Semitransparent organic solar cell and preparation method thereof

Abstract

The invention belongs to the technical field of solar cells, and discloses a semitransparent organic solar cell and a preparation method thereof. The crystallinity of the polymer is reduced by adopting a random copolymerization method of the donor unit, so that the content of the donor is greatly reduced, the photovoltaic conversion efficiency PCE is reduced slightly, 94% of that of a conventional opaque device can be kept, the transmittance of the device is greatly improved, the light utilization rate (LUE) is remarkably improved through the synergistic effect of the donor unit and the donor unit, and the application prospect is wide. And a new path is provided for developing an efficient semitransparent organic solar cell.

Description

Technical Field

[0001] The present invention belongs to the field of organic solar cells, and in particular relates to a semi-transparent organic solar cell and a preparation method thereof. Background Art

[0002] Solar energy, due to its core advantages of being green, pollution-free, unlimited, and widely distributed, is considered one of the most promising alternative energy sources. New photovoltaic technologies, represented by organic solar cells (OSCs), offer broad application prospects in industries such as smart wearables, semi-transparent photovoltaic buildings, and greenhouse roofs, thanks to their lightweight, solution-processable, easy-to-prepare, and flexible properties.

[0003] The core structure of conventional organic solar cells usually consists of four parts, including conductive indium tin oxide ITO as the anode, the anode interface layer, the organic active layer, the cathode interface layer and the conductive metal as the cathode. Semi-transparent organic solar cells achieve the semi-transparent effect by replacing the top electrode with a thinner metal electrode. Generally, the performance of semi-transparent organic solar cells is limited by the inherent contradiction between photovoltaic efficiency and transparency. In order to comprehensively evaluate its performance, light utilization efficiency (LUE) was proposed as an important indicator, which is defined as the product of photovoltaic conversion efficiency (PCE) and average visible light transmittance (AVT), which can fully reflect the comprehensive performance of semi-transparent organic solar cells.

[0004] When preparing semi-transparent organic solar cells, significantly reducing the concentration of the donor material, that is, diluting the donor content, can effectively improve the average visible light transmittance (AVT) of the device, making this method a commonly used optimization strategy. Due to the reduction in donor content, the choice of semi-transparent OSC donor materials is no longer limited to narrowband donor materials (absorption spectra in the near-infrared region) but is expanded to wide-bandgap donor materials (absorption spectra in the visible and near-infrared regions). This increases the energy level difference between the lowest unoccupied molecular orbital (LUMO) of the acceptor and the highest occupied molecular orbital (HOMO) of the donor, ultimately promoting the improvement of open circuit voltage and PCE.

[0005] However, in the prior art, for polymer donors, excessively reducing their proportion in the active layer will significantly reduce the photovoltaic conversion efficiency (PCE). This is because most organic semiconductors have a low dielectric constant (ε≈3-4), which will produce Frenkel excitons with high exciton binding energy rather than free charges under light excitation. The donor (D) / acceptor (A) interface is the key source of driving force for exciton dissociation. Therefore, many high-efficiency OSCs are based on bulk heterojunction (BHJ) structures with roughly equal donor and acceptor contents. Dilution of the donor will lead to a reduction in the D / A interface, resulting in insufficient exciton dissociation power, unbalanced charge transport, increased charge recombination, and ultimately a significant reduction in the photovoltaic conversion efficiency (PCE).

[0006] Therefore, developing a reliable and efficient method for constructing semi-transparent devices is crucial. In order to achieve high-efficiency photoelectric conversion while maintaining moderate transmittance, the ideal donor material, in addition to meeting the characteristics of general high-efficiency wide-bandgap donor materials, should also have the following characteristics: The crystallinity should not be too high, so that it does not excessively aggregate in the active layer, but should be evenly dispersed in the active layer to ensure that at low concentrations, there is no excessive phase separation between the donor and the acceptor, reducing the impact on exciton dissociation and charge transport. Summary of the Invention

[0007] In light of this, the present invention aims to provide a semitransparent organic solar cell and a method for its preparation. To address the challenges of the prior art, the present invention employs a random copolymerization method to synthesize a polymer donor material. This innovative design not only significantly reduces the crystallinity of the polymer donor but also maintains excellent photovoltaic performance even at a significantly reduced donor concentration. More importantly, it effectively improves the device's transmittance, providing strong technical support for the preparation of high-performance semitransparent organic photovoltaic devices.

