JP2010509779A - Open reel reaction of precursor film to form solar cell absorber - Google Patents

Abstract

A roll-to-roll rapid temperature treatment (RTP) tool having multiple chambers for forming a solar cell absorber by reacting a precursor layer on a continuous and flexible workpiece. The RTP tool includes an elongated housing having a heating chamber having a predetermined temperature profile, a supply chamber, and a receiving chamber. The heating chamber includes a small process gap where the precursor layer is reacted with the Group VIA material to form the absorber layer. The continuous and flexible workpiece is unrolled from the roll and advanced from the supply chamber to the heating chamber, and the processed continuous and flexible workpiece is wound and wound in the receiving chamber.
[Selection] Figure 1

Description

  The present invention relates to a method and apparatus for processing semiconductor thin films for radiation detectors and photovoltaic applications.

  This application is a continuation-in-part of US patent application Ser. No. 11 / 549,590, filed Oct. 13, 2006. This application claims the benefit of US Provisional Patent Application No. 60 / 865,385, filed Nov. 10, 2006. These applications are hereby incorporated by reference in their entirety.

  A solar cell is a photovoltaic device that converts sunlight directly into electric power. The most common solar cell material is silicon, which is in the form of monocrystalline or polycrystalline wafers. However, the price of power generated using silicon-based solar cells is higher than the price of electricity generated by more traditional methods. Therefore, efforts have been made to reduce the price of solar cells for use on Earth since the early 1970s. One way to reduce the price of solar cells is to develop an inexpensive thin film growth technology that allows solar cell quality absorber material to be placed on a large area substrate and to manufacture these devices with high throughput and low cost methods. is there.

Group IBIIIAVIA compounds consisting of several elements of Group IB (Cu, Ag, Au), Group IIIA (B, Al, Ga, In, Tl) and Group VIA (O, S, Se, Te, Po) of the periodic table These semiconductors are excellent absorber materials for thin film solar cell structures. In particular, Cu, In, Ga, Se, S represented by CIGS (S) or Cu (In, Ga) (S, Se) ₂ or CuIn _1-x Ga _x (S _y Se _1-y ) _k The compounds have already been used in solar cell structures producing conversion efficiencies approaching 20%, where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and k is about 2. Absorbers containing group IIIA element Al and / or group VIA element Te also show promise. Therefore, in summary, it includes i) Cu from group IB, ii) at least one from In, Ga, Al from group IIIA, and iii) at least one of S, Se, Te from group VIA. The compound is very important as a solar cell.

The structure of a conventional IBIIIAVIA group photovoltaic cell, such as a Cu (In, Ga, Al) (S, Se, Te) ₂ thin film solar cell, is shown in FIG. Device 10 is fabricated on a substrate 11 such as a glass sheet, a metal sheet, an insulating foil or web, or a conductive foil or web. Cu (In, Ga, Al) (S, Se, Te) An absorbing thin film 12 containing a Group ₂ material is grown on a conductive layer 13 that is previously deposited on the substrate 11 and acts as an electrical contact to the device. The substrate 11 and the conductive layer 13 form a base 20. Various conductive layers including Mo, Ta, W, Ti, stainless steel, etc. are used in the solar cell structure of FIG. If the substrate itself is a suitably selected conductive material, the substrate 11 can then be used as an ohmic connection to the device, so it is possible not to use the conductive layer 13. After growth of the absorbing thin film 12, a transparent layer 14, such as a CdS, ZnO or CdS / ZnO stack, is formed on the absorbing thin film. Radiation 15 enters the device through the transparent layer 14. A metal grid (not shown) can also be deposited over the transparent layer 14 to reduce the effective series resistance of the device. The preferred conductivity type of the absorption thin film 12 is p-type, and the preferred conductivity type of the transparent layer 14 is n-type. However, n-type absorbers and p-type window layers can also be used. The preferred device structure of FIG. 1 is referred to as a “substrate-type” structure. The “substrate-type” structure also deposits a transparent conductive layer on a transparent substrate such as glass or a transparent polymer foil, followed by an absorbing thin film of Cu (In, Ga, Al) (S, Se, Te) ₂ Can be constructed by depositing and finally forming an ohmic connection to the device by means of a conductive layer. In this substrate structure, light enters the device from the transparent substrate side. Different materials deposited by different methods can be used to provide different layers of the device shown in FIG.

In thin film solar cells using absorbers of IBIIIAVIA compounds, cell efficiency is a strong function of the IB / IIIA molar ratio. If the composition is a Group IIIA material of 2 or more, the relative amounts or molar ratios of these Group IIIA elements also affect the properties. For example, for an absorption layer of Cu (In, Ga, Al) (S, Se, Te) ₂ , the efficiency of the device is a function of the molar ratio of Cu / (In + Ga). In addition, some important parameters of the cell, such as its open circuit voltage, short circuit voltage, and fill factor, vary with the molar ratio of group IIIA elements, ie the molar ratio of Ga / (Ga + In). In general, for good device performance, the Cu / (In + Ga) molar ratio is maintained at or below about 1.0. On the other hand, as the Ga (Ga + In) molar ratio increases, the optical band gap of the absorber layer increases, and thus the open circuit voltage of the solar cell increases while the short circuit current typically decreases. It is important that the thin film deposition process has the ability to control both the group IB / IIIA molar ratio and the group IIIA component molar ratio in the composition. The chemical formula is often written as Cu (In, Ga) (S, Se) ₂ , but the more accurate formula for the compound is Cu (In, Ga) (S, Se) _k , where k is typically close to 2. Note that may not be exactly 2. For simplicity, keep using the value of k as 2. Furthermore, the notation “Cu (X, Y)” in the chemical formula means all chemical compositions of X and Y from (X = 0% and Y = 100%) to (X = 100% and Y = 0%). Should be noted. For example, Cu (In, Ga) means all compositions from CuIn to CuGa. Similarly, Cu (In, Ga) (S, Se) ₂ represents the entire group of compounds having a Ga / (Ga + In) molar ratio that varies from 0 to 1 and a Se / (Se + S) molar ratio that varies from 0 to 1. means.

