ROLL-TO-ROLL ELECTROPLATING PHOTOVOLTAIC FILMS

Abstract

The present invention provides methods of electroplating a film or films onto a top surface of a continuously moving roll-to-roll sheet. In one aspect, the invention includes continuously electroplating a film onto a conductive surface using an electroplating unit as the roll-to-roll sheet moves therethrough.

Description

BACKGROUND

1. Field of the Invention

The present invention relates to methods and apparatus for preparing thin films of Group IBIIIAVIA compound semiconductor films, and more specifically to electroplating of Group IBIIIAVIA compound semiconductor films, for photovoltaic devices.

2. Description of the Related Art

Solar cells are photovoltaic (PV) devices that convert sunlight directly into electrical energy. Solar cells can be based on crystalline silicon or thin films of various semiconductor materials that are usually deposited on low-cost substrates, such as glass, plastic, or stainless steel.

Thin film based photovoltaic cells, such as amorphous silicon, cadmium telluride, copper indium diselenide or copper indium gallium diselenide based solar cells, offer improved cost advantages by employing deposition techniques widely used in the thin film industry. Group IBIIIAVIA compound photovoltaic cells, including copper indium gallium diselenide (CIGS) based solar cells, have demonstrated the greatest potential for high performance, high efficiency, and low cost thin film PV products.

As illustrated in FIG. 1, a conventional Group IBIIIAVIA compound solar cell 10 can be built on a substrate 11 that can be a sheet of glass, a sheet of metal, an insulating foil or web, or a conductive foil or web. A contact layer 12 such as a molybdenum (Mo) film is deposited on the substrate as the back electrode of the solar cell. An absorber thin film 14 including a material in the family of Cu(In,Ga)(S,Se)₂ is formed on the conductive Mo film. The substrate 11 and the contact layer 12 form a base layer 13. Although there are other methods, Cu(In,Ga)(S,Se)₂ type compound thin films are typically formed by a two-stage process where the components (components being Cu, In, Ga, Se and S) of the Cu(In,Ga)(S,Se)₂ material are first deposited onto the substrate or a contact layer formed on the substrate as an absorber precursor, and are then reacted with S and/or Se in a high temperature annealing process.

After the absorber film 14 is formed, a transparent layer 15, for example, a CdS film, a ZnO film or a CdS/ZnO film-stack, is formed on the absorber film 14. Light enters the solar cell 10 through the transparent layer 15 in the direction of the arrows 16. The preferred electrical type of the absorber film is p-type, and the preferred electrical type of the transparent layer is n-type. However, an n-type absorber and a p-type window layer can also be formed. The above described conventional device structure is called a substrate-type structure. In the substrate-type structure light enters the device from the transparent layer side as shown in FIG. 1. A so called superstrate-type structure can also be formed by depositing a transparent conductive layer on a transparent superstrate, such as glass or transparent polymeric foil, and then depositing the Cu(In,Ga)(S,Se)₂ absorber film, and finally forming an ohmic contact to the device by a conductive layer. In the superstrate-type structure light enters the device from the transparent superstrate side.

Contrary to CIGS and amorphous silicon cells, which are fabricated on conductive substrates such as aluminum or stainless steel foils, standard silicon solar cells are not deposited or formed on a protective sheet. Such solar cells are separately manufactured, and the manufactured solar cells are electrically interconnected by a stringing or shingling process to form solar cell circuits. In the stringing or shingling process, the (+) terminal of one cell is typically electrically connected to the (−) terminal of the adjacent solar cell. Circuits may then be packaged in protective packages to form modules. Each module typically includes a plurality of strings of solar cells which are electrically connected to one another.

In a thin film solar cell employing a Group IBIIIAVIA compound absorber, the cell efficiency is a strong function of the molar ratio of IB/IIIA. If there are more than one Group IIIA materials in the composition, the relative amounts or molar ratios of these IIIA elements also affect the properties. For a Cu(In,Ga)(S,Se)₂ absorber layer, for example, the efficiency of the device is a function of the molar ratio of Cu/(In+Ga). Furthermore, some of the important parameters of the cell, such as its open circuit voltage, short circuit current and fill factor, vary with the molar ratio of the IIIA elements, i.e. the Ga/(Ga+In) molar ratio. In general, for good device performance the Cu/(In+Ga) molar ratio is kept at around or below 1.0. On the other hand, as the Ga/(Ga+In) molar ratio increases, the optical bandgap of the absorber layer increases and therefore the open circuit voltage of the solar cell increases while the short circuit current typically may decrease. It is important for a thin film deposition process to have the capability of controlling both the molar ratio of IB/IIIA, and the molar ratios of the Group IIIA components in the composition.

In two-step deposition techniques, which involve deposition of sub-layers to form a precursor film and then reaction of the precursor film to form the compound absorber layer, individual thicknesses of the sub-layers forming the stacked precursor film layer need to be well controlled. The thicknesses of these layers influence the final stoichiometry or composition of the compound layer after the reaction step.

Deposition or growth of layers forming a thin film solar cell in a roll-to-roll or in-line process is attractive for the higher throughput, lower cost and better yield of such approaches. There is still a need to develop roll-to-roll or in-line deposition techniques for the growth of Group IBIIIAVIA materials wherein the critical IB/IIIA molar ratio as well as the IIIA material composition are tightly controlled.

