DE102015104236B4 - Photovoltaic solar cell - Google Patents

Abstract

Photovoltaic solar cell, with at least one semiconductor layer (1), at least one electrically insulating insulation layer (4) and at least one metallic contact structure (5, 5 ', 5' '), the insulation layer (4) between the semiconductor layer (1) and the contact structure (5 , 5 ', 5' ') and the insulation layer (4) has a plurality of contacting recesses (6) on which the contacting structure (5, 5', 5 '') with the semiconductor layer (1) in a contacting area (10) forms an electrical contact and wherein in the semiconductor layer (1) at least one doping area is formed at least on the contacting areas (10) by doping the semiconductor layer (1) with a metal, from which metal the contacting structure (5, 5 ', 5' ') is at least is partially formed, characterized in that the contacting structure (5, 5 ', 5 ") has a plurality of contact fingers, which contact fingers (9, 9', 9", 9 "') sic h each extend over several contacting areas (10) and / or along several contacting areas (10), the contact fingers (9, 9 ', 9' ', 9' '') having a local increase in cross-sectional area at the contacting areas (10) and between adjacent local cross-sectional area increases along a contact finger no contact areas (10) are formed and / or the contact fingers on the contact areas (10) have metallic line structures that are electrically connected in parallel and do not cover the contact areas (10).

Description

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

Photovoltaic solar cells are used to convert the energy of incident photons into electrical energy. For this purpose, typical solar cells have a semiconductor layer, an electrically insulating insulation layer and a metallic contact-making structure.

The photons absorbed in the semiconductor layer generate charge carrier pairs which are separated at a pn junction. The metallic contact structure is connected to the p- or to the n-doped region, so that charge carriers can be removed. Charge carriers of the area of the semiconductor structure with the opposite doping type are correspondingly removed via a further metallic contact-making structure or via a full-area, rear-side metallization.

The insulation layer is arranged between the semiconductor layer and the contacting structure in order, among other things, to reduce losses due to recombination of the minority charge carriers at the metal / semiconductor interface and the losses resulting therefrom. The insulation layer has a plurality of contact-making recesses, on which the contact-making structure forms an electrical contact with the semiconductor layer in a contact-making region.

Such a photovoltaic solar cell is off US 2015/0 068 592 A1 known.

Furthermore, it is known to reduce the minority charge carrier recombination at the remaining interface between metal and semiconductor in the semiconductor layer at the contacting regions by doping the semiconductor layer with a metal, which metal is part of the contacting structure.

As a result, the metal of the metallic contacting structure can be used in a simple manner in the production process of the solar cell to form so-called local high doping areas on the contacting areas in the semiconductor layer and the aforementioned reduction in minority charge carrier recombination in these areas can be achieved in a cost-effective manner.

Despite the successes in reducing the production costs and / or increasing the efficiency of photovoltaic solar cells, there is still high cost pressure on the market. In addition, photovoltaic solar cells are now used in a wide variety of applications, so that an optimal arrangement with regard to the radiation source, for example the sun, is not always guaranteed.

The invention is therefore based on the object of improving a photovoltaic solar cell with an insulation layer and contacting structure as described above by increasing the efficiency due to a reduction in losses achieved.

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

• Wie zuvor beschrieben, wird das Metall der Kontaktierungsstruktur verwendet, um lokale Dotierbereiche an den Kontaktierungsausnehmungen in der Halbleiterschicht zu erzeugen. Hierdurch erfolgt jedoch nicht nur eine lokale Dotierung der Halbleiterschicht durch das Metall, ebenso wird typischerweise Halbleitermaterial in die metallische Kontaktierungsstruktur integriert. Hierdurch verringert sich die Leitfähigkeit der Kontaktierungsstruktur in diesem Bereich.

The present invention is based on the knowledge that especially in the case of solar cells with a contacting structure as described above, a loss in the contacting structure in the area of the contacting recesses is justified:

• As described above, the metal of the contact-making structure is used to produce local doping regions at the contact-making recesses in the semiconductor layer. However, this not only results in local doping of the semiconductor layer by the metal, but also typically semiconductor material is integrated into the metallic contact-making structure. This reduces the conductivity of the contact structure in this area.

Investigations have shown that, particularly when the contacting structure is formed using contact fingers known per se, the line resistance of the contact fingers in known solar cell structures in the area of the contacting recesses due to the semiconductor material embedded in the contact finger increases in such a way that, due to the increased electrical line resistance and corresponding ohmic power losses, significant reductions in the Overall efficiency of the photovoltaic solar cell occur.

• Die erfindungsgemäße photovoltaische Solarzelle weist mindestens eine Halbleiterschicht, mindestens eine elektrisch isolierende Isolierungsschicht und mindestens eine metallische Kontaktierungsstruktur auf. Die Isolierungsschicht ist zwischen Halbleiterschicht und Kontaktierungsstruktur angeordnet.

The photovoltaic solar cell according to the invention leads to an avoidance or at least a reduction of these losses:

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

In order to form electrical contacting of the semiconductor layer by means of the contacting structure, the insulation layer has a plurality of contacting recesses, at which the contacting structure forms an electrical contact with the semiconductor layer in a contacting region.

Furthermore, as described at the outset, a doping region is formed in the semiconductor layer at least on the contacting regions by doping the semiconductor layer with a metal, which metal is a complete or partial component of the metallic contacting structure. As a result, as described above, losses due to surface recombination of the charge carriers in the semiconductor layer at the contacting regions can be reduced.

It is essential that the contacting structure has a plurality of contact fingers, which contact fingers each extend over several contacting areas and / or along several contacting areas, the contact fingers having a local increase in cross-sectional area at the contacting areas and no contacting areas being formed between adjacent local increases in cross-sectional area along a contact finger.

