Solar cell structure

Abstract

This invention relates to the field of battery technology and discloses a solar cell structure, comprising, in sequence: a conductive substrate, a hole transport layer, an active layer, an electron transport layer, and a back electrode layer. The back electrode layer includes a functional layer, a main conductive layer, and a protective layer stacked sequentially, wherein the functional layer is located between the main conductive layer and the electron transport layer; the main conductive layer is a conductive metal layer used for charge transport; the functional layer is used to prevent metal ions in the main conductive layer from migrating towards the electron transport layer; and the protective layer is a dense layer used to protect the main conductive layer. This invention utilizes the protective layer to protect the main conductive layer, preventing corrosion and maintaining its chemical stability. The main conductive layer, being a conductive metal layer, can construct low-loss carrier channels. The functional layer can prevent metal ions in the main conductive layer from migrating towards the electron transport layer, reducing contact resistance and significantly improving the photoelectric conversion efficiency and lifespan of the solar cell structure.

Description

Technical Field

[0001] This utility model relates to the field of battery technology, specifically to the structure of solar cells. Background Technology

[0002] A solar cell is a device that directly converts light energy into electrical energy through the photoelectric effect or photochemical effect. The back electrode is a key functional layer for matching the energy levels and the terminal interface of carrier transport in a solar cell. Its material system and interface characteristics directly determine the limiting photoelectric conversion efficiency and operational stability of the solar cell.

[0003] Traditional processes commonly use vapor deposition or sputtering of noble metals (such as gold and silver) as back electrodes. However, due to the inherent defects of these noble metals, their high work function leads to the formation of a Schottky barrier between them and the light-absorbing layer (such as silicon or perovskite), significantly increasing the contact resistance. In large-area modules, this phenomenon is further aggravated by the film thickness gradient distribution of vapor deposition or sputtering processes, resulting in a lateral resistance polarization effect. This causes a systematic decay of the fill factor (Eff), leading to poor photoelectric conversion efficiency and a short lifespan for the solar cell. Utility Model Content

[0004] In view of this, the present invention provides a solar cell structure to solve the problem that traditional solar cell structures use precious metals as back electrodes, resulting in poor photoelectric conversion efficiency and short service life.

[0005] This utility model provides a solar cell structure, which includes, in sequence, a conductive substrate, a hole transport layer, an active layer, an electron transport layer, and a back electrode layer. The back electrode layer includes a functional layer, a main conductive layer, and a protective layer stacked in sequence, wherein the functional layer is located between the main conductive layer and the electron transport layer.

[0006] The main conductive layer is a conductive metal layer and is used to transmit charge;

[0007] The functional layer is used to block metal ions in the main conductive layer from migrating toward the electron transport layer.

[0008] The protective layer is a dense layer and is used to protect the main conductive layer.

[0009] Beneficial Effects: The solar cell structure of this invention employs a back electrode layer consisting of a functional layer, a main conductive layer, and a protective layer stacked sequentially. The dense structure of the protective layer inhibits oxidation of the main conductive layer surface and prevents external ions from penetrating into the main conductive layer and metal ions from migrating outwards, significantly improving the corrosion resistance and chemical stability of the solar cell structure. The main conductive layer, a conductive metal layer, can construct low-loss carrier channels. The functional layer, acting as a buffer between the main conductive layer and the electron transport layer, prevents metal ions in the main conductive layer from migrating towards the electron transport layer, reducing contact resistance, avoiding fill factor decay, and significantly improving the photoelectric conversion efficiency and lifespan of the solar cell structure.

[0010] In one alternative embodiment, the protective layer comprises any one of a cadmium layer, a molybdenum layer, a tungsten layer, or a molybdenum disulfide layer;

[0011] And / or, the main conductive layer includes any one of a copper layer, a silver layer, a gold layer, an aluminum layer, a silver-based alloy layer, a bismuth-based corrosion-resistant alloy layer, or a graphene-copper composite layer;

[0012] And / or, the functional layer includes any one of an indium tin oxide layer, an aluminum-doped zinc oxide layer, a fluorine-doped tin oxide layer, a silver nanowire layer, or a graphene composite flexible conductive layer.

