Patent Application
20160043247
This invention is directed to a composition, sometimes referred to as a transparent conductive oxide (“TCO”) cap composition or TCO cap layer, that can be applied to a doped zinc oxide-coated glass substrate using a chemical vapor deposition (“CVD”) process. The capping composition of the invention comprises at least nitrogen (“N”), oxygen (“O”), and at least two different metal elements, where at least one of the two metal elements is a Group IIIA element of the Periodic Table. This invention also is directed to a multilayered device having a glass substrate, a doped zinc oxide (“doped ZnO” or “DZO”) layer, and the novel nitrogen containing TCO capping compositions described herein.
There are many applications and devices that require conductive and transparent coatings on substrates. For example, a doped zinc oxide (“doped ZnO” or “DZO”) transparent conductive oxide layer is a prime candidate for multiple opto-electronic and architectural applications, including use in solar panel devices, photovoltaic devices, filters, touch screens, and displays. DZO is known to possesses very low resistivity (104 Ωcm), high electron mobility (5-67 cm2/Vs and concentration (1-20×1020 cm−3), as well as low plasma wavelength, but not the thermal resistance, chemical resistance, and/or scratch resistance, or smoothness needed for certain applications. Low plasma wavelength paves the way for DZO in architectural applications, such as solar controlled coatings, filters, touch screens, and displays, but still lacks the desired properties mentioned above. Good electrical properties allow the utilization of the DZO as an electrode in photovoltaic devices (“PV”). Descriptions of DZO and its applications are provided in U.S. Pat. Nos. 7,732,013; 8,163,342; 7,989,024, the disclosures of which are incorporated herein in their entireties.
DZO displays degradation of electrical properties when exposed to higher temperatures in oxygen (O2) containing environments and also sometimes in inert environments. Degradation refers to an increase of the resistivity as a function of ambient atmosphere, temperature and exposure time. For example, the DZO layer resistivity for a 600 nm thick layer increases by a factor of 6 when exposed to air at 500° C. (
For most useful applications, the thickness of the conductive DZO layer is less than 600 nm, usually in the range of 100-270 nm, so that sheet resistances of 10-50 Ω/sq are achieved. For thinner DZO layers, degradation of resistivity when exposed to high temperatures is faster due to faster diffusivity of species into doped ZnO. For example, for 110 nm thick doped ZnO film, resistivity of the film increases by factors of 10 and 41, when the films are annealed in air at 500° C. (5 min) and 550° C. (10 min), respectively (Table 3). Therefore, development of the protective capping layer technology is important for doped ZnO.
Known capping layers for DZO include SiO2, TiO2, Al2O3, B2O3 (U.S. 2005/0257824), SnO2 (U.S. 2011/0139237), SnO2, and TiO2 (U.S. 2012/0107554), SnO2 (U.S. 2008/0128022). These materials belong to a class of transparent dielectric oxides. Except for doped SnO2, these materials are insulators and as such, possess high resistivity. For effective operation of the semiconductor stack within photovoltaic device (“PV”), a charge transfer from the electrode, doped ZnO, preferably should be substantially unimpeded by the capping layer. Therefore, due to their inherent electrical contact blocking nature, the thickness of these known oxide dielectric materials is limited. Thin layers, however, due to their amorphous/polycrystalline nature, typically provide a poor oxygen protection barrier. Such materials may work well for doped ZnO coatings deposited by sputtering techniques at low temperature and/or pressure. As deposited, DZO layers have poor crystallinity and low mobility that leads to high resistivity. The electron concentrations, mobility and resistivities in these DZO films are typically restricted to 5-7×1020 cm−3, 5-20 cm2/Vs and >6×10−4 Ohm cm, respectively (U.S. 2012/0107554, U.S. 2008/0128022). Thermal annealing at high temperature greater than 400° C. usually helps to improve the overall crystal quality of DZO and consequently maximizes carrier mobility, where an oxide dielectric capping layer serves as a porous membrane for oxygen diffusion in and out of the material stack (D. M. Smyth, Defect Chemistry of Metal Oxides, New York Oxford, Oxford University Press, 2000). Thermal annealing of the low quality sputtered oxides for improving their electrical properties is used for In2O3:Sn activation.
Another approach uses different oxygen barrier layers, such as Ni metal, Ni/Ni coatings (T. Chen, APL 100 013310, 2012) and SiN barrier layers (F. Ruske, J. Applied Phys. 107, 013708, 2010). Nickel capping layers often have very low optical transmission due to a large extinction coefficient and require precise control of the thickness at the percolation barrier. SixNy layers were effective in improving electrical properties of low electron concentration (6×1020 cm−3) DZO layers and require sputtering as the main deposition technique for SixNy. For example, mobility of 67 cm2/Vs was demonstrated in glass/AZO/SixNy construction after high temperature annealing (F. Ruske et al., Improved Electrical Transport in Al-doped Zinc Oxide by Thermal Treatment, Journal of Applied Physics, 107, 013708 (2010).