This refinement is based on the knowledge that there is a need for a contacting structure which covers the local doping regions described above, which contacting structure is not a full-area metallization, such as, for example, previously known full-area rear-side metallizations. There is a need for such a contacting structure which is at least partially transparent to incident photons because the surface is not covered over the entire area by a metal layer. By means of such a contacting structure with a plurality of contact fingers, it is thus possible to use such a contacting structure on a front side of the solar cell facing the light source when the solar cell is used. It is also possible to use it on the back of a solar cell, for example to form a bifacial photovoltaic solar cell, as will be explained in more detail below.

Here, studies have shown that, in contrast to a full-area metallization, the formation of the contact structure with a plurality of contact fingers carries the risk of the aforementioned ohmic power losses due to the local increase in the line resistance in the contact fingers.

In the photovoltaic solar cell according to the invention, the contact fingers each extend over several contact areas and / or along several contact areas, the contact fingers having a local increase in cross-sectional area at the contact areas and no contact areas formed between adjacent local cross-sectional area increases along a contact finger and / or the contact fingers on the contact areas have line structures connected electrically in parallel which do not cover the contacting areas.

The local increase in the specific line resistance of the contact fingers at the contact-making recesses can thus be compensated for or at least reduced by a local increase in cross-sectional area. As a result, such a design of the contact fingers with local increases in cross-sectional area at the contacting areas results in an avoidance or at least a reduction of the aforementioned ohmic power losses.

The contact fingers at the contacting areas preferably have a widening parallel to the surface of the insulation layer and perpendicular to a longitudinal extension of the contact finger.

In this way, a local increase in cross-sectional area is achieved in a simple and, in particular, technically uncomplicated manner by at least local widening of the contact finger at the contacting areas.

• Einerseits erfolgt durch die Verbreiterung an den Kontaktierungsbereichen eine Querschnittflächenerhöhung, so dass aufgrund der Querschnittsflächenerhöhung der Durchleitungswiderstand im Kontaktfinger sinkt, verglichen mit einem Kontaktfinger ohne Querschnittsflächenerhöhung. Darüber hinaus wird in den Bereichen des Kontaktfingers, welche die Isolierungsschicht überlappen, kein oder nur geringfügig Halbleitermaterial eingelagert, da diese Bereiche nicht oder zumindest nicht unmittelbar im Herstellungsprozess in Kontakt mit der Halbleiterschicht stehen. Im Ergebnis ist somit der spezifische Leitungswiderstand in den Bereichen des Kontaktfingers, welche die Isolierungsschicht überlappen, geringer (aufgrund der geringeren Einlagerung von Halbleitermaterial) gegenüber den Bereichen unmittelbar an oder über den Kontaktierungsflächen (aufgrund der höheren Einlagerung von Halbleitermaterial). Im Ersatzschaltbild kann somit von einer Parallelschaltung eines Kontaktfingerbereiches mit höherem spezifischen Widerstand und geringerem spezifischen Widerstand ausgegangen werden, so dass insgesamt keine oder eine nur geringfügige Erhöhung des Leitungswiderstandes im Kontaktfinger aufgrund der Einlagerung von Halbleitermaterial erfolgt und somit diesbezügliche Wirkungsgradverluste vermieden oder zumindest verringert werden.

It is particularly advantageous here that the contact fingers on the contacting areas are designed to overlap the insulation layer. This has a twofold effect of reducing the aforementioned ohmic power losses:

• On the one hand, the widening at the contacting areas results in an increase in cross-sectional area, so that, due to the increase in cross-sectional area, the conduction resistance in the contact finger decreases compared to a contact finger without an increase in cross-sectional area. In addition, no or only slightly semiconductor material is embedded in the areas of the contact finger which overlap the insulation layer, since these areas are not or at least not directly in contact with the semiconductor layer during the manufacturing process. As a result, the specific line resistance in the areas of the contact finger which overlap the insulation layer is lower (due to the lower incorporation of semiconductor material) compared to the areas directly on or above the contacting surfaces (due to the higher storage of semiconductor material). In the equivalent circuit diagram, a parallel connection of a contact finger area with a higher specific resistance and a lower specific resistance can be assumed, so that there is no or only a slight increase in the line resistance in the contact finger due to the inclusion of semiconductor material and the associated efficiency losses are avoided or at least reduced.

In a particularly advantageous embodiment, the contact fingers cover the insulation layer in an area surrounding the contacting area. As a result, on the one hand, the above-described effect of the parallel connection is increased. In addition, a lower processing accuracy is necessary in the production of the solar cell, since there is an overlap of the insulation layer all around the contacting surface by the metallization finger and thus higher tolerances with regard to adjustment inaccuracies are given.

The object on which the invention is based is also achieved in that the contact fingers on the contacting areas have metallic line structures that are electrically connected in parallel and that do not cover the contacting areas. These metallic line structures, which are connected electrically in parallel, therefore have no or only slight deposits of semiconductor material, since they do not cover the contact-making areas. Due to the parallel connection of the area of the contact finger that covers the contacting areas with the aforementioned electrical metallic line structures, increases in the line resistance due to the inclusion of semiconductor material are compensated or at least reduced by the electrically parallel connected metallic line structures. It is within the scope of the invention to alternatively provide local increases in cross-sectional area or metallic line structures connected electrically in parallel. It is also within the scope of the invention to provide both local increases in cross-sectional area and metallic line structures connected electrically in parallel.