One technique for growing thin films of Cu (In, Ga) (S, Se) ₂ type compounds for solar cells involves first attaching a metal component of Cu (In, Ga) (S, Se) ₂ material to the substrate. A two-stage process that is then reacted with S and / or Se in a high temperature tempering process. For example, in the growth of CuInSe _2, a thin layer of Cu and In are first deposited on the substrate, then this stacked precursor layer is reacted with Se at being raised temperature. If the reaction atmosphere also contains sulfur, a layer of CuIn (S, Se) ₂ can be grown. The addition of Ga in the precursor layer, ie the use of a Cu / In / Ga stacked film precursor, allows the growth of Cu (In, Ga) (S, Se) ₂ absorbers.

The two-stage process method can also use stacked layers comprising Group VIA materials. For example, a Cu (In, Ga) Se ₂ film can be obtained by attaching a Ga—Se and Cu—Se layer to an In—Ga—Se / Cu—Se stack and reacting them in the presence of Se. it can. Similarly, a stack of Group VIA materials and metal components can be used. The stack including the VIA group material includes, but is not limited to, an In—Ga—Se / Cu stack, a Cu / In / Ga / Se stack, a Cu / Se / In / Ga / Se stack, and the like.

Selenization and / or sulfidation or sulfidation of precursor layers with metal components can be performed in various forms of Group VIA materials. One method involves the use of a gas such as H ₂ Se, H ₂ S or mixtures thereof to react simultaneously or sequentially with a precursor having Cu, In and / or Ga. In this way, a Cu (In, Ga) (S, Se) ₂ film can be formed after tempering and reaction at an elevated temperature. It is possible to increase the reaction rate or reactivity by impinging the plasma in the reaction gas during the compound formation process. Se vapor or S vapor from elemental sources can also be used for selenization and sulfidation. Alternatively, as described above, Se and / or S can be deposited over a precursor layer containing Cu, In and / or Ga, and the stacked structure is Cu (In, Ga) (S, Se). ) It can be tempered at an elevated temperature to initiate a reaction between the metal element or compound and the Group VIA material to form a _two- compound.

  The reaction step of the two-stage process is typically performed in a batch furnace. In this method, a plurality of pre-cut substrates with a precursor layer attached are placed in a batch furnace and the reaction is carried out in a period ranging from 15 minutes to several hours. The temperature of the batch furnace is typically raised to the reaction temperature after being placed on the substrate, which may be in the range of 400-600 ° C. This rate of temperature increase is nominally less than 5 ° C./second, typically less than 1 ° C./second. One prior art method described in US Pat. No. 5,758,503 uses a rapid thermal tempering (RTP) method in which the precursor layer is reacted on one substrate at a time by a batch method. In this design, the temperature of the substrate with the precursor layer is raised to the reaction temperature at a high rate, typically 10 ° C./second.

  The design of the reaction chamber for conducting the selenization / sulfurization process is critical with respect to the resulting compound film quality, solar cell efficiency, throughput, material usage and process cost. The present invention provides a method and apparatus for reacting a precursor layer for CIGS (S) type absorber formation in a roll-to-roll process. Roll-to-roll or open reel processing increases throughput and minimizes substrate processing. It is therefore a preferred method for large scale manufacturing.

  The present invention provides a method and integrated tool for forming a solar cell absorber layer on a continuous and flexible substrate. A roll-to-roll rapid heat treatment (RTP) tool containing multiple chambers is used to react the precursor layer on a continuous, flexible workpiece.

  One feature of the present invention is an integrated roll-to-roll RTP tool having multiple chambers for forming a solar cell absorber by reacting a precursor layer on the surface of a continuous and flexible workpiece. Is to provide. The tool includes an elongated housing that includes a vacuum line for drawing a vacuum within the elongated housing. Further, the heating chamber of the elongated housing provides a predetermined temperature profile to the continuous and flexible workpiece. The heating chamber extends between a first opening at the first end of the heating chamber and a second opening at the second end of the heating chamber and is defined by the upper wall, lower wall, and side walls of the heating chamber. Includes process gaps. A gas inlet line located adjacent to the first opening of the heating chamber delivers a processing gas, which can be inert or can contain a Group VIA material, to the heating chamber during the process. The continuous and flexible workpiece is configured to be advanced between the first and second openings through the process gap during processing. Based on the speed of the flexible workpiece during the process gap and the predetermined temperature profile of the heating chamber, the portion of the flexible workpiece is given a predetermined temperature versus time profile during the reaction period.

  The supply chamber of the elongated housing holds a continuous and flexible workpiece supply roll. The supply chamber is proximate to the first end of the heating chamber, the first opening is connected to the process gap in the interior space of the supply chamber, and the continuous and flexible workpiece passes from the supply chamber through the first opening. It is configured to be advanced to the heating chamber. The elongated housing receiving chamber receives a continuous and flexible workpiece from the heating chamber. The second opening connects the interior space of the receiving chamber to the process gap, and the continuous flexible workpiece is configured to be advanced from the processing chamber to the supply chamber through the second opening.

  The transfer mechanism feeds a portion of the continuous flexible workpiece pre-rolled from the supply roll in the supply chamber and winds up the processed portion of the continuous flexible workpiece in the receiving chamber, A continuous and flexible workpiece to be processed in the process chamber is held in and moved through the process gap of the heating chamber.

  An exhaust line disposed proximate one of the first and second openings of the heating chamber removes process gas and gaseous byproducts from the process chamber. The gas inlet and exhaust lines are configured to allow a process gas flow to exist over the front of the continuous flexible workpiece when the continuous flexible workpiece is removed within the process gap Has been.

FIG. 1 is a cross-sectional view of a solar cell using an IBIIIAVIA group absorption layer. FIG. 2 shows an apparatus for reacting a precursor layer in a reel-to-reel manner to form a group IBIIIAVIA layer on a flexible foil base. FIG. 3A illustrates an exemplary flexible structure with a flexible base and precursor layer attached. FIG. 3B is a diagram showing a base on which a group IBIIIAVIA absorbing layer is formed by reacting the precursor layer of FIG. 3A. FIG. 4 shows another apparatus for reacting a precursor layer in an open reel manner to form a group IBIIIAVIA layer on a flexible foil base. FIG. 5A is a cross-sectional view showing a different reaction chamber in which a flexible structure is arranged. FIG. 5B is a cross-sectional view showing a different reaction chamber in which a flexible structure is arranged. FIG. 5C is a cross-sectional view showing a reaction chamber having an outer chamber and an inner chamber. FIG. 6 is a diagram illustrating an exemplary variation of the reactor of FIG.

