Absorber, solar cell and process for producing an absorber

Abstract

The invention relates to an absorber (15) for a solar cell that has an empirical formula (Cs,AZ)Pbl3, (Cs,AZ)Pb(l, Br)3, (Cs,AZ)Pb(l, Cl)3 or (Cs,AZ)Pb(l, Br, Cl)3 and a perovskite structure, where AZ represents azetidinium. The invention further relates to a solar cell including the absorber (15). The invention further relates to a process for producing the absorber, comprising: a) providing a substrate (1), b) thermally evaporating Csl and / or CsBr and / or CsCl to form a first vapour jet (4) which is produced proceeding from a first evaporation source (7), c) thermally evaporating Pbl2 and / or PbBr2 and / or PbCl2 to form a second vapour jet (3) which is produced proceeding from a second evaporation source (6), d) thermally evaporating AZI with AZI = azetidine hydroiodide or azetidinium iodide to form a third vapour jet (2) which is produced proceeding from a third evaporation source (5), where steps b), c) and d) are performed simultaneously such that the first vapour jet (4), the second vapour jet (3) and the third vapour jet (2) overlap at least partly, such that the absorber is formed on the substrate (1) provided.

Description

[0001] Title: Absorber, solar cell and method for producing an absorber

[0002] Description:

[0003] The invention relates to an absorber, a solar cell, and a method for producing an absorber. In particular, the invention relates to an absorber with a perovskite structure, a solar cell containing the absorber, and a method for producing such an absorber.

[0004] Absorbers for solar cells that have a perovskite structure are known. The formation of the perovskite structure by condensation on a substrate occurs, in the simplest case, according to the equation:

[0005] AX (g) + BX2(g) ABX3(s) (1 ) when the two starting materials AX and BX2 in gaseous form, denoted by (g), react to form a product ABX3 in solid form, denoted by (s), and the product is deposited on the substrate. For example, A = CHBNHB +, B = Pb 2+ and X = halogen ion such as chloride, bromide or iodide, so that by reaction of gaseous methylammonium halide and gaseous lead(II) iodide methylammonium lead trihalide is formed in solid form.

[0006] In a further development, several components of the same type can be used, so that the above equation (1 ) changes to:

[0007] AX (g) + A'X (g) + BX2(g) (A,A')BX3(S) (2) or

[0008] AX' (g) + A'X (g) + BX2(g) (A,A')B(X,X')3(S) (3) or

[0009] AX' (g) + AX” (g) + A'X (g) + BX2(g) - (A,A')B(X,X',X”)3 (S) (4).

[0010] Material compositions that are mainly Pbl2and / or PbBr2and / or PbCl2for BX2with B=Pb 2+ and X=iodide or bromide or chloride and Csl and / or CsBr and / or CsCl for AX or AX' or AX” with A=Cs +and X = iodide or bromide or chloride and X' = bromide or iodide or chloride and X" = bromide or iodide or chloride, where X, X' and X" are each different, even if they are each selected from the same group of halides, with the organic components MAI (methylammonium iodide) and / or MABr (methylammonium bromide) and / or MACl (methylammonium chloride) or FAI (formamidinium iodide) and / or FABr (formamidinium bromide) and / or FACl (formamidinium chloride) with A' = MA (methylammonium) or FA (formamidinium), processed from wet chemical processes by means of co-evaporation. According to equations (2) or (3) or (4), depending on the starting material used, (CsMA)Pbh, (CsMA)Pb(l,Br)3, (CsMA)Pb(l,Cl)3, (CsMA)Pb(Br,Cl)3, (CsMA)Pb(l,Br,Cl)3, (CsMA)PbBr3, (CsMA)PbCl3, (CsFA)Pbl3, (CsFA)Pb(l, Br)3, (CsFA)Pb(l,Cl)3, (CsFA)Pb(Br,Cl)3, (CsFA)Pb(l,Br,Cl)3, (CsFA)PbBr3 or (CsFA)PbCl3 are formed as so-called organic metal halide perovskites.Generally, the processes for producing these absorbers include wet-chemical methods such as spin coating. Currently, development is still largely carried out on a laboratory scale. Therefore, there is a need for a solar cell absorber that can be produced on an industrial scale.

