A stretchable donor polymer and a preparation method and application thereof

Abstract

The present application relates to a kind of stretchable organic photovoltaic material, specifically discloses a kind of stretchable donor polymer and its preparation method and application.The main chain of the donor polymer is alternately constituted by electron-donating unit benzodithiophene and electron-accepting unit dithienothiophene, while introducing amide structural unit containing C6 alkyl chain in main chain.The polymer is used to prepare organic solar cell active layer, and forms binary blend system with acceptor material.In the absence of third element, the active layer obtains larger crystal coherence length while keeping lower overall crystallinity, so that the device has excellent tensile property and high photovoltaic conversion efficiency.The device constructed by blending polymer D18-C6 of the present application with acceptor material PY-IT has a photoelectric conversion efficiency of 14.67%, and can still work under a 30% strain condition, which significantly improves the performance compared with conventional reference polymer system.

Description

Technical Field

[0001] This invention belongs to the field of organic solar cells, and particularly relates to a stretchable donor polymer, its preparation method and application. Background Technology

[0002] In recent years, the rapid development of stretchable technology has injected strong momentum into wearable electronic devices, enhancing their position in the electronics market. However, maintaining battery life while continuously powering wearable devices remains a key challenge. Against this backdrop, stretchable organic solar cells, as a promising power supply solution, offer a new approach to addressing these issues. These cells not only draw energy from sunlight to provide continuous power to wearable electronic devices but also offer comfort and wearability compatibility, conforming to complex geometries such as joints, flexible prostheses / robots, and curved textiles, thus achieving true stretchable wearable integration. Therefore, stretchable organic solar cells hold significant strategic importance in advancing wearable electronics technology.

[0003] A high-performance, stretchable active layer is crucial for realizing stretchable organic solar cells. In existing technologies, thermoplastic elastomers are typically incorporated into the active layer or polymer blends are designed to improve its mechanical properties. While multi-component blending methods effectively enhance mechanical properties, the complexity of these systems increases the difficulty of controlling the active layer morphology, affecting device consistency and fabrication reproducibility. Another approach is to develop novel stretchable donor or acceptor materials to endow the photoelectric active material with inherent stretchability, thereby achieving mechanical optimization without relying on multi-component systems while maintaining photovoltaic performance stability. However, the current lack of binary blend active layer materials that combine high photoelectric conversion efficiency with excellent stretchability remains a key technological bottleneck restricting further improvements in the performance of stretchable organic solar cells.

[0004] Therefore, designing and synthesizing a novel polymer material that combines high stretchability and excellent photovoltaic performance for constructing the active layer of stretchable organic solar cells is a pressing technical problem that needs to be solved, and it is also the core technical point that this invention needs to overcome.

[0005] The information disclosed in this background section is only intended to enhance the understanding of the background technology of this application and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a stretchable donor polymer, its preparation method, and its applications. An amide unit C6 was designed and synthesized, and introduced into the D18 backbone. Polymer D18-C6 was synthesized via a Stille coupling reaction catalyzed by P(o-tol)3 and Pd2(dba)3. While reducing overall crystallinity, D18-C6 unexpectedly increased the crystal coherence length. L c Therefore, it not only improves the ductility of the material but also enhances its charge transport capability. When applied to organic solar cells, it has achieved significant improvements in both photovoltaic performance and stretchability. Organic solar cells based on the D18-C6:PY-IT blend film have achieved a high power conversion efficiency (PCE) of 14.67% and exhibit excellent stretchability with a crack initiation strain (COS) value of 30%.

[0007] The present invention provides a stretchable donor polymer, wherein the main chain of the polymer is composed of alternating electron-donating units and electron-accepting units, wherein the electron-donating unit is a benzodithiophene unit and the electron-accepting unit is a dithienothiazole unit, and an amide structural unit containing a C6 alkyl chain is introduced into the main chain of the polymer by random copolymerization, wherein the molecular structure of the amide structural unit is shown in formula (I). (I).

[0008] Preferably, the amide structural units form weak interactions between polymer chains through hydrogen bonding, thereby increasing the crystal coherence length while reducing the overall crystallinity of the polymer.

[0009] Preferably, the amide structural unit is a third comonomer embedded in the main backbone repeating unit. The amide group can act as a hydrogen bond donor and acceptor, generating dynamic weak interactions between polymer chains, thereby allowing chain segment slippage during stretching and reconstructing ordered regions after stress release.

