DE102010056333A1 - Thin layer photovoltaic cell, has contact layer, absorber layer and buffer layer arranged on side of substrate, and rear protecting layer arranged on side of substrate and made of corrosion resistant material - Google Patents

Abstract

The cell (50) has a support substrate (52) with two sides (54, 56), and a contact layer (64), an absorber layer (66) and a buffer layer (68) arranged on one of the sides of the substrate. A rear protecting layer (60) is arranged on the other side of the substrate and made of corrosion resistant material such as chrome or molybdenum alloy. The protecting layer comprises a thickness of 150 Nm to 275 Nm. The molybdenum alloy comprises an alloy partner, selected from the group of titanium, zirconium, hafnium, vanadium, niobium, tantalum, aluminum and silicon. An independent claim is also included for a method for manufacturing a flexible thin layer photovoltaic structure.

Description

Cross-reference to connected login

This application claims the benefit of US Provisional Patent Application No. 61 / 284,923, filed on Dec. 28, 2009, No. 61 / 351,245, filed on Jun. 3, 2010, and No. 61 / 425,641, filed on Dec. 21, 2010, the all incorporated by this reference for all purposes here. Also incorporated herein by reference are the following patents and patent applications in their entirety: Patent No. 7,194,197, Application No. 12 / 424,497, filed April 15, 2009, and Application No. 12 / 397,846, filed March 4, 2009.

background

The field of photovoltaics generally relates to multilayer materials that convert sunlight directly into direct current. The basic mechanism for this transformation is the photovoltaic (or photoelectric) effect first observed in 1839 by Antoine-César Becquerel and first described in 1905 by Einstein in a groundbreaking scientific paper for which he was awarded a Nobel Prize in Physics. In the United States, photovoltaic (PV) devices are well known as solar cells or PV cells. Solar cells are typically constructed as a co-acting stack of p-type semiconductors and n-type semiconductors, where the n-type semiconductor material (on one "side" of the layered assembly) has an excess of electrons and the p-type semiconductor material (on the other "side" of the layered structure) ) has an excess of holes, each representing the absence of an electron. Near the p-n junction between the two materials, valence electrons move from the n-layer into adjacent holes in the p-layer, creating a small electrical imbalance within the solar cell. This results in an electric field in the vicinity of the metallurgical contact, which forms the electronic p-n junction.

When an incident photon excites an electron in the cell in the conduction band, the excited electron detaches from the atoms of the semiconductor, creating a free electron / hole pair. As described above, since the pn pad generates an electric field in the vicinity of the pad, electron / hole pairs thus created near the pad tend to separate and move away from the pad, the electron moves to the n-side electrode and the hole moves to the electrode on the p-side of the pad. This altogether creates a charge imbalance in the cell such that when an external conductive path is provided between the two sides of the cell, the electrons move from the n-side back to the p-side along the external path, thereby generating an electrical current becomes. In practice, electrons can be collected from the surface or near the surface of the n-side through a baffle that covers a portion of the surface, while still allowing incidental photons sufficient access into the cell.

Such a photovoltaic structure forms a functional PV device when suitably arranged electrical contacts are included and the cell (or a series of cells) is integrated in a closed electrical circuit. As a stand-alone device, a single conventional solar cell is not sufficient to power most applications. Therefore, solar cells are usually arranged in PV modules or "rows" by connecting the front of one cell to the back of another cell, thereby adding up the voltages of the individual cells together in an electrical series connection. Typically, a very large number of cells are connected in series to achieve a useful voltage. The resulting direct current may then be fed through an inverter, where it is transformed into an alternating current of suitable frequency, which is selected to match the frequency of an alternating current supplied by a conventional power grid. In the United States, this frequency is 60 hertz (Hz), and in most other countries alternating current is provided at 50 Hz or 60 Hz.

One particular type of solar cell that has been developed for commercial use is a "thin film" PV cell. Compared to other types of PV cells, such as. Crystalline silicon PV cells, thin-film PV cells require less light-absorbing material to form a viable cell and thus can reduce manufacturing costs. Thin-film based PV cells are also more cost effective as they employ previously developed electrode layer deposition techniques that are widely used in the industry for protective, decorative and functional coatings. Known examples of low-cost, commercial thin-film products include water-impermeable coatings on polymer-based food packaging, decorative coatings on architectural glass, Low emissivity thermal control coatings on residential and commercial glass, and anti-scratch and anti-reflection coatings on eyeglass lenses. The adoption or adaptation of techniques developed in these other areas has allowed a reduction in the development costs of thin-film deposition techniques for PV cells.