[0011] It is an object of the invention to provide an absorber, a solar cell and a method for producing an absorber which can be produced on an industrial scale.

[0012] According to the invention, this object is achieved by an absorber having the features of patent claim 1, a solar cell having the features of patent claim 3, and a method having the features of patent claim 5. Advantageous developments and modifications are specified in the subclaims.

[0013] The invention is based on the processing of an absorber using a co-evaporation process, which has a novel perovskite structure. The absorber is designed as CsAZPbh, CsAZPb(l,Br)3, CsAZPb(l,Cl)3, or CsAZPb(l,Br,Cl)3, where AZ = azetidinium with the molecular formula C3HsN + . In this case, the perovskite structure is a crystal structure formed from Cs, AZ, and Pb cations and I, possibly Br, and possibly Cl anions.

[0014] The invention relates to the novel compositions of the absorber according to the invention, which can be produced by co-evaporation. Co-evaporation is carried out by simultaneous thermal evaporation of the absorber starting materials in the form of CsI (cesium iodide) and / or CsBr (cesium bromide) and / or CsCl (cesium chloride) with Pbh (lead(II) iodide) and / or PbBr? (lead(II) bromide) and / or PbCl (lead(II) chloride) and AZI (azetidine hydroiodide or azetidinium iodide), forming the absorber with a perovskite-like crystal structure. The absorber is a hybrid material made of organic and inorganic materials. It is an organic metal halide perovskite in which electrons can be released from their bound state and energetically excited in sunlight, while simultaneously leaving positively charged vacancies as "holes." The absorber is primarily intended for use in a solar cell.

[0015] The basic idea of ​​the invention is to form a perovskite structure from starting materials that are more suitable for evaporation processes than those already known from the prior art. This can be based on the vapor pressures of the materials themselves or the vapor pressures of the individual ions of the molecules. The selection of AZI as the starting material for producing the absorber according to the invention is based in particular on the following parameters: vapor pressure of the individual components (AZ = azetidine and HI = hydrogen iodide), size of the molecule, and the dipole moment / polarity of the molecule. The CsAZPbh, CsAZPb(I,Br)3, CsAZPb(I,Cl)3, or CsAZPb(I, Br, Cis) absorber deposited in the co-evaporation process crystallizes directly in the relevant perovskite phase.The thermal stability as well as electrical properties (photoluminescence) of CsAZPbh, CsAZPb(l, Br)3, CsAZPb(l,Cl)3 or CsAZPb(l,Br,Cl) show comparable and partly better results compared to state-of-the-art perovskite absorbers produced in the laboratory.

[0016] The perovskite structure represents a crystal structure in which, in this case, Pb(X, possibly X', possibly X")6-octahedra with X = iodide and possibly X' = bromide, possibly X" = chloride form a structure in whose gaps Cs and AZ cations are intercalated. The perovskite structure is preferably based on a component AX in the form of CsI and / or AX' in the form of CsBr and / or AX" in the form of CsCl with a high compound content, preferably >60%, which forms a basic structure, and a component A'X with a low compound content <40%, which is incorporated into the basic structure and causes a distortion of the crystal structure. The absorber therefore has a distorted perovskite structure because the Cs and AZ cations, with their respective different radii and diameters, are intercalated in the gaps.

