CN107408584B

CN107408584B - Photovoltaic solar cell

Info

Publication number: CN107408584B
Application number: CN201680014291.7A
Authority: CN
Inventors: 卡琳·克劳斯; F·弗蒂格; R·普罗伊; 乌尔里希·耶格尔; S·维尔纳; S·瑞恩
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 2015-03-20
Filing date: 2016-03-18
Publication date: 2021-04-09
Anticipated expiration: 2036-03-18
Also published as: HRP20171417A2; CN107408584A; HRP20171417B1; DE102015104236A1; DE102015104236B4; WO2016150878A1; HRP20171417B8

Abstract

The invention relates to a photovoltaic solar cell having at least one semiconductor layer, at least one electrically insulating layer and at least one metallic contact structure, wherein the insulating layer is arranged between the semiconductor layer and the contact structure and the insulating layer has a plurality of contact gaps, wherein the contact structure makes electrical contact with the semiconductor layer in a contact region at the contact gaps, wherein a doped region is formed in the semiconductor layer at least in the contact region by doping the semiconductor layer with a metal, and the contact structure is formed at least in part from the metal. The invention is characterized in that the contact structure has a plurality of contact fingers, each of which extends over and/or along a plurality of contact-making areas, wherein the contact fingers have a local cross-sectional increase in the contact-making areas.

Description

Photovoltaic solar cell

The present invention relates to a photovoltaic solar cell according to the preamble of claim 1.

Photovoltaic solar cells are used to convert incident photon energy into electrical energy. For this purpose, a typical solar cell has a semiconductor layer, an electrically insulating layer and a metal contact structure.

Photons absorbed within the semiconductor layer generate carrier pairs that are separated at the pn junction. The metal contact structure is connected to the p-doped region or the n-doped region, so that carriers can be output. The charge carriers of the semiconductor structure regions with the opposite doping type are correspondingly output via the further metal contact structure or also via the full-area rear-side metal structure.

The insulating layer is arranged between the semiconductor layer and the contact structure in order to reduce, in particular, losses due to recombination of minority carriers at the metal/semiconductor interface and losses resulting therefrom. The insulating layer has a plurality of contact openings, at which the contact structures make electrical contact with the semiconductor layer in the contact region.

It is also known to provide doped regions in the contact regions by doping the semiconductor layer with a metal, which is a constituent of the contact structure, in order to reduce minority carrier recombination at the remaining interfaces between the metal in the semiconductor layer and the semiconductor.

In this way, it is possible in a simple manner to form a so-called local highly doped region in the contact-making region in the semiconductor layer using the metal of the metal contact-making structure during the solar cell production process, so that the abovementioned reduction in minority carrier recombination is achieved in said region in a cost-effective manner.

Despite the success in reducing the manufacturing cost and/or improving the efficiency of photovoltaic solar cells, there is still a high cost pressure on the market. Furthermore, photovoltaic solar cells are used in a wide range of applications, and therefore an optimal arrangement with respect to the irradiation source, for example the sun, cannot always be guaranteed.

The invention is therefore based on the object of improving a photovoltaic solar cell with an insulating layer and a contact-making structure as described above, so that the efficiency is increased by the reduction in losses.

This object is achieved by a photovoltaic solar cell according to claim 1. Advantageous embodiments of the photovoltaic solar cell according to the invention can be found in claims 2 to 15.

The invention is based on the recognition that, in particular in the case of the solar cell having a contact-making structure as described above, the losses in the contact-making structure are manifested in the contact-making cutout region:

as previously described, the metal of the contact structure is employed to form a local doped region in the semiconductor layer at the contact opening. However, not only local doping of the semiconductor layer with metal is thereby carried out, but semiconductor material is generally also incorporated into the metallic contact structure. In this way, the conductivity of the contact structure in this region is reduced.

Studies have shown that, in particular when a contact structure is formed using known contact fingers, the line resistance of the contact fingers in the solar cell structure described above is increased in the contact cutout region by the semiconductor material incorporated in the contact fingers as follows: a significant reduction in the overall efficiency of the photovoltaic solar cell occurs because of the increased line resistance and the corresponding ohmic power loss.

The photovoltaic solar cell according to the invention can avoid or at least mitigate said losses:

the photovoltaic solar cell according to the invention has at least one semiconductor layer, at least one electrically insulating layer and at least one metallic contact structure. The insulating layer is arranged between the semiconductor layer and the contact structure.

In order to establish the conductive connection of the semiconductor layer by means of the contact structure, the insulating layer has a plurality of contact openings, at which the contact structure makes electrical contact with the semiconductor layer in the contact connection region.

