CN101246930A - Ultra-white reflection layer of thin-film solar cell - Google Patents

Abstract

The present invention discloses a super white reflector of film solar cell. reflection back electrode of film solar cell comprises of thick enough transparent conductive oxide (TCO) film and a super white reflector layer with high light reflectivity placed on back, the long wave light with weak absorption is reflected to semiconductor absorption layer of solar cell at the interface of TCO and super white reflector layer, and the light capture capability and photoelectric conversion efficiency are enhanced.

Description

The ultra-white reflection layer of thin-film solar cells

Technical field

The invention belongs to the solar photovoltaic device field, specially refer to solar cell based on hydrogenated silicon film by utilizing.

Background technology

In recent years, the development of photovoltaic cell and large tracts of land photovoltaic module has caused common people's extensive concern.Especially amorphous silicon hydride and nanocrystal silicon, they demonstrate great potential along with the extensive use of photovoltaic device in commercial and dwelling house facility.A distinguishing feature of producing thin film silicon photovoltaic device under temperature so lower below 260 ℃ is, the semiconductor film relevant of large tracts of land deposition with silicon with electrically contact rete and have premium properties.Simultaneously, use good ripe filming equipment and program, can make to industrialization template cheaply.The laser scribing moulding process (laserpatterning) that is applied to the different films on the same glass substrate allows a plurality of solar cell devices directly to form the large tracts of land photovoltaic module of integrated form in film deposition process, has reduced procedure of processing and has also improved reliability of products.

For photovoltaic device, film photovoltaic device particularly, the key that makes its function admirable is to optimize the absorption of photoelectric conversion semiconductor layer to luminous energy, and reduces the optical loss in the device simultaneously.Can absorb luminous energy to greatest extent in very thin absorbed layer, be the essential condition of high conversion efficiency.Comprise that the solar cell that the hydrogenation thin film silicon of amorphous silicon hydride and nanocrystal silicon is constituted has the p-i-n structure usually, wherein p layer and n layer are sluggish " dead layers ", they set up a built-in electric field in the i of non-doping layer (absorbed layer), thereby make photic charge carrier by effective collection.The thickness of its absorbed layer generally has only a hundreds of micron, is no more than about 2000 microns at most.And the absorption coefficient of the ruddiness of hydrogenated silicon film by utilizing and infrared light is all lower, so there is very most sunlight not to be effectively used.Usually the p-i-n structure based on hydrogenated silicon film by utilizing is sandwiched in former and later two electrodes (electric contacting layer), and forms complete photovoltaic element.Electrode must have good transparency and conductivity before normally used, and it normally is made of transparent conductive oxide (TCO), such as thickness is the tin oxide that is doped or the zinc-oxide film of 600-900 nanometer.Rear electrode is made of jointly a TCO and lighttight metallic film usually, and an one important function is exactly with among the unabsorbed smooth reflected back p-i-n structure.Attempted various ways and improved absorption light, comprising use coarse transparent before electrode, to strengthen scattering of light.In addition, also use the higher back electrode of reflecting rate, and made unabsorbed light be got back in the battery by throwing again.For amorphous silicon battery, absorbed layer i layer can not be done very thickly, and reason is the defective that this material has the light quality decay.So remarkable optical design has played decisive role for the conversion efficiency of the thin-film solar cells as the silane.

Current production comprises amorphous silicon, and during the photovoltaic module of the based thin film silicon of amorphous silicon germanium alloy and nanocrystal silicon, ZnO/Al (zinc oxide/aluminium) is the standard material that people select.The layer structure of a common p-i-n type photovoltaic device comprises glass substrate; The preceding electrode of electrically conducting transparent; The p-i-n structure of based thin film comprises p layer, i layer and n layer respectively; Transparent conductive oxide (zinc oxide) and metallic film (silver or aluminium).The high efficiency hydrogenated silicon film by utilizing solar cell of making in the laboratory is as back electrode with zinc oxide and silver (ZnO/Ag).Yet the cooperation of this ZnO/Ag can produce tangible shunting (shunt), and shunting can cause energy transformation ratio low again, and this problem is especially obvious in the production of large tracts of land photovoltaic module.As time goes on, silver can lose the gloss of itself, and the reflecting power of the back electrode that ZnO/Ag makes will reduce.The diffusivity of silver self is very strong, along with silver is penetrated in the silicon layer, can produce shunting gradually, and this has influenced the useful life of photovoltaic module.And the consumption of restriction silver helps to reduce the production cost of photovoltaic module.

