PREPARATION METHOD AND APPLICATION OF CRYSTALLINE SILICON SOLAR CELL HAVING SHALLOW JUNCTION DIFFUSION EMITTER

Abstract

The present application provides a preparation method and application of a crystalline silicon solar cell having a shallow junction diffusion emitter. The preparation method comprises a diffusion process and a chain oxidation process, the diffusion process comprises low temperature diffusion and high temperature propulsion, and the chain oxidation process comprises high-temperature chain oxidation. According to the present application, firstly, a low-doped diffusion shallow junction having a depth of 0.15 um is prepared by means of optimization of the diffusion process, and doping with a certain dose concentration is formed on the surface of a diffusion layer by using photon thermal activation radiation energy of high-temperature chain oxidation, so as to solve the mismatch problem of alloy ohmic contact subsequently formed with silver paste, and finally, the photoelectric conversion efficiency is improved to a high degree.

Claims

1. A preparation method for a crystalline silicon solar cell with a shallow junction diffusion emitter, comprising a diffusion process and a chain oxidation process; the diffusion process comprises low-temperature diffusion and high-temperature drive-in, and the chain oxidation process comprises high-temperature chain oxidation.

2. The preparation method according to claim 1, wherein the diffusion process sequentially comprises boat loading, a first heating, a first temperature holding, vacuum stabilization, vacuum leak detection, oxidation, a first low-temperature diffusion source introduction, a second low-temperature diffusion source introduction, a second heating, a second temperature holding, high-temperature drive-in, a first cooling, complemental diffusion, purge, a PSG deposition reaction, an oxidation reaction, a second cooling, nitrogen filling, and boat unloading; optionally, the low-temperature diffusion comprises diffusing a constant source at a certain temperature; the constant source is phosphorus oxychloride; optionally, the low-temperature diffusion comprises the first low-temperature diffusion source introduction and the second low-temperature diffusion source introduction; the first low-temperature diffusion source introduction is performed at 770-790 C.; the first low-temperature diffusion source introduction is performed for 220-260 s; the first low-temperature diffusion source introduction is performed with a low nitrogen flow rate of 1000-1100 sccm; the first low-temperature diffusion source introduction is performed with an oxygen flow rate of 450-550 sccm; the first low-temperature diffusion source introduction is performed with a high nitrogen flow rate of 0 sccm; the first low-temperature diffusion source introduction is performed at a furnace tube pressure of 50-60 mbar; the second low-temperature diffusion source introduction is performed at 790-810 C.; the second low-temperature diffusion source introduction is performed for 190-230 s; the second low-temperature diffusion source introduction is performed with a low nitrogen flow rate of 1100-1200 sccm; the second low-temperature diffusion source introduction is performed with an oxygen flow rate of 550-650 sccm; the second low-temperature diffusion source introduction is performed with a high nitrogen flow rate of 0 sccm; the second low-temperature diffusion source introduction is performed at a furnace tube pressure of 50-60 mbar.

3. The preparation method according to claim 1, wherein the high-temperature drive-in comprises driving a phosphorus source on the surface of crystalline silicon into a silicon matrix at a high temperature; the high-temperature drive-in is performed for 350-370 s; the high-temperature drive-in is performed at 800-900 C.; the high-temperature drive-in is performed with a low nitrogen flow rate of 750-850 sccm; the high-temperature drive-in is performed with an oxygen flow rate of 0 sccm; the high-temperature drive-in is performed with a high nitrogen flow rate of 950-1050 sccm; the high-temperature drive-in is performed at a furnace tube pressure of 50-60 mbar.

4. The preparation method according to claim 2, wherein the PSG deposition reaction is performed at 700-800 C.; the PSG deposition reaction is performed for 700-800 s; the PSG deposition reaction is performed by introducing phosphorus oxychloride; the PSG deposition reaction is performed with a low nitrogen flow rate of 1250-1350 sccm; the PSG deposition reaction is performed with an oxygen flow rate of 550-650 sccm; the PSG deposition reaction is performed with a high nitrogen flow rate of 0 sccm; the PSG deposition reaction is performed at a furnace tube pressure of 55-65 mbar.

5. The preparation method according to claim 2, wherein a furnace tube is subjected to a vacuum operation in the first heating and the first temperature holding; optionally, a pipeline is purged by introducing a low nitrogen flow in the first temperature holding, and the purge is performed with a flow rate of 450-550 sccm; optionally, after the pressure is stabilized in the vacuum stabilization, all gas introductions are cut off and the furnace tube pressure is maintained at 50-60 mbar; optionally, the oxidation comprises growing a layer of silicon oxide on the surface of a crystalline silicon wafer for protection.