Furthermore, thin-film cells have achieved efficiencies close to 20%, which equals or exceeds the efficiencies of the most efficient crystalline cells. In particular, the semiconductor material copper-indium-gallium-diselenite (CIGS) is stable, has low toxicity, and is actually thin-layered, requiring less than 2 microns of thickness in a functional PV cell. Thus, CIGS still appears to have the greatest potential for high-performance, low-cost thin-film PV products, and thus for the conquest of large power generation markets. Other semiconductor variants for thin film PV technology include copper indium diselenite, copper indium disulfide, copper indium aluminum diselenite, and cadmium telluride.

Thin-film PV cells that use either solid or flexible substrates generally include a conductive layer that serves as the bottom electrode of a cell disposed between the underlying substrate and the active PV material. When cells are connected by monolithic integration techniques (i.e., when the electrical connections between the cells are generated in situ on the continuous substrate), the so-called P2 patterning step is used to divide the continuously formed PV material into cells for subsequent connection.

Summary

A thin-film photovoltaic cell comprises a carrier substrate; a contact layer disposed adjacent a first side of the substrate; a p-type semiconductor layer disposed on the first side of the substrate; an n-type semiconductor layer disposed on the first side of the substrate and a backside contact protection layer pattern disposed adjacent to a second side of the substrate, wherein the backside contact protection layer pattern may comprise a corrosion resistant material. In some embodiments, the backside layer comprises at least a first layer and a second layer. Additionally and / or alternatively, the backside layer may comprise a molybdenum alloy, wherein the molybdenum alloy may comprise an alloying partner selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Al, and Si.

A method of manufacturing a flexible thin film photovoltaic (PV) structure comprises the steps of: providing a carrier substrate; Depositing a layer of a photovoltaic layer structure on a first side of the substrate; and applying a backside protective layer structure on a second side of the substrate, the backside protective layer structure comprising a corrosion resistant material. In some embodiments, applying the backside protective layer structure comprises applying at least two layers and / or applying a backside protective layer structure comprises applying a first layer and a second layer having a thickness ratio of 1: 2, wherein the first layer comprises chromium and the second Layer comprises molybdenum. Additionally and / or alternatively, the application of a backside protective layer structure may comprise depositing a molybdenum alloy layer, wherein the molybdenum alloy comprises an alloying partner selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Al, and Si.

An additional aspect of the present disclosure is directed to a method of making an elongate flexible strip of photovoltaic (PV) material, comprising: providing an elongated, flexible strip carrier substrate, placing the substrate in sequence, in various self-isolated processing chambers, and within each chamber, performing various sequential sub-layer forming operations that together result in the production of an elongate, roll-form, flexible strip of PV material. The PV material strip may comprise a multi-layer thin film PV cell layer structure on a first side and a backside protective layer structure on a second side, the backside protective layer structure comprising a corrosion resistant material. The backside protective layer structure may include a first layer of chromium and a second layer of molybdenum. Additionally and / or alternatively, the backside protective layer structure may comprise a molybdenum alloy layer, wherein the molybdenum alloy comprises an alloying partner selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Al, and Si.

The advantages of the present disclosure will be better understood after considering the drawings and the detailed description.

Brief description of the drawings

1 Figure 5 is a simplified schematic view generally showing process steps and steps used to make a PV module.

2 is a partial, simplified cross-section of a PV cell with a backside protective layer structure.

3 is a partial, simplified cross-section of a PV cell with a backside protective layer structure.

4 FIG. 12 is a cross-sectional view of a portion of a monolithically integrated thin film photovoltaic module. FIG.

5 Figure 12 is a graph showing the electrical resistance of a thin layer of molybdenum and a thin layer of molybdenum tantalum as a function of hours of wet heat soak time.

Precise description

PV cells may be susceptible to adverse environmental conditions, for example, during deposition of a PV absorber layer by vapor deposition, during a wet heat integrity test, or due to heat, moisture, and / or moisture in the environment, which may be a carrier substrate from the backside can attack the installation of the PV cell or the PV module. Molybdenum coatings or layers disposed on either side of a carrier substrate may be susceptible to corrosion after being exposed to heat and moisture for a period of time. A thin film PV cell according to the present disclosure includes improved corrosion protection over a substrate having only one molybdenum layer alone.

