Laminated solar cell structure comprising selective reflective / light transmissive optical thin film

Abstract

The invention discloses a laminated solar cell structure containing a selective reflection / light transmission optical thin film. The laminated solar cell structure comprises a wide-band-gap solar cell, the selective reflection / light transmission optical thin film and a narrow-band-gap solar cell which are sequentially arranged in the light incidence direction. The selective reflecting / light-transmitting optical thin film is at least used for 1) reflecting high-energy photons to be absorbed and utilized by the wide-band-gap solar cell; and 2) low-energy photons are transmitted to be absorbed and utilized by a narrow-band-gap solar cell. According to the invention, the selective reflection / light transmission optical thin film is used to fully reflect the transmitted high-energy photons to the wide-band-gap top cell without influencing the transmission of low-energy photons, so that the absorption and conversion of the wide-band-gap top cell to the high-energy photons can be improved, the photoelectric conversion efficiency of the laminated cell can be effectively improved, and the laminated cell has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and particularly to a tandem solar cell structure comprising a selective reflection / transmittance optical thin film. Background Art

[0002] Fully developing and utilizing solar energy is crucial for solving the human energy crisis and environmental problems. Converting solar energy into thermal energy through photovoltaic technology has become the mainstream technology for current solar energy utilization. The photoelectric conversion efficiency is one of the important indicators determining the competitive advantages of different photovoltaic technologies. Currently, the highest certified efficiency of commercial monocrystalline silicon solar cells has reached 27.3%, and a complete industrial system has been formed after decades of development. According to the data of the International Roadmap for Photovoltaic Technology, its global market share exceeds 90%. In addition, other types of photovoltaic technologies have also made breakthrough progress. For example, the efficiency of perovskite photovoltaic devices has exceeded 27%, and the efficiency of CIGS devices has exceeded 24%. However, limited by the Shockley-Queisser theoretical limit (29.1% for single-junction silicon cells and 33.4% for single-junction devices), single-junction device technologies (such as silicon-based solar cells) have faced bottlenecks in efficiency improvement.

[0003] In this context, the tandem solar cell structure provides a new path to break through the bottleneck of existing technologies. Based on the spectral management theory, by constructing a tandem architecture of wide-narrow bandgap materials, the segmented absorption optimization of the solar spectrum can be achieved. The most common tandem architectures are two-terminal, three-terminal, and four-terminal tandems. Based on the above structures, high-energy photons will be absorbed by the wide bandgap cell to generate a high open-circuit voltage, and low-energy photons will be absorbed by the narrow bandgap cell to generate photocurrent, thus achieving the effect of balancing heat dissipation and light transmission loss and significantly improving the device performance. According to theoretical calculations, the efficiency of a double-junction tandem photovoltaic device can be as high as 46%. However, the actual achievable efficiency is relatively low. Taking the perovskite / silicon cell as an example, the current efficiency of two-terminal tandem devices is 33.4%. An important reason for the low efficiency is that some high-energy photons pass through the wide bandgap cell, increasing the parasitic absorption loss or being absorbed by the narrow bandgap cell to generate a large heat dissipation loss.

[0004] The patent specification with the publication number CN112614939B discloses a perovskite / silicon tandem solar cell, which includes a bottom cell of P-type crystalline silicon and a top cell of perovskite cell. From bottom to top, it successively includes a back electric field, a passivation layer, a P-type substrate, an N-type layer, an intermediate layer, a hole transport layer, a perovskite absorption layer, an electron transport layer, a buffer layer, a transparent electrode layer, and a top electrode. The back electric field and the passivation layer are connected to a back electrode, and the intermediate layer is an ITO layer doped with ytterbium ions and erbium ions. This patented technology dopes ions with an upconversion effect in the intermediate layer of the perovskite / silicon tandem solar cell to convert long-wavelength light that cannot be absorbed by the perovskite cell into visible light that can be absorbed. In essence, it does not improve the absorption utilization rate of high-energy photons in the incident light that are not utilized by the perovskite cell. These high-energy photons that are not utilized by the perovskite cell will still pass through the intermediate layer and enter the bottom cell. Therefore, this patented technology still has problems such as parasitic absorption loss or heat dissipation loss caused by the absorption of the transmitted high-energy photons by the bottom cell. Summary of the Invention

