Glass substrate mitigating against potential induced degradation and improving thermal tempering, and solar panel and architectural window including the same

Abstract

A glass substrate comprises: a composition comprising, in mol% and on an oxide basis: SiO2, within a range of from 60 to 72; Al2O3, within a range of from 0 to 5.0; B2O3, within a range of from 3.5 to 15.0; MgO, within a range of from 1.0 to 15.0; CaO, within a range of from 1.0 to 15.0; and R2O, within a range of from 6.0 to 20.0, wherein R2O is one or more of K2O, Cs2O, and Rb2O, wherein, the composition is substantially free of Na2O, and Li2O. A solar panel incorporating the glass substrate. An architectural window incorporating the glass substrate.

Description

GLASS SUBSTRATE MITIGATING AGAINST POTENTIAL INDUCED DEGRADATION AND IMPROVING THERMAL TEMPERING, AND SOLAR PANEL AND ARCHITECTURAL WINDOW INCLUDING THE SAMECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application No. 63 / 612,438 filed December 20, 2023, the content of which is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure pertains to glass substrates such as for use in solar panels and architectural windows, and more particularly to glass substrates with alkali ions larger than sodium ions to mitigate against potential induced degradation of photovoltaic cells and further with boron oxide to provide improved thermal tempering at relatively thin thicknesses.BACKGROUND

[0003] Solar panels include photovoltaic cells. Each photovoltaic cell includes two different semi-conductor materials (an n-type material and a p-type material) that are joined together to create a p-n junction. The n-type material includes, from a dopant, unpaired electrons ready to move and thereby conduct electricity. The p-type material includes, from another dopant, valent “holes” ready to accept the electrons and thereby conduct electricity. Upon application of thermal agitation, electrons from the n-type material cross the p-n junction and occupy a hole within the p-type material but additionally leaving behind a hole within the n-type material from where the electron came. An electric field is thus generated about the p-n junction (referred to as a depletion zone) with the n-type material having a positive charge (due to the loss of electrons) and the p-type material having a negative charge (due to the gain of electrons).

[0004] The Sun generates photons. The depletion zone absorbs some of those photons. Energy associated with the photons transfers to the unpaired electrons within the n-type material. Of the absorbed photons, some photons have sufficient energy to cause electrons within the n-material to move to a conduction band and thus leave a hole behind. Because of the electric field at the depletion zone, the excited electron moves away from the depletion zone and to a primary surface of the n-type material, and the created hole moves away from the depletion zone and to a primary surface of the of the p-type material. Assuming that conductors are coupled to both the primary surface of the n-type material and the p-type material, and the conductors are themselves electrically coupled, an electrical current is generated with the electron moving from the n-type material, to the conductor at the primary surface of the n-type material, through the conductive material coupling the conductors, to theconductor at the primary surface of the p-type material, and then into the p-type material, occupying the hole that had migrated there from the depletion zone. The flow of electrons to the primary surface of the n-type material of the photovoltaic cell creates a negative potential relative to ground.

[0005] In addition to photovoltaic cells, solar panels typically include a glass substrate covering at least the n-type material of the photovoltaic cell. Often, the glass substrate has a soda lime glass composition. Soda lime glass is traditionally made from silica, soda ash (Na2COs) (from which the “soda” comes), and limestone (CaCOs) (from which the “lime” comes). Not a glass former, the sodium from soda ash exists in the soda lime glass as sodium ions (Na+) within a glass matrix that the silica forms. Under normal, non-photovol tai c, conditions, the sodium ions (Na+) do not leach out of the glass matrix of the soda lime glass.

[0006] However, there is a problem in that negative potential at the primary surface of the n- type material causes sodium ions to migrate out of the soda lime glass and into the n-type material of the photovoltaic cells. That is a problem, because the presence of the sodium ions disrupts the arrangement of silicon and dopant atoms at the primary surface of the n-type material. The disrupted arrangement of those atoms traps the migration of electrons and holes throughout the n-type material. The trapping of such charge carriers decreases current generation (e.g., efficiency of the PV cell). The migrated sodium ions degrade the photovoltaic cells in other ways as well. These degradations are collectively referred to as “potential induced degradation” or PID for short.SUMMARY

[0007] The present disclosure addresses that problem with a glass substrate with a composition that includes SiCh, B2O3, MgO, CaO, and R2O, in particular mole percentage ranges, and where R2O is one or more of K2O, CS2O, and Rb2O and to the exclusion of Li2O and Na2O. Potassium, cesium, and rubidium ions all have a larger atomic radius than the atomic radii of sodium and lithium ions. Thus, it is believed that the potassium, cesium, and / or rubidium ions would diffuse out of the glass substrate at a slower rate than sodium and lithium ions, which would decrease potential induced degradation. Further, the presence of B2O3 and K2O in the composition of the glass substrate, it is believed, increases high temperature coefficient of thermal expansion and increases the difference between the high temperature and low temperature coefficients of thermal expansion sufficiently so that thermal tempering of the glass substrate is possible and effective at relatively thin thicknesses.

[0008] According to a first aspect of the present disclosure, a glass substrate comprises: a composition comprising, in mol% and on an oxide basis: SiCh, within a range of from 60 to72; AI2O3, within a range of from 0 to 5; B2O3, within a range of from 3.5 to 15.0; MgO, within a range of from 1.0 to 15.0; CaO, within a range of from 1.0 to 15.0; and R2O, within a range of from 6.0 to 20.0, wherein R2O is one or more of K2O, CS2O, and Rb2O, wherein, the composition is substantially free of Na2O, and Li2O.

[0009] According to a second aspect of the present disclosure, the glass substrate of the first aspect is presented, wherein R2O is exclusively K2O.

[0010] According to a third aspect of the present disclosure, the glass substrate of any one of the first through second aspects is presented, wherein the SiCh of the composition is within a range of from 66 to 71.

[0011] According to a fourth aspect of the present disclosure, the glass substrate of any one of the first through third aspects is presented, wherein the B2O3 of the composition is within a range of from 4.0 to 15.0.

[0012] According to a fifth aspect of the present disclosure, the glass substrate of any one of the first through fourth aspects is presented, wherein the B2O3 of the composition is within a range of from 4.0 to 8.0.

[0013] According to a sixth aspect of the present disclosure, the glass substrate of any one of the first through fifth aspects is presented, wherein the MgO of the composition is within a range of from 6.2 to 8.3.

[0014] According to a seventh aspect of the present disclosure, the glass substrate of any one of the first through sixth aspects is presented, wherein the CaO of the composition is within a range of from 8.6 to 12.8.

[0015] According to an eighth aspect of the present disclosure, the glass substrate of any one of the first through seventh aspects is presented, wherein the R2O of the composition is within a range of from 6.5 to 9.6.

[0016] According to a ninth aspect of the present disclosure, the glass substrate of any one of the first through eighth aspects is presented, wherein the composition further comprises AI2O3 at less than or equal to 3.0.

[0017] According to a tenth aspect of the present disclosure, the glass substrate of the ninth aspect is presented, wherein the AI2O3 within the composition is within a range of from 1.00 to 1.10.

[0018] According to an eleventh aspect of the present disclosure, the glass substrate of any one of the first through tenth aspects is presented, wherein the composition consists essentially of SiCh, B2O3, AI2O3, MgO, CaO, K2O, and optionally a fining agent selected from a group consisting of AS2O3, Sb2O3, SnO2, and SO3.

[0019] According to a twelfth aspect of the present disclosure, the glass substrate of any one of the first through eleventh aspects further comprises: a first primary surface, a second primary surface facing away from the first primary surface, and a thickness between the first primary surface, wherein, the thickness is less than or equal to 4.5 mm.