The reaction of a Group IB material, a Group IIIA material, and optionally a Group VIA material or a precursor comprising a component with a Group VIA material can be realized in various ways. These techniques include i) solid Se, S or Te directly attached to the precursor, and ii) H ₂ Se gas, H ₂ S gas, H ₂ Te gas, Se vapor, S vapor, Te vapor, etc. In the presence of at least one of Se, S, Te provided by such a source, the precursor layer has a time period ranging from 1 minute to several hours in a temperature range of 350-600 ° C, preferably in a temperature range of 400-575 ° C. Processing to heat up is included. Se, S, Te vapor can be generated by heating a solid source of these materials away from the precursor layer. Hydride gases such as H ₂ Se and H ₂ S may be bottled gases. Such hydride gases and short-lived gases such as H ₂ Te are also generated in situ by electrolyzing an acidic aqueous solution of the cathode containing, for example, S, Se and / or Te and then feeding it to the reactor. Can be done. Electrochemical methods for generating these hydride gases are suitable for on-site generation.

The precursor layer can be exposed to two or more Group VIA materials simultaneously or sequentially. For example, a precursor layer containing Cu, In, Ga, Se can be tempered in the presence of S to form Cu (In, Ga) (S, Se) ₂ . The precursor layer in this case may be a stacked layer having a metal layer including a Cu, Ga, In, Se layer deposited on the metal layer. Alternatively, Se nanoparticles can be dispersed through a metal layer containing Cu, In, Ga. The precursor layer contains Cu, In, Ga, and S, and this layer forms Cu (In, Ga) (S, Se) ₂ during the reaction period, so that it can be tempered in the presence of Se. is there.

Some preferred embodiments for forming a compound layer of Cu (In, Ga) (S, Se) ₂ are summarized as follows: i) a layer of Se on a metal precursor comprising Cu, In, Ga To form a structure and react the structure at an elevated temperature in a gas S source; ii) a mixed layer of S and Se or a S layer and a Se layer on a metal precursor containing Cu, In, Ga Deposit to form a structure and react the structure at an elevated temperature in a gas environment without S or Se or in a gas environment containing at least one of S and Se, iii) the S layer has Cu, In, Ga Depositing on the metal precursor to form a structure, reacting the structure in a gaseous Se source at elevated temperature, and iv) depositing a Se layer on the metal precursor having Cu, In, Ga to form the structure formed, Cu (In, Ga) Se 2 Oyo / Or Cu, an In, reacted at elevated temperature with mixing phase layer comprising selenides Ga, gas source then Cu (In, Ga) S such as Se ₂ layer and / or the mixed phase layer S layer , React with a liquid source of S, a solid source of S, and v) deposit an S layer on a metal precursor having Cu, In, Ga to form a structure, a Cu (In, Ga) S ₂ layer and / or Alternatively, the structure is reacted at an elevated temperature to form a mixed phase layer containing sulfides of Cu, In, and Ga, and then the Cu (In, Ga) S ₂ layer and / or mixed phase layer is formed as a Se layer. The reaction is performed using a Se gas source, a Se liquid source, and a Se solid source.

  Note that Group VIA materials are corrosive agents. Therefore, the materials of all parts of the reactor or chamber that are exposed to elevated temperature Group VIA materials or material vapors need to be selected appropriately. These parts may be substantially inert materials such as ceramics, such as alumina, tantalum oxide, titania, zirconia, etc., refractory metals such as glass, quartz, stainless steel, graphite, Ta, refractory metal nitrides and / or Made of carbides, eg other nitrides and / or carbides such as Ta nitrides and / or carbides, Ti nitrides and / or carbides, W nitrides and / or carbides, Si nitrides and / or carbides, etc. They must be covered.

  The reaction of the precursor layer comprising Cu, In, Ga and optionally at least one VIA material can be performed in a reactor that applies a processing temperature to the precursor layer at a low rate. Alternatively, rapid heat treatment (RTP) can be used if the temperature of the precursor is raised to a high reaction temperature at a rate of at least about 10 ° C./second. If the VIA material is included in the precursor layer, it can be obtained by vapor deposition, sputtering or electroplating. Alternatively, inks containing Group VIA nanoparticles may be used and these inks can be deposited to form a Group VIA material layer within the precursor layer. Other liquids or solutions such as organometallic solutions having at least one Group VIA material may also be used. Dropping into solution or ink, spraying of solution or ink, or doctor blade or ink writing techniques can be used to deposit such layers.

  An open reel apparatus 100 or roll-to-roll RTP reactor for carrying out the reaction of the precursor layer to form the IBIIIAVIA group compound film is shown in FIG. It should be noted that the precursor layer reacted in this reactor can include at least one Group IB material and at least one Group IIIA material. For example, the precursor layer is Cu / In / Ga, Cu-Ga / In, Cu-In / Ga, Cu / In-Ga, Cu-Ga / Cu-In, Cu-Ga / Cu-In / Ga, Cu / Cu. It may be a stack of -In / Ga or Cu-Ga / In / In-Ga, where the order of the various material layers in the stack can be changed. Here, Cu-Ga, Cu-In, and In-GA mean an alloy or mixture of Cu and Ga, an alloy or mixture of Cu and In, and an alloy or mixture of In and Ga, respectively. Alternatively, the precursor layer can include at least one Group VIA material. There are many examples of such precursor layers. Some of these are Cu / In / Ga / VIA material stack, Cu-VIA material / In / Ga stack, In-VIA material / CuVIA material stack or Ga-VIA material / Cu / In, Here, the Cu-VIA material includes an alloy, a mixture or a compound (Cu selenide, Cu sulfide, etc.) of Cu and a VIA material, and the In-VIA material is an alloy, a mixture or a compound of In and a VIA material ( The Ga-VIA group material includes an alloy, a mixture or a compound (Ga selenide, Ga sulfide, etc.) of Ga and VIA group materials. These precursors are deposited on a base 20 having a substrate 11, which can further comprise a conductive layer 13 as shown in FIG. Other types of precursors that can be processed using the method and apparatus of the present invention are compound electroplating from compound targets, chemical plating, sputtering and ink deposition using IBIIIAVIA nanoparticle-based inks. And a IBIIIAVIA group material layer that can be formed on the base using low temperature methods such as spraying of metal nanoparticles with Cu, In, Ga, optionally Se, etc. These material layers are then tempered in equipment or reactors at temperatures in the range of 350-600 ° C. to improve their crystal quality, composition, and density.

