Coating source for targeted doping of a coating, and method for doping said coating

Abstract

The invention relates to a coating source with additional dopants for a coating installation, to a coating installation having such a coating source, and to a method for coating substrates using such a coating source.

Description

[0001] Coating source for targeted doping of a coating and methods for doping the coating

[0002] Field of invention

[0003] The present invention relates generally to a coating source for a coating system with targeted doping of the coating material. In particular, the present invention relates to a thermal evaporation source such as that used in a close-space sublimation process to achieve targeted doping of a coating. Accordingly, the present invention also relates generally to a coating system with such a coating source and to a method for coating substrates using such a coating source with targeted doping of the coating.

[0004] Background of the invention

[0005] When coating, for example, large areas (approx. 1-3 m²) 2Glass substrates, coated or uncoated, and with or without a carrier, are typically heated uniformly to over 400°C in an in-line system, coated, and then cooled. The coating deposited on the hot substrate often consists of CdTe / CdSe, CdTe / CdS, CdSe(20)Te(80), or Cd(x)Se(y)Te(z), and possibly other suitable elements, and forms, for example, part of a CdTe solar module—such as the absorber layer.

[0006] To increase the efficiency of such CdTe solar modules, dopants are introduced into the absorber layer. Doping results in the presence of one or more additional chemical elements in the main material at low concentrations. These dopants (e.g., p-type doping) can be elements from the transition metals of the main elements in the aforementioned layer. The elements of the absorber layer, as well as any interlayer, can be selected from, for example: Cd in group 12 with, for example, Zn and Hg from groups 12 and 14; Te in group 16 with, for example, Se, S, P, Cl, Br, and I from groups 15 and 17; For example, CdCI2, CdBr2, CdCI2, Cd3As2, Cd3P2, Cd3Sb2, Cd3Pb2, ZnCI2, Znl4, Znl2, ZnS, ZnCI2, ZnBr2, lnCI2 etc. The group with P, As and Sb is already in use (doi: 10.1038 / s41598-018-32745-y).The doping concentration with these substances is typically in the range of 10E15 - 10E20 cmE-1 (doi:10.1016 / j.solener.2020.12.070). Together with adapted contact layers such as FTO / ZnO and ZnTe, a CdSeTe / CdTe solar module with arsenic doping can achieve an efficiency of over 21% (21.4% in doi:10.1002 / adfm.202312528, 22.3% in doi.org / 10.1109 / jphotov.) and forms the basis for the further development of modules with an efficiency of 25% (doi: 10.1038 / s41598-018-32745-y).

[0007] To increase efficiency, the dopants should be precisely incorporated into the absorber layer (e.g. the CdSeTe / CdTe layer) during or after processing in the appropriate concentration and preferably with the appropriate distribution.

[0008] The so-called CSS process (Close Space Sublimation) is frequently used to manufacture CdTe modules. This process is being further developed, for example, by Colorado State University (doi: 10.3791 / 60937) and CTF Solar GmbH (www.ctf-solar.de). In the CSS process, the coating material is transferred from a hot source as directly as possible to a hot substrate at low gas pressure. The evaporation process is limited, depending on the evaporation rate (pressure, temperature, area, etc.), either by sublimation from the source itself or by diffusion in the small space between the source (in the millimeter range) and the substrate.

[0009] In the following, various coating processes are discussed using an example of two coating materials and a doping material, whereby these known processes from the prior art do not lead to the desired success in order to increase the efficiency mentioned above, for example.

[0010] First, it is preferred that the temperature of the source be kept as stable as possible (in the range < 1°C) to allow for precise control of the evaporation process. It is assumed that separate sources are used for different coating materials; for example, one source with a first temperature for CdSe (or CdS) and another source with a second temperature for CdTe. Arsenic (As) from the Cd3As2 compound can be used as a dopant.