[0020] According to a thirteenth aspect of the present disclosure, the glass substrate of the twelfth aspect is presented, wherein the thickness is less than or equal to 2.0 mm.

[0021] According to a fourteenth aspect of the present disclosure, the glass substrate of any one of the first through thirteenth aspects is presented, wherein the glass substrate exhibits a high temperature coefficient of thermal expansion that is within a range of from 28 ppm / °C to 40 ppm / °C.

[0022] According to a fifteenth aspect of the present disclosure, the glass substrate of any one of the first through fourteenth aspects is presented, wherein the glass substrate exhibits a low temperature coefficient of thermal expansion that is within a range of from 6.0 ppm / °C to 8.5 ppm / °C.

[0023] According to a sixteenth aspect of the present disclosure, the glass substrate of any one of the first through fifteenth aspects is presented, wherein the glass substrate exhibits a difference between a high temperature coefficient of thermal expansion and a low temperature coefficient of thermal expansion is greater than 20 ppm / °C.

[0024] According to a seventeenth aspect of the present disclosure, the glass substrate of any one of the first through sixteenth aspects further comprises: (i) a first region of compressive stress; (ii) a second region of compressive stress; and (iii) a region of central tension disposed between the first region of compressive stress and the second region of compressive stress.

[0025] According to an eighteenth aspect of the present disclosure, the glass substrate of the seventeenth aspect is presented, wherein the first region of compressive stress and the second region of compressive stress were generated as a result of thermal tempering of the glass substrate.

[0026] According to a nineteenth aspect of the present disclosure, the glass substrate of any one of the first through eighteenth aspects is presented, wherein the glass substrate exhibits a liquidus temperature that is less than 1400 °C.

[0027] According to a twentieth aspect of the present disclosure, a solar panel comprises: (1) an array of photovoltaic cells; and (2) a glass substrate separating the photovoltaic cell from an external environment, the glass substrate (a) exhibiting an average transmittance through the glass substrate of greater than or equal to 80% for a wavelength of electromagnetic radiation within a range of from 500 nm to 950 nm, (b) comprising a first primary surface facing theexternal environment, a second primary surface facing the photovoltaic cell, and a thickness between the first primary surface and the second primary surface that is less than or equal to 4.5 mm, and (c) comprising a composition comprising, in mol% and on an oxide basis: SiCh, within a range of from 60 to 72; AI2O3, within a range of from 0 to 5.0; B2O3, within a range of from 3.5 to 15.0; MgO, within a range of from 1.0 to 15.0; CaO, within a range of from 1.0 to 15.0; and R2O, within a range of from 6.0 to 20.0, wherein R2O is one or more of K2O, CS2O, and Rb2O, wherein, the composition is substantially free of Na2O, and Li2O.

[0028] According to a twenty-first aspect of the present disclosure, the solar panel of the twentieth aspect is presented, wherein the composition of the glass substrate further comprises AI2O3 at less than or equal to 3.0.

[0029] According to a twenty-second aspect of the present disclosure, the solar panel of the twenty-first aspect is presented, wherein (i) the AI2O3 within the composition is within a range of from 1.00 to 1.10, (ii) R2O is exclusively K2O, (iii) the R2O of the composition is within a range of from 6.5 to 9.6, (iv) the SiCh of the composition is within a range of from 66 to 71, (v) the B2O3 of the composition is within a range of from 4.0 to 8.0, (vi) the MgO of the composition is within a range of from 6.2 to 8.3, and (vii) the CaO of the composition is within a range of from 8.6 to 12.8.

[0030] According to a twenty-third aspect of the present disclosure, the solar panel of any one of the twentieth through the twenty-second aspects is presented, wherein the composition consists essentially of SiO2, B2O3, AI2O3, MgO, CaO, K2O, and optionally a fining agent selected from a group consisting of AS2O3, Sb2O3, SnO2, and SO3.

[0031] According to a twenty-fourth aspect of the present disclosure, the solar panel of any one of the twentieth through the twenty-third aspects is presented, wherein the thickness of the glass substrate is less than or equal to 2.0 mm.

[0032] According to a twenty-fifth aspect of the present disclosure, the solar panel of any one of the twentieth through the twenty-fourth aspects is presented, wherein (i) the glass substrate exhibits a high temperature coefficient of thermal expansion that is within a range of from 28 ppm / °C to 40 ppm / °C; (ii) the glass substrate exhibits a difference between the high temperature coefficient of thermal expansion and a low temperature coefficient of thermal expansion is greater than 20 ppm / °C; and (iii) the glass substrate exhibits a liquidus temperature that is less than 1400 °C.

[0033] According to a twenty-sixth aspect of the present disclosure, an architectural window comprises: (1) a first pane comprising a glass substrate, the glass substrate (a) exhibiting an average transmittance through the glass substrate of greater than or equal to 80% for awavelength of electromagnetic radiation within a range of from 500 nm to 950 nm, (b) comprising a first primary surface facing an external environment, a second primary surface facing away from the external environment, and a thickness between the first primary surface and the second primary surface that is less than or equal to 4.5 mm, and (c) comprising a composition comprising, in mol% and on an oxide basis: SiCh, within a range of from 60 to 72; A12O3, within a range of from 0 to 5.0; B2O3, within a range of from 3.5 to 15.0; MgO, within a range of from 1.0 to 15.0; CaO, within a range of from 1.0 to 15.0; and R2O, within a range of from 6.0 to 20.0, wherein R2O is one or more of K2O, CS2O, and Rb2O, wherein, the composition is substantially free of Na2O, and Li2O; and (2) a second pane separated from the first pane by a space, the second pane comprising the glass substrate or another glass substrate.

[0034] According to a twenty-seventh aspect of the present disclosure, the solar panel of the twenty-sixth aspect further comprises: a frame surrounding perimeters of, and supporting, both the first pane and the second pane.

[0035] According to a twenty-eighth aspect of the present disclosure, the solar panel of any one of the twenty-sixth through twenty-seventh aspects is presented, wherein the composition of the glass substrate of the first pane further comprises AI2O3 at less than or equal to 3.0.

[0036] According to a twenty-ninth aspect of the present disclosure, the solar panel of the twenty-eighth aspect is presented, wherein (i) the AI2O3 within the composition of the glass substrate of the first pane is within a range of from 1.00 to 1.10, (ii) R2O is exclusively K2O, (iii) the R2O of the composition of the glass substrate of the first pane is within a range of from 6.5 to 9.6, (iv) the SiCh of the composition of the glass substrate of the first pane is within a range of from 66 to 71, (v) the B2O3 of the composition of the glass substrate of the first pane is within a range of from 4.0 to 8.0, (vi) the MgO of the composition of the glass substrate of the first pane is within a range of from 6.2 to 8.3, and (vii) the CaO of the composition of the glass substrate of the first pane is within a range of from 8.6 to 12.8.

[0037] According to a thirtieth aspect of the present disclosure, the solar panel of any one of the twenty-sixth through twenty-ninth aspects is presented, wherein the composition of the glass substrate of the first pane consists essentially of SiCh, B2O3, AI2O3, MgO, CaO, K2O, and optionally a fining agent selected from a group consisting of AS2O3, Sb2O3, SnO2, and SO3.

[0038] According to a thirty-first aspect of the present disclosure, the solar panel of any one of the twenty-sixth through thirtieth aspects is presented, wherein (i) the glass substrate of the glass substrate of the first pane exhibits a high temperature coefficient of thermal expansion that is within a range of from 28 ppm / °C to 40 ppm / °C; (ii) the glass substrate of the glass substrate of the first pane exhibits a difference between the high temperature coefficient ofthermal expansion and a low temperature coefficient of thermal expansion is greater than 20 ppm / °C; and (iii) the glass substrate of the glass substrate of the first pane exhibits a liquidus temperature that is less than 1400 °C.

