Process and solar cell

Abstract

Method (100) for processing a solar cell precursor (202), comprising the method (100): • Forming a transparent, electrically conductive first layer (TCO1) over the solar cell precursor (202); • Forming at least one transparent, electrically conductive second layer (TCO2) over the solar cell precursor (202), of which a second layer (TCO2) is arranged between the solar cell precursor (202) and the first layer (TCO1) and has more indium than zinc; • wherein the first layer (TCO1) contains at least indium, zinc and oxygen; • wherein the second layer (TCO2) contains oxygen and a larger proportion of indium than the first layer (TCO1).

Description

[0001] Various embodiments relate to a method and a solar cell.

[0002] Since the development and commercialization of solar cells for energy generation, their efficiency has often been the focus of media attention as the key optimization parameter. However, other parameters also play a very relevant role for the market, including manufacturing costs and durability. Since then, various architectures have been developed to optimize the cost-benefit ratio. One of these architectures uses a so-called transparent conductive oxide (TCO) layer to absorb the generated current. The TCO layer is deposited onto a selective contact layer of doped amorphous silicon (a-Si). A metallic grid is usually printed onto the TCO layer to collect the charge carriers. The doped amorphous silicon layers have a resistance that is too high to conduct the charge carriers generated in the silicon to the metallic grid.The much higher conductivity of the TCO layer enables charge carrier transport to the metallic lattice. This architecture is used, for example, in so-called heterojunction silicon technology (Silicon Heterojunction-J technology), in which crystalline silicon, in the form of a silicon wafer, is sandwiched between at least two layers of amorphous silicon.

[0003] Traditionally, these TCO layers are based on indium oxide, for example, tin-doped indium oxide (ITO). While the general goal is for the TCO layer to exhibit the highest possible transparency and electrical conductivity, these properties are clearly opposing factors, so a compromise is usually required. Furthermore, the properties of the TCO layer are tailored to the underlying doped a-Si layer and the layer above it, usually a metallic layer, for example, so that their contact resistance is as low as possible, resulting in a low series resistance of the solar cell. Adapting these properties promotes high solar cell efficiency. One challenge is depositing TCO layers that exhibit very high transparency, low resistance, and also low contact resistance.Unfortunately, indium, and therefore a TCO layer based on it, is very expensive. In addition, indium is a rare element and only available in limited quantities.

[0004] Therefore, there is a general desire to provide cheaper and more readily available options for providing a TCO layer for a solar cell. Reference is also made to CN 1 14 242 809 A, JP 2010 - 080 358 A, and US 2011 / 0 226 320 A1.

[0005] In various embodiments, aluminum-doped zinc oxide (AZO) has been recognized as a promising candidate to satisfy this requirement. In particular, the established opinion that AZO is unsuitable due to its higher resistivity and its tendency to age rapidly, significantly impairing efficiency, has been overcome. The rapid aging of AZO can be demonstrated, for example, in the so-called damp-heat test, in which the solar cell is exposed to elevated temperature and humidity. This aging is expressed, for example, in a significant increase in resistivity.

[0006] In this context, it was recognized that a layer stack in which a thin layer of AZO is covered with ITO, for example, as part of a layer stack of ITO / AZO / ITO, results in a solar cell efficiency comparable to that of ITO as a reference. In particular, it can be demonstrated that an AZO layer degrades less or not at all in the steam-heat test when it is covered with an ITO layer (then also referred to as a cover layer).

[0007] In this context, various embodiments take into account the cost pressures inherent in solar cell manufacturing. These costs increase with the number and length of process chambers. This limits the possibilities for increasing the number of different layers in a TCO layer stack. The same applies to existing sputtering systems, in which the production of additional layers is difficult to integrate, for example, because they are deposited using different process parameters that differ from those for which the sputtering systems were designed.

[0008] According to various embodiments, a TCO layer stack based on AZO is provided, for example for use as a front contact and / or back contact of a solar cell, which is cheaper to implement, for example without the need to install additional process or gas separation chambers.

[0009] Reference is made herein to various oxides, such as indium tin oxide (also referred to as ITO) and aluminum-doped zinc oxide (also referred to as AZO), which are configured as transparent electrically conductive oxides (also referred to as TCOs). The description may also apply to a transparent electrically conductive oxide (also referred to as TCOs), such as fluorine tin oxide (FTO) and / or antimony tin oxide (ATO).

[0010] It shows Fig. 1 shows a method according to various embodiments in a schematic flow diagram; Fig.2, Fig. 3 and Fig. 4 shows a method according to various embodiments in a schematic view; Fig. 5A and B each show a diagram according to various embodiments; Fig. 6A and B each show a vacuum arrangement according to various embodiments; and Fig. 7A and B each show the coating of the solar cell precursor in different configurations according to different embodiments.

[0011] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology such as "top," "bottom," "front," "back," "fore," "rear," etc., will be used with reference to the orientation of the described figure(s). Since components of embodiments can be positioned in a number of different orientations, the directional terminology is for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention.It is understood that the features of the various exemplary embodiments described herein may be combined with one another unless specifically stated otherwise. The following detailed description is therefore not to be construed in a limiting sense, and the scope of the present invention is defined by the appended claims.

[0012] In this description, the terms "connected," "attached," and "coupled" are used to describe both a direct and an indirect connection (e.g., resistive and / or electrically conductive, e.g., an electrically conductive connection), a direct or indirect connection, and a direct or indirect coupling. In the figures, identical or similar elements are provided with identical reference numerals where appropriate.