Additionally and / or alternatively, a thin film PV cell according to the present disclosure may include a support substrate having a photovoltaic layer structure disposed on a first side of the substrate and a backside protective layer structure disposed adjacent a second side of the substrate, wherein the backside protective layer structure improves the corrosion resistance of the substrate and / or protects the substrate from damaging environmental conditions. According to an embodiment of the present disclosure, a backside protective layer structure may include a corrosion resistant material, such as a Mo-X alloy. Additionally and / or alternatively, a PV cell according to the present disclosure may comprise a backside protective layer structure having more than one layer, also referred to as a double layer, wherein one or more of the layers comprises a corrosion resistant material, for example, chromium (Cr).

A PV cell according to the present disclosure can be made by starting with a substrate and then sequentially depositing a plurality of thin layers of different materials onto the substrate. When the substrate is flexible, this arrangement can be achieved by roll processing wherein the substrate moves from an output roll to a take-up roll passing through a series of deposition areas between the two rolls. Regardless of whether the PV material was produced in a roll processing process or by some other technique, the material is then cut into cells of any size and subsequently joined together. Alternatively, various layers of the deposited material may be etched or otherwise split during manufacture. Additional details regarding the composition and manufacture of thin film PV cells of a type suitable for use with the methods and devices disclosed herein are disclosed, for example, in US Pat U.S. Patent No. 7,194,197 by Wendt et al., Application No. 12 / 424,497, filed April 15, 2009, and Application No. 12 / 397,846, filed March 4, 2009. These references are hereby incorporated into the present disclosure by this reference for all purposes

1 FIG. 12 shows an exemplary process for making a PV cell or PV module having a backside protective layer structure in a continuous roll-to-roll motion in accordance with the present invention. It will be understood by those skilled in the art that, even though continuous roll-to-roll motion processing is employed in the described embodiment, non-roll processing may be used equally efficiently.

1 shows two rollers left and right 10 . 12 , which symbolize multiple roll processing stages in continuous motion used in the manufacture of this new type of PV module. The role 10 represents an output roll, and the roll 12 a pickup roll. It is clear that the roles 10 . 12 representative of the different dispensing and take-up rollers used in different isolated processing chambers. Thus, there are typically multiple dispensing and picking roles that will be used throughout the process.

An extended, flat area of an elongate strip of thin, flexible substrate material 14 that is between the roles 10 . 12 extends is shown. This substrate strip has various numbers of applied (deposited) PV cell layer structures at different positions between the rollers. The strip has opposite end windings which act as wraps on the delivery roller 10 and the pickup roll 12 are distributed. The direction of movement of the strip material during processing is generally indicated by the arrow 16 displayed. Curved arrows 18 . 20 symbolically show the associated direction of rotation of the rollers 10 . 12 around axes 10a . 12a , which are generally perpendicular to the level of 1 lie.

A reference to the substrate strip material 14 It should be understood herein as referring to a strip of material whose overall structural character changes as the material changes according to the processing steps between the rolls 10 and 12 moves forward. During the processing steps, layers of various components that go into the production of the PV module are added.

Nine separate, individual processing chambers 22 . 24 . 26 . 23 . 25 . 27 . 28 . 30 . 29 are as rectangular blocks in 1 shown. The various layers of material used to form a PV module according to this invention are applied or changed in these chambers. The relative size of this in 1 shown blocks is unimportant. It should be noted that the steps represented by some of the processing chambers are optional in some applications. For example, an i-ZnO layer may be present in the chamber 28 are omitted, and / or additional steps may be added in some applications.

The processing begins with a bare starter roll, or strip, of elongated flexible thin film substrate material coming from the output roll 10 is supplied. The uncoated material may have a width of about 33 cm, a thickness of about 0.005 cm and a length of up to 300 m. The width, thickness and length dimensions are of course selectable, depending on the final intended application for the finished PV modules. The substrate may comprise PI, any high temperature polymer or a thin metal such as stainless steel, titanium, kovar, invar, tantalum, brass or niobium, etc.