[0039] Additional features and advantages will be set forth in the detailed description which follows, and will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0040] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understanding the nature and character of the disclosure and the appended claims.

[0041] The accompanying drawings are included to provide a further understanding of principles of the disclosure, and are incorporated in, and constitute a part of, this specification. The drawings illustrate one or more embodiment(s) and, together with the description, serve to explain, by way of example, principles and operation of the disclosure. It is to be understood that various features of the disclosure disclosed in this specification and in the drawings can be used in any and all combinations. By way of non-limiting examples, the various features of the disclosure may be combined with one another according to the following embodiments.BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The following is a description of the figures in the accompanying drawings. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.

[0043] In the Drawings:

[0044] FIG. l is a perspective view of a glass substrate of the present disclosure, illustrating a first primary surface, a second primary surface facing away from the first primary surface, and a thickness between the first primary surface and the second primary surface;

[0045] FIG. 2 is a perspective view of a solar panel including the glass substrate of FIG. 1, illustrating the first primary surface of the glass substrate facing the Sun and an array of photovoltaic cells disposed under the glass substrate;

[0046] FIG. 3 is a plan view of the solar panel of FIG. 2;

[0047] FIG. 4 is an elevational view of a cross-section of the solar panel of FIG. 2 taken through line IV-IV of FIG. 3, illustrating the glass substrate, the array of photovoltaic cells, and a backsheet arranged as a package and supported by a frame;

[0048] FIG. 5 is a magnified view of area V of FIG. 4;

[0049] FIG. 6 is a plan view of an architectural window including the glass substrate of FIG. 1; and

[0050] FIG. 7 is an elevational view of a cross-section of the architectural window of FIG. 6 taken through line VII- VII of FIG. 6, illustrating the architectural window including the glass substrate of FIG. 1 as part of a first pane, a second pane, and a spacer separating the first pane from the second pane.DETAILED DESCRIPTION

[0051] Additional features and advantages will be set forth in the detailed description which follows and will be apparent to those skilled in the art from the description, or recognized by practicing the embodiments as described in the following description, together with the claims and appended drawings.

[0052] Referring now to FIG. 1, a glass substrate 10 is herein described. The glass substrate 10 includes a composition. The composition includes, in mole percentage (“mol%”) and on an oxide basis: (i) SiCh, within a range of from 60 to 72; (ii) AI2O3, within a range of from 0 to 5, (iii) B2O3, within a range of from 3.5 to 15.0; (iv) MgO, within a range of from 1.0 to 15.0, (v) CaO, within a range of from 1.0 to 15.0; and (vi) R2O, within a range of from 6.0 to 20.0. For purposes of this disclosure, R2O means one or more of K2O, CS2O, or Rb2O. In other words, R2O for purposes of this disclosure is the sum of all alkali oxides, except for Na2O and Li2O, in the composition. The composition is substantially free of Na2O and Li2O. The composition can include any combination of K2O, CS2O, and Rb2O, as long as the combined weight percentage(s) thereof is within the range of from 6.0 to 20.0. It should be understood that all numerical values for compositional make up mentioned herein are mole percentages on an oxide basis, without the need to repeat the same every time a value is mentioned. Mole percentages of the constituents of the composition can be determined via X-Ray fluorescence. “Substantially free” here means that the particular oxide, such as Na2O and Li2O, as the case may be, is not intentionally added to the composition but may be present unintentionally in trace (e.g., 0.001 mol% or less) amounts due to manufacturing imprecision. In embodiments, R2O is exclusively K2O. In other words, the only alkali oxide present within the composition is K2O, aside from other alkali oxides that may exist unintentionally in trace amounts.

[0053] In the composition, the SiCh is the largest, by mole percentage, constituent. Similarly, the SiCh is the primary constituent of the glass network that the composition forms. However, raising the mole percentage of SiCh to lower the coefficient of thermal expansion of the glass substrate 10 can also increase the liquidus temperature, which can exacerbate the problem described in Background. For purposes of the glass substrate 10 of the present disclosure, thecompeting concerns are balanced with the mole percentage of SiCh being within the stated range of from 60 to 72. In embodiments, the mole percentage of SiCh in the composition 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, or 72 or within any range bound by any two of those values (e.g., from 66 to 71, from 64 to 66, and so on).

[0054] Like SiCh, B2O3 can form part of the glass network of the glass substrate 10. Without being bound by theory, it is believed that the addition of B2O3 to the composition increases the Young’s modulus and high temperature coefficient of thermal expansion of the glass substrate 10. Boron oxide, B2O3, helps scavenge non-bridging oxygen atoms (NBOs), which are created when the amount or concentration of modifiers, as here, exceeds that of AI2O3. Boron oxide converts the NBOs to bridging oxygen atoms through the formation of BO4 tetrahedra, which increases the rigidity of the glass by increasing the interconnectedness of the glass structure. Too little B2O3 would not increase the Young’s modulus and high temperature coefficient of thermal expansion sufficiently. However, too much B2O3 increases the cost of the composition so as to outweigh the benefits of the property improvements. For purposes of the glass substrate 10 of the present disclosure, the competing concerns are balanced with the mole percentage of B2O3 being within the stated range of from 3.5 to 15.0. In embodiments, the mole percentage of B2O3 in the composition is 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, or 15.0, or within any range bound by any two of those values (e.g., from 4.0 to 15.0, from 4.0 to 8.0, and so on).

[0055] MgO can affect various properties of the glass substrate, such as the viscosity, Young’s modulus, and coefficient of thermal expansion. For purposes of the glass substrate 10 of the present disclosure, the competing concerns are balanced with the mole percentage of MgO being within the stated range of from 1.0 to 15.0. In embodiments, the mole percentage of MgO in the composition is 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.2, 6.5, 7.0, 7.5, 8.0, 8.3, 8.5 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, or 15.0, or within any range bound by any two of those values (e.g., from 6.2 to 8.3, from 4.0 to 8.0, and so on).

[0056] An alkaline earth oxide like MgO, CaO can also affect various properties of the glass substrate, such as the viscosity, Young’s modulus, and coefficient of thermal expansion. More particularly, the presence of CaO in the composition is thought to help convert B2O3 from trigonal planar to tetrahedral coordination, which increases the Young’s modulus. Further, CaO is more effective at converting B2O3 from trigonal planar to tetrahedral than MgO. It is non-intuitive to have a glass with CaO that has a higher Young's modulus than one with MgO because MgO has a higher field strength. However, too much CaO relative to R2O increases the liquidus temperature and density of the glass, which makes it more difficult and expensiveto manufacture, and which also counters efforts to reduce weight of the glass substrate 10. Further, the mole percentage of CaO should not exceed the mole percentage of R2O too much, if at all, in order to prevent phase separation of the glass substrate 10. For purposes of the glass substrate 10 of the present disclosure, the competing concerns are balanced with the mole percentage of CaO being within the stated range of from l.O to 15.0. In embodiments, the mole percentage of CaO is 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 7.5, 8.0, 8.5, 8.6, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 12.8, 13.0, 13.5, 14.0, 14.5, or 15.0, or within any range bound by any two of those values (e.g., from 9.0 to 11.0, from 8.5 to 10.5, and so on).