  The tempering and / or reaction step can be carried out in the reactor of the present invention at substantially atmospheric pressure, at a pressure below atmospheric pressure, or at a pressure above atmospheric pressure. The low pressure in the reactor can be realized by using a vacuum pump.

The open reel device 100 of FIG. 2 is surrounded by a heater system 102 that can have one or more heating zones such as Z1, Z2, Z3 to form a temperature profile along the length of the chamber 101. An elongated heating chamber 101 can be provided. There is preferably a low thermal conductivity buffer region between the zones so that a steep temperature profile can be obtained. Details of the use of such buffer regions are described in “Method and Apparatus for Converting Precursor layers into Photovoltaic Absorbers” filed Oct. 13, 2006, which is hereby incorporated by reference. The chamber 101 is integrally and sealably attached to the first port 103 and the second port 104. By making it integral and sealable, the interior space of the chamber, the first port, the second port is sealed from the air atmosphere and is therefore optional (except for designated exhaust ports) used in the interior space This means that no gas leaks and no air leaks into the interior space. In other words, the integration of the chamber, the first and second ports is vacuum tight. The first spool 105A and the second spool 105B are placed in the first port 103 and the second port 104, respectively, and the continuous flexible workpiece 106 or flexible structure is in either direction, ie from the left. It can be moved between the first spool 105A and the second spool 105B to the right or from right to left. The flexible structure includes a precursor layer that is converted into an absorbent layer in an elongated chamber. The first port 103 has at least one first port gas inlet 107A and a first port vacuum line 108A. Similarly, the second port 104 may have at least one second port gas inlet 107B and may have a second port vacuum line 108B. The elongated heating chamber 101, the first port 103, and the second port 104 can be exhausted through one or both of the first port vacuum line 108A and the second port vacuum line 108B. The chamber 101 is also provided with at least one gas line 113 and at least one exhaust port 112. There may be additional vacuum lines (not shown) connected to the chamber 101. Valve 109 is preferably provided at all gas inlets, gas lines, vacuum lines, exhaust ports, thereby forming a common chamber that can be placed under a single vacuum. Preferably there are slits 110 at the two ends of the system 101 through which the flexible structure 106 passes. Exhaust of the chamber and the first and second ports is a preferred method for removing air from the tool interior space, but cleans the tool interior space with a gas such as N ₂ through the designated exhaust port. It is also possible to do.

  The flexible structure 106A prior to reaction may be a base having a precursor film attached to at least one base surface. The reacted flexible structure 106B includes a base and a group IBIIIAVIA compound layer formed as a result of the reaction of the precursor layer. It should be noted that the reacted and unreacted sections of the flexible structure 106 of FIG. A flexible structure is called a web regardless of whether or not the precursor layer present thereon is reacted. The base substrate may be a flexible metal or polymer foil. As described above, the precursor film on the base includes at least Cu, In, Ga and optionally a VIA group material such as Se. The rear surface 20A of the flexible structure 106 may or may not contact the wall of the chamber 101 as it is moved through the chamber 101. The process of the present invention is illustrated through a special example.

An absorption layer of Cu (In, Ga) (S, Se) ₂ can be formed using the single chamber reactor design of FIG. An exemplary flexible structure 106A prior to reaction is shown in FIG. 3A. Base 20 may be similar to base 20 of FIG. The precursor layer 200 is provided on the base 20. The precursor layer 200 contains at least one of Cu, In, and Ga. Preferably, the precursor layer 200 contains all of Cu, In, and Ga. Se layer 201 may optionally be deposited on precursor layer 200 to form Se support precursor layer 202. Se may be mixed with precursor layer 200 (not shown) in another version of the Se-supported precursor layer. The flexible structure after the reaction step is shown in FIG. 3B. In this case, the flexible structure 106B is an IBIIIAVIA group compound layer such as a Cu (In, Ga) (S, Se) ₂ film obtained by reacting the base 20 with the precursor layer 200 or the Se support precursor layer 202. Includes 203.

After the unreacted flexible structure 106A or web is placed on, for example, the first spool 105A, one end of the web is fed through the chamber 101, passes through the gap 111 in the slit 110, and is wound on the second spool 105B. Taken. The doors (not shown) to the first port 103 and the second port 104 are closed, and the system (including the first port 103, the second port 104, the chamber 101) exhausts to remove air. Is done. The system can be washed to eliminate through the exhaust port 112 supplies an inert gas such as N ₂ entering through any or all of the gas inlet or gas lines for a predetermined period instead. After evacuation or evacuation, the system is filled with an inert gas and the heating system 102 can be turned on to set the temperature profile along the length of the chamber 101. When the desired temperature profile is set, the reactor is ready for processing.

For example, during the process of forming the Cu (In, Ga) (S, Se) ₂ absorption layer, a gas with Se vapor or a source of Se, such as H ₂ Se, preferably enters the chamber through the chamber gas inlet 113. Can be introduced. The exhaust 112 can be opened by opening its valve so that the Se support gas can be directed to a purifier or trap (not shown). Note that Se is a volatile material, and at nearly typical reaction temperatures of 400-600 ° C., its vapor tends to travel to any existing cold surface and adhere in the form of solid or liquid Se. Should. This means that if no precautions are taken during the reaction process, the Se vapor passes through the first port 103 and / or the second port 104, and the unreacted portion of the web of the first port 103 and the second port. It can deposit on all its surfaces, including the already reacted parts of 104 webs. In order to minimize or eliminate such Se deposition, gas is directed through the first port gas inlet 107A to the first port 103 and through the second port gas inlet 107B to the second port 104. It is preferred to induce gas. The introduced gas may be a Se-supporting and / or S-supporting gas that does not decompose into Se and / or S at low temperatures, but preferably the introduced gas is an inert gas such as N ₂ and has two ports To set the flow of the inert gas from the port in the direction of the chamber 101 through the gap 111 of the slit 110.

  This gas flow rate can be increased by reducing the gap 111 in the slit 110 and / or increasing the flow rate of the gas to the port. In this way, the diffusion of Se vapor to the port is reduced or prevented, directing such vapor to the exhaust 112, where the vapor can be trapped away from the treated web. A preferred value for the gap 111 of the slit 110 is in the range of 0.5-5 mm, more preferably in the range of 1-3 mm. The flow rate of the gas to the port can be adjusted according to the width of the slit, which instead follows the width of the flexible structure 106 or web. A typical web width is 1-4 feet (30.48-121.9 cm).