6. The preparation method according to claim 2, wherein the second heating is performed to a target temperature of 830-870 C.; the second heating is performed by introducing nitrogen to remove the residual phosphorus oxychloride; the second heating is performed with a high nitrogen flow rate of 950-1050 sccm; optionally, the second temperature holding is performed by introducing oxygen to further react with the residual phosphorus oxychloride; the second temperature holding is performed with an oxygen flow rate of 550-650 sccm.

7. The preparation method according to claim 2, wherein the first cooling is performed at 750-810 C.; optionally, the complemental diffusion is used to fix the localized low-doping defect of a crystalline silicon wafer caused by the high-temperature drive-in; optionally, the purge removes the residual phosphorus oxychloride in the furnace tube; optionally, the oxidation reaction removes phosphorus oxychloride introduced into the PSG deposition reaction; optionally, the second cooling is used to fix the lattice dislocation in a crystalline silicon wafer; optionally, the nitrogen filling is used to restore the atmospheric pressure in the furnace tube.

8. The preparation method according to claim 1, wherein the chain oxidation process comprises high-temperature chain oxidation; the high-temperature chain oxidation is performed at 660-670 C.; the high-temperature chain oxidation is performed for 1-5 min; the high-temperature chain oxidation is performed with an oxygen flow rate of 95-105 slm; the high-temperature chain oxidation is performed with a nitrogen flow rate of 5-15 slm.

9. The preparation method according to claim 1, wherein the preparation method sequentially comprises the following processes: a texturing process, the diffusion process, a laser doping process, the chain oxidation process, a PSG removal process, a rear-side alkali polishing process, an annealing process, an ALD passivation process, a PECVD process for the front side, a PECVD process for the rear side, a laser grooving process, a screen-printing process, and a current injection process.

10. Use of the preparation method for a crystalline silicon solar cell with a shallow junction diffusion emitter according to claim 1, wherein the preparation method is applied in the field of photovoltaics.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0077] FIG. 1 is an ECV profile showing impurity distribution for phosphorus diffusion in an embodiment of the present application.

[0078] FIG. 2 is ECV profiles showing impurity distribution for diffusion under two conditions in an embodiment of the present application.

[0079] FIG. 3 is a structural diagram of a chain oxidation furnace in an embodiment of the present application.

[0080] FIG. 4 is high-temperature chain oxidation doping profiles (with/without a PSG layer) in an embodiment of the present application.

[0081] FIG. 5 is a process flow chart for a solar cell in an embodiment of the present application.

[0082] FIG. 6 is doping distribution profiles in an embodiment of the present application.

[0083] FIG. 7 is QE quantum efficiency spectra in Example 1 and Comparative Example 1 of the present application.

[0084] FIG. 8 is ECV doping concentration distribution profiles in Example 1 and Comparative Example 1 of the present application.

DETAILED DESCRIPTION

[0085] The technical solutions of the present application are further elaborated below in terms of embodiments. It should be clear to those skilled in the art that the examples are merely used for a better understanding of the present application and should not be regarded as a specific limitation to the present application.

[0086] The present application provides a preparation method for a crystalline silicon solar cell with a shallow junction diffusion emitter, and the preparation method comprises a diffusion process and a chain oxidation process.

[0087] The diffusion process comprises low-temperature diffusion and high-temperature drive-in, and the chain oxidation process comprises high-temperature chain oxidation.

[0088] In the present application, the influence factors are analyzed through the DOE experiment of diffusion process, such as the temperature, time, flow rate, and formula, and the key factors to change the ECV profiles of diffusion process are identified, such as the surface concentration, emitter junction depth, and doping diffusion curves satisfying the complementary error distribution or Gaussian distribution; secondly, based on the understanding of the mechanism of high-temperature chain oxidation, the influence factors of the surface doping are figured out by the experimental process; finally, based on the photovoltaic power generation principle of solar crystalline silicon cells, the diffusion process and the chain oxidation process are combined creatively, a diffusion emitter junction of about 0.15 m is prepared, good ohmic alloy contacts are realized under high surface doping concentration, the absorption in shortwave spectra is improved, and the photoelectric conversion efficiency of solar cells is increased.

[0089] In the present application, firstly, the low-doping diffusion shallow junction of 0.15 m in depth is prepared through the optimization of the diffusion process, and meanwhile, a certain dose concentration of doping is formed on the surface of diffusion layer by using the photon thermal activation radiant energy of high-temperature chain oxidation, so as to solve the subsequent mismatch problem in formation of alloy ohmic contacts with silver paste. Finally, the photoelectric conversion efficiency is greatly improved.

