Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
  • C23C14/24—Vacuum evaporation
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
  • C23C14/0623—Sulfides, selenides or tellurides
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
  • C23C14/34—Sputtering
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/58—After-treatment
  • C23C14/5806—Thermal treatment
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/58—After-treatment
  • C23C14/5846—Reactive treatment
  • C23C14/5866—Treatment with sulfur, selenium or tellurium

Definitions

• the present invention relates to methods for making chalcogenide-based photoabsorbing materials as well as to photovoltaic devices that incorporate these materials. More specifically, the present invention relates to methods for making chalcogenide-based photoabsorbing materials, desirably in the form of thin films as well as to photovoltaic devices that incorporate these materials, in which a precursor film is prepared and then converted to the desired photoabsorbing composition via a chalcogenization treatment.
• n-type chalcogenide materials and/or p-type chalcogenide materials have photovoltaic functionality (also referred to herein photoabsorbing functionality). These materials absorb incident light and generate an electric output when incorporated into a photovoltaic device. Consequently, these chalcogenide-based photoabsorbing materials have been used as the photovoltaic absorber region in functioning photovoltaic devices.
• Illustrative p-type chalcogenide materials often include selenides (S), sulfides (also referred to as S; in some embodiments, SS indicates that sulfur is being used in combination with selenium), and/or tellurides (T) of at least one or more of copper (C), indium (I), gallium (G), and/or aluminum (A).
• Specific chalcogenide compositions may be referred to by acronyms such as CIS, CISS, CIGS, CIGST, CIGSAT, and/or CIGSS compositions, or the like, to represent the constituents of the composition.
• Photoabsorbers based upon chalcogenide compositions offer several advantages. As one advantage, these compositions tend to have a very high cross-section for absorbing incident light. This means that a very high percentage of incident light can be captured by chalcogenide-based absorber layers that are very thin. For example, in many devices, chalcogenide-based absorber layers have a thickness in the range of from about 1 ⁇ to about 2 ⁇ . These thin layers allow devices incorporating these layers to be flexible. This is in contrast to crystalline silicon-based absorbers. Crystalline silicon-based absorbers have a lower cross-section for light capture and generally must be much thicker to capture the same amount of incident light. Crystalline silicon-based absorbers tend to be rigid, not flexible.
• the films are formed by sputtering from one or more metal targets in the presence of selenium and/or sulfur containing gas or vapor from an evaporated source.
• these conventional evaporation approaches are not easily scalable for industrial applications.
• using only a gas as a chalcogen source during sputtering typically requires that enough gas be used to supply the desired chalcogen content in the precursor film plus an overpressure of chalcogen.
• Using so much chalcogen- containing gas tends to cause equipment degradation and chalcogen (e.g.
• An alternative manufacturing approach involves initially forming a precursor film of the desired metal constituents.
• This film may include one or more layers.
• Chalcogen(s) are incorporated into the precursor at a later processing stage under conditions effective to incorporate chalcogen into the film and convert it to the desired tetragonal, chalcopyrite phase. Due to the incorporation of chalcogen into the film after precursor formation, this approach may be referred to as a "post-chalcogenization" approach. This approach appears to be easier to integrate into industrial scale processes. Yet, serious challenges remain.
• the present invention provides strategies for making high quality chalcogenide- based, photoabsorbing compositions from sputtered precursor film(s).
• the precursors are converted into the chalcogenide photoabsorbing material via a chalcogenizing treatment (also referred to as "post-chalcogenization,” including, e.g., "post-selenization” when Se is used and/or "post-sulfurization” when S is used) using techniques that allow the post- chalcogenizing treatment to occur under atypically and surprisingly low pressure conditions without significant indium loss. Consequently, the strategies of the invention are readily incorporated into batch processes or continuous processes such as roll-to-roll process occurring under vacuum.
• the present invention is useful at lab, pilot plant, and industrial scales.
• the present invention provides a method of making a chalcogen- containing photoabsorbing composition, comprising the steps of:
• a cap on the precursor comprising at least one chalcogen
• heating is carried out in the presence of at least one gas or vapor that comprises a chalcogen.
• the gas or vapor comprises t1 ⁇ 4S or F ⁇ Se.
• heating is carried out in an inert gas.
• a solid cap incorporates a chalcogen in elemental form.
• a process according to the invention occurs in a continuous and/or semicontinuous roll-to-roll manufacturing process. Such preferred aspects may be practiced singly, or two or more of these may be practiced in combination.
• Fig. 1 is a schematic diagram of an illustrative photovoltaic device that incorporates principles of the present invention
• Fig. 2 is a schematic diagram showing an exemplary structure for a substrate that may be used in the device of Fig. 1;
• Fig. 3 is a schematic diagram illustrating how the principles of the present invention may be used to fabricate a chalcogen-containing photoabsorbing layer useful in the device of Fig. 1.
• Fig. 1 schematically shows an illustrative embodiment of a photovoltaic device 10 that is prepared according to principles of the present invention.
• Device 10 desirably is flexible to allow device .10 to be mounted to surfaces incorporating some curvature.
• device 10 is sufficiently flexible to be wrapped around a mandrel having a diameter of 50 cm, preferably about 40 cm, more preferably about 25 cm without cracking at a temperature of 25°C.
• Device 10 includes a light incident face 12 that receives light rays 16 and a backside face 14.
• Device 10 includes a chalcogenide-containing photovoltaic absorber region 20 formed on an underlying substrate 18.
• Substrate 18 generally refers to the body on which the CIGS precursor film is formed and often incorporates multiple layers.
• One illustrative embodiment of a multilayer structure for substrate 18 is shown in Fig. 2.
• substrate 18 generally includes support 22, barrier region 23, and backside electrical contact region 24.
