WO2020239175A1

WO2020239175A1 - Wafer solar cell, solar module and method for producing the wafer solar cell

Info

Publication number: WO2020239175A1
Application number: PCT/DE2020/100453
Authority: WO
Inventors: Martin Schaper
Original assignee: Hanwha Q Cells Gmbh
Priority date: 2019-05-29
Filing date: 2020-05-28
Publication date: 2020-12-03
Also published as: DE102019114498A1; CN114175278A

Abstract

The invention relates to a wafer solar cell (100), having: a semiconductor substrate (1) with a front side (11) and a rear side (12); at least one functional layer (2), which is arranged on the rear side (12) and which is selected from a group consisting of at least one dielectric layer, at least one semi-conductive layer, at least one transparent conductive layer, a monolithic light-reflection layer (3), which is arranged on a side of the at least one functional layer (2) facing away from the rear side (12) and is selected from a group consisting of a layer with a refractive index that is lower than 1.7, a layer that is white in the infrared range, with a reflection of more than 80% at 1000 nm wavelength, and a homogeneous metal layer; and a metal-particle-containing metallisation layer (4), which is arranged on a side of the light reflection layer (3) facing away from the at least one functional layer (2). The invention also relates to a solar module comprising a plurality of such wafer solar cells (100) and to a method for producing such a wafer solar cell (100).

Description

Wafer solar cell, solar module and process for manufacturing the wafer

Solar cell

Description:

The invention relates to a wafer solar cell, a solar module and a method for producing the wafer solar cell. A wafer solar cell has a processed semiconductor substrate, often in the form of a silicon wafer, with a front side and a rear side, on each of which in addition to the inside of the semiconductor substrate

existing p-n-layers further functional layers are arranged. The wafer solar cell is an electrical component that directly converts sunlight incident on its front and, in the case of bifacial cells, on the rear side into electrical energy. For commercial use of this effect, interconnected wafer solar cells are built into a solar module. Such a solar module usually has a glass pane on which wafer solar cells that are electrically connected to one another are arranged as so-called strings, with a permanent

weatherproof plastic film or alternatively with another

Glass pane is masked and thus encapsulated. The wafer solar cells are laminated between the glass pane and the plastic film or second glass pane, for example using EVA (ethylene vinyl acetate) or, as another example, using polyolefin as an embedding polymer. The glass panel forms a solar module front side of the solar module, on which light falls, and the weather-resistant plastic film or the second

The glass panel forms a rear side of the solar module. On the back of the semiconductor substrate, at least one functional layer is selected from the group of dielectric layer (s), semiconducting

Layer (s) and / or transparent-conductive layer (s) arranged. It is important to emphasize that usually a plurality of functional layers are present, with a plurality of dielectric, semiconducting or transparent-conductive layers or a combination of several of these variants. On at least one

Functional layer is still a full-area or not a full-area, i.e. structured metallization layer arranged. For example, in the case of so-called PERC solar cells, these are at least one

Functional layer usually in the form of a plurality of dielectric layers, for example in such a way that the metallization layer for contacting the semiconductor substrate on part of the surface through the dielectric

Contacting the semiconductor substrate through layers and also forming a so-called local back surface field, BSF for short, under the contacting areas, which optimizes the function of the wafer solar cell. In another example, such as when using passivated contacts such as TOPCON or heterojunction solar cells, the metallization layer rests on the semiconducting and / or transparent-conductive back layers and the layers themselves are designed in such a way that they enable charge transport from the semiconductor substrate to the metal contact on the back. These

Metallization layer is usually applied to the semiconductor substrate by means of pastes containing metal particles. The applied paste is then "fired", i.e. subjected to a heat treatment step. During the firing, the metal particles of the paste sinter to form a layer that appears macroscopically homogeneous. This is microscopic

However, the metallization layer is inhomogeneous. The expression “inhomogeneous” means for a rear-side metallization layer in the context of this invention that, viewed microscopically, spaces filled with air or other substances such as glass are formed between metal particles that are unevenly distributed in the layer. The metal particles have on average dimensions in the range from a few to many tens of micrometers. These metal particles sinter through the said

Heat treatment step to the microscopically inhomogeneous

Metallization layer. Light incident on the wafer solar cell from the front side passes through the semiconductor substrate unless the light photons are absorbed by the photoelectric effect. The light that has passed through the semiconductor substrate once can be reflected back into the semiconductor substrate from the area of the rear side of the wafer solar cell and again given the opportunity to be absorbed there. This light or back reflection is in particular due to the rear

Functional layers and caused by the interface of these to the metal contact or other adjacent layers. However, this reflection is due to the precursor used to produce the metallization layer.

