Solar Cells

Abstract

A solar cell is disclosed. The solar cell includes: a first conductive region located at the front surface of a semiconductor substrate and containing impurities of a first conductive type or a second conductive type; a second conductive region located at the rear surface of the semiconductor substrate and containing impurities of a conductive type opposite to that of the impurities of the first conductive region; a first electrode located on the front surface of the semiconductor substrate and connected to the first conductive region; and a second electrode located on the rear surface of the semiconductor substrate and connected to the second conductive region. Each of the first electrode and the second electrode includes metal particles and glass frit.

Description

[0001] This application is a divisional application of the original invention patent application with application number 201810110898.6 (application date: February 5, 2018, invention name: solar cell). Technical Field

[0002] Embodiments of the present invention relate to solar cells. Background Art

[0003] Recently, as existing energy sources such as oil and coal are expected to be exhausted, interest in alternative energy sources that replace existing energy sources is increasing. Among alternative energy sources, solar cells for generating electricity from solar energy have attracted attention because they are abundant in energy resources and have no environmental pollution problems.

[0004] A solar cell generally includes a substrate and an emitter region formed of semiconductors having different conductivity types (eg, p-type and n-type), and electrodes connected to the substrate and emitter regions of different conductivity types, respectively. In this case, the substrate and the emitter region form a pn junction.

[0005] When light is incident on a solar cell, multiple electron-hole pairs are generated in the semiconductor by the incident light and separated into electrons and holes. The electrons move to the n-type semiconductor (e.g., the emitter region), and the holes move to the p-type semiconductor (e.g., the substrate). Then, the electrons and holes are collected by electrodes electrically connected to the substrate and the emitter region. The electrodes are connected to each other using wires, thereby obtaining electricity.

[0006] A solar cell including a conductive region formed by doping a rear surface of a semiconductor substrate with impurities and a passivation layer between the conductive region and the semiconductor substrate is being developed recently to increase an open circuit voltage Voc.

[0007] However, since the thickness of the conductive region in the solar cell having the above structure is much smaller than that according to the related art, the back electrode is short-circuited with the semiconductor substrate because metal particles included in the back electrode penetrate the passivation layer between the conductive region and the semiconductor substrate when the back electrode connected to the conductive region is formed. Therefore, there is a problem of causing defects in the solar cell. Summary of the invention

[0008] Embodiments of the present invention provide a solar cell having a structure capable of reducing defects of the solar cell while improving an open circuit voltage.

[0009] In one aspect, a solar cell is provided, comprising: a semiconductor substrate; a first conductive region located at a front surface of the semiconductor substrate, the first conductive region containing impurities of a first conductive type or impurities of a second conductive type; a second conductive region located at a rear surface of the semiconductor substrate, the second conductive region containing impurities of a conductive type opposite to the conductive type of the impurities contained in the first conductive region, the second conductive region comprising a silicon material; a first electrode, the first electrode being located on the front surface of the semiconductor substrate and connected to the first conductive region; and a second electrode, the second electrode being located on the rear surface of the semiconductor substrate and connected to the second conductive region, wherein each of the first electrode and the second electrode comprises metal particles and glass frit, and wherein a content of the glass frit per unit volume contained in the second electrode is less than a content of the glass frit per unit volume contained in the first electrode.

[0010] For example, the content of the glass frit contained in the first electrode per unit volume may be 6 wt % to 8 wt %, and the content of the glass frit contained in the second electrode per unit volume may be 2.5 wt % to 5.0 wt %.

[0011] The content of the metal particles per unit volume contained in the first electrode may be greater than the content of the metal particles per unit volume contained in the second electrode. For example, the content of the metal particles per unit volume contained in the first electrode may be 82 wt % to 92 wt %, and the content of the metal particles per unit volume contained in the second electrode may be 68 wt % to 73 wt %.

[0012] The solar cell may further include: an anti-reflection layer on the front surface of the first conductive region; a control passivation layer between the rear surface of the semiconductor substrate and the second conductive region, the control passivation layer comprising a dielectric material; and a back passivation layer on the rear surface of the second conductive region. The thickness of the back passivation layer may be less than the thickness of the anti-reflection layer and may be greater than the thickness of the control passivation layer.

[0013] For example, the thickness of the anti-reflection layer is 100 nm to 140 nm, and the thickness of the back passivation layer may be within a range smaller than that of the anti-reflection layer and be 65 nm to 105 nm.

[0014] The thickness of the control passivation layer may be less than that of the back passivation layer, and may be, for example, 0.5 nm to 10 nm.

[0015] In addition, the thickness of the second conductive region may be smaller than that of the first conductive region. For example, the thickness of the first conductive region may be 300 nm to 700 nm, and the thickness of the second conductive region may be within a range smaller than that of the first conductive region and be 290 nm to 390 nm.

[0016] The glass frit of the second electrode may include at least one of a PbO-based material and a BiO-based material.

[0017] The glass frit of the second electrode may further include tellurium oxide (TeO).

[0018] The glass frit including tellurium oxide TeO may have a melting point of 200°C to 500°C.

[0019] The second electrode may include: a first layer in which the glass frit including tellurium oxide TeO is located at an interface between the second electrode and the second conductive region; and a second layer in which the metal particles and the glass frit not including tellurium oxide TeO are located on the first layer.

[0020] Furthermore, crystallites formed by combining the metal particles of the second electrode and the silicon of the second conductive region may be distributed at the interface between the first layer and the second conductive region.

[0021] The glass frit of the first electrode may include at least one of a PbO-based material and a BiO-based material. The glass frit of the first electrode may further include tellurium oxide (TeO).