[0013] Beneficial effects: Cadmium, molybdenum, tungsten, or molybdenum disulfide layers all possess highly dense and stable structures, effectively inhibiting oxidation of the main conductive layer surface and preventing external ions from penetrating into the main conductive layer and metal ions from migrating outward from the main conductive layer. Copper, silver, gold, aluminum, silver-based alloy, bismuth-based corrosion-resistant alloy, or graphene-copper composite layers all exhibit low-resistance current-sharing characteristics, adapting to the current distribution requirements of large-area components and achieving stable compatibility with protective and functional layers. Indium tin oxide, aluminum-doped zinc oxide, fluorine-doped tin oxide, silver nanowire, or graphene composite flexible conductive layers can all prevent metal ions in the main conductive layer from migrating towards the electron transport layer, reducing contact resistance and preventing fill factor decay.

[0014] In one optional embodiment, the protective layer is a cadmium layer with a thickness of T1, satisfying 10nm≤T1≤20nm.

[0015] Beneficial effects: The cadmium layer, through its dense lattice structure and low chemical activity, can inhibit the oxidation reaction on the surface of the main conductive layer, block the penetration path of external ions (such as Cl-, SO42-), and significantly improve corrosion resistance in humid and hot environments. Simultaneously, the gradient design of the thermal expansion coefficient alleviates the accumulation of interfacial stress during thermal cycling, inhibits crack initiation and propagation, and utilizes the difference in lattice constants to form a bidirectional ion migration barrier, preventing metal ions in the main conductive layer from migrating outwards and maintaining interfacial chemical stability. By controlling the thickness of the cadmium layer within a suitable range, it can be ensured that the cadmium layer is thin enough to avoid increasing series resistance, while ensuring that the cadmium layer effectively covers the main conductive layer.

[0016] In one optional embodiment, the main conductive layer is a copper layer with a thickness of T2, satisfying 40nm≤T2≤80nm.

[0017] Beneficial effects: The copper layer, through its high-purity bulk conductivity, constructs low-loss carrier channels, adapting to the current distribution requirements of large-area components and achieving stable compatibility with protective and functional layers. By controlling the thickness of the copper layer within a suitable range, it can achieve high reflectivity, enhancing light capture.

[0018] In one optional embodiment, the functional layer is an indium tin oxide layer, and the thickness of the indium tin oxide layer is T3, satisfying 20nm≤T3≤50nm.

[0019] Beneficial effects: The indium tin oxide layer has transparent and conductive properties, enabling incident light transmission and back reflection. Combined with the surface plasmon resonance effect, it can also enhance the visible light capture capability of the active layer. The work function of the indium tin oxide layer is adjustable, which can reduce the interface barrier, improve the fill factor, achieve uniform resistance distribution, and suppress local hot spot effects.

[0020] In one optional embodiment, the protective layer is a molybdenum layer, the main conductive layer is a copper layer, and the functional layer is an indium tin oxide layer.

[0021] Beneficial effects: The molybdenum layer has high chemical stability, is resistant to oxidation and corrosion, and can effectively protect the copper layer. At the same time, the molybdenum layer is a highly efficient diffusion barrier layer, which can effectively prevent external ions from penetrating into the copper layer and also prevent copper ions from diffusing outward.

[0022] In one alternative embodiment, the conductive substrate comprises a fluorine-doped tin oxide substrate or an indium tin oxide substrate.

[0023] Beneficial effects: Fluorine-doped tin oxide substrates have high temperature stability, while indium tin oxide substrates have high light transmittance.

[0024] In one alternative embodiment, the hole transport layer comprises a nickel oxide thin film.

[0025] Beneficial effects: Energy level alignment between the nickel oxide film and the active layer enables efficient hole extraction and reduces interfacial recombination, thereby improving open-circuit voltage. The high hole mobility and conductivity of the nickel oxide film reduce contact resistance and increase the fill factor.

[0026] In one alternative embodiment, the active layer is a perovskite layer.

[0027] Beneficial effects: The active layer is a perovskite layer with ultra-high photoelectric conversion efficiency, excellent photoelectric properties, and is easy to process and has low usage cost.