[0011] The evaporation rates of the respective materials depend on the saturation pressure above the material in a vacuum:

[0012] LogP(CdTe, atm) = 6.572 - (9764 / T(K)) (doi.org / 10.1088 / 2515-7655 / abd297);

[0013] LogP(CdSe, atm) = 6.85 (540-740°C) - (10957 / T(K)) (Nov. 1961, WJWösten, Phys. Lab. of the Nat. Def. Org. TNO The Hague);

[0014] LogP(Cd3As2, mmHg) = 9 - (6600 / (T(K)), (Oct. 1959, VJ. Lyonsa and VJ. Silvestri Res. Lab. Intr. Bus. Mach. Corp., Poughkeepsie, New York)

[0015] Thus, the Cd3As2 pressure at approximately 520°C would correspond to about 1 mbar, and the CdTe pressure at approximately 520°C to about 0.01 mbar. The ratio between these two pressure values ​​is therefore a factor of 100. At typical process temperatures of 700°C and 800°C, the CdTe pressure would be approximately 1 mbar and 10 mbar, respectively, and consequently, the pressure of the dopant would already be in the range of 100–1000 mbar, or close to atmospheric pressure.

[0016] In the VTD (Vapor Transport Deposition) process with CdTe at 840°C, CdsAs2 is vaporized at 310°C and transported into the coating with a carrier gas in order to achieve an As concentration of approximately 1 at% in the layer, which corresponds to the doping concentration of 4xl0E20 cmE-1 (doi:10.1038 / s41598-018-32745-y).

[0017] Arsenic itself has a high saturation vapor pressure at relatively low temperatures: a vapor pressure of 0.01 mbar corresponds to a temperature of approximately TITZ. If concentrations of 10¹⁶ instead of 10²⁰ in cmE⁻¹ are desired, the evaporator temperature should also be below the aforementioned values.

[0018] In the CSS process, the substrate reaches temperatures of up to 600°C, depending on the chamber pressure and the desired evaporation rate. For example, if the first CdTe source has a temperature of approximately 700°C and the second CdsAs2 source has a temperature of approximately 300°C, the substrate temperature is preferably in the range of 500-600°C, i.e., higher than the temperature of the CdsAs2 source after the CdTe process step.

[0019] It was found that the absorption of CdsAs2 onto the aforementioned hot CdTe layer on the substrate and its subsequent incorporation into the CdTe layer is very poor. In other words, applying the dopant material CdsAs2 directly onto the hot substrate layer has disadvantages.

[0020] If, on the other hand, the Cd3As2 coating is applied later to a substrate that has already cooled down further, e.g., if the substrate has a temperature < 300°C, an additional subsequent heating step (annealing) at temperatures between 550° and 700°C is necessary to accelerate the As diffusion into the CdTe layer. However, this additional heating step does not lead to the desired uniform As distribution (which is crucial for the efficiency of the absorber layer), but rather to a pronounced differentiation in the distribution between grains and their grain boundaries.

[0021] Existing state-of-the-art approaches for improving doping are based on the following technical solutions: a) In VTD technology, where CdTe is used as the vaporization material, a carrier gas at a relatively high pressure (1–10 mbar) is also used, so that sublimation is always limited by diffusion into the carrier gas. Doping is achieved, for example, by means of an additional zone for the dopants. In this zone, the carrier gas is saturated with the dopants and is then carried along to the next hotter zone for CdTe. Subsequently, the carrier gas with CdTe vapor, together with the vapor of the dopant, is applied to the hot substrate surface. b) According to another approach, the absorber material can be produced by co-evaporation. For example, a thermal source with CdTe is oriented towards the substrate to be coated, and a second thermal source with dopant, e.g.,Cu is also oriented towards the substrate, so that the materials could be simultaneously evaporated from the separate sources onto the substrate (doi: 10.1143 / jjap.29.11376). c) According to another known approach, the absorber material is prefabricated and evaporated together with the dopant from a CSS crucible. The absorber layer of the perovskite cell, which consists of a material Pbh that evaporates at higher temperatures and a material MAI that evaporates at lower temperatures, is also a suitable example (doi: 10.1063 / 5.0085221).

[0022] It is therefore an object of the present invention to provide a coating source, a coating system and a coating process by means of which targeted doping is achieved.

[0023] Summary

[0024] This task is solved by the subject matter of the independent claims.

[0025] Preferred features of the invention are described in the dependent claims.

[0026] The present invention relates firstly to a coating source for a coating system, wherein the coating source comprises a first crucible for evaporating coating material and at least one outlet opening for evaporated coating material. The coating source further comprises a second crucible for evaporating at least one dopant material, wherein evaporated dopant material is transferred from the second crucible to the first crucible in such a way that the evaporated dopant material mixes with the evaporated coating material in the first crucible and can be applied to a substrate via the outlet opening in the first crucible.