A stress-conforming metal interlayer, for example Ni-V, selected to have thermal expansion properties between those of the substrate and subsequently applied layers may optionally be used as the first layer deposited on the substrate. This step is in 1 not shown, but can either be in a chamber of similar construction as the chamber 22 or within a separate processing zone in the chamber 22 be performed.

Inside the chamber 22 can have two or more layers on opposite sides or faces of the substrate 32 be formed. These two layers are on the opposite surfaces (top and bottom in 1 ) of a section 32 at 34 . 36 over the chamber 22 shown. The layer 34 forms a back contact layer for the PV module of the present disclosure. The layer 34 may contain molybdenum or, in the case of a strip of stainless steel substrate, the back molybdenum contact layer may be replaced with a Cr / Mo double layer.

The layer 36 forms a backside protective layer structure according to the present disclosure. The backside protective layer structure 36 may include a corrosion resistant material, such as a Mo-X alloy. Additionally and / or alternatively, the backside protective layer structure 36 According to the present disclosure, comprising more than one layer, which is referred to as a double layer, wherein one or more of the layers comprises a corrosion resistant material. For example, the backside protective layer structure 36 comprise a Cr / Mo double layer.

The back contact layer 34 and the backside protective layer structure 36 can be applied by sputtering and / or can be in the same chamber 22 within separate processing zones be applied and / or can be applied in separate chambers. Remarkable properties of the layers 34 . 36 include: (a) that each of the layers adheres firmly to the associated substrate strip surface; and (b) these layers are capable of withstanding temperature variations that occur in subsequent processing without suffering cracks or breaks due to temperature. In addition, the layers can 34 . 36 , arranged as they are on the opposite surfaces of the substrate strip material, mechanically "balance" each other to prevent curling of the product or "out of plane" bending. Such bending could be a problem and / or inconvenience if only a single layer on one side were used. For example, the induced internal compression in a single molybdenum layer - without the counterbalancing effect of the opposite layer - would be sufficient to roll the substrate to the diameter of a pen.

That from the chamber 22 leaking material is ready to enter the chamber 24 to be introduced, wherein an absorber layer 38 how to form a p-type semiconductor in the form of copper-indium-gallium-diselenide (CIGS) or its permissible equivalent, copper-indium-diselenide (CIS), for example via simultaneous deposition processes occurring in the fog environment, the in the chamber 24 exists, take place.

In the chamber 26 becomes a window or buffer layer in the form of cadmium sulphide (CdS) as a layer 40 applied across the CIGS or CIS layer in the chamber 24 was trained. The CdS layer is preferably applied in a non-wet manner by radio frequency sputtering. This results in an overall multi-layered structure, as generally over the chamber 26 is shown.

After the deposition of Mo, CIGS and CdS, the strip continues through a sequence of operations 23 . 25 . 27 to first divide areas, and then subsequently serially connect adjacent "shared" areas. The first process is to scrape all the deposited layers to expose bare uncoated substrate. This first scoring expediently divides the elongate strip of deposited layers into individual segments and thereby electrically isolates each segment. These segments are held together by the substrate, which remains intact. The scribing technique used can be chosen freely, the method preferred here being achieved using a high power density laser.

Immediately after the first scoring operation, a second selective scoring operation is performed to remove the CdS and CIGS layers, but the molybdenum is left intact in the as-deposited states. This selective scoring forms a passage or channel which is later filled with conductive oxide.

In order to prevent the conductive oxide in the upper contact layer from being filled into the first groove, Mo / CIGS / CdS, thereby rejoining adjacent shared Mo regions, the gap must be filled with an insulator. Preferably, this is achieved by means of a UV-curable ink, in the process 27 is deposited with a commercially available matched inkjet ejection head which coincides with the high power density laser.

If the optional, electrically insulating, intrinsic zinc oxide i-ZnO layer is used, then it will be in the processing chamber 28 made to create a layer arrangement as it is above the chamber 28 is shown. In this layer arrangement, the i-ZnO layer is at 42 shown superimposing the CdS layer.

An upper contact layer in the form of a transparent overlayer 44 Conductive oxide, such as an ITO or ZnO: Al layer, is deposited in the processing chamber 30 trained, either directly on the CdS layer 40 if no i-ZnO layer is used, or directly on the i-ZnO layer 42 , if available. The resulting composite layered structure is generally above the chamber 30 in 1 shown.

