CN103367545A - Method for synchronously implementing local contact and local doping at back of solar cell by utilizing laser - Google Patents

Abstract

The invention discloses a method for simultaneously realizing local contact and local doping on the back of a solar cell by using a laser. The method is to redeposit a material containing boron on the passivation layer on the back surface of the solar cell, and use a laser to act on the surface. The doping of the local contact area is completed while forming the local contact window on the back side, and the boron-containing material is finally cleaned and removed. The invention adopts laser film opening, high precision of electrode pattern making, and simultaneously completes doping of local contact area, simplifies process, reduces production cost, and has great advantages in industrialization.

Description

A method for simultaneous localized contact and localized doping on the backside of solar cells using laser light

technical field

The invention belongs to the field of passivation solar cells, in particular to a method for synchronously realizing local contact and local doping on the back of the solar cell by using laser light.

Background technique

In order to reduce the cost of crystalline silicon, the use of thinner silicon wafers is one of the future development trends of the crystalline silicon solar cell industry. However, as the thickness of the silicon wafer becomes thinner, the diffusion length of minority carriers may be close to or greater than the thickness of the silicon wafer, and part of the minority carriers will diffuse to the back of the battery to cause recombination. If no effective measures are taken to reduce this part of the recombination loss , which will adversely affect the battery efficiency. Therefore, for thinned cells, a good rear passivation effect is required. The rear passivated crystalline silicon solar cell has both optical and electrical advantages, and can further improve the efficiency of industrialized solar cells, which is the focus of the next research and development. The PERL (passivated emitter rear local diffused) solar cell prepared by the University of New South Wales (UNSW) has a P-type monocrystalline silicon efficiency as high as 25.0%. Its main feature is double-sided passivation, that is, the front and back of the battery are coated with a passivation layer. Localization and small-area boron diffusion are carried out on the back of the battery. This back design will reduce the contact resistance of the back electrode and increase the boron back field to the battery. The aluminum-steamed back electrode itself is a good back reflector, thereby further Improve the photoelectric conversion efficiency of the battery. For this kind of battery, it is necessary to carry out local film opening treatment on the back passivation layer to form a local contact area; and carry out heavy doping on the local contact area to reduce contact resistance.

At present, the two technologies are often completed independently. The heavy doping of the local contact area is mainly formed on the back surface of the silicon wafer through the mask technology, and finally the high-temperature diffusion is completed. This process increases the production steps. The process is complex.

The local film opening technology of the back passivation layer mainly includes the mask opening technology. This technology is to screen-print an acid and alkali resistant mask material on the surface of the dielectric film, and then use acid and alkali to etch away the area not protected by the mask. , thereby forming an electrode pattern. The mask material can be printed with a screen printing machine, and the minimum line width of the film can reach 40 μm; the direct opening technology of inkjet printing, this technology is to spin-coat a polyacrylic film of a certain thickness on the silicon wafer, and use an inkjet printer The ammonium fluoride solution is ink-jetted on the polyacrylic film according to the electrode pattern, so that hydrofluoric acid is formed at the position of the electrode pattern, and the dielectric film can be opened. This method is simpler than the photolithography process, and the diameter of the opening can reach 40-50 μm. Since hydrofluoric acid is only generated at the position that needs to be etched, the operation is relatively safe. However, the above two technologies require masks or materials similar to masks, and the manufacturing process is complicated, which is not conducive to the industrialization of products. Recently, Merck has developed a slotting technology for screen-printable phosphate-containing corrosive slurry. This slurry can be printed with a screen printing machine commonly used in the PV industry. Depending on the accuracy of screen printing, it is difficult to prepare a pore size below 80 μm.

Contents of the invention

The purpose of the invention is to provide a method for synchronously realizing local contact and local doping on the back side of a solar cell by using a laser.

The technical solution adopted by the present invention is a method for synchronously realizing local contact and local doping on the back of the solar cell by using laser light, which is to redeposit a material containing boron on the passivation layer on the back surface of the solar cell, and use The laser acts on its surface to complete the doping of the local contact area while forming the local contact window on the back, and finally clean and remove the boron-containing material.

Preferably, the material for depositing boron-containing material is a liquid such as boric acid, or a slurry such as boron-containing silicon ink slurry.

Preferably, when the deposited boron-containing material is a slurry such as a boron-containing silicon ink slurry, the silicon wafer needs to be dried at a drying temperature of 60° C. to 90° C. and a drying time of 3 minutes to 10 minutes.

Preferably, the method of depositing the boron-containing material is spin coating, vapor deposition or screen printing.

Preferably, the laser used for the laser action is a green light with a wavelength of 532nm or an ultraviolet solid laser with a wavelength of 355nm, and the process conditions when the laser is applied to the surface are: the laser frequency is 60KHZ~200KHZ, and the energy density is 0.5J/cm ² ~8J/cm ² , the scanning speed is 100mm/s ~8m/s.

