TW201438267A - Method for the edge isolation of solar cells and for the third step of a monolithic integration process - Google Patents

Abstract

Method for the edge isolation of solar cells and for the third step in a monolithic integration process (P3) of a thin-film solar cell by means of applying a picosecond pulsed infrared laser on the active face of the cell, thus achieving the elimination of the p-type and n-type semiconductor material layers and the layer of transparent conductive oxide (TCO) forming part of the solar cell, leaving open to the air the rear contact thereof without damaging the barrier and/or substrate layer.

Description

Edge insulation for solar cells and method for the third step of monolithic integration processing

The present invention relates to edge insulation of thin film solar cells and methods of defining end points. The proposed invention can be used in the fields of microelectronics and optoelectronics. In the field of optoelectronics, the invention has a wide range of applications in the design and manufacture of thin film photovoltaic solar modules, wherein the concept of edge insulation and monolithic integration is used for the interconnection of solar cells.

The elimination of the transparent conductive oxide (TCO) applied to the thin film solar cell, which is the front contact point of the solar cell, and the elimination of the n-type and p-type semiconductors have two purposes: It is used to bond batteries and form photovoltaic modules, and achieve greater efficiency in generating electricity, because connecting the batteries in series produces more power in the photovoltaic device (known as the third in monolithic integration processing). Step or P3 step); on the other hand, referring to the battery itself, it is used to achieve edge insulation in the step of defining the battery end point, which is absolutely necessary, because otherwise, the front contact point (TCO) will be large To the layer resistance that may not be able to maintain efficiency.

For example, copper indium selenide (CIS), CuInSe ₂ , which is a part of a solar cell composed of copper, indium, and selenium, or copper gallium technology (copper gallium) The monolithic integration technique of the chalcogen compound of selenide, CGS) is composed of three cuts (P1, P2, P3) in the selective material, which are transverse to the layer structure of the solar cell (see Figure 1). .

Conventionally, in a device formed on a glass substrate, the first dicing (P1) is performed after depositing the first deposited layer until reaching the barrier layer (if present) between the substrate or the substrate and the back contact. . That is, the cutting system is performed on the molybdenum layer, which is the back contact point (negative electrode) of the battery. Its function is to indicate the starting point of the battery.

The second dicing (P2 step) is performed on the absorption layer and the buffer layer of the battery (p-type and n-type semiconductor layers, respectively). This allows current to pass from the front contact (positive) of the battery to the metal layer used as the electrode under the adjacent battery.

The third dicing (P3 step) is performed on the front contact layer and the semiconductor layer. It limits the passage of current through the electrodes, that is, it defines the end point of the solar cell.

In the case of a glass substrate, the conventional method of joining thin film solar cells is by the monolithic integration process described above, which uses a nanosecond infrared (ns-IR) laser derived from the P1 step and mechanically engraved in the P2 and P3 steps.

To date, thin layer modules that interconnect monolithic on a metal or polymer flexible substrate using a monolithic integration do not exist. This is due to the following three main limitations:

i. Technology limitations, as the laser source of ablated deposition material has only just developed: on such opaque substrates (metals and polymers), the material on the side of the active layer must be ablated instead of the glass substrate that is normally ablated . Achieving this ablation without damaging the adjacent material requires a laser source with a pulse wave that is shorter than the conventional nanosecond pulse.

Ii. Conceptual limitations because of the lack of dielectric material to electrically insulate the metal substrate from the back electrode of the battery.

Iii. Scientific limitations because of the lack of knowledge about the use of new sources (picoseconds and femtoseconds) for material-laser interactions that are developing in the optical industry.

In the case where a thin film battery is grown on a metal substrate, each pair of cells is individually connected by soldering a plurality of dots between the positive and negative electrodes of two adjacent cells, and the connection is similar to that of crystallization technology. The person who performed it. Due to the technical barriers identified above, it has not been possible to make monolithic interconnections of these types of substrates to date.