Metallization layer dependent and relatively bad. This leads to inherent losses in short circuit current (Jsc) at the cell level. Likewise, in non-metallized areas, the back reflection by the encapsulation materials is compared with. adversely affects the transition to air. Therefore, additional Jsc losses can arise when the wafer solar cells are encapsulated to form a solar module. These rear reflective properties are all the more important, the thinner the semiconductor substrate of the wafer solar cell, since the proportion of the light absorbed in the first pass through the semiconductor substrate decreases with decreasing wafer thickness and thus the proportion of the light arriving at the wafer rear increases with decreasing wafer thickness.

It is therefore an object of the invention to provide a wafer solar cell, a solar module and a method for producing the wafer solar cell which have further improved short-circuit current properties.

According to the invention, this problem is solved by a wafer solar cell with the features of patent claim 1, a solar module with the features of patent claim 13 and a method for producing the wafer solar cell with the features of patent claim 14. Advantageous configurations and developments of the invention emerge from the subclaims described below.

The invention relates to a wafer solar cell having a semiconductor substrate with a front side and a rear side, at least one functional layer arranged on the rear side, which is selected from a group consisting of at least one dielectric layer,

- at least one semiconducting layer,

at least one transparent conductive layer,

a monolithically formed light reflection layer which is arranged on a side of the at least one functional layer facing away from the rear side and is selected from a group consisting of

a layer with a refractive index less than 1.7,

a white layer in the infrared, with a reflection of over 80% at 1000nm wavelength and

- a homogeneous metal layer,

and

a metallization layer containing metal particles,

which is arranged on a side of the light reflection layer facing away from the at least one functional layer.

By means of this structure having a monolithic one

Light reflective layer will be optical changes in the

Backside metallization decoupled from the solar cell properties, and the

Light reflection can take place independently of the laminate material used to manufacture the solar module. With the light reflection layer, an additional, light-reflecting layer is introduced into the solar cell structure in order to bring the light that has once passed through the semiconductor substrate back into the semiconductor substrate and thus increase the short-circuit current of the solar cell. The light reflective layer is preferably so

designed that this is either in the form of a layer with a refractive index that is less than 1.7, or in the form of a white in the infrared layer, with a reflection of over 80% at 1000 nm wavelength or in the form of a homogeneous metal layer. In the context of this invention, a homogeneous metal layer is to be considered in contrast to the metal-particle-containing rear-side metallization layer. The - also microscopically - homogeneously formed metal layer is usually in the monolithic composite by a suitable one

Deposition processes such as physical and / or chemical deposition has been produced via the gas phase.

The semiconductor substrate is preferably a silicon wafer substrate. The silicon wafer substrate can be mono- or multi-crystalline.

The at least one functional layer can have one or more dielectric layers. The at least one dielectric layer arranged on the rear side is preferably a transparent one

Passivation. The at least one dielectric layer arranged on the rear side is more preferably a NIR (near infrared) transparent passivation layer (s). The at least one dielectric layer is preferably designed as one or more AlOx layers, one or more SiNx layers and / or one or more SiNxOy layers. More preferably, the wafer solar cell has the AlOx layer and the SiNx layer as dielectric layers arranged on the rear side, the AlOx layer being arranged between the semiconductor substrate and the SiNx layer. In a preferred embodiment, the wafer solar cell is therefore designed as a PERC solar cell. A refractive index of the AlOx layer is preferably in the range from 1.5 to 1.7. The refractive index of the SiNx layer is preferably in the range from 1.9 to 2.4. The refractive index of the SiOxNy layer is preferably in the range from 1.5 to 1.9. All the refractive indices described are measured according to DIN at a wavelength of 632 nm.

The at least one functional layer can alternatively have one or more semiconducting layers. The at least one semiconducting layer arranged on the rear side is preferably a doped one Layer to generate a charge carrier selectivity. The at least one doped semiconducting layer is preferably designed as a layer stack of several layers, which are different or none

Contain doping concentrations and / or dielectric and semiconducting layers. In this case, an undoped layer is preferably arranged thin and directly on the semiconductor substrate and the doped semiconducting layer is arranged thereon. Alternatively or additionally, the doped semiconducting layer is formed in combination with a preferably thin dielectric layer, preferably AlOx, SiOx or SiCx, between the doped semiconducting layer and the semiconductor substrate. Alternatively or additionally, one or more SiNx layers are preferred on the semiconductor substrate

side facing away from the doped semiconducting layer (s) and / or one or more SiNxOy layers are formed on the side of the doped semiconducting layer (s) facing away from the semiconductor substrate.

In a further preferred embodiment, the wafer solar cell is therefore designed as a TOPCON or heterojunction solar cell, which is also referred to as a HIT (heterojunction with intrinsic thin layer) solar cell. The layer thickness of the layer between the doped semiconducting layer and the semiconductor substrate is preferably one to a few nm

The refractive index of the doped semiconducting layer is preferably between 3.6 and 4.6. The refractive index of the SiNx layer is preferably in the range from 1.9 to 2.4. The refractive index of the SiOxNy layer is preferably in the range from 1.5 to 1.9. All the refractive indices described are measured according to DIN at a wavelength of 632 nm.