SUMMARY OF THE INVENTION

The present invention provides methods and apparatus for electroplating a film or films onto a top surface of a continuously moving roll-to-roll sheet.

In one aspect, the invention includes continuously electroplating a film onto a conductive surface using an electroplating unit as the roll-to-roll sheet moves therethrough.

In one aspect, the aforementioned needs are satisfied by the present invention which in one embodiment comprises an electrodeposition apparatus for electrodepositing a material film from an electrodeposition solution onto a front surface of a flexible workpiece as the flexible workpiece is advanced through the apparatus in a roll to roll manner. In this embodiment, the apparatus comprises an electrodeposition unit to electrodeposit the material film onto the front surface of the flexible workpiece as the flexible workpiece is advanced through the electrodeposition unit. In this embodiment, the electroplating unit comprises a solution chamber having a peripheral wall configured for retaining the electrodeposition solution at a predetermined level and at least one solution inlet to receive a first flow of the electrodeposition solution wherein the at least one solution inlet is positioned adjacent an upper end of the peripheral wall and below the predetermined level of the electrodeposition solution. In this embodiment, the apparatus includes at least one flow regulator attached to the at least one solution inlet to transform the first flow into a second flow of the electrodeposition solution and deliver the second flow into the solution chamber. The chamber further includes an entrance opening and an exit opening positioned at a lower end of the peripheral wall so that the flexible workpiece is advanced through the electrodeposition solution by entering from entrance opening and exiting through the exit opening of the solution chamber. In this embodiment, the chamber further includes an anode plate positioned in the solution chamber and between the flexible workpiece and the at least one solution inlet, wherein the front surface of the flexible workpiece is positioned across from the anode plate as the flexible workpiece is advanced through the solution chamber. In this embodiment, the apparatus includes a support mechanism to support the flexible workpiece within the solution chamber as the flexible workpiece is advanced therethrough. In this implementation, the support mechanism comprising a first support member positioned outside the solution chamber and adjacent the entrance opening, the first support member including a first roller contacting a back surface along the width of the flexible workpiece. The support member further includes a second roller having end portions and a central portion, wherein the end portions contact only edge regions of the front surface, and wherein the central portion extend over a selected region located between the edge regions while not contacting the selected region thereby forming a first gap between a surface of the selected region and the central portion of the second roller, wherein a first leak flow leaking through the entrance opening is flowed out through the first gap of the first support member. In this implementation, the support mechanism includes a second support member positioned outside the solution enclosure and adjacent the exit opening, the second support member including a first roller contacting a back surface along the width of the flexible workpiece, and a second roller having end portions and a central portion, wherein the end portions contact only the edge regions of the front surface, and wherein the central portion extend over the selected region located between the edge regions while not contacting the selected region thereby forming a second gap between the surface of the selected region and the central portion of the second roller, wherein a second leak flow leaking through the exit opening is flowed out through the second gap of the second support member.

In another aspect the aforementioned needs are satisfied by the present invention which in one embodiment comprises an electrodeposition system for depositing material film on a continuous moving web. In this embodiment, the system comprises a chamber that defines an inner volume that receives an electrodeposition solution. The chamber has a first and a second end, and wherein the chamber includes a first and a second web opening adjacent a first end of the chamber so that the web can be transported through the chamber between the first and the second web openings. In this implementation, an anode positioned in a first location within the chamber, wherein a portion of the web that is positioned between the first and second web openings defines a cathode that corresponds to the anode so that electrical potential therebetween results in electrodeposition of the film on the web as the web moves through the chamber. In this implementation, the embodiment further comprises a solution supply system that provides solution to the chamber to replace solution that is lost or removed from the chamber, wherein the solution supply system includes a flow regulator that reduces the pressure of the solution being provided to the chamber so as to reduce the turbulence of the electrodeposition solution adjacent the cathode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a thin film solar cell including a Group IBIIIAIVA compound absorber layer;

FIG. 2A is a schematic view of an embodiment of an electrodeposition apparatus processing a continuous flexible workpiece;

FIG. 2B is a schematic side view of the electrodeposition apparatus shown in FIG. 2A, which includes an embodiment of a flow regulator;

FIG. 3 is a schematic top view of the electrodeposition apparatus including another embodiment of a flow regulator;

FIGS. 4-6 are schematic views of a workpiece support member of the electrodeposition apparatus, wherein the support member has been supporting the continuous flexible workpiece during a roll-to-roll electrodeposition process;

FIG. 7A is a schematic view of an embodiment of an electrodeposition apparatus including an embodiment of a support assembly supporting the continuous flexible workpiece horizontally;

FIG. 7B is a schematic view of an embodiment of an electrodeposition apparatus including another embodiment of a support assembly supporting the continuous flexible workpiece in an angled manner;

FIG. 8A is a schematic view of an embodiment of a roll-to-roll electrodeposition system; and

FIG. 8B is a schematic view of another embodiment of a roll-to-roll electrodeposition system.

