Disclosure of Invention
The invention aims to provide a preparation method of a selective emitter battery, which can reduce the damage area of laser to a battery piece and improve the conversion efficiency of the battery piece.
The purpose of the invention is realized by the following technical scheme:
a preparation method of a selective emitter battery comprises the steps of forming a PN junction by doping source diffusion and manufacturing a selective emitter by laser doping, and is characterized in that in the step of manufacturing the selective emitter by laser doping, doped elements in a region are enriched by changing the energy and the spot size of laser irradiating the region to be metalized on a silicon wafer, so that the selective emitter is formed.
In the invention, the doping source is a phosphorus source.
In the invention, the uniformity and the size of the focused light spot are adjusted by changing the laser incident aperture to obtain a flat-topped light beam.
Further, the laser incident aperture is 6-12 mm.
In the invention, the laser spot width is 80-100 um.
Further, the laser spot width is 80 um.
In the invention, the laser wavelength is 532nm, the laser frequency is 100-260kHZ, and the laser power is 1-100%.
Further, the laser frequency was 190kHZ and the laser power was 100%.
In the invention, the engraving speed of the laser on the silicon wafer is 10000-50000 mm/s.
Preferably, the laser engraves on the silicon wafer at a speed of 26000 mm/s.
In the invention, the thickness of the silicon wafer is 120-240 um.
Compared with the prior art, the invention has the following beneficial effects:
(1) according to the preparation method of the selective emitter battery, the damage area of the laser to the battery piece is reduced by adjusting the energy and the spot size of the laser, different doping areas of the SE in a grid line contact area and a non-contact area are realized, and the battery efficiency is improved.
(2) According to the preparation method disclosed by the invention, the light spot is reduced from 120um to 80um, the open voltage (uoc) is increased by 0.12v, and the Efficiency (ETA) is increased by 0.05%, so that the efficiency is increased.
(3) The preparation method of the Selective Emitter (SE) solar cell does not need to additionally purchase new equipment, and can be realized by only modifying equipment of a laser path on the original SE machine. The method has the advantages of simple process and lower equipment cost, can greatly improve the conversion efficiency of the battery, meets the requirement of high conversion efficiency of the batteries of silicon chips with different thicknesses, and is suitable for large-scale industrial production.
Detailed Description
The present invention is further described below in conjunction with specific examples to better understand and implement the technical solutions of the present invention for those skilled in the art.
The mechanism for improving the battery conversion effect of the embodiment of the invention is as follows:
the particles are in a ground state at normal temperature, and can be pumped to an excited state in a large amount only by injecting energy into a pumping source, so that necessary conditions for generating laser by reversing the number of the particles at upper and lower energy levels are created. The population inversion is only a necessary condition for generating stimulated radiation, and can not generate laser, and only by placing an activating substance in an optical resonant cavity and selecting the frequency and direction of light, continuous light amplification and laser oscillation output can be obtained. When the pumping starts, the loss of the resonant cavity is increased, the oscillation threshold value is improved, the oscillation is difficult to form, at the moment, the number density of the reversed particles of the upper energy level of the laser can be accumulated in a large amount, when the maximum value is accumulated, the loss of the resonant cavity is suddenly reduced, the Q value is suddenly increased, extremely strong oscillation is established in the cavity at an extremely high speed, the reversed particles are greatly consumed in a short time, the particles are converted into light energy in the cavity, and an extremely strong laser pulse is output. The loss is increased by utilizing the diffraction generated by an ultrasonic field in an acousto-optic medium, and laser oscillation cannot be formed; when the population inversion number reaches saturation, the ultrasonic field is suddenly removed, laser oscillation is rapidly established, and giant pulse output is obtained, so that laser doping is realized. The melting temperature of Si is 1414 ℃, and the gasification threshold is 3265 ℃; removing the oxide layer: SiO2 has a band gap width of 9eV (355nm violet photon energy of 3.5eV), Si has a band gap width of 1.12eV, and meltingThe point is 1650 ℃, so that 532nm green light can transmit SiO2Directly reacting with the substrate; doping P for diffusion: p has a diffusion rate of 10 in the liquid phase-4cm2The diffusion speed is 7 orders of magnitude higher than that of a solid phase, and the doping junction depth depends on the diffusion rate of impurities and the melting depth; solidification of Si in molten state: and cooling the molten Si to form a polycrystalline silicon layer. As the laser power increases, the doping concentration increases and the sheet resistance becomes smaller; when the power is continuously increased, the doped silicon material is melted and gasified, so that the sheet resistance is increased; thickness W of laser doped layer 17.5+0.3Nlasernm surface impurity concentration n-1.1 x 1014nlasercm-2,nlaserThe number of laser pulses; the longer the laser wavelength is, the stronger the penetration capability is, the deeper the position of the silicon for the maximum absorption of the laser is, and the larger the corresponding maximum doping depth is; the textured surface has a good light trapping effect, and more effective laser coupling can be obtained; laser heat diffusion length: l ═ 4D τ1/2τ is the laser pulse width; the maximum melting depth of the short-pulse-width laser is less than that of the long-pulse-width laser, and the maximum doped junction depth of the short-pulse-width laser is larger than that of the long-pulse-width laser, so that the minimum value of the sheet resistance of the short-pulse-width laser doping is larger.
