A kind of solar cell selective doping method based on counter diffusion
Technical field
The present invention relates to a kind of solar cell selective doping method based on counter diffusion, belong to technical field of solar cell manufacturing.
Background technology
Along with the raising of people's environmental consciousness, day by day vigorous for the demand of clean energy resource.In the new cleaning fuel of people's research, solar energy becomes as a kind of clean energy resource of regional limits that is not subjected to the main direction that Future New Energy Source develops.Solar cell is that people utilize the transform light energy of the sun to be the main device of electric energy.But the conversion efficiency of solar cell can't reach people's requirement at present.Improve the conversion efficiency of solar cell, the manufacturing cost that reduces solar cell becomes the focus of people's research.
The selective doping solar cell is a kind of solar cell of effective low-cost high-efficiency.The design feature of selective doping solar cell is to carry out in the top electrode overlay area of solar cell the contact resistance that heavy doping reduces battery, simultaneously carry out light dope in non-top electrode district, improve the spectral response of battery and reduce the compound of photo-generated carrier in battery.The method of carrying out at present the solar cell selective doping mainly contains: two step diffusion methods, silk screen printing phosphorus slurry method, diffusion mask method etc.Wherein, two step diffusion methods are first the top electrode district heavily to be spread, more whole emitter region is gently spread, and its advantage is that preparation is simple, and still, the district first spreads due to top electrode, the more difficult control of the quadratic distribution of impurity; Silk screen phosphorus slurry method is at part printing high concentration phosphorus slurry with silk screen, by its diffusion and volatilization, One Diffusion Process just can make top electrode district's formation heavy doping, other zones form light dope, but owing to having utilized local phosphorus slurry as diffuse source, the inhomogeneities that must cause diffusion into the surface, this can reduce the efficient of battery.The diffusion mask method is exactly first light dope, carry out again laser or photo etched mask, and then to the top electrode district carrying out secondary heavy doping, the method is owing to first having carried out light dope, reduced the top electrode district when carrying out selective doping and the impurity concentration of substrate poor, can control preferably the selective doping zone of battery, but need to be with the method for laser or photoetching, improve cost, reduced production efficiency.
In sum, at present all there is certain defective in the method for main selective doping, therefore, must seek a kind of manufacture of solar cells technique of novel selective doping.
Summary of the invention
The object of the invention is to: overcome the defective of above-mentioned prior art, propose a kind of solar cell selective doping method based on counter diffusion, technique realizes simple, and production cost is low, and the solar cell properties of acquisition is good.
In order to achieve the above object, the solar cell selective doping method based on counter diffusion that the present invention proposes comprises the steps:
The 1st goes on foot, silicon chip is placed in carries out High temperature diffusion under the wet oxygen environment, forms PN junction, and the silicon chip upper surface generates oxide layer simultaneously, contains the doped chemical of high concentration in this oxide layer;
The 2nd goes on foot, removes silicon chip upper surface top electrode district oxide layer in addition;
The 3rd the step, at silicon chip upper surface deposition of intrinsic amorphous silicon layer;
The 4th step, silicon chip is placed in the wet oxygen environment carries out High temperature diffusion, make the doped chemical in the non-top electrode of silicon chip district diffuse into amorphous silicon layer, reduce the non-top electrode of silicon chip district doped chemical concentration, realize the reverse diffusion of doped chemical; Doped chemical in top electrode district oxide layer realizes the heavy doping in top electrode district to the diffusion of top electrode district, simultaneously the oxidized formation oxide layer of silicon chip surface in amorphous silicon layer and non-top electrode district;
The 5th goes on foot, removes the oxide layer of silicon chip surface, completes the counter diffusion selective doping of solar cell.
