KR20090025998A - Manufacturing method of high efficiency solar cell using laser - Google Patents

Abstract

The present invention provides a method of preparing a semiconductor substrate, depositing a conductive layer on the entire surface of the semiconductor substrate, and annealing the conductive layer using a laser to partially diffuse the conductive layer material into the substrate, thereby moving electrons. It relates to a method of manufacturing a high efficiency solar cell using a laser comprising the step of forming a passage.

According to this configuration of the present invention, in recent years, as the substrate becomes thinner, in the solar cell which exhibits a limit in increasing the efficiency of the solar cell by increasing the contact area between the substrate and the electrode, the electron transfer path is formed by diffusion of the conductive layer. Since it can be added, it is possible to minimize the resistive loss during electron transfer, and to provide a highly efficient solar cell by minimizing the shielding loss of the electrode.

Description

Manufacturing method of high efficiency solar cell using laser {METHOD FOR MANUFACTURING A SOLAR CELL USING A LASER ANEANING}

The present invention relates to a method of manufacturing a high efficiency solar cell using a laser, and more particularly, to provide a charge transfer path between a substrate and an electrode by using a laser to reduce the contact resistance therebetween, and to reduce the shielding loss of the electrode. It relates to a method for manufacturing a high efficiency solar cell using a laser to provide a high efficiency solar cell.

In general, as illustrated in FIG. 1, a solar cell generates a pair of electrons and holes inside a semiconductor of a solar cell by light from outside, and generates an electron by an electric field generated at a pn junction of the electron and hole pair. Moves to the n-type semiconductor and holes move to the p-type semiconductor to produce power.

To increase the efficiency of the solar cell 1, as shown in FIG. 2, the front surface of the substrate is formed by forming a groove 2a on the front surface of the silicon substrate 2 with a laser or the like and filling the inside of the groove 2a with a conductive material. The metal electrode 3 is formed in a recessed shape. This is called a buried contact solar cell (BCSC).

The solar cell of the recessed electrode structure has a low contact resistance because the contact area with the substrate is larger than that of the electrode formed on the upper surface of the substrate, and a loss caused by the electrode being disposed on the upper surface of the substrate to prevent absorption of sunlight. The shading loss can be reduced by 2-3%. Therefore, the solar cell of the recessed electrode structure is known to be suitable for high efficiency and low price of the solar cell.

However, in recent years, research for manufacturing a high efficiency solar cell using a substrate having a thickness of 200 μm or less, which is thinner than a conventional thickness of about 300 to 400 μm, has been conducted according to the increase in the substrate price.

As the substrate of the solar cell is thinned to a thickness of 200 μm or less, there is a limit in lowering the contact resistance by increasing the contact area between the electrode and the substrate, and mechanically, chemically, and physically Since the substrate must be formed, there is a problem that the substrate is easily damaged.

In addition, solar cells generally form electrodes in an emitter layer doped with impurities on the front surface of a semiconductor substrate so that electrons move to the emitter layer and are collected at the electrode. At this time, a loss occurs during the movement of electrons to the electrode. To minimize this, a high concentration of doping is performed on the emitter layer so as to reduce the resistance or minimize the loss due to the movement. .

However, when the doping amount in the emitter layer was increased, there was a problem in that the short wavelength photoresponsiveness was deteriorated or recombination loss was increased. When the electrode spacing was narrowed, the area of the front electrode was increased so that the shadowing loss of light was large. There is a problem.

In addition, in order to increase the doping amount of the impurity in the epitaxial layer, the semiconductor substrate must be subjected to a high temperature heat treatment at 800 or higher, so that impurities such as metals from the electrode or the substrate are damaged by thermal load.

Accordingly, the present invention has been made to solve the above problems, and an object of the present invention is to provide a highly efficient solar cell using a laser to form an electrode to minimize the loss of resistance and electron blocking on the thin film silicon substrate. It is to provide a manufacturing method.

 In addition, an object of the present invention is to reduce the contact resistance of the substrate and the electrode even if the semiconductor substrate is thin, and do not cause mechanical, chemical, physical damage to the substrate, the impurities are introduced over a wide area or the substrate is heated by thermal load It is to provide a method of manufacturing a high efficiency solar cell that can prevent damage.