[0027] In other words, the present invention is based, among other things, on the idea of ​​providing two physically separate crucibles that are nevertheless connected in fluid, in order to control the doping of a coating material. This makes it possible, for example, to ensure that the amount of dopant material in the coating as well as its distribution within the coating can be controlled.

[0028] In particular, the present invention relates to a coating source in the form of a thermal evaporation source, for example a bottom-up or top-down evaporation source, such as can be used for CSS (Close Space Sublimation (CSS)) processing of an absorber layer with dopants.

[0029] The coating source according to the invention can be used, for example, for CSS processes, with CSS processes without carrier gas being preferred in the production of CdTe modules.

[0030] It has been found that it is advantageous if the dopant is processed simultaneously or together with the main material, e.g. CdTe.

[0031] Accordingly, the present invention relates to a device that constitutes a thermal evaporation source which can simultaneously and controllably coat the hot substrate from below or above with both the CdTe solar cell material (such as CdTe) to be evaporated at high temperatures and the doping material (such as As-containing) to be evaporated at significantly lower temperatures in relatively small quantities (<10% at.).

[0032] The present invention can be briefly characterized, for example, by the following preferred features.

[0033] A CSS evaporation chamber according to the invention can, for example, be used in an in-line system, wherein the system preferably comprises one or more of the following components: a hot substrate to be coated, for example in the range of 400-650°C; a first (hotter) crucible at approximately 600-800°C containing the coating material; a substrate transport system for continuously applying the coating material to the substrate. For example, the substrate moves as close as possible to an opening of the crucible, preferably in the range of 1-10 mm.

[0034] The temperatures of the crucible(s), crucible opening(s), and substrate, the spacing, crucible geometries, material quantities, gas-vacuum environment, etc., define the evaporation rate and the layer morphology. Typical layer thicknesses are in the range of 1–5 pm, and the desired deposition rate is preferably 0.5–5 pm / min.

[0035] According to the invention, a second, preferably smaller, crucible is attached to a CSS evaporation chamber (first crucible), for example, in a volume ratio to the CSS evaporation chamber of approximately 1-10 to 100. This additional (second) crucible contains the dopant material and is preferably colder (for example, < 400°C). The second crucible is preferably located close to the first crucible and is preferably thermally insulated from the first crucible, but in fluid communication (the flow of the partial pressure change of the material towards the substrate) with the first crucible, so that the dopant material can be transferred from the second crucible to the first crucible.

[0036] Preferably, this second additional crucible is equipped with a steam distributor, the steam distributor being preferably mounted inside the first hot crucible, so that openings provided in the steam distributor are located close to the outlet opening of the first hot crucible.

[0037] Thus, vapor of the dopant will be present in small quantities in the vapor of the coating material and will be incorporated into the layer during the CSS process.

[0038] Additional parameters determine the proportion of dopant in the coating, e.g.: the temperature of the second crucible; the temperature of the vapor distributor; the amount of dopant; the crucible geometries; the vapor distributor geometries (diameter, length, openings, etc.); the positioning of the vapor distributor in the first hot crucible with the

[0039] Coating material; etc.

[0040] The amount of dopant in the granular material defines the surface area from which the material is evaporated or sublimated into the vacuum at a specific temperature. The typical crucible with a volume of approximately 2 liters should, for example, be filled to about half its capacity so that the decrease in material changes the surface area in such a way that the corresponding decrease in the evaporation rate due to the temperature increase can be compensated for, e.g., to 300–400°C. The temperature of the vapor distributor, which is, for example, approximately 10–50 mm in diameter and whose openings are located approximately 50–10 mm from the opening of the large crucible, is preferably between the temperature of the material and the temperature of the opening of the large crucible, e.g., at 700°C, between 650°C of the material and 750°C of the opening. Since the openings of the vapor distributor are dimensioned, for example, in the millimeter or even millimeter range, such that a flow of dopant material is either blocked or becomes trapped in the Knudsen flow pattern, the vapor distribution is controlled by the vapor distributor.Since the process is even in the molecular range, the length of the steam distributor can be in the m range, e.g. 1-3 m.

