CN110010721B - A SE-based Alkali Polishing High Efficiency PERC Cell Process - Google Patents

Abstract

The invention discloses a high-efficiency PERC battery process for alkali polishing based on SE. Alkali polishing: using an optimized alkali polishing formula to perform alkali polishing on silicon wafers; additives and alkali replenishing solutions used in alkali polishing are all added in a stepped manner. : Batch 1-15, the additive rehydration volume is 200-350ml, the alkali rehydration volume is 300-1000ml, and the pure water rehydration volume is 7-9L; the 16-30 batch, the additive rehydration volume is 250-400ml, the alkaline rehydration volume is 250-400ml The volume is 850-1150ml, and the pure water replenishment volume is 8-10L; for batch 31-60, the additive replenishment volume is 300-500ml, the alkali replenishment volume is 1000-1300ml, and the pure water replenishment volume is 9-11L. The invention adopts the optimized alkali polishing formula, and the supplementary method of additives and alkali replenishment adopts the step supplementary method, which effectively prolongs the service life of the alkali polishing tank and achieves the improvement of production capacity, and meanwhile, the consumption of additives and alkali is greatly reduced. , to break through the capacity bottleneck of alkali polishing SE.

Description

A SE-based Alkali Polishing High Efficiency PERC Cell Process

technical field

The invention relates to the technical field of photovoltaic solar cells, in particular to an alkali polishing high-efficiency PERC cell process based on SE.

Background technique

PERC cell technology has significant performance and cost advantages, driving the application of p-type solar-grade monocrystalline silicon wafers. At the same time, high efficiency, low cost and environmental protection are the mainstream directions for the development of crystalline silicon solar cells. PERC cells mainly form a passivation film on the back side, which requires the back surface to have good flatness. The main research of alkali polishing equipment focuses on polishing the back side, which not only solves the flatness problem of the backside coating, but also can Remove the back N-type diffusion layer, promote the formation of the P+ layer, improve the minority carrier lifetime, and increase the reflectivity of the back surface. Therefore, the introduction of polishing process into the existing production process of PERC cells is an effective means to further improve the efficiency of PERC cells.

Alkali-polished cells have attracted much attention in the photovoltaic market due to their simple equipment process, unique process flow and high cell efficiency. Laser doping (SE) has the advantages of strong controllability, simple process, and small laser-induced damage to materials, and is an ideal technical choice for the preparation of high-efficiency crystalline silicon solar cells. The selective melting and diffusion characteristics of the laser doping process can be used to fabricate selective emitter structures in silicon-based solar cells. In this structure, light doping is carried out in the light absorption region, which reduces the surface minority Auger recombination, and the short-wave spectral response is good; heavy doping is carried out in the metal contact region to form a good bond between the metal electrode and the battery emitting region. Ohmic contact, its short circuit current, open circuit voltage, fill factor and conversion efficiency are higher.

Regarding the alkali polishing technology and SE technology, it can be concluded that there are still obvious defects in the PERC battery technology in the prior art: the existing formulations and usage methods of alkali polishing additives and alkali replenishment solutions, the original formula is 1-30 batches. Add the same amount of additives and alkali infusion. Add 300ml of additives in each batch, add 1050ml of alkali infusion, and add 9L of pure water infusion. The above-mentioned existing infusion method cannot effectively extend the liquid in the alkali throwing tank. Long life, so that the production capacity cannot be increased, and the consumption of additives and alkalis cannot be used to save production capacity, so it is impossible to break through the production capacity bottleneck of alkali polishing SE.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an alkali-polished high-efficiency PERC cell process based on SE, so as to solve the problems raised in the above-mentioned background art.

To achieve the above object, the present invention provides the following technical solutions:

A SE-based alkali-polished high-efficiency PERC cell process, comprising the following steps:

Step S01, texturing: the monocrystalline silicon wafer is subjected to surface texturing to obtain a textured structure;

Step S02, diffusion: introducing phosphorus oxychloride and silicon wafer to react to realize diffusion junction;

Step S03, SE process: the selective emitter is on the lightly doped silicon substrate, and the heavy doping of impurity atoms is selectively carried out by a micron-sized laser beam;

Step S04, thermal oxygen: after the SE process, a high-temperature thermal oxygen process is added to produce and deposit a silicon dioxide protective layer on the surface of the silicon wafer;

Step S05, removing the PSG: removing the edge PN junction by etching the PSG;

Step S06, alkali polishing: using the optimized alkali polishing formula to perform alkali polishing on the silicon wafer;

Step S07, annealing: annealing the silicon wafer after alkali polishing, and producing and depositing a silicon dioxide film on the surface of the silicon wafer;

Step S08, back passivation: depositing an aluminum oxide passivation film on the back of the silicon wafer by ALD or PECVD;

Step S09, back film: growing and depositing a silicon nitride film on the back of the silicon wafer;

Step S10, positive film: growing and depositing a silicon nitride film on the front side of the silicon wafer;

Step S11, laser slotting: laser slotting is performed on the back of the coated silicon wafer;