As mentioned above, in the conventional monolithic integration method, the P1 step is performed by laser, and the P2 and P3 steps are performed by mechanical engraving with mechanical dots, which involves the following serious drawbacks: the battery material is easy The depth of fracture and spalling, cutting or grinding is not controlled, wide cutting results in loss of effective area of the battery, no clean cut profile, and the like. Incidentally, in the case of a flexible substrate, since these substrates are easily broken, it is impossible to use mechanical points.

The distance between the cutting performed in the P1 step and the P3 step is inactive, that is, the photons absorbed in the region of the semiconductor do not generate an electron-hole pair and thus do not generate electricity. Therefore, the smaller the distance, the greater the power generated by the photovoltaic module. This distance is large when using mechanical points, because the points require more physical space for cutting, thus resulting in less power in the solar module. It would be desirable to be able to cut as narrow as possible, thereby minimizing the distance between them, thus increasing the power of the module.

On the other hand, during the manufacture of the solar cell, the edge insulation of the battery is necessary, that is, the material of the positive and negative electrode layers is physically separated, so as to avoid short-circuiting of the battery; otherwise the semiconductor device will have no effect.

From a product design point of view, there are multiple possibilities for this treatment:

• All solar cell layers are removed by controlled cutting up to the substrate so that there is no any type of interdiffusion and the contacts or front and back electrodes of the cell are not in contact.

• Eliminate all solar cell layers except the contacts or the back electrode without damaging the back electrode. In this way, the front contact of the battery will not touch the rear contact. This is the most common form of operation at the commercial level. This process is equivalent to the one-piece integration of the P3 step, even if it is performed on the battery for different purposes. The edge insulation achieved by the step of defining the end of the battery can be performed in the same manner as the P3 step of the monolithic integration process.

In order to achieve edge insulation, the mechanical methods used in the conventional art have the disadvantages already mentioned, as already explained above.

The present invention thus describes a method capable of simultaneously performing edge insulation in a process for defining a solar cell end point and a P3 step of monolithic integration processing in a solar module, which avoids the disadvantages of mechanical techniques in which the solar cell includes a flexible Substrate.

The elimination of the transparent conductive oxide (TCO, which is the front contact point of the solar cell) applied to the thin film solar cell and the elimination of the n-type semiconductor and the p-type semiconductor are performed for two purposes: on the one hand, it is used Bonding the battery and forming a photovoltaic module, achieving greater efficiency in generating electricity, because connecting the cells in series produces greater power in the photovoltaic device (known as the third or P3 step of the monolithic integration process) On the other hand, referring to the battery itself, it is used to achieve edge insulation in the step of defining the end of the battery.

According to the method of the present invention, for both the edge insulation of the battery and the definition of its end point, as in the P3 step (third step) in the monolithic integration process, the focus is primarily on the chalcogenide battery, such as CIS ( A battery comprising a CuInSe ₂ semiconductor layer) formed of a flexible substrate and a metal layer found above, which is a back contact (negative electrode) of the battery. Alternatively, there may be a barrier layer between the back contact and the substrate. The p-type semiconductor material layer, the n-type semiconductor material layer, and the final transparent conductive oxide layer (the front contact (positive electrode) of the battery) are instead found on the metal layer or the back contact.

The method according to the invention comprises at least one step consisting of eliminating the front contact and the p-type and n-type semiconductor layers to respectively dope the aluminum-doped zinc oxide (AZO) layer in the same cell (post-contact) ) and the front layer to insulate the Mo layer (front contact). In this way, the following are achieved:

An edge insulation defines the end of the solar cell.

A monolithic integration is achieved between adjacent cells that make up the photovoltaic solar module.

The metal layer (which is the back contact) is maintained because the use of a laser allows the depth of the cut to be controlled with high precision, preventing the metal layer or the back contact of the battery from being affected. The fact that the metal layer or the back contact remains open to the air without being eliminated enables the electrical connection of the battery to be interconnected in series with the positive and negative terminals of the photovoltaic module in its junction box.