[0090] Furthermore, the diffusion process sequentially comprises boat loading, a first heating, a first temperature holding, vacuum stabilization, vacuum leak detection, oxidation, a first low-temperature diffusion source introduction, a second low-temperature diffusion source introduction, a second heating, a second temperature holding, high-temperature drive-in, a first cooling, complemental diffusion, purge, a PSG deposition reaction, an oxidation reaction, a second cooling, nitrogen filling, and boat unloading.

[0091] Furthermore, the low-temperature diffusion comprises diffusing a constant source at a certain temperature.

[0092] Furthermore, the constant source is phosphorus oxychloride.

[0093] Furthermore, the low-temperature diffusion comprises the first low-temperature diffusion source introduction and the second low-temperature diffusion source introduction.

[0094] Furthermore, the first low-temperature diffusion source introduction is performed at 770-790 C.

[0095] Furthermore, the first low-temperature diffusion source introduction is performed for 220-260 s.

[0096] Furthermore, the first low-temperature diffusion source introduction is performed with a low nitrogen flow rate of 1000-1100 sccm.

[0097] Furthermore, the first low-temperature diffusion source introduction is performed with an oxygen flow rate of 450-550 sccm.

[0098] Furthermore, the first low-temperature diffusion source introduction is performed with a high nitrogen flow rate of 0 sccm.

[0099] Furthermore, the first low-temperature diffusion source introduction is performed at a furnace tube pressure of 50-60 mbar.

[0100] Furthermore, the second low-temperature diffusion source introduction is performed at 790-810 C.

[0101] Furthermore, the second low-temperature diffusion source introduction is performed for 190-230 s.

[0102] Furthermore, the second low-temperature diffusion source introduction is performed with a low nitrogen flow rate of 1100-1200 sccm.

[0103] Furthermore, the second low-temperature diffusion source introduction is performed with an oxygen flow rate of 550-650 sccm.

[0104] Furthermore, the second low-temperature diffusion source introduction is performed with a high nitrogen flow rate of 0 sccm.

[0105] Furthermore, the second low-temperature diffusion source introduction is performed at a furnace tube pressure of 50-60 mbar.

[0106] In the present application, a constant source (phosphorus oxychloride) is introduced at a limited temperature of the present application during the low-temperature diffusion, i.e., the diffusion is constant source diffusion, in which case the diffusion distribution curve satisfies the complementary error distribution. The low-temperature diffusion (complementary error distribution) and high-temperature drive-in (Gaussian distribution) compose the impurity distribution curve of phosphorus diffusion doping.

[0107] The impurity distribution curve of phosphorus diffusion doping is shown in FIG. 1, where I is associated with PSG layer doping; on one hand, SE laser doping is promoted, and on the other hand, thermal photon radiation can activate doping by the high-temperature chain thermal oxidation; II is associated with surface layer doping; on one hand, a high concentration of doping will bring about dead layers caused by the lattice mismatch and reduce the shortwave response, and on the other hand, a low concentration of doping will affect the subsequent screen in ohmic contacts; III is a junction depth curve, which on one hand affects the ohmic contacts of the paste, and on the other hand, associated with photo-induced absorption.

[0108] Furthermore, the high-temperature drive-in comprises driving a phosphorus source on the surface of crystalline silicon into a silicon matrix at a high temperature.

[0109] Furthermore, the high-temperature drive-in is performed for 350-370 s.

[0110] Furthermore, the high-temperature drive-in is performed at 800-900 C.

[0111] Furthermore, the high-temperature drive-in is performed with a low nitrogen flow rate of 750-850 sccm.

[0112] Furthermore, the high-temperature drive-in is performed with an oxygen flow rate of 0 sccm.

[0113] Furthermore, the high-temperature drive-in is performed with a high nitrogen flow rate of 950-1050 sccm.

[0114] Furthermore, the high-temperature drive-in is performed at a furnace tube pressure of 50-60 mbar.

[0115] Furthermore, the PSG deposition reaction is performed at 700-800 C.

[0116] Furthermore, the PSG deposition reaction is performed for 700-800 s.

[0117] Furthermore, the PSG deposition reaction is performed by introducing phosphorus oxychloride.

[0118] Furthermore, the PSG deposition reaction is performed with a low nitrogen flow rate of 1250-1350 sccm.

[0119] Furthermore, the PSG deposition reaction is performed with an oxygen flow rate of 550-650 sccm.

[0120] Furthermore, the PSG deposition reaction is performed with a high nitrogen flow rate of 0 sccm.

[0121] Furthermore, the PSG deposition reaction is performed at a furnace tube pressure of 55-65 mbar.