[0041] One advantage of the CSS process is that it does not require a deposition rate-limiting carrier gas, as is used, for example, in the VTD process to transport the coating and doping material onto the substrate. A disadvantage of using a carrier gas, however, is that larger material particles from the material granules or parasitic coating are also transported along with the substrate. These particles are either disruptive during the coating process (because they must be subsequently removed from the substrate surface) or require complex filtering to remove them (see US 2021 / 0301387).

[0042] The sublimation-limited CSS process without a carrier gas also allows for higher deposition rates, for example in the range of 1-5 pm / min. Using the CSS process with a dopant can, for instance, achieve improved absorption efficiency. The resulting high module efficiency makes the cost-effective CSS technology even more attractive.

[0043] Similarly, the evaporation rate is crucial in mass production when comparing the CSS process with the co-evaporation process. Co-evaporation occurs from sources located further away from the substrate than those in the CSS process: 5-10 mm range vs. 10-30 cm range. Therefore, the coating rates in CdTe co-evaporation are approximately 100 times lower. 2 Equation.

[0044] Another important point is the stability and controllability of the new CSS process using the dopant from the second crucible. The separate temperature control of the second crucible allows the amount of dopant to be precisely adjusted over time. Such stability is not present in a CSS process where the mixed coating material and dopant are evaporated from a single crucible, because the dopant typically has a much higher vapor pressure and would therefore escape relatively quickly from the crucible towards the substrate vacuum chamber. This would cause the dopant concentration set at the beginning of the evaporation process to decrease over time or even approach zero.

[0045] Therefore, these types of mixtures are hardly applicable in mass production. In contrast to the two-crucible solution according to the invention, the evaporation of both materials (coating plus dopant) takes place simultaneously in the same confined space of the CSS process between the opening of the hotter crucible and the substrate. Thus, the dopant with its higher vapor pressure can be uniformly incorporated directly into the absorber layer on the hot substrate during deposition.

[0046] According to a first aspect, the present invention relates to a coating source for a coating system, wherein the coating source comprises a first crucible for evaporating coating material with at least one outlet opening for evaporated coating material, and wherein the coating source comprises at least one first heating source for heating the first crucible and / or the coating material. Furthermore, the coating source comprises a second crucible for evaporating dopant material, wherein the second crucible comprises at least one second heating source for heating the second crucible and / or the dopant material. Preferably, the second crucible is connected to the first crucible such that evaporated dopant material can flow from the second crucible into the first crucible or is transported there. The first and second crucibles are preferably connected by a fluid.

[0047] The coating source is preferably designed such that the evaporated coating material mixes with the evaporated doping material in the first crucible and this mixture can exit via the outlet opening to coat a substrate.

[0048] The at least one first heating source can comprise one or more heating elements integrated into the walls of the first crucible, and / or the at least one second heating source can comprise one or more heating elements integrated into the walls of the second crucible. It is also possible for the heating elements to be attached to the crucible in such a way as to, for example, (partially) outside the crucible walls, in order to achieve the same heating effect.

[0049] Preferably, the first crucible is larger than the second crucible. Furthermore, it is preferred that the first crucible is configured to be heated to a higher temperature than the second crucible.

[0050] It is also preferred that the at least one first heat source and the at least one second heat source can be operated independently of each other.

[0051] The first crucible can have a guide section through which the vaporized coating material is guided to the at least one outlet opening. In such an embodiment, it is preferred if the inner cross-section of the guide section tapers towards the at least one outlet opening.

[0052] According to a further preferred embodiment, a vapor distributor arranged in the first crucible can be connected to the second crucible such that the dopant material is transferred from the second crucible to the first crucible via the vapor distributor. Preferably, such a vapor distributor can be arranged in the guide section. The vapor distributor is preferably designed as a tubular element, preferably having several openings along its length. It is also preferable that at least one heater is arranged inside the tubular element.

[0053] The coating source according to the invention can be implemented as a top-down or bottom-up coating source. Thus, the at least one outlet opening can be arranged on the lower side of the first pot or on the upper side of the first pot. The outlet opening is not limited to a specific shape. Preferably, the outlet opening is round or elongated, for example, as a slot extending over at least 50% of the length of the coating source. More preferably, the elongated outlet opening extends over at least 60%, 70%, 80%, 90%, or 100% of the length of the coating source.