It is also an object of the present invention to provide a method of manufacturing a high efficiency solar cell using a laser that does not dopant impurities to the emitter layer at high concentration by high temperature heat treatment, so that the short wavelength photoresponse characteristics are not reduced or recombination loss is increased.

According to an embodiment of the present invention, a method of manufacturing a high efficiency solar cell using a laser may include preparing a semiconductor substrate, depositing a conductive layer on the entire surface of the semiconductor substrate, and annealing the conductive layer using a laser. Allowing the conductive layer material to partially diffuse into the substrate to form an electron transfer path.

According to one embodiment of the invention, by forming a charge transfer path formed of a conductive material diffused from a low resistance conductive layer between the semiconductor substrate and the electrode, electrons can move through the charge transfer path to the electrode, thereby reducing the resistance loss It can be minimized, and the electrode gap can be widened to minimize the loss of light obstruction by the electrode.

In addition, according to an embodiment of the present invention, there is no need to mechanically, chemically, or physically form grooves on the semiconductor substrate, and do not need to dopants with high concentrations of impurities on the entire surface of the semiconductor substrate. This can prevent it from falling.

Hereinafter, a solar cell manufacturing method using a laser according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

3 is a cross-sectional view illustrating a method of manufacturing a solar cell according to an embodiment of the present invention. 4 is a flowchart of a method of manufacturing a solar cell according to an embodiment of the present invention.

3 and 4, according to an embodiment of the present invention, the solar cell 10 prepares a semiconductor substrate 11 (S10), and emitter layer 12 on one surface of the semiconductor substrate. The emitter layer 11 by forming a conductive layer 13 on the emitter layer 12 (S20) and locally annealing the conductive layer 13 according to an electrode pattern using a laser. In the electron transfer passage 13a (S40), and an electrode 15 electrically connected to the semiconductor substrate 11 corresponding to the electron transfer passage 13a is formed on the conductive layer 13 (S50) is prepared.

The semiconductor substrate 11 may be prepared as a p-type silicon substrate by doping a group III element as an impurity, wherein the group III element may include B, Ga, Al, and the like.

In general, the concentration of carriers (electrons or electrons) generated by light absorption is changed depending on the resistivity (doping concentration of impurities) of the semiconductor substrate 11. In addition, recombination, in which carriers are lost and not transported to the electrode, is also affected by the doping concentration. Accordingly, when the impurities are doped to the semiconductor substrate 11 at a high concentration and the specific resistance is small, the concentration of the carriers generated by light absorption increases and recombination increases, while the impurities are doped to the semiconductor substrate 11 at low concentration. Therefore, when the specific resistance is large, the concentration of carriers generated by light absorption decreases and recombination also decreases. That is, the loss due to carrier generation and recombination becomes a trade-off relationship.

The emitter layer 12 is prepared as an n-type silicon substrate by doping a Group 5 element as an impurity. Examples of the Group 5 element include P, As, and Sb.

In addition, an n-type silicon substrate doped with P, which is a Group 5 element, may be used as the semiconductor substrate 11. In this case, it is preferable to use a p-type silicon substrate doped with a Group 3 element as the emitter layer 12. Do.

Doping in the emitter layer 12 is carried out using a thermal diffusion process, the emitter layer 12 prepared by such a process has a profile that the doping concentration is high on the surface and the doping concentration is lowered toward the inside The resistance value can be large. Typically, the surface resistance measurement can be used to evaluate the degree of doping (the doping concentration and the depth of the doping is taken into account) from the measured surface resistance, which is the smaller the higher the doping concentration on the surface and the deeper the doping depth. Has. Therefore, in the related art, high temperature heat treatment may be performed such that a high concentration of impurities are doped on the surface of the emitter layer 12.

However, according to one embodiment of the invention, the conductive layer 14 is locally annealed for 1.5 to 3 sec at an output of 20 W on average using a laser in the 300 to 2000 nm wavelength band, as shown in FIG. As a result, even when the doping depth is limited to the thickness of the semiconductor substrate even if the doping depth is not performed on the surface of the emitter layer 12, the electron resistance passage 12a can be formed to lower the surface resistance value.