• Support 22 may be rigid or flexible, but desirably is flexible in those embodiments in which the photovoltaic device may be used in combination with non-flat surfaces.
• Support 22 may be formed from a wide range of materials. These include glass, quartz, other ceramic materials, polymers, metals, metal alloys, intermetallic compositions, woven or non-woven fabrics, combinations of these, and the like. Stainless steel is preferred.
• the support 22 desirably is cleaned prior to use to remove contaminants, such as organic contaminants.
• a wide variety of cleaning techniques may be used. As one example, plasma cleaning, such as by using F plasma, would be suitable to remove organic contaminants from metal-containing supports. Other examples of useful cleaning techniques include ion etching, wet chemical bathing, and the like.
• the barrier region 23 helps to isolate the photovoltaic absorber region 20 from the support 22 to prevent contamination. For instance, barrier region 23 can help to block the migration of Fe and other constituents from a stainless steel support 22 into the absorber region 20. The barrier region 23 also can protect the support 22 against Se migration if Se is used in the formation of the photovoltaic absorber region 20. Desirably, the barrier region
• a film comprising Nb desirably has a thickness of at least about 30 nm, preferably at least about 50 nm, and more preferably at least about 100 nm.
• the thickness of such a film desirably is less than about 1000 nm, preferably less than about 400 nm and more preferably less than about 300 nm.
• a Nb barrier having a thickness of about 150 nm would be suitable.
• the backside electrical contact region 24 provides a convenient way to electrically couple the device 10 to external circuitry (not shown).
• the backside electrical contact region 24 also helps to isolate the photovoltaic absorber region 20 from the support 22 to minimize cross-contamination. As is the case with any of the regions of device 10, region
• Electrode 24 may be formed from a single layer or multiple layer using a wide range of electrically conductive materials, including one or more of Cu, Mo, Ag, AI, Cr, Ni, Ti, Ta, Nb, W combinations of these, and the like. Conductive compositions incorporating Mo may be used in an illustrative embodiment.
• Region 24 optionally may incorporate one or more agents such as Na, Li, H, combinations of these, and the like.
• Na for instance, is believed to favorably impact the growth of crystalline grains in the formation of the photovoltaic absorber region 20. It also is believed that the Na acts as a Se flux and/or mobilizing agent to facilitate the formation of high quality chalcogen-containing photoabsorber materials. Na might also contribute favorably to the electronic performance of the chalcogen-containing photoabsorbing materials.
• a separate layer incorporating NaF, Na-doped metals, or the like may be incorporated into region 24, This layer may exist on the top of region 24, be buried at any other location in region 24, or mixed evenly within the layer.
• a Na-containing target may be co-sputtered or otherwise concurrently supplied with one or more electrically conductive materials to incorporate Na into at least a portion of the resultant sputtered region 24.
• a target containing 97 atomic percent Mo and 3 atomic percent Na can be sputtered to form a suitable film having a thickness of at least about 30 nm, preferably at least about 50 nm.
• Such a film desirably has a thickness of less than about 2000 nm, preferably less than about 500 nm.
• such a target is sputtered to provide a film that is about 350 nm thick.
• chalcogenide-containing photovoltaic absorber region 20 absorbs light energy embodied in the light rays 16 and then photovoltaically converts this light energy into electric energy.
• Region 20 can be a single integral layer as illustrated or can be formed from one or more layers.
• the chalcogenide absorber region 20 preferably incorporates at least one ⁇ - ⁇ - chalcogenide, such as D3-IIIB-selenides, IB-IIIB-sulfides, and/or ⁇ - ⁇ -selenides-sulfides that include at least one of copper, indium, and/or gallium. In many embodiments, these materials are present in polycrystalline form. Some embodiments include sulfides or selenides of copper and indium. Additional embodiments include selenides or sulfides of copper, indium, and gallium.
• Such chalcogenide materials optionally may include aluminum, tellurium, and the like. Aluminum could be used, for instance, instead of or in addition to gallium. Such chalcogenide materials also may be doped with other materials, such as Na, Li, H or the like, to enhance performance. In many embodiments, CIGS materials have p- type characteristics.
• Oxygen (O) is technically a chalcogen according to its placement in the periodic table of the elements.
• oxygen is deemed not to be a chalcogen for purposes of the present invention inasmuch as oxygen does not contribute to photoabsorbing functionality to the extent of the other chalcogens such as S and/or Se.
• oxygen may still be incorporated into chalcogenide photoabsorbing materials purposefully for other reasons such as to contribute to electronic properties, as an artifact of manufacture, and/or the like.
• many chalcogen materials incorporate at least some oxygen, e.g., from 0 atomic percent to about 5 atomic percent based on the total composition of the region 20.
• One preferred class of chalcogenide photoabsorbing materials may be represented by the formula
• c is 0 to 0.5, preferably 0.05 to 0.35
• (w+x+y) is 1 to 3, preferably 2 to 2.8 (note, (w+x+y) ⁇ 2 for substoichiometric precursor films)
• w is 0 or more, preferably at least 1 and more preferably at least 2 to 3
• x is 0 to 3, preferably 0 to 0.5
• z is 0 to 0.5, preferably 0.005 to 0.02
• the copper indium selenides/sulfides and copper indium gallium selenides/sulfides are preferred.
• Illustrative examples of such photoelectronically active chalcogenide materials may be represented by the formula
• such films usually include additional In, Ga, Se, and/or S.
• chalcogen-containing, photoabsorbing materials exhibit excellent cross-sections for light absorption that allow region 20 to be very thin and flexible.
• a typical absorber region 20 may have a thickness of at least about 1 um, preferably at least about 1.5 um. Region 20 desirably has a thickness of less than about 5 um, preferably less than about 3 ⁇ .