[0017] According to the invention, A'X = AZI (azetidine hydroiodide or azetidinium iodide) is used as the organic component in the process, which leads to crystallization and the desired thermal stability of the perovskite structure using the co-evaporation process. Due to its lower vapor pressure, AZI can be evaporated in a more controlled manner than established organic perovskite starting materials such as MAI and FAI. Furthermore, the absorber with a perovskite structure in the form of CsAZPbh, CsAZPb(l,Br)3, CsAZPb(l,Cl)3, or CsAZPb(l,Br,Cl)3 is itself more stable than comparable absorbers with a perovskite structure according to the state of the art, especially under thermal stress. For example, the absorber is stable at 100°C for more than 10 hours and shows no degradation.

[0018] Furthermore, the absorber according to the invention is relatively stable in air and can be stored in air for more than 3 days without visible changes and / or degradation. In electrical characterization using photoluminescence (PL), the absorber according to the invention shows comparably good results to laboratory-produced perovskite structures according to the state of the art. The absorber according to the invention also shows no visible changes in the PL measurement after thermal stress (>10 hours) or storage in air (max. 3 days). In contrast to laboratory-produced perovskite absorbers according to the state of the art, the absorber according to the invention is stable even under increased solar irradiation, for example, for 10 suns, without any change in the measured spectrum.

[0019] The invention relates to an absorber having a perovskite structure of the formula (Cs,AZ)Pb13, (Cs,AZ)Pb(I, Br)3, (Cs,AZ)Pb(I, Cl)3, or (Cs,AZ)Pb(I, Br, Cl)3, where AZ is azetidinium. The absorber is cost-effective and can be thin.

[0020] The perovskite structure is formed by solid solution formation by incorporating several components A, A' of the same type, for example according to equation (2), (3) or (4) with A= Cs + and A'=azetidinium, where in this case in equations (2), (3) and (4) X is iodide, X' is bromide and X" is chloride. The Pb and X ions, such as I and possibly X', such as Br and possibly X", such as Cl, preferably form a Pb(X, possibly X', possibly X")6-octahedral structure and the Cs and AZ ions are embedded in this structure. This results in a distorted perovskite structure. One reason for the distorted perovskite structure is the different radii or diameters of the Cs and AZ cations.

[0021] The absorber is preferably formed as a thin film and has a layer thickness of <1 μm, preferably in the range of 200 to 800 nm, more preferably in the range of 300 to 700 nm, and even more preferably in the range of 400 to 600 nm. Alternatively, the absorber can preferably be formed as a wafer.

[0022] The invention further relates to a solar cell comprising the absorber according to the invention. The solar cell comprises a cost-effective, highly efficient absorber that can be thin. In a preferred embodiment, the solar cell is designed as a thin-film solar cell. Alternatively or additionally, the solar cell is preferably designed as a tandem solar cell. The thickness of a thin-film solar cell varies from a few nanometers (nm) to several tens of micrometers (pm), while a wafer solar cell has a thickness of up to 250 pm. Thin-film solar cells are therefore hundreds of times thinner than wafer solar cells.

[0023] Preferably, the solar cell

[0024] - a front metallization as a front electrode,

[0025] - an adjacent hole conductor designed to transport positively charged holes to the front side electrode,

[0026] - the absorber according to the invention, which is adjacent to the hole conductor and absorbs the radiation of sunlight, generating positive (“holes”) and negative charge carriers (electrons),

[0027] - an electron conductor adjacent to the absorber, which conducts the electrons to a rear electrode, and

[0028] - a backside metallization as a backside electrode.

[0029] The front is a side facing the light, and the back is a side facing away from the light.

[0030] Alternatively, the solar cell preferably has

[0031] - a front metallization as a front electrode,

[0032] - an adjacent electron conductor which transmits the electrons to the front electrode,

[0033] - the absorber according to the invention, which is adjacent to the hole conductor and absorbs the radiation of sunlight, generating positive (“holes”) and negative charge carriers (electrons),

[0034] - a hole conductor adjacent to the absorber, which is designed to transport positively charged holes to the back electrode, and

[0035] - a rear-side metallization as a rear-side electrode. The solar cell is preferably designed as a tandem solar cell. The tandem solar cell preferably has at least two subcells, more preferably two subcells. The subcell containing the absorber according to the invention preferably represents an upper subcell of the tandem solar cell, wherein the upper subcell is the subcell closest to the incident light. The tandem solar cell can be manufactured such that the subcells are deposited directly monolithically on top of one another. Alternatively, the tandem solar cell can be manufactured such that the subcells are manufactured separately from one another and mounted electrically separately.