[0057] The presence of R2O in the composition helps increase the coefficient of thermal expansion of the glass substrate 10, decrease the liquidus temperature, and can lower the cost of the composition, depending on the alkali oxide chosen. However, in general, too much R2O would lower the Young’s modulus of the glass substrate 10. For purposes of the glass substrate 10 of the present disclosure, the competing concerns are balanced with the mole percentage of R2O being within the stated range of from 6.0 to 20.0. In embodiments, the mole percentage ofR2O is 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 9.6, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, 15.0, 15.5, 16.0, 16.5, 17.0, 17.5, 18.0, 18.5, 19.0, 19.5, or 20.0, or within any range bound by any two of those values (e.g., from 6.5 to 9.6, from 11.0 to 12.5, and so on).

[0058] In embodiments, the composition of the glass substrate further includes AI2O3. Like SiCh and B2O3, AI2O3 can form part of the glass network of the glass substrate 10. The presence of AI2O3 can reduce the liquidus temperature of the composition. However, too much AI2O3 can increase the viscosity of the composition as melted, and thus hinder formability of the glass substrate 10. For purposes of the glass substrate 10 of the present disclosure, the competing concerns are balanced with the mole percentage of AI2O3 being less than or equal to 5.0, such as within the range of from 0 to 5.0, or in embodiments less than or equal to 3.0, such as within the range of from 0 to 3.0. In embodiments, the mole percentage of AI2O3 in the composition is 0, 0.1, 0.5, 1.00, 1.10, 1.2, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 5.0, or within any range bound by any two of those values (e.g., from 0 to 3.0, from 1.00 to 1.10, from 0.5 to 4.5, from 0.1 to 5.0, and so on).

[0059] In embodiments, the composition optionally further includes a fining agent. The fining agent can be selected from a group consisting of AS2O3, Sb2C>3, SnCh, and SO3. In embodiments, the fining agent is SnCh. In embodiments, the composition consists essentially of SiCh, B2O3, CaO, Na2O, and optionally a fining agent selected from a group consisting of AS2O3, Sb2O3, SnO2, and SO3.

[0060] Referring again to FIG. 1, in embodiments, the glass substrate 10 further includes a first primary surface 12 and a second primary surface 14. The second primary surface 14 faces away from the first primary surface 12. The first primary surface 12 and the second primary surface 14 can face in directions 16, 18 that are opposite of each other. The glass substrate 10 further includes a thickness 20, which in those embodiments is the straight-line distance between the first primary surface 12 and the second primary surface 14. In embodiments, the thickness 20 is within a range of from 0.5 mm to 4.5 mm. The thickness 20 can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, 2.6 mm, 2.7 mm, 2.8 mm, 2.9 mm, 3.0 mm, 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm, 3.5 mm, 3.6 mm, 3.7 mm, 3.8 mm, 3.9 mm, 4.0 mm, 4.1 mm, 4.2 mm, 4.3 mm, 4.4 mm, or 4.5 mm, or within any range bound by any two of those values (e.g., from 0.5 mm to 3.1 mm, from 1.8 mm to 2.5 mm, and so on). The thickness 20 can be less than or equal to 4.5 mm, such as less than or equal to 3.1 mm, such as less than or equal to 2.0 mm. Thicknesses 20 of less than 0.5 mm are envisioned.

[0061] Due to the composition as described herein, the glass substrate 10 exhibits characteristic properties. For example, in embodiments, the glass substrate 10 exhibits a Young’s modulus within a range of from 65 GPa to 80 GPa. The Young’s modulus that the glass substrate 10 exhibits is comparable to the Young’s modulus that a typical soda lime glass exhibits. In embodiments, the Young’s modulus that the glass substrate 10 exhibits is 65 GPa, 66 GPa, 67 GPa, 68 GPa, 69 GPa, 70 GPa, 71 GPa, 72 GPa, 73 GPa, 74 GPa, 75 GPa, 76 GPa, 77 GPa, 78 GPa, 79 GPa, or 80 GPa,, or within any range bound by any two of those values (e.g., from 69 GPa to 73 GPa, from 72 GPa to 75 GPa, and so on). Unless specified otherwise, the Young's modulus values disclosed in this disclosure refer to a value as measured by a resonant ultrasonic spectroscopy technique of the general type set forth in ASTM C623-21 titled “Standard Test Method for Young’s Modulus, Shear Modulus, and Poisson’s Ratio for Glass and Glass-Ceramics by Resonance.”

[0062] In embodiments, the glass substrate 10 exhibits a high temperature coefficient of thermal expansion (CTE) that is within a range of from 28 ppm / °C to 40 ppm / °C. High temperature CTE refers to the coefficient of thermal expansion of the glass composition above the glass transition temperature of the glass composition. The high temperature CTE is determined by plotting the instantaneous CTE (y-axis) as a function of the temperature (x-axis). The high temperature CTE is the value of the CTE where the slope of the CTE v. temperature curve is approximately zero following a pronounced increase (e.g., where the CTE v.temperature curve “plateaus”). The value of the high temperature CTE can be a measure of the volume change of the glass during cooling from high temperatures, such as during a thermal tempering process. In embodiments, the high temperature CTE is 28 ppm / °C, 29 ppm / °C, 30 ppm / °C, 31 ppm / °C, 32 ppm / °C, 33 ppm / °C, 34 ppm / °C, 35 ppm / °C, 36 ppm / °C, 37 ppm / °C, 38, 39, or 40 ppm / °C, or within any range bound by any two of those values (e.g., from 30 ppm / °C to 33 ppm / °C, from 35 ppm / °C to 39 ppm / °C, and so on).

[0063] In embodiments, the glass substrate 10 exhibits a low temperature coefficient of thermal expansion (CTE) that is within a range of from 6.0 ppm / °C to 8.5 ppm / °C. Low temperature CTE refers to the coefficient of thermal expansion of the glass composition below 300 °C (e.g., from 250 °C to 300 °C). In embodiments, the low temperature CTE is 6.0 ppm / °C, 6.25 ppm / °C, 6.5 ppm / °C, 6.75 ppm / °C, 7.0 ppm / °C, 7.25 ppm / °C, 7.5 ppm / °C, 7.75 ppm / °C, 8.0 ppm / °C, 8.25 ppm / °C, or 8.5 ppm / °C, or within any range bound by any two of those values (e.g., from 6.5 ppm / °C to 8.5 ppm / °C, from 7.5.0 ppm / °C to 8.25 ppm / °C, and so on).

[0064] The high temperature CTE that the glass substrate 10 of the present disclosure exhibits, which may be attributable to increased mole percentages of B2O3, is much higher than the high temperature CTE that a typical soda lime glass exhibits. The relatively high high temperature CTE of the glass substrate 10 of the present disclosure increases the effectiveness of thermal tempering the glass substrate 10 when the thickness 20 of the glass substrate 10 is relatively thin (e.g., less than 2.0 mm) in imparting compressive stress to the first primary surface 12 and the second primary surface 14 of the glass substrate 10. When the thickness 20 is relatively thin, the distance between the mid-plane of the glass substrate 10 and the first primary surface 12 becomes sufficiently small that it is very difficult to impart a thermal gradient that can be sustained long enough to develop the final tempering stresses. The high high temperature CTE of the glass substrate 10 helps to overcome that difficulty. Further, the low temperature CTE that the glass substrate 10 exhibits is less than the low temperature CTE that a typical soda lime glass exhibits.

