This invention relates generally to methods and systems for depositing multiple materials on a substrate. More particularly, this invention relates to methods and systems for deposition of multiple materials on a substrate using co-sublimation processes for solar or photovoltaic cells.
Photovoltaic systems (or “solar cells”) are used for converting solar energy into electrical energy. Power production by photovoltaic systems may offer a number of advantages over conventional systems, including low operating costs, high reliability, modularity, low construction costs, and environmental benefits.
The thin film solar cells have the potential to lower costs since such cells require significantly smaller amounts of semiconductor materials relative to conventional photovoltaic modules to produce a comparable amount of power. Currently, some thin film solar cells employ cadmium telluride (CdTe) films because CdTe has a direct bandgap of 1.5 eV and can improve solar conversion efficiency of such solar cells.
In some applications, in order to improve various properties of the solar cells, such as the electrical conductivity of CdTe films, dopants may be introduced in the CdTe films. However, conventional processes, such as conventional close spaced sublimation (CSS) and vapor transport (VTM) processes are not suited to co-depositing CdTe with other materials, due to the different melting points and vapor pressures of the materials. One process that has been shown to co-deposit CdTe with other materials is co-evaporation. However, co-evaporation processes are inherently time-consuming and may not be suitable for co-deposition of CdTe and certain other materials for photovoltaic applications.
Therefore, there is a need for a new and improved method and system for co-deposition of multiple materials on a substrate for solar or photovoltaic cells.
A system for depositing two or more materials on a substrate is provided in accordance with one embodiment of the invention. The system comprises one or more susceptors configured to define two or more recesses for accommodating at least a first material and a second material different from the first material respectively. The system further comprises one or more heaters for heating the first material and the second material to sublime for deposition on the substrate.
Another embodiment of the invention provides a system for depositing of two or more materials on a substrate. The system comprises a deposition device, one or more susceptors, and one or more heaters. The deposition device defines a sublimation zone, one or more inlets and one or more outlets in fluid communication with the sublimation zone. The one or more susceptors are disposed within the sublimation zone and define two or more recesses for accommodating at least a first material and a second material different from the first material respectively. The one or more heaters are configured to heat the first material and the second material for sublimation of the first and second materials. The deposition system further comprises one or more carrier gas sources configured to supply one or more carrier gases into the sublimation zone through the one or more inlets to carry sublimated gases of the first and second materials out of the sublimation zone through the one or more outlets for deposition on the substrate.
Another aspect of the invention further provides a method for depositing of two or more materials on a substrate. The method comprises providing one or more susceptors configured to define two or more recesses for accommodating a first material and a second material different from the first material respectively, and heating the first material and the second material for sublimation of the first and second materials for deposition on the substrate.
The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the subsequent detailed description when taken in conjunction with the accompanying drawings in which:
Embodiments of the present disclosure are described herein with reference to the accompanying drawings. In the subsequent description, well-known functions or constructions are not described in detail to avoid obscuring the disclosure in unnecessary detail.
A variety of substrates 100 may be employed, depending on the specific applications. In one non-limiting example, the substrate 100 comprises a glass layer (not shown) with a transparent conducting oxide (TCO) layer deposited on the glass layer. Non-limiting examples of the glass layer include borosilicate glass, low-alkaline glass, soda-lime glass, low-iron galss, and similar materials. Non-limiting examples of the TCO layer include tin oxide and indium tin oxide.
In other non-limiting examples, the substrate 100 may comprise a polymer layer with a metal layer deposited on the polymer layer. In one example, the polymer layer may comprise polyimide and the metal layer may comprise molybdenum. Additionally, in certain applications, the substrate 100 may comprise other suitable materials, for example, a stainless steel layer with a molybdenum layer deposited on the stainless steel layer.
For the example illustrated in
In some applications, the susceptor 11 may be formed of thermally conductive materials. Non-limiting examples of the thermal conductive materials include graphite, tungsten, silicon carbide (SiC) coated graphite, and high temperature metals and alloys, such as stainless steel and alloy steel. The first and second materials 13, 14 may comprise cadmium telluride (CdTe), tellurium (Te), zinc tellurium (ZnTe), arsenic (As), cadmium chloride (CdCl2), cadmium sulfide (CdS), other materials containing dopants to CdTe, and combinations thereof. Non-limiting examples of the dopants may include silver (Ag), copper (Cu), gold (Au), bismuth (Bi), antimony (Sb), arsenic (As), phosphor (P), and nitrogen (N). In one example, the first material 13 comprises cadmium telluride (CdTe) and is different from the second material 14.