By contrast, the film photovoltaic module that ZnO/Al makes is more long-lived, more reliable, because aluminium is difficult for causing distributary phenomenon, this production for the large tracts of land template is highly beneficial.But compare with ZnO/Ag, the luminous reflectanc of aluminium is far short of what is expected, so limited photoelectric conversion efficiency.Because the cost of photovoltaic module depends on its energy conversion efficiency (power output) to a great extent, so not good enough back reflector has seriously limited the commercial appeal of this device.

So, necessary seek a kind of reflectivity near or surpass ZnO/Ag, and stability is not second to the high reflective rear electrode with enough conductivity of ZnO/Al.

Summary of the invention

Based on above-mentioned consideration, the applicant has worked out primary and foremost purpose of the present invention: improve the conversion efficiency based on the film solar photovoltaic device of silane.

Another object of the present invention is to provide the back reflection structure of a novelty, to improve the response of solar cell to longwave optical.

In order to achieve the above object, the invention describes the way that a kind of back of the body reflective that can make thin-film solar cells strengthens greatly.A kind ofly be applicable to that the ultra-white reflection layer of hydrogenated silicon film by utilizing solar cell is the reflecting coating material that is used for optical mirror plane, such as BaSO ₄, they have the high reflectivity from the ultraviolet light to the infrared light (surpassing 98% usually), and highly stable, and this is a very important consideration for the long-term photovoltaic device that uses out of doors.For this high reflection ultra-white reflection layer is attached in the film photovoltaic device, traditional metal film that covers cell backside (such as silver or aluminium) must be excluded, and is replaced by transparent conductive material fully.Reflecting material is applied on the transparent back electrode, is zinc oxide film for example, replaces the employed metallic film of common thin-film solar cells.The super unabsorbed longwave optical reflected back photoelectricity transition region that the overwhelming majority can be passed transparent back electrode from the reflector that this rear surface of solar cell applies.The efficient of this reflection process will be apparently higher than the reflectivity of any metal back electrode, because the reflection of metallic film inevitably causes optical absorption loss.

Description of drawings

The present invention will be further described below in conjunction with drawings and Examples.

Accompanying drawing has shown a layer structure according to the thin-film solar cells of the present invention's formation.

Embodiment

As shown in drawings, a p-i-n type photovoltaic device, its structure comprises successively along the incident direction of light: a glass substrate 1; One transparent before electrode 2, comprise such as be the transparent conductive oxide (TCO) of tin oxide; One or more by the p-i-n type photovoltaic cells 8 that constitutes based on hydrogenated silicon film by utilizing (device that a plurality of p-i-n type photovoltaic cells are formed by stacking is referred to as multijunction solar cell); A transparent back electrode 22, it can be made of a transparent conductive oxide (the 2nd TCO), such as zinc oxide film; A ultra-white reflection layer 84.Ultra-white reflection layer is not less than 95% to the reflection of light rate that wavelength is no more than 1200 nanometers, and this reflector can be stable insulator, semiconductor or a conductor.When this ultra-white reflection layer did not have satisfactory electrical conductivity, the rete resistance of transparent back electrode was not more than 60 Ω/.This transparent back electrode can be not less than the zinc-oxide film that the aluminium of 350 nanometers or gallium mix by thickness and constitute, and its thickness is not less than 700 nanometers, to avoid the ohmic loss of photovoltaic template.The manufacture method of zinc oxide is magnetron sputtering and chemical vapour deposition technique.Described ultra-white reflection layer is by BaSO for example ₄The material of making superbright optical reflecting mirror constitute.

Claims (3)

1. p-i-n type photovoltaic device, its structure comprises successively along the incident direction of light: a glass substrate; One transparent before electrode, comprise such as be the transparent conductive oxide (TCO) of tin oxide; One or more by the p-i-n type photovoltaic cells that constitutes based on hydrogenated silicon film by utilizing; A transparent back electrode, it can be made of a transparent conductive oxide (the 2nd TCO) rete; A ultra-white reflection layer.It is characterized in that: the ruddiness of ultra-white reflection layer and infrared reflectivity be greater than 95%, and this reflector is a stable insulator, semiconductor or conductor, when this ultra-white reflection layer does not have satisfactory electrical conductivity, the rete resistance of transparent back electrode be not more than 60 Ω/

2. p-i-n type photovoltaic device according to claim 1 is characterized in that: described transparent back electrode is that thickness is not less than the aluminium of 350 nanometers or the zinc-oxide film that gallium mixes, and its manufacture method is magnetron sputtering and chemical vapour deposition technique.

3. p-i-n type photovoltaic device according to claim 1 is characterized in that: described ultra-white reflection layer is by BaSO for example ₄The material of making superbright optical reflecting mirror constitute.

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