Solar cell and method for manufacturing the same

A solar cell and a method for manufacturing the same are discussed. The solar cell includes a substrate of a first conductive type, an emitter region of a second conductive type opposite the first conductive type positioned at the substrate, a first electrode which is positioned on the substrate and is connected to the emitter region, at least one second electrode which is positioned on the substrate and is connected to the substrate, and an aluminum oxide layer positioned on a front surface and a back surface of the substrate excluding areas of the substrate on which the first electrode and the at least one second electrode are formed.

This application claims priority to and the benefit of Korean Patent Application No. 10-2011-0073520, filed in the Korean Intellectual Property Office on Jul. 25, 2011, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention relate to a solar cell and a method for manufacturing the same.

2. Description of the Related Art

Recently, as existing energy sources such as petroleum and coal are expected to be depleted, interests in alternative energy sources for replacing the existing energy sources are increasing. Among the alternative energy sources, solar cells for generating electric energy from solar energy have been particularly spotlighted.

A solar cell generally includes semiconductor parts, which respectively have different conductive types, for example, a p-type and an n-type and thus form a p-n junction, and electrodes respectively connected to the semiconductor parts of the different conductive types.

When light is incident on the solar cell, carriers including electrons and holes are produced in the semiconductor parts. The carriers move to the n-type semiconductor part and the p-type semiconductor part under the influence of the p-n junction. Namely, the electrons move to the n-type semiconductor part, and the holes move to the p-type semiconductor part. Then, the electrons and the holes are collected by the different electrodes respectively connected to the n-type semiconductor part and the p-type semiconductor part. The electrodes are connected to each other using electric wires to thereby obtain electric power.

SUMMARY OF THE INVENTION

In one aspect, there is a solar cell including a substrate of a first conductive type, an emitter region of a second conductive type opposite the first conductive type, the emitter region being positioned at the substrate, a first electrode which is positioned on the substrate and is connected to the emitter region, at least one second electrode which is positioned on the substrate and is connected to the substrate, and an aluminum oxide layer positioned on a front surface and a back surface of the substrate excluding areas of the substrate on which the first electrode and the at least one second electrode are formed.

The aluminum oxide layer on the front surface of the substrate and the aluminum oxide layer on the back surface of the substrate may have the same thickness, the same refractive index, the same material, and the same composition.

The aluminum oxide layer may be additionally positioned on a lateral surface of the substrate.

The aluminum oxide layer on the front surface of the substrate, the aluminum oxide layer on the back surface of the substrate, and the aluminum oxide layer on the lateral surface of the substrate may have the same thickness, the same refractive index, the same material, and the same composition.

The solar cell may further include an anti-reflection layer positioned on the aluminum oxide layer on the front surface of the substrate.

The anti-reflection layer may be formed of silicon nitride.

A thickness of the anti-reflection layer may be greater than a thickness of the aluminum oxide layer.

The first conductive type of the substrate may be a p-type.

The solar cell may further include a capping layer positioned between the aluminum oxide layer on the back surface of the substrate and the at least one second electrode.

The capping layer may be formed of silicon nitride or silicon oxide.

The solar cell may further include a plurality of surface field regions which are locally positioned at the back surface of the substrate and are separated from one another. The at least one second electrode may be one second electrode including a plurality of contact portions abutting the plurality of surface field regions. The one second electrode may be connected to the substrate through the plurality of contact portions.

The aluminum oxide layer may have a thickness of about 10 nm to 30 nm.

The first electrode may be positioned on the front surface of the substrate, and the one second electrode may be positioned on the back surface of the substrate.

The solar cell may further include a capping layer positioned between the aluminum oxide layer on the back surface of the substrate and the at least one second electrode.

The capping layer may be formed of silicon nitride or silicon oxide.

When the capping layer is formed of silicon nitride, the capping layer may have a thickness of about 50 nm to 100 nm.

When the capping layer is formed of silicon oxide, the capping layer may have a thickness of about 70 nm to 150 nm.

The solar cell may further include a plurality of surface field regions which are locally positioned at the back surface of the substrate and are separated from one another. The at least one second electrode may include a plurality of contact portions abutting the plurality of surface field regions. The at least one second electrode may be connected to the substrate through the plurality of contact portions.

The solar cell may further include a plurality of surface field regions locally positioned at the back surface of the substrate. The first conductive type may be an n-type. The at least one second electrode may be a plurality of second electrodes positioned on the plurality of surface field regions.

The first electrode may be positioned on the front surface of the substrate, and the plurality of second electrodes may be positioned on the back surface of the substrate. Both the front surface and the back surface of the substrate may be incident surfaces on which light is incident.

In another aspect, there is a solar cell including a p-type semiconductor substrate, an emitter region positioned at a first surface of the semiconductor substrate, an aluminum oxide layer positioned directly on a second surface of the semiconductor substrate opposite the first surface, a passivation region positioned directly on the emitter region, an anti-reflection layer positioned on the passivation region, a first electrode which is positioned on the first surface of the semiconductor substrate and is connected to the emitter region, and a second electrode which is positioned on the second surface of the semiconductor substrate and is connected to the semiconductor substrate.

The passivation region may be formed of aluminum oxide.

The anti-reflection layer may be formed of silicon nitride or silicon oxide.

The aluminum oxide layer may be additionally positioned on a lateral surface of the semiconductor substrate.

In yet another aspect, there is a method for manufacturing a solar cell, the method including forming an emitter region of a second conductive type opposite a first conductive type at a first surface of a semiconductor substrate of the first conductive type, forming a first aluminum oxide layer directly on a second surface of the semiconductor substrate opposite the first surface using an atomic layer deposition (ALD) method, and forming a first electrode connected to the emitter region on the first surface of the semiconductor substrate and forming a second electrode connected to the semiconductor substrate on the second surface of the semiconductor substrate.

The forming of the first aluminum oxide layer may include forming the first aluminum oxide layer on a third surface of the semiconductor substrate different from the first and second surfaces.

The method may further include forming a second aluminum oxide layer on the emitter region.

The forming of the second aluminum oxide layer may be performed at the same time as the forming of the first aluminum oxide layer.

The method may further include forming a capping layer on the first aluminum oxide layer.

