CN117766619A - Preparation method of P-doped cdTe-based thin film solar cell device - Google Patents
Preparation method of P-doped cdTe-based thin film solar cell device Download PDFInfo
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- 239000010409 thin film Substances 0.000 title claims abstract description 52
- 238000002360 preparation method Methods 0.000 title claims abstract description 10
- 239000006096 absorbing agent Substances 0.000 claims abstract description 188
- 239000000463 material Substances 0.000 claims abstract description 121
- 229910004613 CdTe Inorganic materials 0.000 claims abstract description 56
- 238000000151 deposition Methods 0.000 claims abstract description 47
- 239000000758 substrate Substances 0.000 claims abstract description 20
- 238000010521 absorption reaction Methods 0.000 claims abstract description 14
- UHYPYGJEEGLRJD-UHFFFAOYSA-N cadmium(2+);selenium(2-) Chemical compound [Se-2].[Cd+2] UHYPYGJEEGLRJD-UHFFFAOYSA-N 0.000 claims abstract description 13
- 239000007772 electrode material Substances 0.000 claims abstract description 12
- 229910021478 group 5 element Inorganic materials 0.000 claims abstract description 10
- 239000002019 doping agent Substances 0.000 claims description 44
- 238000000034 method Methods 0.000 claims description 42
- 238000000137 annealing Methods 0.000 claims description 14
- 229910007709 ZnTe Inorganic materials 0.000 claims description 13
- 238000004519 manufacturing process Methods 0.000 claims description 13
- 238000001994 activation Methods 0.000 claims description 10
- 238000000859 sublimation Methods 0.000 claims description 6
- 230000008022 sublimation Effects 0.000 claims description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims description 5
- 229910052715 tantalum Inorganic materials 0.000 claims description 5
- 229910052720 vanadium Inorganic materials 0.000 claims description 5
- 238000009826 distribution Methods 0.000 claims description 2
- 238000005253 cladding Methods 0.000 abstract description 2
- 239000010410 layer Substances 0.000 description 380
- 239000011669 selenium Substances 0.000 description 29
- 230000002745 absorbent Effects 0.000 description 26
- 239000002250 absorbent Substances 0.000 description 26
- 230000008021 deposition Effects 0.000 description 24
- 239000010949 copper Substances 0.000 description 16
- 230000004913 activation Effects 0.000 description 8
- 229910052711 selenium Inorganic materials 0.000 description 8
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 7
- 229910052802 copper Inorganic materials 0.000 description 7
- 239000000203 mixture Substances 0.000 description 7
- 150000001875 compounds Chemical class 0.000 description 6
- 230000007423 decrease Effects 0.000 description 5
- 229910052698 phosphorus Inorganic materials 0.000 description 5
- 239000012190 activator Substances 0.000 description 4
- BUGBHKTXTAQXES-UHFFFAOYSA-N Selenium Chemical compound [Se] BUGBHKTXTAQXES-UHFFFAOYSA-N 0.000 description 3
- 229910052785 arsenic Inorganic materials 0.000 description 3
- 239000012298 atmosphere Substances 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
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- 238000007738 vacuum evaporation Methods 0.000 description 2
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- 230000003213 activating effect Effects 0.000 description 1
- 229910052787 antimony Inorganic materials 0.000 description 1
- WATWJIUSRGPENY-UHFFFAOYSA-N antimony atom Chemical compound [Sb] WATWJIUSRGPENY-UHFFFAOYSA-N 0.000 description 1
- RQNWIZPPADIBDY-UHFFFAOYSA-N arsenic atom Chemical compound [As] RQNWIZPPADIBDY-UHFFFAOYSA-N 0.000 description 1
- -1 arsenic ions Chemical class 0.000 description 1
- 229910052797 bismuth Inorganic materials 0.000 description 1
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 1
- 238000005234 chemical deposition Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- ORTQZVOHEJQUHG-UHFFFAOYSA-L copper(II) chloride Chemical compound Cl[Cu]Cl ORTQZVOHEJQUHG-UHFFFAOYSA-L 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
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- 238000001704 evaporation Methods 0.000 description 1
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- 239000011574 phosphorus Substances 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
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- 238000004544 sputter deposition Methods 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 238000002207 thermal evaporation Methods 0.000 description 1
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/543—Solar cells from Group II-VI materials
Abstract
The invention provides a preparation method of a p-doped CdTe-based thin film solar cell device with a cladding plate configuration, which at least comprises the steps of providing a substrate, forming a front electrode, forming an absorption layer and forming a back electrode. The step of forming the absorber layer includes at least alternately depositing layers of first and second absorber layer materials, wherein the first absorber layer material is CdSe and the second absorber layer material is CdTe. The doping source layer comprises at least one first doping element selected from group V elements, which is deposited at least one interface of the first and second absorber layer materials. The back electrode is formed by depositing a p-doped back electrode material. The invention also provides a p-doped CdTe-based thin film solar cell device.