Once the Se support gas and inert gas flow are set and the desired temperature profile of the chamber 101 is reached, the flexible structure 106 is moved from the first port 103 to the second port 104 at a predetermined rate. Can do. In this way, the unreacted portion of the flexible structure 106 exits the first roll 105A, enters the chamber 101, passes through the chamber 101, and reacts on the base of the web to absorb Cu (In, Ga) Se _2. A layer is formed and wound on the second spool 105B of the second port 104. It should be noted that there may be an optional cooling zone (not shown) in the second port 104 to cool the reacted web before being wound on the second spool 105B. It is.

The above description can also be applied to the formation of an absorption layer containing S. For example, to form a Cu (In, Ga) S ₂ layer, the Se support gas described above can be replaced with an S support gas such as H ₂ S. To form Cu (In, Ga) (S, Se) ₂ , a mixture of Se support gas and S support gas can be used. Alternatively, a Se-supported precursor can be used and the reaction can be carried out in an S-supported gas.

  One feature of the system 100 of FIG. 2 is that the flexible structure 106 can be moved from left to right and from right to left. In this way more than one reaction step can be performed. For example, a first reaction can be performed when the web is moved from left to right, and a second reaction can be performed and reacted when the web is moved from right to left The web can be withdrawn from the first spool 105A. Of course, more steps such as reaction and tempering can be performed by moving the web more between the first spool 105A and the second spool 105B. Reaction conditions such as gas flow rate and reaction temperature can be different in the various reaction steps. For example, the temperature profile of chamber 101 can be set to a maximum temperature of 400 ° C. with the first reaction profile when the web is moved from left to right. In this way, the web precursor is partially or fully reacted and tempered at 400 ° C.

  After substantially all of the web has been wound on the second spool 105B, the maximum temperature of the temperature profile can be adjusted to a higher value such as 550 ° C. and the web is already tempered and reacted. This precursor layer can now be moved from right to left as it is further reacted, tempered or crystallized at a higher temperature of 550 ° C. A similar process can be realized by making the chamber 101 longer and setting a temperature profile along the chamber 101 so that, for example, when the web moves from left to right, it passes through the 400 ° C zone and then Note that it moves through the 550 ° C. zone. However, using bi-directional motion as described above, the length of the chamber 101 can be reduced and still a two step / two temperature response can be realized. To keep the temperature of the web high, either the first port 103 and / or the second port 104 when wound on either the first spool 105A or the second spool 105B between reaction steps A heater (not shown) may optionally be disposed on both.

It should be noted that in addition to the reactor temperature and web speed, the composition of the reaction gas can also be altered in the multi-step reaction process described above. For example, during the first reaction step, when the web is moved from left to right, a first gas such as H ₂ Se is used in chamber 101 to form a selenized precursor layer. Can do. During the second reaction step, another gas, such as H ₂ S, can be introduced into the chamber 101 as the web is moved from right to left. As a result, when the web is moved from the second spool 105B to the first spool 105A, the selenized precursor layer can be reacted with S and thus Cu (In, Ga) (S, Se). _{The two} layers can be grown by converting the already selenized precursor layer to sulfoselenide. The amount of Se and S in the absorbent layer can be controlled by selecting the gas concentration, web speed, and reaction temperature. For example, the S / (Se + S) molar ratio in the final absorbent layer is increased by increasing the web speed and / or decreasing the reaction temperature during the first process step when the reaction with Se is performed. Can be done. Similarly, the S / (Se + S) molar ratio can be increased by decreasing the web speed and / or increasing the reaction temperature during the second reaction step in which the reaction with S is carried out. This gives great flexibility for optimizing the absorption layer composition by optimizing the two reaction steps independently of each other.

  Another embodiment of the present invention is shown in FIG. The reactor system 400 of FIG. 4 includes a three-section chamber 450, which is an example of a more general multi-chamber design. The three section chamber 450 of FIG. The heating means and the first port, the first spool, the second port, and the second spool around each section are not shown in this drawing for the sake of simplicity. However, a design similar to the design shown in FIG. 2 can be used for such omitted parts. The heating means may be a heating lamp, a thermal coil, etc., but these can have independent controls to produce different temperature values and profiles in the A, B, C sections.

  An important feature in the design of FIG. 4 is that sections A and C are separated by a small volume segment 410, preferably in section B of the three-section chamber 450. There are means for directing the gas to each section A, B, C. For example, inlets 401 and 402 can direct gas to sections A and C, respectively, and inlet 403 can direct gas to a small volume segment 410 in section B. Exhaust ports 404 and 405 can be provided to exhaust gas from sections A and C, respectively. The flexible structure 106 to be treated or reacted passes through the first gap 111A of the first slit 110A, enters the three-section chamber 450, and then exits through the second gap 111B of the second slit 110B. be able to.

The Cu (In, Ga) (S, Se) ₂ absorption layer can be formed using the three-section chamber reactor of FIG. After loading unreacted flexible structure 106 as described in Example 1, pumping, and evacuating the contents, the process can begin. Sections A, B, and C of the three-section chamber 450 can have temperatures of T1, T2, and T3 that are equal to or not equal to each other. Furthermore, each section A, B, C can have a temperature profile along their length rather than just a constant temperature. During operation, the first process gas such as N ₂ may be introduced through an inlet 403 to the small volume segment 410 of section B, the second process gas and the third process gas, respectively inlet 401 and 402 Can be introduced into sections A and C respectively.

The second process gas and the third process gas may be the same gas or may be two different gases. For example, the second process gas can include Se and the third process gas can include S. Thus, when a portion on flexible structure 106 enters section A of three-section chamber 450 through first gap 111A of first slit 110A, the precursor layer on that portion initiates reaction with Se. Then, a selenized precursor layer is formed on the portion. When a portion enters the small volume segment 410, it is tempered with N ₂ gas in this segment before entering section C (if section B is heated). In section C, sulfidation or sulfidation takes place due to the presence of gaseous S species, and the Cu (In, Ga) (S, Se) ₂ absorption layer is therefore partly in the second gap of the second slit 110B. Formed in part before exiting 3-section chamber 450 through 111B. The S / (Se + S) molar ratio of the absorber layer can be controlled by the relative temperatures and lengths of sections A and C. For example, at a given web speed, the S / (Se + S) ratio can be increased by decreasing the length of section A and / or decreasing its temperature.

