CN101246916A

CN101246916A - Method for reducing internal reflection of silicon hydride thin film photovoltaic device

Info

Publication number: CN101246916A
Application number: CNA2007100049681A
Authority: CN
Inventors: 李沅民; 马昕
Original assignee: BEIJING XINGZHE MULTIMEDIA TECHNOLOGY Co Ltd
Current assignee: BEIJING XINGZHE MULTIMEDIA TECHNOLOGY Co Ltd
Priority date: 2007-02-14
Filing date: 2007-02-14
Publication date: 2008-08-20

Abstract

The present invention discloses a method for reducing inner reflection of hydrogenated Si film photovoltaic devices. Before sediment of p-i-n type photovoltaic cell, partially deoxidizing metal oxide surface layer as transparent front electrode by plasma processing method and making it low value oxide, the light refraction coefficient is between original metal oxide and the first p layer to act as anti-refraction, and the conversion efficiency of photovoltaic is enhanced.

Description

Reduce the method for internal reflection of silicon hydride thin film photovoltaic device

Technical field

The present invention relates to the solar photovoltaic device field, specially refer to film solar photovoltaic device.

Background technology

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.Producing distinguishing feature of 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 (laser patterning) that is applied to the different films on the same 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.

Solar cell is the device of multiple film layer, and wherein every layer all has specific function for total.Structural analysis according to the solar cell of known use amorphous silicon hydride and nanocrystal silicon and alloy thereof, internal electric field is the p type of being made by amorphous silicon and/or nanocrystal silicon and alloy thereof containing, and produces in the structure of intrinsic i type and n type rete (p-i-n).And the material of these retes is amorphous silicons and/or based on the material of nanocrystal silicon, comprises the silicon alloy as amorphous germanium silicon (a-SiGe).Therefore, a typical thin film silicon solar cell comprises the skin of a doping type, with feature and an intermediate layer of generating p type (positive pole and hole) and n type (negative pole and electronics), this intermediate layer is made by the i section bar material of the non-doping type of intrinsic-OR, is commonly called the i layer.Comprise the p type, the thin film silicon solar cell and the relevant large tracts of land photovoltaic module of i type and n type rete are called as p-i-n type photovoltaic cell.They are normally made by plasma chemical vapor deposition under cryogenic conditions.Doping type p layer and n layer produce an electric field in the i layer in other words at absorbed layer, and incident light is changed into electric energy.

To sandwich between the conductive film electrode based on the p-i-n N-type semiconductor N rete of silicon, just made a solar cell that can operate.The common solar cell based on hydrogenated silicon film by utilizing comprises: glass substrate; By transparent conductive oxide (TCO) (as tin oxide) make transparent before electrode; The p layer, i layer and the n layer that constitute by thin film silicon; Back side transparent conductive oxide film and metal film as zinc oxide, normally silver or aluminium.Solar absorbing layer i layer (being also referred to as the photoelectricity conversion coating) is to be made by the film based on intrinsic silicon, especially as amorphous silicon, and nanocrystal silicon and the such material of amorphous germanium silicon.

The key that makes the film photovoltaic device function admirable is to optimize optical absorbing layer, and reduces the optical loss in the membrane structure.Usually, the material of p layer is boron doped amorphous silicon alloy with wide bandgap, as non-crystal silicon carbon or nanocrystal silicon.These materials are to the refraction coefficient N of visible light and infrared light (wavelength 400-1200 nanometer) _S, scope is higher than the refraction coefficient N of transparent preceding electrode far away between 3.5-4.0 _TSo, the solar cell of traditional based thin film silicon can produce certain optical loss because of the reflection of the boundary layer between TCO and the silicon film (TCO/Si).This reflection of incident light loss at TCO/Si interface is with reflectance formula R=(N _S-N _T) ²/ (N _S+ N _T) ²Calculate, the numerical value of R for tin oxide commonly used and zinc oxide greater than 8%, because their N _TValue is about 2.0-2.1.This serious reflection loss of light is one of the principal element of the solar cell properties of restriction based thin film silicon.Optical refractive index value at the best reflectance coating at TCO/Si interface is 2.7-2.8.

Usually deposition just can plate antireflection film in air/glass interface as magnesium fluoride or multilayer optical rete on glass substrate, if still how similar methods has been used on the TCO/Si interface with regard to difficulty.It is exactly to plate the nesa coating of one deck refraction coefficient between 2.2-2.9 again on the TCO surface that a kind of way is arranged, and is that 2.7 metal oxide is uncommon but have near refraction coefficient, and does not have good electrical conductivity usually.Most of in addition metal oxides also often form the obstacle that hinders electric current with contacting of silicon thin film.Therefore the TCO/Si interface plays an important role to the carrier transport of entire device, and any antireflection film all must have good electrical conductivity and transparency, also wants and based on the semi-insulating p layer height compatibility of silicon.Simultaneously, because the silicon deposited film process uses the plasma enhanced chemical vapor deposition method usually, so antireflection film also preferably makes and uses the same method and obtain.

Summary of the invention

Based on above-mentioned consideration, the applicant has worked out primary and foremost purpose of the present invention: a kind of p-i-n type photovoltaic device based on silicon thin film is provided, and this device has good opto-electronic conversion effect.

Further purpose of the present invention is, a kind of antireflection film is provided in the photovoltaic device of based thin film silicon, thereby reduces transparency electrode and based on the light reflection at interface between the p layer of silicon.