Description
Technical Field
The invention relates to a preparation method of a P-doped cdTe-based thin film solar cell device.
Background
P doping is typically performed on CdTe-based thin film solar cell devices by Cu. Cu as a doping element has some drawbacks such as reduced long-term stability and reduced solar cell efficiency. Accordingly, there is a need for a method of p-doping CdTe-based thin film solar cell devices with alternative doping elements. In the study, as showed great potential to overcome the disadvantages associated with Cu.
At present, how As is incorporated into CdTe-based absorber layers is an unsolved problem. Conventional copper doping techniques include a copper coating step and a subsequent diffusion step, but this technique does not allow arsenic ions to diffuse into the CdTe-based absorber layer. Still other methods use vapor-Transport-Deposition (VTD) by sublimating a raw material in a gas stream and adding doping elements to the gas stream. Furthermore, pre-doped raw materials can also be used, but are only suitable for special coating processes to ensure that a constant dopant concentration can be maintained over a long period of time.
WO 2017/081477 A1 discloses a method of producing a Cu-doped CdTe-based thin film solar cell, in which a continuous organic layer is applied between an absorber layer and a back contact. The Cu is provided onto the CdTe absorber layer by thermal evaporation or by treating the surface of the organic layer with Cu, thereby incorporating the Cu into the CdTe absorber layer.
WO 2017/100393 A2 discloses a process for manufacturing a high efficiency photovoltaic device. The absorber layer within the semiconductor layer stack may be formed, for example, from CdTe or Cd (S, se, te). Cu may be contained in the back contact layer or the absorber layer may be directly doped with Cu, but there is no clear description of how the doping is performed. If the back contact layer comprises copper, an oxide layer formed between the absorber layer and the back contact layer may limit diffusion of Cu from the back contact into the absorber layer.
US 9899 B2 discloses a method for producing a solar cell, wherein a sacrificial doped layer comprising a doping element selected from the group consisting of copper, phosphorus, antimony, bismuth, molybdenum and manganese is applied between a first CdTe absorber layer having large grains and a second CdTe absorber layer having small grains. During the temperature treatment, a uniformly doped CdTe absorber layer is formed.
US 2019/0341506 A1 describes doping copper with copper chloride. However, while arsenic is mentioned as an additional or alternative dopant, the doping method is not described.
Disclosure of Invention
The invention aims to provide a preparation method of a P-doped cdTe-based thin film solar cell device and a P-doped CdTe-based thin film solar cell device.
The object of the invention is achieved by a method as defined in the independent claims. Preferred embodiments are provided in the dependent claims.
The invention provides a preparation method of a p-doped CdTe-based thin-film solar cell device with a cladding plate configuration, which at least comprises the following steps: providing a substrate, forming a front electrode, forming an absorption layer and forming a back electrode. The step of forming the absorber layer includes at least: layers of a first absorber layer material and a second absorber layer material are alternately deposited, wherein CdSe is deposited as the first absorber layer material and CdTe is deposited as the second absorber layer material. The doping source layer comprises at least one first doping element selected from group V elements, which is deposited at least one interface of the first and second absorber layer materials. The P-doped material is deposited as a back electrode.
The processes of forming the front electrode, forming the absorber layer, and forming the back electrode may be performed by any known method, such as sublimation, evaporation, sputter deposition, wet deposition, chemical deposition, and the like.
The superstrate configuration means that the thin film solar cell device has a structure distributed in the following order: the front electrode is deposited on the substrate, followed by deposition of the absorber layer and the back electrode. In some embodiments, the method further comprises depositing some intermediate layers known in the art, for example, between the substrate and the front electrode, between the front electrode and the absorber layer, and between the absorber layer and the back electrode. In a superstrate configuration, the substrate is typically a transparent substrate and the front electrode is a transparent front electrode. It is self-evident that the front and back electrodes can be deposited as a stack of layers as known in the art.
Alternating deposition refers to alternating deposition of multiple layers of first and second absorbent layer materials, wherein multiple layers refer to at least two layers of first absorbent layer materials and at least two layers of second absorbent layer materials. An alternately deposited absorber layer stack is finally formed comprising the following sequence of layers: a first layer of a first absorbent layer material, a first layer of a second absorbent layer material, a second layer of a first absorbent layer material, a second layer of a second absorbent layer material, and so on. That is, first, a first step of depositing a first layer of a first absorber layer material; a second step follows, depositing a first layer of a second absorber material, and so on. In some embodiments, the first step and the second step are repeated 1 to 5 times. Finally, the alternately deposited absorber layer stack further comprises at least one doped source layer, as described below, having a thickness in the range of 500nm to 1 μm.