It should be noted that the arrangements illustrated in
For some arrangements, each of the recesses 12 may be in the form of cell, so that, as illustrated in
Alternatively, each of the recesses 12 may be in the form of trench, so that, as illustrated in
The system 10 further comprises one or more heaters, such as a resistive heater 21 shown in
In operation, the one or more heaters heat the susceptor 11, so that the first and second materials 13, 14 in the respective recesses 12 are heated to a certain temperature to sublimate simultaneously. Then, the two sublimated gases mix together during transmission towards the substrate 100 so as to deposit on the substrate 100 in the form of film, which is referred to as a co-sublimation process.
In some examples, the first and second materials 13, 14 in the recesses 12 may be heated to the same temperature. In other examples, the first material 13 and the second material 14 may be heated to different temperatures.
Additionally, in some applications, in operation, the substrate 100 may be stationary relative to the susceptor(s) 11. Alternatively, the substrate 100 may move relative to the susceptor(s) 11. The substrate 100 may be preheated to a lower temperature than the respective heated temperatures of the first and second materials 13, 14.
Various techniques may be used to heat the first and second materials to different temperatures. For example, the geometry may differ for the respective recesses 12 for receiving the two materials. Thus, when one or more heaters are disposed below the susceptor 11 for heating the recesses 12, the recesses 12 having larger depths receive more thermal energy than the recesses with shallower depths, due to the thermal gradient. In this manner, the first and second materials are heated to different temperatures.
In other examples, the thermal conductivity for a subset of the recesses may be enhanced relative to that of the other recesses. For example, the system 10 may employ one or more materials disposed on periphery of and/or into the respective recesses 12 so as to react to, for example absorb more thermal energy from the one or more heaters. For example, one or more heat absorbing materials, such as titanium, may be disposed around the recesses 12 accommodating the first material 13, so that the first material 13 is heated to a higher temperature than the second material 14 for sublimation.
In the illustrated embodiment, the system 10 further employs a plurality of lids 15 disposed on respective ones of the recesses 12 for accommodating the second material 14. Each lid 15 defines an opening 16 that is in fluid communication with the recess 12.
In some applications, the system 10 may employ one or more thermal monitoring devices to monitor the temperatures of the recesses 12. As depicted in
As depicted above, in some examples, the recesses 12 for accommodating the first and second materials may be heated to the same temperature. For many applications, however, the recesses 12 accommodating the first material and/or the second material are heated to different temperatures.
In certain applications, the first and second thermocouples 17 and 18 may be connected to a monitoring device 19 to monitor the temperature of each recess 12. In other examples, two or more monitoring devices may be used. Additionally, in some examples, the monitoring device(s) may be operatively connected to heater(s) to provide feedback for thermal control.
For certain arrangements, in order to independently control the temperature of each recess 12 and avoid interference from adjacent recesses 12, thermal insulation may be disposed on the susceptor 11. For example, one or more thermal insulation layers may be provided to better thermally isolate respective ones of the recesses from neighboring recesses.
Non-limiting examples of the thermal insulation include polystyrene, polyurethane, polystyrene foam, and ceramic materials. For the illustrated arrangement, the thermal insulation layer 20 is further disposed on a bottom surface (not labeled) of the susceptor 11 to reduce thermal convection via the bottom surface of the susceptor 11. In other examples, thermal insulation is not employed on the bottom surface of the susceptor 11.
In the illustrated example of
In the illustrated example, the coil 23 has more turns on the recesses 12 receiving the first material 13 than those on the recesses 12 receiving the second material 14. In this manner, the first material 13 and the second material 14 are heated separately and the first material 13 may be heated to a higher temperature than the second material 14. In other examples, the number of turns of the coil wound around the first material recesses 12 may be equal or less than those wound around the second material recesses 12.
Additionally, the example system 10 shown in
Similarly, the system 10 may comprise one or more heaters for heating the susceptors 11. In some examples, the heater(s) may be disposed outside the deposition device 24. In other examples, the heater(s) may be disposed within the sublimation zone 25, and/or within an upper wall 50 and/or sidewalls 51 of the deposition device 23 for heating the susceptors 11.