[0010] A method for preparing a stretchable donor polymer includes the following steps: (1) Preparation of amide monomer C6: Chloride with C6 alkyl chain and thiophene ethylamine compound were dissolved in dichloromethane respectively. Under alkaline and low temperature conditions, the dissolved thiophene ethylamine compound was added dropwise to the dissolved chloride and stirred to react. After the reaction was completed, the amide monomer C6 was obtained by washing with water, drying and purification. (2) Bromination of amide monomer C6: The amide monomer C6 is dissolved in a mixed system containing a polar co-solvent. N-bromosuccinimide is used as the bromine source. The bromine source is added in batches under low temperature and the reaction is stirred. After the reaction is completed, the bromoamide monomer C6-Br is obtained by extraction, drying and purification. (3) Synthesis of the target polymer D18-C6: Under an inert atmosphere, tin-terminated monomer Sn-BDT-Sn, dibromo-terminated block monomer DTBT-Br, and the bromoamide monomer C6-Br were fed into the reactor, along with Pd2(dba)3 and P( o The catalyst (-tol)3 was heated to 130-150℃ in an aromatic solvent to carry out Stille coupling polymerization for 20-30 hours. After polymerization, the temperature was lowered, the reactants were precipitated in methanol, and purified by Soxhlet extraction. The reactants were washed successively with methanol, acetone, n-hexane and chloroform, and finally collected with chlorobenzene. The chlorobenzene solution was concentrated and precipitated in methanol. The solid was collected and dried under vacuum to obtain the target polymer D18-C6.

[0011] Preferably, the mixing system in step (2) is a mixed solution of chloroform and N,N-dimethylformamide.

[0012] Preferably, the molar ratio of Sn-BDT-Sn, DTBT-Br and C6-Br in step (3) is 1.00:0.95:0.05.

[0013] Preferably, the aromatic solvent in step (3) is o-xylene.

[0014] An organic photovoltaic active layer material comprises a binary blend of the donor polymer and a non-fullerene acceptor material, wherein the acceptor material is PY-IT or a derivative thereof.

[0015] A stretchable organic solar cell uses the aforementioned binary blend material as the active layer and is stacked with a stretchable electrode, a stretchable substrate, and a stretchable encapsulation layer.

[0016] Preferably, the crack initiation strain (COS) value of the active layer reaches 30%.

[0017] Preferably, the power conversion efficiency (PCE) of the stretchable organic solar cell is ≥14.5%.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The device using D18-C6:PY-IT blend film as active layer has a power conversion efficiency (PCE) of 14.67% and a tensile performance index (COS) of 30% for D18-C6:PY-IT blend film, which is significantly better than the reference polymer system. That is, while maintaining excellent photovoltaic performance, the tensile performance is significantly improved, realizing the synergistic optimization of photoelectric performance and mechanical flexibility. (2) While reducing the overall crystallinity, D18-C6 unexpectedly increased the crystal coherence length. L c Lower crystallinity means easier stretching and increased crystallinity.L c Facilitating charge transport, the C6 chain length maximizes hydrogen bonding while minimizing rigidity, thus balancing photovoltaic and mechanical properties. Compared to multiple systems, the D18-C6:PY-IT blend film achieved the highest... L c (28.52 Å), even exceeding the reference polymer D18 (26.74 Å); (3) By designing a sophisticated donor polymer molecule, namely introducing an amide unit containing a C6 alkyl chain, high stretchability and good photovoltaic efficiency can be achieved without a third element in a simple binary device structure, providing a simple, efficient and repeatable solution for the preparation of stretchable organic solar cells. Attached Figure Description

