CN101246923A - Back electrode of thin film silicon photovoltaic device - Google Patents
Back electrode of thin film silicon photovoltaic device Download PDFInfo
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- CN101246923A CN101246923A CNA2007100049766A CN200710004976A CN101246923A CN 101246923 A CN101246923 A CN 101246923A CN A2007100049766 A CNA2007100049766 A CN A2007100049766A CN 200710004976 A CN200710004976 A CN 200710004976A CN 101246923 A CN101246923 A CN 101246923A
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Abstract
The present invention discloses a new back electrode of film silicon photovoltaic devices. In order to gain advantage of film back electrode of silver and aluminum and avoid the disadvantage of them, the present invention piling up silver and aluminum as compounded back electrode, and adding a thin alumina film between them to avoid interdiffusion of silver and aluminum. The back electrode has high reflectivity, high stability and is convenient for produce of large-area photovoltaic template.
Description
Technical field
The invention belongs to photovoltaic equipment field, specially refer to the silicon hydride thin film photovoltaic device technology.
Background technology
Back electrode is for the solar cell (also being called film photovoltaic or photoelectric device) of based thin film amorphous silicon hydride and nanocrystal silicon, especially it is important that the high-performance of large tracts of land photovoltaic module and reliability cause the pass, wherein catching luminous energy power efficiently, is indispensable factor for effectively catching weak absorbing light.Back electrode with high reflectance can be effectively in the unabsorbed longwave optical line reflection light echo volt device.Reflection is preferably carried out with a very big angle (diffuse transmission type), and long optical path is arranged when making light enter silicon layer once more like this, increasing its absorbed probability, thereby increases photoelectric current.
In the laboratory, obtained efficient good film amorphous silicon and nanocrystal silicon (nano-silicon) solar cell.This solar cell uses transparent conductive oxide film and reflective metallic film, preferably with zinc oxide and silver (ZnO/Ag) as back electrode.Yet the cooperation of this ZnO/Ag can produce serious problem.Thick silver layer can cause tangible shunting, and shunting can cause energy transformation ratio low again, thereby causes the output of photovoltaic module low.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, and this has influenced the useful life of photovoltaic module (along with silver is penetrated into silicon layer, can produce shunting gradually).At last, compare with aluminium, silver is a kind of invaluable metal.So the consumption of restriction silver helps to reduce the production cost of photovoltaic module.
When the back electrode of ZnO/Ag was used for solar cell at first, people used thicker silicon layer.Because silicon thin film thicker (such as in three-joint solar cell and photovoltaic module) is not obvious by the branch flow problem that silver causes.Yet in order to produce more stable photovoltaic module, photovoltaic module of today is used thin silicon thin film instead.When using ZnO/Ag (perhaps simple silver), just be easy to produce the problem of shunting like this as the back electrode material.Even it is found that the diode for small size, ZnO/Ag electrically contacts also to electrically contact than ZnO/Al and more is easy to generate the branch flow problem.Current production comprises amorphous silicon, and during the photovoltaic module of the based thin film silicon of amorphous silicon germanium alloy nano crystal silicon, ZnO/Al is the standard material of people's general choice.Fig. 1 has shown a layer structure with p-i-n type photovoltaic device of standard back electrode.The composition of this battery comprises glass substrate 1; The preceding electrode 2 of electrically conducting transparent; P-i-n structure 8 based on hydrogenated silicon film by utilizing; Transparent conductive oxide 22 (zinc oxide) and metal film 45 (silver or aluminium).The back electrode of common silicon thin-film battery uses silver or aluminium, but both can not be used simultaneously.Different with ZnO/Ag, the back electrode that ZnO/Al makes not only is difficult for causing shunting, even and produce the branch flow problem also than being easier to solve (by so-called " shunting weakens " program).We have carried out a large amount of experiments at this problem, and other research has also been done relevant report to this problem with establishment.Under many circumstances, use the photovoltaic module of the back electrode of ZnO/Ag, lower than the photovoltaic module energy transformation ratio that uses the ZnO/Al back electrode.This is that the increase of closed current is filled the reduction of the factor (and open circuit voltage) and offsets because when using ZnO/Ag as back electrode.ZnO/Al is a kind of back electrode material very reliably, but compares with ZnO/Ag, and its reflecting power is far short of what is expected.