[0036] The tandem solar cell preferably has the following structure in the specified order:

[0037] - a front metallization,

[0038] - an electrically conductive layer such as an ITO layer (transparent indium tin oxide layer), for example with a layer thickness of 100 nm,

[0039] - a buffer and electron conductor layer such as an SnOz layer, for example with a layer thickness of 20 nm,

[0040] - a passivation and hole blocking layer such as a LiF / C60 layer, for example with a LiF layer thickness of 1 nm and a C60 layer thickness of 18 nm,

[0041] - the absorber according to the invention, for example with a layer thickness of about 500 nm,

[0042] - a hole-conducting layer such as NiO / 2PACz layer (nickel oxide / [2-(9H-carbazol-9-yl)ethyl]phosphonic acid layer),

[0043] - another electrically conductive layer such as an ITO layer, for example with a layer thickness of 20 nm,

[0044] - a TopCon layer (charge carrier selective contact layer, with TOPCon = Tunnel Oxide Passivated Contact),

[0045] - another absorber such as a silicon substrate, for example a p-type or n-type Cz-Si substrate, - a p + or n + doped silicon layer, a backside passivation,

[0046] - a backside metallization, wherein the backside metallization has local contacts with the substrate through the backside passivation.

[0047] The invention further relates to a method for producing the absorber according to the invention, comprising: a) providing a substrate, b) thermally evaporating Csl and / or CsBr and / or CsCl to form a first vapor jet generated from a first evaporation source, c) thermally evaporating Pbh and / or PbBr and / or PbCl to form a second vapor jet generated from a second evaporation source, d) thermally evaporating AZI with AZI = azetidine hydroiodide or azetidinium iodide to form a third vapor jet generated from a third evaporation source, wherein steps b), c) and d) are carried out simultaneously such that the first vapor jet, the second vapor jet and the third vapor jet at least partially overlap, so that the absorber according to the invention is formed on the provided substrate.

[0048] The deposition of the absorber is carried out in a single step, as steps b), c), and d) are performed simultaneously. The at least partial overlap of the vapor jets is essential for the process.

[0049] The temperatures for thermally evaporating the starting materials vary: In a preferred embodiment, a temperature for thermally evaporating CsI and / or CsBr and / or CsCl in step b) is between 450 and 600°C. Preferably, a temperature for thermally evaporating Pbh and / or PbBr and / or PbCl in step c) is between 220 and 350°C. Preferably, a temperature for thermally evaporating AZI in step d) is between 100 and 250°C.

[0050] In a preferred embodiment, the process is carried out under high vacuum. The high vacuum preferably has a pressure range of <10 -5 mbar.

[0051] A mixing ratio of CSI and / or CsBr and / or CsCl and AZI in the range of 75%-90% to 10%-25% is preferred. In other words, the mixing ratio of CSI to AZI and / or CsBr to AZI lies in a mixing ratio range between a first mixing ratio of 75% to 25% and a second mixing ratio of 90% to 10%. Pbh and / or PbBr are preferred. and / or PbCb and CsI and / or CsBr and / or CsCl and the organic component AZI with the mixing ratio of CsI and / or CsBr and / or CsCl and AZI of 75%-90% to 10%-25% to CsIAZPbh, CsAZPb(l,Br)3, CsAZPb(l,Cl)3 or CsAZPb(l,Br,Cl)3. This ensures that the perovskite structure is formed based on the component AX in the form of CsI and / or AX' in the form of CsBr and / or AX" in the form of CsCl with a high compound content, preferably >60%, and the component A'X in the form of AZI with a low compound content <40%.One advantage is that the proportion of the organic component is significantly lower compared to other organic components such as FAI. Furthermore, the vapor pressure of AZI is lower than that of FAI and is therefore more suitable for evaporation processes, so the use of AZI instead of FAI enables higher throughputs and lower plant costs.