[0022] The metal particles of the first electrode may include first metal particles having a circular or elliptical shape and second metal particles having a major axis and having a plate shape including an uneven surface. The metal particles of the second electrode may include first metal particles and may not include second metal particles.

[0023] A length of a major axis of a second metal particle included in the first electrode may be greater than a size of the first metal particle included in each of the first electrode and the second electrode.

[0024] In another aspect, a solar cell is provided, comprising: a semiconductor substrate; a first conductive region located at a front surface of the semiconductor substrate, the first conductive region containing impurities of a first conductive type or impurities of a second conductive type; a control passivation layer located on a rear surface of the semiconductor substrate, the control passivation layer comprising a dielectric material; a second conductive region located at the rear surface of the semiconductor substrate, the second conductive region containing impurities of a conductive type opposite to the conductive type of the impurities contained in the first conductive region, the second conductive region comprising a polysilicon material; a first electrode located on the front surface of the semiconductor substrate and connected to the first conductive region; and a second electrode located on the rear surface of the semiconductor substrate and connected to the second conductive region, wherein each of the first electrode and the second electrode comprises metal particles and glass frit, and wherein the glass frit of the first electrode comprises tellurium oxide (TeO).

[0025] The glass frit of the second electrode may include tellurium oxide (TeO).

[0026] An embodiment of the present invention allows the content of glass contained in the second electrode located on the rear surface of the semiconductor substrate to be less than the content of glass contained in the first electrode located on the front surface of the semiconductor substrate, so when the second electrode is connected to the second conductive region by heat treatment, the depth of the second electrode burn-through can be controlled.

[0027] Therefore, the embodiments of the present invention can prevent metal particles penetrating the second conductive region and the second electrode controlling the passivation layer from being short-circuited with the semiconductor substrate and prevent defects that may occur while increasing the open circuit voltage Voc of the solar cell during the manufacturing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The accompanying drawings illustrate embodiments of the present invention and together with the description serve to explain the principles of the present invention. In the drawings:

[0029] Figure 1 is a partial perspective view of a solar cell according to an embodiment of the present invention.

[0030] Figure 2 yes Figure 1 A cross-sectional view of a solar cell shown in FIG.

[0031] Figure 3 is a table indicating experimental results of contact resistance, passivation function (or composite level), and open circuit voltage according to the content of glass frit included in the second electrode.

[0032] Figure 4 When Figure 3 An enlarged cross-sectional view of a portion of a solar cell including a semiconductor substrate, a control passivation layer, a second conductive region, and a second electrode when the content of the glass frit exceeds an appropriate level.

[0033] Figure 5 When Figure 3 An enlarged cross-sectional view of a portion of a solar cell including a semiconductor substrate, a control passivation layer, a second conductive region, and a second electrode when the content of the glass frit is at an appropriate level.

[0034] Figure 6 is Figure 3 and Figure 4 An enlarged cross-sectional view of a portion of a solar cell including a semiconductor substrate, a control passivation layer, a second conductive region, and a second electrode when the glass frit further includes tellurium oxide (TeO) while the content of the glass frit is maintained at an appropriate level.

[0035] Figure 7 The metal particles included in the first electrode and the second electrode according to the embodiment of the present invention are illustrated. DETAILED DESCRIPTION

[0036] Reference will now be made in detail to embodiments of the present invention, examples of which are shown in the accompanying drawings. However, the present invention may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. Whenever possible, the same reference numerals will be used throughout the accompanying drawings to refer to the same or similar parts. It will be noted that a detailed description of known techniques will be omitted if it is determined that such a detailed description would obscure embodiments of the present invention.

[0037] In the following description, unless otherwise specified, the content of metal particles and the content of glass frit indicate the content per unit volume.

[0038] Will refer to Figures 1 to 7 Embodiments of the present invention are described.

[0039] Figure 1 is a partial perspective view of a solar cell according to an embodiment of the present invention. Figure 2 yes Figure 1 A cross-sectional view of a solar cell shown in FIG.

[0040] like Figure 1 As shown, an example of a solar cell according to an embodiment of the present invention may include a semiconductor substrate 110 , a first conductive region 120 , an anti-reflection layer 130 , a control passivation layer 160 , a second conductive region 170 , a back passivation layer 190 , a first electrode 140 , and a second electrode 150 .

[0041] Figure 1 The solar cell according to the embodiment of the present invention includes the anti-reflection layer 130 by way of example. However, the embodiment is not limited thereto. For example, if necessary or necessary, the anti-reflection layer 130 can be omitted. However, when the solar cell includes the anti-reflection layer 130, the efficiency of the solar cell can be further improved. Therefore, the embodiment of the present invention is described using a solar cell including the anti-reflection layer 130 as an example.

[0042] The semiconductor substrate 110 may be formed of at least one of single crystal silicon and polycrystalline silicon each containing impurities of the first conductivity type or the second conductivity type. For example, the semiconductor substrate 110 may be formed of a single crystal silicon wafer.

[0043] The semiconductor substrate 110 may include impurities of a first conductivity type or impurities of a second conductivity type. In the embodiments disclosed herein, the impurities of the first conductivity type may be n-type impurities or p-type impurities, and the impurities of the second conductivity type may be impurities of a conductivity type opposite to the first conductivity type.

[0044] For example, when the first conductivity type is p-type, the second conductivity type may be n-type. Conversely, when the first conductivity type is n-type, the second conductivity type may be p-type.