[0122] In the present application, the doping distribution of the diffusion curve of the present application is established by controlling the amount of low-temperature diffusion source and the time of high-temperature drive-in. As shown in FIG. 2, it can be seen that the shallow emitter of about 0.15 m is prepared in the present application, but at the same time, the surface doping concentration shown by the diffusion curve is relatively low, which will lead to the failure of the subsequent alloy ohmic contacts, and therefore, it is necessary to introduce the high-temperature chain oxidation to activate the surface doping.

[0123] Furthermore, the chain oxidation process comprises: oxidation chamber loading, high-temperature chain oxidation, and oxidation chamber unloading.

[0124] Furthermore, the high-temperature chain oxidation is performed at 660-670 C.

[0125] Furthermore, the high-temperature chain oxidation is performed for 1-5 min.

[0126] Furthermore, the high-temperature chain oxidation is performed with an oxygen flow rate of 95-105 slm.

[0127] Furthermore, the high-temperature chain oxidation is performed with a nitrogen flow rate of 5-15 slm.

[0128] In the present application, the chain oxidation furnace shown in FIG. 3 is used for heating, and the current and power are high during the heating. Tungsten halogen lamps emit a large number of high-energy electrons during the heating process, the high-energy electrons bombard silicon wafers, and the radiant electrons act on the lattice and destroy the position of the atoms in the lattice, causing atom displacement effects, and at the same time, vacancy-interstitial atom pairs are also formed; meanwhile, phosphorus diffusion occurs, and there are two ways of phosphorus diffusion: interstitial diffusion and substitutional diffusion, and the bombardment of high-energy electrons reduces the difficulty of phosphorus diffusion. The chain oxidation equipment uses tungsten halogen infrared lamps to perform heating, and with the presence of a constant source on the silicon wafer surface, triggers the diffusion enhancement mechanism, resulting in phosphorus source redistribution.

[0129] In the present application, it is found through experiments that the PSG doping layer (FIG. 1-I) is the source for surface phosphorus activation doping under chain oxidation conditions, and the surface concentration shows different changes after chain oxidation with or without the PSG layer; as shown in FIG. 4, the wafer with PSG layer retained and wafer with PSG layer removed have different surface doping concentrations shown by the ECV test profiles after the high-temperature chain oxidation, and the doping curve obtained from high-temperature chain oxidation with the PSG layer retained is a key solution to handle the surface doping influence on alloy ohmic contacts.

[0130] Furthermore, as shown in FIG. 5, the preparation method sequentially comprises the following processes: [0131] a texturing process, the diffusion process, a laser doping process, the chain oxidation process, a PSG removal process, a rear-side alkali polishing process, an annealing process, an ALD passivation process, a PECVD process for the front side, a PECVD process for the rear side, a laser grooving process, a screen-printing process, and a current injection process.

[0132] In order to better understand the preparation method for a crystalline silicon solar cell with a shallow junction diffusion emitter in the present application, the examples and comparative examples below are used for illustration.

Example 1

[0133] This example provides a preparation method for a crystalline silicon solar cell with a shallow junction diffusion emitter.

[0134] The preparation method sequentially comprises the following processes, as shown in FIG. 5: [0135] a texturing process, a diffusion process, a laser doping process, a chain oxidation process, a PSG removal process, a rear-side alkali polishing process, an annealing process, an ALD passivation process, a PECVD process for the front side, a PECVD process for the rear side, a laser grooving process, a screen-printing process, and a current injection process.

