JPS5810872A - Manufacture of solar battery - Google Patents

Abstract

PURPOSE:To improve the effect of the electric field at the back surface, by heating the interface between a substrate and the electrode layer on the back surface by laser light, diffusing aluminum, and forming a P<+> type layer on the surface of the semiconductor substrate. CONSTITUTION:An N type semiconductor layer (2) is formed on the surface of one side of the P type silicon semiconductor substrate (1). Then the back surface electrode layer (4) comprising aluminum or alloy including aluminum is formed on the back surface 3, i.e. on the other side of the substrate (1). Then the laser light is irradiated, diffusion is selectively performed in the substrate (1) which is adjacent to the back surface electrode (4), and the P<+> type layer (5) is formed. Then a surface electrode layer (6) is formed. Since furnace burning is not used in forming the aluminum diffused layer, the degradation in a life time in the silicon substrate is avoided, and the manufacture of the highly efficient solar battery having the effect of the electrid field at the back surface can be facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a solar cell, and more particularly to a method of manufacturing a solar cell or cell that improves the back surface field effect.

Conventional methods for manufacturing solar cells, such as solar cells using a silicon semiconductor substrate, involve thermally diffusing phosphorus on the surface at high temperatures when using P-type silicon as the substrate. By forming a conductive layer? First, P twill is formed. Next, the electrode metal is formed in a lattice shape on the back surface in order to increase the incidence of light on each surface. Furthermore, each step of forming an anti-reflection film on the surface is followed.

In recent years, the efficiency of solar cells obtained in this way has been improved, and in particular, back surface field effects have been used to significantly improve sensitivity to long wavelength light that generates carriers near the back electrode.
cffs+ct). According to this device, the structure is not changed on the front side, but on the back side, an impurity of the same conductivity type is introduced into the substrate surface to form a high concentration layer of the same type, and the carriers generated near the back side are driven by an internal electric field. The aim is to collect waste effectively and increase efficiency. In order to implement this technique, a high concentration layer is formed on the back surface of the substrate with the same type of impurity by alloying by heating in a furnace or by a diffusion method, or a low concentration layer is epitaxially grown on a high concentration plate and applied to this type of substrate. Measures are being taken. For pH silicon substrates, attach a film such as an aluminum vapor-deposited film, an aluminum paste printed film, or a thermocompression-bonded film of aluminum foil, and heat the film to 800 to 850% in a furnace.
The most commonly used method is to diffuse aluminum into silicon by sintering at 0°C.

However, with this heat treatment, the silicon substrate suffers heat damage and the minority carrier lifetime in the P-type layer is significantly reduced, so even if a back electric field is provided, a sufficient improvement in efficiency cannot be achieved.

The present invention provides a method for manufacturing a solar cell that eliminates these drawbacks and improves the back electric field effect, namely (1)
A step of forming an n-type semiconductor layer on one surface of the P-type silicon semiconductor substrate, a step of forming a back electrode layer made of aluminum or an alloy containing aluminum on the other surface of the semiconductor substrate, and irradiating the semiconductor substrate with a laser beam. "tsq, bx thirstq
a step of selectively heating the interface between the semiconductor substrate and the back electrode layer to diffuse aluminum into the semiconductor substrate adjacent to the back electrode layer to form a P9 type layer; and a step of forming a front electrode. Battery manufacturing method, and (2) P
forming an n-type layer by diffusing an n-type impurity on one surface of the type silicon semiconductor substrate; forming a back electrode layer made of aluminum or an alloy containing aluminum on the other back surface of the semiconductor substrate; A process of selectively heating the interface between the semiconductor substrate and the back electrode layer by irradiating laser light to diffuse aluminum into the semiconductor substrate adjacent to the back electrode layer to form a P9 type layer; The method for manufacturing a solar cell according to item 1 above includes the step of forming a layer. This invention suppresses heat damage to the substrate by heating the interface between the substrate and the back electrode layer using a laser beam and diffusing the aluminum, without impairing the lifetime of the P-type layer (back surface electrode layer). A P" type layer is formed on the surface of a semiconductor substrate adjacent to an electrode layer to obtain a solar cell with improved efficiency.

It was a problem that if the backside electric field was made 90%, it would be possible to form a backside electric field without impairing the lifetime in the silicon substrate. Using the conventional method, a 305 mm thick aluminum vapor-deposited film or printed film of aluminum paste is formed on the back surface of an R-type silicon substrate, and this substrate is heat-treated in a furnace to produce P''!
When a method of forming one layer is adopted, the lifetime is significantly reduced. For example, even if the original wafer had a lifetime of 8asec, it became 2.7μSec after heat treatment.
It drops to c. Here, this lifetime was measured by a well-known method of generating electron-hole pairs with a laser beam, irradiating them with microwaves, and determining the attenuation of the reflected intensity. Form a film, heat slowly in 9 elemental gas, slowly cool,
The condition is to hold the maximum temperature at 815-820° C. for ~3 minutes.

On the other hand, in the case of the method of the present invention in which aluminum is diffused using I/-the light to form a similar P''' type layer, the lifetime is, for example, 64 lee, and a slight decrease can be expected. In this example as well, the aluminum vapor deposited film formed on the back surface of the substrate has a thickness of 30. In order to achieve the same aluminum diffusion as in the case of furnace firing described above, the aluminum vapor deposited film is formed on the substrate side from the interface between the back electrode layer and the substrate. The sheet resistance and diffusion depth of the aluminum-silicon alloy layer were sequentially measured and irradiated with laser light for 4 hours, with the laser power and irradiation conditions appropriate.The back electric field effect produced by furnace burning was made effective. In the solar cell described above, the sheet resistance of the aluminum silicon alloy surface was 18 Ω/hole, so the laser beam irradiation conditions were adjusted accordingly, and the output of the YAG laser was changed in various ways to achieve the appropriate conditions. .