The capping layer may be formed of silicon nitride or silicon oxide.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Example embodiments of the invention will be described with reference toFIGS. 1to11.

A solar cell according to an example embodiment of the invention is described in detail with reference toFIGS. 1 to 3.

As shown inFIG. 1, a solar cell11according to an embodiment of the invention includes a substrate110, an emitter region121positioned at an incident surface (hereinafter, referred to as “a front surface or a first surface”) of the substrate110on which light is incident, a passivation region191which is positioned on the emitter region121(i.e., on the front surface of the substrate110), a back surface (or a second surface) of the substrate110opposite the front surface, and a lateral surface (or a third surface) of the substrate110, an anti-reflection layer130positioned on the passivation region191on the front surface of the substrate110, a capping layer193positioned on the passivation region191on the back surface of the substrate110, a front electrode part (or a first electrode part)140which is positioned on the front surface of the substrate110and is connected to the emitter region121, a back electrode part (or a second electrode part)150which is positioned on the capping layer193and is connected to the substrate110, and a plurality of surface field regions172selectively (or locally) positioned on the back surface of the substrate110.

The substrate110is a semiconductor substrate formed of a semiconductor such as first conductive type silicon, for example, p-type silicon, though not required. The semiconductor used in the substrate110is a crystalline semiconductor, such as single crystal silicon or polycrystalline silicon.

When the substrate110is of the p-type, the substrate110is doped with impurities of a group III element such as boron (B), gallium (Ga), and indium (In). Alternatively, the substrate110may be of an n-type and/or may be formed of a semiconductor material other than silicon. If the substrate110is of the n-type, the substrate110may be doped with impurities of a group V element such as phosphorus (P), arsenic (As), and antimony (Sb).

As shown inFIGS. 1 and 2, a separate texturing process may be performed on the flat front surface of the substrate110to form a textured surface corresponding to an uneven surface having a plurality of protrusions15and a plurality of depressions16or having uneven characteristics. In this instance, the emitter region121, the passivation region191, and the anti-reflection layer130positioned on the front surface of the substrate110have the textured surface.

As described above, because the front surface of the substrate110is textured, an incident area of the substrate110increases and a light reflectance decreases due to a plurality of reflection operations resulting from the textured surface. Hence, an amount of light incident on the substrate110increases, and the efficiency of the solar cell11is improved.

As shown inFIGS. 1 and 2, maximum diameters D1and maximum heights D2of the plurality of protrusions15of the textured surface of the substrate110are non-uniformly determined. Therefore, the plurality of protrusions15have the different maximum diameters D1and the different maximum heights D2.

The emitter region121positioned at the front surface of the substrate110is an impurity doped region doped with impurities of a second conductive type (for example, n-type) opposite the first conductive type (for example, p-type) of the substrate110. Thus, the emitter region121of the second conductive type forms a p-n junction along with a first conductive type region (for example, a p-type region) of the substrate110.

Regarding carriers, for example, electrons and holes produced by light incident on the substrate110, the electrons and the holes respectively move to the n-type semiconductor and the p-type semiconductor by a built-in potential difference resulting from the p-n junction between the substrate110and the emitter region121. Thus, when the substrate110is of the p-type and the emitter region121is of the n-type, the holes and the electrons move to the substrate110and the emitter region121, respectively.

Because the emitter region121forms the p-n junction along with the first conductive type region of the substrate110, the emitter region121may be of the p-type when the substrate110is of the n-type in another embodiment of the invention. In this instance, the electrons move to the substrate110and the holes move to the emitter region121.

The passivation region191may be positioned on at least one of the front surface of the substrate110(i.e., the emitter region121positioned at the front surface of the substrate110), the back surface of the substrate110, and the lateral surface of the substrate110. For example, the passivation region191shown inFIG. 3is positioned on all of the front surface, the back surface, and the lateral surface of the substrate110. In this instance, the passivation region191is positioned on at least one of four lateral surfaces of the substrate110.

In the embodiment of the invention, the passivation region191on the front surface, the passivation region191on the back surface, and the passivation region191on the lateral surface of the substrate110have the same characteristics. Thus, the passivation region191on the front surface, the passivation region191on the back surface, and the passivation region191on the lateral surface of the substrate110have the same thickness, the same properties, the same material, the same composition, the same refractive index, etc. Alternatively, the passivation regions191on the front surface, the back surface, and the lateral surface of the substrate110have the same properties, the same material, the same composition, the same refractive index, but at least one of the passivation regions191may have a different thickness, for example, if necessary or desired.

In the embodiment of the invention, the passivation region191may be formed of aluminum oxide (AlxOy), for example, Al2O3and may have a thickness of about 10 nm to 30 nm. In this instance, the passivation region191may have a refractive index of about 1.4 to 1.6.

The passivation region191performs a passivation function which converts a defect, for example, dangling bonds existing at and around the surface of the substrate110into stable bonds to thereby prevent or reduce a recombination and/or a disappearance of carriers moving to the surface of the substrate110. Thus, the passivation region191reduces an amount of carriers lost by the defect at the surface of the substrate110.

In the embodiment of the invention, because the passivation region191is positioned on all of the front surface, the back surface, and the lateral surface of the substrate110, the passivation function of the passivation region191is further improved by an increase in a formation area of the passivation region191. For example, because the most of the defect generally exists at and around the surface of the substrate110, the defect mostly exists at and around the front surface, the back surface, and the lateral surface of the substrate110to thereby lead to a loss of carriers produced in the substrate110.

Further, when the emitter region121is formed at the substrate110using, for example, a thermal oxidation method, the emitter region121is formed at both the front surface and the back surface of the substrate110. When the back surface of the substrate110is immersed in an etchant, etc., so as to remove the emitter region121formed at the back surface of the substrate110, the etchant penetrates into the lateral surface as well as the back surface of the substrate110. Hence, a damage layer having many defects is generated in the lateral surface of the substrate110, thereby resulting in an increase in a loss amount of carriers at and around the lateral surface of the substrate110.

On the other hand, in the embodiment of the invention, because the passivation region191is positioned on the lateral surface as well as the front and back surfaces of the substrate110, the defect leading to the loss of carriers is removed. As a result, the efficiency of the solar cell11is further improved.

