NL1003705C2 - Thin film solar cell. - Google Patents

Description

Thin film solar cell.

The invention relates to a thin-film solar cell provided with at least one pin junction comprising at least one pi junction, which is at an angle α to the operating light-catching surface of the thin-film solar cell, and at least one in transition, which is at an angle β to the light-catching surface.

Such a thin-film solar cell is known from international patent application WO95 / 27314. The known thin-film solar cell comprises alternatively stacked p- and n-doped layers, with or without an intermediate layer of intrinsic material. In the known thin film solar cell, the active p-n junctions and p-i-n junctions, respectively, lie parallel to the light-capturing surface of the thin-film solar cell on which the sunlight falls in operation.

In the known thin-film solar cell, the doped layers determine both the optical and the electrical properties of the thin-film solar cell. This makes it difficult to optimize the operation of the thin-film solar cell. For example, increasing the doping concentration of the p-doped layers leads to a higher field strength of the internal electric field. This higher field strength leads to a higher probability of collection of the charge carriers and thus to a higher photocurrent. On the other hand, however, this increase in the doping concentration of the p-doped layers leads to an increase in the absorption of sunlight by these regions. Less sunlight therefore reaches the intrinsic layer, so that less charge carriers are generated. As a result, the photostream from the thin-film solar cell decreases. The negative effect of the increase in light absorption cancels out the positive effect of the higher field strength, with the result that the resulting photocurrent of the thin film solar cell remains virtually unchanged.

The present invention aims to provide a thin-film solar cell of the type mentioned at the outset that obviates this drawback.

The thin-film solar cell according to the invention is therefore characterized in that 45 <α <135 degrees and 45 <β <135 degrees, and more particularly 80 <α <100 degrees and 80 <β <100 degrees.

Due to this position of the p-i transition and the i-n transition with respect to the light-catching surface, the sunlight at least partly falls directly on the intrinsic material without first one of the 1003705.

2 pass through doped regions as in the above-described known thin film solar cell. In the context of the example described above, this means that an increase in the doping concentration of the p-doped regions results in a higher electric field strength, without the corresponding increase in the absorption of sunlight canceling out the positive effect thereof. In general, this means that the optical and electrical properties of the thin-film solar cell according to the invention can thus be optimized separately. Thus, a higher conversion efficiency for the conversion of solar energy to electrical energy can be achieved with the thin-film solar cell according to the invention than with the known thin-film solar cell.

In a preferred embodiment of the thin film solar cell, the p-i junction and / or the i-n junction is at least meandrical in cross-section.

In a further preferred embodiment, the p-doped region and / or the n-doped region each comprise one or more fingers. In these preferred embodiments, the surface area of the transition region between the intrinsic material and the doped regions is advantageously increased, resulting in a higher resulting photocurrent for the thin film solar cell.

The invention also relates to a panel provided with a plurality of thin-film solar cells, wherein the thin-film solar cells are mutually electrically connected.

The invention also relates to a method of manufacturing a thin-film solar cell according to the invention, which method comprises the following steps: (a) depositing a layer of intrinsic material on a substrate; (b) defining the location of the p-doped region in the layer of intrinsic material; (c) defining the desired angle α for the p-i junction with respect to the light trapping surface of the thin film solar cell, where 45 <α <135 degrees; (d) ion implanting the p-doped region at the position as defined in step (b) and at the angle α as defined in step (c); (E) defining the location of the n-doped region in the layer of intrinsic material; (f) defining the desired angle β for the i-n junction with respect to the light-trapping surface of the thin film solar cell, 1003705.

3 where 45 <β <135 degrees; (g) ion implanting the n-doped region at the location as defined in step (e) and at the angle β as defined in step (f).

Just like the method according to the invention, a thin-film solar cell according to the invention can be manufactured quickly and reliably. This method further has the advantage that the intrinsic material is deposited directly on the substrate, without the intervention of a doped layer which would affect the manufacturing conditions of the intrinsic material. Many types of substrates can also be used for this method, including both transparent and non-transparent substrates.