• the principles of the present invention are used to form high quality, chalcogenide- based photovoltaic materials for use in region 20. These principles allow these materials to be formed at low pressure in a manner that is compatible with continuous roll to roll manufacturing strategies that occur under vacuum.
• the methodologies of the invention include at least three main stages that can be practiced sequentially or at least partially co- currently with one or more of the other stages. These stages include forming a precursor of the desired chalcogenide photoabsorbing composition, forming a chalcogen-containing cap on the precursor, and then converting the capped precursor into the desired photoabsorbing material.
• an initial stage 100 involves preparing a precursor film 112. In many embodiments, this is accomplished by using one or more targets to sputter the constituents onto substrate 18 to form precursor film 112. Sputtering may occur in one step or in a sequence of two or more steps. If multiple sputtering steps are used, these may occur sequentially, concurrently, or in overlapping fashion.
• the resultant precursor film structure may include one or more layers. If the precursor film 112 has multiple layers, the interfaces between layers may be distinct or can be graded transitions. The constituents of precursor film 112 may be incorporated into the same and/or different layers.
• a single target 110 is used in stage 100 to form a precursor film 112 with a single layer structure.
• the precursor film includes the desired metal constituents and optionally at least a portion of the desired chalcogen content. Consequently, target 110 would have a composition that is effective to deposit at least the metal constituents of the desired region 20 in the desired proportions.
• target 110 of this illustrative embodiment generally would include copper, indium, and gallium in proportions effective to form precursor film 112 including these elements.
• One such suitable target 1 10 may include about 35 to about 50 atomic percent Cu, about 50 to about 65 atomic percent In, and about 0 to about 30 atomic percent Ga. Other targets having other proportions of the constituents may also be used.
• a specific embodiment of an exemplary target of this type includes 45 atomic percent Cu, 42 atomic percent In, and 13 atomic percent Ga.
• a target can be used to form a precursor film 112 including Cu, In, and Ga having a thickness of at least about 0.75 um, preferably at least about 0.8 ⁇ .
• Such a film desirably has a thickness of less than about 2 ⁇ , preferably less than about 1 um.
• Such a film 1 12 in many embodiments may have a target mass of about 65 mg to about 75 mg of CIG material per 4 inch x 4 inch area of the substrate 18.
• the target containing 45:42: 13 atomic percent C:In:Ga could be pre-sputtered for a suitable time period, such as about 3 minutes, to pre-condition the target.
• the precursor film 112 may be formed at any suitable pressure.
• a suitable pressure may be at least about 1 millibar (mBar), preferably at least about 3 mBar. Such a pressure desirably is less than about 10 mBar, preferably less than about 5 mBar. A pressure of about 4 mBar would be suitable for instance.
• Sputtering desirably occurs in the presence of a suitable sputtering gas supplied at a suitable flow rate to establish the desired pressure.
• An exemplary sputtering gas is argon. It is understood that the flow rate(s) used are a function of a number of factors including pumping speed and the configuration of the chamber. Sputtering occurs for a suitable time period, such as for about 28 minutes at a suitable sputtering power, such as about 125W to form a precursor Film 112.
• Additional constituents such as Na, Li, Te, and/or the like may also be incorporated into precursor film 112 via sputtering or other techniques as well. If sputtered, these can be incorporated into the same target 110 or supplied from additional target(s) (not shown). Optionally, such additional constituents or even a portion of the metal constituents can be supplied via other sources, such as by sputtering in the presence of one or more suitable gases or vapors.
• precursor film 112 could be formed from multiple targets such as a pair of confocal targets. Using this strategy, for instance, a CuGa target and an In target could be used confocally to form a C:I:G precursor film.
• the precursor film may be formed from multiple targets by passing the substrate through a plurality of sputtering zones.
• Confocal target or other multiple-target strategies such as this are also useful in some embodiments to pre-incorporate at least a portion of the chalcogen content of the desired region 20 (Fig, 1) into at least a portion of the precursor film 112.
• a precursor film incorporating overall a substoichiometric amount of selenium is formed from confocal first and second targets, wherein the first target includes the composition Cu x Se y , wherein x is approximately 2 and y is approximately 1, and the second target incorporates Cu, In, and Ga according to the formula CuIn p Ga ( i_ p) , wherein p desirably is in the range from about 0.5 to about 1. Details of incorporating chalcogen into precursor film 112 are further described in
• a chalcogen-containing film also referred to herein as a cap 114 is formed in stage 102 over the precursor film 112,
• the cap 1 14 is in the form of a solid cap including one or more chalcogens.
• the cap 114 incorporates Se, Te, and/or S. Se and/or S are preferred. Se is most preferred. If both Se and S are used, the atomic ratio of Se to S in illustrative embodiments may be in the range from about 1000: 1 to about 1000: 100, preferably about 1000: 10 to about 1000:50.
• the chalcogens can be present in cap 114 as compounds and/or in elemental form. The elemental form is preferred.
• the amount of chalcogen(s) incorporated into the cap 114 relative to the stoichiometric amount needed to complete region 20 can vary over a wide range. However, if the amount of chalcogen(s) in the cap is too low, lesser amounts of In and/or Se may be incorporated into the resultant region 20 than might be desired. Also, the reproducibility of the stage 102 may be less than desired.
• the cap 114 includes at least the stoichiometric amount (Ix) of chalcogen(s) needed to convert substantially the entirety of the precursor film 112 to the desired tetragonal photoabsorbing phase, taking into account chalcogen content that might already be present in the precursor film 112. More preferably, it is desirable that at least 2x, and more preferably at least about 5x the stoichiometric amount of chalcogen(s) are incorporated into the cap 114.
• the cap incorporates no more than about 1 OOx, preferably no more than about 60x, preferably no more than about 30x, of the stoichiometric amount of chalcogen(s).
• the cap incorporates no more than about 1 OOx, preferably no more than about 60x, preferably no more than about 30x, of the stoichiometric amount of chalcogen(s).
