Applicants have found that in a typical thin film silicon solar cell, a relative increase in conversion efficiency of 7% to 12% can be expected.

For some applications of the present invention, it may be desired to suppress the iridescent effect that may occur when light is reflected or transmitted from the glass substrate on which the film is formed. In connection with the present invention, any suitable single-layer or multi-layer color-suppressing film laminate may be utilized, which may be a single metal oxide layer, a metal oxide layer and a silica layer, or a gradient coating layer. including.

In a preferred embodiment, both the metal oxide layer and the silica layer are incorporated herein by reference, eg, known from Gordon's US Pat. Nos. 4,377,613 and 4,419,386. As described above, an excellent color-suppressing film laminate is formed. The color-suppressing film laminate is deposited on the substrate material prior to the deposition of the conductive metal oxide layer. The color-suppressing film laminate is relatively thin, the tin oxide layer has a film thickness of 250 to 600 A, and the silica layer has a film thickness of 250 to 350 A.

The solar cell containing the coated glass article according to the present invention may be a single sheet of glass that is substantially transparent to solar radiation. Photoactive materials such as titanium oxide, cadmium / telluride compounds, amorphous silicon, and crystalline silica are preferably the first major surface of the glass substrate, i.e. the major substrate closest to the direct source of solar radiation. It is deposited on the surface. The titanium oxide layer can be one component of a multilayer laminate deposited by any suitable method, including various CVD and sputter coating techniques on a glass substrate.

Uniform gaseous containing halogenated inorganic titanium compounds, halogenated inorganic niobium or tantalum dopant compounds, oxygen-containing organic compounds and one or more inert carrier gases to carry out the APCVD method of film deposition. The mixture is maintained below the temperature at which it reacts to form the deposited material and delivered closer to the flat glass substrate to be coated, which substrate at a temperature above the reaction temperature of the reactants. is there. This precursor gas mixture is then introduced directly into the vapor space onto the substrate. The heat from the substrate raises the temperature of the precursor gas above the thermal decomposition temperature of the precursor compound.

High deposition rates are important from a commercial point of view when coating substrates in the manufacturing process. This is especially true for online float glass processes where the glass ribbon is moving at a given line speed and the specified coating thickness must be achieved in approximately seconds.

Float glass attachment is utilized as a means for performing the method of the present invention. One particular embodiment of float glass mounting is described below herein. More specifically, the float glassware comprises a tube portion along which molten glass is fed from the melting furnace to the float tank portion and a continuous glass ribbon is formed according to a well-known float process. The glass ribbon travels from the tank portion through the adjacent annealed glass annealing furnace and cooling section. The continuous glass ribbon acts as a substrate on which the desired coating is deposited according to the present invention. The temperature in the float tank portion is typically in the range of 1050F (566C) and 1350F (732C).

The float portion includes a bottom portion, which includes a molten tin tank, a roof, a contralateral side wall and an end wall. The roof, sidewalls, and end walls all define the enclosure, in which a non-oxidative atmosphere is maintained to prevent the oxidation of molten tin.

Further, the beam of the gas distributor is preferably located in the tank portion, but other locations, such as a glass annealing furnace or a glass annealing furnace gap, may be possible. The gas distributor beam (preferably located in the tank portion) can be used to apply an additional coating on the substrate before applying the metal oxide coating according to the method of the invention. Additional coatings may include silicon and silica.

During operation, the molten glass flows in a downwardly controlled amount along the channel under the adjustable twill and over the surface of the tin tank. On a tin tank, the molten glass spreads laterally under the influence of gravity and surface tension, as well as certain mechanical influences, and travels across the tank to form a ribbon. The ribbon is picked up from the roll and then transported via an annealed glass annealing furnace and a cooling portion on the aligned roll. The application of the coatings of the present invention may be made in the float tank portion, or further along the production line, for example, in the gap between the float tank and the annealing glass annealing furnace, or in the annealing glass annealing furnace. It may be done in.

To prevent oxidation of the tin tank, a suitable non-oxidizing atmosphere, generally nitrogen, or a mixture of nitrogen and hydrogen (mainly nitrogen) is maintained within the tank enclosure. The atmospheric gas is introduced through a conduit that is operably connected to the distribution manifold. This non-oxidizing gas is introduced at a rate sufficient to compensate for normal losses and maintains a slight positive pressure of about 0.001 to about 0.01 atm above atmospheric pressure, thereby maintaining a slight positive pressure on the outside. Prevents the invasion of the atmosphere. For the purposes of the present invention, the pressure range described above is believed to constitute normal atmospheric pressure. The heat to maintain the desired temperature regimen in the tin bath and enclosure can be provided by the radiant heater in the enclosure. The atmosphere inside the glass annealing furnace is typically air. The reason for this is that the cooling part is not surrounded and the glass ribbon is open to the atmosphere. Atmospheric air can be directed against the glass ribbon in the cooling portion, for example by a fan. The heater may also be provided in the annealed glass annealing furnace so that the temperature of the glass ribbon is gradually reduced according to a predetermined regimen as the glass ribbon is carried through it.