In some embodiments, the layers of the first absorber layer material are deposited at a thickness of 20nm to 150nm per layer, and at least two of the layers of the first absorber layer material may be different in thickness from one another. For example, the thickness of the first layer of the first absorbent layer material may be half the thickness of the second layer, and, if applicable, half the thickness of the subsequent layers of the first absorbent layer material. Furthermore, of all the layers of the first absorbent layer material, there may be at least two layers or the thickness of all the layers may be the same.
In some further embodiments, the layers of the second absorber layer material are deposited at a thickness of 20nm to 3000nm per layer, preferably 50nm to 500nm per layer. The thickness of each individual layer of the second absorbent layer material may be 1 to 5 times the thickness of the layer of the adjacent first absorbent layer material. Also, at least two of the layers of the second absorbent layer material may be different in thickness from each other and/or at least two of the layers may be the same in thickness. In one embodiment, the deposited thickness of all layers of the second absorber layer material is the same within the stack of alternately deposited absorber layers.
In a further embodiment, the step of forming the absorber layer further comprises depositing a layer of a second absorber layer material on the stack of alternately deposited absorber layers. Advantageously, the final thickness of the absorbent layer is between 2.5 μm and 4 μm.
In a further embodiment, the step of forming the absorber layer further comprises depositing an additional layer of a second absorber layer material prior to depositing the stack of alternately deposited absorber layers. In some further embodiments, the additional layer of such second absorber layer material has a thickness in the range of 10nm to 1500nm, preferably 25nm to 250nm, before deposition of the stack of alternately deposited absorber layers.
All depositions of the first absorber layer material may be performed under the same processing conditions, resulting in a deposited layer having substantially the same properties in terms of grain size, density or otherwise. The same is true for all depositions of the second absorber material. However, it is also possible to deposit the individual layers of the first or second absorbent layer material under different process conditions to achieve the desired different properties of the individual layers.
The above method can be used to fabricate a CdSeTe absorber layer. CdSeTe refers to CdSe x Te 1-x Wherein 0.ltoreq.x.ltoreq.0.6, preferably 0.ltoreq.x.ltoreq.0.4, x may vary with the thickness of the absorbent layer. By selecting the thickness and properties of the individual layers of the first absorber layer material and of the individual layers of the second absorber layer material, the thin-film solar cell device is further processed, and the Se content in the absorber layer and the Se gradient in the final thickness direction of the absorber layer resulting from the further processing can be defined precisely and finely as desired. The person skilled in the art knows how to obtain the desired composition of the CdSeTe absorber layer.
In some embodiments, the Se gradient within the CdSeTe absorber layer may refer to a higher concentration of Se near the front electrode relative to the concentration toward the back electrode of the thin film solar cell device. In some further embodiments, the Se gradient within the CdSeTe absorber layer comprises a Se content of at most 30at. -% Se (x.ltoreq.0.6) near the front electrode and a Se content of at most 10at. -% Se (x.ltoreq.0.2) near the back electrode; preferably, the Se content near the front electrode is at most 13at-%, and the Se content near the back electrode is at most 1at-%.
According to the invention, a doping source layer is deposited at least one interface of the first and second absorber layer materials. This means that after depositing the layer of the first absorber layer material and before depositing the layer of the second absorber layer material, at least one doping source layer is deposited; alternatively, the dopant source layer is deposited at least once after depositing the layer of the second absorber layer material and before depositing the layer of the first absorber layer material. The dopant source layer may be deposited anywhere between the first absorber layer material layer and the second absorber layer material layer.
In a further embodiment, a dopant source layer is deposited at each interface of the first and second absorber layer material layers. In a further embodiment, the number of doping source layers is one time less than the total number of interfaces of the first and second absorption layer material layers within the alternately deposited layer stack.
In some embodiments, the thickness of the deposited dopant source layer is from 1nm to 50nm. If multiple dopant source layers are deposited, the thickness of each dopant source layer may be the same or different. Furthermore, each dopant source layer may be deposited under the same process conditions, resulting in deposited layers having substantially the same properties in terms of composition (e.g., ratio of first dopant element to other elements), grain size, density, or otherwise. However, each dopant source layer may also be deposited under different processing conditions or to achieve different characteristics as desired for the respective layers.
Advantageously, a CdSeTe absorber layer doped with the first doping element can be produced therewith. By selecting the thickness and position of the respective dopant source layers as well as other properties, the content of the first dopant element in the absorber layer and the gradient of the first dopant element in the absorber layer resulting from further processing can be precisely and finely defined as desired. In some embodiments, the first gradient of the first doping element within the CdSeTe absorber layer shows a higher concentration of the first doping element near the front electrode than the concentration of the first doping element near the back electrode.