• using a cap with LOx, 1.5x, 2.0x, 2.5x, lOx, 25x, or 5 Ox of the stoichiometric amount of chalcogen(s) would be suitable.
• the stoichiometric amount of chalcogen can be calculated based upon the relative amounts of metal constituents in the precursor.
• a cap 114 with a suitable stoichiometric excess of chalcogen(s) has a thickness in the range from about 15 ⁇ to about 20 ⁇ .
• the target mass desirably involves depositing an amount of chalcogen(s) effective to provide the stoichiometric quantity (lx) relative to the precursor or the desired excess of chalcogen(s) (e.g., about 2X to about 50X in illustrative embodiments) relative to the precursor.
• the cap 114 may be formed by evaporation from a resistively heated stainless steel boat or ceramic crucible.
• the pre-weighed substrate is suspended facedown over the crucible. Based on calibration, the amount of selenium needed to achieve the desired cap is loaded into the crucible.
• the chamber is pumped to a base pressure of less than about 10 "4 mBar, and then the crucible is heated to greater than about 300°C (based on a temperature reading from a thermocouple immersed in the molten chalcogen). The full selenium load is evaporated.
• a cap 1 14 may be desirable to form a cap 1 14 from multiple layers in view of factors including to enhance uniformity, to accommodate equipment limitations, to prevent radiative heating of the substrate over extended deposition times, and/or the like.
• the crucible may be loaded two or more times to form the cap in two or more steps.
• the capped precursor film 108 is subjected to
• This stage also may be referred to as a "post- chalcogenization" treatment to connote that at least a portion of the treatment occurs after precursor formation.
• the stage 104 can be referred to as a post-selenization treatment.
• the stage 104 can be referred to as a post-sulfurization.
• this stage 104 occurs under thermal conditions effective to also anneal the capped film 108, thereby converting the precursor film 1 12 to the desired tetragonal, chalcopyrite phase to the extent the capped precursor does not already have that crystal structure at this stage.
• stage 104 also may be referred to as an annealing treatment to recognize the conversion of the precursor film 112 into the desired chalcopyrite, tetragonal phase.
• Chalcogenization generally occurs by positioning the capped film 108 in a suitable processing chamber (not shown) in which the capped film 108 is exposed to thermal conditions effective to convert the precursor into the photoabsorbing region 20.
• the chamber can be the same or different from the chamber(s) used to form other layers of the capped film 108.
• the capped film 108 In a continuous roll-to roll process occurring under vacuum, the capped film 108 generally is transferred from a capping station to one or more dedicated, downstream stations at which chalcogenization occurs.
• the sample temperature desirably is maintained at a suitably low temperature during the transfer to avoid undue loss of In and/or Se.
• the sample temperature may be about 150°C or less, more preferably about 100°C or less during the transfer.
• a transfer temperature of about 80°C would be suitable.
• the temperature of the capped film 108 is then increased to an. annealing temperature effective to cause the desired conversion.
• the rate at which the temperature is increased to the annealing temperature can impact the incorporation of In and/or Se into the resultant product. If the temperature ramp rate is too low, undue loss of In and/or Se may occur. On the other hand, if the ramp rate is too fast, undue loss of In, Se, and/or Ga could occur. Other problems that may be encountered include pinholing of the final film. It could also be possible that damaging microbursts could result from volatilization of constituents of the capped precursor film 108.
• the temperature ramp rate is at least about 1°C/ min, preferably at least about 20°C/Min, more preferably at least about 30°C/min, and most preferably at least about 60°C/min. Additionally, the temperature ramp rate is desirably less than about 500°C/min, preferably less than about 400°C/min, and most preferably less than about 200°C/min. In one illustrative embodiment, a ramp rate of about 30°C/min to about 60°C/min would be suitable. In another illustrative embodiment, a ramp rate of 100 °C/min to 150°C/min would be suitable. '
• the annealing temperature desirably is at least about 450°C, preferably at least about 500°C, and less than about 600°C, more preferably less than about 550°C.
• annealing temperature of about 350°C would be suitable such as when annealing with a Se cap in the presence of a chalcogen containing gas such as 3 ⁇ 4Se.
• Annealing generally occurs for a time sufficient to chalcogenize the film and to convert the film to the tetragonal phase to the desired degree. In many embodiments, annealing occurs for a time period of at least about 1 minute, preferably at least about 5 minutes, but less than about 36 hours, preferably less than about 3 hours.
• a suitable control strategy is implemented in order to maintain the annealing temperature at a steady level during the course of annealing.
• Feedback control using ⁇ strategies would be suitable.
• stage 104 can occur in a low-pressure regime that is compatible with continuous roll-to-roll processes occurring under vacuum. It is quite significant to find process conditions that work under such low pressure inasmuch as process strategies that work at higher pressures do not necessarily translate to vacuum processes. Generally, the risk of In loss increases if the pressure at stage 104 is too low. On the other hand, if the pressure is too high, it could be harder to practically and economically integrate stage 104 into a continuous roll-to-roll process occurring under vacuum.
• stage 104 desirably occurs at a pressure no greater than about 300 millitorr (4e _1 mBar), preferably no greater than about 100 millitorr (le “1 mBar), more preferably no greater than about 50 millitorr (6e “2 mBar), and most preferably no greater than about 15 millitorr (2e “2 mBar).
• the pressure is at least about 0.1 millitorr (le “ mBar), more preferably at least about 1 millitorr (le “3 mBar), and most preferably at least about 3 millitorr (le “3 mBar).
• a pressure of about 5 millitorr (7e "3 mBar) would be 3 ⁇ 3 ⁇ 4 ⁇ .
• a pressure of about 10 millitorr (le "2 mBar) would be suitable.