In a first variant, the monolithically configured light reflection layer is configured as a layer with a refractive index less than 1.7. To implement a monolithically formed light reflection layer, which is formed as a layer with a refractive index less than 1.7, microscopically inhomogeneous glass bead-air mixtures can be used. The monolithically formed light reflection layer is preferably formed as a layer with a refractive index that is less than 1.5 and even further is preferably less than 1.3. All the refractive indices described are measured according to DIN at a wavelength of 632 nm. Such a layer is designed to reflect light due to the jump in the refractive index that has been implemented. This will make optical changes in the

Backside metallization is decoupled from the solar cell properties, for example during the encapsulation process of the solar module.

In a second variant, the monolithic one

Light reflection layer is formed as a white layer in the infrared with a reflection of over 80% at 1000 nm wavelength. The monolithic

formed light reflection layer, which is formed as a white layer in the infrared, is preferably with a reflection of more than 60% at 1000 nm wavelength, more preferably of more than 40% at 1000 nm wavelength

educated. Such a layer is also designed to be light-reflecting. As a result, optical changes in the rear-side metallization are avoided, for example during the encapsulation process of the solar module

Solar cell properties decoupled.

In a third variant, the monolithic one

Light reflection layer formed as a homogeneous metal layer. For the purposes of the invention, a homogeneous metal layer is a microscopically homogeneous layer of metal, i.e. a metal layer that is formed without gaps or gaps. A homogeneous metal layer can e.g. can be realized by PVD processes such as sputtering or vapor deposition. The term "homogeneous" means that no metal particles can be seen under the microscope and that they appear uniform under the microscope. The metal layer is preferably smooth i.e. reflective or essentially smooth. The metal layer represents strong

Light reflective properties ready.

The back metallization layer is through a paste with it

contained microscopic metal particles realized. The metallization layer containing metal particles is therefore designated. The The metallization layer preferably has aluminum particles and / or

Silver particles. The metallization layer is preferably an Ag (silver) layer, more preferably an Al (aluminum) layer or a mixture of Al (aluminum) and Si (silicon). The metallization layer is preferably produced by means of paste metallization and a subsequent firing step. This forms a macroscopically homogeneous but microscopically inhomogeneous layer of metal. The microscopically inhomogeneous layer has metal particles between which there are spaces that are filled with air or glass. Caused by a lamination process associated with the action of heat and pressure of the interconnected strings

Solar modules can also be used in the spaces mentioned for the

Embedding polymer used for lamination, e.g. EVA penetrate. In a preferred embodiment, the light reflection layer is designed as the layer white in the infrared as a layer containing white pigment. The white pigment is preferably designed as a titanium dioxide particle. The

White pigments can be applied, for example, by screen printing, spraying or roller processes. Such a layer is designed to be light-reflecting in such a way that optical changes in the rear-side metallization, for example caused by the lamination process in the manufacture of solar modules, are effectively decoupled from the solar cell properties. In one of the preferred embodiments, the light reflection layer is designed as a microscopically porous layer. That is, the light-reflecting layer has pores in the form of fine holes and can therefore be at least partially permeable to fluids. It can be porous open or closed. The light reflection layer preferably has at least 30% SiOx. The light reflection layer may, for example, have such an amount of SiOx

Have particles which are preferably sufficiently small in size so that they form one together with air located between the SiOx particles effectively produce a lower refractive index than SiOx itself. As a result, a light reflection layer with a refractive index less than 1.7, preferably less than 1.5, more preferably less than 1.3 can be implemented. The light reflection layer with a refractive index less than 1.7, preferably less than 1.5, more preferably less than 1.3 can, for example, by

Roll process, screen printing, spraying or dipping to which at least one functional layer is applied.

In the second and third variant, the light reflection layer is opaque. As a result, the effect of the light reflection is independent of the optical properties of the embedding polymer, which is in the spaces between the metal particles during the production of the solar module

Metallization layer penetrates. The term "opaque" means

opaque or substantially opaque.

In a preferred embodiment, the metallization layer is designed in such a way that it has local electrical properties at several points through the light reflection layer and through the at least one functional layer

Forms contacts. In this embodiment it is designed as a PERC cell, for example.