The metallic line structures connected electrically in parallel are preferably designed as local, parallel secondary fingers. These secondary fingers are part of a finger, but in the area of the contacting areas they run parallel to a main branch of the contact finger and are spaced apart from them. Before and / or after, preferably before and after the contacting areas, the secondary fingers are electrically conductively and particularly preferably materially connected to the main branch of the contact finger.

It is particularly advantageous here if the main branch does not cover the contacting areas and thus only the secondary fingers cover the contacting areas. This has the advantage, on the one hand, that the current flow in the main branch is not or only slightly impaired by the inclusion of semiconductor material. In addition, the secondary fingers are spaced apart from the main branch in the area of the contacting areas, so that even when such a contact finger is manufactured, semiconductor material which is embedded in the metal of the secondary finger does not get into the material of the main branch of the contact finger, or only slightly - due to the spatial spacing can.

The contacting recesses are preferably arranged in pairs, the contacting recesses assigned to a pair being arranged on opposite sides of the contact finger.

In this advantageous embodiment, a main line or a main branch of the contact finger thus runs between the pair of contacting recesses, the contact finger being widened in the area of the contacting recesses so that it at least covers the contacting recesses.

The contact finger thus has a main branch which runs between the two contacting recesses that form a pair. The main branch of the contact finger has a widening in the area of the contacting recesses in the form of side branches or laterally attached extensions which at least cover the contacting recesses.

The main branch of the contact finger is thus guided between the contacting recesses on the insulation layer and thus has no or only comparatively slight deposits of semiconductor material in this area and accordingly no or only a comparatively small increase in the specific electrical line resistance. Due to the overlap of the contacting recesses, charge carriers are thus brought laterally to the main branch of the contact finger. However, the total current density with this lateral approach is comparatively low, since only the charge carriers from the respectively assigned contact-making recesses within these areas have to be fed to the main branch of the contact finger. The charge carriers from adjacent pairs of contacting recesses, on the other hand, flow through the main branch of the contact finger, which as described above is not or only slightly impaired by the inclusion of semiconductor material.

As an alternative and / or in addition to the formation of a local increase in cross-sectional area through local widening of the contact finger, the contact finger has a local increase in thickness at the contacting areas. In this case, with a constant width, a local increase in cross-sectional area can be achieved solely by increasing the thickness, in order to reduce the ohmic power losses as described above.

A comparatively greater increase in cross-sectional area and a correspondingly greater reduction in the transmission resistance can also be achieved by a combination of widening and increasing the thickness.

The contacting structure preferably comprises a plurality of contact fingers and at least one busbar, the contact fingers preferably being connected to the busbar in a materially and electrically conductive manner.

A busbar represents a partial area of the contacting structure which collects charge carriers from the plurality of contact fingers and forwards them to a connection such as a cell connector or a soldering pad for connection to an external circuit or cell connector.

The busbar preferably does not cover any contacting areas, i. H. the busbar is connected to the semiconductor structure in an electrically conductive manner exclusively via the contact fingers and the contact surfaces covered by them. This has the advantage that there is no reduction in the conductivity in the busbar due to the inclusion of semiconductor material.

Contact fingers and busbar can have the structure of known contact grids, in particular comb-like or double-comb-like contact grids. The contact fingers preferably extend parallel and the busbar extends perpendicular to the contact fingers. As a result, with regard to the busbar and contact finger (or with regard to the busbar and main branch, the contact finger in a preferred embodiment as described above), geometries and manufacturing methods known per se can essentially be used.

In a further preferred embodiment, the contacting structure comprises a plurality of contact fingers, the contact fingers not having any metallic, electrically conductive connection to one another. An electrically conductive connection of the contact fingers thus exists at best via the semiconductor layer or via subsequently via an external circuit or, for example, when the solar cell module is completed and the solar cell is connected to several adjacent solar cells via additional components.

This results in a cost-effective production, since no busbars, which connect contact fingers, are formed as part of the solar cell.

Preferably, at least a subset of the contacting surfaces, particularly preferably all of the contacting surfaces, have an elongate extension, the contacting surfaces being arranged perpendicular to a longitudinal extension of the contact finger. In this advantageous embodiment, the contact finger can thus be viewed as consisting of a main branch, on which main branch the contacting surfaces are arranged laterally, which preferably extend approximately perpendicular to the main branch of the contact finger. Here, too, the contact finger covers at least the contacting surfaces, preferably additionally a region of the insulation layer surrounding the contacting surfaces. With regard to the electrical conduction paths, the contacting surfaces due to their elongated extension and the areas of the contact finger covering these contacting surfaces can thus be viewed as “micro-fingers” which feed charge carriers to the main branch of the contact finger.

This results in the previously mentioned advantage that there is no or only a slight increase in the line resistance in the main branch of the contact finger due to the inclusion of semiconductor material. In addition, the elongated extension of the contacting surfaces offers the possibility of good coverage of the semiconductor layer by contacting surfaces, which also reduces losses due to the conduction resistance in the semiconductor layer, so-called series resistance losses within the semiconductor layer due to shorter flow paths of the majority charge carriers in the semiconductor layer.

A further reduction in ohmic power losses in the contacting structure is achieved in a further preferred embodiment in which the contact finger on the contacting surfaces with an elongated extension has a cross-sectional area that increases along the elongated extension in the direction of the contact finger, particularly preferably an increasing width. The aforementioned micro-fingers are thus designed in the form of a “tapered finger”, which is known per se. It is taken into account here that charge carriers enter the contacting area over the entire contacting area Metallization occur and thus the total current increases along a main current flow direction in the contacting structure along the contacting surface. A continuous or step-like quasi-continuously increasing cross-sectional area along this main flow direction, in this case in the direction of the main branch of the contact finger, thus leads to an optimization in that on the one hand the current density does not or only slightly increases due to the increasing cross-sectional area and on the other hand the shading of the surface of the solar cell is nonetheless can be kept as low as possible due to the contact structure.