In addition, since the spot size is controlled to about 20㎛, the laser has a laser beam depth of about 60㎛ to 90㎛ can form an electron transport passage of about 20㎛ width, depth of about 60㎛ to 90㎛ Since the electron transfer passage can be formed, the electron transfer passage 12a can be formed while minimizing the thermal effect on the periphery to help the movement of the electrons, thereby exhibiting excellent photoelectric conversion efficiency of the battery.

The electron transfer path 12a is made of a conductive material of the conductive layer 12, that is, a material having a lower specific resistance than the emitter layer 12, so that carriers generated in the emitter layer 12 are lost due to charge recombination. It can move toward the electrode 15 without.

5 is a graph showing the surface contact resistance of the conventional solar cell and the surface contact resistance of the solar cell according to an embodiment of the present invention.

In Fig. 5, the slope of graph A shows the surface contact resistance value in the recessed electrode structure, and the graph B shows the surface contact resistance value in the solar cell using the semiconductor substrate of about 200 mu m or less. In the solar cell according to the exemplary embodiment of the present invention, the surface contact resistance value is shown.

In the case of the recessed electrode structure, the contact area was increased to have a contact resistance of about 30 ohm / cm. However, when the thickness of the semiconductor substrate 11 is about 200 μm or less, there is a limit to widening the contact area. It can be seen that the contact resistance value of from 100 ohm / cm.

However, even when the thickness of the semiconductor substrate 11 is 200 μm or less, the solar cell 10 according to the exemplary embodiment of the present invention uses a laser beam even if the doping concentration of impurities is not increased or the doping depth is deepened. It can be seen that having a low resistance electron transfer passage 13a formed by locally annealing the layer 13 exhibits a contact resistance value of about 20 ohm / cm to 100 ohm / cm or less.

The semiconductor substrate 10 and the emitter layer 12 are in contact with each other to form a p-n junction.

The conductive layer 13 formed on the emitter layer 12 is a movement path of electrons having a low resistance value and may serve as an antireflection film in a conventional solar cell.

Specifically, the conductive layer 13 is made of a conductive transparent electrode layer, has a lower specific resistance (ρ) than the emitter layer 12, has a wavelength range of about 300 to 2000nm, Nd: YAG to provide an infrared wavelength range It consists of a material that can absorb about 90% or more of the laser beam of the laser.

When the transparency of the conductive layer 13 is less than 90%, the amount of light incident is reduced, which is not preferable.

To this end, the conductive layer 13 is made of indium tin oxide (ITO), tin oxide (SnO _2, etc.), AgO, ZnO- (Ga ₂ O ₃ or Al ₂ O ₃ ), fluorine tin oxide (fluorine tin oxide: FTO), and mixtures thereof are preferably used.

The conductive layer 13 having such a configuration has a low refractive index as well as a low absorption rate of the film itself and a low transmittance so as to minimize the physical properties and the reflection loss required for the conventional antireflection film and to reduce the recombination loss on the substrate surface. High and good surface passivation properties are preferred.

The electrode 15, which may be formed separately on the electron transfer path 13a of the conductive layer 13, has a low resistance value of Al, Ag, Ni, Cu, Ti, Pd, Cr, W, a conductive polymer, and their It is preferably selected from the group consisting of combinations. In particular, by using the Ag paste, the contact resistance value was lowered and the electrode could be easily formed by screen printing or the like.

As described above, the electrode 15 is electrically connected to the conductive layer 13 by using the electron moving passage 13a, so that the electrode 15 may be spaced apart from each other in consideration of the loss during the electron movement. Can be solved.

That is, a plurality of electrodes 15 are spaced apart at regular intervals on the conductive layer 13 while considering a trade-off relationship between the resistive loss according to the resistivity of the conductive layer 13 and the strong reflection loss due to the electrode area. can do.

Accordingly, the electrodes 16 are preferably spaced at intervals of 2.5 to 8mm. When the separation distance between the electrodes 15 is less than 2.5 mm, the total area of the electrodes 15 formed on the conductive layer 13 is increased, which may cause a loss of light obscured by the electrodes. In addition, if the separation distance exceeds 8mm it is not preferable because the resistance loss may occur.

The electrode 15 may form a first electrode on a front surface of the semiconductor substrate 11 and a second electrode formed on a rear surface of the semiconductor substrate 11 to be electrically connected to the semiconductor substrate 11.