The previously mentioned method of selectively eliminating the battery is carried out by applying an infrared (IR) pulsed laser source applied to the picosecond (ps) range on the side of the layer of active material, that is, applying On the side of the front contact and the p-type and n-type semiconductor layers (or also on the positive side of the portion).

This IR laser application step must sometimes be repeated to achieve complete edge insulation or physical separation of the material forming the positive and negative electrodes of the battery, thus avoiding short circuits.

The flexible substrate can be a metal, polymer or flexible glass having a thickness of from 20 to 700 microns. In the process according to the invention, in order to achieve a monolithically integrated P3 step, the laser strikes the side of the transparent metal oxide because when a non-transparent substrate (for example a metal substrate) is used At this time, it is impossible to strike the laser on the side of the substrate.

The metal oxide layer may be Al:ZnO, Ga:ZnO, SnO ₂ :F, SnO ₂ :In ₂ O ₃ or a combination thereof.

The metal layer (post joint) of the battery is molybdenum (Mo).

CIS (CuInSe ₂ ), which is a chalcogenide from CIGS (CuInGa(Se,S) ₂ ) or sulphide sulphide (Cu ₂ ZnSn(Se,S) ₄ ) family, preferably used as p-type semiconductor Floor. Cadmium sulfide (CdS), zinc sulfide (ZnS or ZnS (O, H)), and indium selenide (In ₂ Se ₃ ) are preferably used as the n-type semiconductor layer.

The steps of using IR lasers to define the cell end point for edge insulation and for monolithic integration processing relate to the following advantages over classical methods based on mechanical points:

‧The quality of the edges is high (there are fewer products discarded at the end of the line).

‧ Manufacturing speed is faster.

‧ The cost of the final product is lower.

‧ The material is eliminated less and the area of action is larger (the solar module produces more power).

For the specific case where a complete monolithic integration is desired, in addition to the previously explained laser application step that defines each battery end point, two first steps are required: the first step is in the module. The starting point of the solar cell is defined (P1 step), and for this purpose, all layers existing on the substrate are eliminated without damaging the substrate. This first step is performed by applying an IR pulsed laser for several nanoseconds; and the second step (P2 step) is formed by connecting the front contact of the battery to the rear contact of the adjacent battery. . Its function is to allow current to pass from a solar cell in the module to an adjacent solar cell. This P2 step is performed by mechanical engraving (mechanical engraving).

1‧‧‧Substrate

2‧‧‧Battery junction (metal layer)

3‧‧‧p-type semiconductor layer

4‧‧‧n type semiconductor layer

5‧‧‧ Front contact point of the battery (transparent metal oxide layer)

P1‧‧‧The first cut in a monolithic integration process

P2‧‧‧Second cutting in a monolithic integration process

P3‧‧‧ Third cut in monolithic integration

Figure 1: Schematic representation of the steps P1, P2, P3 of a monolithic integration process for a solar cell.

Figure 2: Current density versus voltage curve after solar cell edge insulation has been performed by the process according to the invention.

Figure 3: Scanning electron microscope (SEM) image of a battery in which the method according to the invention has been carried out.

In order to better understand the present invention, the method according to the present invention will be described below in terms of preferred embodiments.

First, in the prior art of Fig. 1, an illustration of a photovoltaic solar cell formed by a substrate (1), a metal layer (2) forming a contact after the battery, a p-type semiconductor layer (3), an n-type is shown. a semiconductor layer (4), a transparent metal oxide layer (5) forming a junction before the battery. In the figure, the cutting of steps 1, 2, 3 (P1, P2, P3, respectively) of the monolithic integration process is shown.

In a special case, a chalcogenide solar cell, for example, made of CIS technology, consists of a flexible stainless steel substrate, a metal molybdenum layer (post-contact of the battery), and a CIS (CuInSe ₂ ) p-type semiconductor. Layer, cadmium sulfide (CdS) n-type semiconductor layer, aluminum-doped zinc oxide (Al: ZnO) made of transparent conductive oxide layer (battery front contact), and irradiated at 1 kHz The picosecond IR laser with a frequency of 30 mW and a sweep speed of 40 mm per second. Linear sweeping was performed with an interline shift of Δx = 50 μm and Δy = 22 μm.