As described above, the semiconductor layer is doped with a metal, which is a constituent of all or part of the metal contact structure, at least in the contact region, to form doped regions. In this way, the losses described above, which are caused by the recombination of the charge carriers in the semiconductor layer at the surface of the contact-making region, can be reduced.

It is essential that the contact structure has a plurality of contact fingers, each of which extends over and/or along a plurality of contact-making areas, wherein the contact fingers have a local cross-sectional increase in the contact-making areas.

This embodiment is based on the recognition that there is a need for a contact structure covering a local doped region as described above, which contact structure is not a full-side metallization structure, such as the aforementioned full-side back-side metallization structure. There is also a need for a contact structure that at least partially allows incident photons to pass through because it is not covered entirely by a metal layer. With such a contact structure having a plurality of contact fingers, it is therefore possible to apply such a contact structure to the front side of the solar cell which faces the light source during use of the solar cell. Application to the back side of a solar cell is also possible, for example to form a bifacial photovoltaic solar cell as described in detail below.

In this case, it has been found that, unlike full-area metallization, the design of the contact structure with a plurality of contact fingers entails the above-described risk of ohmic power losses, because of the local increase in the line resistance in the contact fingers.

In the photovoltaic solar cell according to the invention, the contact fingers extend over and/or along a plurality of contact-making regions, wherein the contact fingers have a local cross-sectional increase in the contact-making regions and/or the contact fingers have electrically parallel conductive structures which do not cover the contact-making regions.

Thus, the local cross-sectional increase may compensate for or at least mitigate the local increase in line resistivity of the contact fingers at the contact opening. As a result, the aforementioned ohmic power losses are avoided or at least reduced by designing the fingers with a local cross-sectional increase in the contact-making region.

The contact fingers preferably have a widened portion in the contact-making area, which widened portion extends parallel to the surface of the insulating layer and perpendicular to the longitudinal extension of the contact fingers.

Thus, a local cross-sectional enlargement is thereby obtained by an at least local widening of the contact fingers in the contact-making area in a manner that is simple and, in particular, technically uncomplicated to implement.

In this case, it is particularly advantageous if the contact fingers are formed overlapping the insulating layer in the contact-making region. The double effect of reducing the aforementioned ohmic power losses is thus obtained:

on the one hand, the cross-sectional area is increased by the widening in the contact-making region, so that the transmission resistance in the contact finger is reduced by the increase in cross-sectional area compared to a contact finger without an increase in cross-sectional area. Furthermore, no or only a small amount of semiconductor material is added in the region of the contact fingers which overlaps the insulating layer, since this region does not contact the semiconductor layer or at least does not contact it directly during the production process. As a result, the line resistivity in the region of the fingers which overlap the insulating layer is therefore lower (because of the small addition of semiconductor material) than in the region immediately adjacent to or directly above the contact level (because of the greater addition of semiconductor material). It can therefore be assumed in the equivalent circuit diagram that the higher-resistivity finger regions are connected in parallel with the lower-resistivity finger regions, so that, as a result of the addition of the semiconductor material, there is no or only a slight increase in the resistance of the finger circuit overall, so that the power losses associated therewith are avoided or at least reduced.

In a particularly advantageous embodiment, the contact fingers then cover the insulating layer in a region surrounding the contact-making region. Therefore, on one hand, the effect of the parallel connection is enhanced. Furthermore, a low degree of processing precision is required in the production of solar cells, since the overlapping of the metallization fingers on the insulating layer occurs around the contact surfaces, so that a high tolerance with respect to the adjustment precision is obtained.

The task of the invention is also accomplished as follows: the contact fingers have electrically parallel metal conductive structures in the contact-making areas, which do not cover the contact-making areas. Thus, electrically parallel metal conductive structures have no or only a small amount of added semiconductor material, since they do not cover the contact-making regions. Since the finger areas covering the contact-making areas are connected in parallel with the aforementioned electrically conductive metal conductive structures, the increase in line resistance due to the addition of the semiconductor material is compensated for or at least reduced by the electrically parallel metal conductive structures. In this case, it is within the scope of the invention to provide metallic conducting structures which are electrically connected in parallel or have a locally enlarged cross section. It is also within the scope of the invention to provide both a local cross-sectional enlargement and an electrically parallel metal conducting structure.

The electrically parallel metal conductive structures are preferably formed in the form of partially parallel "sub-fingers". These secondary fingers are integral parts of the "fingers", but extend parallel to the finger stems and spaced apart therefrom in the region of the contact field. Before and/or after, preferably before and after, the contact-making region, the secondary fingers are electrically conductively connected, preferably materially bonded, to the finger stem.