[0054] The temperature of the first and second crucibles preferably depends significantly on the material to be evaporated. The coating material to be evaporated in the first crucible is preferably a material with an evaporation temperature of no more than 1,000°C. The doping material to be evaporated in the second crucible is preferably a material with an evaporation temperature of no more than 800°C, and particularly preferably a chemical combination or physical mixture of the following materials: Cd, Te, Se, S, Cu, Zn, Hg, P, Cl, Br, As, Sb.

[0055] According to a further aspect, the invention also relates to a coating system with a coating source according to the invention. Preferably, the coating source is used to coat a substrate, and the invention is not limited to specific substrates. Preferably, glass substrates are coated, for example, for solar cells, which may already be coated or uncoated. Furthermore, the substrates to be coated can be with or without a carrier.

[0056] Depending on whether the coating source is designed as a top-down coating source or as a bottom-up coating source, the coating system can be set up to coat substrates from above or from below.

[0057] According to a further aspect, the invention also relates to a method for coating substrates, preferably using a coating source according to the invention. The method preferably comprises the following steps: positioning a substrate to be coated below or above the coating source and coating the substrate using the coating source.

[0058] The substrate can remain stationary relative to the coating source during coating, or the substrate can be moved relative to the coating source during coating, or vice versa.

[0059] Brief description of the drawings

[0060] Preferred embodiments of the present invention are described below.

[0061] The figures are described in more detail below. They show: Figure 1a a schematic longitudinal section of a top-down coating source according to a preferred embodiment parallel to an optional substrate transport direction;

[0062] Figure 1b shows a schematic cross-section of the coating source according to Fig. 1a transverse to the substrate transport direction;

[0063] Figure 2a shows a schematic longitudinal section of a bottom-up coating source according to a further preferred embodiment parallel to an optional substrate transport direction; and

[0064] Figure 2b shows a schematic cross-section of the coating source according to Fig. 2a transverse to the substrate transport direction.

[0065] Detailed description of preferred embodiments

[0066] Figure 1a schematically shows a longitudinal section through a coating source 1 according to a preferred embodiment of the present invention. The coating source 1 has a first pot 2 for evaporating coating material 5 and at least one outlet opening 6 for evaporated coating material, wherein the coating source 1 has at least one first heating source 7a for heating the pot 2 and the coating material 5. Preferably, the outlet opening 6 is elongated, for example, as a slot. The elongated extent of the outlet opening 6 is shown, for example, in Figure 1b by the unhatched lower double line on the lower side. Preferably, the outlet opening 6 extends over at least 50% of the length of the coating source 1. More preferably, the elongated outlet opening 6 extends over at least 60%, 70%, 80%, 90%, or 100% of the length of the coating source 1. In Figure 1b, the elongated outlet opening 6 is shown, for example, by the unhatched lower double line on the lower side.For example, the outlet opening 6 extends over the entire length, that is, over the entire inner length of the chamber, with the outlet opening 6 being located on the underside of the coating source 1.

[0067] In the preferred embodiment shown, the at least one first heating source 7a comprises several heating elements 7a integrated into the crucible walls or into the crucible base and / or the crucible lid. According to the invention, the terms "top" and "bottom" are used with respect to gravity. Alternatively, however, only one or more heating elements 7a could be integrated into the crucible walls or into the base or lid.

[0068] To dope the coating material 5 with a dopant material 12, the coating source according to the invention has a second crucible 4 which is connected to the first crucible in such a way that vaporized dopant material 12, which is vaporized in the second crucible 4, can enter the first crucible 2. The two crucibles are thus preferably in fluid connection. In addition, it is preferred that the pV values ​​in the two crucibles are the same or that the pV value in the second crucible 4 is higher than the pV value of the first crucible 2. This reduces back-diffusion from the material 5 into the material 12.

[0069] Preferably, the vaporized dopant material 12, which enters the first crucible from the second crucible, mixes with the vaporized coating material 5 within the first crucible 2, so that the coating material 5 doped with the dopant material 12 can be applied to a substrate 3 via an (outlet) opening 6. The spatially separate, but process-technically connected design of the two crucibles for the coating material 5 and the dopant material 12 allows the vaporization of the coating material 5 and the dopant material 12 to be controlled independently of each other, making it possible to adjust the desired doping concentration of the coating material.