Deterioration of electrical properties as a function of annealing temperature is a known disadvantage when using DZO for architectural and PV applications. During glass tempering process, the DZO substrates are often reheated above the glass transition temperature ˜650° C. in air. Currently, DZO stacks are deposited and cooled in O2-free environment. Introduction of DZO plus cap mutilayer stack may reduce the cost of providing an O2-free environment during deposition and cool down cycles.
As far as PV device process is concerned, as part of solar cell deposition process, DZO undergoes multiple temperature cycle steps (500-650° C.). In each of these cycles, the ambient environment may contain 0-rich species as well as other DZO harmful environments (A. Luque et al. Handbook of Photovoltaic Science and Engineering 2012).
As compared to fluorine-doped SnO2, DZO possesses poor scratch resistance and is easily etched by conventional acids. Also, a DZO layer may or may not have an optimum surface morphology, which for some applications is highly smooth or conversely very rough. Thus, there is a need to improve the properties of DZO transparent conductive oxide layers.
This invention relates to compositions, including transparent conductive oxide (“TCO”) cap compositions or TCO cap layers, that can be applied in a continuous or discontinuous fashion to the surface of a substrate by deposition or other process. In one embodiment, a substrate is a glass substrate. The cap composition or cap layer may or may not be in direct contact with the TCO layer. In one embodiment, the cap composition or cap layer of the invention is in direct contact with a DZO transparent conductive oxide composition or layer. In another embodiment, the cap composition or cap layer of the invention is not in direct contact with a DZO transparent conductive oxide composition or layer. There may be an additional composition(s) and/or layer(s) positioned on either face of the capping compositions or layers.
In one embodiment, the TCO cap compositions/layers of the invention are nitrogen-containing compositions that comprise, consist essentially of, or consist of, nitrogen, oxygen, and at least two different metal elements, where at least one of the metal elements is chosen from Group IIIA of the Periodic Table (including B, Al, Ga, In, and Tl).
In another embodiment, the TCO cap compositions/layers of the invention are compositions that comprise, consist essentially of, or consist of, ZnwOxNyYz, where w, x, y and z are atomic percent concentration ranges for each element in the composition, and where the sum of w+x+y+z equals 100−χ, such that χ represents atomic percent of unintentionally incorporated impurities, such as carbon and sulfur. The total concentration of unintentionally incorporated impurity is usually 10 atomic percent or less, and preferably less than 10 atomic percent. Y is chosen from the Group IIIA elements of the Periodic Table (also called Group 13) (e.g., B, Al, Ga, and In), preferably B, Al, and/or Ga, more preferably Ga.
In another embodiment, the TCO cap compositions/layers of the invention comprise, consist essentially of, or consist of, NyYz, and optionally ZnwOx. where w, x, y and z are atomic percent concentration ranges for each element in the composition, and where the sum of w+x+y+z equals 100−χ, such that χ represents atomic percent of unintentionally incorporated impurities, such as carbon and sulfur. The total concentration of unintentionally incorporated impurity is usually 10 atomic percent or less, and preferably less than 10 atomic percent. Y is chosen from the Group IIIA elements of the Periodic Table (also called Group 13) (e.g., B, Al, Ga, and In), preferably B, Al, and/or Ga, more preferably Ga.
The invention also is directed to novel methods for manufacturing such TCO cap compositions/layers/coatings. The invention also relates to architectural coatings incorporating such multilayer compositions or multilayer stacks that undergo annealing and tempering.
The present invention also is directed to a deposition technique for ZnwOxNyYz materials. Deposition methods are not limited to chemical vapor deposition but also may include other techniques that are known to those skilled in the art, such as, for example, sputtering, spray pyrolysis, pulse laser deposition and others. The APCVD (atmospheric pressure chemical vapor deposition) apparatus used herein is similar to that described in U.S. Pat. No. 6,268,019 which is incorporated herein in its entirety.
This invention also relates to photovoltaic devices comprising glass substrates and the multilayer coatings and TCO capping compositions/layers described herein.
This invention also is directed to a process of online or off-line production of DZO plus cap process in the open air environment as a way to produce electrodes for organic light emitting diodes (OLEDS), touch screens, and displays. Using an online process, each coating layer may be deposited in sequential fashion as the glass substrate is being produced.