In the embodiment of the invention, when the thickness of the passivation region191is equal to or greater than about 10 nm, the passivation region191is more uniformly formed on the substrate110and more stably performs the passivation function. When the thickness of the passivation region191is equal to or less than about 30 nm, the passivation region191stably performs the passivation function without the unnecessary increase in the thickness of the passivation region191. Hence, the manufacturing cost and time may be reduced.

The anti-reflection layer130positioned on the front surface of the substrate110reduces a reflectance of light incident on the solar cell11and increases selectivity of a predetermined wavelength band, thereby increasing the efficiency of the solar cell11.

The anti-reflection layer130may be formed of hydrogenated silicon nitride (SiNx:H). The anti-reflection layer130has a thickness greater than the passivation region191. For example, the anti-reflection layer130may have the thickness of about 70 nm to 100 nm and a refractive index of about 2.0 to 2.2. For example, the anti-reflection layer130is 3 to 7 times thicker than the passivation layer191.

When the refractive index of the anti-reflection layer130is equal to or greater than about 2.0, the reflectance of light decreases and an amount of light absorbed in the anti-reflection layer130further decreases. Further, when the refractive index of the anti-reflection layer130is equal to or less than about 2.2, the reflectance of the anti-reflection layer130further decreases.

When the thickness of the anti-reflection layer130is equal to or greater than about 70 nm, an anti-reflection effect of light is more efficiently obtained. When the thickness of the anti-reflection layer130is equal to or less than about 100 nm, an amount of light absorbed in the anti-reflection layer130decreases and an amount of light incident on the substrate110increases. Further, in the process for manufacturing the solar cell11, the front electrode part140easily and smoothly passes through the anti-reflection layer130and is stably and smoothly connected to the emitter region121.

The anti-reflection layer130performs the passivation function at and around the surface of the substrate110using hydrogen (H) contained in the anti-reflection layer130. Thus, the anti-reflection layer130serves as a passivation part at the front surface of the substrate110in the same manner as the passivation region191.

As described above, because the passivation function is additionally performed by the anti-reflection layer130as well as the passivation region191, the passivation effect of the solar cell11is greatly improved. Hence, the efficiency of the solar cell11is further improved.

Further, the passivation region191positioned on the front surface of the substrate110performs an anti-reflection function of light along with the anti-reflection layer130using its refractive index and thickness. Thus, the passivation region191positioned on the front surface of the substrate110serves as an anti-reflection part in the same manner as the anti-reflection layer130.

The anti-reflection layer130shown inFIGS. 1 and 2has a single-layered structure, but may have a multi-layered structure, for example, a double-layered structure. Further, the anti-reflection layer130may be omitted, if necessary or desired.

The front electrode part140includes a plurality of front electrodes (or a plurality of first electrodes)141positioned on the front surface of the substrate110and a plurality of front bus bars (or a plurality of first bus bars)142which are positioned on the front surface of the substrate110and are connected to the plurality of front electrodes141.

The plurality of front electrodes141are connected to the emitter region121and are separated from one another. The plurality of front electrodes141extend parallel to one another in a fixed direction. The plurality of front electrodes141collect carriers (for example, electrons) moving to the emitter region121.

The plurality of front bus bars142are connected to the emitter region121and extend parallel to one another in a direction crossing the front electrodes141.

In this instance, the front bus bars142are positioned at the same layer level as the front electrodes141and are electrically and physically connected to the front electrodes141at crossings of the front electrodes141and the front bus bars142.

Accordingly, as shown inFIG. 1, the plurality of front electrodes141have a stripe shape extending in a transverse (or longitudinal) direction, and the plurality of front bus bars142have a stripe shape extending in a longitudinal (or transverse) direction. Hence, the front electrode part140has a lattice shape on the front surface of the substrate110.

The front bus bars142collect not only carriers (for example, electrons) moving from the emitter region121but also carriers collected by the front electrodes141crossing the front bus bars142, and move the collected carriers in a desired direction. Thus, a width of each front bus bar142is greater than a width of each front electrode141.

The front bus bars142are connected to an external device and output the collected carriers to the external device.

The front electrode part140including the front electrodes141and the front bus bars142is formed of at least one conductive material such as silver (Ag).

In the embodiment of the invention, the number of front electrodes141and the number of front bus bars142may vary, if necessary or desired.

As described above, the passivation region191positioned on the back surface of the substrate110reduces an amount of carriers lost by the defect at and around the back surface of the substrate110.

Further, the passivation region191positioned on the back surface of the substrate110reflects light passing through the substrate110back to the substrate110and increases an amount of light incident on the substrate110. A light reflection operation of the passivation region191may be carried out by a relation between metal (for example, aluminum (Al)) contained in the passivation region191and the refractive index of the passivation region191.

In general, aluminum oxide (AlxOy) has the characteristic of negative fixed charges.

In the embodiment of the invention, the substrate110is of the p-type, and the passivation region191, which is formed directly on the back surface of the substrate110using aluminum oxide (AlxOy), has the characteristic of negative fixed charges. Hence, positive charges (i.e., holes) moving to the passivation region191have a polarity opposite the passivation region191formed of aluminum oxide (AlxOy). As a result, the holes are drawn to the passivation region191because of the polarity of the passivation region191. On the other hand, negative charges (i.e., electrons) have the same polarity as the passivation region191formed of aluminum oxide (AlxOy) and thus are pushed out of the passivation region191because of the polarity of the passivation region191. Hence, when the passivation region191is formed on the p-type substrate110using aluminum oxide (AlxOy), an amount of carriers moving to the back surface of the substrate110further increases because of the influence of negative fixed charges.

Accordingly, when the passivation region191having the characteristic of negative fixed charges is positioned on the n-type emitter region121, the passivation region191adversely affects the movement of electrons to the n-type emitter region121because of the above-described reason. However, because the anti-reflection layer130formed of silicon nitride (SiNx) having the characteristic of positive fixed charges has the thickness greater than the passivation region191, the anti-reflection layer130stably prevents the adverse influence of negative fixed charges of the passivation region191. As a result, even if the passivation region191having the negative fixed charges is positioned directly on the n-type emitter region121, the anti-reflection layer130makes it possible for electrons to stably move to the emitter region121.