[0065] In embodiments, a difference between the high temperature CTE that the glass substrate 10 exhibits and the low temperature CTE that the glass substrate 10 exhibits is greater than 20 ppm / °C. For example, if the glass substrate 10 exhibits a high temperature CTE of 35 ppm / °C, then the low temperature CTE that the glass substrate 10 exhibits is (35-20=15) less than 15 ppm / °C. In embodiments, the difference between the high temperature CTE that the glass substrate 10 exhibits and the low temperature CTE that the glass substrate 10 exhibits is 20 ppm / °C, 21 ppm / °C, 22 ppm / °C, 23 ppm / °C, 24 ppm / °C, 25 ppm / °C, 26 ppm / °C, 27 ppm / °C, 28 ppm / °C, 29 ppm / °C, or 30 ppm / °C, or greater, or within any range bound by any two ofthose values (e.g., from 22 ppm / °C to 29 ppm / °C, from 23 ppm / °C to 25 ppm / °C, and so on). It is believed that the difference between the high temperature CTE and the low temperature CTE that the glass substrate 10 exhibits, as well as the high temperature CTE that the glass substrate 10 exhibits, affects the compressive stress that the glass substrate 10 exhibits upon thermal tempering - which increases as the difference increases.

[0066] In embodiments, the glass substrate 10 exhibits a density that is within a range of from 2.450 g / cm3to 2.500 g / cm3. Density for purposes of this disclosure can be as measured by the buoyancy method of ASTM C693-93 (2013). In embodiments, the density that the glass substrate 10 exhibits is 2.450 g / cm3, 2.460 g / cm3, 2.470 g / cm3, 2.480 g / cm3, 2.490 g / cm3, or 2.500 g / cm3, or within any range bound by any two of those values (e.g., from 2.460 g / cm3to 2.490 g / cm3, from 2.470 g / cm3to 2.480 g / cm3, and so on).

[0067] In embodiments, the glass substrate 10 exhibits a liquidus temperature that is less than 1400 °C, such as less than 1100 °C. The liquidus temperature of a glass is the temperature above which no crystalline phases can coexist in equilibrium with the glass. Stated another way, the liquidus temperature of a glass is defined as the highest temperature at which a crystalline phase would appear if a glass were held indefinitely at that temperature. For purposes of this disclosure, the liquidus temperature can be measured using the standard gradient boat liquidus method of ASTM C829-81 titled “Standard Practice for Measurement of Liquidus Temperature of Glass by the Gradient Furnace Method.” That method involves placing crushed glass particles in a platinum boat, placing the boat in a furnace having a region of gradient temperatures, heating the boat in an appropriate temperature region for 24 hours, and determining by means of microscopic examination the highest temperature at which crystals appear in the interior of the glass. More particularly, the glass sample is removed from the Pt boat in one piece and examined using polarized light microscopy to identify the location and nature of crystals which have formed against the Pt and air interfaces, and in the interior of the sample. Because the gradient of the furnace is very well known, temperature as a function of location can be well estimated, within 5-10° C. The temperature at which crystals are observed in the internal portion of the sample is taken to represent the liquidus of the glass (for the corresponding test period). Testing is sometimes carried out at longer times (e.g., 72 hours), to observe slower growing phases. In embodiments, the liquidus temperature that the glass substrate 10 exhibits is within a range of from 950 °C to 1200 °C. In embodiments, the liquidus temperature that the glass substrate 10 exhibits is 950 °C, 975 °C, 1000 °C, 1025 °C, 1050 °C, 1075 °C, 1100 °C, 1125 °C, 1150 °C, 1175 °C, or 1200 °C, or within any range bound by any two of those values (e.g., from 1000 °C to 1150 °C, from 1050 °C to 1200 °C, and so on).

[0068] In embodiments, the glass substrate 10 has a first region of compressive stress 22 contiguous with the first primary surface 12 and a second region of compressive stress 24 contiguous with the second primary surface 14. A region of central tension 26 is disposed between the first region of compressive stress 22 and the second region of compressive stress 24.

[0069] In embodiments, the first region of compressive stress and the second region of compressive were generated as a result of thermal tempering of the glass substrate and, in further embodiments, not via an ion-exchange process. The thermal tempering can be performed via any process that heats and then quickly cools the glass substrate 10. For example, an overall process for thermal tempering the glass substrate 10 can include heating the glass substrate 10 in a hot zone and then cooling the glass substrate 10. In the hot zone, the glass substrate 10 is heated to a temperature, for example, where the viscosity is within a range of from 1012to 1013 3Poise. Optionally, the glass substrate 10 can be transitioned from the hot zone to a cool zone through a transition zone. The first primary surface 12 and the second primary surface 14 of the glass substrate 10 are positioned adjacent to heat sinks, one on either of the primary surfaces 12, 14 with a gap in between the primary surface 12, 14 and the heat sink. Gas is delivered into the gaps through multiple apertures in the heat sinks. The glass substrate 10 is cooled by conduction more than by convection and sufficiently to thermally induce the first region of compressive stress 22, the second region of compressive stress 24, and the central tension 26. As mentioned, the increase in high temperature CTE, the decrease in low temperature CTE, and the increased difference between the high temperature CTE and the low temperature CTE that the glass substrate 10 exhibits relative to a typical soda lime glass increase the ability to thermally temperature (and the effectiveness of thermal tempering) the glass substrate 10 as the thickness 20 thereof decreases (e.g., less than or equal to 2.0 mm).

[0070] Referring additionally to FIGS. 2-5, a solar panel 100 includes the glass substrate 10 and an array of photovoltaic cells 102 disposed beneath the glass substrate 10. In particular, the array of photovoltaic cells 102 is disposed beneath the second primary surface 14 of the glass substrate 10. The glass substrate 10 separates the array of photovoltaic cells 102 from an external environment 104. The first primary surface 12 of the glass substrate 10 faces the external environment 104. The first primary surface 12 of the glass substrate 10 is intended to face the sun 106 during daytime hours. The second primary surface 14 of the glass substrate 10 faces the array of photovoltaic cells 102. During use of the solar panel 100, photons 108 from the sun 106 enter the solar panel 100 through the glass substrate 10 and impinge upon the array of photovoltaic cells 102. The type of photovoltaic cells 102 are not particularly limited,though in preferred embodiments, the photovoltaic cells 102 are monocrystalline silicon photovoltaic cells 102.

[0071] The glass substrate 10 exhibits an average transmittance through the glass substrate 10 of greater than or equal to 80% for a wavelength of electromagnetic radiation within a range of from 500 nm to 950 nm. In embodiments, the glass substrate 10 exhibits an average transmittance through the glass substrate 10 of greater than or equal to 80% for a wavelength of electromagnetic radiation across an entire wavelength range of from 600 nm to 850 nm. All transmittance values mentioned herein are two-surface average transmittance values reported at an angle of incidence of 0 degrees and with no coatings on the second primary surface 14 of the glass substrate 10. An uncoated second primary surface 14 of a substrate having a glass composition typically has a reflectance of about 4%. Consequently, the maximum possible two-surface average transmittance value for the glass substrate 10 with the second primary surface 14 uncoated is approximately 96%. The two-surface average transmittance is the average of the two-surface transmittance throughout the stated wavelength range.

[0072] In embodiments, the solar panel 100 further includes a backsheet 110. The array of photovoltaic cells 102 are disposed between the glass substrate 10 and the backsheet 110. The backsheet 110 can have a glass composition. The glass composition of the backsheet 110 can be the same as the composition of the glass substrate 10 but need not be. One glass substrate 10 of the present disclosure can be the glass substrate 10 of the solar panel 100 and another glass substrate 10 of the present disclosure can be the backsheet 110 of the solar panel 100.

[0073] Having the array of photovoltaic cells 102 sandwiched between the glass substrate 10 and the backsheet 110 having a glass composition allows the array of photovoltaic cells 102 to receive photons 108 transmitting through both the glass substrate 10 and the backsheet 110. That arrangement in theory should increase the electricity production of the solar panel 100 compared to if the array of photovoltaic cells 102 received photons 108 transmitting only through the glass substrate 10 but not the backsheet 110.