DETAILED DESCRIPTION

Various embodiments of the present invention provide methods and apparatus to electrodeposit films or layers on continuous flexible substrates or bases, which may be used in the formation of CIGS(S) type absorber layers for photovoltaic cells, through a roll-to-roll processing technique, which is also called reel-to-reel or web processing. Various embodiments of the present invention may be used for the electrodeposition of Group IB and Group IIIA materials and optionally Group VIA materials on a continuous flexible base to form precursor layers which are then converted into Group IBIIIAVIA compound absorber layers by annealing at elevated temperatures, optionally in presence of additional Group VIA material or materials. Electrodeposition of Group IB, Group IIIA and Group VIA materials may be performed by a roll-to-roll system wherein layers or sub-layers of Group IB-containing, Group IIIA-containing and Group VIA-containing materials are deposited onto the base consecutively, one after another, at a pre-determined sequence.

In one implementation, a roll-to-roll electrodeposition system including one or more electrodeposition units may form a precursor stack comprising Cu, and at least one of In and Ga on a continuous flexible workpiece or web with substantial thickness control and uniformity. The electrodeposition units may comprise at least one Cu electrodeposition unit, and at least one of a Ga electrodeposition unit and at least one In electrodeposition unit, and optionally a Se electrodeposition unit. There may be integrated cleaning or cleaning/drying stations before and/or after each electrodeposition unit so as to clean any chemical residues on the continuous flexible workpiece. The continuous flexible workpiece is supplied from a supply roll, advanced through each electrodeposition unit and other units and taken up and wound as a receiving roll with the desired structure. The number and order of the electrodeposition units may be changed to deposit various precursor stacks comprising Cu, In, Ga and optionally Se from electrolytes containing these elements on the continuous flexible workpiece. For example, if there are Cu, In and Ga electrodeposition units in the roll-to-roll system, a Cu/In/Ga precursor stack can be formed on the continuous flexible workpiece by advancing it through the electrodeposition units. With multiple runs, the number of deposited films can be increased. Changing the order of electrodeposition units and optionally adding other electrodeposition units such as a Se electrodeposition unit, one may obtain stacks such as Cu/Ga/In, In/Cu/Ga, Ga/Cu/In, Cu/Ga/Cu/In, Cu/Ga/Cu/In/Cu, Cu/In/Cu/Ga, Cu/In/Cu/Ga/Cu, Cu/In/Ga/Se, In/Cu/Ga/Se, Ga/Cu/In/Se, Cu/Ga/Cu/In/Se, Cu/Ga/Cu/In/Cu/Se, Cu/In/Cu/Ga/Se, Cu/In/Cu/Ga/Cu/Se or other possible stack orders.

Alternatively, using one or more electrodeposition units of the present invention, alloy films including at least two of Cu, In, Ga and optionally Se may also be electrodeposited onto the continuous flexible workpiece from appropriate electrodeposition electrolytes. The composition of the precursor stack may be determined by changing the deposition sequence and the thickness of each film selected to attain a targeted Cu/(Ga+In) molar ratio and a Ga/(Ga+In) molar ratio in the resulting CIGS absorber. The precursor electrodeposition may be completed in a reduced number of steps using binary, ternary and quaternary electrodeposition solution formulations. In one embodiment, the entire CIGS precursor may be electrodeposited in a single step process using a quaternary electrodeposition solution.

The continuous flexible workpiece may be a substrate including a metallic foil. The continuous flexible workpiece may be a 20-250 micrometers thick stainless steel foil, Mo foil, Ti foil, Al or Al-alloy foil. The continuous flexible workpiece may also include a contact layer or a conductive layer on the metallic foil substrate. The conductive layer, which establishes an ohmic contact between the substrate and subsequently formed absorber layer, may be in the form of a single layer or alternately a stack of various sub-layers. This layer establishes ohmic contact between the substrate diffusion barrier layer which prevents diffusion of impurities from the flexible foil substrate into the layers to be electrodeposited and into the CIGS(S) layer during its formation. Materials of the conductive film include but are not limited to Ti, Mo, Cr, Ta, W, Ru, Ir, Os, and compounds such as nitrides and oxy-nitrides of these materials. Preferably, the free surface of the conductive layer comprises at least one of Ru, Ir and Os for better nucleation of the electroplated layers. It will be appreciated that, in this application, the continuous flexible workpiece refers to a flexible foil and any conductive layer on its front surface including the contact layer and any other electrodeposited layers such as Cu, Ga, In, and optionally Se, layers and their possible binary, ternary and quaternary alloys.