[0045] In the following description, an embodiment in which the first conductivity type is a p-type, the second conductivity type is an n-type, and the semiconductor substrate 110 contains impurities of the second conductivity type (ie, n-type impurities) will be described as an example.

[0046] When the semiconductor substrate 110 is a p-type, the semiconductor substrate 110 may be doped with impurities of a group III element such as boron (B), gallium (Ga), and indium (In). Alternatively, when the semiconductor substrate 110 is an n-type, the semiconductor substrate 110 may be doped with impurities of a group V element such as phosphorus (P), arsenic (As), and antimony (Sb).

[0047] In the following description, the embodiment of the present invention is described using an example in which the impurities included in the semiconductor substrate 110 are impurities of the second conductivity type and are n-type impurities. However, the embodiment of the present invention is not limited thereto.

[0048] The front and rear surfaces of the semiconductor substrate 110 may be uneven surfaces having a plurality of textured uneven portions or having uneven characteristics. Therefore, the first conductive region 120 located on the front surface of the semiconductor substrate 110 may have an uneven surface, and the second conductive region 170 located on the rear surface of the semiconductor substrate 110 may have an uneven surface.

[0049] In the embodiments disclosed herein, a “textured uneven portion” refers to an uneven portion formed on a surface of a solar cell in order to reduce the amount of reflected light and may have, for example, a pyramid shape.

[0050] Therefore, the amount of light reflected from the front surface of the semiconductor substrate 110 may be reduced, and the amount of light incident to the inside of the semiconductor substrate 110 may be increased.

[0051] The first conductive region 120 is located at the front surface of the semiconductor substrate 110 where light is incident, and may contain impurities of the first conductive type or impurities of the second conductive type.

[0052] Therefore, the first conductive region 120 may contain n-type impurities or p-type impurities.

[0053] For example, when the semiconductor substrate 110 includes n-type impurities, the first conductive region 120 may include p-type impurities and form a pn junction with the semiconductor substrate 110. In this case, the first conductive region 120 may function as an emitter region.

[0054] In contrast, when the semiconductor substrate 110 includes p-type impurities, the first conductive region 120 may include n-type impurities at a higher concentration than the semiconductor substrate 110 and may function as a front surface field region.

[0055] Alternatively, when the semiconductor substrate 110 includes p-type impurities, the first conductive region 120 may include n-type impurities or p-type impurities. When the first conductive region 120 is n-type, impurities of group V elements such as phosphorus (P), arsenic (As), and antimony (Sb) may be distributed into the front surface of the semiconductor substrate 110 by heat treatment to form the first conductive region 120.

[0056] In contrast, when the first conductive region 120 is of p-type, impurities of group III elements such as boron (B), gallium (Ga), and indium (In) may be distributed into the front surface of the semiconductor substrate 110 through thermal treatment to form the first conductive region 120 .

[0057] In the following description, the embodiment of the present invention is described using an example in which the first conductive region 120 contains impurities of a conductivity type opposite to that of impurities contained in the semiconductor substrate 110 to function as an emitter region.

[0058] Since the first conductive region 120 is formed by distributing n-type impurities or p-type impurities to the front surface of the semiconductor substrate 110 as described above, the first conductive region 120 may be formed of the same single crystal silicon material or polycrystalline silicon material as the semiconductor substrate 110 .

[0059] Therefore, when the semiconductor substrate 110 is formed of a single crystalline silicon wafer, the first conductive region 120 may be formed of a single crystalline silicon wafer. When the semiconductor substrate 110 is formed of a polycrystalline silicon wafer, the first conductive region 120 may be formed of a polycrystalline silicon wafer.

[0060] The thickness of the first conductive region 120 may be 300 nm to 700 nm.

[0061] The anti-reflection layer 130 is located on the first conductive region 120. The anti-reflection layer 130 may be formed of aluminum oxide (AlOx), silicon nitride (SiNx), silicon oxide (SiOx), and silicon oxynitride (SiOxNy), and may be formed as a single layer or a multilayer.

[0062] The anti-reflection layer 130 may reduce reflection of light incident on the solar cell and increase selectivity of a predetermined wavelength band, thereby increasing efficiency of the solar cell.

[0063] The thickness of the anti-reflection layer 130 may be 100 nm to 140 nm.

[0064] The first electrode 140 is disposed on the first conductive region 120 and directly contacts the first conductive region 120. The first electrode 140 may be electrically connected to the first conductive region 120.

[0065] like Figure 1 and Figure 2 As shown, the first electrode 140 may include a plurality of first finger electrodes 141 extending along a first direction x (e.g., x-axis direction) and a plurality of first bus bar electrodes 142 extending along a second direction y (e.g., y-axis direction) intersecting the plurality of first finger electrodes 141 and connected to the plurality of first finger electrodes 141.

[0066] like Figure 1 and Figure 2 As shown, when the semiconductor substrate 110 is of the n-type, the first electrode 140 may collect carriers (eg, holes) moving to the p-type first conductive region 120 .

[0067] The first electrode 140 is connected to an interconnector (not shown) connecting the solar cells to each other, and outputs the collected carriers to an external device.

[0068] The first electrode 140 may include metal particles and glass frit. More specifically, the metal particles may include at least one of nickel (Ni), copper (Cu), silver (Ag), aluminum (Al), tin (Sn), zinc (Zn), indium (In), titanium (Ti), gold (Au), and combinations thereof.

[0069] The melting point of the metal particles may be higher than that of the glass frit. Therefore, after the first electrode 140 is completed, the metal particles may maintain their original shape in the slurry state, and the glass frit may be fired after it is completely melted. Therefore, the glass frit may have a shape different from that in the slurry state.