As stated above, the production methods which, in such contacting structures, involve local doping in the area of the contacting areas with a metal that is the sole or partial component of the metallization structure, also lead to an embedding of semiconductor material in the metallization structure in the area of the contacting areas. The contact fingers can thus contain semiconductor material of the semiconductor layer in the contacting region.

• Aufgrund der Ausbildung der Kontaktierungsstruktur mit einer Mehrzahl von Kontaktfingern ist es nicht notwendig, eine ganzflächige Metallisierung der Rückseite vorzusehen. An den nicht durch die Kontaktierungsstruktur bedeckten Bereichen der Rückseite können somit Photonen in die Halbleiterschicht eindringen und zur Ladungsträgergeneration beitragen. Vorteilhafterweise wird die erfindungsgemäße photovoltaische Solarzelle somit als bifaciale Solarzelle ausgebildet, so dass sowohl von der Vorderseite, als auch von der Rückseite auf die Solarzelle auftreffende Photonen zur Stromerzeugung beitragen können.

The above-described contacting structure is particularly suitable for arrangement on the rear side of the solar cell. In this way, the well-known and favored structure of a local contacting (through the local recesses in the insulation layer to form the contacting areas) and the local high doping in the semiconductor layer in the area of the contacting areas can be maintained and a bifacial solar cell can be formed at the same time:

• Due to the formation of the contacting structure with a plurality of contact fingers, it is not necessary to provide an all-over metallization of the rear side. In the areas of the rear side not covered by the contacting structure, photons can thus penetrate into the semiconductor layer and contribute to the generation of charge carriers. The photovoltaic solar cell according to the invention is thus advantageously designed as a bifacial solar cell, so that photons striking the solar cell from both the front and the rear can contribute to the generation of electricity.

The contacting structure is advantageously used to contact a p-doped region: a typical metal for forming the contacting structure is, for example, aluminum. By means of these metals, as described above, the local high doping can take place in p-doped regions of the solar cell, but not in the regions doped in the opposite direction to this, the n-doped regions.

The majority of the solar cells currently produced have n-doped emitters and a corresponding p-doped base. The contacting structure is therefore advantageously used to contact the base of the solar cell.

However, due to improved material properties, solar cells which have an n-doped base are increasingly of interest. In solar cells of this type, the contacting structure is advantageously used to contact the p-doped emitter, for example when using an emitter p-doped by means of aluminum.

The photovoltaic solar cell is particularly advantageously designed as a PERC solar cell. The basic structure of such a solar cell is in Blakers, et al. (1989): 22.8% efficient silicon solar cell. In: Appl. Phys. Lett. 55 (13), p. 1363 . DOI: 10.1063 / 1.101596.

The local increase in cross-sectional area is preferably designed in such a way that the cross-sectional area in the area of the contacting areas is increased 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 to the cross-sectional area of those areas of the contact fingers, which are spaced from the contact areas in the main current flow direction.

The local increase in cross-sectional area is preferably designed in such a way that the cross-sectional area in the area of the contacting areas is increased by a maximum of a factor of 10, preferably by a maximum of a factor of 7, in particular by a maximum of a factor of 5, compared to the cross-sectional area of those areas of the contact fingers which are affected by the contacting areas are spaced apart in the main flow direction.

In the main current flow direction of the contact finger or a main branch of the contact finger, the local increase in cross-sectional area extends preferably a maximum of twice the length of the contact surface in the main current flow direction, preferably a maximum of the single length of the contact surface, particularly preferably a maximum of half the length of the contact surface.

The contact finger or at least one main branch of the contact finger typically has an elongate extension. In this case, the main flow direction typically runs along this elongated extent.

• 1 ein erstes Ausführungsbeispiel einer erfindungsgemäßen photovoltaischen Solarzelle, welche als PERC-Solarzelle ausgebildet ist in perspektivischer Darstellung;
• 2 die Kontaktierungsstruktur der Solarzelle gemäß 1;
• 3 eine alternative Kontaktierungsstruktur gemäß eines zweiten Ausführungsbeispiels, welche Mikro-Finger umfasst;
• 4 eine weitere alternative Ausführung einer Kontaktierungsstruktur gemäß eines dritten Ausführungsbeispiels, welche keine Busbars aufweist;
• 5 ein viertes Ausführungsbeispiel in Schnittdarstellung, wobei die Schnittebene durch einen Kontaktfinger verläuft und
• 6 ein fünftes Ausführungsbeispiel, bei welchem die Kontaktfinger an den Kontaktierungsbereichen elektrisch parallel geschaltete Leitungsstrukturen aufweisen, welche die Kontaktierungsbereiche nicht überdecken.

Further preferred features and embodiments are described below with reference to FIG Embodiments and the figures explained. It shows:

• 1 a first embodiment of a photovoltaic solar cell according to the invention, which is designed as a PERC solar cell, in a perspective view;
• 2 the contacting structure of the solar cell according to 1 ;
• 3 an alternative contact structure according to a second exemplary embodiment, which comprises micro-fingers;
• 4th a further alternative embodiment of a contacting structure according to a third exemplary embodiment, which has no busbars;
• 5 a fourth exemplary embodiment in a sectional view, the sectional plane running through a contact finger and
• 6th a fifth exemplary embodiment, in which the contact fingers on the contacting areas have line structures that are electrically connected in parallel and that do not cover the contacting areas.

All figures show schematic representations that are not true to scale. Same reference numerals in 1 until 5 denote elements that are the same or have the same effect.