When an insulating i-ZnO layer, such as the layer 42 , the resulting overall layer structure comprises what will be referred to later as a sandwich substructure, generally indicated by the arrows 46 in 1 is shown. The substructure 46 includes the i-ZnO layer disposed between the CdS layer and the ZnO: Al layer. Thus, if such a sandwich substructure is utilized, then a continuous protective interlayer (i-ZnO) is provided between the CIGS / CIS layer and the upper contact layer 44 is arranged.

1 and 2 12 show cross-sectional views (not to scale) of a portion of the exemplary PV cells according to the present disclosure, including successive layers deposited on a first side of a carrier substrate and a backside protective layer structure deposited adjacent to a second side of the carrier substrate.

Generally, thin film PV cells according to the present disclosure may be based on solid or flexible substrates. Solid glass substrates are relatively inexpensive, generally have a coefficient of thermal expansion that fits relatively precisely to the CIGS or other absorber layers, and allow the use of vacuum deposition systems. However, comparing the technology options that are applicable during the deposition process, solid substrates have several disadvantages in processing, such as the need for a significant footprint for processing equipment and storage, expensive and specialized equipment for uniform heating of glass to elevated temperatures up to or near the glass annealing temperature, a high potential of breakage of the substrate with the resulting production losses, and a higher heat output with the consequent higher power costs for the heating of the glass. In addition, solid substrates require increased shipping costs due to the weight and sensitivity of the glass. Thus, the use of glass substrates for the deposition of thin films is not the best choice for the low-cost, large-scale, high-yield, commercial production of multilayer, functional thin-film materials, such as photovoltaics.

Suitable flexible substrate materials include, for example, a high temperature polymer such as polyimide, or a flexible metal foil (stainless steel foil, titanium foil, aluminum foil or others) or thin metal such as stainless steel, aluminum or titanium, and the like. a. For example, a flexible stainless steel substrate may have a thickness of the order of 0.025 mm (25 microns), while all other layers of the cell may have a combined thickness of the order of 0.002 mm (2 microns) or less. In the case of the flexible substrates, the production of the PV cells can be carried out by means of roll processing. In addition to being able to perform roll processing, flexible substrates may have certain advantages over solid substrates. For example, roll processing of thin, flexible substrates allows the use of compact, lower-cost vacuum systems and non-specialized equipment already developed for other thin-film industrial applications. In addition, flexible substrate materials inherently have a lower heat capacity than glass so that the amount of energy required to raise the temperature is minimized. Flexible substrates also offer a relatively high tolerance to rapid heating and cooling and large thermal gradients, resulting in a low likelihood of breakage or failure during processing.

Furthermore, once the active PV materials are deposited on the flexible substrate materials, the resulting uncoated cells or cell rows may be transported to another factory for lamination and / or assembly into flexible or solid solar modules. This strategic option reduces transportation costs (such as lightweight flexible substrates as opposed to glass) and also enables the development of partner companies to complete and distribute PV modules around the world. Notwithstanding the potential benefits of using flexible substrates for thin film PV cells, the present disclosure relates to improving the corrosion resistance of PV cells based on flexible as well as solid substrates.

A photovoltaic layer structure according to the present disclosure may comprise successive layers, including at least one contact layer disposed adjacent to a first side of the substrate, a p-type semiconductor layer disposed on the first side of the substrate, and / or an n-type layer. Semiconductor layer disposed on the first side of the substrate. The photovoltaic layer structure may be deposited on the substrate of a PV cell in individual processing chambers by various processes such as sputtering, sputtering, vacuum deposition, and / or printing. The exact thickness of each layer depends on the exact choice of materials and the particular deposition process chosen for the formation of each layer. Further details regarding these layers, including possible specific layer materials, layer thicknesses and suitable application processes for each layer, are e.g. In the U.S. Patent No. 7,194,197 described.

In particular, the semiconductor material copper-indium-gallium-diselenite (CIGS) is stable, has low toxicity, and is actually thin-layered, requiring less than 2 microns of thickness in a functional PV cell. Other semiconductor variants for thin film PV technology include copper indium diselenite, copper indium disulfide, copper indium aluminum diselenite, and cadmium telluride.