The dopant source layer is made of a material comprising at least one first dopant element, wherein the first dopant element may be present in elemental form, i.e. unbound, or in bound form, e.g. as a salt. The first doping element is an element suitable for doping the CdSeTe absorber material and may also be suitable for doping the dopant source layer material. The separate dopant source layers may be made of different materials or the same material containing the first dopant element.
The first doping element is a V group element. The group V element means an element contained in the V main group, i.e., the 15 th group, according to IUPAC convention of the periodic table of elements. In some embodiments, the group V element is As. Advantageously, an As doped CdSeTe absorber layer can be obtained. The doping source layer is, for example, as 2 Te 3 . In some further embodiments, the group V element is N and the dopant source layer is, for example, N-doped ZnTe.
According to the invention, a p-doped material is deposited as a back electrode. The P-doped material includes a second doping element selected from the group including N, ag, li, na, K, P, as, sb, rb, cu, au, V, cd, nb and Ta. The second doping element may be the same as or different from the first doping element. The second doping element causes p-doping of the back electrode material. Thereby enabling the production of a CdSeTe absorber layer having a second gradient of the second doping element in the further processing of the thin film solar cell device. In some embodiments, the second gradient of the second doping element within the CdSeTe absorber layer shows a higher concentration of the second doping element near the back electrode than the concentration of the second doping element near the front electrode.
In some embodiments, the first gradient of the first doping element and the second gradient of the second doping element are distributed in opposite directions.
In some embodiments, the method further includes other known steps required to prepare a p-doped CdTe-based thin film solar cell device, such as an activation treatment or a heat treatment.
In the preparation process of the CdTe-based thin film solar cell, the doping source layer is at least partially decomposed, and the first absorption layer material, the second absorption layer material and the doping source layer are at least partially mixed. These processes are performed at elevated temperatures during deposition of the individual layers or during a separate heat treatment step, such as an annealing treatment. When the first absorber layer material dissolves and mixes with the second absorber layer material, a CdSeTe absorber layer is formed. This causes volume shrinkage, which results in lattice stress, dislocations and vacancies. These vacancies will be occupied by ions or atoms of the first doping element, which ions or atoms can be moved by the elevated temperature. The extent of the volume shrinkage depends on the composition of the CdSeTe absorber layer formed. For example, if 20% of Te atoms are replaced by Se atoms, the resulting CdSeTe absorber layer has a composition similar to CdSe 0.2 Te 0.8 The volume shrinkage is about 3%. For another example, if 40% of Te atoms are replaced by Se atoms, a CdSeTe absorber layer is formed having a composition similar to CdSe 0.4 Te 0.6 The volume shrinkage is about 6%. The composition of the formed CdSeTe absorber layer can be controlled by the thickness ratio of the first absorber layer material layer and the second absorber layer material layer, which are CdSe and CdTe, respectively.
In some embodiments, the composition of the formed CdSeTe absorber layer is that of CdSe 0.4 Te 0.6 To CdSe 0.2 Te 0.8 Within the range of 6% to 3% volume shrinkage can thus be obtained to fully dope the CdSeTe layer.
Furthermore, the second doping element diffuses from the back electrode layer into the CdSeTe absorber layer, for example, during deposition of the back electrode layer or during a subsequent annealing treatment step. Finally, a p-doped CdSeTe absorption layer containing the first doping element and the second doping element is formed. Further, a first gradient of the first doping element and a second gradient of the second doping element are formed.
Advantageously, by the process of the invention, p-doped CdTe-based thin film solar cell devices having a high doping level of the first doping element can be produced with a doping level of 10 15 /cm 3 To 10 19 /cm 3 . The first absorber layer material, the second absorber layer material, the doping source layer and the optional p-doped back electrode material, the well-defined layer sequence of which is deposited enabling simultaneous mixing of the first and second absorber layer materials to dope the absorber layer with the first doping element and the second doping element during the process of the method, i.e. during deposition of the respective layers or during further processing of the thin film solar cell device. Se of the first absorber layer material may act As a "gate opener" for the first doping element, especially for heavily doped ions like As, and Se may enhance incorporation of the first doping element in the absorber layer lattice. It would also be advantageous to be able to manufacture CdSeTe thin film solar cell devices having a p-doped CdSeTe absorber layer with defined Se content and Se gradient, with defined first and second doping element content and gradient. In addition, the method provided by the invention can also eliminate the defects such as reduced long-term stability caused by copper as the main p-doped element in the absorption layer.
In an embodiment, the layers of the first and second absorber materials and the dopant source layer are deposited by near-space sublimation.
Near-space sublimation deposition advantageously allows for the rapid and simple fabrication of p-doped thin film solar cell devices. In particular, the method enables group V element doping during near-space sublimation growth of the absorber layer and/or during further processing of the thin film solar cell device. Deposition parameters such as near-space sublimated substrate temperature and deposition rate are well known to those skilled in the art.