[0005] In view of the above technical problems and deficiencies in the art, the present invention provides a structural design of a tandem solar cell including a selective reflection / transmission optical thin film. This optical thin film can selectively reflect high-energy photons transmitted through the wide-bandgap solar cell back to the wide-bandgap solar cell, while transmitting low-energy photons. Therefore, it can suppress parasitic absorption, current mismatch loss (series tandem), and heat dissipation loss, and improve the photoelectric conversion efficiency of the device.

[0006] The specific technical solutions are as follows:

[0007] A structural design of a tandem solar cell including a selective reflection / transmission optical thin film, which includes a wide-bandgap solar cell, a selective reflection / transmission optical thin film, and a narrow-bandgap solar cell arranged in sequence along the direction of incident light;

[0008] The selective reflection / transmission optical thin film is at least used for: 1) reflecting high-energy photons for absorption and utilization by the wide-bandgap solar cell; 2) transmitting low-energy photons for absorption and utilization by the narrow-bandgap solar cell.

[0009] It can be understood that in the present invention, the bandgap of the wide-bandgap solar cell is greater than that of the narrow-bandgap solar cell, and the energy of high-energy photons is higher than that of low-energy photons.

[0010] The present invention is based on the principle of selective reflection / transmittance and does not involve light conversion. When the stacked solar cell structure of the present invention operates, sunlight first enters the wide-bandgap solar cell. Some high-energy photons are absorbed to generate a high open-circuit voltage, while low-energy photons and the remaining high-energy photons that cannot be absorbed and utilized by the wide-bandgap solar cell during a single incidence pass through. When passing through the selective reflection / transmittance optical thin film, the high-energy photons that cannot be absorbed and utilized by the wide-bandgap solar cell during a single incidence are reflected back to the wide-bandgap solar cell and absorbed and utilized, while the low-energy photons continue to pass through. Finally, the low-energy photons are absorbed and utilized by the narrow-bandgap solar cell.

[0011] The present invention introduces a selective reflection / transmittance optical thin film between the two sub-cells of a stacked solar cell, aiming to solve the problems of low utilization rate of high-energy photons and parasitic absorption in the top cell of existing stacked cells, and synergistically improve the overall photoelectric conversion efficiency of the solar cell.

[0012] The present invention uses a selective reflection / transmittance optical thin film to fully reflect the transmitted high-energy photons to the wide-bandgap top cell without affecting the transmission of low-energy photons. Therefore, it can increase the absorption and conversion of high-energy photons by the wide-bandgap top cell, effectively improve the photoelectric conversion efficiency of the stacked cell, and has good application prospects.

[0013] In some embodiments, the wavelength dividing line for the selective reflection / transmittance optical thin film to reflect high-energy photons and transmit low-energy photons can be in a certain or certain regions between 1. .0 - 3.0 eV.

[0014] In some embodiments, the structure of the selective reflection / transmittance optical thin film includes, but is not limited to, one or more combinations of metals, oxides, fluorides, and polymers, such as one or more combinations of tellurium oxide, magnesium fluoride, titanium oxide, silicon oxide, and tin oxide, etc. The reflection spectrum can be effectively controlled by adjusting the material, number of layers, thickness of each layer, and the geometric optical structure between the devices.

[0015] In some embodiments, the main reflection band of the reflection spectrum of the selective reflection / transmittance optical thin film is in the visible light range.

[0016] In some embodiments, the implementation principle and thin film structure for the selective reflection / transmittance optical thin film to reflect high-energy photons and transmit low-energy photons can include one or more combinations of one-dimensional photonic crystal structures and two-dimensional photonic crystal structures.