[0008] To achieve the above object, the present invention provides a semi-transparent organic solar cell, wherein the donor material is PL2, and the structural formula of PL2 is:

[0009]

[0010] Wherein, m and n are the degree of polymerization, m=0.5, n=0.5.

[0011] Furthermore, the receptor material is L8-BO, and the structural formula of L8-BO is:

[0012]

[0013] Furthermore, the semi-transparent organic solar cell comprises an ITO cathode layer, a hole transport layer PEDOT:PSS, an active layer, an electron transport layer PDINN, a transparent electrode and an optical cover layer arranged in sequence from bottom to top;

[0014] The active layer comprises a donor material and an acceptor material;

[0015] The transparent electrode includes a 1 nm thick Au seeding layer and a 15 nm thick Ag layer, wherein the Au seeding layer is located on the lower side;

[0016] The optical cover layer includes a thin layer of MoO3 deposited on the upper surface of a transparent electrode.

[0017] The present invention also provides a method for preparing a semi-transparent organic solar cell, comprising the following steps:

[0018] S1. Configuration of polymer donor material PL2;

[0019] S2. Configure the active layer solution;

[0020] In a nitrogen-filled glove box, polymer PL2 and small molecule L8-BO were dissolved in chloroform, and solid additive DIB was added to the solution. After the solid was completely dissolved, the active layer solution was obtained.

[0021] S3. Pretreatment of ITO substrate;

[0022] The ITO substrate was ultrasonically cleaned with deionized water, acetone, and isopropyl alcohol for 30 minutes in sequence. After cleaning, the ITO substrate was blown dry with nitrogen gas and then treated with ultraviolet ozone for 30 minutes.

[0023] S4. Spin coating of hole transport layer;

[0024] The hole transport layer PEDOT:PSS was spin-coated onto the ITO substrate at 5000 rpm and then thermally annealed on a heating plate at 150 °C for 15 min;

[0025] S5. Spin coating active layer;

[0026] The active layer solution was evenly spin-coated on the surface of the hole transport layer at a speed of 1800-3000 rpm. After the active layer solution dried, a film was formed and fixed on the surface of the hole transport layer. Then, the ITO substrate with the hole transport layer and the active layer solution film was placed on a hot plate at 100°C for annealing for 1 minute.

[0027] S6. Spin coating electron transport layer;

[0028] The electron transport layer PDINN was prepared at 1.5 mg mL -1 The concentration of α-D-H-pyrrolidone was dissolved in methanol, and the dissolved solution was spin-coated on the surface of the active layer at a speed of 3000 rpm;

[0029] S7. Depositing a transparent electrode;

[0030] A 1 nm thick Au seeding layer and a 15 nm thick Ag layer are sequentially deposited on the surface of the electron transport layer, that is, a transparent electrode is deposited on the surface of the electron transport layer;

[0031] S8. depositing an optical cover layer;

[0032] A thin layer of MoO3 is deposited on the surface of the transparent electrode.

[0033] Furthermore, in step S1, the configuration process of the polymer donor material PL2 is:

[0034] S1.1 Mix DTBT-2, BDD-Br, FBDT-Sn, Pd2(dba)3, and P(o-Tol)3 in a Schlenk flask, add 2 mL of toluene under argon, and heat to reflux at 110°C for 16 h;

[0035] S1.2 After the mixture in step S1.1 is cooled to room temperature, it is added dropwise to 150 ml of methanol. The precipitate is collected and purified by Soxhlet extraction with dichloromethane and chloroform.