The passivation region191may be formed using various layer formation methods such as a plasma enhanced chemical vapor deposition (PECVD) method and an atomic layer deposition (ALD) method.

When the passivation region191is formed using the ALD method, the passivation regions191having the same characteristic (i.e., the same thickness, properties, material, composition, refractive index) may be formed on the front surface, the back surface, and the lateral surface of the substrate110through one process. In this instance, manufacturing time of the passivation region191is reduced.

Alternatively, when the passivation region191is formed using the PECVD method, the passivation regions191may be individually formed on the front surface, the back surface, and the lateral surface of the substrate110. Thus, because the passivation region191having the proper thickness may be formed on each of the front surface, the back surface, and the lateral surface of the substrate110, at least one of the passivation regions191formed on the front surface, the back surface, and the lateral surface of the substrate110may have the thickness different from the other passivation regions191. In this instance, because the thickness of the passivation region191may be controlled depending on a function of each location of the substrate110, the effect of the passivation regions191is further improved. Even if the passivation region191is formed using the ALD method, the passivation region191may be formed only on one desired surface of the front surface, the back surface, and the lateral surface of the substrate110.

The capping layer193positioned on the passivation region191positioned on the back surface of the substrate110is formed of hydrogenated silicon oxide (SiOx:H) and/or hydrogenated silicon nitride (SiNx:H).

When the capping layer193is formed of hydrogenated silicon oxide (SiOx:H), the capping layer193may have a thickness of about 70 nm to 150 nm and a refractive index of about 1.4 to 1.6.

Alternatively, when the capping layer193is formed of hydrogenated silicon nitride (SiNx:H), the thickness of the capping layer193formed of hydrogenated silicon nitride (SiNx:H) may be less than the thickness of the capping layer193formed of hydrogenated silicon oxide (SiOx:H) because hydrogenated silicon nitride (SiNx:H) has reactivity less than hydrogenated silicon oxide (SiOx:H). For example, the capping layer193formed of hydrogenated silicon nitride (SiNx:H) may have a thickness of about 50 nm to 100 nm and a refractive index of about 2.0 to 2.2.

In general, silicon oxide (SiOx) and silicon nitride (SiNx) have the characteristic of positive fixed charges.

Accordingly, when the capping layer193is formed of silicon oxide (SiOx) and/or silicon nitride (SiNx) and the substrate110is of the p-type, the movement of carriers (i.e., holes) to the back surface of the substrate110may be adversely affected by the capping layer193. However, in the embodiment of the invention, the passivation region191between the substrate110and the capping layer193prevents the adverse influence of the positive fixed charges of the capping layer193on the substrate110. Hence, holes from the substrate110stably move to the back electrode part150.

The capping layer193performs the passivation function using hydrogen (H) contained in the capping layer193. Further, the capping layer193prevents aluminum (Al), which is contained in the passivation region191and performs the passivation function, from moving to the front surface opposite the back surface of the substrate110, thereby further improving the passivation function of the passivation region191.

Thus, the back surface of the substrate110has a double passivation structure including the passivation region191, which is positioned directly on the back surface of the substrate110and is formed of aluminum oxide (AlxOy), and the capping layer193, which is positioned on the passivation region191and is formed of silicon oxide (SiOx) and/or silicon nitride (SiNx).

The passivation region191is a first passivation layer corresponding to a lower layer of the double passivation structure, and the capping layer193is a second passivation layer corresponding to an upper layer of the double passivation structure. In another embodiment of the invention, the capping layer193may be omitted.

Each of the plurality of surface field regions172locally or selectively positioned at the back surface of the substrate110is a region (for example, a p+-type region) that is more heavily doped than the substrate110with impurities of the same conductive type as the substrate110. Thus, each surface field region172has a sheet resistance less than the substrate110and has conductivity greater than the substrate110.

As shown inFIG. 1, because the plurality of surface field regions172are locally or selectively positioned at the back surface of the substrate110, a portion not including the surface field regions172exists at an edge of the back surface of the substrate110and in the middle of the back surface of the substrate110.

A potential barrier is formed by a difference between impurity concentrations of a first conductive region (for example, a p-type region) of the substrate110and the surface field regions172. Hence, the potential barrier prevents or reduces electrons from moving to the surface field regions172used as a moving path of holes and makes it easier for holes to move to the surface field regions172. Thus, the surface field regions172reduce an amount of carriers lost by a recombination and/or a disappearance of the electrons and the holes at and around the back surface of the substrate110and accelerate a movement of desired carriers (for example, holes), thereby increasing an amount of carriers moving to the back electrode part150.

The back electrode part150is positioned on the capping layer193and includes a back electrode (or a second electrode)151and a plurality of back bus bars (or a plurality of second bus bars)152connected to the back electrode151.

The back electrode151is positioned on the capping layer193except a formation area of the plurality of back bus bars152. Alternatively, the back electrode151may be not positioned on a portion of the capping layer193, on which the plurality of back bus bars152are formed, and at an edge of the back surface of the substrate110.

The back electrode151includes a plurality of contact portions155, which sequentially pass through the capping layer193and the passivation region191and are connected to the plurality of surface field regions172. Hence, the back electrode151is selectively or locally connected to a portion (i.e., the plurality of surface field regions172) of the substrate110through the plurality of contact portions155.

Accordingly, as shown inFIGS. 1 and 2, because the surface field regions172are positioned at and around the back surface of the substrate110abutting the contact portions155, the surface field region172is not positioned at the back surface of the substrate110between the adjacent contact portions155.

As shown inFIG. 1, the plurality of contact portions155are spaced apart from one another at a predetermined distance (for example, about 0.5 mm to 1 mm) therebetween and are connected to the substrate110. Each contact portion155has various cross-sectional shapes such as a circle, an oval, and a polygon.

In the embodiment of the invention, the cross-sectional shape of the contact portion155is the cross-sectional shape obtained by cutting the contact portion155parallel to the flat front surface or the flat back surface of the substrate110.

Alternatively, each contact portion155may have a stripe shape elongating in one direction in the same manner as the front electrode141and may be electrically connected to the substrate110. In this instance, the number of contact portions155having the stripe shape is much less than the number of contact portions155having the circle, the oval, or the polygon.

