CN101235492A

CN101235492A - Chemical annealing method for making amorphous silicon battery more stable

Info

Publication number: CN101235492A
Application number: CN 200710002576
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: 2007-01-29
Filing date: 2007-01-29
Publication date: 2008-08-06

Abstract

The invention discloses a chemical annealing method for improving the stability of intrinsic amorphous silicon thin film, which comprises: alternating the growth of silicon film whose thickness is 2-10 nanometers and the chemical annealing treatment in the process that plasmas are used to intensify a chemical vapor deposition method to generate hydrogenated amorphous silicon, sufficiently rebuilding and loosening atomic structures of hydrogenated silicon material, and lowing the electronic defect concentration. The material is in particular suitable for i layers in p-i-n type photovoltaic devices.

Description

Make the chemistry annealing way of amorphous silicon battery more stable

Technical field

The invention belongs to solar energy electric material field, specially refer to the growing technology of hydrogenation non crystal silicon film.

Background technology

Solar energy power generating is to obtain to help one of important channel of the renewable energy source of environment, and thin-film solar cells is being represented the development trend of photovoltaic technology.Solar cell based on silicon film has low cost, is convenient to the advantage of the integrated manufacturing of big area, but its efficiency of conversion is on the low side.The process of opto-electronic conversion occurs among the i layer that is made of intrinsic amorphous silicon fully, and the effect of p layer and n layer is to set up built-in electric field in relative thick i layer, so that collect the photic current carrier in the i layer.The stability of non-crystalline silicon p-i-n type solar cell almost completely depends on the stability of non-doped amorphous silicon i layer.The initial photoelectric conversion efficiency of this class battery improves along with the increase of i layer thickness, but the photo attenuation that amorphous silicon battery had is also more obvious with the increase of i layer thickness, particularly when the i layer thickness of p-i-n type solar cell surpasses 300 nanometers, that is to say, efficiency of conversion and stability are difficult for getting both, thereby have limited the application of this class battery greatly.Because the efficiency of conversion of thin battery is lower usually, a popular solution to this problem adopts the multijunction cell technology exactly, just two or more solar cells based on non-crystalline silicon is overlaped.But the technology that adopts this multijunction cell has many shortcomings, and it is higher to comprise that device architecture complexity, production process are difficult to grasp, equipment and production cost, so be difficult to be applied in the solar electrical energy generation on a large scale.So the necessary film coating method of seeking a kind of stability of the i of improvement layer makes it improve the stability and the efficiency of conversion of p-i-n type non-crystal silicon solar cell.

The major cause that causes the photic decline of non-crystalline silicon is owing to networks of atoms in the non-crystalline silicon is unordered, the atomic bond broken of being easy to that a lot of high distortion are arranged, and the fracture of this key is the immediate cause that causes that electronic defects density increases under illumination, its basic terms of settlement is the interior pressure that reduces in this disordered material, just reduce by high distortion the density of atomic bond.The method of common growth non-crystalline silicon is to use one group of fixed plasma parameter, and feasible film of being grown is to beginning all successive formation under a certain conditions extremely eventually.Even so in the PECVD process, use the diluted silane of hydrogen height, the hydrogen atom of plasma exciatiaon does not have enough chances constantly to improve formed Siliciumatom structure yet.

Summary of the invention

Based on above-mentioned consideration, the applicant has worked out purpose of the present invention: make the method for hydrogenation non crystal silicon film by improvement PECVD, thereby improve the stability and the photoelectric properties of hydrogenation non crystal silicon film.

Further purpose of the present invention is to improve the p-i-n type and use the permanent efficiency of conversion of hydrogenation non crystal silicon film as the thin-film solar cells of i layer.