In some embodiments, the dopant source layer comprising the first dopant element is deposited as an elemental layer or a compound layer. A compound layer containing a group V element including, but not limited to, for example, as 2 Te 3 、Sb 2 Te 3 、Bi 2 Te 3 、As 2 Se 3 、Sb 2 Se 3 、Bi 2 Se 3 N-doped ZnTe.
In some embodiments, the compound layer is deposited by co-depositing the elements contained by the compound. In other embodiments, the compound layer is deposited from a compound source.
In an embodiment, the method of the present invention further comprises, after depositing the layers of the first and second absorber layer materials and doping the source layer, performing an annealing treatment. In some embodiments, the method may include a plurality of annealing treatment steps performed at different locations within the process flow of the method.
Advantageously, the annealing treatment is a heat treatment capable of mixing the above-mentioned layers and simultaneously doping the absorber layer with the first doping element, thereby producing a p-doped CdSeTe absorber layer.
In some embodiments, the annealing treatment may be performed after deposition of the alternately deposited absorber layer stack or after deposition of another layer of the second absorber layer material onto the alternately deposited absorber layer stack.
In embodiments, the annealing treatment is performed at a temperature in the range of 300 ℃ to 500 ℃, preferably 350 ℃ to 480 ℃, more preferably 380 ℃ to 460 ℃. The duration of the annealing treatment depends on the thickness of the layers of the first and second absorber materials and the dopant source layer, and the final thickness of the absorber layer, and in some embodiments, the duration is from 5 minutes to 30 minutes, preferably from 7 minutes to 25 minutes, more preferably from 10 minutes to 20 minutes.
In a further embodiment, the method of the present invention may comprise, after deposition of the p-doped back electrode material, performing a further annealing treatment. The further annealing treatment may be carried out at different temperatures, for example in the temperature range 150 ℃ to 250 ℃.
In embodiments, the annealing treatment is performed as an activation treatment.
In the manufacture of CdTe-based materialsIn the thin film solar cell device of (2), an activation process is known. According to the method of the invention, the activation treatment can be carried out according to the prior art. The step of usually carrying out the activation treatment comprises the step of applying an activating agent (e.g. CdCl) by wet chemical means or vacuum evaporation 2 ) Applied to the absorber layer and then annealed in an air atmosphere at a specified temperature (typically in the range of 380 c to 460 c) and cleaned. Of course, the activator may be applied by other methods.
The presence of the activator may aid in the process caused by the elevated temperature. In some embodiments, no further annealing treatment is required other than the activation treatment.
In a preferred embodiment, p-doped ZnTe is deposited as back electrode material.
Advantageously, p-doped ZnTe is a well known back electrode material for CdTe-based thin film solar cell devices.
P-doped ZnTe refers to ZnTe doped with a second doping element selected from N, ag, li, na, K, P, as, sb, rb, cu, au, V, cd, nb and Ta, preferably N. This enables the preparation of a CdSeTe absorber layer having a second gradient of a second doping element during further processing of the thin film solar cell device, in which second gradient the second doping element concentration is higher near the back electrode compared to the second doping element near the front electrode.
The invention also includes a p-doped CdTe-based thin film solar cell device comprising at least a substrate, a front electrode, a p-doped absorber layer, and a p-doped back electrode comprising a second doping element, wherein the p-doped absorber layer is a p-doped CdSeTe absorber layer comprising a Se-gradient, a first gradient of a first doping element, and a second gradient of a second doping element, wherein the first doping element is selected from group V elements.
In an embodiment, the second doping element is selected from N, ag, li, na, K, P, as, sb, rb, cu, au, V, cd, nb and Ta. Advantageously, such a p-doped CdTe based thin film solar cell device achieves a high doping of the first doping element, as compared to prior art CdTe based thin film solar devicesLevel at 10 13 /cm -3 To 10 19 /cm -3 In the scope of this, there is excellent long-term stability, wherein the prior art CdTe-based absorber layer is mainly p-doped with copper.
In some embodiments, the Se gradient is a higher concentration of Se near the front electrode than towards the back electrode. In a further embodiment, the first gradient of the first doping element is shown as a higher concentration of the first doping element near the front electrode than the concentration of the first doping element near the back electrode. In a further embodiment, the second gradient of the second doping element is shown as a higher concentration of the second doping element near the back electrode than near the front electrode. In some further embodiments, the first gradient and the second gradient extend in opposite directions. Each gradient may be stable, wherein the slope of the respective gradient may vary with the thickness of the absorbent layer, or may include a step. Furthermore, each gradient may change its direction over the thickness of the absorbent layer.