The contact portions155collect carriers (for example, holes) moving from the substrate110and transfer the carriers to the back electrode151.

Because the surface field regions172, which have the conductivity greater than the substrate110due to the impurity concentration higher than the substrate110, abut the contact portions155, the mobility of carriers from the substrate110to the contact portions155is improved.

The back electrode151may contain a conductive material (for example, aluminum (Al)) different from the front electrode part140. Alternatively, the back electrode151may contain the same conductive material as the front electrode part140.

The contact portions155contacting the substrate110may contain only the material of the back electrode151or may contain a mixture of the materials of the capping layer193, the passivation region191, and the substrate110as well as the material of the back electrode151.

More specifically, before the formation of the back electrode151, a plurality of openings exposing the back surface of the substrate110are formed at a corresponding location of the capping layer193and the passivation region191underlying the capping layer193. Then, the back electrode151is formed on the capping layer193and on the back surface of the substrate110exposed through the plurality of openings. Because the back electrode151positioned inside the plurality of openings is formed as the contact portions155, the surface field regions172positioned at the back surface of the substrate110are electrically connected to the back electrode151. In this instance, the contact portions155contain only the material of the back electrode151.

Alternatively, a back electrode paste containing a metal material for the back electrode151is coated on the capping layer193and then is dried without a separate process for forming the openings. Then, a laser beam is applied to a corresponding location of the dried back electrode paste to selectively (or locally) apply heat to the back electrode paste. Hence, a portion of the back electrode paste, to which the heat is applied, is mixed with the materials of the capping layer193and the passivation region191underlying the portion of the back electrode paste and is electrically connected to the back surface of the substrate110. The portion of the back electrode paste, to which the heat is applied, serves as the contact portions155, and the materials of the back electrode151, the capping layer193, the passivation region191, and the substrate110are mixed with one another in each contact portion155.

When the plurality of openings are formed in the capping layer193and the passivation region191and then the back electrode151is formed, the electrical connection between the back surface of the substrate110and the back electrode151is more stably carried out. On the other hand, when the heat is selectively (or locally) applied to the back electrode paste and then the back electrode151selectively (or locally) connected to the substrate110is formed, the thermal process for forming the plurality of openings in the capping layer193and the passivation region191is not necessary. Therefore, the manufacturing time of the solar cell11is reduced.

If the back electrode151is positioned directly on the passivation region191and contacts the passivation region191, the material (for example, the back electrode paste containing aluminum) of the back electrode151may chemically react with the passivation region191formed of aluminum oxide in the thermal process for forming the back electrode151. Hence, the passivation region191may be electrically connected to the back electrode151. As a result, a loss of carriers moving to the back electrode151may be generated.

However, when the capping layer193is formed between the passivation region191and the back electrode151, the capping layer193prevents the chemical reaction between the formation material of the back electrode151and the passivation region191. Hence, the electrical connection between the passivation region191and the back electrode151is prevented more stably. As a result, when carriers move from the substrate110to the back electrode151, a loss of carriers resulting from the electrical connection between the passivation region191and the back electrode151is prevented or reduced.

When the thickness of the capping layer193formed of silicon oxide (SiOx) and/or silicon nitride (SiNx) is equal to or greater than about 70 nm, the capping layer193stably prevents the reaction between the back electrode part150and the passivation region191. Hence, the capping layer193makes it possible for the back electrode part150to stably operate.

Further, when the thickness of the capping layer193formed of silicon oxide (SiOx) and/or silicon nitride (SiNx) is equal to or less than about 150 nm, the capping layer193stably prevents the reaction between the back electrode part150and the passivation region191while preventing an unnecessary increase in its thickness.

Alternatively, if the substrate110is of the n-type, the emitter region121is of the p-type, and each surface field region172is of the n-type, the back electrode151may be formed using a paste containing silver (Ag).

In this instance, when a paste (for example, a silver paste) for the back electrode151is coated directly on the passivation region191, and then the thermal process is performed on the back electrode paste to form the back electrode151, the passivation region191formed of aluminum oxide does not react with the back electrode151formed of the silver paste in the thermal process. Therefore, the capping layer193may be omitted. Further, when the substrate110is of the p-type and the emitter region121is of the n-type, the capping layer193may be omitted if the back electrode part150is formed of a material which does not react with the passivation region191. As described above, if the capping layer193is omitted, the manufacturing cost and the manufacturing time of the solar cell11may be reduced.

The back bus bars152connected to the hack electrode151are positioned on the capping layer193, on which the back electrode151is not positioned. The back bus bars152extend in the same direction as the front bus bars142and have a stripe shape. The back bus bars152and the front bus bars142are positioned opposite to each other with the substrate110between them.

The back bus bars152collect carriers transferred from the back electrode151, similar to the front bus bars142. Thus, the back bus bars152may be formed of a material with conductivity greater than the back electrode151. For example, the back bus bars152contain at least one conductive material such as silver (Ag).

The back bus bars152are connected to the external device and output the collected carriers (for example, holes) to the external device.

Unlike the configuration illustrated inFIG. 1, the back bus bars152may partially overlap the back electrode151in another embodiment. In this instance, a contact resistance between the back electrode151and the back bus bars152may decrease by an increase in a contact area between the back electrode151and the back bus bars152. Hence, an amount of carriers transferred from the back electrode151to the back bus bars152may increase.

Further, the back electrode151may be positioned on the capping layer193on which the back bus bars152are formed. In this instance, the back bus bars152may be positioned on the back electrode151to be opposite to the front bus bars142with the substrate110between them. Thus, because the back electrode151may be positioned on the capping layer193irrespective of the formation location of the back bus bars152, the back electrode151may be more easily formed.

In an alternative example, each of the back bus bars152may include a plurality of conductors, each of which may have a circle, an oval, or a polygon shape instead of the stripe shape, and are disposed at a uniform or non-uniform distance therebetween along an extension direction of the front bus bars142. In this instance, because, the use of an expensive material, for example, silver (Ag) for the back bus bars152decreases, the manufacturing cost of the solar cell11is reduced.

The number of back bus bars152shown inFIG. 1may vary, if necessary or desired.