[0136] Among the processes, the diffusion process comprises the following steps: [0137] a. crystalline silicon wafers for the diffusion were neatly inserted onto a quartz boat waiting to be conveyed into a furnace tube; [0138] b. boat loading: the crystalline silicon wafers were sent into a high-temperature quartz furnace tube, for which a time parameter was set at 630 s, a temperature parameter was set at 770 C., a nitrogen-introducing flow rate was set at 2000 sccm, and a pressure parameter was set at 1000 mbar, close to the atmospheric pressure; [0139] c. first heating: when the furnace tube was heated to the set temperature, a time parameter was set at 60 s, a temperature parameter was set at 770 C., a nitrogen flow rate was set at 2000 sccm, and a vacuum pressure parameter of the furnace tube was set at 700 mbar, and the furnace tube was subjected to a pre-vacuum operation; [0140] d. first temperature holding: when the furnace tube remained stable within the range of the set temperature5 C., and the furnace tube was subjected to a vacuum operation, a time parameter was set at 180 s, a temperature parameter was set at 770 C., a nitrogen flow rate was set at 2000 sccm, and a pressure parameter of the furnace tube was set at 55 mbar, and additionally, a low nitrogen flow (phosphorus oxychloride was cut off) was introduced in advance to purge a pipeline with a flow rate set at 500 sccm; [0141] e. vacuum stabilization: when the furnace tube was vacuumized to the set vacuum pressure, a time parameter was set at 60 s, a temperature parameter was set at 770 C., all the gas introductions were cut off, and a pressure parameter of the furnace tube was set at 55 mbar; [0142] f. vacuum leak detection: the furnace tube was checked for cracks and untight seal in case that the vacuum pressure rose or fluctuated; a time parameter was set at 60 s, a temperature parameter was set at 770 C., all the gas introductions were cut off, and a pressure parameter of the furnace tube was set at 55 mbar; [0143] g. oxidation: the crystalline silicon wafers needed to grow a layer of silicon oxide on the surface before doping diffusion to protect the surface of crystalline silicon wafers from corrosion by phosphorus oxychloride in the subsequent reaction process; a time parameter was set at 300 s, a temperature parameter was set at 775 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was cut off) was set at 500 sccm, a flow rate of oxygen was set at 900 sccm, a flow rate of a high nitrogen flow was 0, and a pressure parameter of the furnace tube was set at 55 mbar; [0144] h. first low-temperature diffusion source introduction: a first phosphorus oxychloride diffusion doping reaction was performed at 775 C., wherein a time parameter was set at 240 s, a temperature parameter was set at 775 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was introduced) was set at 1050 sccm, a flow rate of oxygen was set at 500 sccm, a flow rate of the high nitrogen flow was 0, and a pressure parameter of the furnace tube was set at 55 mbar; [0145] i. second low-temperature diffusion source introduction: the temperature parameter was adjusted to 795 C. and then a second phosphorus oxychloride diffusion doping reaction was performed; the purpose is to activate the doping phosphorus source in the oxidation layer by the temperature-changing diffusion, so that the diffusion reaction is more uniform; a time parameter was set at 210 s, a temperature parameter was set at 795 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was introduced) was set at 1150 sccm, a flow rate of oxygen was set at 600 sccm, a flow rate of the high nitrogen flow was 0, and a pressure parameter of the furnace tube was set at 55 mbar; [0146] j. second heating: the second heating was a process of increasing the temperature from 795 C. to 850 C. to realize the subsequent high-temperature doping drive-in reaction; meanwhile, a large amount of nitrogen was introduced to carry away part of the residual phosphorus oxychloride to avoid safety risks; a time parameter was set at 300 s, a temperature parameter was set at 850 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was cut off) was set at 800 sccm, a flow rate of oxygen was set at 0 sccm, a flow rate of the high nitrogen flow was 1000 sccm, and a pressure parameter of the furnace tube was set at 55 mbar; [0147] k. second temperature holding: the temperature needed to be held stably for a period after rising up to the set temperature; meanwhile, a certain amount of oxygen was introduced to remove the residual phosphorus oxychloride by reacting to avoid safety risks; a time parameter was set at 240 s, a temperature parameter was set at 850 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was cut off) was set at 500 sccm, a flow rate of oxygen was set at 600 sccm, a flow rate of the high nitrogen flow was 500 sccm, and a pressure parameter of the furnace tube was set at 55 mbar; [0148] l. high-temperature drive-in: when the temperature reached the set high temperature and assuredly no reaction gas remained in the furnace tube, the high-temperature doping drive-in operation was performed to drive the phosphorus source of the crystalline silicon surface to the silicon matrix; the time and temperature are very critical to this step and will directly affect the junction depth of the diffusion emitter; a time parameter was set at 360 s, a temperature parameter was set at 850 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was cut off) was set at 800 sccm, a flow rate of oxygen was set at 0 sccm, a flow rate of the high nitrogen flow was 1000 sccm, and a pressure parameter