[0070] The first electrode 140 may be formed by patterning a first electrode paste on the anti-reflection layer 130 in a state where the anti-reflection layer 130 is formed on the front surface of the first conductive region 120, penetrating the first electrode paste while the first electrode paste is burned through the anti-reflection layer 130 by heat treatment, and firing the first electrode paste in a state where the first electrode paste is electrically connected to the first conductive region 120.

[0071] The control passivation layer 160 is entirely located on the rear surface of the semiconductor substrate 110 and may include a dielectric material.

[0072] For example, Figure 1 and Figure 2 As shown, the control passivation layer 160 on the rear surface of the semiconductor substrate 110 may directly contact the rear surface of the semiconductor substrate 110 .

[0073] In addition, the control passivation layer 160 may be formed on the entire rear surface of the semiconductor substrate 110 except for the edge of the rear surface.

[0074] The control passivation layer 160 may perform a dopant control function or diffusion barrier to prevent the dopant of the second conductive region 170 from excessively diffusing into the semiconductor substrate 110. In addition, the control passivation layer 160 may perform a passivation function of the rear surface of the semiconductor substrate 110.

[0075] The control passivation layer 160 may include various materials capable of controlling the diffusion of dopants and transporting various carriers. For example, the control passivation layer 160 may include oxides, nitrides, semiconductors, conductive polymers, and the like.

[0076] For example, the control passivation layer 160 may be a silicon oxide layer including silicon oxide. This is because the silicon oxide layer has good passivation characteristics and smoothly transfers carriers.

[0077] In addition, a silicon oxide layer may be easily formed on the surface of the semiconductor substrate 110 through various processes.

[0078] The control passivation layer 160 may be formed by various methods such as vapor deposition, thermal oxidation, and chemical oxidation. However, if necessary or desired, the control passivation layer 160 may be omitted.

[0079] The thickness of control passivation layer 160 may be less than that of back passivation layer 190 and may be, for example, 0.5 nm to 10 nm. Control passivation layer 160 may be formed by an oxidation process, a low pressure chemical vapor deposition (LPCVD) process, or a plasma enhanced chemical vapor deposition (PECVD) process.

[0080] The reason why the thickness of the control passivation layer 160 is limited to 0.5 nm to 10 nm is to achieve a tunneling effect. The control passivation layer 160 may perform a portion of a passivation function on the rear surface of the semiconductor substrate 110.

[0081] The second conductive region 170 is located at the rear surface of the semiconductor substrate 110. The second conductive region 170 may contain impurities of a conductivity type opposite to that of the impurities contained in the first conductive region 120, and may be formed of a polysilicon material.

[0082] Therefore, when the first conductive region 120 functions as an emitter region, the second conductive region 170 may function as a back surface field region.

[0083] like Figure 1 and Figure 2 As shown, the second conductive region 170 may be located at the rear surface of the control passivation layer 160 and spaced apart from the semiconductor substrate 110 .

[0084] The second conductive region 170 may be formed on the control passivation layer 160 by using a chemical vapor deposition (CVD) method. For example, the second conductive region 170 may be formed by depositing a polysilicon material containing impurities of the first conductive type on the control passivation layer 160. Alternatively, the second conductive region 170 may be formed by depositing an amorphous silicon material containing impurities of the first conductive type on the control passivation layer 160 and then crystallizing the amorphous silicon material into a polysilicon material by heat treatment.

[0085] Therefore, if Figure 1 and Figure 2 As shown, the second conductive region 170 is not formed inside the semiconductor substrate 110, but is formed on the rear surface of the semiconductor substrate 110, so that the second conductive region 170 does not directly contact the semiconductor substrate 110 and is spaced apart from the semiconductor substrate 110. As described above, when the second conductive region 170 is formed on the rear surface of the control passivation layer 160, the open circuit voltage Voc of the solar cell can be further improved.

[0086] Since the second conductive region 170 is not formed inside the semiconductor substrate 110 but is formed outside the semiconductor substrate 110, heat treatment of the semiconductor substrate 110 can be minimized in a process for forming the second conductive region 170. Therefore, degradation of the characteristics of the semiconductor substrate 110 can be prevented, and the efficiency of the solar cell according to the embodiment of the present invention can be further improved.

[0087] The thickness of the second conductive region 170 may be determined in consideration of the deposition time of the second conductive region 170, and is also selected to be an appropriate thickness capable of sufficiently performing the function of the second conductive region 170. For example, the thickness of the second conductive region 170 may be 290 nm to 390 nm within a range smaller than the thickness of the first conductive region 120.

[0088] The second electrode 150 is disposed on the second conductive region 170 and directly contacts the second conductive region 170. The second electrode 150 may be electrically connected to the second conductive region 170.

[0089] like Figure 1 and Figure 2 As shown, the second electrode 150 may include a plurality of second finger electrodes 151 extending along a first direction x and a plurality of second bus bar electrodes 152 extending along a second direction y crossing the plurality of second finger electrodes 151 and connected to the plurality of second finger electrodes 151 .

[0090] The second electrode 150 is connected to an interconnector connecting the solar cells to each other, and outputs the collected carriers to an external device.

[0091] The second electrode 150 may include metal particles and glass frit. More specifically, the metal particles having a melting point higher than that of the glass frit may include at least one of nickel (Ni), copper (Cu), silver (Ag), aluminum (Al), tin (Sn), zinc (Zn), indium (In), titanium (Ti), gold (Au), and combinations thereof.