[0052] The absorber is preferably formed as a thin film. Alternatively, the absorber is preferably formed as a wafer.

[0053] In a preferred embodiment, the substrate is coated with the absorber statically. Alternatively, the substrate is preferably coated with the absorber in an inline production facility. Both variants enable large-scale production of the absorber.

[0054] The invention is explained below using exemplary embodiments with reference to the figures. These show schematically and not to scale

[0055] Fig. 1 is a sketched representation of a method according to the invention;

[0056] Fig. 2 shows a sketched representation of an absorber not according to the invention; Fig. 3 shows a sketched representation of an absorber according to the invention; and Fig. 4 shows a solar cell according to the invention.

[0057] Fig. 1 shows a sketch of a method according to the invention. The method for producing an absorber comprises: a step a) providing a substrate 1. The method is carried out in an inline production plant (not shown), in which the substrate 1 is transported in a direction indicated by an arrow. Steps b) thermal evaporation of CsI and / or CsBr and / or CsCl to form a first vapor jet 4, which is generated from a first evaporation source 7, c) thermal evaporation of Pbh and / or PbBr and / or PbCl to form a second vapor jet 3, which is generated from a second evaporation source 6, and d) thermal evaporation of AZI, where AZI = azetidine hydroiodide or azetidinium iodide, to form a third vapor jet 2, which is generated from a third evaporation source 5, are carried out.Steps b), c) and d) are carried out simultaneously such that the first vapor jet 4, the second vapor jet 3 and the third vapor jet 2 at least partially overlap, so that an absorber (not shown) with a perovskite structure having the formula (Cs,AZ)Pbh, (Cs,AZ)Pb(I, Br)s, (Cs,AZ)Pb(I, Cl)s or (Cs,AZ)Pb(I, Br, Cl)B is formed on the provided substrate 1. Fig. 2 shows a sketched representation of a non-inventive absorber. The absorber has a perovskite structure with the formula CsPbh, where Pb and Cs ions are cations and I ions are anions. The crystal structure is formed as a basic structure of Pbk octahedra 31, with Cs cations 30 embedded in gaps 32 between Pbk octahedra 31. The gaps 32 and the Pbk octahedra 31 are of equal size and regularly arranged.

[0058] Fig. 3 shows a sketch of an absorber according to the invention. The absorber has a crystal structure in the form of a mixed structure of Pbk octahedra 31, with Cs in gaps 32 between Pbk octahedra 31 + 30 and AZ + 33 are embedded. The Cs cations 30 have a diameter that is smaller than the diameter of the AZ cations 33. Compared to the diameter shown in Fig.

[0059] In the basic structure shown in Figure 2, the mixed structure has distorted gaps 32, i.e., they are not all the same size, and the Pbk octahedra are not evenly arranged, so that the crystal structure is distorted. The absorber can be manufactured according to the process shown in Figure 1.

[0060] Fig. 4 shows a solar cell according to the invention. It is designed as a tandem solar cell and has the following structure in the order given:

[0061] - a front metallization 11 ,

[0062] - an electrically conductive layer 12 such as an ITO layer with a layer thickness of 100 nm,

[0063] - a buffer and electron conductor layer 13 such as an SnOz layer with a layer thickness of 20 nm,

[0064] - a passivation and hole blocking layer 14 such as a LiF / C60 layer with a layer thickness of the LiF layer of 1 nm and a layer thickness of the C60 layer of 18 nm,

[0065] - an absorber 15 shown in Fig. 3 with a layer thickness of about 500 nm,

[0066] - a hole-conducting layer 16 such as NiO / 2PACz layer, - another electrically conductive layer 17 such as an ITO layer with a layer thickness of 20 nm,

[0067] - a TopCon layer 18,

[0068] - a further absorber 19 such as a silicon substrate in the form of a p-type or n-type Cz-Si substrate,

[0069] - a p + or n + doped silicon layer 34

[0070] - a backside passivation 20,

[0071] - a backside metallization 21, wherein the backside metallization 21 has local contacts 22 through the backside passivation 20 with the further absorber 19.