of the furnace tube was set at 55 mbar; [0149] m. first cooling: the temperature was reduced to about 800 C. as a set temperature for complemental diffusion, wherein a time parameter was set at 1380 s, a temperature parameter was set at 790 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was cut off) was set at 800 sccm, a flow rate of oxygen was set at 0 sccm, a flow rate of the high nitrogen flow was 1000 sccm, and a pressure parameter of the furnace tube was set at 55 mbar; [0150] n. complemental diffusion: the complemental diffusion can fix the localized low-doping problem of crystalline silicon wafers brought by high-temperature drive-in; a time parameter was set at 90 s, a temperature parameter was set at 790 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was introduced) was set at 1300 sccm, a flow rate of oxygen was set at 600 sccm, a flow rate of the high nitrogen flow was 0, and a pressure parameter of the furnace tube was set at 60 mbar; [0151] o. purge: after the diffusion was completed, the residual phosphorus oxychloride in the furnace tube was removed thoroughly by nitrogen and vacuuming, wherein a time parameter was set at 120 s, a temperature parameter was set at 780 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was cut off) was set at 800 sccm, a flow rate of oxygen was set at 0 sccm, a flow rate of the high nitrogen flow was 1000 sccm, and a pressure parameter of the furnace tube was set at 60 mbar; [0152] p. PSG deposition reaction: this step can, on one hand, provide sufficient phosphorus source for the subsequent laser localized doping, and on the other hand, match with the subsequent high-temperature chain oxidation for phosphorus source activation and high surface doping which is a significant finding from the present application; a time parameter was set at 760 s, a temperature parameter was set at 750 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was introduced) was set at 1300 sccm, a flow rate of oxygen was set at 600 sccm, a flow rate of the high nitrogen flow was 0 sccm, and a pressure parameter of the furnace tube was set at 60 mbar; [0153] q. oxidation reaction: a large amount of oxygen was introduced to thoroughly remove the residual phosphorus oxychloride in the furnace tube by reacting to avoid leakage risks caused by the subsequent furnace door opening; a time parameter was set at 180 s, a temperature parameter was set at 700 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was cut off) was set at 500 sccm, a flow rate of oxygen was set at 1500 sccm, a flow rate of the high nitrogen flow was 0, and a pressure parameter of the furnace tube was set at 60 mbar; [0154] r. second cooling: the temperature was set at a very low value in this step of cooling, the purpose is to subject the crystalline silicon wafers after undergoing diffusion to a temperature-changing process, and such process will promote the displacement of the lattice, partially fix the lattice dislocation caused by high-temperature diffusion, and further improve the quality of the diffusion emitter; a time parameter was set at 360 s, a temperature parameter was set at 700 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was cut off) was set at 1000 sccm, a flow rate of oxygen was set at 0 sccm, a flow rate of the high nitrogen flow was 0 sccm, and a pressure parameter of the furnace tube was set at 60 mbar; [0155] s. nitrogen filling: the furnace tube was filled with a large amount of nitrogen to restore the atmospheric pressure, so as to prepare for the subsequent furnace door opening and crystalline silicon wafer taking, wherein a time parameter was set at 240 s, a temperature parameter was set at 700 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was cut off) was set at 1000 sccm, a flow rate of oxygen was set at 0 sccm, a flow rate of the high nitrogen flow was 3000 sccm, and a pressure parameter of the furnace tube was set at 1000 mbar; and [0156] t. boat unloading the furnace door was opened, the quartz boat was taken out, and the entire diffusion process was completed; a time parameter was set at 630 s, a temperature parameter was set at 750 C., a flow rate of the low nitrogen flow was set at 0 sccm, a flow rate of oxygen was set at 0 sccm, a flow rate of the high nitrogen flow was 2000 sccm, and a pressure parameter of the furnace tube was set at 1000 mbar;
wherein the chain oxidation process comprises the following steps: [0157] a. carrier box loading: a carrier box containing crystalline silicon wafers was put on an automated loading machine; [0158] b. preparation for being conveyed into an oxidation chamber: the crystalline silicon wafers were pushed out of the carrier box and neatly arranged on a conveyor belt in front of the chain oxidation furnace chamber; [0159] c. the crystalline silicon wafers were conveyed into the high-temperature oxidation furnace chamber, wherein a speed of the conveyor belt was set at 3.8 m/min, a temperature parameter of an infrared halogen lamp was set at 665 C., a flow rate of oxygen was 100 slm, a flow rate of nitrogen was 10 slm; [0160] d. the crystalline silicon wafers were conveyed out of the oxidation chamber; the silicon wafers after undergoing high-temperature chain oxidation activation were arranged integrally on an unloading end via the conveyor belt, waiting to be sent into the carrier box; and [0161] e. the crystalline silicon wafers were put into the carrier box; the crystalline silicon wafers after undergoing oxidation activation were sequentially pushed into the carrier box from the conveyor belt, and, after wafer loading, sent to the subsequent PSG removal process.