[0092] The second electrode 150 may be formed by patterning the second electrode paste on the rear surface of the back passivation layer 190 in a state where the back passivation layer 190 is formed on the rear surface of the second conductive region 170, penetrating the second electrode paste through the back passivation layer 190 while the second electrode paste is burned through the back passivation layer 190 by heat treatment, and firing the second electrode paste in a state where the second electrode paste is electrically connected to the second conductive region 170.

[0093] like Figure 1 and Figure 2 As shown, the back passivation layer 190 may be located on a remaining portion excluding a portion where the second electrode 150 is formed from the rear surface of the second conductive region 170 .

[0094] The back passivation layer 190 may include a dielectric material and may be formed as a single layer or a multi-layer. The back passivation layer 190 may have specific fixed carriers in consideration of the conductivity type of the second conductive region 170 .

[0095] The back passivation layer 190 may be formed of at least one of silicon carbide (SiC), silicon oxide (SiOx), silicon nitride (SiNx), hydrogenated SiNx, aluminum oxide (AlOx), silicon oxynitride (SiON), or hydrogenated SiON.

[0096] The back passivation layer 190 may perform a passivation function of the rear surface of the second conductive region 170 .

[0097] The thickness of the back passivation layer 190 may be greater than that of the control passivation layer 160 and may be less than that of the anti-reflection layer 130 in order to sufficiently perform a passivation function of the rear surface of the second conductive region 170 .

[0098] Therefore, the thickness of the back passivation layer 190 may be, for example, 65 nm to 105 nm within a range greater than the thickness of the control passivation layer 160 and less than the thickness of the anti-reflection layer 130 .

[0099] So far, the embodiments of the present invention describe, by way of example, that the first conductive region 120 is used as the emitter region and the second conductive region 170 is used as the back surface field region.

[0100] For example, the semiconductor substrate 110 may include p-type impurities, the first conductive region 120 may include p-type impurities and function as a front surface field region, and the second conductive region 170 may include n-type impurities and function as a back surface field region.

[0101] In the above-described solar cell, each of the first electrode 140 and the second electrode 150 may include metal particles and glass frit.

[0102] In the embodiments disclosed herein, the metal particles may be, for example, Ag particles and may be related to the conductivity of each of the first electrode 140 and the second electrode 150. The glass frit may be related to the depth to which each of the first electrode 140 and the second electrode 150 is fired through.

[0103] The glass frit used in the first electrode 140 and the second electrode 150 according to the embodiment of the present invention may include at least one of a PbO-based material or a BiO-based material.

[0104] The content of the metal particles and the content of the glass frit included in each of the first electrode 140 and the second electrode 150 may be variously determined in consideration of the materials and thicknesses of the first conductive region 120 and the second conductive region 170 .

[0105] For example, the content of the metal particles contained in the first electrode 140 per unit volume may be greater than the content of the metal particles contained in the second electrode 150 per unit volume.

[0106] The first electrode 140 collects holes having a relatively slow moving speed, and the line width of the first electrode 140 must be smaller than that of the second electrode 150 so as to receive more light. Therefore, the first electrode 140 may have to have a relatively greater conductivity than that of the second electrode 150.

[0107] To this end, the content of the metal particles contained in the first electrode 140 per unit volume may be greater than the content of the metal particles contained in the second electrode 150 per unit volume.

[0108] For example, the content of the metal particles contained in the first electrode 140 per unit volume may be 82 wt % to 92 wt %, and the content of the metal particles contained in the second electrode 150 per unit volume may be 68 wt % to 73 wt %.

[0109] As mentioned above Figure 1 and Figure 2 As described, in the structure of the solar cell according to an embodiment of the present invention, the first conductive region 120 can be formed by, for example, a single crystal silicon substrate that is the same as the semiconductor substrate 110; the second conductive region 170 can be formed by a polycrystalline silicon material; the thickness of the second conductive region 170 can be relatively smaller than the thickness of the first conductive region 120; and the thickness of the back passivation layer 190 can be smaller than the thickness of the anti-reflection layer 130.

[0110] When the second electrode paste containing the same content of glass frit as that contained in the first electrode paste is patterned on the very thin or relatively thin control passivation layer 160, the second conductive region 170, and the back passivation layer 190 and is heat-treated, the second electrode paste may penetrate the control passivation layer 160 and the back passivation layer 190 and the second conductive region 170 during the heat treatment, may be directly electrically connected to the semiconductor substrate 110, and may be short-circuited with the semiconductor substrate 110.

[0111] Therefore, the embodiment of the present invention may allow the content of the glass frit included in the second electrode 150 to be different from the content of the glass frit included in the first electrode 140 .

[0112] More specifically, embodiments of the present invention may allow the content of glass frit per unit volume contained in the second electrode 150 to be less than the content of glass frit per unit volume contained in the first electrode 140 , so as to control the depth of the second electrode paste that penetrates the back passivation layer 190 and burns through toward the second conductive region 170 .

[0113] Therefore, the depth of the second electrode paste firing can be controlled by adjusting the content of the glass frit per unit volume.

[0114] More specifically, for example, when the content of the glass frit per unit volume in the first electrode 140 is 6 wt % to 8 wt %, the content of the glass frit per unit volume in the second electrode 150 may be 2.5 wt % to 5.0 wt %.