The invention also relates to an alternative method for manufacturing a thin-film solar cell according to the invention, which method comprises the following steps: (a) depositing a layer of p-doped material and a layer of n-doped material, respectively. on a substrate; (b) defining the position of the n-doped region or the p-doped region in the layer of p-doped material 20 and n-doped material, respectively; (c) removing a portion of the deposited doped material at the position as defined in step (b); (d) depositing a layer of n-doped material or p-doped material on the thin film solar cell obtained in step 25 (c); (e) defining the position of the intrinsic region in the layer of p-doped and n-doped material; (f) removing a portion of the p-doped material and the n-doped material at the position as defined in step (e); (G) depositing a layer of intrinsic material on the thin film solar cell obtained in step (f).

The alternative method has the advantage that it is cheaper than the first method mentioned.

The invention will now be further elucidated with reference to the accompanying drawings, in which figure 1 shows a schematic cross-section of a part of a first preferred embodiment of a thin-film solar cell according to the invention; 1003705.

Figure 2 shows the first preferred embodiment as a whole in top view; figure 3 schematically shows a cross-sectional top view of a unit comprising a number of series-connected thin-film solar cells 5 according to the preferred embodiment of figure 2; and figure 4 shows a bottom view of a panel provided with several units connected in parallel according to figure 3

Figure 1 shows a schematic cross-section of a part of a first preferred embodiment of a thin-film solar cell 1 according to the invention. The section is taken along the line I-I in Figure 2, showing the first preferred embodiment in its entirety in top view. Figure 1 and Figure 2 will be largely described in combination.

Thin film solar cell 1, also referred to as "Transverse Junction Solar Cell" 13, includes a substrate 2 on which an area of intrinsic material i is applied. The intrinsic material i comprises in figure 1 two doped regions p and n {6 and 7 respectively) with which p-i junction 8 and i-n junction 9 are defined, respectively. Thin film solar cell 1 has a surface 5 that catches the sunlight in operation. In the following, surface 5 will be referred to as "light trapping surface".

In operation, when thin-film solar cell 1 receives (sun) light (indicated by arrow A), charge carriers are released in the intrinsic material i by means of the received light. Between the doped regions p and n there is an electric field which causes the positive charge carriers in the intrinsic material i to move in the direction of arrow B. These charge carriers then arrive in the p-doped region p. By making external electrical connections to the p-doped and the n-doped region, a photocurrent jp 30 (shown in Fig. 2) can be taken from the thin-film solar cell 1.

According to the invention, at least one pi transition, for example 8, is at an angle α with the light-catching surface 5 and at least one in-transition, for example 9. is at an angle β with the light-catching surface 5. Both angles α and B are at preferably between 35 and 135 degrees. More preferably, the angles α and β are between 80 and 100 degrees. Most preferred are angles α and β of approximately 90 degrees, as shown in the figure. Preferably the angles α and β are approximately the same, but this is not necessary.

1003705.

5

This position of the transitions ensures that the intrinsic material i at least partly captures the sunlight directly, without the sunlight first having to pass through one or more doped areas. In the thin-film solar cell according to the invention, the incident sunlight will therefore largely lead directly to the release of charge carriers in the intrinsic material i, whereby only a relatively small part will be absorbed by the doped areas, also depending on the angles. aenfi. As a result, the intrinsic material i and the doped regions p, n can be greatly optimized separately, whereby the operation of the thin-film solar cell 1 can be considerably improved compared to the known thin-film solar cell. .

Figure 2 clearly shows that the p-doped region 3 and the n-doped region A are both preferably provided with fingers 15 6 and 7 respectively. The p-doped fingers 6 are approximately transverse to the pi junction of region 3 to area i. The n-doped fingers 7 are approximately transverse to the in-transition from region i to region. Preferably, the p-doped fingers 6 and the n-doped fingers 7 are placed alternately in a plane which is approximately parallel to the light-capturing surface 5 »which is shown in figure 1. Thin-film solar cell 1 has in this plane at least further pi junctions 8 and further in-junctions 9. In other words, with the aid of fingers 6 and 7, in the preferred embodiment, Figure 2 advantageously increases the total surface area of the pi junction and the in junction, respectively. In addition, there is still sufficient intrinsic material i present that can capture direct sunlight. Thus, in the preferred embodiment shown, the thin film solar cell 1 provides a larger resulting photocurrent. More generally, the above-mentioned advantage according to the invention is achieved by using one or more p-i / i-n junctions with at least a meandric cross section. In the following, the area containing the fingers 6, 7 and the intrinsic material i will be referred to as i '.