FIGS. 2A and 2B show, in frontal and side schematic views respectively, an embodiment of an electrodeposition unit 100, or electrodeposition apparatus or electrodeposition cell, of the present invention for electrodepositing precursor films onto a continuous flexible workpiece 102, or workpiece hereinafter. The workpiece 102 has a rectangular sheet shape and has a width of 1-85 inches (in) and length of 4-200,000 in. The electrodeposition unit 100 includes a solution chamber or enclosure 104 to contain a process solution 106 or an electrodeposition electrolyte (solution hereinafter). This solution is used to deposit films of desired materials, such as Group IB, IIIA and VIA precursor materials, to form a Group IBIIIAVIA compound absorber for photovoltaic or solar cells. An anode 108, e.g., an anode plate, is immersed in the solution 106 held in the solution chamber 104, and the solution 106 is delivered to the solution chamber 104 through one or more solution inlets 110 located adjacent an upper end 104A of the solution chamber 104 and above the anode plate 108 and the workpiece 102. Additional solution outlets 112 are located above the solution inlets 110 which allows the excess solution to flow out of the solution chamber 104 thereby keeping the solution surface 107 or the top surface of the solution at a predetermined solution level. A lower end 104B of the solution chamber 104 includes an entrance opening 114A and an exit opening 114B to continuously advance the workpiece 102 through the solution chamber 104 and expose the electrodeposition conditions therein during the electrodeposition process.

The solution chamber 104 has a chamber wall 116 that defines the solution chamber 104 which is preferably made of corrosion resistant alloy, stainless steel or ceramic material, or more preferably made of polymeric materials such as polyvinyl chloride, polypropylene, polyethylene, polycarbonates and Teflon, and the like. In one embodiment the chamber wall 116 is made of a first side wall 116A, a second side wall 116B, a front wall 116C, and a back wall 116D all extending upwardly from a bottom wall 116E, thereby forming a cubic or rectangular prism shaped chamber wall.

Depending on the width of the workpiece, an exemplary solution chamber 104 of the electrodeposition unit 100 may have a length ranging from 2 to 200 in, a width ranging from 2 to 100 in and a height ranging from 3 to 40 in for the roll-to-roll electrodeposition applications. An exemplary solution chamber to process a 12 in wide workpiece may have a length of 4 to 30 in, a width of 13 to 18 in and a height of 8 to 20 inches. For a 40 in wide workpiece, the exemplary solution chamber may have a length of 4 to 50 in, a width of 40 to 46 in and a height of 10 to 20 in. Depending on its size, the solution chamber 104 may hold 10-120, preferably 18-25, gallons of electrodeposition solution 106 at any given time during the electrodeposition process. Depending on the materials in it, the electrodeposition solution 106 may have a density up to 2 g/cm³ and a viscosity up to 10 centipoise. During the process, the temperature of the solution 106 may be kept at a temperature range of 5-90° C., preferably 15-30 C.

As shown in FIGS. 2A-2B, a section of the workpiece 102 enters the solution chamber through the entrance opening 114A located adjacent the bottom of the first side wall 116A, travels through a horizontal plane in a process direction ‘P’, and leaves the solution chamber through the exit opening 114B located adjacent the bottom of the second side wall 116B. The process direction is parallel to the long edges of the rectangular shape workpiece. The entrance and exit openings 114A, 114B are aligned along a horizontal plane and may be shaped as rectangular slits with a width and height slightly larger than the width and height of the workpiece so as not to damage any electrodeposited layer on the front. In one example, the slit height may be in the range of 0.01-0.4 in, preferably 0.01-0.05 in.

A front surface 102A of the workpiece 102 faces towards the solution surface 107 and is parallel to the anode plate 108 placed between the workpiece and the solution inlets 110. In this configuration, during the electrodeposition process, when the workpiece 102 is cathodically polarized, deposition material within the solution 106 deposits on the front surface 107A of the workpiece 104 and forms a material film as described above. The workpiece portion in the solution chamber or at least a section of it forms the cathode. The anode plate 108 is aligned with respect to the front surface 102A of the workpiece 102 (cathode) such that the material selectively and uniformly deposits at a central region of the workpiece 102. Edge regions of the front surface may receive no depositing material or less depositing material than the central region that will be used to form photovoltaic cells. During the electrodeposition process, a roll-to-roll moving mechanism (not shown) moves the workpiece with a velocity in the range of 1-15 ft/minute, preferably 1-7 ft/minute in the direction of process direction ‘P’.

Depending on the dimensions of the solution chamber 104 and the front surface 102A of the workpiece 102 advancing through the solution chamber 104 at any given time, the anode plate 108 may have a surface area having a length of 4-98 in, preferably 14-28 in, and a width of 4-98 in, preferably 9-24 in. The anode plate may have thickness of 0.04-4 in. Instead of a single anode plate, multiple anodes plates with smaller size can alternatively be used. Both inert anodes, such as Pt, Ti, Pt coated Ti, Ir-oxide coated Ti, and the like, and metallic anodes which are anodes made of the metal to be plated, for example, Cu-anode for Cu electrodeposition, can be used. The metallic anode plates may be solid plates with no holes; however, the inert anodes may have through-holes. The distance between the surface of the anode plate 108 and the front surface 102A of the workpiece 102, which face one another, may be 0.1-20 in, preferably 0.2-4 in, depending on the height of the solution chamber.

