Decorative Composite Body Comprising a Solar Cell

Abstract

There is proposed a decorative element containing (a) a transparent gemstone with a faceted surface comprising convex curved regions, (b) a wavelength-selective layer, and (c) a photovoltaic cell.

Claims

1. A decorative element containing (a) a transparent gemstone with a faceted surface comprising convex curved regions, (b) a wavelength-selective layer, and (c) a photovoltaic cell.

2. The decorative element according to claim 1, characterized in that said gemstone is made of glass or plastic.

3. The decorative element according to claim 1, characterized in that said gemstone has a plano-convex or plano-convexo-concave geometry.

4. The decorative element according to claim 1, characterized in that said wavelength-selective layer is selected from a wavelength-selective coating or a wavelength-selective film.

5. The decorative element according to claim 4, characterized in that said wavelength-selective coating contains at least one metal and/or metal compound.

6. The decorative element according to claim 1, characterized in that said wavelength-selective layer reflects a fraction of the light within a range of from 380 to 850 nm.

7. The decorative element according to claim 1, characterized in that said wavelength-selective layer reflects at least 50% of the incident light in a 50 to 250 nm wide reflection interval within a range of from 380 to 850 nm.

8. The decorative element according to claim 7, characterized in that said wavelength-selective layer has an average transmission of >80% outside the reflection interval in a range of 400 to 1200 nm, as measured under an incident angle of the light beams of 0°.

9. The decorative element according claim 1, characterized in that said wavelength-selective layer has been applied to (a) the side opposing the faceted side, or (b) the photovoltaic cell.

10. The decorative element according to claim 1, characterized in that said wavelength-selective coating comprises at least one compound selected from the group consisting of Cr, Cr.sub.2O.sub.3, Ni, NiCr, Fe, Fe.sub.2O.sub.3, Al, Al.sub.2O.sub.3, Au, SiO.sub.x, Mn, Si, Si.sub.3N.sub.4, TiO.sub.x, Cu, Ag, Ti, CeF.sub.3, MgF.sub.2, Nb.sub.2O.sub.5, Ta.sub.2O.sub.5, SnO.sub.2, ZnO.sub.2, MgO, CeO.sub.2, WO.sub.3, Pr.sub.2O.sub.3, Y.sub.2O.sub.3, BaF.sub.2, CaF.sub.2, LaF.sub.3, NdF.sub.3, YF.sub.3, ZrO.sub.2, HfO.sub.2, ZnS, Oxynitrides of Al, Si, and SnZnO, or any combination of these compounds in any sequence of layers.

11. The decorative element according to claim 1, characterized in that said photovoltaic cell is a backside-contacted solar cell.

12. The decorative element according claim 1, characterized in that components (a), (b) and (c) of the decorative element are bonded together by means of an adhesive.

13. The decorative element according to claim 12, characterized in that the refractive index of the adhesive deviates by less than ±20% from the refractive index of the gemstone.

14. An energy source for a wearable electronic device, the energy source comprising the decorative element according claim 1.

15. An object containing at least one decorative element according to claim 1.

Description

[0067] In the following, the invention will be illustrated further by means of Examples and Figures without being limited thereto. The Figures show the following objects:

[0068] FIG. 1a: Structure of a decorative element with a wavelength-selective coating on the planar side opposing the faceting.

[0069] FIG. 1b: Structure of a decorative element with a wavelength-selective coating on the solar cell.

[0070] FIG. 1c: Structure of a decorative element with a wavelength-selective film.

[0071] FIG. 2a: Focusing light beams on the solar cell in a plano-convex optical element with faceting.

[0072] FIG. 2b: Beam path for a planar covering of the solar cell.

[0073] FIG. 3a: Refraction of laterally entering light beams in a plano-convex optical element with faceting.

[0074] FIG. 3b: Beam path for laterally entering light beams for a planar covering of the solar cell.

[0075] FIG. 4a: Spectrum of the wavelength-selective filter coating according to Table 1; T=transmission; R=reflection.

[0076] FIG. 4b: Angular dependence of reflection in the wavelength-selective filter coating; R=reflection.

[0077] FIG. 5a: Geometry of the optical element; in perspective.

[0078] FIG. 5b: Base area of the optical element; 45° chamfer at the base area.