In order to achieve the above object, the present invention has adopted a kind of chemical method for annealing that improves the stability of intrinsic amorphous silicon film.Using the plasma enhanced chemical vapor deposition method to generate in the process of amorphous silicon hydride, the growth of 2-10 nanometer thickness silicon fiml and the chemical anneal of hydrogen gas plasma hocket, make the atomic structure of silicon hydride material be rebuild fully and become flexible, and reduce electronic defects density.This material is specially adapted to the i layer in the p-i-n type photovoltaic device.

The periodic chemistry annealing that relies on the hydrogen atom of plasma generation can be rebuild and the atomic structure of loosening amorphous silicon membrane surface portion, in fact the atomic hydrogen of plasma generation can be deep into 5 nanometers under the silicon top layer, so the atom under the top layer is organized the anneal that also can effectively obtain atomic hydrogen.Specific practice is just interrupt film growth behind the amorphous silicon material of several nanometer thickness of every growth, and the lower plasma body of energy that contains pure hydrogen of migrating to be handled the amorphous silicon membrane that has just plated.The effect that contains the plasma body of pure hydrogen is not the atom of silicon will to be etched away from the surface, but relies on hydrogen atom to penetrate among the silicon structure, promotes the optimization that reconfigures of silicon and chemistry of silicones key, makes atomic structure more loosen, and reduces local stress.Cause after so just having avoided that defective produces based on the inducement on the atomic structure.Certainly when using hydrogen plasma to carry out chemistry annealing, rare gas element also can be added among the hydrogen.

Embodiment

The most conspicuous method is, when forming non-adulterated film based on silicon hydride with the plasma enhanced chemical vapor deposition method, following two steps hocket 1) use the mixed gas of silane and hydrogen, substrate temperature is remained between 150-220 ℃, use 20-100mW/cm ²The radio frequency discharge power density, the amorphous silicon membrane of growth 2-10 nanometer thickness, its growth velocity is not higher than 0.6 nm/sec, stops glow discharge (just stopping the electric energy to negative potential supply activated plasma) after film forms, and extracts remaining silane out vacuum chamber; 2) with pure hydrogen or contain the proportional mixture that is no more than 50% rare gas element and hydrogen and introduce in the vacuum chamber, on above-mentioned amorphous silicon membrane, apply plasma glow discharge, thereby generation hydrogen atom, and silicon film is carried out chemistry anneal, its time length, between second, employed radio frequency discharge power density was 20-80mW/cm at 20-300 ², air pressure is not less than 2mbar, to reduce to bombard silicon face ionic average energy.

The most clear-cut way is between film growth that hockets and chemical annealing steps, not interrupt plasma body glow discharge, thereby simplify the operation course, and obtain effective sedimentation rate of higher silicon film.Mixed gas at use silane and hydrogen carries out periodically silane gas being turned off in the glow discharging process, causes periodically having only the glow discharging process of pure hydrogen, thereby periodically film is carried out chemical anneal.This way is easy to be put in the large-scale production process.

Claims

1. a non-adulterated film based on silicon hydride is formed by the plasma enhanced chemical vapor deposition method of using two parallel electrode plates, and it is characterized in that: its formation is made up of following two steps that hocket:

A) amorphous silicon membrane of growth 2-10 nanometer thickness, its way is to use the mixed gas of silane and hydrogen, and substrate temperature is remained between 150-220 ℃, uses 20-100mW/cm ²The radio frequency discharge power density, its growth velocity is not higher than 0.6 nm/sec;

B) apply the plasma discharge of pure hydrogen on above-mentioned amorphous silicon membrane, its time length is at 20-300 between second,

Employed radio frequency discharge power density is 20-80mW/cm ², air pressure is not less than 2mbar.

2. non-adulterated film according to claim 1 based on silicon hydride, it is characterized in that: between described two steps that hocket, the plasma body glow discharging process is not interrupted, and only periodically silane gas is got rid of from the gaseous mixture that is provided.

3. the p-i-n type solar cell of the based thin film silicon of a unijunction or many knots is characterized in that: wherein have at least an i layer to contain non-adulterated film based on silicon hydride according to claim 1 and 2.