[0013] Various examples are described below which relate to what is described herein and what is shown in the figures.

[0014] Example 1 is a method according to claim 1 for processing (e.g. coating and / or by means of a continuous process, e.g. in-line coating) a solar cell precursor (herein also referred to as solar cell precursor, solar cell precursor, solar cell stack or solar cell substrate) (e.g. for depositing one or more than one layer on the solar cell precursor), the method comprising, inter alia: forming a transparent, electrically conductive first layer on the solar cell precursor (e.g. in physical contact with the solar cell precursor); forming one or more than one transparent, electrically conductive second layer on the solar cell precursor (e.g. in physical contact with the first layer and / or the solar cell precursor); wherein the first layer comprises oxygen and indium (e.g.a chemical compound of indium with oxygen and preferably a first dopant of the chemical compound of indium with oxygen), and wherein the first layer further comprises zinc and / or aluminum (e.g. a chemical compound of oxygen with zinc and preferably a second dopant, e.g. the aluminum, of the chemical compound of oxygen with zinc); wherein the or each second layer comprises oxygen and a larger proportion (e.g. a larger concentration) of one or more than one of indium, aluminum and / or zinc and / or smaller gradients of the proportion than the first layer.

[0015] Example 2 is a method (e.g. according to Example 1) according to claim 10 for processing a solar cell precursor, the method comprising, inter alia: emitting a first material stream, which comprises zinc and oxygen, towards the solar cell precursor; emitting a second material stream, which comprises indium and oxygen, towards the solar cell precursor; wherein the emitting of the first material stream and the emitting of the second material stream are carried out in such a way that a (e.g. homogeneous) material mixture (also referred to simply as a mixture) is formed, with which the solar cell precursor is coated, which is transparent and electrically conductive and has a proportion of indium which (e.g.continuously) increases or decreases along a direction (for example the direction of the layer thickness) away from the solar cell precursor, wherein the material mixture comprises, for example, at least indium, zinc and oxygen and / or provides a first layer.

[0016] Example 3 is a solar cell (preferably manufactured by the method according to Example 1 or 2) according to claim 11, comprising, inter alia: a semiconductor (e.g. as a substrate), preferably providing a semiconductor junction; a transparent, electrically conductive first layer over the semiconductor (e.g. in physical contact with the semiconductor); one or more than one transparent, electrically conductive second layer over the semiconductor (e.g. in physical contact with the semiconductor and / or the first layer); wherein the first layer comprises oxygen and indium (e.g. a chemical compound of indium with oxygen and preferably a first dopant of the chemical compound of indium with oxygen), and wherein the first layer comprises zinc and / or aluminum (e.g. a chemical compound of oxygen with zinc and preferably a second dopant, e.g.the aluminium, the chemical compound of oxygen with zinc); wherein the or each second layer comprises oxygen and has a larger proportion of one or more than one of indium, aluminium and / or zinc and / or smaller gradients of the proportion than the first layer.

[0017] Example 4 is one of Examples 1 to 3, wherein a first material stream for forming the first layer and a second material stream for forming the second layer interpenetrate each other and / or are exposed to the same process gas (e.g., the same chemical composition thereof and / or the same pressure thereof). This optimizes the coating properties.

[0018] Example 5 is one of Examples 1 to 4, wherein the second layer comprises a chemical compound of oxygen with indium or zinc and preferably the first dopant, e.g., tin, of the chemical compound of oxygen with indium. This optimizes the coating properties.

[0019] Example 6 is one of Examples 1 to 5, wherein a first rate (e.g., specified as the amount of material per unit time) at which the first layer is formed is greater than a second rate (e.g., specified as the amount of material per unit time) at which the second layer is formed. This optimizes the cost-benefit ratio.

[0020] Example 7 is any one of Examples 1 to 6, wherein the first layer is disposed between the solar cell precursor and the second layer, or wherein the second layer is disposed between the solar cell precursor and the first layer.

[0021] Example 8 is any one of Examples 1 to 7, wherein the first layer and / or the second layer are in physical contact with a semiconductor of the solar cell precursor and / or an oxide of the semiconductor. This optimizes the electrical coating properties.

[0022] Example 9 is one of Examples 1 to 8, wherein the second layer comprises a chemical compound of oxygen with one or more of indium, aluminum, and / or zinc. This optimizes the coating properties, e.g., with regard to electrical conductivity.

[0023] Example 10 is one of Examples 1 to 9, wherein the first layer comprises a homogeneous mixture of indium and zinc or their chemical compounds with oxygen (ie, their oxide). This optimizes the coating properties, e.g., with regard to electrical conductivity.

[0024] Example 11 is one of Examples 1 to 10, where the second layer is free of zinc. This optimizes the coating properties, e.g., with regard to optical properties.

[0025] Example 12 is one of Examples 1 to 11, wherein the second layer has a higher specific conductivity than the first layer. This optimizes the coating properties, e.g., with regard to electrical conductivity.

[0026] Example 13 is one of Examples 1 to 12, wherein the second layer has a higher transmission coefficient than the first layer. This optimizes the coating properties, e.g., with regard to efficiency.

[0027] Example 14 is one of Examples 1 to 13, wherein a coating (e.g., a layer stack) of the solar cell precursor comprising the first layer and the second layer, preferably at a wavelength of 600 nm, has a reflection coefficient of less than 1%. This optimizes the coating properties, e.g., with regard to efficiency.