  Alternatively or additionally, the length and / or temperature of section C can be increased. The inversion can be performed to reduce the S / (Se + S) molar ratio. It should be noted that, as in the previous example, it is possible to move the flexible structure or web backward from right to left to continue the reaction. It is also possible to change the gas introduced into each section A, B, C of the three-section chamber 450 in order to obtain an absorption layer having a different composition. The design of FIG. 4 allows two different gases or vapors to be present in two different sections of the reactor, so that an open-reel continuous process sequentially processes different reaction temperatures and different reaction gases. With unique features that can be performed on the web substrate by applying to each part of the web. Introducing an inert gas into the reduced volume segment between the two sections (sections A and C in FIG. 4) acts as a diffusion barrier and reduces the mixing between the different gases used in these two sections. Minimize or eliminate. The first gas introduced through the inlet 403 in FIG. 4 flows through the small volume segment 410 in the opposite direction to any right and left opposing gas flow from sections A and C. More sections can be added to the reactor design of FIG. 4 with more small volume segments in between, each section being process flexible for the formation of high quality IBIIIAVIA compound absorber layers Note that it is possible to run at different temperatures and gases to provide Also, more gas inlets and / or exhausts can be added to the system of FIG. 4, and the positions of these gas inlets and exhausts can be changed.

  A variety of different cross-sectional shapes can be used in the chamber of the present invention. Two such chambers 500A and 500B having circular and square cross sections, respectively, are shown in FIGS. 5A and 5B. A substantially cylindrical reaction chamber with a circular cross section is good for drawing a vacuum in the chamber even if the chamber is made of a material such as glass or quartz. However, circular chambers become very large when the substrate or web width increases to 1 foot (30.48 cm), 2 feet (60.96 cm) or more. Temperature profiles with abrupt temperature changes cannot be sustained using such large cylindrical chambers, so the roll-to-roll RTP process is 1-4 feet (30.48-121.9 cm). ) Cannot be performed on a wide flexible substrate such as a substrate that can be wider or wider.

  As shown in FIG. 5B, chamber 500B includes a rectangular gap defined by upper wall 510A, lower wall 510B, and side wall 510C. In this case, in order to draw a vacuum in such a chamber without breakage, if the chamber is made of crystal or glass, a very thick wall (more than half of an inch (2.54 cm)) is required. Is preferably made of metal. In this structure, the upper wall 510A and the lower wall 510B are substantially parallel to each other, and the flexible structure 106 is disposed therebetween. Since the width of such a chamber is reduced to less than 10 mm and the width is approximately close to the width of a flexible structure (1-4 feet (30.48-121.9 cm)), a chamber having a rectangular cross section or structure is It is effective in reducing the consumption of the reaction gas. Such a small height also allows reaction with Group VIA vapor without the need to introduce very large Group VIA materials into the chamber. The height of the chamber 500B, ie the gap size, is the distance between the upper and lower walls, and a small gap size is necessary to maintain a high overpressure of the Group VIA material at the surface of the precursor layer during the reaction period. It should be noted. These chambers can also maintain a rapidly changing temperature profile even with flexible substrate widths exceeding 4 feet (121.9 cm). For example, a temperature profile along the length of a chamber having a rectangular cross-section can have a temperature change of 400-500 ° C. within a distance of a few centimeters. Such a chamber can therefore be used in roll-to-roll RTP mode, where the section of precursor film on the substrate moving at a rate of a few centimeters per second via the aforementioned temperature change is 400 Experience a temperature rise rate of -500 ° C / sec. Even higher speeds of several thousand degrees per second can be achieved by increasing the speed of the substrate.

  As shown in the cross-sectional view of FIG. 5C, another preferred chamber design includes a double chamber 500C, where the inner chamber 501B having a rectangular cross section is within a cylindrical outer chamber 501A having a circular cross section. Has been placed. In this case, the flexible structure 106 or web passes through the inner chamber 501B, which can be orthorhombic in shape, and all gas flows preferably into the inner chamber 501B having a much smaller volume than the outer chamber 501A. Guided and passed there. In this way, waste of reaction gas is minimized, but at the same time the chamber can be made from a material like quartz, but the entire chamber is easily evacuated due to the cylindrical shape of the outer chamber 501B. Can. In this case, the heater (not shown) is placed outside the internal chamber 501B, but is placed inside the external chamber 501A. In this way, an abrupt temperature profile can be maintained along the length of the rectangular cross-section chamber with the ability to evacuate the reactor body.

  FIG. 6 shows such an exemplary variation of the reactor of FIG. Only the chamber portion is shown to simplify the drawing. As can be seen from this drawing, the double chamber 600 includes a cylindrical chamber 601 and an orthorhombic chamber 602 disposed in the cylindrical chamber 601. The gas inlet 113 and the exhaust outlet 112 are connected to the orthorhombic chamber 602. The cylindrical chamber 601 need not be hermetically sealed from the orthorhombic chamber so that when the entire chamber is pumped, the pressure is balanced between the cylindrical chamber 601 and the orthorhombic chamber. It should be noted that. Otherwise, if these chambers are sealed from each other, they may have to be pumped together at the same time so that there is no large pressure difference between them.

  Solar cells can be made with compound layers formed in the reactor of the present invention using materials and methods well known in the art. For example, a thin (less than 0.1 micron) CdS layer can be deposited on the surface of the compound layer using a chemical immersion method. A transparent window of ZnO can be deposited on the CdS layer using MOCVD or sputtering techniques. A metal finger pattern is optionally deposited on the ZnO to complete the solar cell.

  Although the present invention has been described in terms of certain preferred embodiments, variations thereof will be apparent to those skilled in the art.