An operation of the solar cell11having the above-described structure is described below.

When light irradiated to the solar cell11is incident on the substrate110, which is the semiconductor part, through the anti-reflection layer130, the passivation region191, and the emitter region121, electrons and holes are generated in the substrate110by light energy produced based on the incident light. In this instance, because a reflection loss of the light incident on the substrate110is reduced by the anti-reflection layer130and the textured surfaces, an amount of light incident on the substrate110increases.

The electrons move to the n-type emitter region121and the holes move to the p-type substrate110by the p-n junction of the substrate110and the emitter region121. The electrons moving to the emitter region121are collected by the front electrodes141and the front bus bars142and then are transferred to the front bus bars142. The holes moving to the substrate110are transferred to the contact portions155and then are collected by the back bus bars152via the back electrode151. When the front bus bars142are connected to the back bus bars152using electric wires, current flows therein to thereby enable use of the current for electric power.

The passivation region191formed of aluminum oxide is positioned on the entire surface of the substrate110except the formation area of the front electrode part140and the formation area of the back electrode part150. Thus, the passivation region191is positioned on the lateral surface as well as the front and back surfaces of the substrate110. An increase in the formation area of the passivation region191results in a large reduction in an amount of carriers lost by the defect.

Because the passivation region191having the refractive index between a refractive index of air and a refractive index of the substrate110is positioned on the lateral surface of the substrate110, an amount of light incident on the lateral surface of the substrate110increases. Hence, the efficiency of the solar cell11is improved.

More specifically, when the plurality of solar cells11are arranged in a matrix form and are connected in series or parallel to one another to form a solar cell module, light is incident on the lateral surface as well as the front surface of the substrate11because of an incident angle or several reflection operations of the light incident on the solar cells11or the solar cell module.

Accordingly, a difference between the refractive indexes of the passivation region191and the substrate110when the passivation region191is positioned on the lateral surface of the substrate110is less than a difference between the refractive indexes of air and the substrate110when the passivation region191is not positioned on the lateral surface of the substrate110.

In other words, when the passivation region191is not positioned on the lateral surface of the substrate110, light is incident from air (having the refractive index of about 1) to the substrate110(having the refractive index of about 3.1). On the other hand, when the passivation region191is positioned on the lateral surface of the substrate110, the light is incident from air (having the refractive index of about 1) to the substrate110(having the refractive index of about 3.1) via the passivation region191(having the refractive index of about 1.6). Thus, a refractive index going from air to the substrate110gradually increases.

An amount of change of the refractive index from air to the substrate110when the passivation region191is positioned on the lateral surface of the substrate110is less than an amount of change of the refractive index from air to the substrate110when the passivation region191is not positioned on the lateral surface of the substrate110. Therefore, an amount of light incident on the substrate110when light is incident from air to the substrate110via the passivation region191is greater than an amount of light incident on the substrate110when light is incident from air to the substrate110.

As described above, because the passivation region191is positioned on the lateral surface of the substrate110, a loss amount of carriers decreases, and an amount of light incident on the substrate110increases. Hence, the efficiency of the solar cell11is improved.

A method for manufacturing the solar cell11is described below.

First, the emitter region121of the second conductive type (for example, n-type) is formed inside the front surface of the crystalline semiconductor substrate110of the first conductive type (for example, p-type) using a thermal diffusion method or an ion implantation method.

Next, a layer (i.e., the passivation region191) formed of aluminum oxide is formed on at least one of the back surface, the lateral surface, and the front surface (i.e., the emitter region121) of the substrate110using a layer deposition method such as the ALD method and the PECVD method. In this instance, the passivation region191may be formed on the back surface and the lateral surface of the substrate110and on the emitter region121using a separate layer deposition method. The passivation region191may be simultaneously formed on the back surface and the lateral surface of the substrate110and on the emitter region121through one layer deposition process using the ALD method. When the passivation region191is simultaneously formed on the back surface and the lateral surface of the substrate110and on the emitter region121, the passivation regions191on the back surface and the lateral surface of the substrate110and on the emitter region121may have the same thickness, properties, material, composition, refractive index, etc.

Next, the anti-reflection layer130is formed on the passivation region191positioned on the front surface of the substrate110using the PECVD method. Further, the capping layer193is formed on the passivation region191positioned on the back surface of the substrate110using the PECVD method. In this instance, the capping layer193may be formed of silicon oxide and/or silicon nitride.

In the embodiment of the invention, a formation order of the anti-reflection layer130and the capping layer193may vary.

Next, a front electrode part paste or a front electrode part ink is coated on the anti-reflection layer130using a screen printing method or an inkjet printing method and then dried to form a front electrode part pattern. Further, a back electrode paste or a back electrode ink and a back electrode bar paste or a back electrode bar ink are coated on the capping layer193using the screen printing method or the inkjet printing method and then are dried to form a back electrode pattern and a back bus bar pattern. In the embodiment of the invention, a formation order of the front electrode part pattern, the back electrode pattern, and the back bus bar pattern may vary.

Next, heat is locally or selectively applied to a back electrode part pattern including the back electrode pattern and the back bus bar pattern using a laser beam, etc., to form the plurality of surface field regions172at the back surface of the substrate110.

Next, the thermal process is performed on the substrate110including the front electrode part pattern, the back electrode pattern, and the back bus bar pattern to form the front electrode part140, which passes through the anti-reflection layer130and the passivation region191underlying the anti-reflection layer130and thus is physically and chemically connected to the emitter region121, using the front electrode part pattern, to form the back electrode151, which has the plurality of contact portions155physically and chemically connected to the surface field regions172and is electrically connected to the substrate110, and the back bus bars152connected to the back electrode151respectively using the back electrode pattern and the back bus bar pattern. A portion of the back electrode pattern, to which the laser beam is applied, is formed as the plurality of contact portions155. Each of the plurality of contact portions155may contain a mixture of the materials of the capping layer193, the passivation region191, and the substrate110as well as the material of the back electrode151.

In another embodiment, before the back electrode pattern is formed on the capping layer193, a portion of the capping layer193and a portion of the passivation region191underlying the capping layer193are removed using an etching paste, etc., to form a plurality of openings exposing a portion of the back surface of the substrate110in the capping layer193and the passivation region191.