A number of optional features are described below which are of particular advantage with the thin film solar cell according to the invention. The measures are not shown, but will be best understood with reference to Figure 1.

In a further preferred embodiment, the thin film solar cell is 100 3 7 0 5.

6 according to the invention provided with an additional 18¾ intrinsic material which is disposed substantially between the p-i-n junction and the light-catching surface 5 (not shown). This additional layer advantageously increases the total photocurrent of the thin-film solar cell, which leads to a higher efficiency. The additional layer preferably has a thickness of 50 nm to 5 µm and more preferably a thickness of 150 nm.

Optionally, the thin film solar cell is provided with a layer of electrically conductive material that contacts the p-doped region and / or a layer of electrically conductive material that contacts the n-doped region. The use of the electrically conductive material ensures that the loss of electric power due to the lower series resistance of the fingers is limited as much as possible.

Also optionally, the thin film solar cell according to the invention is provided with a textured surface on the light-catching side. The use of such a textured surface increases efficiency.

It is noted that the substrate 2 in Figure 1 is of a translucent material, for example glass. However, the substrate 2 may also be of non-translucent material, the regions p and n and the intrinsic material i being of course applied to the substrate.

Furthermore, it will be clear to a person skilled in the art that in practice the p-i transitions and i-n transitions will usually not proceed as ideally as indicated in the figures. These will rather have a spatial distribution that is partly determined by the doping technique used. In the context of this patent application, 'transition' is therefore understood to mean that flat surface that best represents the transition area. This is particularly important when defining the angle of a given transition with the light-trapping surface.

With reference to the above definition of the term "transition", it should be noted that the doping of the areas concerned does not need to be homogeneously distributed in depth. If desired, a doping gradient can be applied. This can increase in depth, for example.

Figure 3 schematically shows a cross-sectional plan view of a unit 10 comprising a number of k series-connected thin-film solar cells.

7 according to FIGS. 1 and 2. The p-doped regions are indicated by pj, while the n-doped regions in the unit are indicated by nJt where j = 1, ... k. The thin-film solar cells 1 to k are connected in series by electrically connecting the n-doped region nj of the underlying thin-film solar cell j to the p-doped region pJ + 1 of the neighboring thin film. film solar cell j + 1. For illustrative purposes, in Figure 3 such an electrical connection between region n1 of the first solar cell from unit 10 and region p2 of the second solar cell from unit 10 is indicated by reference numeral 11. Connection 11 is an n-p-10 junction. If the doping of the regions n2 and p2 is sufficiently effective, junction 11 acts as a low resistance contact. Such an n-β junction is known in the art and will therefore not be further discussed in the context of this patent application.

Through the series connection of the thin-film solar cells 1 to k, the resulting photocurrent Jp of unit 10 passes through p-doped region px and n-doped region nk, as indicated by arrows in Figure 3. For simplicity, in the following, the region between px and nk of unit 10 is denoted as i ". Unit 10 in operation can supply a voltage of approximately 20 V, which is sufficient for normal use.

Figure 4 shows a partial bottom view of a panel 12 provided with several units 10 connected in parallel according to figure 3. The parallel connection of the different units 10 takes place by electrically connecting all p-doped regions p1 of the units 10 to contact 13- All n-doped regions nk of all units 10 are electrically connected to contact 1 * 1. Preferably, the units 10 within panel 12 are positioned alternately mirrored to each other. Furthermore, parts of the substrate 2 are preferably used on panel 12 to prevent short circuits between the contacts 13 and 1 * +. The resulting photocurrent from panel 12 can be taken from contacts 13 and l * t in operation. For simplification, any protective layers to be applied at the p, i and n regions are not shown.

It is further noted that the figures are not drawn to scale. For the sake of clarification but not in any way limiting the invention, some dimensions of parts of a thin-film solar cell according to the invention are given below.

The fingers 6, 7 preferably have a length of 10 to 100 µm, preferably about 20 µm, and a width of approximately 0.01 to 1003705.

8 2 μη. The width of the i-area is approximately between 0.2 and 10 μη. The thin film solar cell according to the invention preferably has a thickness of 0.02 to 100 μη.

In the following, as an example, two methods are discussed for manufacturing a thin-film solar cell according to the invention with reference to Figures 1 and 2.

