CN202049976U - Thin-film photovoltaic device - Google Patents

Abstract

The utility model provides a photovoltaic device, which comprises a substrate, a first reflective layer and a second reflective layer, the substrate is provided with a semiconductor-based photovoltaic conversion layer, and the first reflective layer and the second reflective layer are used to pass through the substrate and the light from the conversion layer is reflected back to the conversion layer, the first reflective layer being a laminated foil with reflective properties concentrated in the short wavelength region, and the second reflective layer having reflective properties concentrated in the longer wavelength region. A second reflective layer is applied to the back glass or back cover for lamination with the substrate and conversion layer. The present invention combines a thinned laminated foil with some reflective properties plus an additional back cover with another reflective layer. The reflective properties of the laminate foil reflect most of the short wavelength light back into the active layer of the photovoltaic cell, with the longer wavelength portion being reflected by the second reflective layer, which is preferably placed adjacent to the back cover. This reduces material costs without compromising reflective properties and lamination properties of the foil.

Description

Thin Film Photovoltaic Devices

technical field

The utility model generally relates to a photovoltaic device. More specifically, the present invention relates to a photovoltaic device combining a thinned laminated foil with certain reflective properties plus an additional (ie independently prepared) back cover and another reflective layer.

Background technique

Photovoltaic solar energy conversion offers the prospect of generating electricity by an environmentally friendly means. However, in its current state, electricity provided by photovoltaic energy conversion units is still much more expensive than electricity provided by conventional power stations. Therefore, developing more cost-effective means for producing photovoltaic energy conversion units has attracted attention in recent years. Among the different methods of producing low-cost solar cells, thin-film silicon solar cells are favored because they can be prepared by well-known thin-film deposition techniques such as plasma enhanced chemical vapor deposition (PECVD). Such solar panels are generally realized based on rigid glass substrates, onto which the photovoltaically active layer is applied by vacuum deposition. Since these semiconductor layers are sensitive to environmental influences such as moisture, they must be encapsulated. This is typically done by laminating a second glass substrate onto the coated side of the first substrate. It is known in the art to bond the two glass substrates using a lamination foil, which lamination process uses heat and pressure to complete the hermetic assembly. If the laminate foil appears white by providing it with reflective white particles, it may even help to eliminate the use of a separate reflective layer.

Certain photovoltaic (PV) fabrication technologies, primarily related to thin-film silicon photovoltaic upper substrates, have shown improved light-trapping effects by enhancing the reflection of photons that are not converted/collected. Figure 1 shows such an arrangement: the glass substrate or front glass 10 shows the sequence of layers of semiconductor material enabling the photovoltaic effect. This layer sequence is referred to as absorber layer 11 . A transparent back contact 12 comprising a transparent conductive material (TCO) functions as a back electrode. The reflective lamination foil 13 is capable of redirecting "unused" light back into the absorbing layer and laminating the front and back glass together. The arrows in Figure 1 indicate the path of light. The incoming incident light 16 largely enters the base substrate 10; however, a certain proportion 17 is reflected. The unabsorbed photons 18 are partly reflected by the reflective foil 13 and can re-enter the absorber layer 11, thereby increasing the efficiency of the solar panel. However, a certain proportion of light 19 is still transmitted and lost.

In general, the reflective effect can be obtained by means of the metallization of the back contact 12, or by means of a reflective medium such as a reflective barrier paint or polyvinylbutyral (polyvinylbutyral, eg filled with TiO ₂ ) applied thereon. PVB), paraffin or ethylene vinyl acetate (ethylene vinyl acetate, EVA) or the like colored laminate foil 13 transparent back contact 12. Both solutions have been on the market since many years, but only recently have been used as back reflectors in thin film photovoltaics (TF PV).

To reduce the material cost of a TF PV module, it is necessary to reduce the volume of the material, in this case the thickness of the reflective laminate foil. Figure 5 shows such an arrangement with a thinner reflective laminate foil 13b.