4 FIG. 12 is a cross-sectional view of a portion of an exemplary monolithically integrated thin film photovoltaic module, generally incorporated with FIG 200 and shows a portion of the terminology commonly used to describe structuring typically included in monolithic integration schemes. More specifically shows 4 a region of a first PV cell 202 , a second PV cell 204 and an area of a third cell 206 monolithic on a substrate 208 were integrated. To a monolithic integrated module 200 to form a lower electrode layer 210 on the substrate 208 and then patterned as shown at P1 to divide the bottom electrode into discrete sections. The pattern P1 (and subsequent patterns described later) results from the removal of parts of the material, e.g. By etching, scribing, lasers and / or any other suitable method.

An active PV layer 212 , typically with a pn-type semiconductor junction or similar semiconductor pad, is then deposited on top of the bottom electrode layer and within the pattern P1. The pattern P2 then provides a connection path or path between the electrodes. An upper electrode layer 214 then goes over the active PV layer 212 and also arranged within the pattern P2. The upper electrode 214 is then patterned as shown at P3 by selectively removing material from the top electrode to divide it into discrete sections. This isolates the cells and completes their production into a series connection structure.

The connection between the upper electrode 214 and the lower electrode 210 within the pattern P2 can be endangered by corrosion at the interface of the two electrodes. According to the present teaching, this corrosion may be due to the use of a corrosion resistant molybdenum alloy (Mo-X) for the design of the lower electrode 210 or at least those areas of the lower electrode in the vicinity of the pattern P2 are reduced. As described below, it has been found that the use of Mo-X alloys provides better corrosion resistance than molybdenum alone or other non-alloy metals heretofore used for the lower electrode.

Referring again to 2 may be a thin-film PV cell according to the present disclosure, generally with 50 denotes a carrier substrate 52 with a first page 54 and a second page 56 include. A photovoltaic layer structure 58 can on the first page 54 of the substrate, and a backside protective layer structure 60 may be adjacent to the second page 56 of the substrate 52 be arranged. The backside protective layer structure 60 can be a corrosion protection layer 62 include and can provide corrosion protection for the substrate 52 and / or the PV cell 50 provide.

The photovoltaic layer structure deposited on the first side of the substrate may include one or more backside contact layers 64 such as Mo or Cr / Mo; an absorber layer 66 or layers of a material such as copper indium diselenide, copper indium disulfide, copper indium aluminum diselenide or copper indium gallium diselenide (CIGS); a buffer layer 68 or layers such as a layer of cadmium sulfide (CdS); an i-ZnO layer 70 and an upper electrode layer 72 , such as a transparent conductive oxide (TCO). In addition, typically a conductive current collection grid (not shown), which may be comprised primarily of silver (Ag) or other conductive metal, is deposited over the TCO layer.

As previously described, a PV cell having a backside protective layer deposited adjacent to the second side of the substrate may comprise a corrosion resistant material and may provide corrosion protection for the PV cell. According to the present disclosure, the PV cell comprises 50 a backside protective layer structure 60 , The backside protective layer structure 60 can be a layer 62 with a corrosion protection material. The layer 62 can be directly adjacent to the second page 56 of the substrate 52 be deposited. Alternatively, an intermediate layer (not shown) may be interposed between the layer 62 and the second side of the substrate.

The layer 62 may include a corrosion resistant material, such as a Mo-X alloy. Various Mo-X alloys or a combination of several different Mo-X alloys can be used to resist corrosion. For example, dual, triple or multiple component films may be used as Mo-X molybdenum alloy. The additional element (or elements) X can be selected from Groups IVb, Vb, IIIA and / or IVA of the Periodic Table of the Elements (PSE), and Ti, Zr, Hf, V, Nb, Ta, Al and Si may be particularly suitable. In some embodiments, it may be desirable for the alloying partner to form a mixed crystal with the molybdenum matrix for reasons of production process integration and feasibility. Furthermore, it may be preferred in some embodiments that the free reaction enthalpy for the Forming the oxide state forms of the alloying partner or the alloying partner is higher than the free reaction enthalpy of the molybdenum itself, so that the alloying partner preferably corrodes.

The alloy may be selected to have a small total line resistance, so that the increase in electrical line resistance due to alloying is kept to a minimum by selecting a small amount of the alloying element. For example, the amount of alloying element (i.e., atomic concentration) may be chosen to be below 25%, or even below 10%. The Mo-X alloy can be formed by any type of thin film deposition process, such as sputtering, sputtering, chemical vapor deposition, laser ablation, chemical solution deposition, spray deposition, thin film reaction processes, implantation of an alloying partner, or other combined thin film fabrication processes.