In another preferred embodiment, the light reflection layer is designed in such a way that it is electrically conductive, so that there is a large-area electrical contact between the metallization layer and the at least one functional layer. This is the structure of the so-called TOPCON solar cell concept. In this embodiment there are usually no local electrical contacts that reach through the functional layer, but rather the functional layer has sufficient electrical conduction properties so that it is sufficient to make contact with the functional layer for rear-side contacting of the wafer solar cell. If the functional layer and the light reflection layer are then also electrically conductive, the current flows through the rear side metallization, light reflection layer and functional layer to / from the semiconductor substrate. In the case of a heterojunction solar cell, one or more layers of doped and intrinsic, amorphous silicon and TCO (transparent-conductive oxide layers) as a transparent semiconducting layer for absorbing the generated current are preferably applied to the semiconductor substrate. In this embodiment, the at least one functional layer preferably has TCO.

In a preferred embodiment, the wafer solar cell is a PERC

Solar cell formed. Alternatively, the wafer solar cell is preferably designed as a TOPCON solar cell. Furthermore, as an alternative, the wafer solar cell is preferably designed as a heterojunction solar cell.

The at least one functional layer preferably has at least one dielectric layer. The at least one dielectric layer is preferably formed from an AlOx layer and a SiNx layer. This embodiment is advantageous if the wafer solar cell is designed as a PERC solar cell.

In a preferred embodiment, the at least one

Functional layer on at least one semiconducting layer, wherein the at least one semiconducting layer is formed from amorphous or microcrystalline silicon. As a result, the functional layer can be made particularly thin and is also inexpensive. Such a layer can be realized by sputtering, vacuum vapor deposition, CVD, APCVD or PECVD.

The at least one functional layer preferably has the at least one semiconducting layer, the at least one semiconducting layer being doped with an element selected from the following group:

Phosphorus, boron, gallium or aluminum. The efficiency of the wafer solar cell can thereby be further improved. In a preferred embodiment, the at least one

Functional layer on at least one semiconducting layer and at least one dielectric layer, wherein the at least one dielectric layer is formed between the at least one semiconducting layer and the semiconductor substrate.

The at least one functional layer preferably has at least one dielectric layer and the at least one dielectric layer is embodied as a tunnel layer with a thickness of less than 5 nm, preferably less than 3 nm. This means that charge carriers can tunnel through this layer. This embodiment is particularly advantageous if the wafer solar cell is designed as a TOPCON solar cell.

In a preferred embodiment, the at least one

Functional layer on at least one transparent-conductive layer, wherein the at least one transparent-conductive layer is formed from at least one TCO (transparent conductive oxide, transparent-conductive oxide), wherein the at least one TCO is preferably selected from the group consisting of:

ZnO (zinc oxide), ITO (indium tin oxide, indium tin oxide), AZO (aluminum doped zinc oxide, aluminum zinc oxide), ATO (antimony tin oxide, antimony tin oxide) and FTO (fluoro tin oxide , Fluorine tin oxide). This embodiment is advantageous if the wafer solar cell is designed as a heterojunction solar cell.

In a preferred embodiment, the at least one

Functional layer on at least one semiconducting layer, the at least one semiconducting layer being composed of two layers which differ in their dopant concentration. The weaker or non-doped layer is preferably designed with a layer thickness of less than 5 nm, preferably less than 3 nm. This embodiment is advantageous if the wafer solar cell is designed as a TOPCON or heterojunction solar cell. By means of the doped layer a Charge carrier selectivity generated. The at least one doped semiconducting layer is preferably designed as a layer stack of several layers which contain different or even no doping concentrations and / or have dielectric and semiconducting layers. In this case, an undoped layer is preferably arranged directly on the semiconductor substrate and the doped semiconducting layer is arranged thereon. Alternatively or additionally preferably, a dielectric layer, preferably AlOx, SiOx, SiCx, is arranged between the doped semiconducting layer and the semiconductor substrate. Alternatively or additionally, one or more SiNx or SiNxOy layers are preferably arranged on the side of the doped semiconducting layer facing away from the semiconductor substrate. The refractive index of the doped semiconducting layer is preferably between 3.6 and 4.6. The refractive index of the SiNx layer is preferably in the range from 1.9 to 2.4. The refractive index of the SiOxNy layer is preferably in the range from 1.5 to 1.9. All the refractive indices described are measured according to DIN at a wavelength of 632 nm.

Silicon is preferably used as the semiconductor substrate of the wafer solar cell. The wafer solar cell in one of those described above

Embodiments with a semiconductor substrate can be combined with a solar cell constructed from a perovskite substrate to form a tandem solar cell. A tandem solar cell, also known as a stacked solar cell, consists of two or more solar cells made of different material systems that are stacked on top of one another. The wafer solar cell preferably has an emitter layer and / or a passivation layer on the front side. It preferably has front electrode fingers and busbars, for example made of silver, on the front side. In this embodiment, the wafer solar cell is preferably a PERC solar cell.