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view of a solar cell formed by the manufacturing method of the present invention. A de-type silicon substrate (1) with a surface index (10G) and a specific resistance of 1Ω·− is prepared. This substrate is manufactured by the FZ method, and the minority carrier lifeter (2) is attached to the substrate.
Formed on the side surface side. For this purpose, phosphorus oxytrichloride (POCJ) is deposited for 20 minutes at 890° C. using a gas phase, followed by 10 minutes of drive-in to diffuse it to a high concentration. This results in a highly doped region of damaged holes on the surface, the so-called multi-defect layer (
The lead layer (lead 1 ayer) is removed by etching, and a bond with a bond depth of 0.2 jm is formed with moderate surface preparation and little damage.

Next, an aluminum film is formed as a back electrode (4) on the back surface (3) of the other side of the substrate. Aluminum is evaporated by irradiating a pure [99.99% aluminum evaporation source with a beam current of 0.2 μm and an accelerating voltage of 3 KV with a concentrated electron flux] in a vacuum of less than 1 orr. The so-called electron beam evaporation method may be used in which a film is formed on a substrate placed in the same vacuum chamber. However, in order to increase the adhesion of the film, the substrate temperature during evaporation is set at 300" C, and the evaporation rate is set at 30,001" C.
/w+! A film of 30 IAm was formed using a.

Next, a laser beam is irradiated onto this aldinium film to heat the vicinity of the aluminum-silicon boundary layer, forming a P′″ type layer (5
) is formed. The laser used was a Q-switched YAG laser with an oscillation wavelength of 1.06 .mu.m, an output of IKW, and a pulse frequency of 5 KH, and a galvanometer mirror scanner was used to uniformly irradiate the entire 3-inch aluminum surface of the substrate.

Next, a surface electrode (Ω) is formed. First, the surface oxide film is removed with a dilute aqueous solution of hydrofluoric acid, and then a lattice-like fine three-layer metal electrode is formed by repeating vacuum evaporation and photoetching. The surface electrode is formed as an example surface electrode.This surface electrode is composed of 8001 titanium (7), 500X palladium (8), and 5j1m silver (9) from the silicon side. A silver layer 01 having a thickness of 5 Jm is formed by vapor deposition for the purpose of reducing resistance and facilitating lead wire extraction.

Furthermore, in order to reduce reflection loss on the incident surface of sunlight, a tantalum pentoxide film aυ is formed on the surface electrode (2) using a sputtering method. Finally, the diffusion layer on the periphery of the substrate is removed, and an encap material az and a lead (13°a numbering) are applied.

When the formed solar cell was irradiated with sunlight at 100 mW/- and its characteristics were investigated, the open circuit voltage was 0.61 V, and the short circuit current was 3.
A conversion efficiency of 6 mA/j and a conversion efficiency of $16.5% was obtained, compared to a conversion efficiency of 14.7% for the same structure made using the conventional furnace annealing method of alloying aluminum and silicon. The characteristics have been significantly improved. Moreover, when the spectral ratio is measured including both of them, the results shown in FIG. 2 are obtained. Actual es*a B relates to a conventional example that does not have a back electric field effect, point S** relates to an example in which a back electric field effect is provided by firing in a furnace, and the dot-dash line curve C relates to a conventional example that does not have a back electric field effect. This relates to an example that has an electric field effect. Example 0 has better characteristics in the long wavelength range than Example A, but is rather inferior in the short wavelength range due to the reduced lifetime in the substrate.

In example C, there is less decrease in lifetime in the substrate, so an improvement effect is seen in both long wavelength and short wavelength regions compared to example A [7].
This results in improved efficiency under sunlight.

In this embodiment, the II9 type layer is formed by diffusing impurities into the P type substrate, but the substrate may also be one in which an n type layer is epitaxially grown on a p type layer to form a junction.

As described above, according to the present invention, it is possible to easily manufacture a solar cell without using furnace firing to form an aluminum diffusion layer adjacent to an electrode layer on the back surface of a substrate.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a solar cell according to the manufacturing method of the present invention;
FIG. 2 is a comparative characteristic diagram of solar cells according to the present invention and conventional manufacturing methods. (1)...Substrate (2)...Otori''' type layer (4)...Back electrode layer (5)...P0 type layer (6)...Surface electrode agent Patent attorney Inoue -Column 1st figure 2nd figure wave-1c (pm)

Claims (2)

[Claims] (1) A process of forming an n-type semiconductor layer on a PIN silicon semiconductor substrate and selectively heating the interface between the semiconductor substrate and the back electrode layer by irradiating aluminum or ν laser light at t'5-ax. Including the process of aluminizing 4! A method for manufacturing solar cells. (2) Step of diffusing nWi impurities onto m surfaces of the Flu silicon semiconductor substrate to form mm, and forming a back electrode layer made of aluminum or an alloy containing aluminum on the other back surface of the semiconductor substrate. Aluminum is diffused into the semiconductor substrate adjacent to the back electrode layer by heating the interface between the semiconductor substrate and the back electrode layer. Claim 1 characterized in that it includes a step of forming a pQ m layer and a step of forming a surface electrode layer.
The method for manufacturing the solar cell described in section.