[0074] A first polymer layer 112 can be disposed between the glass substrate 10 and the array of photovoltaic cells 102. Similarly, a second polymer layer 114 can be disposed between the backsheet 110 and the array of photovoltaic cells 102. The first and second polymer layers 112, 114 can further reduce migration of ions (e.g., K+) from the glass substrate 10 and the backsheet 110 (e.g., further in addition to the glass substrate 10 already not having the more mobile Li+andNa+ions), respectively, to the photovoltaic cells 102 that could cause potential- induced degradation, which is degradation of the photovoltaic cells 102 that lowers efficiency thereof. The first and second polymer layers 112, 114 can be formed of a transparent polymer,such as ethylene-vinyl acetate (EVA). The first and send polymer layers 112, 114 can encapsulate the array of photovoltaic cells 102.

[0075] In embodiments, the solar panel 100 further includes a frame 116. When the solar panel 100 is oriented horizontally such that the first primary surface 12 of the glass substrate 10 is horizontal and facing upwards, the frame 116 defines a top 118 and a bottom 120 of the solar panel 100 where the top 118 is most elevated portion of the solar panel 100 and the bottom 120 is the least elevated portion of the solar panel 100, excluding wiring that may extend from the solar panel 100. In a more detailed example, the frame 116 includes sidewall 122, a C-channel 124 that is contiguous with the sidewall 122, and a tab 126 that extends inward relative to the sidewall 122. The C-channel 124 is disposed at or near the top 118 of the frame 116, and the tab 126 is disposed at or near the bottom 120 of the frame 116. The tab 126 forms a plane 128 that is generally parallel to an outward primary surface 130 of the backsheet 110. The glass substrate 10, the array of photovoltaic cells 102, and the backsheet 110 are all coupled to each other as a package 132. The sidewall 122 extends around a perimeter 134 of the package 132 with the perimeter 134 of the package 132 secured within the C-channel 124 of the frame 116.

[0076] Referring now to FIGS. 6-7, an architectural window 200 includes at least a first pane 202 and a second pane 204. The first pane 202 includes the glass substrate 10. As when included with the solar panel 100, the glass substrate 10 when included with the architectural window 200 exhibits an average transmittance through the glass substrate 10 of greater than or equal to 80% for a wavelength of electromagnetic radiation within a range of from 500 nm to 950 nm. The first primary surface 12 of the glass substrate 10 faces the external environment 104. The second primary surface 14 of the glass substrate 10 faces away from the external environment 104.

[0077] The architectural window 200 may be integral with an opening between the external environment 104 and interior of an enclosure or building. Further, the architectural window 200 may be part of a door system on an enclosure or building. In embodiments, the architectural window 200 is movable with respect to an opening in a building. The architectural window 200 may be a double pane (as illustrated) or a triple pane window. Of course, the architectural window 200 may include any number of glass panes greater than one pane.

[0078] The architectural window 200 may further include a spacer 206 between its panes, such as to define a space 208 separating the first pane 202 from the second pane 204. The spacer 206 may be an edge seal formed around respective edges of its glass panes (e.g., the first pane 202 and the second pane 204), a metallic pillar between the surfaces of its glass panes, a low thermal conduction material, or a glass bump attached to or formed integral with one or bothglass panes (e.g., the first pane 202 and the second pane 204). The space 208 is further defined at least in part by a distance 210 between the first pane 202 and the second pane 204. The distance can be within a range of from 50 pm to about 50 mm, or within a range of from 5 mm to 25 mm. The space 208 may be sealed and include an insulating gas such as air, argon, krypton, xenon, and combinations thereof. Alternatively, the space 208 may be sealed and include a pressure less than atmospheric pressure.

[0079] In embodiments, the architectural window 200 further includes a frame 212 surrounding perimeters of, and supporting, both the first pane 202 and the second pane 204. In embodiments, the frame 212 is configured to mate or communicate with an opening in a building or enclosure such that architectural window 200 installed with either the first pane 202 or the second pane 204 adjacent the building interior and the other adjacent the building exterior. In embodiments, the frame 212 includes an overhanging edge portion configured to interfere with an edge of an opening in a building or enclosure and to prevent the architectural window 200 from being installed in the opening such that the one of the first pane 202 or the second pane 204 is adjacent the building interior. The architectural window 200 may also include a locking mechanism adjacent the one of the first pane 202 or the second pane 204 and internal to the building or enclosure. In embodiments, the locking mechanism is configured to be accessible only from the building interior so as to limit access through the architectural window 200. In embodiments, the locking mechanism is fixed directly or indirectly to frame 116 and communicates with a portion opening in the building or enclosure.

[0080] The glass substrate 10 addresses the problem set forth in the Background, as well as others, in a variety of ways. The glass substrate 10 lacks sodium ions (Na+). Thus, when the glass substrate 10 is incorporated into the solar panel 100, there are no sodium ions that can migrate from the glass substrate 10 to the photovoltaic cells 102. A cause of PID of the photovoltaic cells 102 (that of migration of sodium ions from the glass substrate 10 to the photovoltaic cells 102) has been eliminated. Soda lime glass, as typically used in solar panel applications includes sodium ions. The glass substrate 10 additionally lacks lithium ions (Li+), which would also migrate to the photovoltaic cells 102 and cause PID.

[0081] Rather, the glass substrate 10 only includes alkali ions (K+, Cs+, and / or Rb+) that are larger than sodium ions and lithium ions. These former alkali ions (K+, Cs+, and / or Rb+) have a significantly larger ionic radii than the ionic radii of the latter alkali ions (Na+and Li+). For example, potassium ions (K+) have an atomic radius of 138pm, while sodium ions (Na+) have an atomic radius of 102 pm. The larger ionic radii of the former alkali ions means that theydiffuse out of the glass substrate 10 at a much slower pace than the latter alkali ions. The slower the diffusion, the less alkali ions that reach the photovoltaic cells 102 to cause PID.

[0082] Alkali ions cannot feasibly be omitted from the glass substrate 10 altogether, for a variety of reasons. For example, alkali oxide is incorporated into the composition to act as a flux and lower the melting temperature of the composition to make the glass substrate 10 manufacturable. When intended to be incorporated into the solar panel 100 as a low-cost component, the low melting temperature afforded by the alkali ions are needed to extend tank lifetimes and to keep manufacturing costs low. Potassium oxide (K2O) is suitable, and has a lower cost than CS2O and Rb2O, although the latter two have larger ionic radii and thus even slower diffusion.

[0083] In addition to addressing the PID problem, the glass substrate 10 is formable via rolling processes, which are relatively inexpensive.

[0084] Still further, the glass substrate 10 having K2O is more easily to thermally tempered than a typical soda lime glass with Na2O. As mentioned, an important parameter for determining whether a glass will be more or less thermally tempered is the difference between the high temperature CTE and the low temperature CTE of the glass. This is because the difference in the expansion when exposed to a temperature gradient plays a significant role in the final stresses that are developed. As further explored in the Examples below, the glass substrates 10 of the present disclosure incorporating K2O but not Na2O have a significantly larger A CTE than the typical soda lime glass that incorporates Na2O but not K2O. The improved ability to thermally temper the glass substrates 10 of the present disclosure containing K2O is important at least in part because tempering glass with the thickness 20 of less than 2.0 mm is very difficult.

[0085] In addition to the presence of K2O instead of Na2O, and without being bound by theory, it is believed that because of the presence of relatively high mole percentages of B2O3 in the composition, the glass substrate 10 provides for a high temperature CTE that is higher than that provided by a typical soda lime glass and, thus, makes thermal tempering feasible at a thickness 20 that is relatively thin. The glass substrate 10 allows for thermal tempering at a thickness 20 that is relatively thin, while keeping manufacturing of the glass substrate 10 low in cost. More particularly, thermal tempering of relatively thin soda lime glass would require extremely energy -intensive air cooling to form the necessary temperature gradient, but the relatively high high temperature CTE of the glass substrate 10 of the present disclosure avoids a need to use air cooling.