[0072] List of reference symbols:

[0073] 1 substrate

[0074] 2 third steam jet

[0075] 3 second steam jet

[0076] 4 first steam jet

[0077] 5 third evaporation source

[0078] 6 second evaporation source

[0079] 7 first evaporation source

[0080] 11 Front metallization

[0081] 12 electrically conductive layer

[0082] 13 Electron conductor layer

[0083] 14 Hole blocking layer

[0084] 15 absorbers

[0085] 16 hole conductor layer

[0086] 17 additional conductive layer

[0087] 18 TopCon

[0088] 19 additional absorbers

[0089] 20 Back passivation

[0090] 21 Backside metallization

[0091] 22 local contact

[0092] 30 Cs +

[0093] 31 Pbk octahedra

[0094] 32 gap

[0095] 33 AZ +

[0096] 34 silicon layer

Claims

Patent claims: 1 . Absorber (15) for a solar cell, which has a molecular formula (Cs,AZ)Pbl3, (Cs,AZ)Pb(l, Br)3, (Cs,AZ)Pb(l, Cl)3 or (Cs,AZ)Pb(l, Br, Cl)3 and a perovskite structure, where AZ stands for azetidinium.

2. Absorber (15) according to claim 1, characterized in that the Pb, I and optionally Br and optionally Cl ions form a basic structure and the Cs and AZ ions are embedded in the basic structure.

3. Solar cell comprising an absorber (15) according to claim 1 or 2.

4. Solar cell according to claim 3, characterized in that it is designed as a thin-film solar cell and / or as a tandem solar cell.

5. A method for producing an absorber according to claim 1 or 2, comprising: a) providing a substrate (1), b) thermal evaporation of Csl and / or CsBr and / or CsCl to form a first vapor jet (4) which is generated from a first evaporation source (7), c) thermal evaporation of Pbh and / or PbBr? and / or PbCb to form a second vapor jet (3) which is generated from a second evaporation source (6), d) thermal evaporation of AZI with AZI = azetidine hydroiodide or azetidinium iodide to form a third vapor jet (2) which is generated from a third evaporation source (5), wherein steps b), c) and d) are carried out simultaneously in such a way that the first vapor jet (4), the second vapor jet (3) and the third vapor jet (2) at least partially overlap, so that the absorber is formed on the provided substrate (1). Process according to claim 5, characterized in that a temperature for thermal evaporation of Csl and / or CsBr and / or CsCl in step b) is between 450 and 600°C and / or a temperature for thermal evaporation of Pbh and / or PbBr and / or PbCl in step c) is between 220 and 350°C and / or a temperature for thermal evaporation of AZI in step d) is between 100 and 250°C. Process according to claim 5 or 6, characterized in that it is carried out under high vacuum, wherein the high vacuum preferably has a pressure range <10 -5mbar. Method according to one of claims 5 to 7, characterized in that a mixing ratio of CSI and / or CsBr and / or CsCl to AZI lies in a mixing ratio range between a first mixing ratio of 75% to 25% and a second mixing ratio of 90% to 10%. Method according to one of claims 5 to 7, characterized in that the absorber is formed as a thin film or as a wafer. Method according to one of claims 5 to 9, characterized in that the coating of the substrate (1) with the absorber is carried out statically or that the coating of the substrate (1) with the absorber is carried out in an inline production system.

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