[0115] When the content of the glass frit per unit volume in the second electrode 150 is 2.5 wt % to 5.0 wt % as described above, the embodiment of the present invention can keep the contact resistance 170 between the second electrode 150 and the second conductive region 170 at a sufficiently low level, and prevent the second electrode 150 from penetrating the control passivation layer 160 and the back passivation layer 190 and the second conductive region 170 from being short-circuited with the semiconductor substrate 110. In addition, the embodiment of the present invention can prevent recombination that may occur in the rear surface of the semiconductor substrate 110 due to metal particles included in the second electrode 150, and can allow the control passivation layer 160 to fully perform a passivation function. In addition, the embodiment of the present invention can prevent damage to the control passivation layer 160 and improve the open circuit voltage Voc of the solar cell to a good level.

[0116] The following will refer to Figure 3 , Figure 4 and Figure 5 The effect according to the content of the glass frit of the second electrode 150 is described in detail.

[0117] Figure 3 is a table indicating experimental results of contact resistance, passivation function (or composite level), and open circuit voltage according to the content of glass frit included in the second electrode 150 .

[0118] Figure 4 When Figure 3 When the content of the glass frit exceeds an appropriate level, a portion of the solar cell including the semiconductor substrate 110, the control passivation layer 160, the second conductive region 170 and the second electrode 150 Figure 2 Enlarged cross-sectional view S1.

[0119] Figure 5 When Figure 3When the content of the glass frit is at an appropriate level, a portion of a solar cell including the semiconductor substrate 110, the control passivation layer 160, the second conductive region 170 and the second electrode 150 Figure 2 Enlarged cross-sectional view S1.

[0120] exist Figure 3 In the illustrated table, the content of the glass frit of the second electrode 150 indicates the content of the glass frit per unit volume, and may be different from the content of the glass frit 150G included in the second electrode paste per unit volume.

[0121] This is because the second electrode paste before the heat treatment may include a binder and a solvent of a resin material in addition to the metal particles 150M and the glass frit 150G, and the binder and the solvent may be mostly oxidized or evaporated during the heat treatment.

[0122] Therefore, if Figure 4 and Figure 5 As shown, after the heat treatment, metal particles 150M and glass frit 150G may exist in the second electrode 150 .

[0123] Therefore, the content of the glass frit 150G of the second electrode paste may be different from that of the second electrode 150 fired after the heat treatment. For example, the content of the glass frit 150G may increase by about 0.5 wt % to 1.0 wt % compared to before the second electrode 150 is fired.

[0124] exist Figure 3 In the table shown, the content of the glass frit 150G of the second electrode 150 is the content in the state where the second electrode 150 is fired after the heat treatment. The appropriate content of the glass frit 150G included in the second electrode paste before the heat treatment may be 2.0 wt % to 4.0 wt %, and may correspond to Figure 3 The appropriate content range is shown in the table (ie, 2.5 wt % to 5.0 wt %).

[0125] The embodiment of the present invention relates to the structure of a solar cell, and thus the structure of the solar cell is described below based on the content of the glass frit 150G of the second electrode 150 fired after the heat treatment.

[0126] exist Figure 3In the table shown, the contact resistance indicates the resistance between the second electrode 150 and the second conductive region 170. Therefore, a poor contact resistance means that the electrical connection between the second electrode 150 and the second conductive region 170 is not properly performed because the second electrode 150 cannot penetrate the back passivation layer 190 due to the very thin depth of the second electrode paste fired through. In addition, a good contact resistance means that the electrical connection between the second electrode 150 and the second conductive region 170 is properly performed.

[0127] The passivation function (or recombination level) indicates the passivation function of the control passivation layer 160. Therefore, a good passivation function means that the control passivation layer 160 is not damaged. In addition, a poor passivation function means that the control passivation layer 160 is damaged by the second electrode 150, and recombination occurs in the rear surface of the semiconductor substrate 110 due to the metal particles 150M of the second electrode 150.

[0128] A good open circuit voltage Voc means that the second conductive region 170 is spaced apart from the semiconductor substrate 110 by the control passivation layer 160, and the solar cell generates an appropriate level of open circuit voltage Voc. A poor open circuit voltage Voc means that the control passivation layer 160 is damaged due to the second electrode 150 deeply penetrating into the second conductive region 170, and the second electrode 150 and the semiconductor substrate 110 are short-circuited.

[0129] like Figure 3 As shown in the table, when the content of the glass frit per unit volume contained in the second electrode 150 is less than 2.5 wt %, the depth of the second electrode paste fired through is very thin. Therefore, the second electrode 150 is not properly connected to the second conductive region 170.

[0130] In addition, if Figure 4 As shown, when the content of the glass frit per unit volume included in the second electrode 150 exceeds 5.0 wt %, the second electrode 150 penetrates the control passivation layer 160 and the second conductive region 170 and short-circuits with the semiconductor substrate 110. Therefore, the function of the control passivation layer 160 is destroyed and the open circuit voltage Voc is deteriorated.

[0131] Figure 4 , “ 150M” denotes metal particles included in the second electrode 150 , and “ 150G” denotes glass frit included in the second electrode 150 .

[0132] When the content of the glass frit per unit volume contained in the second electrode 150 is maintained at an appropriate level of 2.5 wt % to 5.0 wt %, the depth of the second electrode paste firing through is appropriate. Therefore, the contact resistance, the passivation function, and the open circuit voltage are all maintained at excellent levels.

[0133] In addition, if Figure 5 As shown, when the content of the glass frit per unit volume contained in the second electrode 150 is maintained at an appropriate level of 2.5 wt % to 5.0 wt %, the second electrode 150 penetrates the back passivation layer 190 and penetrates into the second conductive region 170 to an appropriate depth. In this case, alloy crystallites (hereinafter referred to as “crystallites”) obtained by combining the metal particles 150M of the second electrode 150 and the silicon of the second conductive region 170 may be formed at the interface between the second electrode 150 and the second conductive region 170.