By this treatment, the elimination of layers of aluminum-doped zinc oxide (Al:ZnO), CIS, cadmium sulfide (CdS) and the like is achieved, leaving a molybdenum layer open to the air. Method of production in this way The edge insulation of the battery is generated, and the connection between the front and rear contacts of the battery is avoided, so that the short circuit is avoided, and the end point of defining the battery is also achieved (P3 step of monolithic integration processing).

In Figure 2, once the edge insulation of the solar cell has been performed by the treatment of the laser described using this preferred embodiment, a current density versus voltage curve is presented. This result is typical of a diode, and no short circuit is observed at the edge.

The scanning electron microscope (SEM) image of Figure 3 shows a solar cell on which the process according to the invention has been performed using a picosecond IR laser at a frequency of 1 kilohertz, 30 mW, Illuminated at a sweep speed of 40 mm per second. In this figure, a cleaner and narrower cut and less material is observed compared to the cut achieved by mechanical engraving.

Other parameters can also be used for processing. Specifically, it can be performed in a frequency range of 0.1 to 100 kHz, a power of 5 to 500 mW, and a speed range of 1 to 3000 mm per second.

Claims (8)

A method for edge insulation of a solar cell and a third step for monolithic integration processing, wherein the battery is formed of a flexible substrate on which a metal layer (which is a back contact of the battery) is found, a p-type semiconductor material layer, an n-type semiconductor material layer, and finally a transparent conductive oxide layer (which is the front contact of the battery); the method is characterized in that it comprises the steps of: applying a picosecond pulse-type infrared ray The p-type semiconductor material layer and the n-type semiconductor material layer and the transparent conductive oxide layer are removed on the side of the active material layer or the positive electrode, leaving the metal layer open to the air. A method for edge insulation of a solar cell and a third step for monolithic integration processing according to the first aspect of the patent application, characterized in that the p-type semiconductor layer is made of CIS (CuInSe ₂ ) or by ClGS (CuInGa(Se,S) ₂ ) or a chalcogenide of the sulphide sulphide (Cu ₂ ZnSn(Se,S) ₄ ) family. A method for edge insulation of a solar cell and a third step for monolithic integration processing according to the first aspect of the patent application, characterized in that the n-type semiconductor layer is made of cadmium sulfide (CdS), zinc sulfide (ZnS) Made of ZnS(O,H) or indium selenide (In ₂ Se ₃ ). A method for edge insulation of a solar cell and a third step for monolithic integration processing according to the first aspect of the patent application, characterized in that the metal layer is made of molybdenum (Mo). A method for edge insulation of a solar cell and a third step for monolithic integration processing according to claim 1 of the patent application, characterized in that the flexible substrate is metal or polymer or glass, and has a Thickness between 700 microns. A method for edge insulation of a solar cell and a third step for monolithic integration processing according to claim 1 of the patent application, characterized in that the picosecond IR laser system is applied to 0.1 to 100 The frequency range of kilohertz, the power of 5~500 mW, and the sweep speed of 1~3000 mm per second. A method for edge insulation of a solar cell and a third step for monolithic integration processing according to claim 6 of the patent application, characterized in that the picosecond IR laser system is applied at a frequency of 1 kHz, 30 mW The power, sweep speed of 40 mm per second. A method for edge insulation of a solar cell and a third step for monolithic integration processing according to claim 1 of the patent application, characterized in that it also comprises two preceding steps: the first step is by applying ultraviolet pulse waves The laser is composed of several nanoseconds, thus allowing the starting point of the solar cell to be defined in the module; and the second step is performed by mechanical engraving to connect the front contact of the battery to the adjacent The rear contact of the battery.