A support mechanism is used to retain and move the workpiece 102 horizontally through the solution chamber 104. In this embodiment, the support mechanism comprises support members 120 such as a first support member 120A located adjacent the entrance opening 114A and a second support member 120B located adjacent the exit opening 114B. Both the first support member 120A and the second support member 120B include a front roller 121A partially contacting the front surface 102A, preferably the edge regions, of the front surface 102A (see FIG. 5) and a back roller 121B contacting a back surface 102B of the workpiece along its entire width so as to support the workpiece 102 before the entrance opening and after the exit opening as shown. The rotation axes of the front and back rollers 121A and 121B are transverse to the process direction ‘P’ and vertically aligned to be in the same vertical plane which is perpendicular to the horizontal plane of the workpiece 102 advancing through the solution chamber 104. The first and second rollers 121A and 121B of the first and second support members 120A and 120B have the same dimensions, and are installed and function in the same manner.

As shown in FIG. 2B, in this embodiment, the solution inlets 110 are connected to a solution reservoir (not shown) through fresh solution lines 110A to deliver the solution 106 to the solution chamber as a fresh solution, or first, flow 1F . Before the solution is delivered to the solution chamber 104, any gas such as oxygen, air, in the solution 106 may be removed by an appropriate degassing process. This enhances the flow characteristics of the first flow 1F. One or more flow regulators 111, such as an exemplary flow regulator 111A in this embodiment, may be attached to the solution inlet 110 and transforms the first flow 1F into a regulated, or second, flow 2F (depicted as a dotted arrow). The flow regulators 111 may also be referred to as solution distributors, sparges, diffusers or meshes. Solution outlets 112 may be connected to a replenishment tank (not shown) through used solution lines 112A to remove the solution 106 from the solution chamber as a used, or third, solution flow 3F which along with a fourth flow 4F described below, keeps the solution level at the predetermined solution level. The fresh solution flow 1F is greater than or equal to the used solution flow 3F. As shown in FIG. 2A, a solution 106 also outwardly leaks from the entrance opening 114A and exit opening 114B over the front surface portions as a fourth flow 4F. As will be described more fully below, the fourth flow 4F may be removed from the electrodeposition unit by flowing it through support members 120 and 122.

The exemplary flow regulators 111 may have a porous body to regulate the first flow 1F of the solution 106 and deliver it to the solution chamber as the second flow 2F. The flow regulator 111A shown in FIG. 2A may include channels or openings which may be distributed in many geometrical and symmetrical patterns. The flow regulator 111A regulates the first flow 1F into the second flow 2F by reducing its pressure while maintaining its high solution volume and controlling its direction. The solution inlet 110 and the flow regulator 111A may be positioned on the side wall 116D and the second flow may be flowed in the process direction ‘P’. The second flow 2F is a high flow rate and low velocity solution. The second solution 2F is preferably parallel to the horizontal plane of the front surface 102A of the workpiece 102.

FIG. 3 shows another embodiment of flow regulators 111B in a top view of the solution chamber 104 to evenly distribute the second flow 2F along the width of the solution chamber 104 by directing the second flow 2F substantially parallel to the workpiece length in a laminar fashion. The flow regulator 111B may be a porous body, such as a pipe, along the width of the chamber with openings or channels 113 to allow second flow 2F to flow out. In this embodiment, the flow regulator 111B may direct the second flow 2F parallel to the workpiece length direction or may be directed slightly upwards, towards the solution surface 107 (FIG. 2A). The second flow 2F may have flow rate in the range of 30-300 liters/minute, preferably 65-75 liters/minute. The second flow 2F may have a pressure in the range of 10-25 psi. The openings 113 of the flow regulator 111B may be distributed in many geometrical and symmetrical patterns. The flow regulator 111B regulates the second flow 2F by reducing its pressure while maintaining its high solution volume and controlling its direction parallel to the web length direction or slightly upwards towards the solution surface 107. In this embodiment the second flow 2F may be parallel to the length of the cathode or might be directed upwards with an angle less than 30 degrees, preferably less than 10 degrees. The distance between each flow regulator 111B and the surface of the workpiece 102 may be the same or varied depending on the process.

The second flow 2F created by the above described flow regulators 111 is a high flow rate and low velocity solution flow. The regulated and directional delivery of the electrodeposition supply solution, as the second flow 2F, is designed to be located a predetermined distance away from the cathode surface so that the turbulence or disturbance in the solution near the cathode surface is reduced, which in turn significantly improves deposition efficiency and deposition uniformity of the depositing film.

The described flow distribution system above is particularly useful for electrodeposition processes, which are desired to be operated under a diffusion controlled regime, requiring the establishment of an undisturbed or less disturbed diffusion boundary layer or region extending within the solution right above the cathode surface. In other words, ions to be reduced slowly travel or diffuse to the cathode where they are reduced to metal ions. However, the forces involved in the activity of inflowing fresh solution and out flowing used solution create turbulence or disturbance in the electrodeposition solution during the electrodeposition process and inhibit the formation of a uniform and thick diffusion boundary layer which is essential for a uniform deposition. An advancing workpiece within this solution may further aggravate this disturbance. When the deposition is not diffusion controlled, the cathode surface is saturated with ions to be reduced, which can cause dendritic growth and rough morphology. Surface coverage might also be compromised with growth mainly taking place only at electrochemically favorable locations rather than over the entire surface. Such faulty deposition behavior may especially be seen in electrodeposition of indium, gallium and selenium containing deposits if the electrodeposition is performed in more turbulent solutions.