It is particularly advantageous here if the stem does not cover the contact-making area, so that only the sub-fingers cover the contact-making area. This yields the advantage, on the one hand, that the current flow in the stem is not or only slightly influenced by the addition of the semiconductor material. Furthermore, the sub-fingers are spaced apart from the stem in the region of the contact-making area, so that even when such a finger is produced, the semiconductor material incorporated in the metal of the sub-fingers does not or only slightly penetrate into the material of the stem of the finger, because of the spatial spacing.

The contact openings are preferably arranged in pairs, wherein the contact openings belonging to a pair are arranged on opposite sides of the finger.

In this advantageous embodiment, the main wire or trunk of the finger extends between the pair of contact openings, wherein the finger has a widening in the region of the contact openings, so that it covers at least the contact openings.

The contact finger therefore has a stem which extends between the two contact-making apertures of a pair. The finger stem has a widening in the form of a side branch or a lateral widening in the area of the contact opening, which covers at least the contact opening.

The stem of the finger thus extends between the contact openings over the insulating layer and thus has no or only a small addition of semiconductor material in this region, and accordingly has no or only a small increase in the line resistivity. Because of the coverage of the contact opening, the current carriers are guided laterally to the finger stem. However, the overall current density in the case of lateral approach is comparatively low, since the charge carriers only have to be transported from the respective contact opening in this region to the finger stem. While the charge carriers of adjacent pairs of contact gaps flow through the finger stems, which, as mentioned, are not or only slightly affected by the addition of the semiconductor material.

As an alternative and/or in addition to the design of the contact fingers with a local increase in cross section by local widening, the contact fingers have a local increase in thickness in the contact-making region. In this case, with a constant width, a local increase in cross section can be obtained by thickening alone, in order to reduce the ohmic power losses as described above.

Also, a comparatively large increase in the cross-section and a corresponding comparatively significant reduction in the transmission resistance can be achieved by a combination of widening and thickening.

The contact structure preferably comprises a plurality of contact fingers and at least one busbar, wherein the contact fingers are preferably connected in an electrically conductive manner to the busbar in a bonded manner.

The bus bars are in this case part regions of a contact structure, which collect the charge carriers of a plurality of contact fingers and transfer them to terminal elements, for example cell connections or pads for connection to an external circuit or cell connections.

The bus bar preferably does not cover the contact-making area, i.e. the bus bar is electrically conductively connected to the semiconductor structure only via the contact fingers and the contact surfaces covered by the contact fingers. This provides the advantage that the conductivity in the busbar is not reduced by the addition of the semiconductor material.

The contact fingers and busbars may have a structure of contact-making grids known per se, in particular comb-shaped or double comb-shaped contact grids. The contact fingers preferably extend parallel, while the bus bars extend perpendicular to the contact fingers. Thus, it is possible to use substantially the known geometries and production methods for the bus bars and the fingers (or for the bus bar and the finger backbone in a preferred embodiment as described above).

In a further preferred embodiment, the contact structure comprises a plurality of contact fingers, wherein the contact fingers are not connected to one another in a metal-conductive manner. The electrically conductive connection of the contact fingers is therefore at most via the semiconductor layer or via an external circuit afterwards, or via additional components, for example, during the production of the solar cell module and the connection of the solar cell to a plurality of adjacent solar cells.

This results in a low-cost production, since no bus bar is formed as part of the solar cell, which bus bar connects the contact fingers.

At least a part of the contact surfaces, in particular preferably all of the contact surfaces, preferably have a longitudinal extent, wherein the contact surfaces are arranged perpendicular to the longitudinal extent of the contact fingers. In this advantageous embodiment, the contact finger can therefore be regarded as being formed by a stem, on the side of which the contact-making surface is arranged, which contact-making surface preferably extends approximately perpendicularly to the stem of the contact finger. Here, the contact fingers also cover at least the contact surface, preferably also the region of the insulating layer surrounding the contact surface. In relation to the conductive paths, the contact surface can therefore be regarded as a "micro finger" because of its longitudinal extent and the finger area covering the contact surface, which supplies carriers to the finger stem.

This results in the advantage already described above that no or only a slight increase in the line resistance in the finger stem is caused by the semiconductor material filling. Furthermore, the longitudinal extent of the contact surface offers the possibility of good coverage of the semiconductor layer by the contact surface, whereby losses due to line resistance in the semiconductor layer, i.e. so-called series resistance losses in the semiconductor layer, are additionally reduced, since the flow path of the majority carriers in the semiconductor layer is shorter.