Claims (43)

In an integrated roll-to-roll rapid heat treatment (RTP) tool for forming a solar cell absorber by reacting a precursor layer on the surface of a continuous flexible sheet workpiece,
An elongated housing including a sealed common chamber including a heating chamber, a supply chamber, and a receiving chamber, wherein
The heating chamber has a narrow process gap that provides a predetermined temperature profile to the portion of the continuous flexible sheet workpiece disposed therein, the narrow process gap being defined by the top wall, the bottom wall, and the side walls. The height is substantially less than its width and a narrow process gap is disposed between the input opening, the output opening, and the input and output openings to remove gases from the narrow process gap of the heating chamber. And an exhaust line
The supply chamber holds a continuous and flexible sheet workpiece supply roll and has a supply chamber opening, which is aligned with the narrow process gap input opening, and the continuous flexible sheet workpiece is Configured to be advanced from the supply chamber to the heating chamber,
The receiving chamber holds a receiving roll for collecting continuous and flexible sheet workpieces from the heating system and has a receiving chamber opening that is aligned with the output opening of the narrow process gap and is continuous and flexible. The sheet workpiece is configured to be advanced from the heating chamber to the receiving chamber;
Holds a continuous and flexible sheet workpiece in a common chamber and feeds a previously unrolled portion of the continuous and flexible sheet workpiece from the supply roll onto the receiving roll in the receiving chamber A tool including a movable mechanism for moving a continuous flexible sheet workpiece through a narrow process gap in a heating chamber by winding up a processing portion of the continuous flexible sheet workpiece.   The tool of claim 1, further comprising a vacuum line associated with the common chamber and enabling the formation of its vacuum and exhaust.   The tool of claim 2, further comprising a cylindrical enclosure around the heating chamber, the cylindrical enclosure being sealed to an elongated housing.   The process gap of the heating system is heated by a heating element located outside the narrow process gap, thereby forming a predetermined temperature profile on the outer surface of the upper wall, lower wall, and sidewalls that define the process gap. The tool according to claim 1, wherein heating is performed.   Furthermore, it is arranged adjacent to the narrow process gap input opening and is configured to introduce process gas into the narrow process gap of the heating chamber so that the process gas is in the direction of movement of the continuous and flexible sheet workpiece. A tool according to claim 4, comprising a flowing gas inlet line.   The supply chamber and the receiving chamber each include a gas inlet for transmitting an inert gas to the supply chamber and the receiving chamber, respectively, so that from the supply chamber to the narrow process gap through the input opening and from the receiving chamber to the narrow process gap through the output opening. 6. A tool according to claim 5, wherein an inert gas flow is set up thereby preventing gases in a narrow process gap from entering the supply chamber and the receiving chamber.   The tool of claim 6, wherein the distance between the upper and lower walls varies across the length of the narrow process gap in the heating chamber.   8. The tool of claim 7, wherein the narrow process gap input opening and output opening each include a spacer defining a gap smaller than the narrow process gap.   The tool of claim 5, wherein the gas inlet line provides a VIA material processing gas to the heating chamber.   The supply chamber and the receiving chamber each include a gas inlet for transmitting an inert gas to the supply chamber and the receiving chamber, respectively, so that from the supply chamber to the narrow process gap through the input opening and from the receiving chamber to the narrow process gap through the output opening. 5. A tool according to claim 4, wherein an inert gas flow is established thereby preventing gases in a narrow process gap from entering the supply chamber and the receiving chamber.   The tool of claim 10, wherein the distance between the upper and lower walls varies across the length of the narrow process gap in the heating chamber.   The tool of claim 11, wherein the narrow process gap input opening and the output opening each include a spacer defining a gap smaller than the narrow process gap.   The tool of claim 4, wherein the upper wall of the narrow process gap is substantially parallel to the lower wall of the narrow process gap.   14. A tool according to claim 13, wherein the height of the narrow process gap is 0.5-10 mm.   The tool according to claim 14, wherein the width of the narrow process gap is in the range of 100 to 2000 mm. In a rapid thermal processing (RTP) system for forming a solar cell absorber by reacting a pre-deposited precursor layer on the surface of a continuous flexible sheet workpiece,
A continuous flexible sheet workpiece that allows the formation of its vacuum and evacuation and includes a first processing section, a diffusion barrier section, and a second processing section that are advanced through a predetermined temperature profile A heating chamber that feeds the portion of
The first processing section includes a first narrow process gap and heats and processes a portion of the continuous flexible sheet workpiece disposed therein in the presence of at least one first gas. And
The second processing section includes a second narrow process gap and heats a portion of the continuous flexible sheet workpiece disposed therein in the presence of at least one second gas. Process,
The first narrow process gap and the second narrow process gap are each continuous and flexible with different portions of the predetermined temperature profile disposed within the respective first narrow process gap and second narrow process gap. To the work piece part of
The first narrow process gap and the second narrow process gap are defined by an upper wall, a lower wall, and a side wall forming an opening, and the height is substantially smaller than the width of the first narrow process gap and the second narrow process gap. Has an input opening, an output opening, and an exhaust line disposed between the input opening and the output opening for removing gases from each of the first and second narrow process gaps;
A diffusion barrier section disposed between the first and second narrow process gaps passes through its output opening from the central region of the diffusion barrier section to the first narrow process gap and through its inlet opening to the second narrow process gap. Creating a barrier to reduce the mixing of at least one first gas and at least one second gas, and
The pre-drawn and unrolled portion of the continuous and flexible sheet workpiece is fed from the supply roll to the heating chamber and the processed portion of the continuous and flexible sheet workpiece around the receiving roll is wound. A system comprising a movable mechanism for holding or moving a continuous flexible sheet workpiece within a section of a heating chamber by taking.   The system of claim 16 further comprising a supply chamber for holding a continuous and flexible sheet workpiece supply roll, the supply chamber being integrated with the heating chamber.   The system of claim 17, further comprising a receiving chamber for holding a receiving roll of continuous and flexible sheet workpieces, the receiving chamber being integrated with the heating chamber.   The supply chamber and the receiving chamber each include a gas inlet for transmitting an inert gas to the supply chamber and the receiving chamber, respectively, so that the supply chamber and the first narrow process gap through the input opening and the second from the receiving chamber through the output opening. 18. A system according to claim 17, wherein an inert gas flow to a narrow process gap is set, thereby preventing gases in the first and second narrow process gaps from entering the supply chamber and the receiving chamber, respectively. .   21. The system of claim 19, wherein the first and second narrow process gaps each include a gas inlet for at least one first type gas and at least one second type gas, respectively.   21. The system of claim 19, wherein the first and second narrow process gaps each include a gas inlet for at least one first type gas and at least one second type gas, respectively.   