[0079] FIG. 6: Measuring set-up—schematically.

[0080] FIG. 7a: Relative change of power at the maximum power point as a function of the angle of incidence of the radiation.

[0081] FIG. 7b: Relative change of power at the maximum power point after application of optical elements, averaged over the angles of incidence of 0-75°.

[0082] FIG. 8: Geometry of the optical element for the simulation.

[0083] FIG. 9: Geometry of the optical element with plano-convexo-concave curvature.

[0084] FIG. 10: Geometry of the optical element with plano-concave curvature.

INDUSTRIAL APPLICABILITY

[0085] The invention further relates to, on the one hand, the use of the decorative element according to the present invention as an energy source, especially in wearable electronic devices, and to objects, especially jewelry, such as rings, necklaces, bracelets and the like, containing at least one decorative element according to the present invention.

Examples

Materials

[0086] Different decorative elements of different materials and geometries were examined. The decorative elements were assembled from solar cells and optical elements. The Examples according to the invention were additionally provided with a wavelength-selective layer.

[0087] Solar Cells.

[0088] Solar cells of the type Sunpower C60 (10 mm×10 mm) were used.

[0089] Optical Elements—with and without Coating.

[0090] The optical elements of glass were produced by methods known to the skilled person from commercially available “Chessboard Flat Back” 2493 elements (30 mm×30 mm) of the company Swarovski.

[0091] The optical elements of Pleximid TT70 were produced by plastic injection molding methods in a mold prefabricated for this purpose. For this method, an injection molding machine of the company Engel of the type e-victory 80/50 was used; temperature of barrel: 210° C. increasing to 280° C., nozzle 280° C.; temperature of mold: 180° nozzle side, 140° ejector side; injection pressure limit: 1200 bar; injection speed: about 15 cm.sup.3/s; embossing pressure: about 800 bar; no solvents.

[0092] Geometry.

[0093] The optical elements of Examples 1 and 2 according to the invention and of Comparative Examples C2 and C3 are faceted bodies with 12 mm edge length and a square base area with slightly rounded corners (FIGS. 5a and 5b). A chamfer at an angle of 45° is provided on the base area, so that the actually remaining base area is 10 mm×10 mm (cf. FIGS. 5a and 5b). The faceted upper part with 25 facets in a square arrangement forms a ball segment. The total height of the solid is 5.56 mm, the corner edge height is 1.93 mm.

DESCRIPTION OF THE EXAMPLES AND COMPARATIVE EXAMPLES

[0094] Comparative Example C1: 12 mm×12 mm glass sheet of 0.5 mm thickness; refractive index n=1.52.

[0095] Comparative Example C2: An optical element produced from glass according to FIGS. 5a and 5b; dimensions as described above (Geometry); without wavelength-selective coating.

Example 1

[0096] An optical element produced from glass according to FIGS. 5a and 5b; dimensions as described above (Geometry); with the wavelength-selective coating described below.

Comparative Example C3

[0097] An optical element produced from Pleximid TT70 according to FIGS. 5a and 5b with n=1.54; dimensions as described above (Geometry); without wavelength-selective coating (Comparative Example).

Example 2

[0098] An optical element produced from Pleximid TT70 according to FIGS. 5a and 5b; dimensions as described above (Geometry); with the wavelength-selective coating described below.

Wavelength-Selective Layer

[0099] The optical elements according to Examples 1 and 2 were coated in a PVD facility (see above). The structure of the wavelength-selective coating is represented in Table 1:

TABLE-US-00001 TABLE 1 Layer structure of the wavelength-selective coating N Material Physical layer thickness [nm] 1 TiO.sub.2 23.9 2 SiO.sub.2 43.2 3 TiO.sub.2 64.8 4 SiO.sub.2 28.7 5 TiO.sub.2 61.5 6 SiO.sub.2 33.7 7 TiO.sub.2 57.7 8 SiO.sub.2 37.5 9 TiO.sub.2 66.1 10 SiO.sub.2 30.5 11 TiO.sub.2 42.6 12 SiO.sub.2 141.4

Measuring Set-Up and Measurements

[0100] The measurements aimed at examining the influence of the optical element and of the coating on the energy yield of the solar cell as a function of the incident angle of the light beams.