Locating the flow regulators 111 away from the surface 102A of the workpiece 102 (cathode surface) and regulating the first flow 1F into the second flow 2F help to establish a laminar flow regime in the solution 106 in the solution chamber 104 near the cathode surface. Less turbulence or laminar flow near the cathode surface ensures a large and even diffusion boundary layer on the front surface 102A of the workpiece 102, which in turn provides the electroplating process to proceed in diffusion-controlled regime. A low Reynolds number characterizes a solution with smooth, constant fluid motion. With the use of the flow regulators 111, Reynolds number in the solution chamber 104 and particularly near the surface 102A of the workpiece 102 can be advantageously kept under 2000. Further, with the use of the flow regulator 111, a solution body adjacent the front surface 102A may especially have a low Reynolds number in the range of 0-2000, preferably less than 1500, and more preferably 100-1000. In fact, the reduction of turbulence in the solution 106 near the cathode surface also evens out the solution velocity distribution next to the front surface 102A. Since the source of disturbance is reduced or minimized, the cathode sees substantially the same amount of ion flux at every location over the entire area, thereby ensuring a uniform thickness distribution on the front surface. In this respect, to improve deposition uniformity, the solution inlets 102 are positioned away from the cathode and anode. With these conditions, cathodic efficiencies in the range of 40% to 100% may be obtained.

In the preferred embodiment the flow regulators 111 are located above the cathode surface, i.e. a portion of the front surface 102A within the solution chamber 104, above the anode plate 108, between the anode plate 108 and the solution outlet 112, and below the solution surface 107. For a solution chamber height of 5 to 20 in, the perpendicular distance between the front surface 102A and the centers of the flow regulators 111 may be in the range of 4.5-19 in, where the distance between the anode plate 108 and the front surface 102A may be in the range of 0.25-10 in. The flow regulators 111 are immersed in the solution 106 at all times and the distance between the centers of the flow regulators 111 and the solution surface 107 may be in the range of 0.5-5 in. There may be more than two flow regulators and they may have various geometries such as circular, square, or hexagonal. For circular shape, a flow regulator may have a diameter in the range of 0.5-4 in, preferably, 1-2 in. Depending on the length of the solution chamber and the number of the flow regulators, the distance between them may be in the range of at least 1 in.

FIG. 4 illustrates an embodiment of the support assembly using one of the support members 120, for example the second support member 120B, which is adjacent the exit opening 114B and which is the same as the support member 120A, as mentioned above. It is understood that the description given below for the second support member 120B is applicable to the first support member 120A. As shown in FIG. 4 and also in a perspective view in FIG. 5, the upper roller 121A may have surface recesses that may not contact the workpiece 102 and surface protrusions that may touch the workpiece 102. In one embodiment, the upper roller 121A may be a step-roller including a mid portion 130 extending between two side portions 132 which have the same diameter. The diameter of the side portions 132 is greater than the diameter of the mid portion 130, and thus only the surfaces 133 of the side portions 132 of the upper roller 121A touch the upper surface at edge regions 103A but not a central region 103B on which the absorber layer is formed. The width of the edge regions 103A may be in the range of 0.25-0.8 in. In this respect, the workpiece 102 is held between the side portions 132 at the top and the back roller 121B at the bottom as the workpiece is advanced. A surface 123 of the back roller 121B touches the entire width of the back surface 102B of the workpiece 102. As further shown in FIG. 4, the recessed mid-portion 130 of the upper roller allows the solution leaking from the exit opening 114B as the fourth flow 4F to flow away from the solution chamber 104 without spilling over the moving parts of the system. This leaking solution 4F flows on the front surface 102A and is directed to a drain or cleaned off by various methods.

In this embodiment, the back roller 121B and the side portions 132 of the upper roller 121A may have a diameter in the range of 0.5-1.5 in, preferably 1.0 in. The mid-section 130 of the upper roller 121A may have diameter in the range of 0.9-0.95 in. The width of the side portions may be in the range 0.25-0.8 in.

As shown in FIG. 6, the upper and back rollers 121A and 121B may have upper and lower enclosures 136 and 138 or shields respectively to better control the solution leaking onto the workpiece 102 as the workpiece enters and exits the solution chamber 104 as described above. Although FIG. 6 shows the upper and lower enclosures 136 and 138 for the support member 120B adjacent the exit opening, it is understood that the same enclosures are also used for the support member 120A adjacent the entrance opening 114A. In one embodiment, a first end 140A of the upper enclosure 136 may be connected to the exit opening 114B so as to direct the leakage solution to the opening at the second end 140B under the mid-portion 130 of the upper roller 121A.

FIG. 7A shows another embodiment of the electrodeposition unit 100 where the support mechanism includes more support members 120 such as a third support member 120C and a fourth support member 120D. The third and fourth support members 120C and 120D may either have the upper and back rollers 121A and 121B as the support members 120A and 120B, or optionally only the back support rollers 121B supporting only the back surface 102B of the workpiece 102. The third and fourth support members 120C and 120D along with the first and second support members 120 and 122 retain the workpiece 102 in a horizontal plane as it is moved through the solution chamber during the process. In one embodiment, there may be solution removal stations 150, for example a first solution removal station 150A between the first and third support members 120A and 120C, and a second solution removal station 150B between the second and fourth support members 120B and 120D. The solution removal stations 150 may include solution drains, nozzles to apply DI water to workpiece surfaces, and air dryers, such as air knives, to remove solution from the workpiece.