Next, the back electrode pattern is coated on the capping layer193and on the back surface of the substrate110exposed through the plurality of openings.

Next, as described above, the thermal process is performed on the substrate110including the front electrode part pattern, the back electrode pattern, and the back bus bar pattern to form the front electrode part140connected to the emitter region121, the plurality of surface field regions172which are positioned at the back surface of the substrate110exposed through the openings by injecting a portion of the material contained in the back electrode pattern into the substrate110, the back electrode151, which has the plurality of contact portions155physically and chemically connected to the surface field regions172and is electrically connected to the substrate110, and the back bus bars152connected to the back electrode151.

In this instance, the back electrode pattern positioned in the plurality of openings is formed as the plurality of contact portions155. Thus, each of the plurality of contact portions155may contain only the material of the back electrode151.

A solar cell12according to another example embodiment of the invention is described below with reference toFIGS. 4 to 6.

Structures and components identical or equivalent to those described in the solar cells11and12according to the embodiments of the invention are designated with the same reference numerals, and a further description may be briefly made or may be entirely omitted.

The solar cell12shown inFIGS. 4 to 6includes a passivation region191positioned on at least one of a front surface, a back surface, and a lateral surface of a substrate110. Configuration of the solar cell12shown inFIGS. 4 to 6is substantially the same as the solar cell11shown inFIGS. 1 to 3, except a formation location of the passivation region191and an anti-reflection layer130on the front surface of the substrate110. Namely, the passivation region191and the anti-reflection layer130shown inFIGS. 4 to 6are substantially the same as the passivation region191and the anti-reflection layer130shown inFIGS. 1 to 3in a material, a thickness, a refractive index, etc.

In the solar cell11shown inFIGS. 1 to 3, the passivation region191is positioned directly on the emitter region121on the front surface of the substrate110, and the anti-reflection layer130is positioned on the passivation region191on the front surface of the substrate110.

On the other hand, in the solar cell12shown inFIGS. 4 to 6, the anti-reflection layer130is positioned directly on the emitter region121on the front surface of the substrate110, and the passivation region191is positioned on the anti-reflection layer130.

In this instance, after the emitter region121is formed on the front surface of the substrate110, the passivation region191is formed on the anti-reflection layer, the back surface of the substrate110, and the lateral surface of the substrate110. As described above, the passivation region191is formed using various layer formation methods such as the PECVD method and the ALD method.

When the passivation region191is positioned on the anti-reflection layer130on the front surface of the substrate110, a refractive index going, from air to the substrate110gradually increases because the anti-reflection layer130formed of silicon nitride has a refractive index of about 2.1. Namely, air (having a refractive index of about 1), the passivation region191(having a refractive index of about 1.6), the anti-reflection layer130(having a refractive index of about 2.1), and the substrate110(having a refractive index of about 3.1) are sequentially arranged in the order named and thus have gradually increasing refractive indexes.

Accordingly, a reduction effect of a reflectance of light incident from the outside (i.e., air) increases. Hence, an amount of light incident on the substrate110in the solar cell12shown inFIGS. 4 to 6is more than the solar cell11shown inFIGS. 1 to 3. As a result, the efficiency of the solar cell12is further improved.

In the solar cell12shown inFIGS. 4 to 6, the passivation region191on the front surface of the substrate110serves as an anti-reflection part, and the anti-reflection layer130serves as a passivation part in the same manner as the solar cell11shown inFIGS. 1 to 3.

Since a method for manufacturing the solar cell12shown inFIGS. 4 to 6is substantially the same as the method for manufacturing the solar cell11shown inFIGS. 1 to 3, except that before the passivation region191is formed, the anti-reflection layer130is formed on the emitter region121on the front surface of the substrate110, a further description may be briefly made or may be entirely omitted.

Changes in a reflectance of light at the front surface (i.e., the incident surface) of the substrate110depending on changes in the thickness of the passivation region191is described below with reference toFIGS. 7 and 8.

More specifically,FIG. 7illustrates a reflectance AWR of light depending on changes in the thickness of the passivation region191when the passivation region191formed of aluminum oxide (for example, Al2O3) is positioned on the emitter region121and the anti-reflection layer130formed of silicon nitride (SiNx) is positioned on the passivation region191. Further,FIG. 8illustrates a reflectance AWR of light depending on changes in the thickness of the passivation region191when the anti-reflection layer130formed of silicon nitride (SiNx) is positioned on the emitter region121and the passivation region191formed of aluminum oxide (for example, Al2O3) is positioned on the anti-reflection layer130.

As shown inFIGS. 7 and 8, when the thickness of the passivation region191increased to about 30 nm and the anti-reflection layer130formed of silicon nitride had a single-layered structure, the reflectance AWR of light was similar to the reflectance AWR of light when the thickness of the passivation region191was substantially zero (i.e., when the passivation region191was omitted). Thus, when the thickness of the passivation region191was about 10 nm to 30 nm, additional effects including the above-described passivation effect and the effect of fixed charges was obtained without a large increase in the reflectance AWR of light. Hence, the efficiency of the solar cells11and12was greatly improved.

FIG. 9is a graph indicating a reflectance AWR of light depending on whether or not the passivation region191is formed on the lateral surface of the substrate110.

As shown inFIG. 9, when the passivation region191was not formed on the lateral surface of the substrate110, the reflectance AWR of light was about 39%. On the other hand, when the passivation region191formed of aluminum oxide (for example, Al2O3) was formed on the lateral surface of the substrate110, the reflectance AWR of light was less than about 39%. Namely, as the thickness of the passivation region191increased, the reflectance AWR of light decreased. Thus, when the passivation region191was formed on the lateral surface of the substrate110and the thickness of the passivation region191increased, an amount of light incident on the lateral surface of the substrate110increased.

As in the embodiment of the invention, when the passivation region191was formed on the lateral surface of the substrate110, an amount of light incident on the solar cells11and12increased, and thus the efficiency of the solar cells11and12was improved.

