CN102956742B - Manufacturing method of solar cell - Google Patents

Abstract

A method of fabricating a solar cell, comprising: step A: etching a first conductive substrate by dry etching to form a light incident surface with a rugged pattern and a plasma damage layer; and B: oxidizing the plasma damage layer to convert into an oxide layer; and C: removing the oxide layer by wet etching; step D: thermal diffusion treatment is performed to form an emitter layer of the second conductivity type. The oxidation process oxidizes the plasma damage layer, so that the KOH etching step in the prior method can be omitted before the thermal diffusion treatment, and the oxide layer can be removed by only one-time wet etching, thereby greatly shortening the processing time, improving the productivity and taking the feasibility of mass production and the conversion efficiency of the solar cell into consideration.

Description

Manufacturing method of solar cell

technical field

The invention relates to a manufacturing method of a solar cell, in particular to a manufacturing method of a solar cell whose surface is roughened by reactive ion etching (RIE) technology.

Background technique

The general silicon solar cell manufacturing process is to thermally diffuse a p-type silicon substrate to form an n-type emitter layer on the surface of the substrate, thereby forming a p-n junction. However, studies have found that when the light incident surface of the battery is a rough surface with up and down bumps, it can reduce light reflection, increase the proportion of light incident into the battery, and improve conversion efficiency. Therefore, there is currently an improved process that uses reactive ion etching (RIE) before the diffusion process to etch the surface of the substrate to form a rough surface.

Referring to FIG. 1, although the RIE process can etch the substrate 11 to meet the requirements of the uneven surface of the substrate 11, the charged particles (plasma) in this process will also react with the material of the substrate 11 to form a plasma damage layer 12 on the surface of the substrate 11. The existence of the plasma damage layer 12 will increase the carrier recombination rate (Recombination), thereby reducing the photoelectric conversion efficiency of the solar cell, so after the RIE process, the plasma damage layer 12 must be removed by wet etching, Since the material of the plasma damage layer 12 is mainly silicon (Si) and silicon oxide (SiO _x ), two etchings are usually required to remove it, respectively etching SiO _x with hydrofluoric acid (HF) etching solution, And etching Si with potassium hydroxide (KOH) etchant. After the plasma damage layer 12 is removed, thermal diffusion treatment is performed to form a pn junction.

The disadvantage of the above process is that when using KOH to etch Si, due to the characteristics of Si itself, the temperature and KOH concentration during etching must be precisely controlled to remove the predetermined thickness of Si, but the thickness of Si and etching The control between temperature and concentration is not easy to control. In addition, when performing wet etching, the substrate 11 must first be moved to an etching tank filled with KOH solution for etching, and then the substrate 11 will be moved to another etching tank filled with HF solution for etching. time, not to mention that the above-mentioned process is wet-etched twice in two different etching tanks, so the time spent on moving the substrate 11 will be doubled, so the process time is long and the production efficiency is low, which is not conducive to industrial mass production . Moreover, in order to carry out the etching of KOH and HF above, two etching equipments are needed to carry out, so the cost of the machine equipment will increase greatly, which will cause the problem of cost control in mass production, and the two equipments will occupy a relatively large area on the production line of the factory. The problem of multiple spaces.

Contents of the invention

The object of the present invention is to provide a solar cell manufacturing method that shortens the manufacturing process time and can take into account the cell conversion efficiency and mass production requirements. Therefore, the cost of equipment procurement can be reduced and the problem of occupying too much production line space in the factory area can be avoided.

The manufacturing method of the solar cell of the present invention comprises:

Step A: Etching a substrate of the first conductivity type by dry etching, so that a light incident surface of the substrate of the first conductivity type becomes undulating, and a plasma damage layer is also formed on the light incident surface;

Step B: oxidizing the plasma damage layer to convert the plasma damage layer into an oxide layer;

Step C: removing the oxide layer by wet etching;

Step D: performing thermal diffusion treatment on the substrate of the first conductivity type to form a second conductivity type emitter layer on the light-incident surface of the substrate of the first conductivity type, so as to complete the semi-finished product of the solar cell; and

Step E: forming electrodes on the semi-finished solar cell.

In the method of the present invention, the oxidation temperature in step B is 300°C to 500°C.

In the method of the present invention, the thickness of the oxide layer is 5 nm to 10 nm.