[0028] In one alternative embodiment, the electron transport layer comprises a carbon-60 layer.

[0029] Beneficial effects: The electron transport layer using a carbon-60 layer can synergistically achieve electron extraction. The contact resistance between the carbon-60 layer and the perovskite layer is small, which helps to reduce the electron extraction barrier. Carbon-60 molecules can also fill perovskite grain boundaries or surface defect states. Attached Figure Description

[0030] To more clearly illustrate the specific embodiments of this utility model or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of a solar cell structure according to an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the back electrode layer of a solar cell structure according to an embodiment of the present invention;

[0033] Figure 3 This is a graph showing the normalized efficiency of a solar cell structure according to an embodiment of the present invention as a function of time.

[0034] Explanation of reference numerals in the attached figures:

[0035] 1. Conductive substrate; 2. Hole transport layer; 3. Active layer; 4. Electron transport layer; 5. Back electrode layer; 501. Functional layer; 502. Main conductive layer; 503. Protective layer. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0037] The following is combined Figures 1 to 3 The following describes embodiments of the present invention.

[0038] According to embodiments of the present invention, such as Figure 1 and Figure 2 As shown, a solar cell structure is provided, comprising, in sequence: a conductive substrate 1, a hole transport layer 2, an active layer 3, an electron transport layer 4, and a back electrode layer 5. The back electrode layer 5 includes a functional layer 501, a main conductive layer 502, and a protective layer 503 stacked sequentially, wherein the functional layer 501 is located between the main conductive layer 502 and the electron transport layer 4. The main conductive layer 502 is a conductive metal layer used for charge transport. The functional layer 501 is used to prevent metal ions in the main conductive layer 502 from migrating towards the electron transport layer 4. The protective layer 503 is a dense layer used to protect the main conductive layer 502.

[0039] Therefore, the solar cell structure provided in this embodiment of the invention employs a functional layer 501, a main conductive layer 502, and a protective layer 503 stacked sequentially in the back electrode layer 5. The dense structure of the protective layer 503 inhibits oxidation of the surface of the main conductive layer 502 and also prevents external ions from penetrating into the main conductive layer 502 and metal ions from migrating outwards, significantly improving the corrosion resistance of the solar cell structure and exhibiting good chemical stability. The main conductive layer 502 is a conductive metal layer that can construct low-loss carrier channels. The functional layer 501, acting as a buffer layer between the main conductive layer 502 and the electron transport layer 4, prevents metal ions in the main conductive layer 502 from migrating towards the electron transport layer 4, reducing contact resistance, avoiding fill factor decay, and significantly improving the photoelectric conversion efficiency and lifespan of the solar cell structure.

[0040] In one embodiment, the protective layer 503 includes any one of a cadmium layer, a molybdenum layer, a tungsten layer, or a molybdenum disulfide layer. The cadmium layer, molybdenum layer, tungsten layer, or molybdenum disulfide layer all have a highly dense and stable structure, effectively inhibiting oxidation of the surface of the main conductive layer 502, blocking the penetration of external ions into the main conductive layer 502, and preventing the outward migration of metal ions from the main conductive layer 502.

[0041] In one embodiment, the main conductive layer 502 includes any one of a copper layer, a silver layer, a gold layer, an aluminum layer, a silver-based alloy layer, a bismuth-based corrosion-resistant alloy layer, or a graphene-copper composite layer. The copper layer, silver layer, gold layer, aluminum layer, silver-based alloy layer, bismuth-based corrosion-resistant alloy layer, or graphene-copper composite layer all have low-resistance current-sharing characteristics, enabling them to adapt to the current distribution requirements of large-area components and achieve stable compatibility with the protective layer 503 and the functional layer 501.

[0042] In one embodiment, the functional layer 501 includes any one of an indium tin oxide (ITO) layer, an aluminum-doped zinc oxide (AZO) layer, a fluorine-doped tin oxide (FTO) layer, a silver nanowire layer, or a graphene composite flexible conductive layer. The indium tin oxide layer, aluminum-doped zinc oxide layer, fluorine-doped tin oxide layer, silver nanowire layer, or graphene composite flexible conductive layer can all prevent metal ions in the main conductive layer 502 from migrating towards the electron transport layer 4, reducing contact resistance and preventing fill factor decay.