[0101] Decorative Elements:

[0102] Five different decorative elements assembled from the optical elements according to the Examples and Comparative Examples and the solar cells of the type Sunpower C60 (10 mm×10 mm) were examined.

[0103] The measurements were performed with an Oriel Instruments LED sun simulator Verasol-2 (class AAA) using a Keithley 2602A Sourcemeter and a Linos rotary support including the corresponding fixture.

[0104] A schematic representation of the measuring set-up is shown in FIG. 6. The reference symbols represent as follows:

(7) decorative element;
(8) sun simulator;
(9) rotary support;
(10) sourcemeter.

[0105] Using a sun simulator (8) certified according to class AAA (spectral matching, spatial uniformity, time stability), a constant irradiance of 1000 W/m.sup.2 was selected for the complete experimental series. The incident angle of the radiation from the light source onto the specimens to be measured according to Examples 1 and 2 as well as Comparative Examples C1 to C3 was varied by means of a rotary support (9), on which the specimens were positioned. The distance z between the center of the solar cell and the sun simulator was kept constant (cf. FIG. 6).

[0106] Using a sourcemeter (10), the current-voltage characteristic of each of the solar cells was measured at an irradiance of 1000 W/m.sup.2, and the power in the maximum power point was determined therefrom.

[0107] Each of the five solar cells was measured first without optical elements. The incident angle of the light beams was varied in 15° steps from 0° to 75° (cf. FIG. 6). Subsequently, an optical element (see above) with a wavelength-selective coating (Table 1) was applied to each solar cell using a UV-curable adhesive with a refractive index n=1.461, and the complete measuring series was repeated. Each individual measurement was repeated three times; from this, the arithmetic mean was formed, and the relative standard deviation (standard deviation/mean) was calculated; the results are summarized in Table 2.

TABLE-US-00002 TABLE 2 Relative change of the power of the solar cell in the maximum power point as a function of the incident angle of the light beams for the above described experimental set-ups Incident angle C1 C2 1 C3 2  0° −11.5% 38.2% 12.7% 9.4% −5.1% 15° −12.8% 50.3% 45.5% 16.0% −5.0% 30° −0.6% 56.4% 42.5% 19.4% 10.9% 45° 0.1% 79.9% 27.2% 15.5% 9.4% 60° 4.7% 84.0% 43.3% 48.8% 47.4% 75° −18.5% 140.0% 99.5% 76.1% 68.1% mean of 0-75° −6.4% 60.8% 35.9% 19.7% 8.7%

[0108] A graphical evaluation of the results obtained in Table 2 can be found in FIGS. 7a and 7b. Meanings: black: C1; gray: C2; double hatching: 1; hatching from top left to bottom right: C3; hatching from bottom left to top right: 2.

Discussion of the Results

[0109] The power losses in Example C1 result, on the one hand, from losses because of different refractive indices for the transitions glass/UV-curable adhesive and UV-curable adhesive/solar cell. On the other hand, part of the light beams is lost by reflection when impinging on the glass sheet. Basically, both kinds of power loss occur in all optical elements, but they are greatest with planar glass sheets.

[0110] The enhancement of the power of the solar cell in the maximum power point is predominantly determined by geometric effects, as schematically represented in FIGS. 2a/2b and FIGS. 3a/3b. The relevance of the convex geometry with faceting can be seen, above all, as the incident angle of the light beams increases. The power of the decorative element increases highly (Examples C2 and C3). For glass, this is even more significant as compared to the optical elements prepared from Pleximid® TT70.

[0111] From the wavelength-selective coating (Examples 1 and 2), losses in energy yield necessarily result, as expected, as compared to C2 and C3 because of the reflection of part of the visible spectrum. However, these can be more than compensated by the convex geometry in combination with the faceting, as seen from Table 2.

[0112] The differences between the optical elements of glass and Pleximid TT70 result from the clearly improved transmission behavior of the glass and the better surface quality of the glass specimens for manufacturing reasons.

[0113] Computer Simulation

[0114] The influence of a plano-concavo-convex geometry or plano-concave geometry of the gemstone on the power of a solar cell was examined by means of computer simulation. The simulations were performed by physical ray tracing using the program Speos of the company Optis.