FIG. 7B shows an alternative embodiment of the electrodeposition unit 100 in which the support mechanism includes auxiliary rollers 152 such as a first auxiliary roller 152A and a second auxiliary roller 152B. The first and the second auxiliary rollers 152A and 152B contact the back surface 102B and are placed at an elevated position so that the workpiece is inclined at an angle of ‘α’ between the auxiliary rollers 152 and the support members 120. The α-angle may be 1-180 degrees, preferably 5-60 degrees, more preferably 25-50 degrees. Due to the inclination of the workpiece 102, the leakage flow 4F or the fourth flow described above (see FIG. 5) is flowed out from the front surface 102A after passing through the support members 120A and 120B. The solution flowed out of the front surface 102A is directed to a solution drain. Although the use of workpiece inclination eliminates the need for solution removal units between the auxiliary rollers 152 and the support members 120, in an alternative approach, the solution removal units may be located between the auxiliary rollers 152 and the support members 120. The auxiliary rollers 152A and 152B may be dimensioned and applied in the same manner as the back rollers 121B.

In one example, with the embodiments above, the chemical loss or solution loss from entrance and exit of the solution chamber is reduced by 70% which results in a 50% reduction in the required chemical flow or solution flow into the solution chamber and, consequently, a reduction in turbulence in the solution near the cathode. Further, the solution level height in the solution chamber is increased by 25%. The increase in the chemical bath solution level allows for the anode to workpiece distance to be optimized further improving the electrodeposited film uniformity.

FIGS. 8A and 8B show exemplary roll-to roll electrodeposition systems 200A and 200B respectively including more than one electrodeposition unit 100 to electrodeposit films of Group IB, Group IIIA and Group VIA materials. The support mechanism of the system 200A shown in FIG. 8A uses multiple support members 120 illustrated in the embodiment shown in FIG. 7A, and the support mechanism of the system 200B shown in FIG. 8B uses support members 120 with auxiliary rollers 152 illustrated in the embodiment shown in FIG. 7B. In each system, the workpiece 102 is unwound from a supply spool 160A and advanced through the electrodeposition units 100A, 100B and 100C for processing while being supported and retained by the support mechanism, and received and rewound around a receiving spool 160B as a processed workpiece. During the process, the workpiece 102 is moved through the systems by a moving mechanism (not shown). In one example the first electrodeposition unit 100A may deposit a Cu film on a contact layer on the workpiece, the second electrodeposition unit 100C may electrodeposit an In film on the Cu film, and the third electrodeposition unit 100C may electrodeposit a Ga film on the In film. An optional fourth electrodeposition unit (not shown) may also electrodeposit a Se film on the Ga film thereby completing a precursor stack for a CIGS compound absorber. In another example, a ternary CIGS solution may be used in each electrodeposition unit, and the CIGS precursor film stack may be formed as the workpiece advances through the successive electrodeposition units.

Although the present invention is described with respect to certain preferred embodiments, modifications thereto will be apparent to those skilled in the art. Thus, the scope of the present invention should not be limited to the foregoing description, but should be defined by the appended claims.

Claims

1. An electrodeposition apparatus for electrodepositing a material film from an electrodeposition solution onto a front surface of a flexible workpiece as the flexible workpiece is advanced through the apparatus in a roll to roll manner, the apparatus comprising:

an electrodeposition unit to electrodeposit the material film onto the front surface of the flexible workpiece as the flexible workpiece is advanced through the electrodeposition unit, the electroplating unit comprising: a solution chamber having a peripheral wall configured for retaining the electrodeposition solution at a predetermined level; at least one solution inlet to receive a first flow of the electrodeposition solution wherein the at least one solution inlet is positioned adjacent an upper end of the peripheral wall and below the predetermined level of the electrodeposition solution; at least one flow regulator attached to the at least one solution inlet to transform the first flow into a second flow of the electrodeposition solution and deliver the second flow into the solution chamber; and an entrance opening and an exit opening positioned at a lower end of the peripheral wall so that the flexible workpiece is advanced through the electrodeposition solution by entering from the entrance opening and exiting through the exit opening of the solution chamber;

an anode plate positioned in the solution chamber between the flexible workpiece and the at least one solution inlet, wherein the front surface of the flexible workpiece is positioned across from the anode plate as the flexible workpiece is advanced through the solution chamber;

a support mechanism to support the flexible workpiece within the solution chamber as the flexible workpiece is advanced therethrough, the support mechanism comprising: a first support member positioned outside the solution chamber and adjacent the entrance opening, the first support member including a first roller contacting a back surface along the width of the flexible workpiece, and a second roller having end portions and a central portion, wherein the end portions contact only edge regions of the front surface, and wherein the central portion extends over a selected region located between the edge regions while not contacting the selected region thereby forming a first gap between a surface of the selected region and the central portion of the second roller, wherein a first leak flow leaking through the entrance opening is flowed out through the first gap of the first support member; and a second support member positioned outside the solution enclosure and adjacent the exit opening, the second support member including a first roller contacting a back surface along the width of the flexible workpiece, and a second roller having end portions and a central portion, wherein the end portions contact only the edge regions of the front surface, and wherein the central portion extends over the selected region located between the edge regions while not contacting the selected region thereby forming a second gap between the surface of the selected region and the central portion of the second roller, wherein a second leak flow leaking through the exit opening is flowed out through the second gap of the second support member.