[0134] The metal particles 150M—silicon microcrystals (“microcrystals”) 153 may further reduce the contact resistance between the second electrode 150 and the second conductive region 170 .

[0135] So far, the embodiment of the present invention describes the content of the glass frit 150G per unit volume included in the second electrode 150 in order to control the depth of the second electrode 150 burning through the back passivation layer 190 inside the second conductive region 170 .

[0136] Embodiments of the present invention are described below. The glass frit 150G further includes tellurium oxide (TeO) so that the second electrode 150 penetrating the back passivation layer 190 is properly fired toward the second conductive region 170 and connected to the surface of the second conductive region 170 at an optimal level.

[0137] Figure 6 is Figure 3 and Figure 4 When the glass frit further includes tellurium oxide (TeO), a portion of a solar cell including a semiconductor substrate 110, a control passivation layer 160, a second conductive region 170, and a second electrode 150 is Figure 2 Enlarged cross-sectional view S1.

[0138] As described above, the second electrode 150 according to the embodiment of the present invention may include 2.5 wt % to 5.0 wt % of the glass frit 150G per unit volume, and the glass frit 150G may include at least one of a PbO-based material or a BiO-based material and tellurium oxide (TeO).

[0139] The melting point of the glass frit 150G containing tellurium oxide (TeO) may be relatively low. For example, the melting point of the glass frit 150G containing tellurium oxide (TeO) may be 200°C to 500°C.

[0140] Therefore, when the second electrode paste is fired and the back passivation layer 190 is etched in a heat treatment, the glass frit 150G containing tellurium oxide (TeO) may be melted first.

[0141] In this case, the glass frit 150G containing tellurium oxide (TeO) may first be widely disposed on the surface of the second conductive region 170 to form a layer. Thereafter, the metal particles 150M and the glass frit 150G not containing tellurium oxide (TeO) may be located on the layer where the glass frit 150G containing tellurium oxide (TeO) is located.

[0142] Therefore, if Figure 6 As shown, the second electrode 150 may include a first layer L1 and a second layer L2, in which the glass material 150G containing tellurium oxide (TeO) is located at the interface between the second electrode 150 and the second conductive region 170, and in the second layer L2, the metal particles 150M and the glass material 150G not containing tellurium oxide (TeO) are located above the first layer L1.

[0143] Crystallites 153 formed by combining the metal particles 150M and silicon of the second conductive region 170 may be distributed at an interface between the first layer L1 and the second conductive region 170 .

[0144] Therefore, the open circuit voltage Voc and the contact resistance between the second electrode 150 and the second conductive region 170 can be further improved, and the depth of the second electrode paste firing can be more easily controlled. As a result, the process margin of the solar cell can be further improved.

[0145] So far, the embodiments of the present invention have described the material and the material content of the second electrode 150 which are capable of controlling the depth of the second electrode paste fire-through to an appropriate level.

[0146] However, the glass frit 150G including tellurium oxide (TeO) may be applied to the first electrode 140 as well as the second electrode 150 .

[0147] For example, the glass frit 150G included in the first electrode 140 may include at least one of a PbO-based material or a BiO-based material, and the glass frit 150G may further include tellurium oxide (TeO).

[0148] So far, the embodiment of the present invention mainly describes the glass frit included in each of the first electrode 140 and the second electrode 150. Hereinafter, metal particles included in the first electrode 140 and the second electrode 150 will be described in detail.

[0149] Figure 7 The metal particles included in the first electrode 140 and the second electrode 150 according to the embodiment of the present invention are illustrated.

[0150] More specifically, for ease of explanation, Figure 7Only the metal particles M1 and M2 included in the first electrode 140 and the second electrode 150 are illustrated, and the Figure 5 and Figure 6 An example of a glass frit is shown in .

[0151] like Figure 7 As shown, metal particles M1 and M2 may be included in the first electrode 140 and the second electrode 150 .

[0152] More specifically, the metal particles included in the first electrode 140 may include first metal particles M1 each having a spherical shape of a circle or an ellipse and second metal particles M2 each having a long axis and having a plate shape including an uneven surface. In addition, the metal particles included in the second electrode 150 may include the first metal particles M1, and may not include the second metal particles M2.

[0153] For example, Figure 7 As shown, the first finger electrodes 141 of the first electrode 140 may include first metal particles M1, and the first bus bar electrodes 142 of the first electrode 140 may include first metal particles M1 and second metal particles M2.

[0154] In addition, the second finger electrodes 151 and the second bus bar electrodes 152 of the second electrode 150 may include the first metal particles M1 , and may not include the second metal particles M2 .

[0155] The length of the major axis of the second metal particles M2 included in the first electrode 140 may be greater than the size of the first metal particles M1 included in each of the first electrode 140 and the second electrode 150 .

[0156] For example, the diameter of the first metal particles M1 may be 200 nm to 2.5 μm, more preferably 300 nm to 2.0 μm. In addition, the size of the second metal particles M2 may be 3.0 μm to 6.0 μm.

[0157] Therefore, the first electrode 140 may include second metal particles M2 having a volume greater than that of metal particles in the second electrode 150 .

[0158] Since the first electrode 140 includes the second metal particles M2 having a relatively large size as described above, the reactivity of the metal particles can be further improved in the heat treatment of firing. In addition, the electrode can be fired more easily at a relatively low temperature, and the electrical characteristics (e.g., resistance) of the first electrode 140 can be further improved.