[0017] In some embodiments, the preparation process of the selective reflection / transmittance optical thin film can include one or more combinations of vacuum deposition, melt casting, nanoimprinting, and solution deposition methods.

[0018] In some embodiments, the stacked solar cell structure can be a two-terminal, three-terminal, or four-terminal structure.

[0019] In some embodiments, the connection manner of the wide-bandgap solar cell and the narrow-bandgap solar cell can be one or more combinations of series connection and parallel connection.

[0020] In some embodiments, the bandgaps of the wide-bandgap solar cell and the narrow-bandgap solar cell can be independently in the range of 0.5 - 4.0 eV respectively.

[0021] In some embodiments, the wide-bandgap solar cell and the narrow-bandgap solar cell can independently include one or more combinations of crystalline silicon cells, amorphous silicon cells, group III-V solar cells (such as CdTe, etc.), copper indium gallium selenide solar cells, perovskite solar cells, and organic solar cells.

[0022] Exemplarily, the wide-bandgap solar cell can include: a wide-bandgap perovskite solar cell, and the perovskite such as FAPbI3, FAPbBr3, MAPbI3, CsPbI3, MAPbBr3, CsPbBr3, etc., where FA represents formamidinium cation and MA represents methylammonium cation; an organic photovoltaic device based on a non-fullerene acceptor.

[0023] Exemplarily, the narrow-bandgap solar cell can include: a narrow-bandgap perovskite solar cell, and the perovskite such as FASnI3, MASnI3, CsSnI3, etc., where FA represents formamidinium cation and MA represents methylammonium cation; PM6:Y6 and its derivative system organic photovoltaic devices; commercially available n-type TOPCON, HJT, and IBC cells, CIGS cells, CdTe cells, etc.

[0024] The present invention provides a preferred stacked solar cell structure including a selective reflection / transmission optical thin film, comprising a wide-bandgap solar cell, a selective reflection / transmission optical thin film, and a narrow-bandgap solar cell arranged in sequence along the light incident direction;

[0025] The wide-bandgap solar cell is an ultra-wide-bandgap perovskite solar cell with a bandgap of not less than 2.0 eV; further, the wide-bandgap solar cell includes a conductive base layer, a hole transport layer, a perovskite layer, a passivation layer, an electron transport layer, and a transparent electrode layer that are sequentially stacked, and a selective reflection / transmissive optical thin film is disposed between the transparent electrode layer and the narrow-bandgap solar cell; the hole transport layer may include at least one of nickel oxide, self-assembled monolayers SAMs, and PTAA (CAS No.: 1333317-99-9), and the self-assembled monolayers SAMs may include at least one of 2PACZ (CAS No.: 20999-38-6), MeO-2PACZ (CAS No.: 2377770-18-6), 4PACZ (CAS No.: 20999-36-4), and Me-4PACZ (CAS No.: 2747959-96-0); the thickness of the perovskite layer may be 20-10,000 nm, such as 150 nm, 200 nm, 210 nm, 220 nm, 250 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 2000 nm, 5000 nm, 8000 nm, etc., and the perovskite layer may be an ultra-wide-bandgap perovskite material ABX3 type perovskite with a bandgap greater than or equal to 2.0 eV, wherein the A site is one or a mixture of cesium ions, methylammonium cations, and formamidinium cations, the B site is one or a mixture of lead ions and tin ions, and the X site is one or a mixture of iodide ions, bromide ions, and chloride ions. Further, the chemical formula of the perovskite layer in terms of atomic ratio is FA x Cs 1-x PbBr3, where FA represents formamidinium cation, 0.9 ≤ x ≤ 1.0, preferably 0.9 ≤ x < 1.0, and more preferably x = 0.95. The pure bromide-based perovskite has both a suitable bandgap and can solve the phase separation problem faced by mixed halogens in conventional wide-bandgaps. FAPbBr3 has a long carrier diffusion length, and the incorporation of a small amount of Cs helps to adjust the lattice parameters, optimize the crystal structure, and inhibit harmful lattice distortion, thereby enhancing the stability of the perovskite phase; the passivation layer may include a bimolecular passivation layer of 4-F-PEABr (4-fluorophenethylammonium bromide, CAS No.: 1807536-06-6) and EDA (ethylenediamine). Further, the bimolecular passivation layer includes a bilayer structure of a 4-F-PEABr layer and an EDA layer. Further still, in the ultra-wide-bandgap perovskite solar cell, the perovskite layer, the 4-F-PEABr layer, and the EDA layer are sequentially stacked; the electron transport layer may include at least one of fullerene derivatives PCBM, C 60 、SnO2、ZnO、BCP (CAS No.: 4733-39-5), and the fullerene derivative PCBM may include PC61 BM (CAS No.: 160848-22-6), PC 71 At least one of BM (CAS No.: 609771-63-3). Further, the electron transport layer has a structure of two or more layers, including a PC 61 BM layer and BCP layer, or, PC 61 BM layer and SnO2 layer. Even further, in the ultra-wide bandgap perovskite solar cell, the BCP layer or SnO2 layer is closer to the transparent electrode layer than the PC 61 BM layer. The SnO2 layer can play a protective role to avoid damage to the existing structure during the preparation process (such as magnetron sputtering, etc.) of the transparent electrode layer; the transparent electrode layer may include at least one of gold, silver, copper, ITO (indium tin oxide), IZO (indium zinc oxide), IWO (indium tungsten oxide), FTO (fluorine-doped tin oxide);