The present invention proposes a kind of selective doping method of counter diffusion, absorb the impurity of non-electrode district by amorphous silicon, the doping content of non-electrode district is reduced, electrode district has carried out secondary doping simultaneously, cause the poor further increase of doping content of electrode district and non-electrode district, improved the effect of selective doping; And when counter diffusion technique was carried out, due to the protection that is subject to oxide layer, the silicon chip surface degree of oxidation of electrode district was low; but not the silicon face of electrode district oxidized formation oxide layer; thereby after removing oxide layer, electrode district presents to a certain degree evagination, is conducive to the location of subsequent electrode.
The present invention further improves and is:
1, described silicon chip is p type single crystal silicon, in the 1st step, at first silicon chip is placed in and carries out the High Temperature Pre diffusion under the wet oxygen environment, makes P elements diffuse into silicon chip and forms PN junction, simultaneously the oxidized formation phosphorosilicate glass of silicon chip surface.
2, in the 1st step, oxidated layer thickness is about 0.05 micron, and in oxide layer, the concentration of P elements is about 1e19/cm
3, the technological temperature of High Temperature Pre diffusion is 1000 ℃, the duration is 30 minutes.
3, described silicon chip is n type single crystal silicon, in the 1st step, at first silicon chip has been placed in and has carried out the High Temperature Pre diffusion under the wet oxygen environment, makes boron element diffuse into silicon chip and forms PN junction, simultaneously the oxidized formation Pyrex of silicon chip surface.
4, in the 1st step, oxidated layer thickness is about 0.05 micron, and in silicon thin layer, the concentration of boron element is about 1e19/cm
3, the technological temperature of High Temperature Pre diffusion is 1000 ℃, the duration is 30 minutes.
5, in described the 2nd step, the method for employing silk screen printing keeps the oxide layer in top electrode district, utilizes buffered hydrofluoric acid solution to get rid of other regional oxide layer on silicon chip.
6, in described the 3rd step, the intrinsic amorphous silicon layer thickness of deposit is about 40-50nm.
7, in described the 4th step, the technological temperature of High temperature diffusion is 900 ℃-1100 ℃, and the duration is 30-2 minute.
8, in described the 5th step, adopt buffered hydrofluoric acid solution to remove the oxide layer of silicon chip surface.
The characteristics of this process of the present invention are:
1, be different from traditional selective doping technique, employing be first full sheet heavy doping, rear reverse diffusion sensitive surface impurity reduces the method for the impurity doping content of sensitive surface.
2, use the intrinsic amorphous silicon film absorption battery surface impurity of doped region, make the battery surface can be by other different element pollutions.
3, keep the phosphorosilicate glass of electrode district as the electrode impurities protective layer of the reverse diffusion technology of high temperature impurity, guaranteed the heavy doping of electrode district.
4, adopt the method for wet oxidation in the reverse diffusion process of impurity, make the amorphous silicon layer oxidation, reduced the step of removing amorphous silicon membrane, improved production efficiency.
Description of drawings
The present invention is further illustrated below in conjunction with accompanying drawing.
Fig. 1 is the process flow diagram of the inventive method.
Fig. 2 is the embodiment of the present invention one resulting silicon chip Impurity Distribution of method emulation schematic diagram.
Fig. 3 is the embodiment of the present invention two resulting silicon chip Impurity Distribution of method emulation schematic diagrames.
Fig. 4 is the embodiment of the present invention three resulting silicon chip Impurity Distribution of method emulation schematic diagrames.
Embodiment
The present invention will be further described below in conjunction with the drawings and specific embodiments.