[0028] Example 15 is one of Examples 1 to 14, wherein the first layer and / or the second layer comprise a first dopant of a chemical compound of indium with oxygen, wherein the first dopant preferably comprises tin and / or tin and / or zirconium and / or titanium and / or cerium, and / or tungsten, or consists thereof (e.g., a combination of two or more of these different chemical elements). This optimizes the coating properties, e.g., with regard to the electrical properties.

[0029] Example 16 is one of Examples 1 to 15, wherein the second layer contains more indium than zinc and / or more indium than aluminum. This optimizes the coating properties, e.g., with regard to lifetime.

[0030] Example 17 is one of Examples 1 to 16, wherein the first layer is formed by sputtering a first, preferably ceramic, sputtering target and / or wherein the second layer is formed by sputtering a second, preferably ceramic, sputtering target. This optimizes the coating properties, e.g., with regard to manufacturing costs.

[0031] Example 18 is any one of Examples 1 to 17, wherein the first layer has a greater thickness (extension along a direction away from the solar cell precursor) than the second layer, for example, wherein the first layer has a thickness of at least twice the thickness of the second layer and / or greater than approximately 50 nanometers (e.g., approximately 80 nanometers). This optimizes the coating properties, e.g., with respect to the cost-benefit ratio.

[0032] Example 19 is one of Examples 1 to 18, wherein the first layer is disposed between the second layer and the solar cell precursor and / or wherein the second layer has a higher indium content than the first layer. This optimizes the coating properties, e.g., with regard to lifetime.

[0033] Example 20 is any one of Examples 1 to 19, wherein the solar cell precursor is covered on a side on which the first layer and / or second layer are formed with a transparent, electrically conductive additional second layer (preferably wherein the first layer is arranged between the second layer and the additional second layer and / or preferably wherein the additional second layer is arranged between the first layer and the solar cell precursor); wherein the additional second layer has a larger proportion of indium or zinc than the first layer; for example, wherein the additional second layer physically contacts the second layer or the first layer. This optimizes the coating properties, e.g. with regard to adhesion and / or degradation of the solar cell precursor.

[0034] Example 21 is one of Examples 1 to 20, wherein the second layer has a smaller proportion of tin and / or aluminum than the first layer and / or the additional second layer. This optimizes the coating properties, e.g., with regard to the electrical properties.

[0035] Example 22 is any one of Examples 1 to 21, wherein the solar cell precursor or solar cell comprises a semiconductor junction.

[0036] Example 23 is one of Examples 1 to 22, wherein the semiconductor junction comprises multiple layers comprising silicon and / or differing from one another in their degree of crystallinity (degree of structural order in a solid, e.g., expressed as the proportion of crystals), and / or comprising a layer of crystalline silicon between two layers of amorphous silicon. This optimizes manufacturing costs.

[0037] Example 24 is any one of Examples 1 to 23, wherein the solar cell further comprises a metallization that contacts the second layer (e.g., electrically and / or physically) and / or that contacts a coating (e.g., a layer stack) of the solar cell precursor that comprises the first layer and the second layer (e.g., electrically and / or physically). This optimizes the coating properties, e.g., with regard to electrical contacting.

[0038] Example 25 is Example 24, wherein the metallization comprises a plurality of ohmically coupled strips and / or is arranged in a trench formed in the second layer. This improves the electrical properties.

[0039] Example 26 is any one of Examples 1 to 25, wherein the first layer has a proportion of zinc that continuously decreases over an extent of the first layer (e.g., toward or away from the solar cell precursor), the extent being greater than 15 nm.

[0040] Example 27 is any one of Examples 1 to 26, wherein forming the first layer over the solar cell precursor occurs when (e.g., during) transporting the solar cell precursor; and / or wherein forming the second layer over the solar cell precursor occurs when (e.g., during) transporting the solar cell precursor.

[0041] Reference is made herein to various statements about the proportion of a chemical element or material in a reference, where the reference comprises the chemical element or material. The proportion may be stated as - proportion of the total mass (then also referred to as mass fraction, e.g. given as wt%) of a reference, - Proportion of the total volume (then also referred to as volume fraction, e.g. given as vol%) of the reference - proportion of the amount of substance in the reference (then also referred to as the molar fraction, e.g. given as at%), or - as concentration (e.g. given as number of atoms per volume, e.g. in at / cm 3 ).

[0042] The reference can be, for example, the body (e.g. the sputtering target or a layer) which contains the chemical element or material, or a homogeneous material mixture which contains the chemical element or material.

[0043] With regard to the layer-forming process, reference is made here as an example to so-called sputtering. The term "sputtering" refers to the atomization of a material (also referred to as coating material or target material) using a plasma. The atomized components of the coating material (e.g. individual atoms and / or ions) are separated from one another, forming a material stream and can, for example, be deposited elsewhere to form a layer. Sputtering can be carried out using a so-called sputtering device, which can have one or more than one magnet system (in this case also referred to as a magnetron). The coating material can be provided by means of a so-called sputtering target (also referred to as target for short), which can, for example, be tubular (in this case also referred to as a tubular target) or plate-shaped (in this case also referred to as a plate target or planar target).To generate the plasma, a voltage (also called sputtering voltage) can be applied to the sputtering target (also referred to as the target for short), so that the sputtering target acts as a cathode. Even if the sputtering voltage is an alternating voltage, the term "cathode" is often retained.