In this case, in a further preferred embodiment, a further reduction of the ohmic power loss in the contact structure is achieved in that the contact fingers, at the contact surface having a longitudinal extent, have a cross-sectional area which increases along the longitudinal extent towards the contact fingers, in particular preferably have an increasing width. The micro-fingers described above are thus constructed according to the per se known shape of the "conical finger". In this case, it is to be taken into account that, over the entire contact surface, charge carriers enter the metallization structure covering the contact surface, so that the total current increases along the contact surface in the main current flow direction in the contact structure. The continuous or stepped almost continuously increasing cross section in the main current direction, and in this case in the direction of the finger stem, therefore leads to an optimization in that, on the one hand, the current density is not or only slightly increased because of the increased cross section, and, on the other hand, the surface of the solar cell can be kept as small as possible covered by the contact structure.

As already mentioned, the production method for the local metal doping in the contact surface in such a contact structure also results in the semiconductor material being incorporated into the metallization structure in the region of the contact surface, wherein the metal is the only or partial component of the metallization structure. The contact fingers can thus contain the semiconductor material of the semiconductor layer in the contact-making region.

The contact-making structures described above are particularly suitable for placement on the rear side of a solar cell. In this way, a local contact structure (via local recesses in the insulating layer to form contact surfaces) and a local high-concentration doping in the semiconductor layer in the region of the contact surface can be maintained, which is known per se and preferred, while at the same time forming a bifacial solar cell:

since the contact structure is designed with a plurality of contact fingers, no metallization of the entire rear side is required. In the region of the rear side not covered by the contact structure, photons can thus enter the semiconductor layer and contribute to the generation of charge carriers. The photovoltaic solar cell according to the invention is therefore preferably constructed in the form of a bifacial solar cell, so that photons of the solar cell can contribute to the current generation both from the front side and from the back side.

The contact structure is advantageously used for contacting the p-doped region: a typical metal used to form the contact structure is, for example, aluminum. As described above, a locally high concentration of doping in the p-doped region of the solar cell can be achieved by means of the metal, but not in the opposite doped region, i.e. the n-doped region.

These actually fabricated solar cells have an n-doped emitter and correspondingly a p-doped base. The contact structure is therefore advantageously used for contacting the base of a solar cell.

However, solar cells with n-doped bases are gaining increasing attention due to the improved material properties. In such solar cells, a contact structure is advantageously used for contacting the p-doped emitter, for example when using a p-doped emitter with aluminum.

The photovoltaic solar cell is particularly advantageously designed as a PERC solar cell. The basic structure of such a solar cell is described in Blakers et al (1989) "22.8% high efficiency silicon solar cell" (applied Physics journal, 55(13), p.1363, DOI: 10.1063/1.101596).

The local cross-sectional increase is preferably designed such that the cross-sectional area in the region of the contact-making region increases by at least a factor of 1.2, preferably by at least a factor of 1.5, in particular by at least a factor of 2, compared with the cross-sectional area of the region of the contact finger spaced from the contact-making region in the main current direction.

The local cross-sectional increase is preferably designed such that the cross-sectional area in the region of the contact-making region increases by a maximum factor of 10, preferably by a maximum factor of 7, in particular by a maximum factor of 5, compared to the cross-sectional area of the region of the contact finger spaced apart from the contact-making region in the main current direction.

In the main current direction of the fingers or finger stems, the local cross-sectional increase preferably extends over a length which is at most twice the length of the contact surface in the main current direction, preferably over a length which is at most twice the length of the contact surface, particularly preferably over half the length of the contact surface.

Typically, the finger or at least one stem of the finger has a longitudinal extension. In this case, the main current direction generally extends along this longitudinal extension.

As already mentioned, the adverse effects caused by the incorporation of semiconductor materials in the fingers are avoided by means of the invention. In general, the contact fingers have a local addition of semiconductor material in the region of the contact surface in a concentration of more than 20 wt.%, in particular more than 12.6 wt.%, which concentration in the contact fingers occurs in particular when the doped regions grow epitaxially, preferably by the metal of the contact structure, on the semiconductor in the liquid mixed phase of metal and semiconductor.

The contact areas, on which the contact fingers extend and/or along which they extend, are spaced apart from one another. The distance between the contact-through regions is preferably at least 100 μm, in particular at least 200pm, in order to reduce the negative effects due to recombination events at the contact regions. The optimization between the series resistance effect and the recombination effect generally occurs in a preferred embodiment if the contact-making region distance is in the range from 100 μm to 4mm, in particular in the range from 200 μm to 3 mm.

In particular in contact-making structures for contacting p-doped semiconductor materials, in particular p-doped bases, the adverse effect of the addition of the semiconductor material on the quality of the electrical conduction occurs as a function of the process. The contact structure is therefore preferably designed for contacting the p-doped region and in particular the base of a solar cell. It is particularly preferred that the contact-making structures are arranged on the back side of the solar cell facing away from the irradiation source when in use.