Alternatively, e.g. also TOPCON-like,

Be arranged heterojunction or TCO junctions, as well as for a

In a tandem structure, another solar cell, e.g. based on perovskite, can be arranged on the front. The invention also relates to a solar module having a front side and a rear side

a sheet of glass forming the front or a plastic film or a plastic plate,

a backside encapsulation element which has either an EVA or a polyolefin as an embedding polymer, and

several wafer solar cells according to one or more of the embodiments described above, which are laminated between the front side and the rear side of the solar module.

The invention also relates to a method for producing a wafer solar cell, having the following steps

a) providing a semiconductor substrate with a front side and a rear side and a p-n junction arranged in the semiconductor substrate or a p-n junction applied adjacent to the semiconductor substrate,

b) applying at least one functional layer to the back of the semiconductor substrate, which is selected from a group consisting of at least one dielectric layer,

at least one semiconducting layer and

at least one transparent conductive layer,

c) applying a monolithically formed light reflection layer on a side of the at least one facing away from the rear side

Functional layer, the light reflection layer being selected from a group consisting of

a layer with a refractive index that is less than 1.7, measured according to DIN at a wavelength of 632 nm,

a white layer in the infrared, with a reflection of over 80%

1000nm wavelength and

a homogeneous metal layer, and

d) Applying a metallization layer containing metal particles to a side of the light reflection layer facing away from the at least one functional layer. Embodiments and descriptions disclosed for the wafer solar cell apply accordingly to the method, and conversely, embodiments and descriptions disclosed for the method for the wafer solar cell apply accordingly.

According to step a), a semiconductor substrate is provided. In which

The semiconductor substrate provided is preferably a partially processed semiconductor solar cell. The partially processed semiconductor solar cell is a semi-finished product that has already passed through one or more, but not yet all, process steps for manufacturing the PERC or TOPCON or heterojunction solar cell. The semiconductor solar cell is usually made from a semiconductor wafer. To provide the semiconductor wafer, semiconductor single crystals or polycrystalline semiconductor blocks are usually produced and cut into wafers, for example by sawing. Such a semiconductor wafer becomes what is provided in step a)

Semiconductor substrate or the partially processed semiconductor solar cell produced. The semiconductor wafer is subjected, for example, to the following steps to produce the semiconductor substrate: Texturing on one or both sides (to enlarge the surface and increase the light absorption), then doping to form a p / n junction by executing a

Diffusion process. The semiconductor substrate provided in step a) has preferably been subjected to the above steps if the

The end product is a PERC solar cell. This is preferred in step a)

The semiconductor substrate provided has been subjected to the steps of edge isolation and / or PSG etching if the end product is a PERC solar cell. Alternatively, the semiconductor substrate can be saw-damage-etched and texture-free, for example if the end product is a tandem solar cell. If the end product is a heterojunction solar cell and possibly with transparent-conductive contacts, the semiconductor substrate can be a partially processed solar cell in which a pn junction is produced by applying separate layers. Furthermore, the semiconductor solar cell provided in step a) can be coated on the front side. For example, in step a)

semiconductor wafer solar cell provided on the front side

Have emitter layer and / or a passivation layer and a

Front electrode structure with front electrode fingers and busbars. Alternatively, e.g. also TOPCON-like, heterojunction or TCO junctions can be arranged. For a tandem solar cell, another solar cell, e.g. B. be arranged based on perovskite on the front.

Step b) comprises depositing the at least one functional layer on the semiconductor substrate. Step b) can be carried out by means of PVD or CVD, for example by means of a PECVD (Plasma Enhanced Chemical Vapor Deposition) method. However, it is also possible to deposit one or more dielectric layers in the form of AlOx layer (s) by means of “atomic layer deposition” (ALD) or microwave remote plasma. The dielectric layer (s) serves or serve for electrical

Rear side passivation of the solar cell. Applying the

Functional layer (s) on the semiconductor substrate in step b) is preferably carried out over the entire area or essentially over the entire area. The at least one functional layer is preferably applied on one side, that is to say only on the rear side of the semiconductor substrate.

Applying the light reflection layer to the at least one

Functional layer in step c) is preferably carried out over the entire area or essentially over the entire area. The light reflection layer is preferably applied to the rear side of the at least one functional layer by means of screen printing, spraying, dipping or rolling. Depending on the properties of the light reflective layer and the

Metallization layer, the application of an additional protective layer before the deposition of the metallization layer can be necessary and take place accordingly. Step d) is preferably carried out by applying a metal paste and a subsequent firing step. An Ag paste, Al paste or an Al / Si paste is preferably used as the metal paste. Such metal pastes have metal particles, binders and solvents and optionally a glass frit such as SiO2, B203 and / or ZnO. The metal pastes usually have metal particle diameters of 1 to 40 μm.