[0026] The selective reflection / transmittance optical thin film may include a one-dimensional photonic crystal thin film with an alternating structure of TiO2 and SiO2. The emission-transmission wavelength may be about 5:30 nm, the emissivity at 400 - 530 nm reaches more than 95%, and the transmittance at 530 - 1200 nm exceeds 93%; the selective reflection / transmittance optical thin film can be prepared by PECVD (plasma-enhanced chemical vapor deposition);

[0027] The narrow bandgap solar cell may include one or a combination of a crystalline silicon solar cell, a cadmium telluride solar cell, a copper indium gallium selenide solar cell, a copper indium tin sulfide solar cell, a perovskite solar cell.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] The present invention places an optical thin film that can selectively reflect high-energy photons and transmit low-energy photons between the two sub-cells of the stacked device, which can effectively reflect the high-energy photons transmitted by the wide bandgap device back to the wide bandgap device without affecting the transmission of low-energy photons. Therefore, the efficiency of the device can be effectively improved, and it has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the structure and working principle of an exemplary stacked solar cell including a selective reflection / transmittance optical thin film of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be further described below with reference to the drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The operating methods without specific conditions noted in the following embodiments are usually in accordance with conventional conditions or the conditions recommended by the manufacturer.

[0032] Example 1:

[0033] (1) Clean the indium tin oxide (ITO) conductive glass in an ultrasonic bath in the order of deionized water, glass cleaner, deionized water, and ethanol for 20 min, and then dry it at 80 °C for later use.

[0034] (2) Prepare a hole electron layer on the conductive base layer. Treat the conductive glass substrate obtained in (1) with plasma cleaning for 1 min, and then immediately transfer it into a glove box filled with N2. Spin-coat the self-assembled molecule 2PACZ (0.5 mg / mL, solvent ethanol) on the conductive substrate at a speed of 4000 rpm for 30 s, and anneal it at 100 °C for 10 min. Obtain the hole transport layer.