The first method begins with a first step of depositing a layer of intrinsic material i on a substrate 2. All materials known in the art can be used for the intrinsic material 10 i and the substrate 2. Preferably the intrinsic material is crystalline silicon, polycrystalline silicon, amorphous silicon and its alloys, cadmium telluride, cadmium sulfide, copper indium diselenide, an alloy of the form CuI ^ Ga ^ SySej.y or other suitable semiconductor material with or without graded bandgap . The intrinsic material can optionally be built up from a combination of the mentioned materials, the materials mutually having a different band distance. The substrate is preferably made of glass, ceramic material or plastic.

In step 2, the desired location for the p-doped region p20 in the layer of intrinsic material i is defined. This definition can take place in a known manner, such as using an appropriate mask and / or lithographic techniques. In step 3, the desired angle α for the p-i junction 3 with respect to the light-catching surface 5 of the thin-film solar cell 1 is then defined. Preferably 25 α is between 45 and 135 degrees, more preferably α is between 80 and 100 degrees. Most preferred is an angle a vein of approximately 90 degrees. In step 4 the p-doped region p is then applied in the intrinsic layer i at the position as determined in step 2 and at the angle α as determined in step 3, using the technique of ion implantation known per se. 2 through 4 are then repeated for the n-doped region n, the desired angle for the in-transition being called 4 β. Preferably, ≤ 5 <B <135 degrees, more preferably, 80 <B <100 degrees. Most preferred is an angle β of 90 degrees.

It is noted that boron is preferably used to obtain the p-doping. Phosphorus is preferably used for the n-doping. However, any other suitable materials known in the art can be used as an alternative.

1003705.

9

With the method according to the invention, thin-film solar cells according to the invention can be manufactured in a reliable and rapid manner. Since the Intrinsic layer according to the method according to the invention is directly deposited on the substrate, this intrinsic layer can be optimized in many ways. This optimization is limited only by the physical properties of the substrate.

; The following is an example of a thin film solar cell manufactured by the above-described method and tested in practice.

10 EXAMPLE

In this example, the substrate is a SiO 2 coated monocrystalline V * slice ("wafer"). 13.56 MHz PECVD was used as the deposition method for the i-layer. The position determination for the doped areas was performed using photolithography. The p-doping was performed using Boron ion implantation and the n-doping was performed using Phosphorus ion implantation, both with an initial estimate of dose and energy. Aluminum is used for the contacting and bridging of n-p interfaces for the series connection. Finally, the entire thin-film solar cell is baked for 1 hour at a temperature of 200 ° C.

The thin-film solar cell in this example has the following dimensions: thickness i-layer: 400 nm width p, i and n regions: lym finger length: 40 ym 25 number of fingers: 100

It should be noted that the width of the i region is preferably greater than the width of the p and n regions.

Of these thin-film solar cells, 30 are connected in series, which yielded the following results:

30 I.c * Ί0 nA

Voc * 23 V η = 0.12%

An alternative method for manufacturing a thin film solar cell according to the invention is further discussed below. The same applies to the materials mentioned in the context of the alternative method as to the materials mentioned in the context of the first-mentioned method.

1003705.

10

In the alternative method, in a first step, a layer of p-doped material or a layer of n-doped material is optionally deposited on a substrate 2. To simplify the description, it is assumed below that a layer of p-doped material is deposited on the substrate. It will be understood that in the event that a layer of n-doped material is deposited in the following description, everywhere "p-doped" should be replaced with "η-doped" and vice versa.

In the second method step, the position is then defined at which the n-doped material is to be applied in the deposited p-doped material-10 layer. This position determination can take place in known manner, such as with the aid of a suitable mask and / or lithographic techniques. Then, in a third step, part of the p-doped material deposited in step one is removed at the position as defined in step two. In step four, the n-doped material is then deposited on the thin film solar cell obtained in step three. The position of the intrinsic region i in the p-doped and n-doped material is then defined in the manner known per se in step five. Step six involves removing a portion of the p-doped material and the n-doped material at the position 20 as defined in step five. All techniques known in the art can be used for this, such as etching. Finally, in step seven, a layer of intrinsic material i is deposited on the thin film solar cell obtained in step six.

