An organic solar cell with reduced metal electrode reflection loss and preparation method thereof

Abstract

The invention discloses an organic solar cell with reduced metal electrode reflection loss, comprising a transparent substrate, a high refractive index medium layer, a semi-transparent metal electrode, an active layer and a back reflection electrode stacked in sequence; a microcavity mode exists between the semi-transparent metal electrode and the back reflection electrode, light reflected by the semi-transparent metal electrode is confined in the high refractive index medium layer in a waveguide mode, and the waveguide mode is cross-coupled with the microcavity mode so that the energy in the waveguide mode is coupled to the active layer, thereby reducing the semi-transparent metal film electrode reflection loss, increasing the light absorption intensity of the organic solar cell, and improving the problem of low transmittance of the semi-transparent inert metal.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to an organic solar cell capable of reducing reflection loss of a metal electrode and a preparation method thereof. Background Art

[0002] Solar cells convert light energy into electricity and are generally categorized into two main types: inorganic solar cells and organic solar cells. Organic solar cells are increasingly favored by researchers due to their environmental friendliness, lightweight design, low manufacturing cost, and flexibility. In recent years, countries around the world have been competing to develop various organic solar cell technologies. Organic solar cells consist of an organic photoactive layer sandwiched between two electrodes of opposite polarity. In organic solar cells, ITO is commonly used as the transparent electrode because of its high transmittance of 90% and its high electrical conductivity. However, the scarcity of indium in ITO, its high deposition temperature, and its brittleness limit its future applications. Semi-transparent inert metal films (such as Au and Ag) are a promising alternative to ITO due to their simple vapor deposition process, excellent electrical conductivity, and relatively good ductility. However, the high reflection loss and low transmittance of inert metal films have hindered their widespread application in organic solar cells.

[0003] Current research on reducing reflection loss primarily focuses on reducing reflection loss on glass or plastic substrates. This is typically achieved by introducing an anti-reflection layer with a thickness of one-quarter wavelength onto the outer surface of the substrate. However, there has been relatively little research on reducing reflection loss on semi-transparent metal electrodes. Addressing this issue is crucial for promoting the widespread application of semi-transparent inert metal electrodes in organic solar cells and also provides a viable option for selecting transparent electrodes for flexible solar cells. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide an organic solar cell and a preparation method that reduces the reflection loss of metal electrodes. A high-refractive-index dielectric layer is used to induce reflected light to form a waveguide mode, thereby confining the energy of the reflection loss within the waveguide mode. The cross-coupling between the waveguide mode and the microcavity mode inside the cell is then used to couple the energy of the reflection loss to the active layer absorption layer of the organic solar cell.

[0005] In order to achieve the above objectives, the technical solution of the present invention is:

[0006] An organic solar cell that reduces metal electrode reflection loss comprises a transparent substrate, a high-refractive-index dielectric layer, a semi-transparent metal electrode, an active layer, and a back-reflecting electrode stacked in sequence, wherein the transparent substrate serves as a light incident surface, and a microcavity mode exists between the semi-transparent metal electrode and the back-reflecting electrode; the refractive index of the transparent substrate is 1.5 to 1.7, and the refractive index of the high-refractive-index dielectric layer is ≥2; light reflected by the semi-transparent metal electrode is confined in the high-refractive-index dielectric layer in a waveguide mode, and the waveguide mode is cross-coupled with the microcavity mode so that energy in the waveguide mode is coupled to the active layer.

[0007] Optionally, the material of the high refractive index medium layer is ZnS or ZrO2.

[0008] Optionally, the thickness of the high refractive index medium layer is 10-80 nm.

[0009] Optionally, the material of the semi-transparent metal electrode is an inert metal.

[0010] Optionally, the material of the semi-transparent metal electrode is Au or Ag, and the thickness is 15 to 25 nm.

[0011] Optionally, the organic solar cell includes a small molecule system organic solar cell and a polymer system organic solar cell.

[0012] Optionally, the transparent substrate is a glass substrate or a plastic substrate with a thickness of 1 μm to 1.1 mm.

[0013] The above-mentioned method for preparing an organic solar cell that reduces the reflection loss of a metal electrode comprises the following steps: forming a high-refractive-index dielectric layer on a transparent substrate by vacuum deposition or magnetron sputtering; and sequentially forming a semi-transparent metal electrode, an active layer, and a back-reflecting electrode on the high-refractive-index dielectric layer.