The beam of the gas distributor is generally placed in the float tank to deposit various coatings on the glass ribbon substrate, but may be placed downstream of the float tank. The gas distributor beam is one form of reactor that can be used to carry out the processes of the present invention.

A conventional configuration of a distributor beam suitable for supplying the precursor material according to the invention is generally an inverted, substantially channel-shaped skeleton formed by spaced inner and outer walls. It defines at least two enclosed cavities. A suitable heat exchange medium is circulated through the enclosed cavity to maintain the distributor beam at the desired temperature. Preferred distributor beams are disclosed in US Pat. No. 4,504,526 to Hofer et al., Which is incorporated herein by reference.

The precursor gas mixture is supplied through a fluid cooling supply conduit. This supply conduit extends along the distributor beam and introduces gas through spaced drop lines along the supply conduit. This supply conduit leads to a delivery chamber in the header carried by the skeleton. Precursor gas introduced through the drop line is discharged from the delivery chamber through the passage towards the coating chamber, which flows along the surface of the glass and defines the vapor space released onto the glass.

The baffle plate may be provided in the delivery chamber to equalize the flow of precursor material across the distribution beam, with respect to the glass at a smooth, laminated, uniform flow rate where the material crosses the distributor beam as a whole. Guarantee that it will be released. The consumed precursor material is collected and removed through the exhaust chamber along the sides of the distributor beam.

Various forms of distributor beams used for chemical vapor deposition are suitable for this method and are known in the prior art.

One such alternative distributor beam configuration generally introduces a precursor gas mixture through a gas supply duct, which is cooled by a coolant circulating through the cooling duct. This gas supply duct opens into the gas flow restrictor through an elongated opening.

The gas flow restrictor comprises a plurality of vertically mounted metal strips that are sinusoidally crimped in the longitudinal direction and extend along the length of the distributor, adjacent to each other. Adjacent crimped metal strips are placed "out of phase", defining multiple vertical channels between them. These vertical channels have a small cross-sectional area relative to the cross-sectional area of the gas supply duct, so that the gas is discharged from the gas flow restrictor at a substantially constant pressure along the length of its distributor. To.

The inlet side of a substantially U-shaped guide channel that typically includes an inlet leg, a coating chamber (releasing onto the hot glass substrate to be coated) and an exhaust leg (which sucks the coating gas used from the glass). In addition, the coating gas is released from the gas flow rate restrictor. The rounded corners of the block defining the coating channel promote a uniform laminar flow of the coating parallel to the glass surface across the coated glass surface.

<p> The following examples, which constitute the best embodiment currently considered by the inventors for practicing the invention, are shown only for the purpose of further illustrating and disclosing the invention and are limiting the invention. Should not be interpreted.</p><p> Comparative Examples 1-5 show that the titanium oxide coating can be deposited at a commercially feasible film thickness and deposition rate using an inorganic titanium precursor and an oxygen-containing organic compound in the APCVD process. However, these coatings cannot be said to be conductive to any substantially useful level. Therefore, these coatings are not useful within the scope of the present invention.</p><p> Examples 1 to 4 according to the present invention are shown in Table 2. In addition to vaporized TiCU and EtOAc, vaporized NbF was added in an amount of 0.07-0.17 mol% to the gaseous precursor mixture. Note that molecular oxygen is not used in Examples 1-4. In addition, membranes were deposited essentially at atmospheric pressure, primarily in a nitrogen atmosphere. The temperature of the substrate surface during deposition varied from 550C to 650C.</p><p> The results are shown in Table 1 herein.<tables num="1"></tables><tables num="2"></tables></p><p> The film thickness formed is in the range of 550A to 1430A, which is substantially thicker than the non-doping film of the comparative example. The deposition rate ranges from 37 to 95 A / sec, which is a useful deposition rate, although it does not substantially exceed the comparative examples. However, importantly, the conductivity of the film was significantly higher than that of the comparative example, especially in the range of 3.54E-02S / cm to 9.79E-01S / cm. These conductivity levels are to the extent useful in improving the capabilities of photovoltaic devices for the reasons previously noted herein.</p><p> From the above disclosure and detailed description of certain preferred embodiments, it is expected that various modifications, additions and other embodiments are possible without departing from the true scope and intent of the invention. .. The embodiments considered have been selected and described to provide the best examples of the principles of the invention, and by their practical application, one of ordinary skill in the art will be able to adapt to the particular use considered. The present invention can be used in embodiments and with various modifications. All such modifications and variations are within the scope of the invention as determined by the appended claims, if they are construed to the extent that they are properly, legally and equitably entitled. is there.</p>