[0044] For sputtering, the sputtering target can be arranged in a vacuum processing chamber (also referred to simply as a processing chamber or vacuum chamber) so that sputtering can take place in a vacuum. For this purpose, the ambient conditions (the process parameters) within the vacuum processing chamber (e.g., process pressure, temperature, gas composition, etc.) can be adjusted or regulated during sputtering. For example, a working gas can be provided within the processing chamber, which refers to the plasma-forming gas or the plasma-forming gas mixture. The processing chamber can, for example, be designed to be airtight, dusttight, and / or vacuum-tight, so that a gas atmosphere with a predefined composition (also referred to as the working atmosphere) or a predefined pressure (also referred to as the working pressure or process pressure) can be provided within the processing chamber (e.g., according to a setpoint), e.g.a vacuum.

[0045] The plasma can be formed by means of the working gas (also referred to as plasma-forming gas). According to various embodiments, the working gas can comprise a gaseous material that is inert, in other words that participates in few or no chemical reactions. A working gas can, for example, be or become defined by the target material used and be or become adapted to this. For example, a working gas can comprise a gas or a gas mixture that does not react with the target material to form a solid or is even inert towards it. The working gas can, for example, comprise a noble gas (e.g., helium, neon, argon, krypton, xenon, radon) or several noble gases. If a reactive gas is used as the process gas or a component thereof, the reactive gas can have a higher chemical reactivity than the working gas, e.g., with regard to the target material.In other words, the atomized target material can react more quickly with the reactive gas (if present) (i.e., form more reaction product per unit time) than with the working gas (e.g., if it reacts chemically with the working gas at all). The reactive gas and the working gas can be supplied together or separately as a process gas (e.g., as a gas mixture), for example, using the gas supply device.

[0046] It should be understood that what is described herein for sputtering can apply analogously to any other coating process, e.g., physical vapor deposition, in which the target material is present as a solid at room temperature. For example, physical vapor deposition (e.g., sputtering) involves transferring the chemical composition of the target or coating material into the layer to be formed. Using a reactive gas, a layer comprising the reaction product of the target material and the reactive gas can be formed.

[0047] In contrast to CVD (Chemical Vapor Deposition), in PVD (Physical Vapor Deposition), e.g. sputtering, a solid material is first transferred into the gas phase (also referred to as the gaseous phase or vapor), and a layer is formed using this gas phase. In PVD, the gas phase of the target material can optionally be chemically reacted (e.g. in reactive PVD) with a reactive gas to form a chemical compound (also referred to as reactive PVD or reactive sputtering), which is then incorporated into the layer or forms it. During the chemical reaction in PVD, two or more materials are combined to form the chemical compound.

[0048] For example, sputtering is used to form a semi-crystalline to amorphous silicon thin film, which is then post-treated by a high-temperature step for doping and / or crystallization (so-called “solid phase crystallization”).

[0049] A semiconductor junction (also called a pn junction) can be understood as an interface where two semiconductors with opposite doping levels touch. At the semiconductor junction, the doping changes, for example, from positive (p) to negative (n).

[0050] Reference is made herein to a method and a vacuum arrangement (e.g., its vacuum system), which is configured, for example, to carry out the method, in connection with the processing of a solar cell precursor (also referred to as solar cell precursor or as partially processed solar cell) as an exemplary substrate. The solar cell precursor may comprise or consist of a preprocessed wafer. Alternatively or additionally, the solar cell precursor may comprise a solar cell layer stack (e.g., comprising a semiconductor junction). It can be understood that what is described for the solar cell precursor may apply to any other substrate comprising a semiconductor and / or coated with one or more than one (e.g., amorphous) semiconductor, preferably comprising silicon. With regard to the coating and / or with regard to the processing, it can further be understood that the method suitable for a specific side (e.g.,What is described analogously can apply to the opposite side (then front or back) of the solar cell precursor (or substrate).

[0051] Fig. 1 illustrates a method 100 according to various embodiments, for example according to one of Examples 1 to 25, in a schematic flow diagram.

[0052] The formation 101 of the transparent, electrically conductive first layer (also referred to as first TCO layer) on the solar cell precursor and / or the formation 103 of the or each transparent, electrically conductive second layer (also referred to as second TCO layer) on the solar cell precursor can preferably be carried out in a vacuum.

[0053] The first TCO layer can, for example, comprise indium oxide (IO), a chemical compound of indium and oxygen, with the indium oxide preferably doped with tin as the first dopant (then also referred to as ITO). It is understood that, alternatively or in addition to tin, cerium and / or tungsten can also be used as the first dopant. This leads to other electrical and optical properties that can be beneficial for the solar cell properties.

[0054] The first TCO layer can, for example, comprise zinc oxide (ZnO) as a chemical compound of zinc and oxygen, wherein the zinc oxide is preferably doped with aluminum as a second dopant (then also referred to as AZO).

[0055] For example, the first TCO layer may comprise a (eg homogeneous) mixture of indium oxide (eg ITO) and zinc oxide (eg AZO) and / or a gradient (ie a gradual change) in the proportion of indium or of zinc, wherein the gradient is directed, for example, towards or away from the second TCO layer.

[0056] According to various embodiments, the first TCO layer is provided as a so-called mixed layer, which comprises or is formed from a (e.g. homogeneous) mixture of ITO and AZO.

[0057] In a first exemplary implementation of the first TCO layer, its indium content (also referred to as In content) may be in a range from approximately 5 to approximately 95% and / or may have a gradient in a range from approximately 1 at% / nm to at least 30 at% / nm, e.g., approximately 4 at% / nm. The gradient may, for example, be directed toward or away from the second TCO layer and / or extend over a range from approximately 1 nm to at least 15 nm in the first TCO layer.