[0014] The beneficial effects of the present invention are:

[0015] 1) Using a high-refractive-index dielectric layer, sunlight reflected from a semi-transparent metal electrode is confined to the layer in a waveguide mode. By adjusting the thickness of the high-refractive-index dielectric layer, cross-coupling occurs between the waveguide mode and the microcavity mode within the organic solar cell, coupling the energy in the waveguide mode to the active layer of the organic solar cell. This reduces reflection losses in the semi-transparent metal thin film electrode, increases the light absorption intensity of the organic solar cell over a wide spectral range, and improves the low transmittance of the semi-transparent inert metal.

[0016] 2) The device structure is simpler in preparation process, does not affect the main device structure of organic solar cells, has good stability, and is compatible with flexible substrates;

[0017] 3) This structure has wide applicability and is suitable for organic solar cells of various systems;

[0018] 4) It can achieve anti-reflection in a wide broadband and large angle range, which is different from the mechanism of ordinary anti-reflection films. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic structural diagram of an organic solar cell that reduces metal electrode reflection loss according to the present invention;

[0020] Figure 2 is the absorption spectrum of the organic solar cell calculated using the rigorous coupled wave method (RCWA) in the examples;

[0021] Figure 3 Calculated using the RCWA algorithm Figure 2 Electromagnetic field distribution diagram of the cross section of the organic solar cell at point A;

[0022] Figure 4 The reflectance spectra of organic solar cells calculated using the RCWA algorithm when the ZnS thickness is 0nm and 40nm;

[0023] Figure 5 The experimentally measured reflectance spectra of organic solar cells when the ZnS thickness is 0nm and 40nm;

[0024] Figure 6 The difference spectrum of the angle-dependent reflectance spectrum of the organic solar cell when the ZnS thickness is 0 nm and 40 nm is calculated using RCWA. DETAILED DESCRIPTION

[0025] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments. The accompanying drawings are merely for illustration to facilitate understanding of the present invention, and their specific proportions may be adjusted according to design requirements.

[0026] refer to Figure 1The structure of the organic solar cell for reducing the reflection loss of the metal electrode of the present invention includes a transparent substrate 2, a high refractive index dielectric layer 3, a semi-transparent metal electrode 4, an active layer 5 and a back reflection electrode 6 stacked in sequence, wherein the transparent substrate 2 is the incident surface of the sunlight 1. The transparent substrate 2 includes but is not limited to a glass or plastic substrate with a refractive index of approximately 1.6, and a thickness between 1 micron and 1.1 mm. The refractive index of the high refractive index dielectric layer 3 is ≥ 2 and is transparent and non-absorbent within the absorption spectrum of the solar cell, such as ZnS or ZrO2, and the thickness is between 10 nm and 80 nm. The semi-transparent metal electrode is an inert metal, including but not limited to Au or Ag, and the thickness is between 15 nm and 25 nm. The active layer includes but is not limited to the active layer of the known small molecule system organic solar cell and the polymer system organic solar cell. The back reflection electrode 6 is a metal cathode, including but not limited to Al or Ag, and the thickness is between 80 nm and 100 nm. A high-refractive-index dielectric layer 3 is inserted between the transparent substrate 2 and the semi-transparent metal electrode 4. The high-refractive-index dielectric layer 3 is used to confine the reflected light therein to form a waveguide mode. The waveguide mode is then coupled with the microcavity mode of the organic solar cell to transmit the energy of the reflection loss back to the active layer of the cell, thereby effectively reducing the reflection loss of the organic solar cell and increasing its optical transmittance. This mechanism is different from that of ordinary anti-reflection films.

[0027] In one embodiment, the structure of the organic solar cell is: glass / ZnS / metallic silver (20 nm) / molybdenum oxide (5 nm) / phthalocyanine (20 nm) / carbon-60 (45 nm) / 2,9-dimethyl-4,7-biphenyl-1,10-phenanthroline (bathocuproine BCP) (8 nm) / Ag (100 nm), with ZnS serving as the high-refractive-index dielectric layer 3 and 20 nm of metallic silver serving as the semi-transparent metal electrode 4.

[0028] The fabrication method involves forming a high-refractive-index dielectric layer on a glass substrate using vacuum thermal deposition, followed by conventional fabrication of the remaining organic solar cell structures. The high-refractive-index dielectric layer is prepared prior to and independently of the organic solar cell fabrication, ensuring no disruption to the fabrication process. Furthermore, the process is mature and results in high-quality films.