In the embodiments of the invention, n-type impurities and p-type impurities are injected into a crystalline semiconductor substrate for a solar cell to form an n-type impurity region and a p-type impurity region in a portion of the crystalline semiconductor substrate. The n-type impurity region and the p-type impurity region serve as the emitter region121and the surface field region172, respectively. A remaining semiconductor substrate excluding the n-type impurity region and the p-type impurity region from the crystalline semiconductor substrate serves as the substrate110according to the embodiments of the invention. The substrate110, the emitter region121, and the surface field region172are formed of the same crystalline semiconductor, and thus form a homojunction. Thus, the embodiments of the invention are described based on the solar cells11and12forming the homojunction using the substrate110, the emitter region121, and the surface field region172.

Alternatively, the substrate110may be formed of a crystalline semiconductor, such as single crystal silicon or polycrystalline silicon, and the emitter region121and the surface field region172may be formed of an amorphous semiconductor, such as amorphous silicon, different from the crystalline semiconductor of the substrate110. Thus, the substrate110, the emitter region121, and the surface field region172may form a heterojunction. The embodiments of the invention may be applied to a solar cell forming the heterojunction.

In the embodiments of the invention, the front electrode part140and the back electrode part150are positioned on the front surface and the back surface of the substrate110, respectively. Alternatively, the embodiments of the invention may be applied to a solar cell, in which both the front electrode part140and the back electrode part150are positioned on the back surface of the substrate110. In the following embodiments, structural elements having the same functions and structures as those discussed previously are designated by the same reference numerals, and a further description may be briefly made or may be entirely omitted.

As shown inFIG. 10, in a back contact solar cell13according to the embodiment of the invention, a plurality of emitter regions121aand a plurality of surface field regions172aare alternately positioned at a back surface of an n-type substrate110and extend parallel to one another in a fixed direction. A passivation region191formed of aluminum oxide is positioned on at least one of a front surface, the back surface, and a lateral surface of the substrate110.

A plurality of first electrodes141aare positioned on the plurality of emitter regions121a, and a plurality of second electrodes151aare positioned on the plurality of surface field regions172a. A capping layer may be positioned on the passivation region191positioned on the back surface of the substrate110, i.e., between the adjacent first and second electrodes141aand151a. A first bus bar connected to the plurality of first electrodes141aand a second bus bar connected to the plurality of second electrodes151amay be positioned on the back surface of the substrate110.

The passivation region191positioned on the front surface of the substrate110performs a passivation function, but mainly performs an anti-reflection function as compared to the passivation function. Thus, the back contact solar cell13may further include an anti-reflection layer under the passivation region191positioned on the front surface of the substrate110, so as to complement the anti-reflection function of the front surface of the substrate110. In this instance, the anti-reflection layer may be formed of silicon oxide (SiOx) and/or silicon nitride (SiNx) and has positive fixed charges. In the back contact solar cell13according to the embodiment of the invention, because the n-type substrate110is used, minority carriers (i.e., holes) of the substrate110easily move to the back surface of the substrate110instead of the front surface of the substrate110by the anti-reflection layer having the positive fixed charges. Hence, the holes of the substrate110more smoothly move to the plurality of emitter regions121a.

A method for manufacturing the back, contact solar cell13shown inFIG. 10is described below. The plurality of emitter regions121aand the plurality of surface field regions172aare formed in the back surface of the substrate110using the thermal diffusion method or the ion implantation method. The passivation region191is formed on at least one of the front surface, the lateral surface, and the back surface (i.e., on the emitter regions121aand the surface field regions172a) of the substrate110through the process discussed previously.

Next, the plurality of first electrodes141aconnected to the plurality of emitter regions121aand the plurality of second electrodes151aconnected to the plurality of surface field regions172aare formed using a through operation of the passivation region191or an etching paste through the above-described thermal process.

The embodiments of the invention may be applied to a bifacial solar cell, in which light is incident on both the front surface and the back surface of the substrate110.

For example, as shown inFIG. 11, in a solar cell14according to the embodiment of the invention, an emitter region121is positioned on a front surface of an n-type substrate110, a plurality of surface field regions172are positioned on a back surface of the substrate110, and a capping layer193is positioned directly on the back surface of the substrate110. A passivation region191formed of aluminum oxide is positioned on at least one of a front surface (i.e., directly on the emitter region121), a back surface (i.e., directly on the capping layer193), and a lateral surface of the substrate110. An anti-reflection layer130is positioned on the passivation region191on the front surface of the substrate110. A plurality of front electrodes141are positioned on the front surface of the substrate110and are connected to the emitter region121. A plurality of back electrodes151are positioned directly on the back surface (i.e., on the plurality of surface field regions172) of the substrate110and are connected to the plurality of surface field regions172. Because the plurality of back electrodes151are respectively positioned on the plurality of surface field regions172, the back electrodes151are separated from one another. Further, the surface field regions172are not positioned at the back surface of the substrate110between the adjacent back electrodes151. A front bus bar connected to the plurality of front electrodes141may be positioned on the front surface of the substrate110, and a back bus bar connected to the plurality of back electrodes151may be positioned on the back surface of the substrate110. Hence, the plurality of front electrodes141may be connected to one another using the front bus bar, and the plurality of back electrodes151may be connected to one another using the back bus bar. A surface field region may be additionally positioned at the back surface of the substrate110on which the back bus bar is positioned. In this instance, the plurality of surface field regions172may be connected to the surface field region positioned under the back bus bar.

Because the capping layer193having positive fixed charges is positioned directly on the back surface of the substrate110, the capping layer193performs a passivation function and makes it easier for electrons to move from the n-type substrate110to the back surface of the n-type substrate110. Hence, an amount of electrons transferred from the substrate110to the plurality of back electrodes151increases.

Configuration and function of the emitter region121a(121) and/or the surface field region172a(172) and the first and second electrodes141a(141) and151a(151) connected to the regions121a(121) and172a(172) in the solar cells13and14shown inFIGS. 10 and 11are substantially the same as those in the solar cells11and12shown inFIGS. 1 to 6, except their location. Therefore, a further description may be briefly made or may be entirely omitted.

A method for manufacturing the solar cell14shown inFIG. 11is substantially the same as the manufacturing method described with reference toFIGS. 1 to 3, except a coating location (or a coating shape) of a back electrode pattern for the back electrodes151. Therefore, a further description may be briefly made or may be entirely omitted.