[0035] (3) Prepare a perovskite layer on the hole electron layer. Dissolve 117.8 mg of FABr (CAS No.: 146958-06-7), 10.6 mg of CsBr, and 367 mg of PbBr2 in 1 mL of a mixed solvent of DMF (N,N-dimethylformamide) and DMSO (dimethyl sulfoxide) with a volume ratio of 4:1 to form a 1.0 M stoichiometric solution, and prepare the perovskite precursor solution. Spin 50 μL of the perovskite precursor solution at a speed of 4000 rpm for 20 s, quickly add 150 μL of the antisolvent chlorobenzene dropwise in 10 s, and then transfer the perovskite precursor film to a hot stage and anneal it at 100 °C in the glove box for 20 min. Obtain the perovskite layer with a thickness of 210 nm.

[0036] (4) Prepare a bimolecular passivation layer on the perovskite layer. Spin-coat the 4-F-PEABr solution (1 mg / mL dissolved in isopropanol) on the surface of the perovskite film at a speed of 5000 rpm for 30 s, and anneal it at 100 °C in the glove box for 10 min; then spin-coat the EDA solution (solvent toluene, volume ratio of EDA in the solution 1:100000) on the surface of the perovskite film at a speed of 5000 rpm for 30 s, and anneal it at 100 °C in the glove box for 10 min. Obtain the bimolecular passivation layer.

[0037] (5) Prepare an electron transport layer on the passivation layer. Spin-coat the PC 61 BM solution (20 mg / mL dissolved in chlorobenzene) on the surface of the perovskite film at a speed of 2000 rpm for 20 s, and anneal it at 70 °C in the glove box for 5 min. Subsequently, spin-coat the BCP solution (0.5 mg / mL, solvent ethanol) on the surface of the perovskite film at a speed of 5000 rpm for 20 s, and anneal it at 70 °C in the glove box for 5 min to obtain the composite electron transport layer.

[0038] (6) Prepare a transparent electrode layer on the electron transport layer. At 1×10 -4Pa vacuum deposits 100 nm of ITO to complete the preparation of the ultra-wide bandgap perovskite solar cell. Under the AM1.5G simulated sunlight irradiation with an illumination intensity of 100 mw / cm 2 , the current-voltage curve of the device is tested, and the open-circuit voltage (Voc) is 1.61 V, the short-circuit current density (Jsc) is 7.51 mA / cm 2 , the fill factor (FF) is 81.60%, and the power conversion efficiency (PCE) is 9.88%.

[0039] (7) Prepare a selective reflection / transmissive optical thin film on the transparent electrode layer. Use the PECVD (plasma-enhanced chemical vapor deposition) method to prepare a one-dimensional photonic crystal thin film with an alternating structure of TiO2 and SiO2 to obtain a selective reflection / transmissive optical thin film. The deposition rate is 0.1 - 3 nm / s, and the number of deposition layers is 3 - 50 layers. Combine the optical simulation data to optimize the process conditions and regulate the reflection and transmission characteristics of the optical structure, such as the emission-transmission wavelength / band. For one of the prepared photonic crystals, its emission-transmission wavelength is about 530 nm, the emission rate from 400 - 530 nm reaches more than 95%, and the transmittance from 530 - 1200 nm exceeds 93%.

[0040] (8) Use a commercially purchased silicon cell (Si-PV efficiency is 26.5%) and combine it with the above-obtained wide bandgap perovskite solar cell to prepare a four-terminal solar cell, and test the J-V curves of the upper and lower two cells respectively. In the absence of the (7) selective reflection / transmissive optical thin film, the efficiency of the top wide bandgap cell is 9.2%, the efficiency of the bottom silicon cell is 22.3%, and the overall power conversion efficiency is 31.5%. After adding the (7) selective reflection / transmissive optical thin film, a stacked solar cell structure containing the selective reflection / transmissive optical thin film as shown in Figure 1 is formed. The efficiency of the top perovskite cell is 11.3%, the efficiency of the bottom silicon cell is 21.9%, and the overall power conversion efficiency is 33.2%.

[0041] Example 2:

[0042] (1)-(7) are the same as in Example 1.