The back side of the substrate can be relatively easily corroded when exposed to moisture if it is coated with a single backside layer consisting of pure Mo only. A backside protective layer deposited on the second side of the substrate according to the present disclosure can provide improved corrosion resistance to a backside Mo-only layer and thus better protection for the second side of the substrate. 5 FIG. 12 is a graph comparing the electrical resistance of a thin layer of Mo and a thin layer of molybdenum-tantalum (MoTa) as a function of hours of wet heat soak duration according to aspects of the present disclosure. FIG. The electrical resistance was measured by means of a 4-point test setup. As 5 The surface resistivity of the Mo thin film sample dramatically increases after only about 100 hours in a wet heat (DH) test environment, while the sputtered MoTa film shows very high corrosion resistance, and no significant increase in sheet resistance was observed. The atomic content of Ta for the in 5 MoTa sample shown was 5% (Mo95Ta5).

As a further indication of the corrosion resistance of Mo-X alloys, the table below compares the visual appearance of the sputtered samples of Mo and MoTa after various periods of wet heat (DH) exposure in accordance with the aspects of the present disclosure. DH time (hours) Not a word MoTa 0 Metallic, shiny Metallic, shiny 24 Metallic, single spots Metallic, shiny 95 corroded Metallic, shiny, few spots, spots mainly on the edge 120 Heavily corroded Metallic, shiny, few spots, spots mainly on the edge 147 Heavily corroded Metallic, shiny, few spots, spots mainly on the edge

As if from a comparison of 5 With the table, the increase in electrical resistance is largely consistent with the color change and visible corrosion of the samples. It is believed that the surface of the Mo layer is converted into highly insulating MoO3 while the MoTa alloy successfully prevents the formation of a corroded MoOx insulating layer. This allows the solar cell contacts to be exposed to an environment containing moisture for a long period of time without experiencing deterioration of the connection resistance.

Additionally and / or alternatively, a thin film PV cell according to the present disclosure, generally with 100 with reference to again 3 , a carrier substrate 102 with a first page 104 and a second page 106 include. A photovoltaic layer structure 108 that on the first page 104 of the substrate, and a backside protective layer structure 110 can be adjacent to the second page 106 be arranged of the substrate. The protective layer structure 110 can be a first layer 111 adjacent to the second page 106 and a second layer 112 adjacent to the first layer 110 include. The first layer and / or the second layer may be corrosion resistant. Furthermore, the first layer 110 serve to put stress on the substrate 102 decrease by being relatively smooth and flat and may promote adhesion of the second layer. In some embodiments, the first layer 110 Chromium (Cr) included and the second layer 112 can contain Mo

The photovoltaic layer structure 108 that on the first page 104 of the substrate may be one or more backside contact layers 114 , z. From Mo or Cr / Mo ( 114a / 114b ), an absorber layer 116 or layers of a material such as copper indium diselenide, copper indium disulfide, copper indium aluminum diselenide, or copper indium gallium diselenide (CIGS), a buffer layer 218 or layers such as a layer of cadmium sulfide (CdS), an i-ZnO layer 219 and an upper electrode layer 220 , z. Transparent transparent oxide (TCO). Furthermore, typically a conductive current collecting grid (not shown) made primarily of silver (Ag) or other conductive metal is deposited over the TCO layer.

A protective layer structure having two layers may have a thickness in the range of about 70 nm to 1300 nm, wherein a first layer, for. B. a Cr layer, a thickness in the range of about 20 nm to 300 nm, and a second layer, such as. B. a Mo layer, a thickness in the range of about 50 nm to 1000 nm may have.

The back contact layer may generally have a thickness in the range of about 220 nm to 1300 nm, wherein a chromium layer has a thickness in the range of about 20 nm to 300 nm and a molybdenum layer has a thickness in a range of about 200 nm to 1000 nm. The sputtering powers can be between 5.5 kW and 8.5 kW and / or the working pressures can be between 4 mT and 8 mT. For example, a second layer can be sputtered with Mo at 7.5 kW and a working pressure of 6 mTorr.