[0058] In the first or a second exemplary implementation of the first TCO layer, its zinc content (also referred to as Zn content) may be in a range from approximately 5 to approximately 95% and / or may have a gradient in a range from approximately 1 at% / nm to at least 30 at% / nm, e.g., approximately 4 at% / nm. The gradient may, for example, be directed toward or away from the second TCO layer and / or extend over a range from approximately 1 nm to at least 15 nm in the first TCO layer.

[0059] In the first, second, or an additional second exemplary implementation of the first TCO layer, its aluminum content (also referred to as Al content) may be in a range from approximately 0 to approximately 2% and / or may have a gradient in a range from approximately 1 at% / nm to at least 30 at% / nm, e.g., approximately 4 at% / nm. Alternatively or additionally, a ratio of aluminum to zinc in the first TCO layer may be set equal on opposite sides of the first TCO layer. The gradient may, for example, be directed toward or away from the second TCO layer and / or extend over a range from approximately 1 nm to at least 15 nm in the first TCO layer.

[0060] In the first, second, additional second, or a fourth exemplary implementation of the first TCO layer, its tin content (also referred to as Sn content) may be in a range from approximately 0 at% to approximately 10 at% and / or have a gradient in a range from approximately 1 at% / nm to at least 30 at% / nm, e.g., approximately 4 at% / nm. Alternatively or additionally, a ratio of tin to indium in the first TCO layer may be set equal on opposite sides of the first TCO layer. The gradient may, for example, be directed toward or away from the second TCO layer and / or extend over a range from approximately 1 nm to at least 15 nm in the first TCO layer.

[0061] In a first configuration (see Fig.7A), for example, when the first TCO layer is configured as an intermediary layer and / or a second TCO layer is configured as a protective layer, the first TCO layer can be arranged between the second TCO layer and the solar cell precursor.

[0062] In a second configuration (see Fig. 7B), for example, when the first TCO layer is configured as a protective layer and / or when a second TCO layer is configured as an intermediary layer, the second TCO layer may be arranged between the first TCO layer and the solar cell precursor.

[0063] In an exemplary implementation of method 100, an inline deposition of an ITO-AZO layer stack is performed in a vacuum (e.g., in a process chamber) using a double-tube magnetron or two adjacently arranged tubular magnetrons. To form the layer stack, at least two TCO layers (also referred to as first and second TCO layers) are deposited consecutively. The first of the two TCO layers comprises indium, zinc, tin, aluminum, and oxygen. The second of the two TCO layers comprises indium, tin, and oxygen, or zinc, aluminum, and oxygen.

[0064] The first TCO layer can, for example, be provided as a mixed layer of ITO and AZO. Alternatively or additionally, the second TCO layer can consist of either ITO or AZO.

[0065] According to various embodiments, an inline coating method 100 is thus provided for depositing a transparent and electrically conductive layer stack (also referred to as a TCO layer stack) comprising at least two adjacent (e.g., touching) layers TCO1 and TCO2. The first layer consists of at least the elements A, B, and O. A and B represent two different metals or semimetals, such as In and Zn. O represents oxygen. The TCO2 layer consists of at least the elements B and oxygen.

[0066] According to various embodiments, an inline coating method 100 is thus provided for depositing a transparent and electrically conductive layer stack, wherein the layer stack is formed by sputtering at least two ceramic sputtering targets (also referred to as targets for short). The two targets differ from one another in their chemical composition, are arranged side by side, and are installed in the same process chamber, their vapor lobes overlapping such that two adjacent layers TCO1 and TCO2 are formed. Preferably, the thickness of the layer TCO1 is greater when depositing the layer from two adjacent targets than from two targets that are further spatially separated from one another and arranged in two different process chambers.

[0067] Optionally, the TCO layer stack, which comprises the two adjacent (e.g., touching) layers TCO1 and TCO2, can be configured as an antireflection layer. Then, the TCO layer stack can have a reflection coefficient of less than approximately 10% (e.g., approximately 5% or approximately 1%), preferably at a wavelength in a range from approximately 500 nm to approximately 700 nm. This is achieved by adjusting the refractive index and layer thickness of the TCO layer stack.

[0068] The solar cell precursor can be transported during formation of the first TCO layer and / or the second TCO layer, e.g. along a transport direction 111r (see Fig. 2) and / or in a vacuum, for example in a vacuum chamber 802 (see Fig. 6A and Fig. 6B) is provided.

[0069] Fig.2 illustrates the method 100 according to various embodiments 200, for example according to one of Examples 1 to 25, in a schematic side view or cross-sectional view, which are configured, for example, to implement the first configuration.

[0070] The solar cell precursor 202 may have a side 202o (also referred to as the side to be coated) that is coated with the first TCO layer TCO1. The side to be coated may, for example, be a front side or a back side of the solar cell precursor 202. A semiconductor of the solar cell precursor or an oxide of the semiconductor may be exposed on the side to be coated 202o.

[0071] The first TCO layer TCO1 can be formed using a first material source 104 configured to emit a first material stream 104s to the solar cell precursor 202. The first material source 104 can comprise or consist of a first target material M1, e.g., in the form of a first sputtering target (e.g., an AZO sputtering target). The first sputtering target can be atomized using a plasma to emit the first material stream 104s. The first target material M1 can comprise or consist of zinc oxide, e.g., AZO.