In theory, ZnO/Ag can make composite back electrode with other metal and/or the combination of metal oxide rete, ZnO/Ag/X, and wherein X is " protection " conductive layer, keeps stable rete (the discord silver hair is given birth to reaction) in other words conj.or perhaps.In the ZnO/Ag/X structure, relatively thin silver layer (for example, 50 nanometers or still less) is sandwiched between zinc oxide and the X.The purpose of doing like this is when relating to laser treatment and single battery is connected into the photovoltaic template, the part that allows ZnO/Ag extend as hydrogen amorphous silicon n layer." protection " rete X must satisfy following several condition: good electrical conductivity, the shunting inhibitory action is arranged, can be firm attached on the silver-colored film but the phase counterdiffusion can not take place.In the back electrode of ZnO/Ag/X, ZnO/Ag should dominate optical property rather than electric property, so just can make with silver-colored relevant shunting to minimize.The X layer should be born main current delivery effect, help to reduce the shunting that causes in intrinsic and the processing procedure.Because silver layer is sandwiched between zinc oxide and the X, the laser scribing of using when forming the photovoltaic template is cleaner, does not stay because drawn area does not have too many silver-colored residual thing.So new method has solved the problem that the simple back electrode of traditional Z nO/Ag type exists.
Summary of the invention
Based on above-mentioned consideration, the applicant has worked out primary and foremost purpose of the present invention: provide a kind of novel back electrode that is applicable to thin film silicon solar cell, to improve photoelectric conversion efficiency.
Further purpose of the present invention is to use novel back electrode to have the solar cell stability based on hydrogenated silicon film by utilizing of high conversion efficiency with improvement.
In order to reach the foregoing invention purpose, the present invention adopts the composite back electrode of ZnO/Ag/X type.The X here is to have conductive structure satisfactory electrical conductivity and that can overcome the silver electrode weakness.Clear and definite says that X preferably is made up of two parts, and its major part is a thicker aluminium film, and a very thin aluminum oxide film is arranged in its front, and its thickness is no more than 50 nanometers, preferably is no more than 20 nanometers, and its effect is the counterdiffusion mutually that prevents silver and aluminium.If there is not the aluminium oxide separator, silver and aluminium double-layer films can very fast mutually combining, thereby the optics of back electrode and electric property all are affected, and this phenomenon is more obvious under than higher operational temperature.
According to test, compare ZnO/Ag/AlO with ZnO/Al to the small size solar cell
xThe photoelectric current bigger (3-5%) that/Al back electrode produces.This mainly is because silver is higher to the reflectivity of ruddiness than aluminium.People also find to have ZnO/Ag/AlO
xThe efficient of the photovoltaic module of the back electrode of/Al structure is higher, mainly is because fill factor, curve factor is improved.
By reducing the thickness of silver, with limit " distributary phenomenon " with the auxiliary ZnO/Ag (thin Ag layer) of other conduction contact materials, the back electrode of the such MULTILAYER COMPOSITE of ZnO/Ag/ZnO/Al has good optical and electrical characteristic, and stability and reliability are well arranged.The present invention adopts the multilayer back electrode pattern of silver and aluminium, thereby has kept ZnO/Ag and ZnO/Al type back electrode advantage separately well, has avoided their shortcoming.We find to use silver layer (for example 30 nanometers) as thin as a wafer, and more stable compared with thicker silver-colored thin layer (such as the thickness that uses in traditional ZnO/Ag back electrode silver-colored thin layer between 150 and 250 nanometers), shunt effect also greatly reduces.
The extension of above-mentioned notion comprises: ZnO/Ag/Ni, ZnO/Ag/NiV, ZnO/Ag/Ti or ZnO/Ag/Cr.This back electrode is structurally than ZnO/Ag/AlO
x/ Al is simpler, but the conductivity of these alternative metals is not as aluminium.The Stability Analysis of Structures that these electrically contact, reflectance is better, can deposit simply by traditional filming equipment and program.In addition, all retes in the back electrode of the present invention can large-area high speed form in same sputtering equipment, thereby realize high yield, so the present invention has good industrial prospect.
It should be noted that so its thickness must remain on below the certain limit, otherwise the conversion efficiency of photovoltaic cell also can be affected because the conductivity of aluminium oxide own is not good.
Description of drawings
The present invention will be further described below in conjunction with drawings and Examples.
Fig. 1 is the layer structure of the photovoltaic device of the p-i-n type based thin film silicon with traditional back electrode.
Fig. 2 has shown the layer structure of the photovoltaic device of the p-i-n type based thin film silicon with back electrode of the present invention.
