TW200919740A - Method of fast hydrogen passivation to solar cells made of crystalline silicon - Google Patents

Abstract

A method to quickly improve the performance of solar cells made of crystalline silicon, including monocrystalline, multicrystalline and polycrystalline silicons. The method comprises of steps applying a negative pulse to solar cells at a predetermined voltage, a predetermined frequency, and a predetermined pulse width while immersing the solar cells in a hydrogen plasma. Hydrogen ions are attracted and quickly implanted into solar cells. Thus, the passivation of the crystal defects in solar cells can be realized in a short period. Meanwhile, the properties of the antireflection layer can not be damaged as the proper operating conditions are used. Consequently, both the short-circuit and the open-circuit voltage can be increased. Meanwhile, the serious resistance can be significantly reduced and the filling factor increases as a result. The efficiency can be improved.

Description

200919740 25204twf.doc/n IX. DESCRIPTION OF THE INVENTION: TECHNICAL FIELD OF THE INVENTION The present invention is a hydrogenation method for a Shixia substrate. In particular, a rapid deuteration process for purifying germanium crystal defects in crystalline silicon (c-Si) solar cells. The crystalline ruthenium includes monocrystalline (m-Si), muiticrystalline (mc-Si), and polycrystalline thin film (poly_Si thin film). [Prior Art] Solar cells are a very promising clean energy source that can generate electricity directly from sunlight. However, it is now necessary to effectively reduce the production cost of solar cells in order to be widely accepted as the main source of electricity. Research indicates that germanium wafers account for more than one-third of the total cost of crystalline solar modules. Therefore, in order to reduce costs, the production of solar cells using polycrystalline germanium (mc_Si) or poly-Si thin films has become an important development direction. However, both mc-Si and p〇ly-Si contain defects in the crystal, including the grain boundary and the inter-crystal difference (intmgrain). These shortcomings reduce the conversion efficiency of solar cells (c〇nversi〇n efficiency). In addition, even in the case of a single crystal solar cell, the charge ^ in the lattice table _ recombination (fine mbinatiQn) - # will be detrimental to the conversion efficiency of the battery. It is known in the prior art that by adding a hydrogen atom to a Shi Xi wafer, the influence of crystal defects can be reduced, which is called "gas Jinhua," and the efficiency of the crystallization is high. To improve the general view, these improvements in efficiency are closely related to the hydrogen bond's recombination loss on the lattice 200919740 1 v? 25204twf.doc/π defect in the formation of a bond flip on the Ba lattice. In solar cell process technology, methods using hydrogen passivation to mitigate the deleterious effects of lattice defects include: (1) Heat treatment in a hydrogen atmosphere: P. Sana, A. Rohatgi, J. p. Kalejs, and RO Bell, Appl. Phys. Lett 64, 97 (1994). US Patent US 5,169,791. (2) Diffusion treatment with hydrogen plasma:

W. Schmidt, K.D. Rasch, and K. Roy, 16 IEEE c;

Photovoltaic Specialist Conference, San Diego, 1982, pages 537-542. U.S. Patent No. 4,835,006 and U.S. 4,343,830. (3) Hydrogen-rich SiNx: H thin film deposited by piasina enhanced chemical vapor deposition (PECVD): R. Hezel and R. Schroner, J. Appl. Phys., 52 (4) ), 3076 (1981) 〇