The compositions of the invention provide thermally resistant, chemically resistant, and/or scratch resistant contiguous or incontiguous surfaces or layers for transparent conductive oxide films (TCO) comprising doped zinc oxide.
a-b Optical transmittance (T) and reflectance (R) for the DZO sample #4 and 5: glass/DZO/ZnwOxNyGaz. Light black T and R curves are for the as-grown DZO. Bold black T and R curves are for 500° C. annealed DZO for 5 minutes. Bold white T and R curves are for 550° C. annealed DZO for 10 minutes.
As used herein, “doped ZnO” or “DZO” refers to zinc and oxygen containing oxide film(s), layer(s), or composition(s), that may be combined, alloyed or doped with other elements. The as-obtained doped ZnO coatings are referred to herein as alloys or mixtures. Examples of possible dopants (elements combined into coating layers) include but are not limited to B, Al, Ga and In, as well as Sn, W, Ta, Nb, and halogens. A combination of these elements into a coating provides desired opto-electronic properties.
The invention is directed to a novel capping composition or layer that improves the overall properties of TCOs such as DZO. In this invention, a new compound, material, alloy, or mixture has been discovered, namely, ZnwOxNyYz, where w, x, y, z are atomic percents of the elements zinc (Zn), oxygen (O), nitrogen (N), and Y, in the compound, where w is from 0 to 100, x is from 0 to 100, y is from 0 to 100, z is from 0 to 100, such that the sum of all concentrations (w+x+y+z+χ) is equal to 100%, and where χ represents a total sum of concentrations of unintentionally incorporated impurities. Typically the amount of unintentionally incorporated impurities will be less than about less than 10 atomic percent, preferably less than about 5.5 atomic percent, more preferably less than about 5 atomic percent, more preferably less than about 3 atomic percent, more preferably less than 1 atomic percent.
In one embodiment, Y represents at least one element selected from the group consisting of Group IIIA elements. In one embodiment, Y represents at least one element selected from the group consisting of B, Al, Ga, In and Tl, preferably Ga.
In another embodiment, Y represents at least one element selected from the group consisting of B, Al, Ga, In, Tl, Sn, W, Ta, and Nb.
In another embodiment, Y represents at least one element selected from the group consisting of B, Al, Ga, In, Tl, Sn, W, Ta, Nb, F, Cl, Br, I, and At.
The invention also is directed to a TCO capping composition or layer having at least N, Zn and Y, where 0 is optional.
The invention also is directed to binary capping compositions or layers having at least N and at least Y, where zinc and/or oxygen are optional.
Atomic percents are defined in a way that normalized fractions are obtained: w+x+y+z=100, assuming that unintentional dopant concentration is equal to zero. For example, some of the binary compounds, such as Zn3N2, will have w=60%, x=0, y=40% and z=0. GaN will have w=0, x=0, y=50% and z=50%. The specific concentrations will vary depending upon the application.
Preferably, w is from 0 to about 80%, x is from 0 to about 50%, y is from about 10 to about 50%, and z is from about 10 to about 50%. More preferably, w is from about 20 to 80%, x is from about 10 to 50%, y is from about 10 to 50%, and z is from about 10 to 50%.
The invention also is directed an embodiment where the capping layer composition comprises ZnwOxNyGaz
In another embodiment, ZnwOxNyGaz capping layers are preferred.
An exemplary stack configuration/diagram is shown in
Substrates (100) of various sizes and thickness can be used in the implementation of the present invention. The thickness of the glass can vary from ultra-thin glass 0.01 mm to 20 mm thick glass panels. Other substrates include but are not limited to metals, plastics, and polymers.
The DZO configuration (200) and (201) may comprise multiple layers, such as for example, undercoat layers (that may or may not scatter light or help improve transmission or color suppression) and additional TCO compositions/layers (see, e.g., WO2011/005639 A1).
The capping layer (300) may or may not consist of a single layer. A depth profile of one of the studied stacks suggests a complicated compositional structure of the capping layer as a function distance within a coating (
With respect to the TCO cap compositions/layers of the present invention, the inventors have unexpectedly discovered that an increased amount of nitrogen can be incorporated into ZnO without deleterious impact on transparency by the addition of gallium into the composition. In one embodiment, a ZnwOxNyGaz alloy system is preferred, where the presence of Zn—N and Ga—N helps reduce oxygen diffusion through the DZO layer. DZO films considered here are of high quality (mobility 15-50 cm2/Vs, carrier concentration 5-20×1020 cm−3 and resistivity 1-6×10−4 Ohm cm) These layers are deposited at high temperature (greater than 400° C.) and are highly textured with preferred orientation of (0002).