In a preferred embodiment, step c) is carried out using a process selected from the following group:

Printing prefers screen printing or pad printing

Spray

Diving

roll

PVD (physical vapor deposition) prefers sputtering, and

CVD (chemical vapor deposition) prefers APCVD (atmospheric pressure chemical vapor deposition).

Before step d), a plurality of holes are preferably made in the light reflection layer or in the light reflection layer and in the at least one functional layer by means of a laser so that the semiconductor substrate is locally free at least from the light reflection layer at several locations. These holes are also known as LCO (Laser Contact Openings).

This allows contacting the subsequently applied

Metallization layer can be ensured with the semiconductor substrate in a simple manner. A PERC solar cell architecture, for example, can be implemented using this embodiment.

Alternatively or additionally preferably, step d) takes place with coating of the light reflection layer with a metal paste, which is designed in such a way that it makes contact with the substrate and / or with the firing

Functional layer forms. For example, the metal paste is applied into the holes and preferably also over the entire surface of the light reflection layer and then fired. Alternatively, the metal paste is applied locally to the

Light reflection layer is applied and is designed to “eat through” the light reflection layer and possibly the functional layer when firing.

Metal pastes that are capable of “eating through” layers are known. In the latter case, before, at the same time or after the application of the metal paste forming the contact, another metal paste, which is not designed to eat through the light reflection layer but rather to form a layer on it, can be applied to the light reflection layer and before, simultaneously or after the through the

Eating light reflection layer and possibly functional layer through

Metal paste are fired, whereby the metallization layer is realized with local contact to at least one functional layer or the semiconductor substrate. In a preferred embodiment, step d) is carried out by coating the light-reflecting layer with two different metal pastes and fires. One metal paste is one

metal paste free of glass frits, while the other metal paste is a metal paste containing glass frits. The metal paste containing glass frits "eats" its way through the light reflection layer and optionally the functional layer when the fire is fired.

Furthermore, as an alternative or in addition, step c) is carried out using a screen printing form, so that the semiconductor substrate with the at least one functional layer located thereon after carrying out step c) locally from the

Light reflective layer is free. In this way, contacting of the subsequently applied metallization layer with the semiconductor substrate can be ensured in a simple manner.

Preferably in the case of TOPCON or heterojunction solar cells, the contact is opened only through the light reflection layer. The more preferred

Light reflection layer designed so that full-surface contact is made through it and no opening of the light reflection layer

is required. This has the advantage that either process steps or Materials such as an additional metal paste for local contact formation are omitted.

Embodiments of the invention are shown purely schematically in the drawings and are described in more detail below. It show purely schematically and not to scale

1 shows a cross-sectional view of a wafer solar cell according to the invention;

2a to 2e show a method according to the invention for producing a

Wafer solar cell according to Figure 1;

Figure 3 is a cross-sectional view of another according to the invention

Wafer solar cell; and

4 is a partial cross-sectional view of an inventive

Solar module.

1 shows a cross-sectional view of a wafer solar cell according to the invention. The wafer solar cell has a substrate 1 with a front side 11 and a rear side 12.

At least one functional layer 2 in the form of a first functional layer 21 and a second functional layer 22 is arranged on the rear side 12. The first functional layer 21 is arranged between the rear side and the second functional layer 22. The first functional layer 21 and the second functional layer 22 are selected from the group consisting of a dielectric layer, a semiconducting layer and a transparent conductive layer.

The first functional layer 21 is formed, for example, as an AlOx layer, while the second functional layer 22 is formed as a SiNx layer, without restricting the wafer solar cell shown in FIG. 1 to these materials. A light reflection layer 3 is arranged on a side of the second functional layer 22 facing away from the first functional layer 21. On one of A metallization layer 4 is arranged on the side of the light reflection layer 3 facing away from the second functional layer 22 so that it makes local contact with the semiconductor substrate 1 at several points through the light reflection layer 3 and the dielectric layers 21, 22. 1 therefore shows a PERC solar cell.

An emitter layer 6 is arranged on the front side 11. A passivation layer 7 is arranged on a side of the emitter layer 6 facing away from the front side 11. Furthermore, the wafer solar cell shows front electrode fingers 8 of a front electrode structure (not shown further).

Light 9 incident on the front side 11 of the semiconductor substrate 1 is only partially absorbed in the semiconductor substrate 1. The remaining part goes through the semiconductor substrate 1 and is reflected on the light reflection layer 3, which is indicated by the black arrows.

2a to 2e show a method according to the invention for producing a wafer solar cell, the semiconductor substrate in each case in a

Cross-sectional view is shown.