Implantation of Ci (4) ionized hydrogen atom: U.S. Patent 5,304,509. J. E. Johnson, J. I. Hano Ka, and J. A. Gregory, 18 IEEE Photovoltaic Specialists Conference, Las Vegas 1985, pages 1112-1115. In the hydrogen passivation process, sufficient hydrogen atoms must be provided to form bonds on most of the lattice defects. However, because the diffusion rate of hydrogen atoms through the surface of the wafer is very slow, the hydrogen passivation process in the methods (1) to (3) often requires 200919740 -----------25204twf.doc/n hours as long as. Although in the (4) method, the conventional Kaufman wide ion beam source is used to implant hydrogen ions into the wafer, the process time is reduced. However, in practical industrial applications, the mass production of solar cells requires a large number of ion beam sources to be achieved. An ion beam source device of this size is an expensive and complicated system. In addition, the accelerating electrodes in the Kaufman ion beam source are bombarded by ions during the process. The metal particles that are trapped and become a source of pollution may cause the performance of the solar cell to deteriorate. ^ Amorphous tantalum nitride (a-SiNx: H) films containing hydrogen in solar cell structures have become an important application. The film is grown on a tantalum wafer using plasma chemical vaporization. The first application of a_SiNx: H film is as an antireflection coating. Furthermore, it can provide a surface passivation effect to reduce the recombination of charge carriers on the surface of the germanium wafer in the solar cell. In addition, a_SiNx^ = hydrogen atoms in the film can diffuse into the 7 wafers and passivate the defects of the crystal lattice. To achieve the above objectives, thermalpr〇cess is required to increase the temperature of the solar cell to increase the diffusion of hydrogen atoms to achieve the desired passivation. The operating temperature is around 350 ° C and the process takes 1 to 2 hours. However, in some solar cell production, electrode fabrication is performed after the antireflection layer is completed. Because the electrode fabrication often requires a high-temperature heating and baking step, the bonding of hydrogen and helium is at 40 (the above rc will decompose and cause the hydrogen atoms to leave the wafer, so the hydrogen passivation effect described in the previous paragraph will be destroyed. As described above, the production of a crystalline germanium solar cell requires a rapid hydrogen passivation process to drastically reduce the process time. In particular, this process can be performed after the fabrication of the crystalline germanium solar cell is completed. In other words,