[0086] The glass substrate 10, allowing for reduced thickness 20 due to increase ability to thermally temper at the reduced thickness 20 compared to soda lime glass, requires less raw materials. The less raw materials mean decreased cost and environmental impact.

[0087] In terms of the solar panel 100 and architectural window 200, the glass substrate 10 can be thinner than panes typically used. Typical top panels made from soda lime glass can have a thickness of about 2.0 mm. The glass substrate 10 of the present disclosure, due to the enhanced high temperature CTE, low temperature CTE, and difference between the two, can be utilized as the cover pane for the solar panel 100 while having a thickness 20 less than 2.0 mm. The thickness 20 of the glass substrate 10 can be less than 2.0 mm and still resist fracturing in response to impact events such as hail strikes. All the while mitigating against PID, as described.

[0088] EXAMPLES

[0089] Examples 1-6 and Comparative Example 1 - For Examples 16, glass substrates were formed by batching raw materials in different proportions for each different example, melting the batch, and forming the molten composition into the glass substrate, such as via rollers. The glass substrate representing each of Examples 1-6 were then analyzed to determine composition. The compositions are set forth in Table 1 below. Comparative Example 1 is a typical soda lime glass. In addition, various properties were measured and recorded in the Table 1 below for Examples 1-6. Comparative data is added for Comparative Example 1 as well.

[0090] “ SOC” in the above table means stress optical coefficient, which is related to the birefringence of the glass. Unless specified otherwise, SOC is measured according to Procedure C (Glass Disc Method) described in ASTM standard C770-16, entitled “Standard Test Method for Measurement of Glass Stress-Optical Coefficient,” the contents of which are incorporated herein by reference in their entirety. The refractive index can be measured with a Bausch & Lomb Precision Refractometer, which measures the refractive index of a material by measuring the critical angle, defined as the angle of incidence that provides an angle of refraction of 90°. The refractive index measurements can be performed at the sodium D wavelength (589.3 nm) with a sodium arc lamp. “E” as mentioned is Young’s modulus, discussed further above. “G” is shear modulus, which can be measured by a resonant ultrasonic spectroscopy technique of the general type set forth in ASTM C623. Poisson’s ratio can be determined according to ASTM C624, mentioned above, and relates the transverse strain to the axial strain in a material when subjected to an external load. “Softening” refers to the temperature at which the viscosity of the glass composition is lx IO76Poise, and is measured according to the parallel plate viscosity method which measures the viscosity of inorganic glass from 107to 109poise as a function of temperature, similar to ASTM C 135 IM. The softening temperature is generally the temperature at which glass begins to soften and becomes pliable, making it easier to shape and form. “Strain” refers to the temperature at which the viscosity of the glass composition is U io1468poise as measured in accordance with ASTM C598. Thestrain temperature is generally the temperature at which the glass transitions from a hard and rigid state to a more viscous or "soft" state. “Anneal” means refers to the temperature at which the viscosity of the glass composition is 1 x 1013 18Poise as measured in accordance with ASTM C598. At that viscosity, stresses within the glass can be relieved effectively. “HT CTE” is the high temperature coefficient of thermal expansion, which is further explained above. “LT CTE” is the low temperature coefficient of thermal expansion, which is also further explained above. “A CTE” is the difference between the HT CTE and the LT CTE. “A,” “B,” and “To” refer to fitting parameters of the Vogel-Fulcher-Tammann (VFT) fitting model (and more particularly to a pre-exponential factor, a characteristic energy, and the VFT temperature, respectively. The VFT equation, which follows, is used to describe the temperature (T) dependent behavior of viscosity (q) and other properties of glasses: q(T) = Aexp(B / (T-To)). Experimental data is used to fit into the equation to determine the fitting parameters. “Temp 200 P,” “Temp at 1,000 P,” “Temp at 35,000 P,” and “Temp at 200,000 P” all refer to the temperatures at which the glass substrate has viscosities of 200 P, 1,000 P, 35,000 P, and 200,000 P, respectively, as determined via the VFT equation. “Liquidus (°C)” refers to the temperature at which crystals first appear as a molten glass cools down from the melting temperature (or the temperature at which the very last crystals melt away as the temperature is increased from room temperature), as determined with the gradient furnace method according to ASTM C829-81, titled “titled “Standard Practice for Measurement of Liquidus Temperature of Glass by the Gradient Furnace Method.” Stated another way, the liquidus temperature is the temperature at which the glass transitions from a solid state to a molten state. “Liquidus Viscosity” refers to the viscosity of the glass substrate at the liquidus temperature thereof.

[0091] As Table 1 reveals, Examples 1-6 with the composition for the glass substrate of the present disclosure exhibited Young’s modulus (E) values (69.8 GPa, 71.4 GPa, 73.0 GPa, 72.3 GPa, 72.1 GPa, and 72.1 GPa) that are above the same as the Young’s modulus that the soda lime glass of Comparative Example 1 (72.9 GPa) exhibited. This means, that even before thermal tempering, which is expected to be more effective at relatively thin thicknesses than thermal tempering of the soda lime glass, the glass substrates of Examples 1-6 provide about the same flexural rigidity.

[0092] In addition, the data of Table 1 reveal dramatic increases in high temperature CTE for the glass substrates of Examples 1-6 (32.2 ppm / °C, 29.8 ppm / °C, 29.0 ppm / °C, 31.4 ppm / °C, 31.3 ppm / °C, and 35.6 ppm / °C) compared to Comparative Example 1 (26.5 ppm / °C). The dramatic increase in high temperature CTE leads to less energy intensive thermal tempering at thin thicknesses and with higher compressive stresses resulting therefrom.

[0093] Further, the data of Table 1 reveals that the glass substrate of Examples 1-4 and 6 have a lower low temperature CTE (7.7 ppm / °C, 7.4 ppm / °C, 7.1 ppm / °C, 7.2 ppm / °C, and 6.9 ppm / °C) than the Comparative Example 1 (10 ppm / °C). The higher high temperature CTE and the lower low temperature CTE of the glass substrates of the present disclosure compared to soda lime glass results in a much larger difference (A CTE (ppm / °C)) between the low temperature CTE and the high temperature CTE. In that regard, the data of Table 1 reveals the A CTE for Examples 1-4 and 6 were 24.5 ppm / °C, 22.4 ppm / °C, 21.0 ppm / °C, 24.2 ppm / °C, and 28.7 ppm / °C compared to the 16.5 ppm / °C of Comparative Example 1. The larger difference between high temperature CTE and low temperature CTE, it is believed, causes thermal tempering to more efficiently and more effectively generate compressive stress, which allows the glass substrates of the present disclosure to have thinner thicknesses and provide the same resistance to impact events as thicker soda lime glass substrates.

[0094] While exemplary embodiments and examples have been set forth for the purpose of illustration, the foregoing description is not intended in any way to limit the scope of disclosure and appended claims. Accordingly, variations and modifications may be made to the abovedescribed embodiments and examples without departing substantially from the spirit and various principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

Claims

CLAIM(S)What is claimed is:

1. A glass substrate comprising: a composition comprising, in mol% and on an oxide basis:SiCh, within a range of from 60 to 72;AI2O3, within a range of from 0 to 5.0;B2O3, within a range of from 3.5 to 15.0;MgO, within a range of from 1.0 to 15.0;CaO, within a range of from 1.0 to 15.0; andR2O, within a range of from 6.0 to 20.0, wherein R2O is one or more of K2O, CS2O, and Rb2O, wherein, the composition is substantially free of Na2O, and Li2O.