The great advantage of the alternative method is that it is much cheaper because of the use of deposition instead of ion implantation. It will be apparent to a person skilled in the art that in the alternative method the angles making the transitions between the doped material and the intrinsic material with the light-capturing surface can also be chosen between 45 and 135 degrees, as with the the former method. This can be done in steps five and six, for example. The term 'position' should therefore include 'location and / or angle' in the above.

The application of electrical contacts to the respective resulting p- and n-doped regions can take place using techniques known per se. Preferably, the contacts are made by evaporating metal. The specific metal zone can be defined and positioned relative to the doped areas using masks and lithographic techniques.

1003705.

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The thin film solar cells manufactured by any of the above-described methods can be concatenated, for example as shown in Figures 3 and * », to form a panel. The panel can optionally be equipped with reinforcement elements and can be mounted 5. Preferably, the panel is treated in a known manner to prevent corrosion.

The methods of the invention are in the field of microelectronics technology. This means that the thin film solar cell can be manufactured with relatively small amounts of material.

The present invention is of course not limited to the described and illustrated preferred embodiment, but includes any embodiment consistent with the foregoing description and the accompanying drawings and which is within the scope of the appended claims.

15 1003705.

Claims (10)

1. A thin-film solar cell having at least one pin junction comprising at least one pi junction, which is at an angle α with the operating light-trapping surface of the thin-film solar cell, and at least one in-junction, which is angled β with the light-catching surface, characterized in that ^ 5 <α <135 degrees and ^ 5 <β <135 degrees. The thin film solar cell of claim 1, wherein 80 <α <100 degrees and 80 <β <100 degrees. Thin film solar cell according to claim 1 or 2, wherein the p-i junction (8) and / or the i-n junction (9) is at least meandrical in cross section. The thin film solar cell of claim 1, 2 or 3. wherein the p-doped region (p) and the n-doped region (n) of the pin junction each comprise one or more fingers (6, 7) . 20 The thin film solar cell of claim 4, wherein the p-doped fingers (6) and the n-doped fingers (7) alternate at least in a plane approximately parallel to the light-catching surface (5). 25 Thin film solar cell according to any one of the preceding claims, which is provided with an additional layer of intrinsic material which is arranged mainly between the p-i-n junction and the light-catching surface (5). 30 Panel provided with a plurality of thin-film solar cells according to one of the preceding claims, wherein the thin-film solar cells are electrically connected to each other. Panel according to claim 7, comprising a number of units (10) each comprising a number of series-connected thin-film solar cells (1), the series connection being effected by electrical connection of the n-doped region (nx) of a first thin-film 1003705. solar cell with the p-doped region (p2) of a further thin-film solar cell, which units (10) are connected in parallel by the outer p-doped regions (pj of the units mutually electrically and by electrically connecting the outer n-doped regions (nk) of 5 units. 9. Method for manufacturing a thin-film solar cell according to any one of the preceding claims 1 to 6, characterized in that the method comprises the following steps: (a) depositing a layer of intrinsic material ( i) on a substrate (2); (b) defining the location of the p-doped region (p) in the layer of intrinsic material; (c) defining the desired angle α for the p-i junction (3) with respect to the light-trapping surface (5) of the thin-film solar cell (1), where 45 <α <135 degrees; (d) ion implanting the p-doped region at the location as defined in step (b) and at the angle α as defined in step (c); (E) defining the location of the n-doped region (s) in the layer of intrinsic material; (f) defining the desired angle β for the i-n junction (4) with respect to the light-trapping surface (5) of the thin-film solar cell, where 45 <& <135 degrees; (G) ion implanting the n-doped region at the location as defined in step (e) and at the angle β as defined in step (f). A method of manufacturing a thin film solar cell according to any one of the preceding claims 1 to 6, characterized in that the method comprises the following steps: (a) depositing a layer of p- doped material or a layer of n-doped material on a substrate (2); (b) defining the position of the n-doped region (n) and the p-doped region (p), respectively, in the layer of p-doped material or n-doped material; (c) removing a portion of the deposited doped material at the position as defined in step (b); H (d) depositing a layer of n-doped material or p-doped material on the thin film solar cell obtained in step (c); (e) defining the position of the intrinsic region (i) in the layer p-doped and n-doped material; (f) removing a portion of the p-doped material and the n * doped material at the position as defined in step (e); (g) depositing a layer of intrinsic material (i) on the thin film solar cell obtained in step (f). 10 1003705.