The incorporation of nitrogen in ZnO structures at 500° C. requires modification of the deposition parameters. In addition, the band gap of the zinc nitride is very small (<1 eV) that adds considerable absorption to the visible part of the spectrum. Samples of 120 nm thick ZnwOxNyGaz were deposited by CVD. They were dark to the naked eye suggesting lack of oxygen and potential carbon and Zn metal incorporation. XPS measurement on the film confirmed this theory—up to 4.4 atomic percent of carbon was detected on the surface of these layers. The Zn/O atomic ratio increased from 1 for the normal DZO to 1.5 in nitrogen enriched DZO.
Zinc nitride (Zn3N2) is a known non-transparent/opaque conductor. The inventors discovered, however, that the transparency window of this material can be expanded towards visible with oxygen. The deposition of the zinc nitride is a thermodynamically controlled process. Small heat of formation energies of ZnwNz compared to high negative values for ZnO tends to reduce incorporation of nitrogen within ZnwOyNz system by CVD at high temperatures (>400° C.). It was further discovered that a larger amount of nitrogen can be incorporated into ZnO without harmful effect on transparency by adding small amounts of Ga. Without being bound to any theory, it may be that highly negative heat of formation of GaN allows larger incorporation of nitrogen within the ZnwOxNyGaz system.
A combined DZO stack+cap as described herein has been developed by Arkema Inc. The TCO capping composition or layer comprises, consists essentially of, or consists of ZnwOxNyGaz compound, alloy, or mixture. It possesses several key properties, such as improved thermal, chemical, and scratch resistances. It also has been shown to planarize DZO layers, meaning improved surface smoothness. In addition, the thermal performance of the DZO/cap stack is improved as compared to an unmodified/uncapped DZO stack coating.
A gas mixture of 0.31 mmol/min of ZnMe2-MeTHF in 10 sLpm of nitrogen carrier gas was fed into a primary feed tube at 70° C. A preheated (80° C.) secondary feed containing 5.5 sLpm of NH3 was co-fed with the primary flow. The substrate used for the deposition was borosilicate glass with the thickness of 0.7 mm. The substrate was heated on resistively heated nickel block set at 500° C. The deposition time for these films was 120 seconds in a static mode, and resulting ZnwOxNy films had thickness of 90 nm, for a deposition rate of 0.75 nm/s. The measured atomic percents of the elements are listed in Table 1. Nitrogen was incorporated at 2.6 atomic percent in these film as measured by x-ray photoelectron spectroscopy (XPS) which is a known tool for the skilled in the art. The atomic percents were w=55%, x=37%, y=03% and z=0%, with the remainder being unintentional impurities.
A gas mixture of 0.31 mmol/min of ZnMe2-MeTHF in 10 sLpm of nitrogen carrier gas was mixed with 50 sccm of Me2Gacac stream in a primary feed tube heated at 80° C. The gallium source was kept in a bubbler at 35° C. Preheated to 80° C. secondary feed containing 5.5 sLpm of NH3 was co-fed with the primary flow. The substrate used for the deposition was borosilicate glass with the thickness of 0.7 mm. The substrate was heated on resistively heated nickel block set at 500° C. The deposition time for these films was 120 seconds in a static mode, and resulting ZnwOxNyGaz film had thickness of 80 nm, for a deposition rate of 0.67 nm/s. The measured atomic concentrations of the elements are listed in Table 1. Addition of gallium precursor in the vapor stream helped to improve incorporation of nitrogen. The total nitrogen atomic concentration was 18.3% as determined by XPS. In addition, 8.2 atomic % of Gallium was found in this film. The atomic percents were w=45%, x=26%, y=18% and z=8% with x=3%. Both ZnwOxNy and ZnwOxNyGaz films showed good optical transmittance (
A gas mixture of 1.23 mmol/min of ZnMe2-MeTHF in 11 sLpm of nitrogen carrier gas was fed into a primary feed tube at 80° C. The dopant was introduced into the primary feed tube from a stainless steel bubbler. The bubbler contained GaMe2acac at 35° C. Ga-precursor was picked up by preheated to 40° C. nitrogen with a flow rate of 500 sccm. The oxidants were introduced into a secondary feed tube through two stainless steel bubblers. The first and second bubblers contained H2O and 2-propanol at 60 and 65° C., respectively. H2O was picked by preheated to 65° C. nitrogen with the flow rate of 400 sccm. 2-Propanol was picked up preheated to 70° C. nitrogen with the flow rate of 560 sccm. The secondary feeds were co-fed with the primary flow inside a mixing chamber. The mixing chamber was 1¼ inch in length, corresponding to a mixing time of 250 msec between the primary and secondary feed streams. The substrate used for the deposition was borosilicate glass with the thickness of 0.7 mm. The substrate was heated on resistively heated nickel block set at 500° C. The resulting ZnO films had thickness between 120 and 174 nm. The deposition of the 1st layer (DZO) was followed by deposition of the capping layer. The thickness of the capping layers was varied (Table 2).