• One or more gases can be introduced into the reaction vessel in order to help establish the desired pressure during the course of chalcogenization and annealing.
• a wide variety of strategies can be used to accomplish this.
• annealing and chalcogenization occur in the presence of a flow of an inert gas such as Ar, or the like, introduced into the chamber.
• Ar an inert gas
• annealing at 505°C in the presence of 136 seem Ar would be suitable.
• this flow rate of Ar corresponds to a pressure of about 10 "3 millibarr.
• annealing and chalcogenization occur in the presence of one or more gases or vapors incorporating one or more chalcogens introduced into the chamber.
• gases may serve as additional sources of chalcogen to be incorporated into region 20.
• gases of this type include H 2 S, H 2 Se, mono or dialkylated S, mono or dialkylated Se, combinations of these and the like. Combinations of these strategies also may be used. For instance, annealing can occur in the presence of a combination of one or more inert gases and one or more chalcogen-containing gases.
• a preferred mode of practice involves capping the precursor film 112 with a Se cap 1 14 while annealing in the presence of a sulfur containing gas such as H 2 S.
• a sulfur containing gas such as H 2 S.
• This approach is believed to yield tetraganol CIGSS (Cu:h :Ga:Se:S) and offers significant advantages.
• the Se cap provides sufficient Se to selenize the film while the H 2 S supplies sulfur to sulfurize the film, increasing bandgap.
• the sulfur-containing gas is much easier to handle than a Se- containing gas.
• conversion of the capped precursor to CIGSS using this strategy has been observed to occur at lower temperatures, e.g., as low as 350°C.
• One factor impacting chalcogenization in some embodiments may be whether the reactor walls are chilled or cooled.
• either hot-walled or cold- walled chambers can be used to accomplish selenization.
• Cold-walled reactors are desirably used when the stoichiometric excess of chalcogen(s) in a cap is greater than about 5X, preferably greater than about 7X, more preferably greater than about 10X.
• Cooling of at least a portion of the reactor walls can be accomplished in any desired fashion. Water- cooling is one suitable technique.
• the cooled walls may be maintained at a temperature in the range of about 10 to about 25° C, preferably 15 to about 22°C.
• Evaporated selenium generally would not be expected to be incorporated into the final film in a chamber with chilled walls, but rather would be generally expected to be plated out on the cooled walls of the chamber,
• a benefit of using cold-wall reactors is that the excess selenium is condensed onto the chilled-walls thereby preventing it from entering the pumping system or other system components and causing corrosion or damage to them.
• Hot-walled reactors are desirably used when the stoichiometric excess (if any) of chalcogen(s) in the cap is below about 5x, preferably below about 4x, more preferably below about 3x.
• a hot wall reactor at least some of the reactor walls are at temperatures above the sublimation/evaporation points of the selenium. This is expected to create a dynamic selenium annealing atmosphere.
• Selenium that evaporates from the surface of the capped precursor generally would not be expected to plate against the heated walls of the chamber but instead may contribute to a gaseous selenium environment which then contributes to the evaporation vs. reaction dynamics of the selenium at the CIGS surface during formation.
• Annealing and chalcogenization convert the capped precursor film 108 into the desired photoabsorber region 20.
• the workpiece 108 can be cooled down, or allowed to cool down, and then subjected to further processing to complete device 10. Generally, this involves cooling the sample down to about 200°C. It has been discovered that if the cooling rate is too rapid relative to Se in the surrounding atmosphere, elemental Se could condense at the surface of region 20, which could unduly impair device function. On the other hand, if the substrate cools too quickly relative to Se in the atmosphere, Se can evolve from the surface of the substrate which may unduly impair device function. Balancing these concerns, it is preferred to allow the workpiece to cool passively before transferring it from the chalcogenization chamber.
• the cap 114 and the temperature ramp to the annealing temperature singly or in combination can help allow chalcogenization and annealing to occur at low pressure in a manner that is compatible with roll-to-roll manufacturing strategies occurring under vacuum. In the absence of cap 114 and/or by practicing ramp rates that are too slow or too fast, subsequent chalcogenization is much more difficult to carry out effectively. Indium incorporation is poor, and the resultant region 20 may be severely deficient with respect to In if chalcogenization and annealing occur at low pressure, e.g., at a pressure below about 300 millitorr, preferably below about 100 millitorr, more preferably below about 50 millitorr.
• cap 1 14 optionally with an appropriate temperature ramp rate
• cap 1 14 are features that singly and in combination enable chalcogenization and annealing of CIGS precursor films to occur at low pressures feasible for continuous vacuum roll to roll processes.
• a cap and/or appropriate temperature ramp rate under low pressure chalcogenization conditions, In loss is significantly reduced, and incorporation of both In and Se into the resultant region 20 is greatly improved.
• capping a C:I:G precursor film i.e., a precursor film containing Cu, In, and Ga
• elemental Se prior to annealing in H 2 Se or H 2 S gas substantially reduced the loss of Indium.
• a precursor film with an initial In/Cu ratio of about 1.3 capped with 2 times the stoichiometric amount of elemental Se required.to form a CIGS photoabsorbing material was annealed at 350°C in 5 milliTorr H 2 Se.
• the resultant CIGS material had an In/Cu ratio of greater than 1 per ICP analysis.
• the same process carried out at 10 milliTorr produced a CIGS material with an In/Cu ratio greater than 0.9.
• the In Cu ratio was greater than 1 for the resultant films. Similar data for In retention was obtained when H 2 S was used to carry out chalcogenization of precursor films containing Cu, In, and Ga capped with 5 OX elemental selenium. Annealing occurred in 5 millitorr H 2 S at 150°C, 350°C, and 500°C. In all samples, the In Cu ratio of the resultant CIGS material per ICP analysis was greater than 1.2.