[0019] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the following description is only one embodiment of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 Synthetic routes for donor polymers; Figure 2 The room temperature concentration of compound C6 in CDCl3 1 H NMR spectrum; Figure 3 The room temperature concentration of compound C6-Br in CDCl3 1 H NMR spectrum; Figure 4 The room temperature concentration of compound C2 in CDCl3 1 H NMR spectrum; Figure 5 The room temperature concentration of compound C2-Br in CDCl3 1 H NMR spectrum; Figure 6 The room temperature concentration of compound C4 in CDCl3 1 H NMR spectrum; Figure 7 The room temperature concentration of compound C4-Br in CDCl3 1 H NMR spectrum; Figure 8 The room temperature concentration of compound C8 in CDCl3 1 H NMR spectrum; Figure 9 The room temperature concentration of compound C8-Br in CDCl3 1 H NMR spectrum; Figure 10 Thermogravimetric analysis (TGA) of the donor polymer; Figure 11 Comparison of the optical properties of polymers; (a) Normalized UV-Vis absorption spectrum of the polymer in chloroform solution at room temperature; (b) Normalized UV-Vis absorption spectrum of the polymer in thin film; Figure 12 Electrochemical cyclic voltammetry curves of the donor polymer; Figure 13 Performance characterization of binary organic solar cell devices: (a) JV curve of the best device; (b) EQE curve; Figure 14 Microstructure analysis of the blend membrane: (a) 2D-GIWAXS diagram of the blend film; (b) GIWAXS line cut profile in the in-plane direction; (c) GIWAXS line cut profile in the out-of-plane direction. Figure 15 Optical microscope image of the blended thin film under strain; Figure 16 This is a schematic diagram of the molecular structure of the donor polymer in this invention. Detailed Implementation

[0020] This invention proposes a stretchable donor polymer, its preparation method, and its applications. To facilitate understanding of this invention by those skilled in the art, specific embodiments are described below with reference to the accompanying drawings. Unless otherwise specified, the equipment and reagents used in this invention are commercially available or commonly used in the field.

[0021] Synthetic routes of donor polymers are as follows Figure 1 As shown, compounds C2, C4, C6, and C8 all contain flexible alkyl segments and amide bonds, the difference being the length of the carbon chains between the amide bonds.

[0022] Example 1 The preparation of D18-C6 includes the following steps: (1) Synthesis of compound C6 1,8-Dioctanoyl chloride (1.05 g, 5 mmol) and 2-thiopheneethylamine (1.40 g, 11 mmol) were dissolved separately in 15 mL of dichloromethane. 3 mL of triethylamine was added to the dissolved 2-thiopheneethylamine solution to provide an alkaline environment for the reaction. Then, under ice bath conditions, the dissolved 2-thiopheneethylamine was added dropwise to the dissolved 1,8-dioctanoyl chloride, accompanied by the generation of white fumes during the addition. Finally, the mixture was stirred at room temperature for 24 hours. After the reaction was complete, the mixture was diluted with a small amount of dichloromethane solvent, and then extracted with deionized water. This process was repeated 2-3 times to obtain the organic phase. A small amount of anhydrous sodium sulfate was added to the organic phase, and the organic phase was dried. The solvent was removed by rotary evaporation to obtain the crude product. The crude product was purified by silica gel column chromatography with acetone and chloroform as eluent in a 1:1 (volume ratio) ratio to give a white powder compound C6 (1.68 g, yield 85.7%). 1 H NMR (500 MHz, CDCl3): δ(ppm) 7.16 (d, J =6.6 Hz, 2H), 6.98-6.93 (m, 2H), 6.83 (d, J =3.8 Hz, 2H), 5.71-5.56 (m, 2H),3.57-3.50 (m, 4H), 3.06-3.00 (m, 4H), 2.16-2.09 (m, 4H), 1.64-1.56 (m, 4H),1.34-1.27 (m, 4H) ( Figure 2 ).

[0023] (2) Synthesis of compound C6-Br Compound C6 (0.41 g, 1.02 mmol) was dissolved in a mixed solution of chloroform and N,N-dimethylformamide (10 / 1, v / v). Then, under ice bath conditions, a measured amount of N-bromosuccinimide (0.38 g, 2.15 mmol) was added in portions to the dissolved compound C6. Finally, the mixture was stirred at room temperature for 24 hours. After the reaction was complete, the mixture was diluted with dichloroform and extracted with water, repeated 2-3 times to obtain the organic phase. A small amount of anhydrous sodium sulfate was added to the organic phase to remove water. The organic solvent was removed by rotary evaporation to obtain the crude product. The crude product was purified by silica gel column chromatography using acetone:chloroform = 3:1 (v / v) to give a white powder, compound C6-Br (0.48 g, yield 86.6%). 1 H NMR (500 MHz, CDCl3): δ(ppm) 6.88 (d, J=3.6 Hz, 2H), 6.59 (d, J =3.6 Hz, 2H), 5.74-5.60 (m, 2H), 3.54-3.44 (m, 4H), 3.01-2.91(m, 4H), 2.18-2.09 (m, 4H), 1.64-1.55 (m, 4H), 1.35-1.28 (m, 4H) ( Figure 3 ).