As a preference, the cleaning and removal of boron-containing materials adopts the method of ultrasonic cleaning, and the cleaning solution used is anhydrous ethanol, isopropanol or a hydrofluoric acid solution with a concentration of 5% to 15% by mass. 5min~20min.

The present invention mainly comprises three steps, at first, spin-coat the silicon chip containing boron on the back side or the silicon chip that is coated with passivation layer on the backside or both sides through the silicon chip that has been treated with anti-reflection film on the surface before coating, diffusion, edge junction and plated in advance. liquid, such as boric acid or boron-containing silicon ink with a concentration of 10% to 80% by mass, or screen printing and drying a boron-containing slurry, such as a boron-containing silicon ink slurry; then, use a A solid-state laser with a certain power, frequency and scanning speed acts on its surface, and uses the thermal effect of the laser to melt boron atoms into the silicon substrate. After cooling, that is, after the laser is withdrawn, the boron atoms remain in the silicon to form doping. In this process, the passivation layer on the back side can be removed together, so as to achieve localized grooves or openings and localized doping; finally, ultrasonic cleaning of the liquid or slurry on the backside by spin coating or screen printing, cleaning solution It is anhydrous ethanol or isopropanol or a hydrofluoric acid solution with a mass percentage concentration of 5% to 15%, and the cleaned silicon wafer is printed with the back electrode, the aluminum back field and the front silver electrode, and then sintered to complete the solar energy The production of batteries.

The invention redeposits boron-containing material on the passivation layer on the back surface of the solar cell, and uses laser light to act on the surface to complete the doping of the local contact area while forming the back local contact window. In fact, the materials used for deposition may be materials containing group III elements, such as materials containing boron, aluminum, and the like.

The invention adopts laser film opening, high precision of electrode pattern making, and simultaneously completes doping of local contact area, simplifies process, reduces production cost, and has great advantages in industrialization.

Detailed ways

Embodiment 1: use the spin coater to evenly spin-coat the boric acid with a mass percentage concentration of 60% on the back of the battery plated with a passivation layer; be 100KHZ with a frequency, and the 532nm green solid-state laser with an energy density of ^2J /cm acts on it On the surface, the passivation layer is linearly grooved with a line width of 80 μm and a line spacing of 1.0 mm, and boron doping is performed on the grooved area; then the grooved and doped silicon wafer is ultrasonicated in absolute ethanol Wash for 10 minutes.

Example 2: screen-print the silicon ink slurry containing boron on the back of the battery coated with a passivation layer, the thickness of the slurry is 400nm, and dry at 85°C for 5min; then use the frequency at 80KHZ, and the energy density is 3J /cm ² of 532nm green solid-state laser acts on its surface to make dot-shaped holes in the passivation layer with a hole diameter of 150 μm and a hole spacing of 2.0mm, and B doping is performed on the hole area; finally the hole and doping The finished silicon wafers were ultrasonically cleaned for 15 min in a hydrofluoric acid solution with a concentration of 10% by mass.

Claims (6)

1. A method utilizing laser synchronously to realize local contact and local doping at the back of a solar cell, characterized in that the material containing boron is re-deposited on the passivation layer of the back surface of the solar cell, and its surface is utilized to act on the laser, The doping of the local contact area is completed while forming the local contact window on the back side, and the material containing boron is finally cleaned and removed. 2. The method for synchronously realizing localized contact and localized doping on the back side of a solar cell according to claim 1, wherein the material deposited containing boron is a liquid such as boric acid, or a slurry Such as boron-containing silicon ink paste. 3. The method for synchronously realizing localized contact and localized doping on the back side of a solar cell according to claim 2, wherein when the deposited boron-containing material is a slurry such as boron-containing silicon ink When making slurry, silicon wafers need to be dried, the drying temperature is 60°C~90°C, and the drying time is 3min~10min. 4. The method for synchronously realizing local contact and local doping at the back of a solar cell according to claim 1, 2 or 3, wherein the method of depositing a material containing boron is spin coating, Evaporation or screen printing. 5. The method for synchronously realizing localized contact and localized doping on the back of a solar cell according to claim 1, wherein the laser used for the laser action is a green light with a wavelength of 532nm or a wavelength of 355nm For ultraviolet solid-state lasers, the technological conditions when the laser acts on the surface are: the laser frequency is 60KHZ~200KHZ, the energy density is 0.5J/cm ² ~8J/cm ² , and the scanning speed is 100mm/s~8m/s. 6. The method for synchronously realizing local contact and local doping on the back of a solar cell according to claim 1, characterized in that, the cleaning removes boron-containing materials by ultrasonic cleaning. The cleaning solution is absolute ethanol, isopropanol or hydrofluoric acid solution with a concentration of 5% to 15% by mass, and the time is 5min to 20min.