The invention is particularly suitable for the design of a contact-making arrangement known per se with a plurality of contact fingers. In this case, all contact fingers of the contact structure preferably extend over and/or along a plurality of contact areas spaced apart from one another, wherein the contact fingers have a local cross-sectional enlargement in the contact areas and/or the contact fingers have electrically parallel metal conducting structures which do not cover the contact areas in the contact areas.

Other preferred features and embodiments are described below in conjunction with the examples and the figures, wherein:

figure 1 shows a first embodiment of a photovoltaic solar cell according to the invention in the form of a PERC solar cell in a perspective view,

figure 2 shows a contact-making structure of the solar cell according to figure 1,

figure 3 shows an alternative contact-making structure according to a second embodiment comprising micro-fingers,

figure 4 shows a further alternative implementation of the contact-making structure according to the third embodiment without busbars,

fig. 5 shows a fourth embodiment in a sectional view, in which the sectional plane extends through the contact finger, an

Fig. 6 shows a fifth exemplary embodiment, in which the contact fingers have electrically parallel conductive structures in the contact-making area, which do not cover the contact-making area.

All figures show schematic views, not to scale. Like reference numerals in fig. 1-5 refer to like or functionally-like components.

Fig. 1 shows a first embodiment of a photovoltaic solar cell with a PERC structure according to the invention:

the solar cell has a semiconductor layer 1 in the form of a p-doped silicon wafer. In the view of fig. 1, the back side of the solar cell is shown above and the front side of the solar cell is shown below.

An n-doped emitter 2 is formed on the front side of the solar cell. For optical performance improvement (reflection reduction) and passivation, an antireflection layer 3 is also provided on the front side, which is formed in the form of a dielectric layer and is therefore also electrically insulating. A metal front-contact grid, known per se, is provided (not shown) on the antireflection layer 3, which locally penetrates the antireflection layer 3 in order to form an electrically conductive connection to the emitter 2 in a manner known per se.

An electrically insulating layer 4, here in the form of a silicon nitride layer, is provided on the rear side of the solar cell.

On the insulating layer 4, a contact structure 5 is provided, which is thus a metal back contact structure of the solar cell according to fig. 1. The insulating layer 3 has a plurality of contact-making apertures (e.g., contact-making apertures 6). These contact gaps are produced, for example, by means of partial laser ablation of the insulating layer. At the contact opening 6, the contact structure 5 penetrates the insulating layer 4 and makes an electrically conductive contact with the semiconductor layer 1 in order to contact the p-doped base of the photovoltaic solar cell.

During the production process, the semiconductor material of the semiconductor layer 1 is dissolved to molten metal in the region of the contact-making openings 6 in the so-called "red-hot-contact (kontake)". During the cooling process in contact with the red heat, the dissolved semiconductor material recrystallizes on the semiconductor layer 1 and is thus doped with the metal, and in this case aluminum, with the result that, on the one hand, the metal of the contact-making structure 5 is present as a dopant in the semiconductor layer 1, so that a locally doped region 7 is formed. On the other hand, however, the semiconductor material also migrates into the contact-making structure in the contact-making recess region.

The contact structure is made of aluminum, and the doped region 7 is accordingly doped with aluminum and is therefore a p-doped region. The doping of this region is higher than the basic doping of the base of the semiconductor layer 1, so that the doped region 7 is a local p-highly doped region (also referred to as p)⁺⁺)。

The design of the contact-making structure 5 is described in detail below with reference to fig. 2:

fig. 2 to 4 and 6 each show a detail of the different contact structures in a plan view. Fig. 2 shows a contact structure 5 of the solar cell according to fig. 1.

Fig. 2 to 4 and 6 each show a partial enlarged view of the contact structure with an enlarged partial cross section.

The contact-making structure 5 shown in fig. 2 has a busbar 8 and a plurality of contact fingers, three contact fingers 9 being shown here.

Each finger extends over a plurality of mutually spaced contact fields 10 at a distance (here 500 μm):

as shown in the enlarged detail, in the contact opening 6 of the insulating layer 4, the contact finger 9 penetrates the insulating layer 4 and thus forms an electrical contact with the semiconductor layer 1 in this region. In the contact region 10, there is therefore a contact surface 11, at which contact surface 11 the contact structure 5 and the semiconductor layer 1 lie next to one another and make electrical contact.