• Die Solarzelle weist eine Halbleiterschicht 1 auf, welche als p-dotierter Siliziumwafer ausgebildet ist. In der Darstellung gemäß 1 ist die Rückseite der Solarzelle obenliegend und entsprechend die Vorderseite der Solarzelle untenliegend dargestellt.

1 shows a first embodiment of a photovoltaic solar cell according to the invention, which has a PERC structure:

• The solar cell has a semiconductor layer 1 on, which is designed as a p-doped silicon wafer. In the representation according to 1 the back of the solar cell is shown on top and correspondingly the front of the solar cell is shown on the bottom.

There is an n-doped emitter on the front of the solar cell 2 educated. For passivation and improvement of the optical properties (reduction of reflection) there is an additional anti-reflective layer on the front 3 arranged, which is designed as a dielectric layer and is thus additionally electrically insulating. On the anti-reflective layer 3 a known metallic front-side contacting grid is arranged (not shown), which area-wise the anti-reflective layer 3 reaches through to establish an electrically conductive connection with the emitter 2 to be trained in a manner known per se.

There is an electrically insulating insulation layer on the back of the solar cell 4th arranged, which in the present case is designed as a silicon nitride layer.

On the insulation layer 4th is a contact structure 5 arranged, which thus has a metallic rear-side contacting structure of the solar cell according to FIG 1 represents. The insulation layer 3 has a plurality of contacting recesses (for example contacting recess 6th ) on. This plurality of contact-making recesses is produced, for example, by means of local laser ablation of the insulation layer. At these contact recesses 6th penetrates the contact structure 5 the insulation layer 4th and forms with the semiconductor layer 1 an electrically conductive contact for contacting the p-doped base of the photovoltaic solar cell.

During production, the semiconductor material is used as a so-called “contact fire” to form the semiconductor layer 1 in the area of the contact recesses 6th triggered in molten metal. During the cooling process of contact firing, the released semiconductor material recrystallizes on the semiconductor layer 1 and is thus doped by means of the metal, in the present case aluminum, so that on the one hand the metal of the contacting structure 5 as a dopant in the semiconductor layer 1 is present and thus local doping areas 7th be formed. On the other hand, semiconductor material is also embedded in the contacting structure in the area of the contacting recesses.

In the present case, the contacting structure is made of aluminum, so that the doping regions accordingly 7th represent aluminum-doped and thus p-doped doping regions. The doping of these areas is higher than the basic doping of the base of the semiconductor layer 1 so that the doping areas 7th represent local p-heavily doped areas (also referred to as p ⁺⁺ ).

• Die 2 bis 4 und 6 zeigen jeweils Teilausschnitte von verschiedenen Kontaktierungsstrukturen jeweils in Draufsicht. 2 zeigt hierbei die Kontaktierungsstruktur 5 der Solarzelle gemäß 1.

The design of the contact structure 5 will be referred to below with reference to 2 explained in more detail:

• the 2 until 4th and 6th each show partial sections of various contacting structures, each in a plan view. 2 shows the contact structure 5 according to the solar cell 1 .

In addition, the 2 until 4th and 6th In each case enlarged sections of local increases in cross-sectional area of the contacting structures are shown.

In the 2 contact structure shown 5 has a bus bar 8th and a plurality of contact fingers, three contact fingers in the present case 9 are shown.

• Wie in der Ausschnittvergrößerung ersichtlich, durchgreift in einer Kontaktierungsausnehmung 6 der Isolierungsschicht 4 der Kontaktfinger 9 die Isolierungsschicht 4 und bildet somit in diesem Bereich einen elektrischen Kontakt zur Halbleiterschicht 1 aus. Es besteht somit eine Kontaktierungsfläche 11 im Kontaktierungsbereich 10, an welcher Kontaktierungsfläche 11 die Kontaktierungsstruktur 5 und die Halbleiterschicht 1 unmittelbar aneinander angrenzen und einen elektrischen Kontakt ausbilden.

The contact fingers each extend over several contacting areas 10 :

• As can be seen in the enlarged section, it reaches through in a contacting recess 6th the insulation layer 4th the contact finger 9 the insulation layer 4th and thus forms an electrical contact to the semiconductor layer in this area 1 the end. There is thus a contacting surface 11th in the contact area 10 at which contact surface 11th the contact structure 5 and the semiconductor layer 1 directly adjoin each other and form an electrical contact.

• Wie in der Draufsicht gemäß 2 ersichtlich, weisen die Kontaktfinger 9 an den Kontaktierungsbereichen 10 jeweils eine lokale Verbreiterung parallel zu der Oberfläche der Isolierungsschicht 4 auf. Die lokale Querschnittsflächenerhöhung ist somit eine Querschnittsflächenerhöhung des Kontaktfingers 9 im Bereich der Kontaktierungsfläche 11 gegenüber der Querschnittsfläche des Kontaktfingers im Verlauf vor und nach der Kontaktierungsfläche 11. Die Querschnittsfläche ist vorliegend im Bereich der Kontaktierungsfläche (Bereich „A1“) mit einem Faktor von etwa 1,7 erhöht, verglichen mit der Querschnittsfläche vor und hinter der Kontaktierungsfläche (Positionen „A2“ und „A3“). Vorzugsweise liegt eine Querschnittsflächenerhöhung mit einem Faktor im Bereich 1,10 bis 3, insbesondere im Bereich 1,2 bis 2 vor. Die Finger haben vorliegend im Bereich außerhalb der Kontaktflächen (außerhalb der Querschnittsflächenerhöhung) eine Breite von etwa 300 µm, vorzugsweise liegt diese Breite etwa im Bereich (100 µm bis 500 µm). Im Bereich der Kontaktierungsflächen (im Bereich der Querschnittsflächenerhöhung) haben die Finger vorliegend einer Breite von etwa 500 µm. Vorzugsweise ist die Querschnittsflächenerhöhung in etwa auf den Bereich der Kontaktierungsfläche beschränkt. Ebenso kann die Querschnittsflächenerhöhung sich geringfügig vor und hinter der Kontaktierungsfläche weiter erstrecken, vorzugsweise jedoch weniger als die Hälfte der Länge der Kontaktierungsfläche. Die Bezeichnung „Länge“ bezieht sich auf die Erstreckung der Kontaktierungsfläche in Hauptstromflussrichtung.