[0043] In one embodiment, such as Figure 2 As shown, the protective layer 503 is a cadmium layer with a thickness of T1, satisfying 10nm ≤ T1 ≤ 20nm. The cadmium layer, through its dense lattice structure and low chemical activity, can inhibit the oxidation reaction on the surface of the main conductive layer 502, blocking the penetration path of external ions (such as Cl-, SO42-), and significantly improving corrosion resistance in humid and hot environments. Simultaneously, through a gradient design of the thermal expansion coefficient, it alleviates the accumulation of interfacial stress during thermal cycling, inhibiting crack initiation and propagation. Furthermore, it utilizes the difference in lattice constants to form a bidirectional ion migration barrier, preventing metal ions in the main conductive layer 502 from migrating outwards and maintaining interfacial chemical stability. By controlling the thickness of the cadmium layer within a suitable range, it can be ensured that the cadmium layer is thin enough to avoid increasing the series resistance, while ensuring that the cadmium layer effectively covers the main conductive layer 502. If T1 is too small, the cadmium layer will have difficulty effectively covering the main conductive layer 502; if T1 is too large, the resistance will increase.

[0044] On the other hand, the main conductive layer 502 is generally a conductive metal with good conductivity, such as aluminum or copper. However, aluminum and copper are soft metals with good ductility. When the main conductive layer 502 is the outermost layer, it needs to be laser-scribed to form multiple sub-cells. However, due to its good ductility, the metal on both sides of the scribed line will warp after laser scribe, and some burrs and rough edges will appear. In later use, these burrs on both sides are very likely to come into contact within the scribed groove, causing a short circuit and affecting the efficiency and lifespan of the battery. However, by adding a protective layer 503, the protective layer 503 can suppress the warping of the main conductive layer 502 at the scribed line during laser scribe, thereby suppressing the ductility of the main conductive layer 502 and making the groove at the scribed line smoother.

[0045] For example, in this embodiment of the present invention, the thickness T1 of the cadmium layer can be 10nm, 15nm, 20nm, etc.

[0046] Furthermore, in one embodiment, such as Figure 2 As shown, the main conductive layer 502 is a copper layer with a thickness of T2, satisfying 40nm ≤ T2 ≤ 80nm. The copper layer utilizes high-purity bulk conductivity to construct low-loss carrier channels, adapting to the current distribution requirements of large-area components and achieving stable compatibility with the protective layer 503 and the functional layer 501. By controlling the thickness of the copper layer within a suitable range, it can achieve high reflectivity, enhancing light capture.

[0047] For example, in this embodiment of the present invention, the thickness T2 of the copper layer can be 40nm, 50nm, 60nm, 70nm, 80nm, etc.

[0048] Furthermore, in one embodiment, such as Figure 2 As shown, functional layer 501 is an indium tin oxide (ITO) layer with a thickness of T3, satisfying 20nm ≤ T3 ≤ 50nm. The ITO layer possesses transparent and conductive properties, enabling both incident light transmission and back reflection. Combined with surface plasmon resonance, it also enhances the visible light trapping capability of active layer 3. The work function of the ITO layer is adjustable, which can reduce the interface barrier, improve the fill factor, ensure uniform resistance distribution, and suppress local hot spot effects.

[0049] For example, in this embodiment of the present invention, the thickness T3 of the indium tin oxide layer can be 20nm, 30nm, 40nm, 50nm, etc.

[0050] In one embodiment, the protective layer 503 is a molybdenum layer, the main conductive layer 502 is a copper layer, and the functional layer 501 is an indium tin oxide layer. The molybdenum layer has high chemical stability, is resistant to oxidation and corrosion, and can effectively protect the copper layer. At the same time, the molybdenum layer is a highly efficient diffusion barrier layer, which can effectively prevent external ions from penetrating into the copper layer and also prevent copper ions from diffusing outward.

[0051] In one embodiment, the conductive substrate 1 includes a fluorine-doped tin oxide substrate (FTO substrate) or an indium tin oxide substrate (ITO substrate). The fluorine-doped tin oxide substrate has high temperature stability, while the indium tin oxide substrate has high light transmittance.