Example 2

[0162] In this example, step (8) of the diffusion process is replaced with the following operations: first low-temperature diffusion source introduction: a first phosphorus oxychloride diffusion doping reaction was performed at 770 C., wherein a time parameter was set at 260 s, a temperature parameter was set at 770 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was introduced) was set at 1000 sccm, a flow rate of oxygen was set at 450 sccm, a flow rate of the high nitrogen flow was 0, and a pressure parameter of the furnace tube was set at 50 mbar; [0163] step (9) of the diffusion process is replaced with the following operations: second low-temperature diffusion source introduction: the temperature parameter was adjusted to 790 C. and then a second phosphorus oxychloride diffusion doping reaction was performed; the purpose is to activate the doping phosphorus source in the oxidation layer by the temperature-changing diffusion, so that the diffusion reaction is more uniform; a time parameter was set at 230 s, a temperature parameter was set at 790 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was introduced) was set at 1100 sccm, a flow rate of oxygen was set at 550 sccm, a flow rate of the high nitrogen flow was 0, and a pressure parameter of the furnace tube was set at 50 mbar; [0164] step (12) of the diffusion process is replaced with the following operations: high-temperature drive-in: when the temperature reached the set high temperature and assuredly no reaction gas remained in the furnace tube, the high-temperature doping drive-in operation was performed to drive the phosphorus source of the crystalline silicon surface to the silicon matrix; the time and temperature are very critical to this step and will directly affect the junction depth of the diffusion emitter; a time parameter was set at 370 s, a temperature parameter was set at 800 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was cut off) was set at 750 sccm, a flow rate of oxygen was set at 0 sccm, a flow rate of the high nitrogen flow was 950 sccm, and a pressure parameter of the furnace tube was set at 50 mbar; [0165] step (16) of the diffusion process is replaced with the following operations: PSG deposition reaction: this step can, on one hand, provide sufficient phosphorus source for the subsequent laser localized doping, and on the other hand, match with the subsequent high-temperature chain oxidation for phosphorus source activation and high surface doping which is a significant finding from the present application; a time parameter was set at 800 s, a temperature parameter was set at 700 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was introduced) was set at 1250 sccm, a flow rate of oxygen was set at 550 sccm, a flow rate of the high nitrogen flow was 0 sccm, and a pressure parameter of the furnace tube was set at 55 mbar; [0166] step (3) of the chain oxidation process is replaced with the following operations: the crystalline silicon wafers were conveyed into the high-temperature oxidation furnace chamber, wherein a speed of the conveyor belt was set at 3.8 m/min, a temperature parameter of an infrared halogen lamp was set at 660 C., a flow rate of oxygen was 95 slm, a flow rate of nitrogen was 5 slm.

[0167] All other conditions are the same as in Example 1.

Example 3

[0168] In this example, step (8) of the diffusion process is replaced with the following operations: first low-temperature diffusion source introduction: a first phosphorus oxychloride diffusion doping reaction was performed at 790 C., wherein a time parameter was set at 220 s, a temperature parameter was set at 790 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was introduced) was set at 1100 sccm, a flow rate of oxygen was set at 550 sccm, a flow rate of the high nitrogen flow was 0, and a pressure parameter of the furnace tube was set at 60 mbar; [0169] step (9) of the diffusion process is replaced with the following operations: second low-temperature diffusion source introduction: the temperature parameter was adjusted to 810 C. and then a second phosphorus oxychloride diffusion doping reaction was performed; the purpose is to activate the doping phosphorus source in the oxidation layer by the temperature-changing diffusion, so that the diffusion reaction is more uniform; a time parameter was set at 190 s, a temperature parameter was set at 1200 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was introduced) was set at 650 sccm, a flow rate of oxygen was set at 650 sccm, a flow rate of the high nitrogen flow was 0, and a pressure parameter of the furnace tube was set at 60 mbar; [0170] step (12) of the diffusion process is replaced with the following operations: high-temperature drive-in: when the temperature reached the set high temperature and assuredly no reaction gas remained in the furnace tube, the high-temperature doping drive-in operation was performed to drive the phosphorus source of the crystalline silicon surface to the silicon matrix; the time and temperature are very critical to this step and will directly affect the junction depth of the diffusion emitter; a time parameter was set at 350 s, a temperature parameter was set at 900 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was cut off) was set at 850 sccm, a flow rate of oxygen was set at 0 sccm, a flow rate of the high nitrogen flow was 1050 sccm, and a pressure parameter of the furnace tube was set at 60 mbar; [0171] step (16) of the diffusion process is replaced with the following operations: PSG deposition reaction: this step can, on one hand, provide sufficient phosphorus source for the subsequent laser localized doping, and on the other hand, match with the subsequent high-temperature chain oxidation for phosphorus source activation and high surface doping which is a significant finding from the present application; a time parameter was set at 700 s, a temperature parameter was set at 800 C., a flow rate of the low nitrogen flow (phosphorus oxychloride was introduced) was set at 1350 sccm, a flow rate of oxygen was set at 650 sccm, a flow rate of the high nitrogen flow was 0 sccm, and a pressure parameter of the furnace tube was set at 65 mbar; [0172] step (3) of the chain oxidation process is replaced with the following operations: the crystalline silicon wafers were conveyed into the high-temperature oxidation furnace chamber, wherein a speed of the conveyor belt was set at 3.8 m/min, a temperature parameter of an infrared halogen lamp was set at 670 C., a flow rate of oxygen was 105 slm, a flow rate of nitrogen was 15 slm.

[0173] All other conditions are the same as in Example 1.