In operation, the first and second materials 13, 14 sublime at a certain temperature. Since the temperature of the deposition device 24 is higher than the temperatures to which the first and second materials 13, 14 are heated, the sublimated gases of the first and second materials 13, 14 are not deposited on the inner surfaces of the deposition device 24 and are transmitted in a downward direction for deposition on the substrate 100, as indicated by the dashed arrows.
In the illustrated example of
For the illustrated arrangement, the substrate 100 is disposed below the deposition device 24. More than two spatially separated susceptors 11 are employed and each susceptor 11 defines a recess 12. In other examples, the substrate 100 may also be disposed within the sublimation zone 25 and between the upper wall 50 and the susceptors 11. The system 10 may employ two susceptors, and each susceptor 11 may define more than one recess 12.
Additionally, for the arrangements in
The above-described sublimation and deposition processes may be performed in a variety of environments, for example, in an ambient environment or in the presence of a gas, such as oxygen, hydrogen, nitrogen, chlorine, an inert gas, and combinations thereof. Non-limiting examples of inert gases include argon and helium.
For the illustrated example of
In operation, the one or more heaters heat the susceptors 11 to sublimate the first and second materials 13, 14. The first and second materials may be heated to the same or different temperatures for sublimation. The carrier gas source supplies a carrier gas 36 into the sublimation zone 31 to carry the sublimated gases out of the sublimation zone 31 through the outlet passage 35 and the outlet 32. Subsequently, the first and the second materials are continuously deposited on the substrate 100 while the substrate 100 moves along a direction 37, which is opposite to the direction 38 of the depleted carrier gas.
In the illustrated example, while moving toward the outlet 33, the sublimated gases are mixed in the outlet passage 35, which thus acts as a mixing zone, and thereby improves the quality of the deposition on the substrate 100. In some applications, the outlet passage 35 may not be employed. The carrier gas 36 may be saturated with the sublimated gases of the first and second materials 13, 14 to facilitate deposition on the substrate 100. The substrate 100 may move in the same direction as the depleted carrier gas or may be stationary.
Additionally, the temperatures of the sublimation device 30 and the substrate 100 may be higher and lower than the heated temperatures of the first and second materials 13, 14, respectively, to facilitate deposition of the first and second materials on the substrate 100.
In certain applications, in order to avoid contamination of the two sublimated gases, the carrier gas may first carry the sublimated gas of the material that sublimes at a lower temperature. The carrier gas then carries the sublimated gas of the material that sublimes at a higher temperature. For example, the carrier gas first carries the sublimated gas of the second material and then carries the sublimated gas of the first material if the second material sublimes at a lower temperature than the first material.
In the illustrated example, two susceptors are provided. In other examples, more than two susceptors may be employed to accommodate the respective first and second materials. Thus, for example, in operation, the carrier gas may pass by all of the susceptors accommodating the second materials, and then pass by all of the susceptors accommodating the first material. Additionally, the system 10 may or may not comprise one or more lids 15 disposed on respective ones of the one or two susceptors 11.
For the configuration shown in
Similarly, more than two susceptors may be employed, and one or more lids may be provided on respective ones of the susceptors 11. The first and second carrier gases 54, 55 may be the same or different gases. Non-limiting examples of the first and second carrier gases include inert gases, such as argon and helium.
For the illustrated example of
For the example arrangement illustrated in
In the illustrated example of
For the arrangements illustrated in
Additionally, for some examples, more than two deposition elements and/or more than two susceptors may be employed. One or more lids may or may not be employed on respective ones of the susceptors to adjust the pressures of the one or more sublimated gases. In other applications, the vapor pressure of the one or more sublimated gases in the mixing zone 45 may be adjusted by changing the gas flow resistivity of one or more of the passageways 48, 49.
While the disclosure has been illustrated and described in typical embodiments, it is not intended to be limited to the details shown, since various modifications and substitutions can be made without departing in any way from the spirit of the present disclosure. As such, further modifications and equivalents of the disclosure herein disclosed may occur to persons skilled in the art using no more than routine experimentation, and all such modifications and equivalents are believed to be through the spirit and scope of the disclosure as defined by the subsequent claims.