[0070] In other words, the first and second heating devices can preferably be operated independently of each other. This allows the amount or degree of doping, i.e., the ratio of doping material to coating material, to be adjusted. This also enables the degree of doping to remain stable over a long period, for example, over many hours, days, or weeks.

[0071] In the preferred embodiment shown in Figure 1a, the crucible 2 forms a guide section 8a through which the vaporized coating material 5 is guided to the at least one outlet opening 6. To ensure that the coating material exiting the outlet opening 6 mixes as uniformly as possible with the dopant material, the dopant material vaporized in the second crucible 4 is preferably fed directly into this guide section 8a. Such a feed can be effected, for example, by means of a vapor distributor 8 in which several openings 10 are formed. The vapor distributor 8 is thus to be interpreted as a dopant material distributor.

[0072] Preferably, the vapor distributor 8 can be configured in the form of a tube. According to preferred embodiments, several openings 10 are formed in the tube 8, which are, for example, evenly distributed along the tube or preferably directed towards the outlet opening 6. The embodiment shown in Figures 1a and 1b is a top-down coating source, i.e., a coating source in which the coating material initially rises in the crucible during the evaporation process, then descends to coat the substrate 3, and is finally applied to the substrate located below the crucible 2. Accordingly, in a top-down coating source, it can be advantageous if the openings 19 are directed mainly or exclusively downwards, as shown, for example, in Figure 1b.

[0073] In the illustrated embodiments, the substrate 3 is moved relative to the pot 2 during the coating process (see double arrows in Figs. 1a and 2a), as, for example, in an in-line system. However, a person skilled in the art understands that the present invention is not limited to in-line systems.

[0074] Furthermore, it may be advantageous if the vapor distributor 8 has its own heating source 9, which can preferably be individually controlled. For example, an additional heater 9 can be provided within the vapor distributor 8, for instance, to suppress, minimize, or prevent deposits of the dopant material within the vapor distributor. This heater 9 also enables completely separate control of the vaporization process of the dopant material while the material 5 in the first crucible 2 is not yet at the process temperatures, in order to precisely adjust the dopant vaporization in a ramp-up phase for test substrates without main material. In the illustrated embodiment, this heater 9 is a heating wire (separated from the vapor by the steel jacket as a so-called jacket heater).This heater 9 is implemented (by quartz glass as so-called I R heaters) and preferably extends parallel to the longitudinal direction of the steam distributor tube 8. This heater 9 can preferably be operated independently of other heating devices of the coating source. Preferably, the first crucible 2 and the second crucible 4 are heated to different temperatures. A person skilled in the art understands that the preferred temperature of the crucibles is determined by several factors, the nature of the material to be vaporized being a significant one. In other words, since the coating material 5 and the doping material 12 differ, the temperatures of the two crucibles 2 and 4 also preferably differ.

[0075] Preferably, the first crucible 2 is heated to a higher temperature than the second crucible 4, so that the first crucible can also be referred to as the hotter crucible 2 and the second crucible 4 as the colder crucible 4. To prevent the temperature of the first crucible 2 from undesirably influencing the temperature of the second crucible 4, or vice versa, it is preferred that the two crucibles 2 and 4 are thermally insulated from each other. For example, a simple thermal insulation 11 can be provided between the first crucible 2 and the second crucible 4, as shown schematically in Figures 1b and 2b.

[0076] Since the amount of doping material 12 is smaller than the amount of coating material 5, it is also preferred if the second crucible 4 is smaller than the first crucible 2.

[0077] As illustrated by way of example in the figures, the first (hotter) crucible 2 can have at least one, preferably several, heaters 7a arranged in the crucible walls, the crucible base and / or the crucible lid. Preferably, the heaters 7a of the hotter first crucible 2 can be controlled separately from one another.

[0078] The same applies to the second (cooler) crucible 4, which has at least one, preferably several, heaters 7b arranged in the crucible walls, the crucible base and / or the lid of the second crucible 4. Preferably, the heaters 7b of the cooler second crucible 4 can be controlled separately from one another.