In the method of the present invention, the oxidation time of step B is 1 minute to 25 minutes.

In the method of the present invention, the dry etching in step A utilizes a reactive ion etching method.

In the method of the present invention, the material of the oxide layer includes silicon oxide, and the etchant for wet etching in step C is hydrofluoric acid solution.

The method of the present invention also includes a step F after step D, forming an anti-reflection layer on the second conductivity type emitter layer, and step E is to form an antireflection layer on the surface of the antireflection layer and the first conductivity type substrate The surface forms the electrode.

In the method of the present invention, the thermal diffusion treatment in step D also forms a semiconductor layer on one side of the substrate of the first conductivity type, and then removes the semiconductor layer by wet etching.

In the method of the present invention, the etchant used to remove the semiconductor layer is a hydrofluoric acid solution.

The main carriers of the substrate of the first conductivity type and the emitter layer of the second conductivity type need not be restricted, as long as a p-n junction can be formed. Therefore, when the substrate of the first conductivity type is a p-type semiconductor, the first conductivity type The second conductive type emitter layer is an n-type semiconductor; when the first conductive type substrate is an n-type semiconductor, the second conductive type emitter layer is a p-type semiconductor.

The oxidation temperature for oxidizing the plasma damage layer is 300° C.-500° C., and the oxidation time is 1-25 minutes, so that the thickness of the formed oxide layer is 5 nanometers (nm) to 10 nanometers. Wherein, the lower limit of the oxidation temperature must be limited, because when the temperature is too low, due to insufficient temperature, the reaction gas molecules cannot generate sufficient kinetic energy, which will cause the reaction gas to be unable to fully react with the plasma destruction layer and oxidize; and The oxidation temperature can achieve full oxidation effect within 500°C, and there is no need to increase the temperature, because increasing the temperature will only cause energy waste. In addition, since the oxidation process is carried out following the dry etching of step A, and the two steps are carried out in the same vacuum chamber, the temperature of the chamber is generally maintained at 300° C. to 500° C., so the oxidation temperature does not need to be changed. It is quite convenient to make additional changes.

The limitation of the oxidation time in the present invention is also to enable the plasma damage layer to fully react and oxidize. It should be noted that the oxidation rate of the plasma damage layer will gradually slow down as the oxidation time increases, so within the initial oxidation time It can exert the highest oxidation efficiency, and the oxidation time does not need to be too long.

The beneficial effect of the present invention is that: by performing an oxidation process after the RIE process, the plasma damage layer is oxidized into an oxide layer, so that the present invention can omit the KOH etching step before the thermal diffusion treatment, and only needs one wet etching to remove The oxide layer can greatly reduce the process time and increase the production capacity, and can take into account the feasibility of mass production and the conversion efficiency of solar cells.

Description of drawings

Fig. 1 is the schematic diagram of the partial structure of a kind of known solar cell;

Fig. 2 is a schematic diagram showing a solar cell manufactured by a preferred embodiment of the method for manufacturing a solar cell of the present invention;

Fig. 3 is the schematic diagram when each step of this preferred embodiment is carried out;

Fig. 4 is a block diagram of the steps of the preferred embodiment.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

Referring to Fig. 2, a preferred embodiment of the manufacturing method of the present invention is used to manufacture a solar cell, the solar cell includes a first conductive type substrate 2, a light incident surface 21 located on the first conductive type substrate 2 The second conductivity type emitter layer 4, an antireflection layer 5 located on the second conductivity type emitter layer 4, and two antireflection layers located on the lower surface of the first conductivity type substrate 2 and the surface of the antireflection layer 5 respectively The electrode 6 is used to transmit the electric energy generated by the battery to the outside.

Referring to Fig. 3, Fig. 4, the manufacturing method of solar cell of the present invention comprises:

(1) Go to step 71: prepare the substrate 2 of the first conductivity type, which is a p-type semiconductor silicon (Si) substrate in this embodiment.

(2) Go to step 72: use dry etching to etch the surface of the first conductive type substrate 2. This embodiment uses reactive ion etching (Reactive Ion Etching, referred to as RIE). In the vacuum chamber, the temperature of the chamber is about 300°C-500°C, and a mixed gas of SF ₆ , Cl ₂ and O ₂ is introduced as a reaction gas, so that the light-incident surface 21 of the first conductivity type substrate 2 forms a high and low undulating shape. , that is, to form a rough microstructure (Texturing) in a concave-convex shape. And because the surface of the substrate 2 of the first conductivity type will react with plasma, a plasma damage layer 3 will also be formed on the light incident surface 21, and the material of the plasma damage layer 3 is mainly silicon (Si) and silicon oxide. (SiO _x ).