[0052] In one embodiment, the hole transport layer 2 comprises a nickel oxide thin film. The nickel oxide thin film is aligned with the energy levels of the active layer 3, enabling efficient hole extraction and reducing interfacial recombination, thereby improving the open-circuit voltage. The nickel oxide thin film possesses high hole mobility and conductivity, which can reduce contact resistance and increase the fill factor.

[0053] In one embodiment, the active layer 3 is a perovskite layer, which has ultra-high photoelectric conversion efficiency, excellent photoelectric properties, and is easy to process and has low cost.

[0054] Specifically, the perovskite layer is an ABX3 type crystal, where A = MA+ or FA+ or Cs+.

[0055] In one embodiment, the electron transport layer 4 includes a carbon 60 layer. The use of a carbon 60 layer in the electron transport layer 4 enables synergistic electron extraction. The low contact resistance between the carbon 60 layer and the perovskite layer helps to reduce the electron extraction barrier. Furthermore, carbon 60 molecules can fill perovskite grain boundaries or surface defect states.

[0056] The fabrication process of the solar cell structure in this embodiment of the invention is as follows:

[0057] Conductive substrate 1 uses 400cm 2 The fluorine-doped tin oxide substrate was ultrasonically cleaned to remove surface contaminants. A nickel oxide thin film, or hole transport layer 2, was deposited by high-power magnetron sputtering. The dense, pinhole-free structure of the nickel oxide film, combined with gradient annealing, optimized hole mobility and interfacial contact. Next, a perovskite precursor was solution-coated and annealed at 100°C to form a compositionally tunable perovskite layer, or active layer 3, achieving broad-spectrum absorption and defect suppression. A carbon-60 layer, or electron transport layer 4, was constructed using vacuum evaporation. The high electron affinity of the carbon-60 layer ensures ultrafast electron extraction. The back electrode layer 5 was deposited layer by layer using magnetron sputtering, consisting of indium tin oxide, copper, and cadmium layers. Precise matching of film thickness and interfacial properties was achieved through sputtering power and atmosphere control.

[0058] The process parameters of the solar cell structure of this utility model are further described in detail below with reference to specific embodiments. These examples should not be construed as limiting the scope of protection claimed by this utility model.

[0059] In the following embodiments and comparative examples, the conductive substrate 1 is a fluorine-doped tin oxide substrate, the hole transport layer 2 is a nickel oxide thin film, the active layer 3 is a perovskite layer, and the electron transport layer 4 is a carbon 60 layer.

[0060] Example 1:

[0061] The functional layer 501 of the back electrode layer 5 is a 40nm indium tin oxide layer, the main conductive layer 502 is a 60nm copper layer, and the protective layer 503 is a 15nm cadmium layer. After the above processes are completed, photoelectric conversion efficiency testing and dual 85 (85℃ / 85% RH) aging evaluation are performed. The test and evaluation results are shown in Table 1 and... Figure 3 .

[0062] Example 2:

[0063] The functional layer 501 of the back electrode layer 5 is a 40nm indium tin oxide layer, the main conductive layer 502 is a 60nm copper layer, and the protective layer 503 is a 30nm cadmium layer. After the above processes are completed, photoelectric conversion efficiency testing and dual 85 (85℃ / 85% RH) aging evaluation are performed. The test and evaluation results are shown in Table 1 and... Figure 3 .

[0064] Comparative Example 1

[0065] The back electrode layer 5 adopts a structure of a functional layer 501 and a main conductive layer 502. The functional layer 501 is a 40nm indium tin oxide layer, and the main conductive layer 502 is a 60nm copper layer. After the above processes are completed, photoelectric conversion efficiency testing and dual 85 (85℃ / 85% RH) aging evaluation are performed. The test and evaluation results are shown in Table 1 and Table 2. Figure 3 .

[0066] Comparative Example 2

[0067] The back electrode layer 5 consists only of the main conductive layer 502, which is a 60nm copper layer. After fabrication, photoelectric conversion efficiency testing and dual 85 (85℃ / 85% RH) aging evaluation were performed. The test and evaluation results are shown in Table 1 and Table 2. Figure 3 .