2a shows a cross-sectional view of a semiconductor substrate 1 that is subjected to a step a) which includes providing the semiconductor substrate 1 with a front side 11 and a rear side 12. According to step a), a semiconductor substrate 1 with a semiconductor

Substrate 1 arranged p-n junction provided. The semiconductor substrate 1 provided is a partially processed solar cell. The partially processed solar cell is textured on one or both sides, for example, then doped to form a p / n junction and a

Diffusion process and / or subjected to edge isolation and PSG etching, especially if the end product is a PERC solar cell. The semiconductor substrate 1 shown in FIG. 2a can also be of this type

be partially processed, it is saw damage etched and texture-free, for example when the end product is a tandem solar cell. If the end product is a heterojunction solar cell and possibly with transparent conductive ones

Contacts, the semiconductor substrate 1 can also be a

act partially processed solar cell in which a p-n junction has been created by applying separate layers.

FIG. 2b shows a cross-sectional view of a semiconductor substrate 1 that is subjected to a step b) which involves applying the at least one

Functional layer 2 in the form of a first functional layer 21 and a second functional layer 22 on the rear side 12 of the semiconductor substrate 1. The first functional layer 21 and the second functional layer 22 are each selected from the group consisting of a dielectric

Layer, a semiconducting layer, a transparent-conductive layer. 2c shows a cross-sectional view of a semiconductor substrate 1, which is subjected to a step c), which involves applying a light reflection layer 3 on a side of the second which faces away from the rear side 12

Functional layer 22, wherein the light reflection layer 3 is selected from a group consisting of

- a layer with a refractive index less than 1.7,

measured according to DIN at a wavelength of 632nm,

a homogeneous metal layer.

2d shows a cross-sectional view of a semiconductor substrate 1 that is subjected to a step in which a plurality of holes 5 are introduced into the light reflection layer 3 and the functional layers 21, 22 by means of a laser (not shown), so that the semiconductor substrate 1 is locally free from the light reflection layer 3 and the functional layers 21, 22 at several points. This step d) is optional. It can be used, for example, to manufacture a PERC solar cell. However, the step shown in FIG. 2d is not used in the production of a TOPCON or heterojunction solar cell carried out. In addition, the step shown in FIG. 2d is also not carried out if the local contacts are made in some other way to produce a PERC solar cell, for example using a

Metal paste containing glass frits and firing.

FIG. 2e shows a cross-sectional view of a semiconductor substrate 1, which is subjected to a step d), the application of a rear

Metallization layer 4 on one of the dielectric layer 22

having remote side of the light reflection layer 3. 2e shows a PERC solar cell in which the metallization layer 4 is designed in such a way that it is arranged on the light reflection layer 3 and makes local contact with the semiconductor substrate 1 at several locations. The method is also suitable for producing a TOPCON or heterojunction solar cell in which the metallization layer 4 does not make local contact with the semiconductor substrate 1 and does not locally penetrate the functional layer 2 and possibly the light reflection layer 3, but this is not shown here.

3 shows a cross-sectional view of a further wafer solar cell according to the invention. The wafer solar cell shown in FIG. 4 corresponds to the wafer solar cell shown in FIG. 1 with the difference that the layers and / or components on the front side 11 are different from those shown in FIG. 1

can be formed, are omitted, and that it is not a PERC solar cell but a TOPCON or heterojunction solar cell in which the metallization layer 4 is arranged on the light reflection layer 3 without locally penetrating the light reflection layer 3 and the functional layer 2, so that it does not make local contact with the semiconductor substrate 1. In a further difference, alternatively on the front side 11 e.g. Topcon-like, heterojunction or TCO junctions are also conceivable. A

Implementation of a corresponding architecture of the front side 11 is within the ability of the person skilled in the art and is therefore not described further.

Fig. 4 shows a partial cross-sectional view of an inventive

Solar module. The solar module has a front and a rear. The front side is formed by a glass pane 101. The rear side is formed by a rear side encapsulation structure 103. A plurality of wafer solar cells 100, which are laminated into an embedding polymer 102 made of EVA, are arranged between the glass pane 101 and the rear-side encapsulation structure 103.

List of reference symbols:

1 semiconductor substrate

11 front

12 back

2 functional layer

21 first functional layer

22 second functional layer

3 light reflection layer

4 metallization layer

5 holes

6 emitter layer

7 passivation layer

8 front electrode fingers

9 light

100 wafer solar cell

101 pane of glass

102 embedding polymer

103 Back side encapsulation structure

Claims

Patent claims:

1. having a wafer solar cell (100)

a semiconductor substrate (1) with a front side (11) and a rear side (12),

at least one functional layer (2) which is arranged on the rear side (12) and is selected from a group consisting of

at least one dielectric layer, at least one semiconducting layer, at least one transparent-conductive layer,

a monolithically designed light reflection layer (3) which is arranged on a side of the at least one functional layer (2) facing away from the rear side (12) and is selected from a group consisting of

a layer with a refractive index less than 1.7,

a homogeneous metal layer,

and

a metal-particle-containing metallization layer (4) which is arranged on a side of the light reflection layer (3) facing away from the at least one functional layer (2).