A method of making a selective emitter cell, comprising the steps of:
(1) cleaning and texturing silicon wafers: selecting a lightly doped p-type monocrystalline silicon wafer with the resistivity of 0.1-6 omega-cm, and carrying out alkali texturing on the p-type silicon wafer to form a pyramid-shaped anti-reflection textured surface on the front surface and the back surface of the p-type silicon wafer substrate, wherein the weight reduction range of texturing is 0.5-0.8g, and the reflectivity (full waveband 300-1200nm) range is 10% -18%.
(2) And (3) forming a PN junction by phosphorus source diffusion: and (3) placing the silicon wafer in a furnace tube at 500-800 ℃ for phosphorus diffusion, forming an n-type layer on the surface of the silicon wafer within 5-50 min to form a PN junction, wherein the diffusion sheet resistance is 100-180 ohm/sq.
(3) Removing PN junctions at the edge of the silicon wafer; plasma etching, laser edge etching or chemical etching can be used; please refer to the prior art for a specific process of removing the edge PN junction. And (3) forming a heavily doped region by SE laser grooving: irradiating the region to be metallized on the silicon wafer with laser to dope the regionPhosphorus element enrichment, form the selectivity emitter, laser wavelength is 532nm, laser sculpture speed is 26000mm/s, laser power 100%, laser frequency is 190KHz, laser facula width is 80 um. The reduction of the laser focusing spot is realized by adjusting the laser beam expander to enlarge the beam diameter, as shown in fig. 3, wherein the spot size df≈4·λ·f/Π·d1In the formula d1In this embodiment d is the beam diameter1Is 8 mm. By changing the path of the laser SE light path, the beam expander and the beam shaper, a more uniform flat-top beam is obtained.
(4) Removing the PSG (phosphosilicate glass) on the front surface of the silicon wafer by referring to the prior art. Jijiawei invasive oxidizing annealing for 800-1200s at 760 ℃.
(5) ALD or PECVD backside Al2Ox passivation; the thickness of the Al2Ox film is in the range of 4-12 nm.
(6) PECVD SiN platingXPlating SiNx antireflection films on the front and back surfaces; the SiNx film thickness of the front surface and the back surface is 75-90nm and 100-130nm respectively; the front reflectivity (full wave band 300-1200nm) is between 4% and 9%.
(7) The front and back sides are screen-printed with Ag grid lines, and the sintering furnace is used for co-firing, and the specific process of preparing the electrode and sintering the electrode refers to the prior art.
(8) Back electrode printing: and printing a metal back electrode on the back of the silicon wafer by adopting a screen printing method, wherein the adopted metal is silver aluminum (Ag).
(9) Al back surface field printing: and printing an Al back surface field on the back surface of the silicon wafer by adopting a screen printing method.
(10) Front electrode printing: the metal used for printing the front metal electrode on the front surface by the screen printing method is silver (Ag).
(11) Sintering + LIR: and sintering the printed silicon wafer in a sintering furnace.
Performance testing
The sheet resistance, surface concentration and junction depth of the selective emitter obtained in the example were measured, and the comparative example was different from the example in that the laser spot was 120um, and the results are shown in table 1.
TABLE 1 sheet resistance, surface concentration and junction depth of the selective emitters prepared in the examples and comparative examples
The selective emitter cells prepared in the examples were subjected to electrical performance tests, which included open circuit voltage (Uoc), short circuit current (Isc), series resistance (Rs), parallel resistance (Rsh), Fill Factor (FF), conversion efficiency (Ncell), and reverse current 2(Irev2), and the comparative example was different from the examples in that the laser spot was 120um, and the test results were as shown in table 2.
Table 2 electrical properties of selective emitter cells prepared in examples and comparative examples
The percentage of the damaged area of the cell piece of the selective emitter cell prepared in the example was tested, and the change of the damaged area of the cell piece in the percentage of the area of the cell piece with the change of the laser spot size is shown in table 3 and fig. 5.
TABLE 3 percentage of damaged area of cell sheet to area of cell sheet changing with laser spot size
The sheet resistance of the selective emitter cells prepared in the examples was tested, as shown in table 4.
Table 4 sheet resistance of selective emitter cells prepared in the examples
Diffusion sheet resistance (ohm/sq)
|
SE Square resistance (ohm/sq)
|
Decrease of sheet resistanceValue (ohm/sq)
|
145
|
93
|
52
|
146
|
96
|
50
|
147
|
92
|
55
|
148
|
89
|
59
|
149
|
92
|
57
|
150
|
94
|
56
|
148
|
89
|
59
|
152
|
90
|
62
|
150
|
91
|
59
|
154
|
93
|
61
|
147
|
92
|
55
|
153
|
93
|
60
|
147
|
89
|
58
|
148
|
91
|
57 |
The above embodiments illustrate various embodiments of the present invention in detail, but the embodiments of the present invention are not limited thereto, and those skilled in the art can achieve the objectives of the present invention based on the disclosure of the present invention, and any modifications and variations based on the concept of the present invention fall within the scope of the present invention, which is defined by the claims.