For achieving the above object, the present invention adopts a kind of method of minimizing internal reflection of silicon hydride thin film photovoltaic device of novelty.Before deposition p-i-n type photovoltaic cells, the using plasma method is carried out partial reduction to the top layer as the metal oxide of electrode before transparent, make it become suboxide (oxygen content is lower than the oxide of stoichiometric(al) numerical value), its optical refractive index is between a virgin metal oxide and a p layer, preferably near 2.7-2.8, thereby play the effect of antireflection, strengthen the conversion efficiency of photovoltaic device.

The refraction coefficient N of metal-oxide film _TCan regulate by oxygen atom density in the change material.And the metal oxide that has formed also can change its chemical composition through chemical treatment, thereby changes its optical refractive index, and the refraction coefficient of metal oxide increases along with the reduction of its concentration of oxygen atoms.The low value state of oxidation of tin oxide and zinc oxide can match with the thin film silicon in the photovoltaic device, and does not produce any electric current obstacle.

Description of drawings

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

Accompanying drawing is a structural representation based on the p-i-n type photovoltaic device of silicon thin film that comprises anti-reflection layer.

Embodiment

Accompanying drawing shows is a structural representation based on the p-i-n type photovoltaic device of silicon thin film that comprises anti-reflection layer.The rete that this solar cell and conventional solar cell are used is identical substantially, unique different be before antireflection film 7 is formed on the electrode 2.This photovoltaic device comprises towards the glass substrate 1 of glass incident sunlight, for example is the transparent preceding electrode 2 of tin oxide; The suboxide 7 that forms on the electrode as anti-reflection layer; Based on one or more p-i-n type photovoltaic cells 8 of silane and the reflective rear electrode that constitutes by conducting objects 22 before transparent and metal film 45.The reflectivity of antireflection film 7 preferably is similar to 2.8, can suppress the reflection at TCO/Si interface (interface between the rete 2 and 6) so to greatest extent.

Here we illustrate the formation of anti-reflection layer 7 as electrode before transparent with tin oxide.The glass substrate that is coated with tin oxide after cleaning is inserted in the plasma enhanced chemical gas phase reflection chamber, but in the chamber, introduce the source gas that does not contain deposited material based on hydrogen, substrate temperature is maintained between 150-250 ℃, provide direct current or AC energy to exciting electrode then, to produce plasma, reduction reaction takes place in hydrogen atom that plasma provides and tin oxide top layer, and formation steam also is excluded out outside the reative cell.And hydrogen atom can enter tin oxide inside, and reduction reaction takes place, and can participate in reduction reaction so the surface portion thickness of tin oxide reaches the surface of tens nanometer.The speed of this reaction and the degree of depth are according to the intensity processing time, particularly substrate temperature of plasma and change.A particularly advantageous situation is, the optical refractive index of formed suboxide increases to its surface gradually from tin oxide inside, and the variation of this gradient is rather useful for the anti-reflective function at TCO/Si interface.

Zinc oxide is difficult for and the hydrogen plasma reaction, and institute thinks makes zinc oxide formation suboxide should add an amount of halogen in the gas of the source of plasma treatment.

Characteristics of the present invention are that the plasma treatment procedure of employed formation antireflection film is fully passable, and best In the same plasma enhanced chemical vapor deposition equipment of formation based on the p-i-n type photovoltaic cells of silicon thin film, to finish.

Claims

1. photovoltaic device, its formation comprises as the lower part:

A) transparent roof panels comprises glass plate;

B) transparent preceding electrode, electrode was made by transparent conductive oxide before this was transparent, was deposited on the described transparent roof panels;

C) p-i-n type photovoltaic cells comprises:

I. p layer is made by the amorphous silicon alloy of boron doped p molded breadth band gap or nanocrystal silicon or its alloy;

Ii. a n layer is made by the n type thin film silicon of phosphorus doping or the alloy of silicon;

Iii. an intrinsic i layer is made by the film based on silane or silicon alloy of non-doping, is placed between described p layer and the described n layer;

D) anti-reflection layer is placed between the p layer and described transparent preceding electrode of described p-i-n type photovoltaic cells;

E) back contact comprises the reflectivity back electrode that is made of transparent conductive oxide and reflective metal film, is deposited on the n layer of described p-i-n type photovoltaic cells.

It is characterized in that: described anti-reflection layer be.Before p-i-n type photovoltaic cells forms, described transparent before the surface of electrode with the method formation of plasma chemical treatment.Metal oxide top layer after plasma treatment becomes suboxide, its optical refractive index between described transparent before between electrode and the described p layer, thickness is between the 5-50 nanometer, it has the effect that reduces the light reflection that occurs between described transparent preceding electrode and the described p layer, and its absorptivity to visible light is no more than 1%.

2. photovoltaic device according to claim 1 is characterized in that: described p-i-n type photovoltaic cells is made of the p-i-n type photovoltaic cells that several closely are formed by stacking, thereby makes described photovoltaic device become many knot photovoltaic devices.

3. photovoltaic device according to claim 1 and 2 is characterized in that: described transparent before electrode comprise that tin oxide, titanium oxide, zinc oxide, indium tin oxide and other can be by the metallic compounds of the plasma deoxidization of hydrogeneous or halogen.

4. photovoltaic device according to claim 1 and 2 is characterized in that: the formation of described antireflection film is to carry out in being used for producing the same vacuum coating equipment of described p-i-n type photovoltaic cells.