[0079] Furthermore, it is also preferred that the heaters 7a of the first crucible can be controlled independently of the heaters 7b of the second crucible. This allows, for example, the doping material 12 to be evaporated separately from the coating material 5 in a controlled manner.

[0080] Since the vapor distributor 8 in the hotter crucible 2 is preferably hotter than the temperature of the doping material 12, the doping material flow from the openings 10 in the tube 8 is influenced or determined by the geometry of the vapor distributor, by the saturation pressure of the material 12 and the actual temperature / pressure (vacuum-material partial pressure) conditions in the second crucible 4.

[0081] In a typical application, the first crucible 2 can be approximately 700°C. The outlet opening 6 can, for example, be heated to a higher temperature by its own heating device or by a different arrangement of the heaters, for example, to approximately 750°C. The vapor distributor 8, which is preferably arranged within the guide section 8a, can, for example, have a temperature of approximately 730°C. The second, cooler crucible 4 can, for example, have a temperature of less than 500°C. A person skilled in the art will understand that the present invention is not limited to these temperatures and that these exemplary temperatures serve only to show that, in an application, the cooler second crucible 4 is preferably cooler than the first crucible 2. However, as already described above, the temperature of the two crucibles 2 and 4 depends on several factors, and in particular on the material to be vaporized.

[0082] In the preferred embodiment shown in Figure 1a, the inner cross-section of the guide section 8a tapers towards the at least one outlet opening 6. In this preferred embodiment, the outlet opening 6 is not formed directly by the crucible wall of the crucible 2; rather, a sheet metal plate is provided on the underside of the crucible 2, in which the outlet opening 6 is formed. While the crucible 2 is typically made of graphite, the sheet metal plate 13 can comprise one of the following materials or a combination thereof: CFG, graphite, ceramic, glass, or metal. Heating can thus preferably be performed directly by electricity or indirectly by radiation.

[0083] Figures 2a and 2b show another preferred embodiment of the coating source 1 according to the invention, in which essentially only the outlet opening 6 is arranged at the top instead of at the bottom (bottom-up coating source). In addition, a guide section 8a can also be omitted in such an embodiment.

[0084] To control the flow of the vaporized doping material from the second crucible 4 to the first crucible even more precisely, one or more mechanical, preferably gas-tight, valves or controllable reducers can be provided between the two crucibles 2 and 4. These valve(s) can also be individually heated. Furthermore, any type of insulation 11 between the two crucibles 2 and 4 is possible according to the invention. For example, thermal insulation 11 made of foam material and / or designed as radiation shields can be provided between the two crucibles 2 and 4.

[0085] According to further possible embodiments, an additional heating element can also be present on the pipe of the steam distributor 8 in the area of ​​the insulation 11. The steam distributor can be made, for example, of CFC materials, graphite, quartz, ceramics, or a combination of these materials. Heating can thus be achieved directly by electricity or indirectly by radiation. As described above, it may be preferable to orient the openings 10 upwards or downwards, depending on the type of coating source 1. However, the arrangement of the openings 6 is not limited to this, and other configurations, orientations, and distributions of the openings are possible.

[0086] It is also possible to have a cooled wall or cooled surface between the two crucibles in order to better decouple the influence of the high temperatures from the second crucible, if the second crucible 4 is to be operated in the range of 50-200°C depending on the material 12.

[0087] According to further embodiments, a gas connection can also be provided on the smaller crucible 4, which allows, for example, a precise vacuum or pressure control inside / doping gas to be set.

[0088] Preferably, the first and / or the second crucible 2 and 4 have refilling devices, which, for example, enables simple and continuous operation.

[0089] Connections for pressure gauges or level gauges can also be provided in the first crucible 2 or in the second crucible 4 to monitor operating parameters.

[0090] To control the pressure within crucibles 2 and 3 in a targeted manner, i.e. to change, decrease, increase or maintain it, lockable connections may be provided which can, for example, also be connected to a suitable pumping device.

[0091] Furthermore, the present invention is not limited to two crucibles. For example, it may be advantageous to arrange more than one colder crucible to the side of the first crucible 2, for instance, for different dopants. Thus, for example, different crucibles can be provided for different dopants. Other preferred dopants are, for example, Sb and P, also known as CdSb and CdAdPz.