[0036] S1.3 Concentrate the chloroform fraction and add it dropwise to methanol. Collect the precipitate and dry it in a vacuum overnight to obtain solid PL2.

[0037]

[0038] Furthermore, in step S2, the structural formula of L8-BO is:

[0039]

[0040] Beneficial effects:

[0041] Currently, for most polymer donors in the active layer of OSCs, significantly diluting their content can lead to a rougher active layer morphology, unbalanced charge transfer, and increased charge recombination, resulting in a decrease in overall device performance. The method provided by the present invention, by significantly reducing the polymer donor content, maintains charge transfer balance and inhibits charge recombination, resulting in a smaller decrease in the device's photovoltaic conversion efficiency (PCE) while also improving the device's light transmittance. The synergistic effect of these two factors significantly improves the light utilization efficiency (LUE), providing a new path for the development of high-efficiency semi-transparent organic solar cells.

[0042] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a schematic diagram of the preparation process of a donor material for a semi-transparent organic solar cell according to the present invention;

[0044] Figure 2 A schematic structural diagram of an organic solar cell prepared in Example 1;

[0045] Figure 3 This is a schematic structural diagram of a semi-transparent organic solar cell prepared in Example 2;

[0046] Figure 4 This is the current density-voltage curve of the organic solar cell prepared in Example 1;

[0047] Figure 5 Current density-voltage curves of the semi-transparent organic solar cells prepared in Examples 2 and 3. DETAILED DESCRIPTION

[0048] To make the technical solutions, advantages, and purposes of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0049] The present invention also provides a semi-transparent organic solar cell, the donor material of which is PL2.

[0050] Suitable polymer donor materials are the key to achieving high-efficiency organic solar cells, but those with lower crystallinity and the ability to match the acceptor energy level are more conducive to the preparation of DD-OSCs. Therefore, suitable materials are selected from the following polymers with higher crystallinity for random copolymerization to reduce their crystallinity.

[0051]

[0052] The present invention uses two high-performance donor units, PM6 and D18, and successfully prepares a new polymer donor material PL2 through random copolymerization. Its structural formula is as follows:

[0053]

[0054] Wherein, m and n are the degree of polymerization, m=0.5, n=0.5.

[0055] As a preferred embodiment of this invention, the receptor material is L8-BO, and the structural formula of L8-BO is:

[0056]

[0057] As a preferred embodiment of the present invention, the semi-transparent organic solar cell includes an ITO cathode layer, a hole transport layer PEDOT:PSS, an active layer, an electron transport layer PDINN, a transparent electrode and an optical cover layer arranged in sequence from bottom to top;

[0058] The active layer consists of PL2 donor and L8-BO acceptor;

[0059] The transparent electrode includes a 1nm thick Au seeding layer and a 15nm thick Ag layer, where the Au seeding layer is located on the lower side;

[0060] The optical cover layer consists of a thin layer of MoO3 deposited on the upper surface of the transparent electrode.

[0061] The present invention also provides a method for preparing a semi-transparent organic solar cell, comprising the following steps:

[0062] S1. Configuration of polymer donor material PL2;

[0063] S2. Configure the active layer solution;

[0064] In a nitrogen-filled glove box, polymer PL2 and small molecule L8-BO were dissolved in chloroform at a ratio of 1:1.2 and 1:4, respectively. Solid additive DIB was added to the solution. After the solid was completely dissolved, the active layer solution was obtained.

[0065] S3. Pretreatment of ITO substrate;

[0066] The ITO substrate was ultrasonically cleaned with deionized water, acetone, and isopropyl alcohol for 30 minutes in sequence. After cleaning, the ITO substrate was blown dry with nitrogen gas and then treated with ultraviolet ozone for 30 minutes.