200919740 ........--.. 25204twf.doc/n The rapid purification process after depositing the anti-reflective layer and making the electrode has been completed. Moreover, the equipment equipped with the Kauf_wide beam ion_conventional ion method must be simple and suitable for the large-scale production process of solar cells. SUMMARY OF THE INVENTION The present invention provides a method for purifying a gas of a crystalline solar cell to improve the performance of a solar cell. This method allows for a rapid hydrogen passivation process to mitigate the deleterious effects of the crystal. Moreover, this method must not cause damage to the antireflection layer (e.g., a-SiNx). In addition, the hydrogen passivation method of the crystal solar cell of the present invention can improve the performance of a solar cell that has been completely fabricated. The invention provides a method for purifying a gas of a crystalline solar cell, comprising the steps of: (a) placing a crystalline germanium solar cell into a vacuum chamber, wherein the surface of the crystallized solar cell has an electrode and a layer of anti-reflection Layer/, (b) supply hydrogen gas to the vacuum chamber to a predetermined pressure. (4) Transmitting radio frequency or microwave power into the vacuum chamber to generate hydrogen electropolymerization. (d) Providing a predetermined electric company by using a pulse generator The small, pulse frequency and pulse time width of the partial crystallization of the cation solar cell wafer, and - in the pre-determined age H full amount of hydrogen ion listening (four) solar cell wafer 'where the aforementioned negative pulse voltage is controlled in a fixed range In order to avoid damage to the anti-reflection layer. The invention proposes that the method of hydrogen passivation of the crystalline Shi Xi solar cell is to firstly process the 200919740 25204twf.doc/n crystal solar solar cell wafer. Placed in a vacuum chamber, the solar cell already has an anti-reflection layer and an electrode. Then, hydrogen gas is supplied to the vacuum chamber to a predetermined pressure. Then, by transmitting a radio frequency or microwave power source to the real cavity, Hydrogen. Subsequently, a negative bias pulse is provided to the Moonlight cell wafer to allow hydrogen ions to be implanted therein. In this method, the high density electrode provides a high hydrogen ion dose rate. Therefore, compared with the current technology, the process time can be greatly reduced and reduced. On the other hand, compared with the conventional ion beam method, the device used in the method is simple and economical, and is suitable for mass production. At the end of the bias pulse, electrons in the plasma are attracted to the solar cell wafer to neutralize the accumulated positive charge originally implanted. Therefore, by controlling the pulse width, the damage caused by charge accumulation can be eliminated. Selecting an appropriate pulse voltage can avoid ion bombardment and cause possible degradation of anti-reflective coating. θ [Embodiment] Figure 1 is a typical solar power 10, which includes a crystal (j 夕 wafer 100 ' and has formed a pn junction pn junction 104. The surface of the crystallization wafer 1 has a random pyramid texture 102 and utilizes a thermal process The thin layer of 〇 2 grown is used as a surface passivation layer 106. Then, a layer of a-SiNx: anti-reflective layer film of Η film is deposited by pECVD method. Electrodes and 114 are formed on the front side l〇〇a and the back side l〇〇b, respectively. Further, the electrode 114 is typically formed in a dielectric layer 116 deposited on the back side 100b of the crystalline germanium wafer 100. 200919740 25204twf.doc/n Figure 2 is a diagram showing the hydrogen passivation of a crystalline germanium solar cell wafer. First, the crystal solar cell wafer 2 is placed on a wafer tray 204 in the vacuum chamber 202, and the pressure of the vacuum chamber 202 is lowered to about 1 (Τ6Τοιτ. Then, the gas supply The device 2〇6 supplies hydrogen gas to the vacuum chamber 202 to a predetermined pressure, approximately M〇mT〇n_. Next, the microwave frequency power supplied by a microwave or RF power generator 2〇8 is transmitted to the vacuum chamber 202. Hydrogen plasma is produced. In general, (the plasma should be greater than 10 IG cm-3 to achieve an efficient process. When the hydrogen plasma is excited, a pulse generator (pUlse generator) 212 provides a predetermined schedule. The voltage pulse, pulse frequency and pulse time width of the negative pulse voltage are applied to the wafer tray 204 to apply a bias voltage to the crystallization solar cell wafer 200. The aforementioned negative pulse voltage has a pulse frequency ranging from 100 Hz to 20 kHz. _5〇〇v to _5]^ to ensure that the anti-reflection layer in the crystalline solar cell wafer 200 (Fig. 1) is not destroyed during hydrogen passivation. The time for supplying a negative pulse voltage ( Pulse duration) is from lp Sec to 20MSec. Then, the cesium ions in the plasma source 21〇 are accelerated by the negative voltage and implanted in the crystallization solar cell wafer, and the processing time of the process is between 1 and 10 minutes. During implantation, the crystallization solar cell wafer can be heated from 2 Torr to about 300 ° C to 35 (temperature of TC. The following example will describe the effect of the hydrogen passivation process proposed by the present invention. Example One Piece In this Example, Vacuum The bottom pressure of the cavity is 1〇-6T〇rr, and then hydrogen is input as the working gas and the pressure is raised to 2 mT〇rr. The plasma is passed through an electric 200919740 252〇4twf.doc/n inductively coupled antenna with RF power (13 56 MHz) excitation. The power is 2 〇〇w. The plasma density is about 1 Wm.3, and the pulse voltage of mv is biased to the solar cell. The pulse width is l (^sec and the pulse frequency is 200 Hz. It does not provide power to heat the solar cell, but because the plasma ion implantation will increase the temperature of the sample to 1 〇 (rc). The total process time is 1 〇 minutes. The solar cell uses P type, boring boron to lxl02〇 Polycrystalline germanium of cm-3 Made by circle ^C-Si wafbr. Their average grain size is about 5 mm. An angular structure has been fabricated on the surface of the wafer. NP bonding is used at 850 °C. Diffusion was made for 20 minutes. Then a layer of 2〇mn Si〇2 was formed by thermal oxidation process. Then, a 90-sided a-SiNx was deposited by a capacitively coupled RF plasma reactor at a temperature of 350 °C. :H film is used for anti-reflection, in which NH3 is used as a precursor. As for the metal electrode, it was produced by a metal printing method and sintering at 750 °C. Figure 3 shows a comparison of current-electric U-voltage characteristics of solar cells before and after the hydrogen passivation process. The results clearly show that the series resistance is greatly reduced, and the filling factor is increased from 76.99% to 81.25%. Moreover, the short-circuit current increases. These improvements will increase conversion efficiency from 12 33 % to 13.39 %. ° Example 2 In this example, a single crystal germanium solar cell was fabricated. The structure and process of fabrication are the same as in Example 1. In addition, the plasma conditions and processing conditions are also the same as 200919740 25204twf.doc/n. Figure 4 shows the comparison of the current-voltage characteristics of the Taien battery before and after the hydrogen passivation process. The results show that the fill factor result increases from 75 〇〇% to 80·77 X»The same day, the short-circuit current increases from 0.23 A to 0.25 A'. The open circuit voltage also increased from 0.59 V to 〇.6 v. These improvements have increased conversion efficiency from 14_25% to 17.06%. In summary, the present invention can greatly reduce the time and cost of the hydrogen passivation process and effectively improve the efficiency of the crystallization solar cell compared with the prior art. Moreover, the equipment used is relatively simple and economical for mass production. The invention can be applied to different types of crystalline germanium solar cells. In particular, hydrogen passivation is carried out for solar cells in which the efficiency cannot meet the requirements, so that the efficiency is improved and the production yield is increased. In addition, the present invention does not need to change other existing production methods of solar cells, and is a stand-alone process with high integration. Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. The scope of protection of the present invention is defined by the scope of the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front cross-sectional view of a typical solar cell. Fig. 2 is a schematic view showing a hydrogen passivation process of the crystalline germanium solar cell of the present invention. A multi-crystalline silicon as shown in Fig. 1 is a graph of the electrical (four) curve of the battery under the die-cut (1)-) before and after the hydrogen passivation process. ...., 12 25204twf.doc/n 200919740 Fig. 4 is a graph showing the electrical (I-V) curve of a single crystal silicon solar cell shown in Fig. 1 under simulated ΑΜ1·5 illuminance before and after the hydrogen passivation process. [Main component symbol description] 10: Solar cell 100. Crystalline wafer 102: Random pyramid structure 104: ρη bonding 106: Surface purification layer 108: Antireflection layer 112, 114: Electrode 116: Dielectric layer 200. Too 11⁄4 can Battery wafer 202: vacuum chamber 204: wafer tray 206: gas supply device 208: microwave or radio frequency power generator 210: plasma source 212: pulse generator 13