It is important that the contact fingers 9 each have a local cross-sectional increase in the contact-making area 10:

as shown in the plan view according to fig. 2, the contact fingers 9 each have a local widening parallel to the surface of the insulating layer 4 in the contact-making regions 10. The local cross-sectional increase is therefore an increase in the cross-section of the finger 9 in the region of the contact surface 11 relative to the cross-section of the finger in the extension before and after the contact surface 11. In this case, the cross section increases by a factor of approximately 1.7 in the contact surface region (region a1) compared to the cross sections before and after the contact surface (positions a2 ″ and A3 "). Preferably, there is an increase in the cross-section by a factor in the range from 1.10 to 3, in particular in the range from 1.2 to 2. In this case, the fingers have a width of about 300 μm in the region outside the contact surface (outside the cross-sectional enlargement), which is preferably approximately in the range from (100 μm to 500 μm). In the contact-making surface region (in the region of the increased cross section), the fingers here have a width of approximately 500 μm. The cross-sectional increase is preferably limited approximately to the contact-making surface region. Likewise, the cross-sectional increase may extend slightly further before and after the contact-making face, but preferably less than half the length of the contact-making face. The term "length" relates to the extension of the contact-making face in the main current direction.

Since the widened portion is designed to be larger than the width of the contact surface 11, the contact fingers 9 are formed overlapping the insulating layer 4 in the contact region 10. In particular, the contact fingers each overlap the insulating layer 4 in a region surrounding the contact surface 11, i.e., in the top plan view, the contact surface 11 is surrounded by the region of the contact fingers 9 overlapping the insulating layer 4. The contact fingers 9 therefore cover the contact-making areas 10 and thus also the contact surfaces 11.

When using solar cells, the current in the contact-making structures 5 flows in the direction of the bus bars 8, which current is conductively connected to adjacent solar cells, for example, by cell connectors when forming a solar cell module.

Thus, in the finger 9, a current flows from right to left according to fig. 2. In the contact-making region, the line resistivity of the contact fingers 9 increases, since the semiconductor material of the semiconductor layer 1 is incorporated into the contact fingers in this region. However, the increase in the resistivity of the conductor is compensated for because the cross section is increased and here because the fingers in the contact-making region are widened. Furthermore, the edge regions of the contact fingers 9 surrounding the contact-making regions 10 have no or only a low concentration of semiconductor material, so that accordingly there is no or only a slight increase in the line resistance.

As a result, efficiency losses arising locally from the contact-making structure 5 due to the addition of semiconductor material are avoided or at least significantly reduced.

Fig. 3 shows an alternative embodiment of a contact structure 5 'according to a second exemplary embodiment, which has an alternative design and arrangement of the contact recesses and the contact surfaces 11', respectively. The contact structure 5 'according to fig. 3 can be used in place of the contact structure 5 in fig. 1 with corresponding adjustment of the contact recesses 6, i.e., the contact structure 5' can also be advantageously used as a rear contact structure for a biplanar PERC solar cell.

The contact finger 9 'of the contact structure 5' according to fig. 3 has a stem 12, from which a plurality of micro-fingers 13 extend, as is shown in the enlarged detail. The micro-fingers 13 extend perpendicularly to the longitudinal main extension direction of the stem 12 of the finger 9'.

Correspondingly, the contact surface 11 'also has a longitudinal extent and is arranged perpendicular to the longitudinal extent of the stem 12 of the finger 9'. The micro-fingers 13 completely cover and overlap the contact surface 11'. Furthermore, the insulating layer surrounds the contact surface 11'.

In the contact-making structure 5 'according to fig. 3, current also flows in the contact finger 9' substantially in the direction of the busbar 5 'when the solar cell is in use, i.e. in the stem 12 of the contact finger 9' always from right to left in the view according to fig. 3.

In the micro-fingers, the current flows perpendicular to the stem 12 and toward the stem 12.

The contact fingers 9 'therefore each have a local cross-sectional enlargement at the contact surface 11', which is formed here by the micro-fingers 13 and thus by a local widening (in the direction of the stem 12). Here, the cross-section is increased by a factor of about 3 by a pair of micro-fingers. In this embodiment, the increase in cross-section is preferably performed by a factor in the range of 2 to 5.

Furthermore, the trunk 12 does not cover the contact surface 11', so no semiconductor material or only a low concentration of semiconductor material is added to the trunk 12, so that the current in the trunk 12 towards the busbar 5' is not affected or is only slightly affected by the increase in the line resistance due to the addition of semiconductor material.

Fig. 4 shows a further exemplary embodiment for a contact structure 5 ″ which can also be used for rear contact of solar cells in a similar manner to the illustration of fig. 1. The dimensioning of the local cross-sectional enlargement can be carried out here analogously to the embodiment according to fig. 3.