[0067] S4. Spin coating of hole transport layer;

[0068] The hole transport layer PEDOT:PSS was spin-coated onto the ITO substrate at 5000 rpm and then thermally annealed on a heating plate at 150 °C for 15 min;

[0069] S5. Spin coating active layer;

[0070] The active layer solution was evenly spin-coated on the surface of the hole transport layer at a speed of 1800-3000 rpm. After the active layer solution dried, a film was formed and fixed on the surface of the hole transport layer. Then, the ITO substrate with the hole transport layer and the active layer solution film was placed on a hot plate at 100°C for annealing for 1 minute.

[0071] S6. Spin coating electron transport layer;

[0072] The electron transport layer PDINN was prepared at 1.5 mg mL -1 The concentration of α-D-H-pyrrolidone was dissolved in methanol, and the dissolved solution was spin-coated on the surface of the active layer at a speed of 3000 rpm;

[0073] S7. Depositing a transparent electrode;

[0074] A 1 nm thick Au seeding layer and a 15 nm thick Ag layer are sequentially deposited on the surface of the electron transport layer, that is, a transparent electrode is deposited on the surface of the electron transport layer;

[0075] S8. depositing an optical cover layer;

[0076] Depositing a thin layer of MoO3 on the surface of the transparent electrode can significantly enhance the transmission of visible light.

[0077] As a preferred embodiment of the present invention, in step S1, the configuration process of the polymer donor material PL2 is as follows: Figure 1 As shown:

[0078] S1.1 Mix DTBT-2, BDD-Br, FBDT-Sn, Pd2(dba)3, and P(o-Tol)3 in a Schlenk flask, add 2 mL of toluene under argon, and heat to reflux at 110°C for 16 h;

[0079] S1.2 After the mixture in step S1.1 is cooled to room temperature, it is added dropwise to 150 ml of methanol. The precipitate is collected and purified by Soxhlet extraction with dichloromethane and chloroform.

[0080] S1.3 Concentrate the chloroform fraction and add it dropwise to methanol. Collect the precipitate and dry it under vacuum overnight to obtain solid PL2.

[0081] Example 1

[0082] Conventional organic solar cell manufacturing

[0083] First, the polymer donor material PL2 was prepared. DTBT-2 (45.35 mg, 0.05 mmol), BDD-Br (38.34 mg, 0.05 mmol), FBDT-Sn (95.00 mg, 0.1 mmol), Pd2(dba)3 (3.0 mg, 0.0033 mmol) and P(o-Tol)3 (10.1 mg, 0.033 mmol) were mixed in a Schlenk flask, toluene (2 mL) was added under argon, and the mixture was heated to reflux at 110°C for 16 h. After cooling to room temperature, the cooled mixture was added dropwise to 150 ml of methanol, and the precipitate was collected and purified by Soxhlet extraction with dichloromethane and chloroform. The chloroform fraction was concentrated and added dropwise to methanol, and the precipitate was collected. The precipitate was then dried under vacuum overnight to obtain PL2 solid (143 mg, yield 80%).

[0084] The ITO substrate was then ultrasonically cleaned for 30 minutes using deionized water, acetone, and isopropyl alcohol to remove surface impurities. After cleaning, the substrate was dried with nitrogen and treated with UV-ozone for 30 minutes to improve surface wettability for subsequent spin coating.

[0085] Subsequently, the hole transport layer PEDOT:PSS was spin-coated onto the ITO substrate at a rotation speed of 5000 rpm for 25 s, and then thermally annealed on a heating stage at 150 °C for 15 min.

[0086] The active layer solution is prepared in a glove box filled with nitrogen (O2<0.1ppm, H2O<0.1ppm). In order to verify that the copolymer donor can still maintain the performance advantage of high efficiency when the content is significantly reduced, the donor-acceptor ratio is set to 1:4 in this example. The specific steps are to dissolve the polymer PL2 and the small molecule L8-BO in chloroform at a ratio of 1:1.2 and 1:4 respectively, and add the solid additive DIB to the solution. After the solid is completely dissolved, the active layer solution is evenly spin-coated on the surface of the hole transport layer at a speed of 1800-3000rpm. After the active layer solution dries, a film is formed and fixed on the surface of the hole transport layer. Then, the ITO substrate with the hole transport layer and the active layer solution film is placed on a hot plate at 100°C for annealing for 1 minute to promote orderly arrangement of the molecules.