[0072] The second TCO layer TCO2 can be formed using a second material source 106 configured to emit a second material stream 106s to the solar cell precursor 202. The second material source 106 can comprise or consist of a second target material M2, for example in the form of a second sputtering target (e.g., ITO sputtering target). The second sputtering target can be sputtered using a plasma to emit the second material stream 104s. The second target material M2 can comprise or consist of indium oxide (IO), for example, ITO.

[0073] Portions of the second material stream 106s can contribute to the formation of the first TCO layer TCO1. For this purpose, the first material stream 104s and the second material stream 106s can penetrate each other. Illustratively, the penetration leads to a homogeneous mixture of indium, zinc, and oxygen, e.g., a homogeneous mixture of indium oxide and zinc oxide, e.g., a homogeneous mixture of ITO and AZO. This mixing improves the coating properties.

[0074] This penetration is promoted by arranging the first target material M1 and the second target material M2 close to one another. For example, a distance (also referred to as TT distance) of the first target material M1 from the second target material M2 can be smaller than a distance of the solar cell precursor 202 from the first target material M1 and / or the second target material M2. Alternatively or additionally, a distance of the first target material M1 from the second target material M2 can be smaller than approximately 0.5 meters, e.g., than approximately 0.3 meters, e.g., than approximately 0.2 meters, e.g., than approximately 0.1 meters, e.g., than approximately 0.05 meters. This promotes the mixing of the materials. In the case of tubular magnetrons, which are the preferred coating sources, the TT distance can be the distance between the target surfaces of the two tubular targets arranged side by side.

[0075] The first TCO layer TCO1 can have a larger proportion of the first target material M1 near the solar cell precursor 202 than near the second TCO layer TCO2, i.e., its proportion of the first target material M1 increases toward the solar cell precursor 202. Alternatively or additionally, the first TCO layer TCO1 can have a smaller proportion of the second target material M2 near the solar cell precursor 202 than near the second TCO layer TCO2, or can be free of the second target material M2.

[0076] In an exemplary implementation of embodiments 200, a second TCO layer TCO2 made of ITO may be formed on the first TCO layer TCO1, having an increasing ratio of ITO to AZO toward the second TCO layer TCO2. This slows down the aging process of the first TCO layer TCO1 at low cost.

[0077] Fig.3 illustrates the method 100 according to various embodiments 300, for example, according to one of Examples 1 to 25, in a schematic side view or cross-sectional view. According to the embodiments 300, for example, alternatively or in addition to the embodiments 200, the coating can be carried out using the first target material M1 before the coating is carried out using the second target material M2.

[0078] Portions 311 of the two material streams 104s, 106s can contribute to the formation of the first TCO layer TCO1. For this purpose, the two material streams can penetrate each other. This facilitates the process.

[0079] The first TCO layer TCO1 may comprise a larger proportion of the first target material M2 near the solar cell precursor 202 than near the second TCO layer TCO2. Alternatively or additionally, the first TCO layer TCO1 may comprise a smaller proportion of the second target material M2 near the solar cell precursor 202 than near the second TCO layer TCO2.

[0080] In an exemplary implementation of embodiments 300, an AZO layer may be formed as a second TCO layer TCO2 beneath the first TCO layer TCO1. This further reduces the cost of the process.

[0081] Fig. 4 illustrates the method 100 according to various embodiments 400, for example according to any one of Examples 1 to 25, in a schematic side view or cross-sectional view, which are configured, for example, to implement the second configuration.

[0082] Embodiments 400 may include that the solar cell precursor 202 is covered with a plurality of second TCO layers (TCO2), for example, in physical contact with one another or with the first TCO layer (TCO1) arranged between them. The formation of each second TCO layer may be effected, for example, using the first target material M1 or the second target material M2. During the coating process, the first target material M2 and the first target material M2 may be mixed at at least one location, so that the solar cell precursor 202 is coated with a material mixture that is transparent and electrically conductive and has a proportion of indium that continuously increases or decreases along a direction away from the solar cell precursor.

[0083] In an exemplary implementation of embodiments 400, an ITO layer may be formed as a second TCO layer on the first TCO layer TCO1. This slows down the aging process of the solar cell coated only with the first TCO layer TCO1.

[0084] Fig. 5A and B each illustrate a diagram 500a and 500b, according to various embodiments, for example, according to one of Examples 1 to 25, in a schematic view. Illustrated is the spatial distribution of the chemical composition of two exemplary layer stacks for comparison, each formed using two sputtering targets, for example, configured as tubular cathodes, of which one sputtering target consisted of ITO (also referred to as ITO sputtering target) and the other sputtering target consisted of AZO (also referred to as AZO sputtering target).

[0085] Diagram 500a shows, as a first case, the two sputtering targets arranged so close to each other that the two material streams of ITO and AZO penetrate each other. Diagram 500b shows, as a second case, the two sputtering targets arranged so far apart that the two material streams of ITO and AZO are separated from each other (e.g., gas-separated). For example, in the second case, the two sputtering targets can be arranged in gas-separated processing chambers.

[0086] The optical emission of the chemical elements in the layer stack was measured using glow-discharge optical spectroscopy (GD-OES). In glow discharge spectroscopy, the coating under investigation (e.g., the layer stack) is removed by ion bombardment with a glow discharge. The elements of the coating removed in this process are excited by the glow discharge and emit element-specific, characteristic radiation, which is measured with time resolution. Time is a measure of the location of the measurement, which moves into the coating over time; in this case, it is a measure of the location along the layer thickness. The intensity of the characteristic radiation of an element is a measure of the amount of the element in the layer stack. The higher the intensity of the element, the higher its proportion (e.g., concentration) in the layer stack.