[0029] Figure 2This is the absorption spectrum of the organic solar cell calculated using the rigorous coupled wave method (RCWA), where the ZnS thickness varies from 0 to 300 nm. From the spectrum, we can see that there are two enhanced absorption bands at 600 nm and 450 nm, and the absorption bands do not change with the change of ZnS thickness, indicating that these two absorption bands are microcavity modes formed between the two metal electrodes in the organic solar cell. Since the high-refractive index ZnS layer (refractive index of about 2.3) is sandwiched between the low-refractive index glass (refractive index of about 1.6) and the inert metal Ag electrode, the light reflected by the semi-transparent metal Ag electrode is confined to the ZnS layer in a waveguide mode. Figure 2 As shown in the figure, as the ZnS thickness increases, the waveguide mode that appears in the absorption spectrum is formed by the reflected light. Under the appropriate ZnS thickness conditions, that is, the intersection of the waveguide absorption band and the microcavity absorption band, the waveguide mode will cross-couple with the microcavity mode in the organic solar cell, for example Figure 2 Points A and B in the figure. The ZnS thickness at point A is 40 nm. The corresponding wavelength is 610 nm, which is the position of the intrinsic absorption peak of SubPc.

[0030] Figure 3 Calculated using the RCWA algorithm Figure 2 The electromagnetic field distribution diagram of the cross section of the organic solar cell at point A shows that the electromagnetic field in the active layer of the organic solar cell is significantly enhanced. This is because the cross-coupling of the waveguide mode and the microcavity mode effectively couples the energy of the waveguide mode in the ZnS layer into the active layer of the cell, thereby effectively reducing the reflection loss of the organic solar cell.

[0031] Figure 4 The reflection spectra of organic solar cells when the ZnS thickness is 0nm and 40nm are calculated using the RCWA algorithm. It can be seen from the spectra that by inserting a ZnS high refractive index layer between the glass substrate and the semi-transparent metal electrode, the reflection of the organic solar cell is significantly weakened in the range of 400nm to 650nm.

[0032] Figure 5 The experimentally measured reflection spectra of organic solar cells when the ZnS thickness is 0nm and 40nm show that the experimental data is in good agreement with the theoretical calculation data, which once again confirms the feasibility of this solution.

[0033] Figure 6The difference spectrum of the angle-dependent reflection spectra of organic solar cells when the ZnS thickness is 0nm and 40nm, calculated using RCWA, shows that when the incident light is in the range of 0 to 45 degrees and the wavelength is around 610nm, the reflection spectrum of the organic solar cell with a 40nm ZnS layer is significantly weakened. This shows that the high refractive index ZnS layer not only reduces the reflection loss of vertically incident zero-degree light, but also reduces the reflection loss of light incident at large angles such as 45 degrees.

[0034] The above embodiments are only used to further illustrate an organic solar cell and preparation method for reducing metal electrode reflection loss of the present invention. However, the present invention is not limited to the embodiments. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention fall within the scope of protection of the technical solution of the present invention.

Claims

1. An organic solar cell with reduced metal electrode reflection loss, characterized in that: The invention comprises a transparent substrate, a high refractive index medium layer, a semi-transparent metal electrode, an active layer and a back reflection electrode stacked in sequence, wherein the transparent substrate is a light incident surface, and a microcavity mode exists between the semi-transparent metal electrode and the back reflection electrode; the refractive index of the transparent substrate is 1.5-1.7, and the refractive index of the high refractive index medium layer is ≥2; the light reflected by the semi-transparent metal electrode is confined in the high refractive index medium layer in a waveguide mode, and the waveguide mode is cross-coupled with the microcavity mode so that the energy in the waveguide mode is coupled to the active layer; The transparent substrate is a glass substrate or a plastic substrate with a thickness of 1 μm to 1.1 mm; the material of the high refractive index medium layer is ZnS or ZrO2 with a thickness of 10 to 80 nm; the material of the semi-transparent metal electrode is Au or Ag with a thickness of 15 to 25 nm.

2. The organic solar cell according to claim 1, characterized in that: The organic solar cells include small molecule system organic solar cells and polymer system organic solar cells.

3. A method for preparing an organic solar cell with reduced metal electrode reflection loss according to any one of claims 1 to 2, characterized in that: The method comprises the following steps: forming a high refractive index medium layer on a transparent substrate by vacuum deposition or magnetron sputtering; and sequentially forming a semi-transparent metal electrode, an active layer and a back reflection electrode on the high refractive index medium layer.

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