The capping layer was deposited as follows. A gas mixture of 0.31 mmol/min of ZnMe2-MeTHF in 10 sLpm of nitrogen carrier gas was mixed with 50 sccm of Me2Gacac stream in a primary feed tube heated at 70° C. The gallium source was kept in a bubbler at 35° C. Preheated to 70° C. secondary feed containing 5.5 sLpm of NH3 was co-fed with the primary flow. The deposition time for these films varied. Resulting ZnwOxNyGaz film thicknesses were determined using spectroscopic ellipsometry (SE) measurements (Table 2). Characterization of the thin film stacks using SE is well known technique in the present art.
The introduction of the capping layers reduced the roughness of the DZO coatings. The term ‘roughness’ here refers to the root mean square (RMS) roughness and maximum valley to peak values (Zmax) as measured by Atomic Force Microscopy (AFM) using techniques known to those skilled in the art. The maximum reductions in RMS (46%) and Zmax (54%) values were obtained for 24 and 42 nm thick ZnwOxNyGaz capping layers, respectively.
To characterize electrical properties for as-grown and annealed samples, one skilled in the art uses optical spectroscopy. Again, the term ‘as-grown’ refers to DZO samples deposited as described by (U.S. Pat. Nos. 7,732,013, 8,163,342, 7,989,024, the disclosure of which is incorporated herein by reference in their entireties) patents. The term “annealed’ is used to describe thermal treatment of the as-grown samples. For example, the samples may be annealed in air, vacuum and nitrogen ambient at different annealing temperatures. It is further assumed that the annealing environment may include other gases known to the skilled professional.
The application of the spectroscopic technique to determining electrical properties of the coatings relies on a known relationship between a plasma wavelength and electron concentration (n), such as λp˜n−1/2. Here, the term plasma wavelength (λp) describes a point of intersection of refractive index and extinction coefficient and entire teachings of which are described herein by this reference (J. Pankove, Optical process in semiconductors and R. Y. Korotkov et al., Proc. of SPIE Vol. 7939 793919-1, 2011). Electron mobility and concentration are given by μ=1.15/(m*ΓD) and n=0.73×1021 m*∈∞(hc/λp)2, where m* is an effective mass, ΓD is an oscillator damping term, h is Planck's constant and c is velocity of light. Qualitatively, the presence of the plasma wavelength in the studied spectroscopic range is always accompanied by a strong reflection curve.
Reflection curves for the as-grown sample indicate λp=1.22 nm (
To understand the effect of the ZnwOxNyGaz cap thickness on the electrical properties of the DZO, electrical properties for the sample with 19 nm thick cap were calculated, sample #2 (Table 3). As-grown sample #2 had resistivity of 3.1×10−4 Ωcm. When annealed to 500° C. (5 min) and 550° C. (10 min) in the ambient air, its resistivities increased to 3.95 and 17×10−4 Ωcm, respectively. The plasma wavelength shifted in the red from 1.15 to 3.2 μm, when annealed under the same conditions.
These results indicated that ZnwOxNyGaz capping layers serve as good barrier layers during annealing of the DZO films in air ambient with the optimum thickness of 40-60 nm.
A series of acid sensitivity tests were performed on the coatings discussed in this invention using 10% by volume HCl solution. Each of the coatings glass/DZO ZnwOxNyGaz (capped, i.e., cap+DZO+glass substrate) and glass/DZO (uncapped, i.e., DZO+glass substrate) were placed in this solution. All uncapped coatings were etched within seconds. In contrast, the thickness of capped DZO coatings was unchanged by the etching process within 2 minutes of acid exposure as verified by the SE studies.
As shown above, the capping layer compositions of the invention provide improved thermal resistance properties to the DZO stack, thereby helping to preserve the optical and electrical properties of the stack when it is subjected to annealing in different environments and at elevated temperatures. In addition, it also improves the chemical and scratch resistance properties.
The following detailed description of preferred embodiments is related to examples that are supported by the drawings Skilled in the art scientist will recognize that presented drawings and examples have many alternatives that fall within the scope of this invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2014/027400 | 3/14/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61789018 | Mar 2013 | US |