2. wafer solar cell (100) according to claim 1, characterized in that the light reflection layer (3) is formed as the white layer in the infrared and the white light reflection layer (3) in the infrared is formed as a white pigment-containing layer, the

White pigment is preferably designed as a titanium dioxide particle.

3. wafer solar cell (100) according to one of the preceding claims,

characterized in that the metallization layer (4) such is designed that they are in several places by the

Light reflection layer (3) and through the at least one

Functional layer (2) through local electrical contacts forms.

4. wafer solar cell (100) according to one of the preceding claims,

characterized in that the light reflection layer (3) is designed in such a way that it is electrically conductive, so that there is a large-area electrical contact between the metallization layer (4) and the at least one functional layer (2).

5. wafer solar cell (100) according to one of the preceding claims,

characterized in that it is designed as a PERC solar cell, a TOPCON solar cell or a heterojunction solar cell.

6. wafer solar cell (100) according to one of the preceding claims,

characterized in that the at least one functional layer (2) has at least one dielectric layer and this dielectric layer is formed from AlOx and SiNx.

7. wafer solar cell (100) according to any one of the preceding claims 1 to 5, characterized in that the at least one functional layer (2) has at least one semiconducting layer, wherein the at least one semiconducting layer is formed from amorphous or microcrystalline silicon.

8. wafer solar cell (100) according to any one of the preceding claims 1 to 5 or 7, characterized in that the at least one

Functional layer (2) which has at least one semiconducting layer, the at least one semiconducting layer being doped with an element selected from the following group:

Phosphorus, boron, gallium or aluminum.

9. wafer solar cell (100) according to any one of the preceding claims, characterized in that the at least one functional layer (2) has at least one semiconducting layer and at least one dielectric layer, wherein the at least one dielectric layer between the at least one semiconducting layer and the

Semiconductor substrate (1) is formed.

10. wafer solar cell (100) according to any one of the preceding claims 1 to 6 or 9, characterized in that the at least one

Functional layer (2) has at least one dielectric layer and the at least one dielectric layer with a thickness of less than 5 nm, preferably less than 3 nm, is designed as a tunnel layer.

11. wafer solar cell (100) according to one of the preceding claims 1 to 5, characterized in that the at least one functional layer (2) has at least one transparent-conductive layer, wherein the at least one transparent-conductive layer is formed from at least one TCO , wherein the at least one TCO is preferably selected from the group consisting of:

ZnO, ITO, AZO, ATO and FTO.

12. wafer solar cell (100) according to any one of the preceding claims 1 to 5 and 7 to 9, characterized in that the at least one

Functional layer (2) has at least one semiconducting layer, the at least one semiconducting layer being built up from two layers which differ in their dopant concentration.

13. Solar module with a front and a back, having

a glass pane (101) forming the front side or a

Plastic film or a plastic plate,

a rear-side encapsulation element which has either an EVA or a polyolefin as embedding polymer (102), and A plurality of wafer solar cells (100) according to one of Claims 1 to 12, which are laminated between the front and the rear of the solar module.

14. A method for producing a wafer solar cell (100), comprising

following steps

a) providing a semiconductor substrate (1) with a front side (11) and a rear side (12) and a p-n junction arranged in the semiconductor substrate (1) or a p-n junction applied adjacent to the semiconductor substrate,

b) applying at least one functional layer (2) to the

Rear side (12) of the semiconductor substrate (1), which is selected from a group consisting of

at least one dielectric layer, at least one semiconducting layer and

at least one transparent conductive layer,

c) Applying a monolithic

Light reflection layer (3) on a side of the at least one functional layer (2) facing away from the rear side (12), the light reflection layer (3) being selected from a group consisting of

a layer with a refractive index less than 1.7,

a homogeneous metal layer,

and

d) applying a metal-particle-containing metallization layer (4) to a side of the light-reflecting layer (3) facing away from the at least one functional layer (2).

15. The method according to claim 14, characterized in that step c) is carried out using a process selected from the following group:

Printing prefers screen printing or pad printing

Spray

Diving

roll

PVD and

CVD prefers APCVD

16. The method according to claim 14 or 15, characterized in that before step d) several holes (5) by means of a laser

in the light reflection layer (3) or

in the light reflection layer (3) and in the at least one

Functional layer (2) are introduced,

so that the semiconductor substrate (1) is locally free at least from the light reflection layer (3) at several points

and or

that step d) takes place by coating the light reflection layer (3) with a metal paste which is designed such that it forms a contact with the substrate (1) and / or with the functional layer (2) when fired

and or

that step c) is carried out using a screen printing forme, so that the semiconductor substrate (1) with the at least one functional layer (2) located thereon is locally free from the light reflection layer (3) at several points after step c) has been carried out .