Step S12, printing and sintering: complete the back and front printing by screen printing, and then carry out the sintering process;

Step S13, electric injection: pass through a light decay furnace or an electric injection furnace;

Step S14, testing and sorting: finally, the battery cells are tested and sorted;

The optimized alkaline polishing formula includes three kinds of alkaline polishing solutions, one of which includes 200-350ml of additive rehydration, 300-1000ml of alkaline rehydration and 7-9L of pure water rehydration; the other includes 250-400ml of additive rehydration, 850-1150ml alkaline rehydration solution and 8-10L pure water rehydration solution; the third includes 300-500ml additive rehydration solution, 1000-1300ml alkaline rehydration solution and 9-11L pure water rehydration solution;

In step S06, the optimized alkali polishing formula used in the alkali polishing is supplemented in a stepped manner:

For batches 1-15, the additive rehydration volume is 200-350ml, the alkali rehydration volume is 300-1000ml, and the pure water rehydration volume is 7-9L;

For batches 16-30, the additive rehydration volume is 250-400ml, the alkali rehydration volume is 850-1150ml, and the pure water rehydration volume is 8-10L;

For batches 31-60, the additive rehydration volume is 300-500ml, the alkali rehydration volume is 1000-1300ml, and the pure water rehydration volume is 9-11L.

Preferably, potassium hydroxide solution is selected as the alkali infusion solution.

Compared with the prior art, the beneficial effects of the present invention are:

The invention adopts the optimized alkali polishing formula, and the supplementary method of additives and alkali replenishment adopts the step supplementary method, which effectively prolongs the service life of the alkali polishing tank and achieves the improvement of production capacity, and meanwhile, the consumption of additives and alkali is greatly reduced. , to break through the capacity bottleneck of alkali polishing SE.

Description of drawings

Fig. 1 is the traditional process flow diagram of the prior art;

Fig. 2 is the process flow diagram of the preparation method of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Please refer to Figure 1-2, the present invention provides a technical solution:

A SE-based alkali-polished high-efficiency PERC cell process, comprising the following steps:

Step S01, texturing: the monocrystalline silicon wafer is textured on the surface to obtain a good textured structure, so as to increase the specific surface area to receive more photons (energy), reduce the reflection of incident light, and clean the residual liquid during texturing , reduce the impact of acidic and alkaline substances on the battery junction.

Step S02, Diffusion: Phosphorus oxychloride reacts with the silicon wafer to obtain phosphorus atoms. After a certain period of time, the phosphorus atoms enter the surface layer of the silicon wafer, and penetrate and diffuse into the silicon wafer through the gaps between the silicon atoms, forming a The interface between the N-type semiconductor and the P-type semiconductor completes the diffusion junction process and realizes the conversion of light energy to electrical energy.

Step S03, SE process: (selective emitter) The selective emitter is on the lightly doped silicon substrate, and the heavily doped region of impurity atoms is selectively carried out by a micron-sized laser beam to effectively form a low The surface concentration shallow junction process can also ensure the ohmic contact of the printed grid line area.

Step S04, hot oxygen: in order to prevent the damage of the suede surface in the SE area by alkali polishing, the post-SE hot oxygen process is added. The efficiency of PERC+SE can reach more than 22%, and a silicon dioxide protective layer is formed on the heavily doped region.

Step S05, removing the PSG: Since the diffusion junction forms a short-circuit channel at the edge of the silicon wafer, the photogenerated electrons collected on the front side of the PN junction will flow to the back side of the PN junction along the area where phosphorus is diffused along the edge, resulting in a short circuit. After removing the PSG, the edge PN junction is etched and removed to avoid short circuit caused by the edge. Then, the phosphorous silicate glass on the surface of the silicon wafer is removed through an alkali polishing tank to reduce the influence of the phosphorous silicate glass on the efficiency.

Step S06, alkali polishing: the main principle of the PERC battery is to prepare the aluminum oxide passivation film layer 5 on the back side, which requires the back surface to have good flatness. The current research mainly focuses on polishing the back side, which not only solves the problem of It solves the flatness problem of the backside coating, and can remove the N-type diffusion layer on the backside, promote the formation of the P+ layer, improve the minority carrier lifetime, and increase the reflectivity of the backside surface.

Therefore, the introduction of KOH alkali polishing process and integration into the existing production process of PERC cells is an effective means to further improve the efficiency of PERC cells. The additives and alkali refills used in alkali polishing are supplemented in a step-by-step manner. The additives are selected from Topbond BP. -170 reagent, potassium hydroxide solution is selected for alkali infusion:

The optimized alkali polishing formula includes three kinds of alkali polishing liquids, one of which includes 200-350ml of additive infusion, 300-1000ml of alkali infusion and 7-9L of pure water infusion; the other includes 250-400ml of additive infusion, 850-1150ml alkaline rehydration solution and 8-10L pure water rehydration solution; the third includes 300-500ml additive rehydration solution, 1000-1300ml alkaline rehydration solution and 9-11L pure water rehydration solution;

For batches 1-15, the additive rehydration volume is 200ml, the alkali rehydration volume is 300ml, and the pure water rehydration volume is 7L;

For batches 16-30, the additive rehydration volume is 250ml, the alkali rehydration volume is 850ml, and the pure water rehydration volume is 8L;

For batches 31-60, the additive rehydration volume is 300ml, the alkali rehydration volume is 1000ml, and the pure water rehydration volume is 9L.