• annealing temperature profile impacts the amount of chalcogen that remains on or integrates into the film 1 12.
• the resultant region 20 had a Se/Cu ratio of only about 0.5. This is indicative of poor Se incorporation for a Se cap that included 5 OX times the stoichiometric amount of Se needed to convert the precursor into a photoabsorbing CIGS material.
• An annealing temperature of 150°C is generally too low to successfully convert the precursor film to the desired tetragonal CIGS material in any event. In contrast, when annealing under otherwise identical conditions at 350°C, Se incorporation improves.
• the resultant region 20 showed a Se/Cu ratio of 1.6, and XRD analysis indicated the presence of the desired tetragonal CIGS phase. Se incorporation improves further when annealing under otherwise identical conditions at 500°C.
• the resultant region 20 showed a Se/Cu ratio of 2.5.
• the region 20 was in the form of the pure, tetragonal CIGS phase.
• buffer region 28 generally comprises an n-type semiconductor material with a suitable band gap to help form a p-n junction between the absorber region 20 and the buffer region 28.
• An optional window region 26 also may be present.
• Optional window region 26 can help to protect against shunts.
• Window region 26 also may protect buffer region 28 during subsequent deposition of the transparent conductive layer 30.
• Each of these regions is shown as a single integral layer, but can be a single integral layer as illustrated or can be formed from one or more layers.
• One or more electrical conductors are incorporated into the device 10 for the collection of current generated by the absorber region 20.
• a wide range of electrical conductors may be used.
• electrical conductors are included on both the backside and light incident side of the absorber region 20 in order to complete the desired electric circuit.
• backside electrical contact region 24 provides a backside electrical contact in representative embodiments.
• device 10 incorporates a transparent conductive layer 30 and collection grid 36.
• an electrically conductive ribbon (not shown) may also be used to electrically couple collection grid 36 to external electrical connections.
• a protective barrier system 40 desirably is provided.
• the protective barrier system 40 is positioned over the electronic grid 36 and helps to isolate and protect the device 10 from the environment, including protection against water degradation.
• the barrier system 40 optionally also may incorporate elastomeric features that help to reduce the risk of damage to device 10 due to delamination stresses, such as might be caused by thermal cycling and or localized stress such as might be caused by impact from hail and or localized point load from the weight of an installer or dropped tools during installation.
• Example 1 Fabrication of CIGS solar cell in a roll-to-roll tool
• a roll of 430 series stainless steel is loaded into a continuous roll-to-roll vacuum sputtering system.
• This active side of the web is first cleaned with ion etching and then is coated by magnetron sputtering with a Nb barrier layer, a dual layer of Mo for a back contact and a NaF layer to act as a sodium source.
• the back side of the web is coated with Cr as an adhesion layer and Mo to act as a sacrificial layer during the selenization process.
• the web is then translated into a Cu:In:Ga precursor sputtering chamber. Seven pulsed DC magnetrons are arranged in four zones. Each zone has individual gas control. The web is transported sequentially through the four zones. Each of the first, third, and fourth zones has 2 magnetrons. The second zone has a single magnetron. In this example, all magnetrons are adjusted to sputter parallel to the web.
• the web moves from magnetron number 1 through 7 where magnetrons 1 (Zone 1), 2 (Zone 1), 3 (Zone 2), 5 (Zone 3), and 7 (Zone 4) have targets of composition 45:32: 13 Cu:In:Ga and magnetrons 4 (Zone 3) and 6 (Zone 4) have compositions of 35:46:20 Cu:In:Ga. In stationary tests where the web is not moving, the paired targets show a -15% overlap in the sputter deposition while the four zones are completely separate.
• the precursor film containing Cu, In, and Ga (CIG film) is sputtered between 6e-3 to 8e-3 mBar (4.5 to 6 mTorr) in Argon with a maximum web temperature of ⁇ 80°C,
• the flow rates of the Argon and throttling of the pumping system are used to maintain the pressure range in each individual sputter zone. Depending upon the configuration of each zone, it may be desirable to adjust flow rates, pump settings, or the like, in order to maintain desired pressure(s) in the zones.
• the flow rates (throttling) Ar of the individual zones are 380 seem (90° throttle or full open) in zone 1, 600 seem (25° open throttle) in zone 2, 650 seem (25° throttle) in zone 3 and 400 seem (90° throttle or open) in zone 4.
• the targets are sputtered at 600 watts with no pulsing (straight DC).
• the final film stoichiometric ratio for the precursors ranges from In/Cu 0.95-1.01 and Ga/Cu 0.32-0.34, as measured by ICP on representative calibrations runs.
• the web carrying the CIG precursor film is translated into a selenium evaporation unit for application of a selenium cap.
• the selenium evaporation unit includes a stainless steel boat with a effusion slit at the top with the slit being -1-2 cm from the CIG-coated web face.
• the web temperature is not actively controlled.
• the slit has enough width such that the unit can be considered open-source configuration (i.e. no pressure of selenium vapor is building up inside the unit).
• the selenium melt is heated to 300-305 °C.
• ICP data shows an average Se/Cu ratio for the cap is 14 (i.e.
• the resultant product is a web carrying a CIG-Se stack.
• the resultant web carrying the CIG-Se stack is translated into a hot- wall oven.
• the pressure is estimated to be l-10e-3 mBar (0.75 to 7.5 mTorr) based upon a pressure gauge outside the furnace zone but in the same chamber.
• Adjacent chamber pressures are maintained at le-3 mBar to 8 e-3 mBar(0.75 to 6 mTorr).
• the heating zones are set to achieve a maximum ramping rate of ⁇ 60°C/min to an average web temperature of 580-585°C. This temperature range is estimated based on previous calibration of the system and not actively measured due to the dynamic configuration intrinsic to the continuous roll-to-roll process.