[0087] The electron transport layer PDINN was prepared at 1.5 mg mL -1 The concentration of α-D-H-piperidin was dissolved in methanol, and the dissolved solution was spin-coated on the surface of the active layer at a speed of 3000 rpm.

[0088] Finally, in 1×10 -6 Under a high vacuum environment, 100 nm Ag was deposited on the electron transport layer as the cathode of the device. The active area of ​​each cell was 0.04 cm 2 The organic solar cell prepared in this embodiment is as follows Figure 2 The performance parameters of the organic solar cell prepared in this embodiment are shown in Table 1. The current density-voltage curve of the organic solar cell prepared in this embodiment is shown in Table 1. Figure 4 As shown in Table 1 and Figure 4 It can be seen that with the dilution of the donor, Voc and FF have increased to a certain extent, only Jsc decreased from 25.45 to 23.23mAcm -2 , thus the PCE decreases less, and the diluted donor device still maintains a relatively high PCE (15.16%).

[0089] Table 1

[0090] PL2:L8-BO Voc(V) <![CDATA[Jsc(mAcm -2 )]]> FF(%) PCE (%) 1:1.2 0.909 25.45 69.55 16.12 0.3:1.2 0.911 23.23 71.72 15.16

[0091] Example 2

[0092] Preparation of semi-transparent organic solar cells

[0093] The preparation method of the semi-transparent organic solar cell in this embodiment is the same as the preparation method of the organic solar cell in Example 1, except that: this embodiment uses a composite electrode (1 nmAu / 15 nmAg) instead of an opaque electrode to prepare ST-OSCs.

[0094] Semi-transparent organic solar cells (ST-OSCs) improve the transmittance of the device by replacing the metal top electrode (100nmAg) in traditional devices with a transparent electrode. Reducing the thickness of the top silver is a direct way to improve transmittance, but thinner silver films increase excessive resistance and cause significant electrical performance losses in the device. By pre-depositing a seeding layer, the substrate surface energy can be adjusted, allowing it to form a continuous and dense electrode film layer at a lower silver layer thickness, thereby maintaining excellent light transmission performance. Therefore, this example uses a composite structure of a 1nmAu seeding layer and a 15nmAg layer as the device's transparent electrode.

[0095] Example 3

[0096] Preparation of semi-transparent organic solar cells

[0097] The preparation method of the semi-transparent organic solar cell of this embodiment is the same as that of the organic solar cell of embodiment 1, except that in this embodiment, 35nm MoO3 is evaporated on the transparent electrode as an anti-reflection layer to further improve the transparency of the device. Figure 3 As shown, the structure of the semi-transparent organic solar cell prepared in this embodiment is: ITO / PDEOT:PSS / PL2:L8-BO / PDINN / Au / Ag / MoO3.

[0098] The performance parameters of the semi-transparent organic solar cells prepared in Examples 2 and 3 are shown in Table 2. The current density-voltage curves of the semi-transparent organic solar cells prepared in Examples 2 and 3 are shown in Table 2. Figure 5 As shown in Table 2 and Figure 5 As can be seen, by evaporating a semi-transparent electrode (1nmAu / 15nmAg), Example 2 achieved a semi-transparent cell with both high photovoltaic performance (PCE = 11.59%) and high average visible light transparency (AVT = 30.47%). Its calculated LUE reached 3.53%. By evaporating a MoO3 anti-reflection layer, the AVT was significantly improved, ultimately raising the LUE to 3.62%.