The contact-making structure 5 "has the feature that the solar cell does not have electrical conductors for connecting several individual contact fingers 9" to one another:

the contact structure 5 "has a plurality of contact fingers 9" which extend along a plurality of contact surfaces 11 "along the finger stem. The contact surfaces 11 ″ are also arranged in pairs, as in fig. 3, wherein the contact surfaces belonging to a pair (and correspondingly also the corresponding contact openings in the insulating layer) are formed on opposite sides of the stem of the respective finger 9 ″. The partial enlargement shows a finger 9 "with a pair of contact surfaces 11", which are arranged opposite a stem 12 "of the finger 9". It is also within the scope of the invention for a pair of contact surfaces to be formed in succession as contact surfaces, which in this case therefore also extend under the finger stem.

The contact-making structure 5 ″ also has a micro-finger 13':

as is also shown in the enlarged cross-sectional view, the fingers 9 "are each provided with a micro-finger 13" on the side of the stem 12", which completely covers the contact surface 11". The micro-fingers 13 'are configured in the shape of "tapered fingers", in such a way that the width of the micro-fingers 13' increases towards the stem 12 ".

When using a solar cell, the current in the micro-fingers 13' increases in the direction of the trunk 12", since the current is continuously input via the contact-making face 11". In order to avoid or at least reduce the power loss due to the increased current, the width of the micro-fingers 13' is correspondingly increased towards the stem 12 ".

When the solar cells are connected to one solar cell module, the fingers 9 "are electrically conductively connected to one another via the outer part and/or to the fingers 9" of adjacent solar cells. Thus (and because of the lack of a bus bar structure), the finger 9 "according to fig. 4 is sometimes referred to herein as a bus bar.

In fig. 5, a further exemplary embodiment is shown, in which the local cross-sectional increase is achieved by local thickening:

in principle, the exemplary embodiment according to fig. 5 can be formed on the basis of the solar cell structure according to fig. 1 and also on the basis of the contact-making structure according to the top view of fig. 2. The view according to fig. 5 shows a cross section perpendicular to the insulating layer 4 and extending along the contact finger 9 "'and approximately centrally in the contact finger 9"'. Thus, a local cross-sectional increase of the fingers 9' ″ is achieved here not only by the local widening according to fig. 2, but also by the local thickness increase according to fig. 5. In an alternative embodiment, the local cross-sectional increase is obtained only by a local thickening according to fig. 5. Here, the thickness increases locally, for example by a factor of 2. The local thickening is preferably carried out in a multiple in the range of 1.2 to 4.

Fig. 6 shows a fifth embodiment, where the fingers are formed with electrically parallel metallic conductive structures:

a contact structure as shown in the partial view of fig. 6 can also be used for contacting the PERC solar cell according to fig. 1.

Here, too, a plurality of contact fingers 9"" project from a busbar 8' ". Unlike the preceding embodiments, the finger 9"" has a so-called sub-finger: as shown in the enlarged partial view shown on the right, the stems 12 "' of the fingers not covering the contact-making area are centrally located. Next to the trunk 12 '″, a plurality of

secondary fingers

14a, 14b are provided parallel to the trunk, which are spaced apart from the trunk 12' ″ in the region of the contact-making region 10, i.e., there is no electrically conductive connection in this region. Only between the contact areas are the

secondary fingers

14a, 14b conductively connected to the stem 12' ″ via metal bridges. Such two bridges are schematically indicated in enlarged detail by the reference numeral 15.

This results in the advantage that, in the production of such a contact structure, although the semiconductor material diffuses into the metal in the region of the contact region 10, the semiconductor material does not reach the stem because of the spatial separation from the stem 12' ″. The current along the trunk 12 "'to the busbars 8"' is therefore unaffected or only slightly affected by the addition of the semiconductor material.

The width of the secondary fingers is here approximately 75% of the width of the trunk. Here, the width of the stem is about 200 μm.

Claims

1. A photovoltaic solar cell having at least one semiconductor layer (1), at least one electrically insulating layer (4) and at least one metallic contact structure (5, 5'),

wherein the insulating layer is arranged between the semiconductor layer and the contact structure, and the insulating layer (4) has a plurality of spaced-apart contact gaps (6) at which the contact structure (5, 5') makes electrical contact with the semiconductor layer (1) in a contact region (10), and

wherein doped regions are formed in the semiconductor layer (1) at least in the contact-making regions by doping the semiconductor layer with a metal, the contact-making structures (5, 5') being formed at least in part from said metal,

it is characterized in that the utility model is characterized in that,

the contact structure (5,5 ') has a plurality of contact fingers, the contact fingers (9,9 ') extending in each case over and/or along a plurality of mutually spaced contact zones, at which the contact fingers are in direct contact with the semiconductor layer, wherein the contact fingers (9,9 ') have a local cross-sectional increase in the contact zone and/or have electrically parallel metallic conductive structures at the contact zone, which do not cover the contact zone,

and no contact area is provided between adjacent locally increased cross-sections along the fingers;

wherein the local amount of semiconductor material deposited in the region of the contact-making face is greater than 20% by weight.