Embodiment one
Be illustrated in figure 1 as the schematic flow sheet of the solar cell selective doping method that the present invention is based on counter diffusion, specifically comprise the steps:
1a, the p type single crystal silicon sheet is placed in carries out High Temperature Pre diffusion under the wet oxygen environment, make P elements diffuse into silicon chip and form PN junction, silicon chip surface forms thickness and is about the phosphorosilicate glass layer 1 of 0.05 micron simultaneously, and in phosphorosilicate glass layer 1, the concentration of P elements is about 1e19/cm
3The technological temperature of High Temperature Pre diffusion is 1000 ℃, and the duration is 30 minutes;
The phosphorosilicate glass that the method for 2a, employing silk screen printing keeps the top electrode district utilizes buffered hydrofluoric acid solution to get rid of other regional phosphorosilicate glass on silicon chip;
3a, be about the intrinsic amorphous silicon layer 2 of 40nm at silicon chip upper surface deposition thickness;
4a, the environment that silicon chip is placed in wet oxygen carry out High temperature diffusion, make the doped chemical (phosphorus) in the non-top electrode of silicon chip district diffuse into amorphous silicon layer, reduce the non-top electrode of silicon chip district doped chemical concentration, realize the reverse diffusion of doped chemical; Doped chemical (phosphorus) in top electrode district oxide layer realizes the heavy doping in top electrode district to the diffusion of top electrode district, simultaneously the oxidized formation phosphorosilicate glass layer 1 of silicon chip surface in amorphous silicon layer and non-top electrode district; The technological temperature of High temperature diffusion is 900 ℃, and the duration is 30 minutes;
5a, employing buffered hydrofluoric acid solution are removed the phosphorosilicate glass of silicon chip surface, complete the counter diffusion selective doping of solar cell.
After utilizing simulation software to carry out emulation to the present embodiment one method, the interior impurity of silicon chip divides sees Fig. 2.Curve in simulation result figure represents respectively the concentration of doped chemical (phosphorus) and the position of PN junction.
Embodiment two
The step of the present embodiment is identical with embodiment one, and difference is the 4th step of step 4a() in the technological parameter of High temperature diffusion under dried oxygen environment, in the present embodiment, the technological temperature of High temperature diffusion is 1000 ℃, the duration is 5 minutes.After utilizing simulation software to carry out emulation to the present embodiment two methods, the interior impurity of silicon chip divides sees Fig. 3.Curve in simulation result figure represents respectively the concentration of doped chemical (phosphorus) and the position of PN junction.
Embodiment three
The step of the present embodiment is identical with embodiment one, and difference is the 4th step of step 4a() in the technological parameter of High temperature diffusion under dried oxygen environment, in the present embodiment, the technological temperature of High temperature diffusion is 1100 ℃, the duration is 2 minutes.After utilizing simulation software to carry out emulation to the present embodiment three methods, the interior impurity of silicon chip divides sees Fig. 4.Curve in simulation result figure represents respectively the concentration of doped chemical (phosphorus) and the position of PN junction.
Contrast the present invention three embodiment can find out from simulation result figure, and along with the rising of the High temperature diffusion temperature of reverse diffusion technology, the PN junction of battery is in continuous intensification.The impurity concentration on the surface of battery first increases afterwards and reduces, but the impurity concentration in top electrode district progressively increases along with the increase of temperature.The heavy doping impurity in top electrode district mainly spreads in cell body, and horizontal proliferation is less, and this is absorbed by amorphous silicon layer with relevant at battery surface deposition of intrinsic amorphous silicon layer, too much horizontal proliferation impurity.This application amorphous silicon layer can play restriction heavily doped region impurity horizontal proliferation effect as the counter diffusion layer of battery.The impurity concentration of lightly doped region is more approaching, lower diffusion temperature can form shallow junction effectively, improve battery shortwave spectral response, comprehensively relatively after, step 4a(the 4th step as can be known) in to adopt 900 ℃ of diffusion temperatures, 30 minutes duration of diffusion be the process conditions of impurity counter diffusion preferably.
Embodiment of the present invention part has been described in detail technique of the present invention as an example of p type single crystal silicon example, technique and the condition of n type single crystal silicon being carried out selective doping are similar with it, difference only is that doped chemical has changed boron into by phosphorus, those skilled in the art fully can be by understanding the present embodiment part, draws inferences about other cases from one instance to realize the counter diffusion selective doping to n type single crystal silicon.Therefore this paper repeats no more.
In addition to the implementation, the present invention can also have other execution modes.All employings are equal to the technical scheme of replacement or equivalent transformation formation, all drop on the protection range of requirement of the present invention.