In further embodiments, the p-doped CdTe-based thin film solar device can also include known intermediate layers, such as between the substrate and the front electrode, between the front electrode and the absorber layer, and/or between the absorber layer and the back electrode. The P-doped CdTe-based thin film solar cell device may further comprise a layer stack as front electrode and/or back electrode.
In a preferred embodiment, the p-doped back electrode comprises p-doped ZnTe.
Advantageously, p-doped ZnTe is a known back electrode for CdTe-based thin film solar cell devices.
P-doped ZnTe refers to the doping of ZnTe, wherein the second doping element is selected from N, ag, li, na, K, P, as, sb, rb, cu, au, V, cd, nb and Ta, preferably N. Advantageously, the p-doped back electrode may serve as a doping source comprising the second doping element.
Drawings
The combination of features in the above-mentioned embodiments and in the claims facilitates a better implementation of the invention. However, the embodiments of the present invention described in the foregoing specification are merely examples given by way of illustration, and the present invention is not limited thereto. Any modification, variation and equivalent distribution, and combinations of embodiments, are intended to be included within the scope of this invention.
FIG. 1 illustrates exemplary process steps of a method of making a p-doped CdTe-based thin film solar cell device in accordance with one embodiment of the invention.
Fig. 2 shows an exemplary embodiment of the layer structure of the semi-finished p-doped CdTe based thin film solar cell device after step S4 of fig. 1.
FIG. 3 illustrates one exemplary embodiment of a p-doped CdTe-based thin film solar cell device in accordance with the invention.
Fig. 4 shows an exemplary doping profile of an absorber layer of a p-doped CdTe-based thin film solar cell device.
Detailed Description
Figure 1 schematically illustrates the process steps of a method of making a p-doped CdTe-based thin film solar cell device in one embodiment. First, a starting substrate is provided (step S1). Then, in step S2, a front electrode is formed on the substrate.
In steps S3 and S4, an absorber layer is formed, wherein step S3 comprises alternately depositing a first and a second absorber layer material, wherein a dopant source layer comprising a first dopant element is deposited at least one interface of the first and second absorber layer materials. The first absorbing layer material is CdSe, and the second absorbing layer material is CdTe. That is, step S3 comprises a plurality of sub-steps which can result in an alternately deposited stack of absorber layers, as will be explained in more detail below. In sub-step S3A1, a layer of a first absorber layer material is deposited, i.e. a first layer of the first absorber layer material. In sub-step S3A2, a doping source layer, i.e. a first doping source layer, is deposited. In a subsequent sub-step S3A3, a layer of a second absorber material, i.e. a first layer of the second absorber material, is deposited. In a subsequent sub-step S3A2.1, a further doping source layer, i.e. a second doping source layer, is deposited, followed by a further layer of a first absorber layer material, i.e. a second layer of the first absorber layer material, in a sub-step S3A1.1. In sub-step S3A2.2, another, i.e., third, dopant source layer is deposited. In substep S3A3.1 a layer of a second absorber material is deposited, i.e., a second layer of the second absorber material. In a next sub-step S3A2.3, another, i.e. fourth, doping source layer is deposited. Next in sub-step S3A1.2 a layer of a first absorber layer material, i.e. a third layer of the first absorber layer material, is deposited. In sub-step S3A3.2, a layer of a second absorber layer material, i.e., a third layer of the second absorber layer material, is deposited. The resulting alternately deposited absorber layer stack has a thickness in the range of 500nm to 1 μm and the number of deposited dopant source layers is doubled less than the number of interfaces of the first and second absorber layer materials within the alternately deposited absorber layer stack. In this process step, the alternating deposition layer stack has five interfaces of first and second absorber layer materials, with the dopant source layer deposited at four interfaces. Of course, other numbers of first and second absorber material layers and other numbers of dopant source layers are possible, as well as other proportional relationships of the number of dopant source layers to the number of interfaces between the first and second absorber layers. Furthermore, the dopant source layer may also be deposited at other interfaces of the first and second absorber layer materials. For example, the first doping source layer formed in the sub-step S3A2 may be omitted, or the first and second doping source layers formed in the sub-steps S3A2 and S3A2.1 may be omitted.
In step S4, another layer of a second absorber layer material is deposited on top of the stack of alternately deposited absorber layers to reach a final thickness of the absorber layer of 3 μm. All layers of the first and second absorber layer materials and the dopant source layer are deposited by near-space sublimation. After deposition to the final thickness of the absorber layer, a p-doped back electrode material is deposited as back electrode in step S5, wherein the back electrode material comprises a second doping element.