Example 4

[0174] In this example, the temperature parameter of the first low-temperature diffusion source introduction is replaced with 700 C. in step (8) of the diffusion process, and all other conditions are the same as in Example 1.

Example 5

[0175] In this example, the temperature parameter of the high-temperature drive-in is set at 950 C. in step (12) of the diffusion process, and all other conditions are the same as in Example 1.

Example 6

[0176] In this example, the temperature parameter of the infrared halogen lamp is set at 700 C. instead of 665 C. in the high-temperature chain oxidation process, and all other conditions are the same as in Example 1.

Example 7

[0177] In this example, the second low-temperature diffusion source introduction of step (9) of the diffusion process is omitted, and all other conditions are the same as in Example 1.

Example 8

[0178] In this example, the PSG deposition reaction of step (16) of the diffusion process is omitted, and all other conditions are the same as in Example 1.

Comparative Example 1

[0179] In this comparative example, the chain oxidation is replaced with the conventional high-temperature tube oxidation, and all other conditions are the same as in Example 1.

Comparative Example 2

[0180] In this comparative example, the high-temperature drive-in of step (12) of the diffusion process is omitted, and all other conditions are the same as in Example 1.

Comparative Example 3

[0181] In this comparative example, the chain oxidation process is replaced with a room-temperature chain oxidation process, and all other conditions are the same as in Example 1.

[0182] Several batch productions are carried out according to Example 1 and Comparative Example 1 of the present application, and the results are shown in Table 1:

TABLE-US-00001 TABLE 1 UOC/A Isc/A FF Ncell/% First batch Example 1 0.0013 0.020 0.04 0.09 production Comparative 0 0 0 0 Example 1 Second batch Example 1 0.0015 0.022 0.09 0.11 production Comparative 0 0 0 0 Example 1 Third batch Example 1 0.0009 0.030 0.07 0.10 production Comparative 0 0 0 0 Example 1

[0183] As can be seen from the above table, the conversion efficiency of crystalline silicon solar cells is increased by 0.1% via the shallow junction diffusion emitter prepared in the present application, and the open circuit voltage Uoc and short circuit current Isc are mainly improved.

[0184] The doping distribution curves of Example 1 and Comparative Example 1 in the present application are shown in FIG. 6, the QE quantum efficiency spectra are shown in FIG. 7, and the ECV (electrochemical corrosion) doping concentration distribution profiles are shown in FIG. 8. Through the QE quantum efficiency spectra of FIG. 7, it is observed that the shortwave response of Example 1 in the range of 300-500 nm is obviously higher than that of Comparative Example 1; as can be seen in FIG. 8, for Example 1 of the present application, the junction depth is 0.15 m and the surface concentration is 1.010.sup.21 cm.sup.3, both of which are superior to that of Comparative Example 1.

[0185] The solar cells in Examples 1-8 and Comparative Examples 1-3 are produced in production lines, and test results are shown in Table 2.

TABLE-US-00002 TABLE 2 UOC/A Isc/A FF Ncell/% Example 1 0.0013 0.020 0.04 0.09 Example 2 0.0010 0.0130 0.16 0.101 Example 3 0.0011 0.0300 0.07 0.109 Example 4 0.0007 0.0099 0.00 0.040 Example 5 0.0004 0.0250 0.00 0.056 Example 6 0.0004 0.0100 0.06 0.047 Example 7 0.0007 0.0181 0.08 0.077 Example 8 0.0010 0.0230 0.02 0.067 Comparative 0.0022 0.0169 0.02 0.108 Example 1 Comparative 0.0024 0.0199 0.16 0.158 Example 2 Comparative 0.0035 0.0399 0.10 0.212 Example 3

[0186] As can be seen from the above table, the efficiencies of Examples 1-3 are obviously increased by about 0.1%, and the results are consistent; Example 4 replaces the temperature of the first low-temperature diffusion source introduction with a lower temperature, Example 5 increases the temperature of the high-temperature drive-in in the diffusion process, Example 6 further increases the temperature of the high-temperature chain oxidation process, and Example 7 omits the second low-temperature diffusion source introduction; compared with Example 1, the light-conversion efficiencies of Examples 4-6 all decrease. Comparative Example 1 replaces the chain oxidation with high-temperature tube oxidation, Comparative Example 2 omits the high-temperature drive-in process, and Comparative Example 3 replaces the high-temperature chain oxidation with room-temperature chain oxidation, and it can be observed that the light-conversion efficiencies of solar cells further decrease.

[0187] The applicant has stated that the above description is only embodiments of the present application, but the scope of the present application is not limited thereto, and it should be apparent to those skilled in the art that any change or substitution which can be readily thought of by those skilled in the art within the technical scope disclosed herein shall fall within the protection scope and disclosure scope of the present application.