[0099] Table 2

[0100]

[0101] In summary, the present invention provides organic solar cell donor materials, organic solar cells, and methods for preparing the same. This invention utilizes random copolymerization of donor units to reduce the crystallinity of the polymer. This significantly reduces the donor content while minimizing the decrease in PCE (Photovoltaic Conversion Efficiency), maintaining 94% of conventional opaque devices. The device transmittance is significantly improved. The synergistic effect of these two factors significantly enhances the light utilization efficiency (LUE), providing a new path for the development of high-efficiency semi-transparent organic solar cells.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of protection of the present invention.

Claims

1. A semi-transparent organic solar cell, characterized in that: The donor material is PL2, and the structural formula of PL2 is: Wherein, m and n are the degree of polymerization, m=0.5, n=0.

5.

2. The semi-transparent organic solar cell according to claim 1, characterized in that: The receptor material is L8-BO, and the structural formula of L8-BO is:

3. The semi-transparent organic solar cell according to claim 2, characterized in that: The semi-transparent organic solar cell comprises an ITO cathode layer, a hole transport layer PEDOT:PSS, an active layer, an electron transport layer PDINN, a transparent electrode and an optical cover layer arranged in sequence from bottom to top; The active layer comprises a donor material and an acceptor material; The transparent electrode includes a 1 nm thick Au seeding layer and a 15 nm thick Ag layer, wherein the Au seeding layer is located on the lower side; The optical cover layer includes a thin layer of MoO3 deposited on the upper surface of a transparent electrode.

4. A method for preparing a semi-transparent organic solar cell, characterized in that: The following steps are involved: S1. Configuration of polymer donor material PL2; S2. Configure the active layer solution; In a nitrogen-filled glove box, polymer PL2 and small molecule L8-BO were dissolved in chloroform, and solid additive DIB was added to the solution. After the solid was completely dissolved, the active layer solution was obtained. S3. Pretreatment of ITO substrate; The ITO substrate was ultrasonically cleaned with deionized water, acetone, and isopropyl alcohol for 30 minutes in sequence. After cleaning, the ITO substrate was blown dry with nitrogen gas and then treated with ultraviolet ozone for 30 minutes. S4. Spin coating of hole transport layer; The hole transport layer PEDOT:PSS was spin-coated onto the ITO substrate at 5000 rpm and then thermally annealed on a heating plate at 150 °C for 15 min; S5. Spin coating active layer; The active layer solution was evenly spin-coated on the surface of the hole transport layer at a speed of 1800-3000 rpm. After the active layer solution dried, a film was formed and fixed on the surface of the hole transport layer. Then, the ITO substrate with the hole transport layer and the active layer solution film was placed on a hot plate at 100°C for annealing for 1 minute. S6. Spin coating electron transport layer; The electron transport layer PDINN was prepared at 1.5 mg mL -1 The concentration of α-D-H-pyrrolidone was dissolved in methanol, and the dissolved solution was spin-coated on the surface of the active layer at a speed of 3000 rpm; S7. Depositing a transparent electrode; A 1 nm thick Au seeding layer and a 15 nm thick Ag layer are sequentially deposited on the surface of the electron transport layer, that is, a transparent electrode is deposited on the surface of the electron transport layer; S8. depositing an optical cover layer; A thin layer of MoO3 is deposited on the surface of the transparent electrode.

5. The method for preparing a semi-transparent organic solar cell according to claim 4, characterized in that: In step S1, the configuration process of the polymer donor material PL2 is as follows: S1.1 Mix DTBT-2, BDD-Br, FBDT-Sn, Pd2(dba)3, and P(o-Tol)3 in a Schlenk flask, add 2 mL of toluene under argon, and heat to reflux at 110°C for 16 h; S1.2 After the mixture in step S1.1 is cooled to room temperature, it is added dropwise to 150 ml of methanol. The precipitate is collected and purified by Soxhlet extraction with dichloromethane and chloroform. S1.3 Concentrate the chloroform fraction and add it dropwise to methanol. Collect the precipitate and dry it in a vacuum overnight to obtain solid PL2.

6. The method for preparing a semi-transparent organic solar cell according to claim 5, characterized in that: In step S2, the structural formula of L8-BO is:

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