It is essential that the contact fingers 9 at the contact areas 10 each have a local increase in cross-sectional area:

• As in the top view according to 2 clearly show the contact fingers 9 at the contact areas 10 in each case a local widening parallel to the surface of the insulation layer 4th on. The local increase in cross-sectional area is thus an increase in cross-sectional area of the contact finger 9 in the area of the contact surface 11th compared to the cross-sectional area of the contact finger in the course before and after the contacting area 11th . In the present case, the cross-sectional area in the area of the contacting area (area “A1”) is increased by a factor of approximately 1.7 compared to the cross-sectional area in front of and behind the contacting area (positions “A2” and “A3”). There is preferably an increase in cross-sectional area by a factor in the range 1.10 to 3, in particular in the range 1.2 to 2. In the present case, the fingers have a width of about 300 µm in the area outside the contact areas (outside the increase in cross-sectional area), this width is preferably in the range ( 100 µm to 500 µm). In the area of the contacting areas (in the area of the increased cross-sectional area) the fingers have a width of approximately 500 μm in the present case. The increase in cross-sectional area is preferably limited approximately to the area of the contacting area. Likewise, the increase in cross-sectional area can extend slightly in front of and behind the contacting area, but preferably less than half the length of the contacting area. The term “length” refers to the extension of the contacting surface in the main current flow direction.

Because the widening is greater than the width of the contacting surface 11th is formed, is the contact finger 9 thus at the contact areas 10 the insulation layer 4th designed to overlap. In particular, the contact finger overlaps the insulation layer 4th in one the contacting surface 11th circumferential area, ie in the present case in the plan view from above, is the contacting surface 11th all around the insulation layer 4th overlapping area of the contact finger 9 enclosed. The contact fingers 9 thus cover the contact areas 10 and thus also the contact surfaces 11th .

When using the solar cell, the current flows in the contact structure 5 in the direction of the bus bar 8th which, for example, when a solar cell module is formed, is connected in an electrically conductive manner to an adjacent solar cell via cell connectors.

In the contact fingers 9 the current flow occurs according to 2 thus from right to left. The specific electrical line resistance of the contact finger is in a contact area 9 increased, since in this area semiconductor material of the semiconductor layer 1 is embedded in the contact finger. However, due to the increase in cross-sectional area, in the present case due to the widening of the contact finger in the contacting area, this increase in the specific line resistance is compensated. In addition, the edge areas of the contact finger 9 , which the contacting area 10 enclose, no or only a slight concentration of the semiconductor material, so that accordingly there is no or only a slight increase in the line resistance.

As a result, efficiency losses are due to a local increase in the line resistance of the contacting structure 5 avoided or at least significantly reduced due to embedded semiconductor material.

3 shows an alternative embodiment of a contact structure 5 ' with a corresponding alternative configuration and arrangement of contacting recesses and contacting surfaces 11 ' according to a second embodiment. The contact structure 5 ' according to 3 can with appropriately adapted contact recesses 6th the contact structure 5 in 1 replace, ie also the contacting structure 5 ' can advantageously be used as the rear-side contact structure of a bifacially designed PERC solar cell.

The contact fingers 9 ' the contact structure 5 ' according to 3 have a main branch 12th on which micro-finger 13th as indicated in the enlarged section. The microfingers 13th extend perpendicular to the elongated main direction of extent of the main branch 12th of the contact finger 9 ' .

The contacting surfaces also have a corresponding point 11 ' have an elongated extension and are perpendicular to the longitudinal extension of the Main branch 12th of the contact finger 9 ' arranged. The microfingers 13th cover the contact surfaces 11 ' completely and also overlap all the way around the contacting surfaces 11 ' the insulation layer.

Even with the contact structure 5 ' according to 3 flows into the contact fingers when the solar cell is used 9 ' the current mainly in the direction of the busbar 5 ' , ie in the main branch 12th the contact finger 9 ' in each case from right to left as shown in 3 .

In the microfingers, the current flow is perpendicular to the main branch 12th and towards the main branch 12th .

The contact fingers 9 ' thus point to the contacting surfaces 11 ' in each case local increases in cross-sectional area, which in the present case are caused by the micro-fingers 13th and thus through local widening (in the direction of the main branch 12th ) are trained. In the present case, the cross-sectional area is increased by a pair of microfingers by about a factor 3 . In this embodiment, the cross-sectional area is preferably increased by a factor in the range 2 until 5 .

In addition, the main branch covers 12th no contact surface 11 ' so that little or no concentration of semiconductor material in the main branch 12th is stored and thus the flow of electricity in the main branch 12th in the direction of the bus bar 5 ' is not or only slightly impaired by an increase in the line resistance due to the inclusion of semiconductor material.

4th shows a further exemplary embodiment for a contact-making structure 5 '' , which is also used for rear-side contacting of a solar cell analogous to the illustration in 1 can be used. The dimensioning of the local increase in cross section can here analogously to the exemplary embodiment according to FIG 3 take place.