To complete the preparation of the p-doped CdTe-based thin film solar cell device, further steps known from the prior art can be performed, for example an activation treatment can be performed after reaching the final thickness of the deposited absorber layer, i.e. after step S4. The activation treatment is, for example, by wet chemical methods or vacuum evaporation of an activator (e.g., cdCl 2 ) Is applied to the absorber layer to be activated and then annealed in an air atmosphere at a set temperature, for example 380 ℃ to 440 ℃.
In a particular embodiment according to fig. 1, a transparent glass substrate is provided in step S1. In step S2, a front electrode is formed by depositing 400nm SnO: F. In step S3, an absorber layer is formed by alternately depositing layers of first and second absorber layer materials, wherein a dopant source layer is deposited at least one interface of the first and second absorber layer materials. In sub-step S3A1, a CdSe layer of 25nm thickness is deposited, followed by a deposition of 5nm thickness of As in sub-step S3A2 2 Te 3 Doping the source layer. Next, in sub-step S3A3, a CdTe layer of 100nm thickness is deposited followed by a deposition of 5nm thick As in sub-step S3A2.1 2 Te 3 A layer. In the next substep S3A1.1, a CdSe layer of 50nm thickness is deposited. Next, in sub-step S3A2.2, as is deposited to a thickness of 5nm 2 Te 3 A layer. In sub-step S3A3.1, a CdTe layer of 100nm thickness is deposited followed by a deposition of As of 5nm thickness in sub-step S3A2.3 2 Te 3 A layer. In the next sub-step S3A1.2 CdSe is deposited to a thickness of 50nm, followed by CdTe deposition to a thickness of 100nm in sub-step S3A3.2. The final thickness of the absorber layer is achieved by depositing a CdTe layer with a thickness of 2500nm in step S4. Next, cdCl is evaporated by wet chemical methods or vacuum 2 An activator is applied to the absorber layer for an activation treatment and then annealed in an air atmosphere at a set temperature, for example, 380 ℃ to 460 ℃. In step S5, an N-doped ZnTe back electrode material was deposited as back electrode, having a thickness of 20nm and an N content of 2%. The method of the present invention may further comprise the step of depositing an intermediate layer as known in the art, for example between the substrate and the front electrode, between the front electrode and the absorber layer and/or between the absorber layer and the back electrode.
Fig. 2 schematically shows an exemplary embodiment of the layer structure of the p-doped CdTe-based thin film solar cell device 1 after step S4 of fig. 1. That is, the p-doped CdTe-based thin film solar cell device 1 is only a semi-finished thin film solar cell device.
The p-doped CdTe-based thin film solar cell device 1 comprises a substrate 11 and a front electrode 12 on top of the substrate 11. On top of the front electrode 12, the p-doped CdTe-based thin film solar cell device 1 comprises an alternately deposited stack of absorber layers 13 and a layer 14 of a second absorber layer material on top of said stack of absorber layers 13. The alternately deposited absorber layer stack 13 comprises several layers 151 to 153 of a first absorber layer material, several layers 161 to 163 of a second absorber layer material and several doping source layers 171 to 174 in the order described below. The alternately deposited absorber layer stack 13 comprises a first layer 151 of a first absorber layer material, wherein said first layer 151 is adjacent to the front electrode 12. Next, a first dopant source layer 171 is located on top of the first layer 151 of the first absorber layer material. A first layer 161 of a second absorber layer material is deposited on top of the first dopant source layer 171. Next, a second dopant source layer 172 is deposited, followed by a second layer 152 of the first absorber layer material. Then, a third dopant source layer 173 is deposited followed by a second layer 162 of a second absorber layer material. Next, a fourth dopant source layer 174 is deposited, followed by a third layer 153 of the first absorber layer material. In this embodiment, a third layer 163 of the second absorber material is finally deposited, thereby completing the alternately deposited absorber layer stack 13. Thus, the alternately deposited absorber layer stack comprises four dopant source layers 171 to 174 at the interface of the first and second absorber layer materials, wherein the number of dopant source layers 171 to 174 is twice the number of interfaces of the first and second absorber layer materials. The alternately deposited absorber layer stacks 13 and the layer 14 of the second absorber layer material on top of said absorber layer stacks 13 together form a semi-finished absorber layer 18 of the p-doped CdTe based thin film solar cell device. In the embodiment shown, no intermixing between the layers thereof occurs during the deposition of the individual layers, in particular between the individual layers of the alternately deposited absorber layer stack 13. However, this embodiment is only illustrative. Typically, the temperature at which the deposition of the individual layers is carried out can result in at least partial intermixing between already deposited layers.