Although the exact thickness of each layer of a thin film PV cell depends on the exact choice of materials and the particular deposition process chosen for the formation of each layer, exemplary materials, thicknesses and methods for applying each layer are as described above the PV cell 100 as set forth below, in the typical order of application of each layer to the substrate 102 : Description of the layer Exemplary material Exemplary thickness Exemplary method of application Back protection layer structure Cr / Mo 130 nm sputtering substratum stainless steel 25 μm Not applicable (base material) Back double contact layer Cr / Mo 320 nm sputtering absorber CIGS 1700 nm steaming buffer CdS 80 nm Chemical deposition Front electrode TCO 250 nm sputtering collecting grid Ag 40 μm To Print

Accordingly, a Cr / Mo bilayer applied as a backside protective layer coating can provide greater corrosion resistance to the back side of the substrate than a pure Mo back layer. Corrosion testing of substrate elements coated with back Cr / Mo protective bilayers of various thicknesses support this inference.

The various structural components disclosed herein may be constructed of any suitable material or combination of materials, e.g. As metal, plastic, nylon, plastic, rubber or other materials with sufficient structural strength to withstand the stresses occurring during use. Materials can be selected based on durability, flexibility, weight, and / or aesthetic qualities.

It is believed that the following claims set forth, in particular, certain combinations and sub-combinations that are directed to one of the disclosed inventions, are novel and not obvious. Inventions found in other combinations and subcombinations of characteristics, Functions, elements and / or properties may be claimed by supplementing the present claims or presenting new claims in this or a related application. Such modified or novel claims, whether directed to another invention or the same invention, and whether different, broader, narrower, equal to or more limited in scope of the original claims, are also considered within the scope of the inventions of the present disclosure.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 7194197 [0019, 0042]

Claims (19)

Thin-film photovoltaic cell, comprising: a carrier substrate having a first side and a second side, a contact layer disposed on the first side of the substrate, an absorber layer disposed on the first side of the substrate, a buffer layer disposed on the first side of the substrate, and a backside protective layer on the second side of the substrate, the backside protective layered structure comprising a corrosion resistant material. The thin film photovoltaic cell of claim 1, wherein the backside layer comprises at least a first layer and a second layer. The thin film photovoltaic cell of claim 2, wherein the first layer comprises chromium. The thin film photovoltaic cell of claim 3, wherein the first layer comprising chromium is disposed directly adjacent to the second side of the substrate. The thin film photovoltaic cell of claim 2, wherein the second layer comprises the same material contained in the contact layer on the first side of the substrate. The thin film photovoltaic cell of claim 1, wherein the substrate comprises molybdenum deposited on the first side and the second side of the substrate. The thin film photovoltaic cell of claim 1, wherein the contact layer comprises a layer containing chromium disposed adjacent to the first side of the substrate and a layer containing molybdenum disposed adjacent to the chromium contact layer. The thin-film photovoltaic cell of claim 1, wherein the backside layer has a thickness of 150 nm to 275 nm. The thin film photovoltaic cell of claim 1, wherein the backside layer comprises a molybdenum alloy. The thin film photovoltaic cell of claim 9, wherein the molybdenum alloy comprises an alloying partner selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Al, and Si. The thin film photovoltaic cell of claim 9, wherein the atomic concentration of the alloying partner is less than 25%. The thin-film photovoltaic cell according to claim 11, wherein the atomic concentration of the alloying partner is less than 10%. A method of making a flexible thin film photovoltaic (PV) structure, comprising: Providing a carrier substrate having a first side and a second side, applying a photovoltaic layer on the first side of the substrate, and Depositing a backside protective layer on the second side of the substrate, the backside protective layer comprising a corrosion resistant material. The method of claim 13, wherein applying the backside protective layer comprises applying at least two layers, wherein one of the at least two layers comprises molybdenum (Mo). The method of claim 14, wherein one of the at least two layers comprises chromium (Cr), the step of applying a backside protective layer comprises forming the layer containing chromium directly adjacent to the substrate and forming a layer containing molybdenum (Mo) , directly adjacent to the chromium-containing layer. The method of claim 14, wherein applying a backside protective layer comprises applying a first layer and a second layer having a thickness ratio of 1: 2. The method of claim 13, wherein applying the backside protective layer comprises applying a molybdenum alloy layer. The method of claim 17, wherein the molybdenum alloy comprises an alloying partner selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Al and Si. The method of claim 17, wherein the molybdenum alloy comprises at least one alloying partner selected from Groups IVb, Vb, IIIA and IVA of the Periodic Table.

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