Embodiment
In order to solve in the back electrode issue of inter-diffusion mutually of silver and aluminium, we have embedded the diffusion barrier aluminium oxide between silver and aluminium lamination.As shown in Figure 2, a p-i-n type thin film silicon unijunction solar cell of purchasing according to the present invention comprises as the lower part: glass substrate 1, the preceding contact layer (tin oxide) 2 of electrically conducting transparent, based on the photovoltaic cells 8 that constitutes by p layer, i layer and n layer of hydrogenated silicon film by utilizing with by the back electrode that plural layers constitute, comprise zinc oxide film 22, silver-colored film 45, aluminum oxide film 32 and aluminium lamination 55.Wherein silver-colored film 45 and aluminum oxide film 32 all are extremely thin films, and their thickness is respectively in 20-50 nanometer and 5-30 nanometer range.A concrete example is to use this ZnO/Ag (the approaching)/AlO of magnetron sputtering deposition
xThe thickness of each film of (approaching)/Al (thick) back electrode is respectively 100 nanometers, 40 nanometers, 8 nanometers and 200 nanometers.The silver-colored film 45 of 40 nanometer thickness is enough to provide the light reflective that is similar to extremely thick silver-colored film, and the aluminum oxide film 32 that has only 8 nanometer thickness does not have the phenomenon of phase counterdiffusion yet between sufficient to guarantee silver and the aluminium film.Combined type back electrode described in the invention can effectively be used in the multijunction solar cell that is formed by stacking by a plurality of p-i-n type photovoltaic cells equally.
The film of extremely thin aluminium oxide can obtain by the sputtering method that uses salic target, and another way is exactly to import the oxygen of trace in sputtered aluminum in sputtering chamber, thereby makes the aluminium film of growth obtain oxidation.Also have a kind of way just to be to use plasma chemical vapor deposition, thus the acquisition of using trimethylaluminum and oxygen mixture to be exceedingly fast.
Claims (6)
1. film photovoltaic device comprises:
A) the preceding contact layer of an electrically conducting transparent comprises transparent conductive oxide;
B) a single p-i-n type photovoltaic cells or a plurality of p-i-n type photovoltaic cells that overlaps comprise p type, intrinsic i type and n N-type semiconductor N film based on silane;
C) reflective conduction back electrode is characterized in that: this reflective conduction back electrode structure comprises successively:
I. a transparent conductive oxide film comprises the zinc oxide that aluminium mixes;
Ii. silver-colored film, its thickness is less than 60 nanometers;
Iii. aluminum oxide film, its thickness is no more than 30 nanometers;
Iv. aluminium film, its thickness is greater than 120 nanometers.
2. film photovoltaic device according to claim 1 is characterized in that: described film photovoltaic device is in parallel with one or more other photovoltaic devices or be cascaded, and forms a photovoltaic device that power output is bigger.
3. film photovoltaic device according to claim 1 is characterized in that: the thin layer of p-i-n type film photovoltaic device is made of different silicon and silicon alloy film, and the structure of these films is noncrystal, nanocrystal, mixed-phase or allosome atomic structure.
4. film photovoltaic device according to claim 1 is characterized in that: the aluminium film in the described reflective conduction back electrode is substituted by one or more other metallic films, as nickel, and copper, the metal material that gold is such or the alloy of conduction.
5. film photovoltaic device according to claim 1 is characterized in that: this film photovoltaic device is placed on the hard substrate, such as glass plate.
6. film photovoltaic device according to claim 1 is characterized in that: the aluminum oxide film in the described reflective conduction back electrode has oxygen atom density heterogeneous.
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| Application Number | Priority Date | Filing Date | Title |
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| CNA2007100049766A CN101246923A (en) | 2007-02-14 | 2007-02-14 | Back electrode of thin film silicon photovoltaic device |
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| Application Number | Priority Date | Filing Date | Title |
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| CNA2007100049766A CN101246923A (en) | 2007-02-14 | 2007-02-14 | Back electrode of thin film silicon photovoltaic device |
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| CN101246923A true CN101246923A (en) | 2008-08-20 |
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| CNA2007100049766A Pending CN101246923A (en) | 2007-02-14 | 2007-02-14 | Back electrode of thin film silicon photovoltaic device |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111276553A (en) * | 2015-11-24 | 2020-06-12 | 日立化成株式会社 | Method of forming a solar cell with a sintered multilayer thin film stack |
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- 2007-02-14 CN CNA2007100049766A patent/CN101246923A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111276553A (en) * | 2015-11-24 | 2020-06-12 | 日立化成株式会社 | Method of forming a solar cell with a sintered multilayer thin film stack |
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