Fig. 3 shows an exemplary embodiment of the p-doped CdTe-based thin film solar cell device 10 according to the present invention after the manufacturing process of the p-doped CdTe-based thin film solar cell device 1 shown in fig. 2 is completed. The p-doped CdTe based thin film solar cell device 10 comprises a substrate 11, a front electrode 12 on top of the substrate 11, an absorber layer 180 on top of the front electrode 12 and a p-doped back electrode 19. The back electrode 19 is formed in the process step S5 of the p-doped CdTe-based thin film solar cell device 10 shown in fig. 1. The absorbent layer 180 is formed in the semi-finished absorbent layer 18 shown in fig. 2 by mixing the different layers in the semi-finished absorbent layer 18. In this process, the layers 151 to 153 of the first absorption layer material and the doping source layers 171 to 174 are dissolved and together with the layers 161 to 163 and 14 of the second absorption layer material form an absorption layer 180, the absorption layer 180 including CdSeTe doped with the first doping element. In addition, since the second doping element is out-diffused from the back electrode 19, the absorbing layer 180 further includes the second doping element.
Fig. 4 shows an exemplary doping profile of the absorber layer 180 of the p-doped CdTe-based thin film solar cell device 10 of fig. 3. The x-axis represents position within the absorbent layer, where x 0 To be the interface position of the absorber layer 180 and the front electrode 12, x1 is the interface position of the absorber layer 180 and the back electrode 19. The c-axis represents the element concentration within absorber layer 180. Wherein 3 concentration changes are shown: the first is Se concentration, the second is As concentration As the first doping element, and the third is N concentration As the second doping element. It can be seen that the selenium concentration near the front electrode is higher than the selenium concentration near the back electrode, where the selenium concentration decreases slowly and then decreases strongly as the distance from the front electrode increases, being almost zero (0) near the back electrode. The region with high Se concentration may have a thickness of up to 1 μm, measured from the front electrode. The gradient of the first doping element is somewhat similar to the Se gradient, but at a lower concentration. That is, the concentration of the first doping element first decreases almost constantly or only slowly, and then decreases significantly as the distance from the front electrode becomes larger, reaching a lower level near the back electrode. The concentration of the second doping element is opposite to the concentration gradient direction of the first doping element. That is, the concentration of the second doping element decreases with increasing distance from the back electrode, and is almost near the front electrodeZero. The maximum concentration or content of Se is 20%.
It should be noted that the doping profile of the absorption layer 180 shown in fig. 4 is only an example, and the number and concentration of different elements may be changed as follows: the thicknesses of the layers of the first and second absorber layer materials, the layers of the dopant source materials, etc. are selected accordingly, as well as by selecting the first and second doping elements, and the process conditions of the method of the invention.
Reference sequence number
1. Semi-finished p-doped CdTe-based thin film solar cell device
10 p-doped CdTe-based thin film solar cell device
11. Substrate and method for manufacturing the same
12. Front electrode
13. Alternately deposited absorber layer stacks
14. Layers of a second absorber layer material on top of the alternately deposited layer stack
151-153 first absorbent layer Material layer
161-163 layers of a second absorbent layer material
171-174 doped source layer
18. Semi-finished absorbent layer
180. Absorbent layer
19. Back electrode
Claims (7)
1. A method of making a p-doped CdTe-based thin film solar cell device in a superstrate configuration, comprising at least: providing a substrate, forming a front electrode, forming an absorption layer and forming a back electrode,
wherein the step of forming the absorber layer comprises at least alternately depositing layers of a first absorber layer material and layers of a second absorber layer material, wherein the first absorber layer material is CdSe and the second absorber layer material is CdTe;
wherein the doping source layer comprises at least one first doping element selected from group V elements, the doping source layer being deposited at least one interface of the first absorber layer material and the second absorber layer material;
wherein the back electrode is formed by depositing a p-doped back electrode material, the back electrode material comprising a second doping element.
2. The method of manufacturing of claim 1, wherein the layer of first absorber layer material, the layer of second absorber layer material, and the dopant source layer are deposited by near-space sublimation.
3. The method of manufacturing according to claim 1 or 2, characterized in that an annealing treatment is performed after depositing the layer of the first absorber layer material, the layer of the second absorber layer material and the doping source layer.
4. The method of claim 3, wherein the annealing is performed as an activation process.
5. A method of preparation as claimed in any preceding claim wherein p-doped ZnTe is deposited as back electrode material.
6. A p-doped CdTe-based thin film solar cell device, comprising at least:
the substrate is provided with a plurality of holes,
a front electrode, a front electrode and a rear electrode,
a p-doped absorption layer, and
a p-doped back electrode, the p-doped back electrode comprising a second doping element,
wherein the p-doped absorber layer is a p-doped CdSeTe absorber layer comprising a Se-gradient distribution, a first gradient of at least one first doping element, and a second gradient of a second doping element, the first doping element being selected from group V elements.
7. The apparatus of claim 6, wherein the p-doped back electrode comprises p-doped ZnTe, wherein the second doping element is selected from N, ag, cu, au, li, na, K, rb, V, cd, nb and Ta.
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