Step S07 , annealing: the silicon wafer after alkali polishing is then annealed at a temperature of 700°, and a silicon dioxide layer is produced on the surface of the battery wafer by an oxygen high temperature furnace.

Step S08, back passivation: then, a layer of aluminum oxide passivation film is layered by ALD or PECVD.

Step S09, back film: a layer of silicon nitride film is layered under the aluminum oxide passivation film layer, and the back silicon nitride film plays the role of protecting the aluminum oxide passivation film layer.

Step S10, positive film: the silicon nitride film on the front surface is to reduce reflection and passivation.

Step S11 , laser grooving: laser grooving on the backside of the coated silicon wafer.

Step S12, printing and sintering: the back and front printing are completed by screen printing, and then the sintering process is performed.

Step S13, electric injection: reduce the light-induced attenuation of the battery cell through a light decay furnace or an electric injection furnace.

Step S14, test sorting: the final battery test is sorted.

Comparative Experiment:

Comparative group: Alkali polishing was performed on silicon wafers on the production line by using the medicinal liquid of the original formula in the background technology;

Experimental group: Alkali polishing was performed on silicon wafers on the production line by using the optimized medicinal solution of the present invention;

The rehydration methods of the control group and the experimental group are shown in Table 1 below:

Table 1

According to the data in Table 1, using the optimized formula of the present invention to carry out stepped liquid replenishment, compared with the liquid replenishment method of the original formula, the beneficial effects on different batches of silicon wafers on the production line are: The production capacity was increased from 10,800 pieces to 22,000 pieces, the liquid medicine cycle was increased from 30 batches to 60 batches, and the unit consumption of additives was reduced from 18.5 liters/10,000 pieces to 12.6 liters/10,000 pieces.

Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, and substitutions can be made in these embodiments without departing from the principle and spirit of the invention and modifications, the scope of the present invention is defined by the appended claims and their equivalents.

Claims (2)

1. A SE-based alkaline polishing high efficiency PERC cell process comprising the steps of:

step S01, texturing: texturing the surface of a monocrystalline silicon wafer to obtain a textured structure;

step S02, diffusion: introducing phosphorus oxychloride and a silicon wafer for reaction to realize diffusion and junction preparation;

step S03, SE process: the selective emitter is arranged on a lightly doped silicon substrate, and impurity atoms are selectively and heavily doped by micron-sized laser beams;

step S04, hot oxygen: a high-temperature thermal oxidation process is added after the SE process, and a silicon dioxide protective layer is produced and deposited on the surface of the silicon wafer;

step S05, remove PSG: etching and removing the PN junction at the edge through PSG;

step S06, alkali polishing: performing alkali polishing on the silicon wafer by adopting the optimized alkali polishing formula;

step S07, annealing: annealing the silicon wafer after alkali polishing, and producing a deposited silicon dioxide film layer on the surface of the silicon wafer;

step S08, back passivation: depositing an aluminum oxide passivation film layer on the back of the silicon wafer in an ALD or PECVD mode;

step S09, back film: growing and depositing a silicon nitride film on the back of the silicon wafer;

step S10, positive film: growing and depositing a silicon nitride film on the front surface of the silicon wafer;

step S11, laser grooving: performing laser grooving on the back of the coated silicon wafer;

step S12, printing and sintering: finishing back and front printing through screen printing, and then performing a sintering process;

step S13, electrical injection: passing through a light attenuation furnace or an electric injection furnace;

step S14, test sorting: finally, battery testing and grading are carried out on the battery pieces;

the method is characterized in that: the optimized alkali polishing formula comprises three alkali polishing liquids, wherein one alkali polishing liquid comprises 200-350ml of additive replenishing liquid, 300-1000ml of alkali replenishing liquid and 7-9L of pure water replenishing liquid; the two solutions comprise 250-400ml additive solution, 850-1150ml alkali solution and 8-10L pure water solution; the third step comprises 300-500ml additive solution, 1000-1300ml alkali solution and 9-11L pure water solution;

in step S06, the optimized alkali polishing formula used for alkali polishing is supplemented according to a stepwise manner:

in the 1 st to 15 th batches, the additive liquid supplementing amount is 200-;

in 16-30 batches, the additive liquid supplementing amount is 400ml, the alkali liquid supplementing amount is 1150ml and the pure water liquid supplementing amount is 8-10L;

in 31-60 th batch, the additive liquid supplementing amount is 500ml, the alkali liquid supplementing amount is 1300ml and the pure water liquid supplementing amount is 9-11L.

2. The SE-based alkaline polishing PERC cell process as claimed in claim 1, wherein: the alkali solution is potassium hydroxide solution.

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