[0068] Table 1: Test Results

[0069] Back electrode layer Eff / % Aging degradation / % Example 1 ITO-Cu-Cd 20.51 4.76 Example 2 ITO-Cu-Cd 19.34 4.16 Comparative Example 1 ITO-Cu 20.16 15.98 Comparative Example 2 Cu 17.51 16.73

[0070] From Table 1 and Figure 3 As can be seen, in Example 1, the back electrode layer 5 adopts a composite structure of indium tin oxide, copper, and cadmium layers, and satisfies 10nm≤T1≤20nm, 40nm≤T2≤80nm, and 20nm≤T3≤50nm. Compared with the structure of back electrode layer 5 of Comparative Example 1, which adopts indium tin oxide and copper layers, and the structure of back electrode layer 5 of Comparative Example 2, which adopts only copper layers, Example 1 significantly reduces the degradation of the solar cell structure, improves the lifespan of the solar cell structure, and significantly improves the photoelectric conversion efficiency.

[0071] In Example 2, the back electrode layer 5 adopts a composite structure of indium tin oxide layer, copper layer and cadmium layer. The thickness T1 of the cadmium layer is greater than 20nm. The cadmium layer is too thick, which leads to a decrease in photoelectric conversion efficiency, which is weaker than that of Example 1.

[0072] It should be noted that, Figure 3 In this context, normalized efficiency refers to the relative value of a solar cell's photoelectric conversion efficiency (PCE) or other performance parameters after standardization under specific reference conditions (such as standard test conditions, STC).

[0073] Although embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A solar cell structure, characterized in that, In order, they include: The conductive substrate (1), hole transport layer (2), active layer (3), electron transport layer (4) and back electrode layer (5) are provided. The back electrode layer (5) includes a functional layer (501), a main conductive layer (502) and a protective layer (503) stacked in sequence. The functional layer (501) is located between the main conductive layer (502) and the electron transport layer (4). The main conductive layer (502) is a conductive metal layer and is used to transmit charge; The functional layer (501) is used to block metal ions in the main conductive layer (502) from migrating toward the electron transport layer (4); The protective layer (503) is a dense layer and is used to protect the main conductive layer (502).

2. The solar cell structure according to claim 1, characterized in that, The protective layer (503) includes any one of a cadmium layer, a molybdenum layer, a tungsten layer, or a molybdenum disulfide layer; And / or, the main conductive layer (502) includes any one of a copper layer, a silver layer, a gold layer, an aluminum layer, a silver-based alloy layer, a bismuth-based corrosion-resistant alloy layer, or a graphene-copper composite layer; And / or, the functional layer (501) includes any one of an indium tin oxide layer, an aluminum-doped zinc oxide layer, a fluorine-doped tin oxide layer, a silver nanowire layer, or a graphene composite flexible conductive layer.

3. The solar cell structure according to claim 2, characterized in that, The protective layer (503) is a cadmium layer with a thickness of T1, satisfying 10nm≤T1≤20nm.

4. The solar cell structure according to claim 3, characterized in that, The main conductive layer (502) is a copper layer with a thickness of T2, satisfying 40nm≤T2≤80nm.

5. The solar cell structure according to claim 4, characterized in that, The functional layer (501) is an indium tin oxide layer with a thickness of T3, satisfying 20nm≤T3≤50nm.

6. The solar cell structure according to claim 2, characterized in that, The protective layer (503) is a molybdenum layer, the main conductive layer (502) is a copper layer, and the functional layer (501) is an indium tin oxide layer.

7. The solar cell structure according to any one of claims 1 to 6, characterized in that, The conductive substrate (1) includes a fluorine-doped tin oxide substrate or an indium tin oxide substrate.

8. The solar cell structure according to any one of claims 1 to 6, characterized in that, The hole transport layer (2) comprises a nickel oxide thin film.

9. The solar cell structure according to any one of claims 1 to 6, characterized in that, The active layer (3) is a perovskite layer.

10. The solar cell structure according to any one of claims 1 to 6, characterized in that, The electron transport layer (4) includes a carbon-60 layer.

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