[0043] (8) Use a commercially purchased CIGS cell (efficiency is 22.4%) and combine it with the above-obtained wide bandgap perovskite solar cell to prepare a four-terminal solar cell, and test the J-V curves of the upper and lower two cells respectively. In the absence of the (7) selective reflection / transmissive optical thin film, the efficiency of the top wide bandgap cell is 9.2%, the efficiency of the bottom CIGS cell is 17.5%, and the overall power conversion efficiency is 26.5%. After adding the (7) selective reflection / transmissive optical thin film, a structure as shown in Figure 1The laminated solar cell structure with a selective reflection / transmittance optical thin film shown has a top perovskite cell efficiency of 11.1%, a bottom silicon cell efficiency of 16.8%, and an overall photoelectric conversion efficiency of 27.9%.

[0044] In summary, the present invention can solve the problem of heat dissipation loss caused by insufficient light absorption in the wide-bandgap sub-cell and the transmission of high-energy photons in the existing laminated cells, and synergistically improve the overall photoelectric conversion efficiency of the solar cell. The selective reflection / transmittance optical thin film involved in the present invention can effectively emit high-energy photons and transmit low-energy photons, so that high-energy photons can be fully absorbed by the wide-bandgap sub-cell to generate a high open-circuit voltage. At the same time, it can ensure the transmission of low-energy photons and will not have a great impact on the photoelectric conversion efficiency of the bottom narrow-bandgap cell, thus effectively improving the overall photoelectric conversion efficiency of the device and having good application prospects.

[0045] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A laminated solar cell structure comprising a selectively reflective / transmissive optical thin film, characterized in that, It includes a wide-bandgap solar cell, a selective reflection / transmission optical thin film, and a narrow-bandgap solar cell arranged in sequence according to the light incident direction; The selective reflection / transmission optical thin film is at least used for: 1) reflecting high-energy photons for absorption and utilization by the wide-bandgap solar cell; 2) transmitting low-energy photons for absorption and utilization by the narrow-bandgap solar cell.

2. The laminated solar cell structure comprising a selective reflection / transmissive optical thin film according to claim 1, wherein The wavelength dividing line for the selective reflection / transmission optical thin film to reflect high-energy photons and transmit low-energy photons is in a certain or certain regions between 1.0 - 3.0 eV.

3. The laminated solar cell structure comprising a selective reflection / transmissive optical thin film according to claim 1, characterized in that, The implementation principle and thin film structure for the selective reflection / transmission optical thin film to reflect high-energy photons and transmit low-energy photons include one or a combination of more of a one-dimensional photonic crystal structure and a two-dimensional photonic crystal structure.

4. The laminated solar cell structure comprising a selectively reflective / transmissive optical thin film according to claim 1, characterized in that, The preparation process of the selective reflection / transmission optical thin film includes one or a combination of more of vacuum deposition, melt casting, nanoimprinting, and solution deposition methods.

5. The laminated solar cell structure comprising a selective reflection / transmissive optical thin film according to claim 1, characterized in that, The stacked solar cell structure is a two-terminal, three-terminal, or four-terminal structure.

6. The laminated solar cell structure comprising a selective reflection / transmittance optical thin film according to claim 1, wherein The connection method between the wide-bandgap solar cell and the narrow-bandgap solar cell is one or a combination of more of series connection and parallel connection.

7. The laminated solar cell structure comprising a selective reflection / transmissive optical thin film according to claim 1, wherein, The bandgaps of the wide-bandgap solar cell and the narrow-bandgap solar cell are independently in the range of 0.5 - 4.0 eV respectively.

8. The laminated solar cell structure comprising a selective reflection / transmissive optical thin film according to claim 1, wherein, The wide-bandgap solar cell and the narrow-bandgap solar cell independently include one or a combination of more of crystalline silicon cells, amorphous silicon cells, group III-V solar cells, copper indium gallium selenide solar cells, perovskite solar cells, and organic solar cells.

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