Claims (1)

200919740 25204tw f.doc/] X. Patent application scope: Method of seeding* ... The surface of the wafer has an electrode and an anti-reflection layer; flows to the vacuum chamber to a predetermined pressure; slurry; , pin microwave power is smooth (10) in the body to produce hydrogen electricity O rhyme * 彳 α pulse generation a provides - a predetermined voltage magnitude, pulse = pulse t time width of a negative pulse voltage to the crystalline stone solar energy t Li - Processing time to implant a quantity of hydrogen ions into the crystallized stone, wherein the negative pulse voltage is controlled within a set range so as not to damage the anti-reflection layer. - Section ♦ Patent No. 1 The method of 虱 passivation of a solar cell of a solar cell, wherein the negative pulse voltage is between -5 GG V and · 5 kV. #3·If the application is to supplement the passivation of the sand-binding solar cell described in Item 1. The method of supplying the negative pulse voltage is between 1 20 and 20 psec. The method of hydrogen passivation of the crystalline germanium solar cell according to claim 1, wherein the pulse frequency is Between 100 Hz and 20 kHz <5. The method of hydrogen passivation of a crystalline germanium solar cell according to claim 1, wherein the processing time is between 1 minute and 10 minutes. ^ 6. If the patent application scope is the first item The method for crystallization of a crystalline germanium solar cell, wherein during step d, heating the crystalline germanium solar cell wafer to 3 〇〇t: 〜350. (: temperature. 14