• Die Kontaktierungsstruktur 5'' weist eine Mehrzahl von Kontaktfingern 9'' auf, welche sich mit einem Hauptast des Fingers jeweils entlang einer Mehrzahl von Kontaktierungsflächen 11'' erstrecken. Die Kontaktierungsflächen 11'' sind, wie auch in 3, paarweise angeordnet, wobei die einem Paar zugeordneten Kontaktierungsflächen (und entsprechend auch die zugeordneten Kontaktierungsausnehmungen in der Isolierungsschicht) auf gegenüberliegenden Seiten des Hauptastes des jeweiligen Kontaktfingers 9'' ausgebildet sind. Die Ausschnittvergrößerung zeigt einen Kontaktfinger 9'' mit einem Paar von Kontaktierungsflächen 11'', welche gegenüberliegend dem Hauptast 12'' des Kontaktfingers 9'' angeordnet sind. Ebenso liegt es im Rahmen der Erfindung, ein Paar von Kontaktierungsflächen jeweils durchgängig als eine Kontaktierungsfläche auszubilden, welche sich in diesem Fall somit auch unter den Hauptast des Kontaktierungsfingers erstreckt.

This contact structure 5 '' has the special feature that the solar cell does not have any electrical lines to connect the individual contact fingers 9 '' has among each other:

• The contact structure 5 '' has a plurality of contact fingers 9 '' which is connected to a main branch of the finger along a plurality of contacting surfaces 11 '' extend. The contact surfaces 11 '' are, as well as in 3 , arranged in pairs, the contacting surfaces assigned to a pair (and correspondingly also the assigned contacting recesses in the insulation layer) on opposite sides of the main branch of the respective contact finger 9 '' are trained. The enlarged section shows a contact finger 9 '' with a pair of contacting surfaces 11 '' which is opposite the main branch 12 '' of the contact finger 9 '' are arranged. It is also within the scope of the invention to design a pair of contacting areas continuously as a contacting area, which in this case also extends under the main branch of the contacting finger.

• Wie ebenfalls in der Ausschnittvergrößerung ersichtlich, sind seitlich an dem Hauptast 12'' des Kontaktfingers 9'' jeweils Mikrofinger 13'' angeordnet, welche die Kontaktierungsflächen 11'' vollständig überdecken. Darüber hinaus sind die Mikrofinger 13' als „tapered fingers“ ausgebildet, indem die Breite der Mikro-Finger 13' sich in Richtung des Hauptastes 12'' erhöht.

Also the contact structure 5 '' instructs microfingers 13 ' on:

• As can also be seen in the enlarged section, are on the side of the main branch 12 '' of the contact finger 9 '' each microfinger 13 ″ arranged, which the contacting surfaces 11 '' cover completely. In addition, the microfingers are 13 ' formed as "tapered fingers" by increasing the width of the micro-fingers 13 ' towards the main branch 12 '' elevated.

The flow of electricity in the micro-fingers 13 ' increases when using the solar cell in the direction of the main branch 12 '' on, since it is continuous over the contacting surface 11 '' Electricity is supplied. In order to avoid or at least reduce a power loss due to the increase in current flow, the width of the micro-fingers increases 13 ' towards the main branch 12 '' each to.

The contact fingers 9 '' are connected to each other and / or with contact fingers when connecting the solar cell in a solar cell module via external components 9 '' electrically connected by neighboring solar cells. Therefore (and due to the lack of a busbar structure) the contact fingers 9 '' according to 4th Sometimes referred to as busbars in the literature.

• Grundsätzlich kann das Ausführungsbeispiel gemäß 5 auf einer Solarzellenstruktur gemäß 1 und auch auf einer Kontaktierungsstruktur in Draufsicht gemäß 2 beruhend ausgebildet werden. Die Darstellung gemäß 5 zeigt einen Schnitt senkrecht zur Isolierungsschicht 4 und entlang und in etwa mittig in einem Kontaktfinger 9''' verlaufend. Die lokale Querschnittsflächenerhöhung des Kontaktfingers 9''' wird vorliegend somit nicht nur durch eine lokale Verbreiterung gemäß 2 erzielt, sondern zusätzlich durch eine lokale Dickenerhöhung gemäß 5. In einem alternativen Ausführungsbeispiel wird die lokale Querschnittsflächenerhöhung ausschließlich durch eine lokale Dickenerhöhung gemäß 5 erzielt. Die Dicke erhöht sich vorliegend lokal etwa mit einem Faktor 2. Vorzugsweise erfolgt eine lokale Dickenerhöhung mit einem Faktor im Bereich 1, 2 bis 4.

In 5 Another embodiment is shown, in which the local increase in cross-sectional area is achieved by a local increase in thickness:

• In principle, the embodiment according to 5 on a solar cell structure according to 1 and also on a contacting structure in plan view according to FIG 2 be trained based. The representation according to 5 shows a section perpendicular to the insulation layer 4th and along and roughly in the middle of a contact finger 9 '' 'trending. The local increase in cross-sectional area of the contact finger 9 '' In the present case, 'is therefore not only in accordance with a local broadening 2 achieved, but also by a local increase in thickness according to 5 . In an alternative exemplary embodiment, the local increase in cross-sectional area is achieved exclusively by a local increase in thickness according to FIG 5 achieved. In the present case, the thickness increases locally by approximately a factor of 2. There is preferably a local increase in thickness by a factor in the range 1, 2 to 4.

• Auch die in Teildarstellung in 6 dargestellte Kontaktierungsstruktur kann zur Kontaktierung einer PERC-Solarzelle gemäß 1 verwendet werden.