[0159] The first electrode 140 may be formed by performing a printing process twice on the first electrode paste, and the second electrode 150 may be formed by performing a printing process once on the second electrode paste.

[0160] More specifically, the first electrode 140 may be formed by a first printing process and a second printing process. In the first printing process, a first bus bar electrode paste including first metal particles M1 and second metal particles M2 may be printed on the front surface of the semiconductor substrate 110 along the second direction and then dried. In the second printing process, a first finger electrode paste including first metal particles M1 may be printed on the front surface of the semiconductor substrate 110 along the first direction and then dried. Next, the first electrode 140 may be formed by performing a heat treatment on the first bus bar electrode paste and the first finger electrode paste.

[0161] The second electrode 150 may be formed by once printing a second electrode paste including the first metal particles M1 on the rear surface of the semiconductor substrate 110 according to the pattern of the second finger electrodes 151 and the pattern of the second bus bar electrodes 152 and performing heat treatment on the second electrode paste.

[0162] However, the metal particles M1 and M2 included in the first electrode 140 and the second electrode 150 are not limited to Figure 7 , and can be compared with Figure 7 Differently formed.

[0163] For example, the first electrode 140 may be formed by printing a first electrode paste including first metal particles M1 and second metal particles M2 according to a pattern of the first finger electrodes 141 and a pattern of the first bus bar electrodes 142 and drying it, and then printing a separate first electrode paste including only the first metal particles M1 according to a pattern of the first finger electrodes 141 and a pattern of the first bus bar electrodes 142.

[0164] In this case, the first finger electrodes 141 and the first bus bar electrodes 142 may include the second metal particles M2 having a relatively large volume.

[0165] Therefore, the first electrode 140 may include metal particles having a relatively larger volume than metal particles of the second electrode 150 .

[0166] Although embodiments have been described with reference to a number of illustrative embodiments of the present disclosure, it will be appreciated that those skilled in the art may conceive of many other modifications and embodiments that will fall within the scope of the principles of the present disclosure. More specifically, various changes and modifications may be made to the components and / or arrangements of the subject combination arrangement within the scope of the present disclosure, the drawings, and the appended claims. In addition to changes and modifications to the components and / or arrangements, alternative uses will also be apparent to those skilled in the art.

[0167] CROSS-REFERENCE TO RELATED APPLICATIONS

[0168] This application claims the benefit of priority to Korean Patent Application No. 10-2017-0016816 filed on February 7, 2017, Korean Patent Application No. 10-2017-0044075 filed on April 5, 2017, and Korean Patent Application No. 10-2017-0160457 filed on November 28, 2017, which are hereby incorporated by reference in their entirety.

Claims

1. A solar cell, comprising: Single crystal silicon substrate; an emitter region located at the front surface of the single crystal silicon substrate; an anti-reflection layer located on the emitter region; a dielectric layer on the rear surface of the single crystal silicon substrate; a polysilicon back surface field layer located on the dielectric layer; a back passivation layer located on the polysilicon back surface field layer; a first electrode connected to the emitter region through the anti-reflection layer; as well as A second electrode connected to the polysilicon back surface field layer through the back passivation layer, wherein each of the first electrode and the second electrode comprises silver particles and glass frit, wherein microcrystals formed by the combination of the silver particles of the second electrode and the silicon of the polysilicon back surface field layer are formed at the interface between the second electrode and the polysilicon back surface field layer, but are not formed in the dielectric layer and the back surface of the single crystal silicon substrate, wherein the content of the glass frit per unit volume contained in the second electrode is less than the content of the glass frit per unit volume contained in the first electrode, The content of the glass frit per unit volume contained in the first electrode is 6 wt % to 8 wt %, and Wherein, the content of the glass frit per unit volume contained in the second electrode is 2.5 wt % to 5.0 wt %; Each of the glass frits of each of the first electrode and the second electrode includes tellurium oxide TeO; wherein the second electrode includes: a first layer in which a glass frit including tellurium oxide TeO is located at an interface between the second electrode and the polysilicon back surface field layer; and A second layer, wherein glass frit not including tellurium oxide Te0 is located on the first layer. 2 . The solar cell according to claim 1 , wherein a content per unit volume of silver particles contained in the first electrode is greater than a content per unit volume of silver particles contained in the second electrode.

3. The solar cell according to claim 2, wherein: The content of silver particles per unit volume contained in the first electrode is 82 wt % to 92 wt %, and The content of silver particles per unit volume contained in the second electrode is 68 wt % to 73 wt %.

4. The solar cell according to claim 1, wherein the thickness of the back passivation layer is less than the thickness of the anti-reflection layer, in, The thickness of the anti-reflection layer is 100 nm to 140 nm, and wherein the thickness of the back passivation layer is within a range smaller than the thickness of the anti-reflection layer and is 65 nm to 105 nm.

5. The solar cell according to claim 1, wherein: The thickness of the emitter region is 300nm to 700nm, and The thickness of the polysilicon back surface field layer is within a range smaller than the thickness of the emitter region and is 290 nm to 390 nm.

6. The solar cell according to claim 1, wherein: The glass frit including tellurium oxide Te0 has a melting point of 200°C to 500°C.

7. The solar cell according to claim 1, wherein: The silver particles of the first electrode include first silver particles having a circular or elliptical shape and second silver particles having a major axis and having a plate shape including an uneven surface, and wherein the silver particles of the second electrode include the first silver particles but do not include the second silver particles.

8. The solar cell according to claim 1, wherein: The thickness of the second layer is smaller than the thickness of the back passivation layer.

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