• the web is maintained at an average temperature of 580-585°C for ⁇ 20 minutes before being cooled to ⁇ 425°C at 60 °C/min and then further to ⁇ 300°C at a reduced rate of 20°C/min. * Data
• the completed CIGS films are then transferred into additional process chambers (all within the same vacuum system) for deposition of buffer and window layers before being wound onto a final core.
• the CIGS films are analyzed by ICP.
• Final In/Cu ratios ranged from 0.86 to 0.97 while Ga Cu range from 0.27 to 0.33 giving final III/Cu ratios from 1.13 to 1.30.
• Se/Cu ratios ranged from 2.48 to 2.91 - as sample preparation for the ICP digestion is not specific to the active side vs. the back side, it is likely that some of the stoichiometric excess of selenium is not in the CIGS film but rather in the form of elemental or reacted coatings on the back side of the substrate.
• photoactivity of the material was demonstrated with efficiencies typically ranging from 5-8%.
• a stainless steel coupon is first cleaned by sonication in solvent baths and dried with dry N2 gas and loaded into a multi-chamber vacuum deposition system.
• the face of the substrate is further cleaned using 300 F plasma etching in Argon.
• the substrate is then transferred under vacuum to a second chamber where a niobium adhesion layer and molybdenum back contact layer are deposited by sputtering.
• the sample is removed from vacuum.
• the substrate is later introduced into a precursor sputtering chamber comprising a single, commercially available Cu:rn:Ga alloy target tilted off-axis with respect to the substrate to give a more uniform coating thickness.
• the target is 45:42: 13 Cu:In:Ga.
• the sample is rotated during deposition.
• the substrate bearing the CIG film is removed from vacuum and loaded into a selenium evaporation chamber for application of a selenium cap.
• the selenium evaporation unit includes an open-top ceramic cup nested in a resistive heating element.
• the substrate is mounted face-down over the cup on a metal frame, and 22 g of shot is loaded to give a 25x cap.
• the system is evacuated to ⁇ 5e-6 Torr (7e "6 mBar).
• the selenium crucible is heated to >300°C for sufficient time to allow the full aliquot of shot to be evaporated.
• the system is allowed to cool and then vented for loading of a second 22g aliquot of selenium shot.
• the sample is rotated to improve film thickness uniformity before evaporation of the second full aliquot.
• the process yields a Ox cap.
• the substrate bearing the CIG-Se stack is removed from vacuum and transferred to a selenization chamber.
• the substrate is suspended face down and heated from the back-side with a radiative graphite element.
• the system has water-cooled walls ( ⁇ 25°C recirculating loop).
• the base pressure is 3e-7 mBar prior to the run.
• the pressure in the system is increased to 6.6e-3 mBar using 100% H 2 S gas prior to heating.
• the substrate ramped up at 60°C/min to about 400 °C and then at about 3-5 °C/min to a final temperature >500°C (estimated to be about 515°C) by setting the power supply for the graphite heater at a previously determined power duty cycle value.
• the temperature of the substrate is maintained at >500°C for 30 minutes at which time the power supply is turned off.
• the resulting film is allowed to cooled to ⁇ 80°C before transferring to a vacuum load-lock chamber for removal.
• the substrate bearing the completed CIGS film is removed from the system and analyzed by ICP for elemental composition.
• the In/Cu ratio of the film is 1.3 ((In+Ga)/Cu 1.6) while the Se/Cu is 1.7. Sulfur is not detected in the film by ICP.
• Analysis of the X-ray diffraction pattern of the film shows tetragonal CIGS, InSe, Cu, Mo, Nb, and Fe.
• the substrate is prepared as in Example 2.
• Example 2 Deposition of a CIG precursor on the substrate is carried out as in Example 2.
• a Se cap is formed on the CIG precursor as in Example 2.
• the substrate bearing the CIG-Se stack is removed from vacuum and transferred to a selenization chamber.
• the substrate is suspended face down and heated from the back-side with a radiative graphite element.
• the system has water-cooled walls ( ⁇ 25°C recirculating loop).
• the base pressure is 3e-7 mBar prior to the run.
• the pressure in the system is increased to 1.4e-2 mBar using 100% HiSe gas prior to heating.
• the substrate ramped up to >350°C at 20°C/min by setting the power supply for the graphite heater at a previously determined power duty cycle value.
• the temperature of the substrate is maintained at >300°C for 20 minutes at which time the power supply is turned off.
• the resulting film is allowed to cool to ⁇ 80°C before transferring to a vacuum load-lock chamber for removal.
• the substrate bearing the completed CIGS film is removed from the system and analyzed by ICP for elemental composition.
• the In/Cu ratio of the film is 1.1 ((In+Ga)/Cu 1.4) while the Se/Cu is 1 ,31.
• Analysis of the X-ray diffraction pattern of the film shows tetragonal CIGS, InSe, Cu, Mo, Nb, and Fe.
• Example 4a- Annealing of CIG film in Argon demonstrating baseline for annealing CIG in vacuum
• the substrate bearing the sputtered CIG precursor is transferred to a chalcogenzation chamber under vacuum.
• the substrate is suspended face down and heated from the back- side with a radiative graphite element.
• the system has water-cooled walls ( ⁇ 25°C recirculating loop).
• the base pressure is 6e-7 mBar (4.5e "4 mTorr) prior to the run.
• the pressure in the system is increased to 6.6e-3 mBar (5 mT) using 100% Ar gas prior to heating.
• the substrate ramped up to >350°C (at 30°C/min (highest temperature estimated 400 °C) by setting the power supply for the graphite heater at a previously determined power duty cycle value.
• the temperature of the substrate is maintained at >350°C for 30 minutes at which time the power supply is turned off.
• the resulting film is cooled to ⁇ 80°C before transferring to a vacuum load- lock chamber for removal.