Computer Model

[0115] The CAD data of the corresponding gemstone from the measurements (see above) were used as a gemstone model. The gemstone surface was assumed to be ideal (without roughness, i.e., without surface defects). For the simulation, the refractive index of the glass of experimental Example 1 was employed, which is 1.56 at λ=550 nm.

[0116] A wavelength-selective layer or generally a boundary layer between the gemstone and solar cell was not taken into account for reasons of complexity. With the simulations, merely the influence of the different geometries (convex, concave) of the gemstone on the light yield was examined. Inclusion of the wavelength-selective layer or boundary layer would be irrelevant to this.

[0117] The solar cell was simulated with a reflecting surface with a degree of reflection of 1.3%, which is independent of the incident angle of the light. The absorption of the solar cell was 98.7%.

[0118] The irradiation of the gemstone with light was effected by analogy with the measurement in the simulation, i.e., centrally from above. The dimension of the light source was 30 mm×30 mm. The distance of the light source from the center of the seat area of the gemstone was 15 mm. The aperture angle of the light source was 2×8°. The light distribution was assumed to be Gaussian. The light source had a radiation power of 1 W. The normal light source D65 of the program Speos was used as the light source. Depending on the incident angle of the light (see below), only part of the light hits the gemstone.

Simulations and Results

[0119] Simulation S1: Gemstone with plano-convex geometry, FIG. 8. This gemstone corresponds to the gemstone from the measurement (FIG. 5a).

[0120] Simulation S2: Gemstone with plano-convexo-concave geometry, FIG. 9. The concave recess is spherical. It is obtained by a sphere with a diameter of 18 mm. The center of the sphere lies on the normal of the area that runs through the center of the gemstone seat area. The concave recess corresponds to the ball segment with a height of 0.558 mm.

[0121] Simulation S3: Gemstone with plano-concave geometry, FIG. 10. The concave curvature of the gemstone corresponds to the convex curvature of the original gemstone, FIG. 8, inverted. The height H of the gemstone (FIG. 10) at the edges is 5 mm.

[0122] The simulations aimed at examining the influence of the geometry (concave, convex) of the optical element (gemstone) on the absorption behavior and thus on the energy yield of the solar cell as a function of the incident angle of the light beams.

[0123] The incident angle of the light beams was varied in the simulation by analogy with the measurement (see above). The absorbed radiation power in Watt of the modeled solar cell was calculated. The relative deviation of the absorbed radiation power in percent is obtained according to 100×(S2−S1)/S1 or 100×(S3−S1)/S1 and was determined at different incident angles (Table 3).

TABLE-US-00003 TABLE 3 Absorbed power of the solar cell as a function of the incident angle of the light beams for the above described simulation models, and the relative deviation of the simulation values 100 × (S2 − S1)/S1 or 100 × (S3 − S1)/S1. Deviation Deviation Incident in %: 100 × in %: 100 × angle S1 [mW] S2 [mW] (S2 − S1)/S1 S3 [mW] (S3 − S1)/S1  0° 598.2 598.3 0.017 414.9 −30.642 15° 584.7 584.0 −0.12 433.3 −25.894 30° 526.8 527.2 0.076 451.1 −14.37 45° 454.6 449.9 −1.034 412.2 −9.327 60° 364.6 353.7 −2.99 320.8 −12.013 75° 219.8 214.3 −2.502 147.7 −32.803

Discussion of the Results

[0124] The relative deviation of the values of S3 from S1 (column 6), Table 3, shows that the absorbed radiation power strongly decreases in a purely concave geometry. This is to be expected because concave geometry has a scattering effect.

[0125] In contrast, if the surface proportion of the concave curvature is at most ⅓ (FIG. 9) of the curved area (cf. simulation 2; column 4 in Table 3), the deviation of the power values is negligible.

[0126] The relative deviations (cf. Table 3, columns 4 and 6) are not continuously decreased with respect to the incident angle. This is due to the fact that light beams also impinge on the non-curved side surfaces of the gemstone, and therefore, additional reflections may occur within the gemstone.

[0127] The simulation results show that the influence of a concave curvature having an area proportion of up to at most ⅓ of the curved gemstone surface is negligible with respect to the efficiency of a solar cell.