2. The apparatus of claim 1, wherein the support mechanism further includes a first auxiliary roller positioned before the first support member and a second auxiliary roller positioned after the second support member, wherein the first and the second auxiliary rollers contact only the back surface of the flexible workpiece.

3. The apparatus of claim 2, wherein the first and second auxiliary rollers are horizontally aligned with the first and second support members respectively so that the workpiece travels in a horizontal plane between the first auxiliary roller and the first support member and between the second support member and the second auxiliary roller.

4. The apparatus of claim 2, wherein the first and second auxiliary rollers are aligned in an angled relationship with the first and second support members respectively so that the workpiece travels in a downwardly angled plane between the first auxiliary roller and the first support member and in an upwardly angled plane between the second support member and the second auxiliary roller.

5. The apparatus of claim 1 further including a solution container connected to the at least one solution inlet by solution conduits.

6. The apparatus of claim 5, wherein the electroplating chamber further includes a solution outlet to flow a third flow of the electrodeposition solution out of the solution chamber, wherein the third flow is flowed into the solution container.

7. The apparatus of claim 1, further including a moving assembly of the apparatus to hold and linearly move the flexible workpiece through electrodeposition unit and the support mechanism, wherein the moving assembly comprises a feed spool to unwrap and feed unprocessed sections of the flexible workpiece into the apparatus and a take-up spool to receive processed portions and wrap the processed portions there around.

8. The apparatus of claim 1, wherein the at least one flow regulator delivers the second flow parallel to the front surface of the flexible workpiece.

9. The apparatus of claim 1, wherein the at least one flow regulator is a porous nozzle covering the at least one solution inlet.

10. The apparatus of claim 1, wherein the at least one flow regulator is positioned between the anode plate and the predetermined level of the electrodeposition solution.

11. The apparatus of claim 10, wherein the at least one flow regulator has an elongated body extended into the solution chamber and parallel to the surface of the flexible workpiece.

12. The apparatus of claim 11, wherein the elongated body includes openings to flow the second flow into the solution chamber.

13. An electrodeposition system for depositing material film on a continuous moving web, the system comprising:

a chamber that defines an inner volume that receives an electrodeposition solution, wherein the chamber has a first and a second end, and wherein the chamber includes a first and a second web opening adjacent a first end of the chamber so that the web can be transported through the chamber between the first and the second web openings;

an anode positioned in a first location within the chamber, wherein a portion of the web that is positioned between the first and second web openings defines a cathode that corresponds to the anode so that electrical potential therebetween results in electrodeposition of the film on the web as the web moves through the chamber; and

a solution supply system that provides solution to the chamber to replace solution that is lost or removed from the chamber, wherein the solution supply system includes a flow regulator that reduces the pressure of the solution being provided to the chamber so as to reduce the turbulence of the electrodeposition solution adjacent the cathode.

14. The system of claim 13, wherein the solution supply system includes an inlet that is located so that the anode is interposed between the inlet and the cathode.

15. The system of claim 14, wherein the inlet is positioned adjacent the second end of the chamber at a distance selected so that the introduction of the electrodeposition solution into the chamber does not disrupt substantially laminar flow of the solution adjacent the portion of the web comprising the cathode.

16. The system of claim 15, wherein the inlet with the flow regulator is positioned approximately 4.5 to 19 inches from the portion of the web forming the cathode.

17. The system of claim 16, wherein the flow regulator and the positioning of the inlet reduces the turbulence of the electrodeposition solution adjacent the portion of the web forming the cathode such that the Reynolds number of that solution is below 2000.

18. The system of claim 17, wherein the Reynolds number is the range of approximately 100 to 1000.

19. The system of claim 13, wherein the flow regulator receives the electrodeposition solution through a first opening and then discharges the electrodeposition solution into the chamber via a plurality of outlets having a greater area than the first opening to thereby reduce the pressure of the electrodeposition solution being introduced into the chamber.

20. The system of claim 19, wherein the first opening and the second opening are positioned orthogonally to each other.

21. The system of claim 13, further comprising at least one web support system positioned proximate at least one of the web openings of the chamber.

22. The system of claim 21, wherein the web support system includes a first surface that supports a first side of the continuous web and a second member that engages with a portion of the second side of the continuous web that is to receive the electrodeposited film.

23. The system of claim 22, wherein the second member comprises a roller that defines a central depression so that the second member engages with the second side of the continuous web at the edges of the web.

24. The system of claim 23, wherein the central depression defines a gap that allows excess electrodeposition solution that is escaping the chamber via the web opening in the chamber to be channeled away from the chamber.

25. The system of claim 24, wherein the at least one web support system comprises a first and a second web support system that is positioned adjacent the first and second web openings in the chamber.