• the substrate bearing the completed CIGS film is removed from the system and analyzed by ICP for elemental composition.
• the In/Cu ratio of the film is 1.05 while the Se/Cu was 0.04.
• the substrate bearing the sputtered CIG precursor material is transferred to a chalcogenzation chamber under vacuum.
• the substrate is suspended face down and heated from the back-side with a radiative graphite element.
• the system has water-cooled walls ( ⁇ 25°C recirculating loop).
• the base pressure is 6e-7 rnBar (4,5 ⁇ "4 mT) prior to the run.
• the pressure in the system is increased to 6.6e-3 rnBar (5mT) using 100% H 2 Se gas prior to heating.
• the substrate ramped up to >350°C at 30°C/min (highest temperature estimated to be about 400°C) by setting the power supply for the graphite heater at a previously determined power duty cycle value.
• the temperature of the substrate is maintained at >350°C for 30 minutes at which time the power supply is turned off.
• the resulting film is allowed to cool to ⁇ 80°C before transferring to a vacuum load-lock chamber for removal.
• the substrate bearing the completed CIGS film is removed from the system and analyzed by ICP for elemental composition.
• the In/Cu ratio of the film is 0.61 while the Se/Cu is 0.12.
• Example 4c- Annealing of CIG film w/2x cap in H 2 Se demonstrating improved indium retention when annealing a film with a 2x cap but no CIGS formation yet
• the substrate bearing the CIG precursor film is removed from vacuum and loaded into a selenium evaporation chamber for application of the selenium cap.
• the selenium evaporation unit includes an open-top ceramic cup nested in a resistive heating element.
• the substrate is mounted face-down over the cup on a metal frame and 1.2 g of shot is loaded to give a lx cap.
• the system is evacuated to 2e-6 Torr (3e "6 mBar).
• the selenium crucible is heated to 360 ° C for sufficient time to allow the full aliquot of shot to be evaporated.
• the system is allowed to cool and then vented for loading of a second 1.2 g aliquot of selenium shot and rotation of the substrate to improve uniformity of the selenium film thickness.
• the evaporation process is repeated (base pressure 2e- 6 Torr (3e "6 mBar), maximum temp 331 °C) to yield a 2x cap.
• the substrate bearing the CIG/Se stack is transferred to a chalcogenzation chamber under vacuum.
• the substrate is suspended face down and heated from the back-side with a radiative graphite element.
• the system has water-cooled walls ( ⁇ 25°C recirculating loop).
• the base pressure is 6e-7 mBar (4.5e "4 mTorr) prior to the run.
• the pressure in the system is increased to 6.6e-3 mBar (5 mT) using 100% 3 ⁇ 4Se gas prior to heating.
• the substrate ramped up to >350°C (at 30°C/min (highest temperature estimated to be about 400°C) by setting the power supply for the graphite heater at a previously determined power duty cycle value.
• the temperature of the substrate is maintained at >350°C for 30 minutes at which time the power supply is turned off.
• the resulting film is allowed to cool to ⁇ 80°C before transferring to a vacuum load- lock chamber for removal.
• the substrate bearing the completed CIGS film is removed from the system and analyzed by ICP for elemental composition.
• the In/Cu ratio of the film is 1.02 while the Se/Cu is 0.37.
• X-ray diffraction analysis of this film included peaks for a cubic CIG phase, InSe, In Se 3 , In, and Cu.
• a sample including a CIG precursor film formed on a substrate.
• the precursor film is capped with 25x Se.
• Thermal annealing of the sample takes place in a vacuum quartz tube oven (VQTO).
• the oven includes an 8" diameter X 54" long quartz tube inserted in a 38" long tube furnace.
• the furnace has three heat zones (left, right, and center) that are individually controlled by Watlow controllers.
• the ends of the tubes have stainless steel caps that are sealed to the tube ends via o-rings.
• a vacuum rough pump in conjunction with a vacuum turbo pump provide pressures measured down to 0.1 millitorr (1.3e-4 mBar).
• a mass flow controller (MFC) connected to an argon gas cylinder provides pressure control between 0.1 and 50 millitorr (1.3e-4 to 6.7 e-2 mBar).
• a liquid nitrogen trap located between the turbo pump and the tube traps selenium vapor. Pressure is measured with a Baratron gauge at a point along a 2-inch diameter line between the quartz tube and the selenium trap.
• the configuration includes a stainless steel carrier rack that holds multiple samples, although only a single sample is used in each run of this example.
• the rack can be inserted from the cold end of the tube to the heated zone via a hook coupled magnetically to the outside of the tube.
• the sample can be removed to cool rapidly with the same device.
• Two flexible thermocouples are placed directly in contact with the backside of the sample for accurate temperature monitoring.
• Static thermocouples are also located at various spots in the tube oven to give the temperature profile of the oven. All thermocouples are type "K”. Controller and static oven temperatures and pressure are recorded on a computer using Agilent data collecting software. Temperatures connected directly to the samples are recorded using an Omega S309 system. Data from these two sources are then combined into an Excel spreadsheet.
• the sample bearing the CIG-Se stack is placed on a stainless steel carrier, which is then placed in the center of the oven.
• the mass flow controller set to zero flow
• the endplate is attached and the tube is evacuated via the rough and turbo pump to about 0.1 millitorr.
• the furnace temperature setpoints are entered into the controllers and the recorders are simultaneously started.
• the controller power to the heaters is turned on and the tube is heated.
• the pressure is maintained at about 0.1 mtorr.
• the substrate is heated at a rate of about 20C/min. to 520C for 35 min. then the carrier with the samples is removed to the cool end of the tube outside the furnace and the power turned off.
• the sample is cooled overnight to room temperature.
• An additional sample is processed identically as in example 5, except that the capped sample is heated at a rate of 5C/min to the annealing temperature.

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