Defects in the prior art

Reducing the thickness of the lamination foil (13, 13b) leads to a decrease in the reflectivity of the foil and thus to an increase in the transmittance. One possibility to alleviate this problem is to increase the reflective pigment content of the foil. A disadvantage of this procedure is the limiting charging factor of the laminated foil itself. In fact, this can lead to a loss of reliability due to a decrease in the adhesion/handling capabilities of the foil itself.

Figure 4 shows the transmittance of light as a function of wavelength and another parameter "lamination foil thickness". The figure shows conventional foil C compared to two thinner foils, of which foil A is the thinnest.

Utility model content

The object of the present invention is to provide a thin film photovoltaic device which reduces the material cost without compromising the reflective properties and the lamination properties of the foil.

The thin-film photovoltaic device of the present invention includes a basic substrate or front glass, a photovoltaic active absorbing layer, a rear contact, a reflection device, and a rear glass or a rear sheet. The thin-film photovoltaic device is characterized in that the reflection device includes sequentially divided layer arrangement of two reflective layers.

In a preferred embodiment, the first of said two reflective layers comprises a reflective laminated foil reflecting mainly in the short wavelength region (UV, blue light), and wherein the second reflective layer comprises substantially Reflective layer that reflects in the longer wavelength region (red light, IR).

Beneficial technical effects of the invention are: the reflective properties of the invention allow a substantial reduction in the thickness of the laminated foil without compromising the encapsulation properties of the foil itself; Provides a fully integrated backend structure. The invention will enable to adjust the thickness of the lamination foil by finding the best solution for the distribution of costs between the lamination foil, the back sheet/glass, and the reflective properties.

Description of drawings

Figure 1 shows the arrangement on a substrate on thin-film silicon photovoltaics, which exhibits improved light-trapping effect by enhancing the reflection of photons that are not converted/collected.

Figure 2 shows an arrangement using a reflective back glass or reflective back sheet in combination with a reflective laminate foil.

Figure 3 shows the effect of an integrated rear sheet according to the invention on the transmittance as a function of wavelength.

Figure 4 shows the transmittance of light as a function of wavelength and another parameter "lamination foil thickness".

Figure 5 shows an arrangement of laminated foils with reduced thickness.

Detailed ways

As shown in Figure 2, the thin film photovoltaic device of the present utility model comprises base substrate or front glass 10, photovoltaic active absorbing layer 11, rear contact 12, reflection device and rear glass or rear sheet 15, the thin film photovoltaic device The reflective device comprises two reflective layers 13a, 14 arranged in layers sequentially. The first of said two reflective layers 13a, 14 comprises a reflective laminate foil 13a reflecting mainly in the short wavelength region, and wherein the second reflective layer comprises a reflective reflective material reflecting substantially in the longer wavelength region. Layer 14. The reflectivity as a function of wavelength varies with the layer considered. In fact, the reflective laminated foil 13a according to the present invention is mainly in the short wavelength region, with a reflectivity (average value in each wavelength range) of higher than 85%, preferably higher than 90%, substantially between Reflecting between 400nm and 1100nm, more preferably between 500nm and 800nm, and the reflective layer 14 or reflective sheet/glass 14/15 is substantially higher than 95% or preferably in the longer wavelength region Reflections of greater than 99% (respectively mean value in said wavelength range) reflect between 500 nm and 1400 nm or preferably between 700 nm and 1100 nm.

This enables the customization of a dedicated integrated back sheet comprising a reflective lamination foil 13a "laminated" with the reflective back sheet/glass 14, 15, thereby reducing steps in the production line.

As materials for laminating foils, EVA, polyolefin, PVB _, thermoplastic polyurethane (TPU), silicone, ionomer. In the case of using _TiO2 as white pigment, according to the invention it is recommended to use a loading of more than 7%, preferably more than 9% by weight.