(3) Proceed to step 73: the aforementioned SF ₆ and Cl ₂ gas flow sources are closed, and only O ₂ gas is introduced into the vacuum cavity, and O ₂ is excited into oxygen plasma in the cavity and continues to destroy the layer 3 with the plasma reaction, and then oxidize the plasma damage layer 3 to transform into an oxide layer 3', the material of which is mainly SiO _x . During this oxidation process, the temperature of the cavity, that is, the oxidation temperature is about 300° C. to 500° C., and the oxidation time in this embodiment is 5 minutes, but it is not limited thereto. The formed oxide layer 3 ′ has a thickness of 5 nanometers (nm ) ~ 10 nanometers.

(4) Go to step 74 : remove the oxide layer 3 ′ by wet etching to expose the light incident surface 21 of the first conductive type substrate 2 . In this embodiment, a solution such as hydrofluoric acid (HF) is used as an etching solution, which has a good etching effect on the SiO _x material of the oxide layer 3 ′.

(5) Proceed to step 75: perform thermal diffusion treatment on the first conductive type substrate 2, the thermal diffusion treatment is to first put the first conductive type substrate 2 into a high temperature furnace tube, the temperature in the furnace tube is about 750°C ~800°C, and a reaction gas is passed into the furnace tube. This embodiment is a mixed gas of N ₂ -POCl ₃ (a mixture of nitrogen and phosphorus oxychloride), O ₂ and N ₂ , but it is not limited to this, and further Phosphorus (P) is deposited on the surface of the first conductive type substrate 2 . Next, raise the temperature of the furnace tube to 800° C. to 950° C. and maintain it for tens of minutes, so that phosphorus (P) can diffuse into the surface layer of the substrate 2 of the first conductivity type, and then form the n-type first conductive layer on the light incident surface 21. The second conductivity type emitter layer 4 is mainly made of phosphorus glass (PSG).

It should be noted that the thermal diffusion process will also cause a side surface 22 of the substrate 2 of the first conductivity type connected to the periphery of the light-incident surface 21 to react with the reactive gas, thereby forming a semiconductor layer 40. The material of the semiconductor layer 40 is generally It is the same as the second conductivity type emitter layer 4 .

(6) Go to step 76 : remove the excess semiconductor layer 40 by wet etching to expose the side surface 22 of the first conductive type substrate 2 . In this embodiment, a solution such as HF is used as the etching solution. This step is also called an isolation step.

(7) Proceed to step 77: forming an anti-reflection layer 5 of silicon nitride (SiN _x ) on the surface of the second conductivity type emitter layer 4 to reduce the reflection of sunlight and increase the ratio of incident light. In practice, techniques such as sputtering or plasma-assisted chemical vapor deposition (PECVD) can be used.

At this point, the semi-finished solar cell has been fabricated, but it should be noted that forming the anti-reflective layer 5 is not a necessary step, so the semi-finished solar cell may not include the anti-reflective layer 5 .

(8) Go to step 78: form electrodes 6 on the semi-finished solar cell, the electrodes 6 are mainly formed on the upper surface of the anti-reflection layer 5 and the lower surface of the first conductive type substrate 2 by screen printing. Then put the above sample in a high-temperature sintering furnace. There are multiple high-temperature areas with different temperatures in the sintering furnace. The rollers in the furnace drive the sample to continue to move forward and be sintered at different high temperatures. Therefore, the electrode 6 can be firmly attached, and it is completed. Fabrication of solar cells. It should be noted that the shapes of the electrodes 6 shown in FIG. 2 and FIG. 3 are only illustrative but not limiting, and other designs may also be used.