[0087] In diagrams 500a and 500b, the optical intensity for each of the elements indium, tin, aluminum, zinc, oxygen, silicon, and sodium is plotted as a function of the location along the layer thickness of the coating comprising the first TCO layer and the second TCO layer.

[0088] The coating in diagram 500b was formed by depositing approximately 85 nm (nanometers) of AZO onto a glass substrate in a first process chamber. Immediately thereafter, approximately 20 nm of ITO was deposited onto the AZO in a second process chamber, gas-separated from the first process chamber. The two material streams (also descriptively referred to as vapor lobes) of the AZO and ITO sputtering processes exhibit no penetration (overlap) due to the deposition in gas-separated process chambers. Nevertheless, diagram 500b shows an increase in zinc intensity and a decrease in indium intensity, and thus in its concentrations, between 12 and 22 nm.

[0089] This superposition of indium and zinc in a range of layer thicknesses, in this exemplary case between 12 and 22 nm, is indeed an indication that a mixed layer containing indium, zinc, and oxygen may have formed. However, the spatial resolution limit of the measurement method, which ablates a surface with a diameter of approximately 4 mm, must be taken into account. Furthermore, the layer stack is not ablated perfectly homogeneously by the glow discharge. Depressions, so-called sputter trenches, are created, which can lead to the fact that, despite a sharp interface between two layers, the intensities of the elements of both layers can be measured at the same time. The same applies to the roughness of the interface.

[0090] This compares well with the interface between glass and AZO in the range between 102 and 120 nm in diagram 500b. There, both the optical emission of silicon and zinc is measured, even though a sharp interface exists between the glass and the AZO layer.

[0091] If the intensity curve is corrected for these influences, an abrupt, very steep drop in the indium intensity and an abrupt, very steep increase in the zinc intensity at 20 nm emerge, resulting from the spatial separation of the AZO and ITO sputtering processes. The reason for the non-abrupt increase or decrease in the intensities of zinc and indium is therefore rooted in the measurement method.

[0092] The layer stack of diagram 500a was formed by sputtering from two closely arranged sputtering targets (e.g., tubular cathodes) in the same process chamber, for example, from a double-tube magnetron. This proximity of the tubular cathodes promotes their vapor lobes to overlap, i.e., to penetrate each other and thereby mix. For example, a distance between the target surfaces of the two sputtering targets can be smaller than a distance of the solar cell precursor 202 to the target surfaces. Alternatively or additionally, a distance between the two target surfaces of the sputtering targets can be smaller than approximately 0.5 meters, e.g., approximately 0.3 meters, e.g., approximately 0.2 meters, e.g., approximately 0.1 meters, e.g., approximately 0.05 meters. This promotes the mixing of the materials.

[0093] The deposition rate of the AZO sputtering target was determined experimentally for an AZO layer thickness of 20 nm, and that of the ITO sputtering target for an ITO layer thickness of 90 nm, each separately on glass, and thus adjusted. Diagram 500a shows the presence of both indium and zinc between 0 and 25 nm. The range in which zinc and indium intensities are measured simultaneously, at 25 nm, is significantly larger than the range of approximately 10 nm shown in Diagram 500b.

[0094] These data show that the penetration of the material streams promotes the formation of a mixture with which the solar cell precursor is coated, the mixture comprising indium, zinc and oxygen, and preferably further comprising a first dopant of the chemical compound of indium and oxygen and / or a second dopant of the chemical compound of zinc and oxygen.

[0095] The mixing of the material streams (e.g. ITO and AZO) of two sputtering targets can be influenced by the following parameters: - Degree of penetration of the material flows; - Distance between the two target materials (e.g. sputtering targets); - Alignment of the magnetic fields penetrating the two target materials (e.g. sputtering targets); - spatial distribution of the plasma by means of which the two target materials (e.g. sputtering targets) are atomized; - a physical gas separation between the two target materials (e.g. a partition wall or a gas separation chamber).

[0096] The formation of the mixed layer can be inhibited, for example, - if the process chambers are extended in the transport direction and thus the distance between the two sputtering targets is increased; - when the magnetic fields of the two sputtering targets are aligned outwards towards the chamber wall; - if a partition wall is installed up to the substrate between the two sputtering targets; - by installing additional process or gas separation chambers in the sputtering system in order to sufficiently spatially separate the layer deposition.

[0097] However, this can increase the cost of a sputtering system with extended sputtering chambers. The system length also increases, which is often undesirable. Separation can reduce the vapor utilization of the sputtered material and thus also the deposition rate, since sputtering occurs on the chamber walls and the partition wall. This increases coating costs.

[0098] According to various embodiments, delivered sputtering systems or even recently sold sputtering systems can be cost-effectively converted to deposit ITO and AZO layers, for example, without having to expand them. The use of more cost-effective AZO targets results in significant savings in target costs. A layer stack with one or more mixed layers of two different TCOs, e.g., ITO and AZO, can be sputtered in the same vacuum chamber (also referred to as a vacuum processing chamber or processing chamber). This facilitates the further improvement of the solar cell properties. The sputtering system can be manufactured more cost-effectively because fewer or narrower process chambers can be used. The mixed layer also promotes the adhesion and vapor-heat stability of the TCO layer stack.