For the back sheet/glass, the reflective material for layer 14 could be white pigment or a metal sheet meeting the conditions listed above.

As shown in Figure 4, investigations have shown that a reduction in the thickness of the reflective laminate foil affects the longer wavelengths of a given spectrum more strongly than the shorter wavelengths. Therefore, if a thinner reflective lamination foil should be used, it needs to be compensated by arranging another reflector in the photovoltaic layer stack, e.g. by integrating it or applying it to the rear sheet/rear glass 15 Loss in the long wavelength region. This can be obtained by using a reflective back glass or reflective back sheet in combination with a reflective laminate foil. Figure 2 shows such an arrangement, where a thinner reflective laminate foil is arranged sequentially with an additional reflective layer 14 .

Figure 3 shows the effect of such an integrated back sheet (reflective laminate foil and reflective back sheet) according to the invention on the transmittance as a function of wavelength.

Two aspects should be emphasized:

• The tailored reflective properties allow a substantial reduction in the thickness of the laminated foil without compromising the packaging properties of the foil itself.

• Integrating the foil 13b with the back sheet/glass 14, 15 or support structure can provide a fully integrated backend concept.

The processing of the laminated foil according to the invention as well as the back sheet/glass can be done on standard lamination equipment. It is necessary to properly remove trapped air in the laminate and provide sufficient temperature and pressure to establish adhesion through the lamination foil. The vacuum should be less than 10mbar negative pressure; the heating plate temperature should be in the range of 130°C to 170°C. Depending on the module design (contacts, etc.), the plate pressure needs to be in the range of 500mbar to 900mbar. Treatment times of 3 minutes to 6 minutes for degassing and 5 minutes to 9 minutes for pressurization are achievable; this enables rapid treatment with short cycle times. After lamination, cooling in cold presses or air-cooled buffers enables the next production step to proceed.

Claims (10)

1. film photovoltaic device, comprise base substrate or front glass (10), the active absorbed layer (11) of photovoltaic, back contact (12), reflection unit and back glass or back sheet material (15), described film photovoltaic device (1) is characterised in that, described reflection unit comprises two reflector (13a, 14) of layered arrangement in regular turn.

2. film photovoltaic device as claimed in claim 1, it is characterized in that, described two reflector (13a, 14) first reflector in comprises the reflector blocking (13a) of mainly reflecting in the short wavelength zone, and wherein second reflector comprises the reflector of reflecting in fact (14) in the longer wavelength zone.

3. film photovoltaic device as claimed in claim 2, it is characterized in that, to be higher than 85% reflectivity between 400nm and the 1100nm, reflect between 500nm and 800nm with the reflectivity greater than 90%, described reflectivity is the mean value in each wave-length coverage in fact in described reflector blocking (13a).

4. as each described film photovoltaic device in claim 2 or 3, it is characterized in that, to be higher than 95% reflectivity between 500nm and the 1400nm, reflect between 700nm and 1100nm with the reflectivity greater than 99%, described reflectivity is the mean value in described wave-length coverage in fact in described reflector (14).

5. film photovoltaic device as claimed in claim 2 is characterized in that, described reflector (14) and described back sheet material (15) are combined into sheet material after the reflectivity.

6. film photovoltaic device as claimed in claim 3 is characterized in that, described reflector (14) and described back sheet material (15) are combined into sheet material after the reflectivity.

7. as each described film photovoltaic device in the claim 1,2,3 or 6, it is characterized in that described back sheet material (15) is to be made by glass or multiple field polymeric material.

8. film photovoltaic device as claimed in claim 4 is characterized in that, described reflector (14) and described back sheet material (15) are combined into sheet material after the reflectivity.

9. film photovoltaic device as claimed in claim 4 is characterized in that, described back sheet material (15) is to be made by glass or multiple field polymeric material.

10. film photovoltaic device as claimed in claim 5 is characterized in that, described back sheet material (15) is to be made by glass or multiple field polymeric material.

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