The improvement of the present invention is mainly as follows: after the RIE etching process, the oxidation process is continued in the RIE equipment immediately, so the oxidation process is compatible with the original battery production method, and its method is simple, as long as oxygen is introduced into the RIE equipment. Yes, and the oxidation temperature is the same as that of the original RIE process, which is about 300°C to 500°C, and there is no need to increase the temperature to waste energy and time. In addition, because the plasma damage layer 3 is oxidized into an oxide layer 3', it can be removed by etching with HF etching solution, omitting the step of using KOH etching in the known process. Therefore, the present invention can save a wet etching by increasing the oxidation process, because the oxidation process is directly carried out in the RIE equipment, and the oxidation time does not need to be too long, so the oxidation process is longer than the time required for wet etching (including moving the substrate to The time of the etching tank and the etching process) is much less, which can greatly shorten the production time and improve the production efficiency, and at the same time avoid the problem that the temperature and concentration of the KOH etching are difficult to control in the known method. Of course, it also saves the cost of purchasing KOH etching equipment, and saves the production line space occupied by the original KOH etching equipment.

Referring to Table 1, it is the electrical test results of the present invention and three comparative examples. Comparative example 1 refers to the most traditional process, without RIE process and wet etching before the diffusion process. Comparative examples 2 and 3 are another known process. Before the diffusion process, there are two times of wet etching with KOH and HF. The column of speed in the table refers to the speed at which the sample moves forward in the KOH etching tank. The slower the sample moves Indicates that the etching process is more complete. V _oc of table 1 represents the open circuit voltage, J _sc represents the short-circuit current, FF value (fill factor) represents the fill factor, Eff. is the conversion efficiency, and the cell production number refers to the same time (for example 1 hour), the present invention and each The number of batteries produced in the comparative example.

As can be seen from the results in Table 1, although the production speed of Comparative Example 1 is fast, and the number of cells produced per unit time is the highest, its short-circuit current and conversion efficiency are all low, while Comparative Examples 2 and 3 are relatively low compared to Comparative Example 1. , although the short-circuit current and conversion efficiency can be improved, but the production speed is too slow, which is not conducive to mass production. In contrast to the present invention, compared with Comparative Example 1, the short-circuit current and conversion efficiency of the present invention are increased by 0.59mA/cm ² and 0.2% respectively, which is a considerable improvement. Although the production capacity of the present invention is slightly reduced, the decline is small , and the production capacity of the present invention is still higher than that of Comparative Examples 2 and 3, and the production speed of the present invention is suitable for mass production, so the present invention strikes a balance between battery efficiency and production efficiency.

Table 1

In summary, the plasma damage layer 3 is oxidized into the oxide layer 3' through the oxidation process, so that the present invention only needs one wet etching to remove the oxide layer 3' before the thermal diffusion treatment, greatly reducing the process time and improving the Production capacity, which can take into account the feasibility of mass production and the conversion efficiency of solar cells.

Claims (9)

1. A method for manufacturing a solar cell, comprising: A substrate of the first conductivity type is etched by dry etching, so that a light incident surface of the substrate of the first conductivity type becomes undulating, and a plasma damage layer is also formed on the light incident surface; it is characterized in that the solar cell The manufacturing method also includes the following steps: oxidizing the plasma-damaged layer to form an oxide layer; removing the oxide layer by wet etching; performing thermal diffusion treatment on the substrate of the first conductivity type to form an emitter layer of the second conductivity type on the light incident surface; and An electrode is formed on the first conductive type substrate. 2 . The method for manufacturing a solar cell according to claim 1 , wherein the oxidation temperature for oxidizing the plasma destruction layer is 300° C.˜500° C. 3. The method for manufacturing a solar cell according to claim 1 or 2, characterized in that the oxide layer has a thickness of 5 nm to 10 nm. 4 . The method for manufacturing a solar cell according to claim 3 , wherein the oxidation time for oxidizing the plasma destruction layer is 1 minute to 25 minutes. 5. The method for manufacturing a solar cell according to claim 1 or 2, wherein the dry etching utilizes a reactive ion etching method. 6 . The method for manufacturing a solar cell according to claim 5 , wherein the oxide layer is made of silicon oxide, and the wet etching solution is a hydrofluoric acid solution. 7 . 7 . The method for manufacturing a solar cell according to claim 1 , further comprising forming an anti-reflection layer on the second conductive type emitter layer, and then forming the electrode. 8. The method of manufacturing a solar cell according to claim 1, wherein the thermal diffusion treatment also forms a semiconductor layer on one side of the substrate of the first conductivity type, and then removes the semiconductor layer by wet etching layer. 9 . The method for manufacturing a solar cell according to claim 8 , wherein the etching solution used to remove the semiconductor layer is a hydrofluoric acid solution.