[0099] Fig.6A and B each illustrate a vacuum arrangement 600a and 600b according to various embodiments, for example, according to one of Examples 1 to 25, in a schematic side view or cross-sectional view. The vacuum arrangement 600a and 600b comprises the vacuum chamber 802 and a transport device (not shown) for transporting the solar cell precursor 202 in the vacuum chamber 802 along the transport direction 111r.

[0100] The following table shows the properties of two comparative examples. The first TCO layer stack AZO / ITO (220303#11) was deposited in two separate process chambers 802 (Case 2, see vacuum arrangement 600b), and the second layer stack (220223#5) was deposited in exactly one process chamber 802 (Case 1, see vacuum arrangement 600a), e.g., using two closely spaced tubular magnetrons. One of the tubular magnetrons has a ceramic AZO target, and the other tubular magnetron has a ceramic ITO tubular target. sample 220223#5 220303#11 AZO oxygen [%] 2,0 1,5 ITO oxygen [%] 2,6 Layer thickness [nm] 110 106 Surface resistance [Ohm] 326 348 Specific resistance [µOhmcm] 3580 3696 Transmission averaged between 400 and 1100 nm [%] 82,6 82,6

[0101] The process parameters for forming the TCO layer stack 220303#11 were adjusted so that its coating properties differ as little as possible from the coating properties of the TCO layer stack 220223#5. As can be seen, the process parameters for forming the TCO layer stack 220303#11 exhibit different oxygen contents in the process gas of both processing chambers, which complicates production.

[0102] In contrast, the formation of the TCO layer stack 220223#5 can be subjected to the same gas pressure and / or the same chemical composition of the process gas without compromising the coating properties. This facilitates manufacturing. More generally, these data show that the blending of indium, zinc, and oxygen (e.g., ITO and AZO) improves the coating properties and thus compensates for less favorable manufacturing conditions.

[0103] Fig. 7A and B each illustrate the coating of the solar cell precursor in various configurations. Shown on the left are the basic configuration 700a and 700b of the coating, which comprises the first TCO layer TCO1 and a second TCO layer TCO2, and on the right is a modification 601 of the basic configuration 700a and 700b, in which an additional second TCO layer TCO2 is added to the coating. For example, two second TCO layers TCO2 can either touch each other or each touch the first TCO layer TCO1. Two second TCO layers TCO2 can differ from each other in their chemical composition, for example, in the proportion of zinc or indium. Each second TCO layer TCO2 can, for example, consist of either AZO or ITO.

[0104] The arrow 603 indicates the direction (e.g. direction of the layer thickness) in which the concentration of indium increases.

Claims

[1] Method (100) for processing a solar cell precursor (202), the method (100) comprising: • Forming a transparent, electrically conductive first layer (TCO1) over the solar cell precursor (202); • Forming at least one transparent, electrically conductive second layer (TCO2) over the solar cell precursor (202), of which a second layer (TCO2) is arranged between the solar cell precursor (202) and the first layer (TCO1) and has more indium than zinc; • wherein the first layer (TCO1) comprises at least indium, zinc and oxygen; • where the second layer (TCO2) contains oxygen and a larger proportion of indium than the first layer (TCO1). [2] Method (100) according to claim 1, wherein a first material stream for forming the first layer (TCO1) and a second material stream for forming the second layer (TCO2) penetrate each other and / or are exposed to the same process gas. [3] Method (100) according to claim 1 or 2, wherein the second layer (TCO2) is in physical contact with a semiconductor of the solar cell precursor (202) and / or an oxide of the semiconductor. [4] Method (100) according to one of claims 1 to 3, wherein a stack comprising the first layer (TCO1) and the at least one second layer (TCO2) has a reflection coefficient of less than 10%. [5] Method (100) according to one of claims 1 to 4, wherein the first layer (TCO1) has a greater layer thickness than the second layer (TCO2). [6] Method (100) according to one of claims 1 to 5, wherein the second layer (TCO2) comprises a dopant of a chemical compound of indium with oxygen. [7] The method (100) according to claim 6, wherein the dopant comprises tin and / or zirconium and / or titanium and / or cerium and / or tungsten. [8] Method (100) according to one of claims 1 to 7, • wherein the formation of the first layer (TCO1) is carried out by sputtering a first sputtering target, and • wherein the formation of the second layer (TCO2) is carried out by sputtering a second sputtering target; • wherein the first sputtering target and / or the second sputtering target are ceramic. [9] Method (100) according to one of claims 1 to 8, wherein the at least one second layer (TCO2) comprises the second layer (TCO2) and an additional second layer (TCO2) between which the first layer (TCO1) is arranged. [10] Method (100) for processing a solar cell precursor (202), the method (100) comprising: • Emitting a first material stream comprising zinc and oxygen toward the solar cell precursor (202); • Emitting a second material stream comprising indium and oxygen toward the solar cell precursor (202); • wherein the emission of the first material stream and the emission of the second material stream are carried out in such a way that a material mixture is formed, • with which the solar cell precursor (202) is coated and has more indium than zinc, • which is transparent and electrically conductive, and • which has a proportion of indium that decreases along a direction away from the solar cell precursor (202). [11] Solar cell, comprising: • a semiconductor; • a transparent, electrically conductive first layer (TCO1) over the semiconductor; • one or more than one transparent, electrically conductive second layer (TCO1) over the semiconductor, of which a second layer (TCO2) is arranged between the semiconductor and the first layer (TCO1) and has more indium than zinc; • wherein the first layer (TCO1) comprises indium, zinc and oxygen; • where the second layer (TCO2) contains oxygen and a larger proportion of indium than the first layer (TCO1).

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