When light is irradiated into the p-n junction of the solar cell 10 having the above structure, electrons and holes are generated inside the semiconductor by light energy. In general, when light below the band gap energy enters the semiconductor, the light interacts weakly with electrons in the semiconductor, and when light above the band gap enters the electrons in the covalent bond to generate electrons or holes. The electrons generated by the light energy move toward the emitter layer 12, which is an n-type semiconductor, and then collect through the conductive layer 13 and the electron transfer passage 13a to the first electrode 15. After moving toward the semiconductor substrate 11 which is a p-type semiconductor by an electric field, they are collected at a second electrode (not shown). When the first and second electrodes are connected with a conductive wire, a current flows, which is used as power from the outside.

However, prior to the emitter layer forming process, the semiconductor substrate may be selected from a group consisting of a surface damage removal process during fabrication of the substrate, a substrate surface unevenness forming process for reducing surface reflectance, and a substrate cleaning process. The preliminary step may be optionally further carried out. Since the processes are well known in the art, detailed description thereof is omitted herein.

The solar cell manufactured by the above method may exhibit excellent photoelectric conversion efficiency because the loss due to the resistance to electron transfer and the electrode covering is minimized. In addition, impurities in the emitter layer can be doped at low concentrations, thereby improving short wavelength photoresponse characteristics and minimizing recombination losses.

      1 is a schematic cross-sectional view for explaining the configuration of a general solar cell.

2 is a cross-sectional view illustrating a method of forming a recessed electrode structure for manufacturing a high efficiency solar cell.

3 is a cross-sectional view illustrating a method of manufacturing a solar cell according to an embodiment of the present invention.

4 is a flowchart of a method of manufacturing a solar cell according to an embodiment of the present invention.

5 is a graph showing the surface contact resistance of the conventional solar cell and the surface contact resistance of the solar cell according to an embodiment of the present invention.

[Description of main part of drawing]

1, 10: solar cell 11: semiconductor substrate

12: emitter layer 13: conductive layer

15: electrode

Claims (11)

Preparing a semiconductor substrate, depositing a conductive layer on the entire surface of the semiconductor substrate, and locally annealing the conductive layer using a laser to partially diffuse the conductive layer material into the semiconductor substrate, thereby transferring electrons. Method of manufacturing a high efficiency solar cell using a laser comprising the step of forming a. The method of claim 1, Forming a first electrode electrically connected to an upper portion of the conductive layer connected to the electron transfer path, and forming a second electrode electrically connected to the semiconductor substrate on a rear surface of the semiconductor substrate; Method for manufacturing a high efficiency solar cell using. The method of claim 1, The method of manufacturing a high efficiency solar cell using a laser further comprising the step of forming an emitter layer on the semiconductor substrate. The method of claim 3, The conductive layer is a method of manufacturing a high efficiency solar cell using a laser having a lower specific resistance than the emitter layer The method of claim 1, The electron transfer path is a method of manufacturing a high efficiency solar cell using a laser having a resistance value within the range of 20 ~ 100 ohm / cm. The method of claim 3, The emitter layer is a method of manufacturing a high efficiency solar cell using a laser having a resistance value within the range of 50 ~ 100 ohm / cm. The method of claim 1, The conductive layer is a method of manufacturing a high efficiency solar cell using a laser made of a material having a transmittance of 90% or more in the 300 to 2000nm wavelength range. The method of claim 1, The conductive layer is ITO, tin-based oxide, AgO, ZnO- (Ga ₂ O ₃ or Al ₂ O ₃ ), FTO and a method for manufacturing a high efficiency solar cell using a laser comprising a mixture thereof. The method of claim 1, The electron transfer path is a method of manufacturing a high efficiency solar cell using a laser having a depth of about 60 to 100nm. The method of claim 1, The laser is a pulsed laser, the method of manufacturing a high efficiency solar cell using a laser for irradiating a laser beam of about 300 to 2000nm wavelength range. The method of claim 10, The laser is a method of manufacturing a high efficiency solar cell using a laser locally annealed for 1.5 to 3 sec at a power of 20W on average using a freely adjustable CO2 laser or Nd: YAG laser in the 300 to 2000 nm wavelength band.

Images