2. The glass substrate of claim 1, wherein R2O is exclusively K2O.

3. The glass substrate of any one of claims 1-2, wherein the SiCh of the composition is within a range of from 66 to 71.

4. The glass substrate of any one of claims 1-3, wherein the B2O3 of the composition is within a range of from 4.0 to 15.0.

5. The glass substrate of any one of claims 1-4, wherein the B2O3 of the composition is within a range of from 4.0 to 8.0.

6. The glass substrate of any one of claims 1-5, wherein the MgO of the composition is within a range of from 6.2 to 8.3.

7. The glass substrate of any one of claims 1-6, wherein the CaO of the composition is within a range of from 8.6 to 12.8.

8. The glass substrate of any one of claims 1-7, wherein the R2O of the composition is within a range of from 6.5 to 9.6.

9. The glass substrate of any one of claims 1-8, wherein the composition further comprises AI2O3 at less than or equal to 3.0.

10. The glass substrate of claim 9, wherein the AI2O3 within the composition is within a range of from 1.00 to 1.10.

11. The glass substrate of any one of claims 1-10, wherein the composition consists essentially of SiCh, B2O3, AI2O3, MgO, CaO, K2O, and optionally a fining agent selected from a group consisting of AS2O3, Sb2C>3, SnCh, and SO3.

12. The glass substrate of any one of claims 1-11 further comprising: a first primary surface, a second primary surface facing away from the first primary surface, and a thickness between the first primary surface, wherein, the thickness is less than or equal to 4.5 mm.

13. The glass substrate of claim 12, wherein the thickness is less than or equal to 2.0 mm.

14. The glass substrate of any one of claims 1-13, wherein the glass substrate exhibits a high temperature coefficient of thermal expansion that is within a range of from 28 ppm / °C to 40 ppm / °C.

15. The glass substrate of any one of claims 1-14, wherein the glass substrate exhibits a low temperature coefficient of thermal expansion that is within a range of from 6.0 ppm / °C to 8.5 ppm / °C.

16. The glass substrate of any one of claims 1-15, wherein the glass substrate exhibits a difference between a high temperature coefficient of thermal expansion and a low temperature coefficient of thermal expansion is greater than 20 ppm / °C.

17. The glass substrate of any one of claims 1-16 further comprising: a first region of compressive stress;a second region of compressive stress; and a region of central tension disposed between the first region of compressive stress and the second region of compressive stress.

18. The glass substrate of claim 17, wherein the first region of compressive stress and the second region of compressive stress were generated as a result of thermal tempering of the glass substrate.

19. The glass substrate of any one of claims 1-18, wherein the glass substrate exhibits a liquidus temperature that is less than 1400 °C.

20. A solar panel comprising: an array of photovoltaic cells; and a glass substrate separating the photovoltaic cell from an external environment, the glass substrate (a) exhibiting an average transmittance through the glass substrate of greater than or equal to 80% for a wavelength of electromagnetic radiation within a range of from 500 nm to 950 nm, (b) comprising a first primary surface facing the external environment, a second primary surface facing the photovoltaic cell, and a thickness between the first primary surface and the second primary surface that is less than or equal to 4.5 mm, and (c) comprising a composition comprising, in mol% and on an oxide basis:SiCh, within a range of from 60 to 72;AI2O3, within a range of from 0 to 5.0;B2O3, within a range of from 3.5 to 15.0;MgO, within a range of from 1.0 to 15.0;CaO, within a range of from 1.0 to 15.0; andR2O, within a range of from 6.0 to 20.0, wherein R2O is one or more of K2O, CS2O, and Rb2O, wherein, the composition is substantially free of Na2O, and Li2O.

21. The solar panel of claim 20, wherein the composition of the glass substrate further comprises AI2O3 at less than or equal to 3.0.

22. The solar panel of claim 21, whereinthe AI2O3 within the composition is within a range of from 1.00 to 1.10,R2O is exclusively K2O, the R2O of the composition is within a range of from 6.5 to 9.6, the SiCh of the composition is within a range of from 66 to 71, the B2O3 of the composition is within a range of from 4.0 to 8.0, the MgO of the composition is within a range of from 6.2 to 8.3, and the CaO of the composition is within a range of from 8.6 to 12.8.

23. The solar panel of any one of claims 20-22, wherein the composition consists essentially of SiCh, B2O3, AI2O3, MgO, CaO, K2O, and optionally a fining agent selected from a group consisting of AS2O3, Sb2O3, SnO2, and SO3.

24. The solar panel of any one of claims 20-23, wherein the thickness of the glass substrate is less than or equal to 2.0 mm.

25. The solar panel of any one of claims 20-24, wherein the glass substrate exhibits a high temperature coefficient of thermal expansion that is within a range of from 28 ppm / °C to 40 ppm / °C; the glass substrate exhibits a difference between the high temperature coefficient of thermal expansion and a low temperature coefficient of thermal expansion is greater than 20 ppm / °C; and the glass substrate exhibits a liquidus temperature that is less than 1400 °C.

26. An architectural window comprising: a first pane comprising a glass substrate, the glass substrate (a) exhibiting an average transmittance through the glass substrate of greater than or equal to 80% for a wavelength of electromagnetic radiation within a range of from 500 nm to 950 nm, (b) comprising a first primary surface facing an external environment, a second primary surface facing away from the external environment, and a thickness between the first primary surface and the second primary surface that is less than or equal to 4.5 mm, and (c) comprising a composition comprising, in mol% and on an oxide basis:SiCh, within a range of from 60 to 72;AI2O3, within a range of from 0 to 5.0;B2O3, within a range of from 3.5 to 15.0;MgO, within a range of from 1.0 to 15.0;CaO, within a range of from 1.0 to 15.0; andR2O, within a range of from 6.0 to 20.0, wherein R2O is one or more of K2O, CS2O, and Rb2O, wherein, the composition is substantially free of Na2O, and Li2O; and a second pane separated from the first pane by a space, the second pane comprising the glass substrate or another glass substrate.

27. The architectural window of claim 26 further comprising: a frame surrounding perimeters of, and supporting, both the first pane and the second pane.

28. The architectural window of any one of claims 26-27, wherein the composition of the glass substrate of the first pane further comprises AI2O3 at less than or equal to 3.0.

29. The architectural window of claim 28, wherein the AI2O3 within the composition of the glass substrate of the first pane is within a range of from 1.00 to 1.10,R2O is exclusively K2O, the R2O of the composition of the glass substrate of the first pane is within a range of from 6.5 to 9.6, the SiCh of the composition of the glass substrate of the first pane is within a range of from 66 to 71, the B2O3 of the composition of the glass substrate of the first pane is within a range of from 4.0 to 8.0, the MgO of the composition of the glass substrate of the first pane is within a range of from 6.2 to 8.3, and the CaO of the composition of the glass substrate of the first pane is within a range of from 8.6 to 12.8.

30. The architectural window of any one of claims 26-29, whereinthe composition of the glass substrate of the first pane consists essentially of SiCh, B2O3, AI2O3, MgO, CaO, K2O, and optionally a fining agent selected from a group consisting of AS2O3, Sb2O3, SnCh, and SO3.

31. The architectural window of any one of claims 26-30, wherein the glass substrate of the glass substrate of the first pane exhibits a high temperature coefficient of thermal expansion that is within a range of from 28 ppm / °C to 40 ppm / °C; the glass substrate of the glass substrate of the first pane exhibits a difference between the high temperature coefficient of thermal expansion and a low temperature coefficient of thermal expansion is greater than 20 ppm / °C; and the glass substrate of the glass substrate of the first pane exhibits a liquidus temperature that is less than 1400 °C.

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