[0092] If several doping layers need to be produced in the absorber layer, several crucibles of this type can also be built up in the process, distributed in the transport direction, e.g. CdTe with Sb would come from the first pair of crucibles and CdTe with P would come from the next pair of crucibles.

[0093] Reference symbol list:

[0094] 1 coating source

[0095] 2 larger or hotter crucibles

[0096] 3 Substrat

[0097] 4 smaller or colder crucibles

[0098] 5 Coating material

[0099] 6 Opening / exit opening

[0100] 7a Heating source or crucible heating source for larger crucible

[0101] 7b Heating source or crucible heating source for smaller crucible

[0102] 8 steam distributors

[0103] 8a Guided Section

[0104] 9 stokers

[0105] 10 openings in the steam distributor

[0106] 11 Insulation

[0107] 12 Doping material

[0108] 13 sheets

Claims

PATENT CLAIMS 1. Coating source (1) for a coating system, the coating source comprising: a first crucible (2) for evaporating coating material (5) with at least one outlet opening (6) for evaporated coating material (5), the coating source (1) comprising at least one first heating source (7a) for heating the first crucible (2) and / or the coating material (5); a second crucible (4) for evaporating dopant material (12), the second crucible comprising at least one second heating source (7b) for heating the second crucible (4) and / or the dopant material (12), the second crucible (4) being connected to the first crucible (2) in such a way that evaporated dopant material (12) is transported from the second crucible (4) into the first crucible (5).

2. Coating source according to claim 1, wherein the coating source (1) is configured such that the evaporated coating material (5) mixes with the evaporated doping material (12) in the first crucible and this mixture can exit via the outlet opening (6) to coat a substrate (3).

3. Coating source according to claim 1 or 2, wherein a. the at least one first heating source (7a) comprises one or more heating elements integrated into the crucible walls of the first crucible (2); and / or b. the at least one second heating source (7b) comprises one or more heating elements integrated into the crucible walls of the second crucible (4).

4. Coating source according to claim 1, 2 or 3, wherein a. the first crucible (2) is larger than the second crucible (4), and / or b. the first crucible (2) is configured to be heated to a higher temperature than the second crucible (4).

5. Coating source according to one of the preceding claims, wherein the at least one first heating source (7a) and the at least one second heating source (7b) can be operated independently of each other.

6. Coating source according to one of the preceding claims, wherein the first crucible (2) forms a guide section (8a) through which the evaporated coating material is guided to the at least one outlet opening (6).

7. Coating source according to claim 6, wherein the inner cross-section of the guide section (8a) tapers in the direction of the at least one outlet opening (6).

8. Coating source according to one of the preceding claims, wherein a vapor distributor (8) arranged in the first crucible (2) is connected to the second crucible (4) in such a way that the doping material (12) is transferred from the second crucible via the vapor distributor (8) to the first crucible (2).

9. Coating source according to claim 8, wherein the steam distributor (8) is arranged in the guide section (8a).

10. Coating source according to claim 8 or 9, wherein the vapor distributor (8) is a tubular element with multiple openings along its length.

11. Coating source according to claim 10, wherein a heater (9) is arranged inside the tubular element.

12. Coating source according to one of the preceding claims, wherein the at least one outlet opening (6) is arranged a. on the lower side of the first crucible (2), or b. on the upper side of the first crucible (2).

13. Coating source according to one of the preceding claims, wherein in the first crucible (2) coating material to be evaporated, preferably a material with an evaporation temperature of at most 1,000°C, and in the second crucible (4) doping material to be evaporated, preferably a material with an evaporation temperature of at most 800°C, particularly preferably a chemical combination or physical mixture of the following materials are arranged: Cd, Te, Se, S, Cu, Zn, Hg, P, CI, Br, As, Sb.

14. Coating system with a coating source according to one of the preceding claims.

15. Coating system according to claim 14, wherein the coating system is configured to coat substrates from above or from below.

16. Method for coating substrates using a coating source according to any one of claims 1 to 13, wherein the method comprises: Positioning a substrate (3) to be coated below or above the coating source (1) according to one of claims 1 to 13 and Coating the substrate (3) using the coating source (1).

17. Method according to claim 16, wherein the substrate (3) is at rest relative to the coating source during coating.

18. Method according to claim 16, wherein the substrate (3) is moved relative to the coating source (1) during coating or vice versa.

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