6th shows a fifth embodiment in which contact fingers are formed with metallic line structures connected electrically in parallel:

• The partial representation in 6th The contacting structure shown can be used for contacting a PERC solar cell according to FIG 1 be used.

Here, too, several contact fingers go from a busbar 8 ''' 9 '' '' the end. In contrast to the aforementioned exemplary embodiments, these have contact fingers 9 '' '' Open the so-called "secondary finger": As can be seen in the enlarged section shown on the right, there is a main branch in the middle 12 ''' of the contact finger arranged, which does not cover any contacting areas. Laterally next to the main branch 12 ''' are parallel to the main branch secondary fingers 14a and 14b arranged, which in the area of the contacting areas 10 from the main branch 12 ''' are spaced, ie there is no electrically conductive connection in these areas. The secondary fingers are only between the contacting areas through metallic webs 14a and 14b with the main branch 12 ''' electrically connected. As an example, two such webs with the reference numerals are shown in the enlarged section 15th marked.

This results in the advantages that when such a contacting structure is produced, it is true that semiconductor material is applied to the contacting regions 10 into the metal in the area of the contacting areas 10 diffused in, due to the spatial distance to the main branch 12 ''' but did not get to the main branch. The flow of electricity along the main branch 12 ''' to the busbar 8 '''is therefore not or only slightly impaired by the inclusion of semiconductor material.

The width of the secondary fingers is around 75% of the width of the main branch. In the present case, the main branch has a width of about 200 µm.

Claims (15)

Photovoltaic solar cell, with at least one semiconductor layer (1), at least one electrically insulating insulation layer (4) and at least one metallic contact structure (5, 5 ', 5''), the insulation layer (4) between the semiconductor layer (1) and the contact structure (5 , 5 ', 5 ") is arranged and the insulation layer (4) has a plurality of contacting recesses (6), on which the contacting structure (5, 5', 5") with the semiconductor layer (1) in a contacting region (10 ) forms an electrical contact and wherein in the semiconductor layer (1) at least on the contacting areas (10) in each case a doping area is formed by doping the semiconductor layer (1) with a metal, from which metal the contacting structure (5, 5 ', 5'' ) is at least partially formed, characterized in that the contacting structure (5, 5 ', 5 ") has a plurality of contact fingers, which contact fingers (9, 9', 9", 9 ''') each extend over several contacting areas (10) and / or along several contacting areas (10), the contact fingers (9, 9', 9 '', 9 ''') having a local increase in cross-sectional area at the contacting areas (10) and no contact areas (10) are formed between adjacent local increases in cross-sectional area along a contact finger and / or the contact fingers on the contact areas (10) have metallic line structures that are electrically connected in parallel and do not cover the contact areas (10). Solar cell after Claim 1 , characterized in that the contact fingers (9, 9 ', 9'',9''') at the contact areas (10) have a widening parallel to the surface of the insulation layer (4) and perpendicular to a longitudinal extension of the contact finger (9, 9 ', 9'',9'''). Solar cell after Claim 2 , characterized in that the contact fingers (9, 9 ', 9 ", 9"') on the contacting areas (10) of the insulation layer (4) are designed to overlap. Solar cell according to one of the preceding claims, characterized in that the contact recesses (6) are arranged in pairs, the contact recesses (6) assigned to a pair on opposite sides of a main branch of the contact finger (9, 9 ', 9 ", 9"' ) are arranged. Solar cell according to one of the preceding claims, characterized in that the contact finger (9, 9 ', 9 ", 9"') has a local increase in thickness at the contacting areas (10). Solar cell according to one of the preceding claims, characterized in that the contacting structure (5, 5 ', 5 ") has at least a plurality of contact fingers (9, 9', 9", 9 "'). Solar cell according to one of the preceding claims, characterized in that the contact structure (5, 5 ', 5 ") has a plurality of contact fingers (9, 9', 9", 9 "') and at least one Busbar (8, 8 ', 8 "), the contact fingers (9, 9', 9", 9 "") being connected to the busbar (8, 8 ', 8 ") in a materially and electrically conductive manner . Solar cell according to one of the previous ones Claims 1 until 6th , characterized in that the contact structure (5, 5 ', 5'') comprises a plurality of contact fingers (9, 9', 9 '', 9 '''), the contact fingers (9'') not being electrically metallic Have conductive connection. Solar cell according to one of the preceding claims, characterized in that at least a subset of contacting surfaces have an elongated extension and are arranged perpendicular to a longitudinal extension of the contact finger (9, 9 ', 9 ", 9"'). Solar cell according to one of the preceding claims, characterized in that metallic line structures connected electrically in parallel are designed as local, parallel secondary fingers which are spaced apart from a main branch of the contact finger in the area of the contacting areas (10). Solar cell according to one of the preceding claims, characterized in that the contact fingers (9, 9 ', 9 ", 9"') in the contacting area (10) contain the semiconductor material of the semiconductor layer (1). Solar cell according to one of the preceding claims, characterized in that the solar cell is designed as a bifacial solar cell in that the surface on a rear side of the solar cell is at least partially transparent to electromagnetic radiation. Solar cell according to one of the preceding claims, characterized in that the contacting structure (5, 5 ', 5'') is used for contacting a p-doped region of the semiconductor layer (1). Solar cell according to one of the preceding claims, characterized in that the contacting structure (5, 5 ', 5 ") is designed as a rear-side contacting structure (5, 5', 5") and is arranged on the rear of the solar cell and that on the rear of the solar cell, local highly doped regions are formed at the contact regions (10) in the semiconductor layer (1). Solar cell according to one of the preceding claims, characterized in that the solar cell is designed as a PERC solar cell.

Images