The system of claim 19, wherein the upper wall is parallel to the lower wall of the first and second narrow process gaps, and the diffusion barrier section includes an upper diffusion barrier wall parallel to the lower diffusion barrier wall.   23. The height between the upper and lower walls of each first and second narrow process gap is at least twice the height between the upper and lower diffusion barrier walls of the diffusion barrier section. System.   15. The system of claim 14, wherein the height between the upper and lower walls of the first and second narrow process gaps is in the range of 0.5-10 mm.   25. The system of claim 24, wherein the width between the sidewalls of the first and second narrow process gaps is in the range of 100 to 2000 mm. A roll-to-roll comprising a first processing section, a second processing section, and a diffusion barrier section having a gas inlet disposed in the diffusion barrier section between the first and second processing sections When the continuous flexible sheet workpiece is advanced through a rapid thermal processing (RTP) chamber, a thin film IBIIIAVIA solar cell absorber layer is formed on the surface of the continuous flexible sheet workpiece In the process, the first processing section comprises a first inlet opening, a first outlet opening, a first exhaust outlet, and the second processing section has a second inlet opening, a second outlet opening, a second outlet And the process is
Forming a precursor layer on a workpiece of a continuous and flexible sheet, the precursor layer comprising a Group IB material and at least one of a Group IIIA material and a Group VIA material;
A portion of a continuous flexible sheet workpiece having a precursor layer through a first inlet opening by supplying a continuous flexible sheet workpiece previously drawn and spread from a supply roll. Move to the first treatment section in the direction of the first outlet opening;
A first process by applying a first temperature profile and using a first gas while setting an inert gas flow from the gas inlet to the diffusion barrier section and the first outlet opening and the second inlet opening. Treating the precursor layer in the section, whereby the first gas in the first processing section is substantially prevented from entering the second processing section, and the second gas in the second processing section is substantially To prevent entry into the first processing section,
Advance the workpiece portion of the continuous flexible sheet through the diffusion barrier section in the direction of the second processing section;
Treating the precursor layer in the second treatment section by applying a second temperature profile and using the second gas while continuing the inert gas flow;
Removing the treated portion of the continuous flexible sheet workpiece from the outlet opening of the second processing section and winding it around the receiving roll.   26. The process of claim 25, wherein the group IB material is copper (Cu), the group IIIA material is at least one of indium (In) and gallium (Ga), and the group VIA material is selenium (Se).   The first temperature profile has a profile that varies from substantially room temperature near the inlet opening to a first temperature in a first outlet direction, and the second temperature profile is a second temperature near the second outlet. 28. The process of claim 27, having another profile that varies from temperature to substantially room temperature near the outlet opening.   27. The process of claim 26, wherein the first gas and the second gas are selected from the group consisting of an inert gas, a gas containing selenium, and a gas containing sulfur.   In addition, a first gas flow using the first gas through the inlet opening to the first processing section and a second gas using the second gas through the outlet opening to the second processing section. The first gas flow in the first processing section is prevented from leaving the first processing section through the inlet opening and is generated therefrom. The exhaust gas is directed by the first gas stream toward the first exhaust port, and the second gas in the second processing section is prevented from leaving the second processing section through the outlet opening, from there. 27. The process of claim 26, wherein the generated second exhaust gas is directed toward the second exhaust port by the second gas flow.   31. The process of claim 30, wherein the first gas and the second gas are selected from the group consisting of an inert gas, a gas containing selenium, and a gas containing sulfur.   31. The process of claim 30, wherein the first gas, the second gas, the first gas, and the second gas are selected from a group having an inert gas, a gas containing selenium, and a gas containing sulfur. .   The process according to claim 32, wherein the first gas and the second gas are inert gases, the first gas is a gas containing selenium, and the second gas is a gas containing sulfur.   The process according to claim 32, wherein the precursor layer includes selenium (Se), a first gas, and a second gas, the first gas is an inert gas, and the second gas is a gas including sulfur.   The precursor layer has selenium (Se), includes a first gas and a second gas, the first gas is an inert gas, and the second gas is a gas containing selenium. Process.   The process of claim 32, wherein the precursor layer comprises selenium (Se), includes a first gas and a second gas, wherein the first gas and the second gas are inert gases. Continuous and flexible through a roll-to-roll rapid heat treatment (RTP) chamber that includes a narrow gap processing section having an inlet opening, an outlet opening, and an exhaust opening between the inlet opening and the outlet opening In the process of forming a thin film IBIIIAVIA solar cell absorber layer on the surface of a continuous and flexible sheet workpiece as the complete sheet workpiece is advanced,
Forming a precursor layer on the surface, the precursor layer comprising at least one of a group IB material, a group IIIA material, and a group VIA material;
By providing a pre-drawn and unfolded portion of the continuous flexible sheet workpiece from the supply roll, a continuous flexible sheet workpiece through the inlet opening toward the narrow gap processing section and the outlet opening direction Move
Narrow gap processing by applying a first temperature profile while setting a first gas flow from the inlet opening to the narrow gap processing section and a second gas flow from the outlet opening to the narrow gap processing section Processing the precursor layer of the section, whereby the gas of the processing section is substantially prevented from leaving the processing section through the inlet and outlet openings, and is directed in the direction of the exhaust port;
A process comprising the steps of removing a processing portion of a continuous flexible sheet workpiece from an exit opening of a narrow gap processing section and wrapping it around a receiving roll.   38. The process of claim 37, wherein the group IB material is copper (Cu), the group IIIA material is at least one of indium (In) and gallium (Ga), and the group VIA material is selenium (Se).   The first temperature profile has a profile that varies from substantially room temperature near the inlet and outlet openings of the narrow gap processing section to an elevated temperature between the inlet and outlet openings, and the first gas flow And the velocity of the second gas flow is selected to prevent gas in the narrow gap processing section from diffusing into the inlet and outlet openings and condensing on the continuous flexible sheet workpiece. 38. Process according to 38.   40. The process of claim 39, wherein the first gas and the second gas are selected from the group consisting of an inert gas, a gas containing selenium and a gas containing sulfur.   40. The process of claim 39, further comprising providing a process gas to the narrow gap processing section.   42. The process of claim 41, wherein the first gas and the second gas are inert gases, and the process gas is selected from the group consisting of an inert gas, a gas containing selenium, and a gas containing sulfur.   The precursor layer contains selenium (Se), the first gas and the second gas are inert gases, and the processing gas is selected from the group consisting of an inert gas, a gas containing selenium and a gas containing sulfur. 42. The process of claim 41.

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