2. Solar cell according to claim 1, characterized in that the contact fingers (9,9',9",9"') have a widening in the contact-making area parallel to the surface of the insulating layer (4) and perpendicular to the longitudinal extension of the contact fingers.

3. Solar cell according to claim 2, characterized in that the contact fingers (9,9',9",9"') are formed in the contact-making area in such a way that they cover the insulating layer (4).

4. Solar cell according to claim 3, characterized in that the contact fingers (9,9',9",9'") cover the insulating layer (4) in an area surrounding the contact-making area.

5. Solar cell according to one of claims 1 to 4, characterized in that the contact notches are arranged in pairs, wherein the contact notches belonging to a pair are arranged on opposite sides of the stem of the finger.

6. Solar cell according to one of claims 1 to 4, characterized in that the contact fingers (9,9',9",9"') have a local thickening in the contact-making region.

7. Solar cell according to one of claims 1 to 4, characterized in that the contact-making structure (5,5',5") has at least a plurality of contact fingers.

8. Solar cell according to claim 7, characterized in that the contact fingers (9,9',9",9"') are arranged in parallel.

9. Solar cell according to one of claims 1 to 4, characterized in that the contact-making structure (5,5',5") comprises a plurality of contact fingers and at least one busbar (8,8',8"), wherein the contact fingers (9,9',9",9"') are connected to the busbar in a materially bonded and electrically conductive manner.

10. Solar cell according to claim 9, characterized in that the contact fingers (9,9',9",9" ') extend in parallel and the busbars (8,8',8") extend perpendicular to the contact fingers.

11. Solar cell according to one of claims 1 to 4, characterized in that the contact structure comprises a plurality of contact fingers, wherein the contact fingers (9") are not connected to each other in a metallic electrically conductive manner.

12. Solar cell according to one of claims 1 to 4, characterized in that at least a part of the contact surfaces has a longitudinal extent and is arranged perpendicular to the longitudinal extent of the contact fingers.

13. Solar cell according to one of claims 1 to 4, characterized in that all contact surfaces have a longitudinal extent and are arranged perpendicular to the longitudinal extent of the contact fingers.

14. The solar cell according to claim 12, characterised in that the contact fingers (9,9',9",9"') have, on the contact-making surface with a longitudinal extension, a cross-section which increases along the longitudinal extension towards the contact fingers (9,9',9", 9"').

15. The solar cell according to claim 13, characterised in that the contact fingers (9,9',9",9"') have, on the contact-making surface with a longitudinal extension, a cross-section which increases along the longitudinal extension towards the contact fingers (9,9',9", 9"').

16. The solar cell according to claim 12, characterised in that the contact fingers (9,9',9",9"') have on the contact-making surface with a longitudinal extension a width which increases towards the contact finger (9,9',9",9"') along the longitudinal extension.

17. The solar cell according to claim 13, characterised in that the contact fingers (9,9',9",9"') have on the contact-making surface with a longitudinal extension a width which increases towards the contact finger (9,9',9",9"') along the longitudinal extension.

18. Solar cell according to one of claims 1 to 4, characterized in that the electrically parallel metal conducting structures are formed in the form of partially parallel sub-fingers which are spaced apart from the stem of the contact finger in the region of the contact-making area.

19. The solar cell of claim 18, wherein the sub-fingers cover the contact-making region and the backbone does not cover the contact-making region.

20. Solar cell according to one of claims 1 to 4, characterized in that the contact fingers (9,9',9",9"') comprise the semiconductor material of the semiconductor layer (1) at contact-making regions (10).

21. Solar cell according to one of claims 1 to 4, characterized in that it is constructed in the form of a bifacial solar cell in the following manner: the back side of the solar cell is formed at least partially transparent to electromagnetic radiation.

22. Solar cell according to claim 21, characterized in that the contact structure (5,5',5") is constructed in the form of a back contact structure (5,5',5") and is arranged on the back side of the solar cell.

23. Solar cell according to one of claims 1 to 4, characterized in that the contact-making structure (5,5',5") is used to contact the p-doped region of the semiconductor layer (1).

24. Solar cell according to one of claims 1 to 4, characterized in that the contact-making structure (5,5',5") is formed as a back contact-making structure (5,5',5") and is arranged on the back side of the solar cell, and that the back side of the solar cell is formed with a local highly doped region at the contact junction region within the semiconductor layer (1).

25. Solar cell according to one of claims 1 to 4, characterized in that the contact fingers have locally increased cross-section and/or parallel conducting structures in all contact-making regions and/or the solar cell is constructed as a PERC solar cell.