[0024] (3) Synthesis of D18-C6 In a 25 mL flask, Sn-BDT-Sn (94.0 mg, 0.1 mmol, 1.0 eq), DTBT-Br (0.095 mmol, 0.95 eq), C6-Br (0.005 mmol, 0.05 eq), Pd2(dba)3 (3.0 mg, 0.003 mmol, 0.03 eq) and P( o -tol)3 (10.0 mg, 0.033 mmol, 0.33 eq) was added, followed by the addition of 5 mL of o-xylene. The mixture was stirred thoroughly and heated to 140 °C for 24 hours. After cooling to room temperature, the mixture was precipitated in methanol and purified by Soxhlet extraction. The polymer was washed successively with methanol, acetone, n-hexane, and chloroform, and finally collected with chlorobenzene. The chlorobenzene solution was then concentrated and precipitated in methanol. The resulting polymer was collected and dried under vacuum overnight at 40 °C.

[0025] Black solid D18-C6 was obtained in 53% yield, HT-GPC: M n =62.80 kDa, =1.62. T d =425 ℃.

[0026] Comparative Example 1 The preparation of D18-C2 includes the following steps: (1) Synthesis of compound C2 Similar to step (1) of Example 1, except that 1,8-dioctanoyl chloride (1.05 g, 5 mmol) was replaced with succinyl chloride (0.77 g, 5 mmol), and finally a white powder compound C2 (1.05 g, yield 62.5%) was obtained. 1 H NMR(500 MHz, CDCl3): δ(ppm) 7.15 (d, J=4.9 Hz, 2H), 6.96-6.92 (m, 2H), 6.83 (d, J =2.6 Hz, 2H), 6.26-6.15 (m, 2H), 3.52-3.48 (m, 4H), 3.04-2.99 (m, 4H), 2.50-2.46 (m, 4H) ( Figure 4 ).

[0027] (2) Synthesis of compound C2-Br Similar to step (2) of Example 1, except that compound C6 (0.41 g, 1.02 mmol) was replaced with compound C2 (0.88 g, 2.6 mmol), the amount of N-bromosuccinimide (0.38 g, 2.15 mmol) was changed to (0.98 g, 5.5 mmol), and the ratio of acetone to chloroform in the eluent was changed to 1:2, finally yielding a white powder compound C2-Br (0.89 g, yield 69.3%). 1 H NMR (500 MHz, CDCl3): δ(ppm) 6.88 (d, J =3.7 Hz, 2H), 6.60 (d, J =3.5 Hz, 2H), 6.26-6.11 (m, 2H), 3.51-3.42 (m, 4H), 3.00-2.91 (m, 4H), 2.54-2.45 (m, 4H) ( Figure 5 ).

[0028] (3) Synthesis of D18-C2 Similar to step (3) of Example 1, except that C6-Br is replaced with C2-Br to obtain black solid D18-C2 with a yield of 45%, HT-GPC: M n =70.56 kDa, =1.56. T d =415 ℃.

[0029] Comparative Example 2 The preparation of D18-C4 includes the following steps: (1) Synthesis of compound C4 Similar to step (1) of Example 1, except that 1,8-dioctanoyl chloride (1.05 g, 5 mmol) was replaced with adipicoyl chloride (0.92 g, 5 mmol), and the eluent was replaced with acetone:petroleum ether = 2:1 (volume ratio), and finally a white powder compound C4 (1.15 g, yield 63.0%) was obtained. 1 H NMR (500 MHz, CDCl3): δ(ppm) 7.15 (d, J =6.5Hz, 2H), 6.98-6.91 (m, 2H), 6.83 (d, J =2.5 Hz, 2H), 6.02-5.85 (m, 2H), 3.55-3.48 (m, 4H), 3.06-3.00 (m, 4H), 2.20-2.13 (m, 4H) 1.65-1.58 (m, 4H) ( Figure 6 ).

[0030] (2) Synthesis of compound C4-Br Similar to step (2) of Example 1, except that compound C6 (0.41 g, 1.02 mmol) was replaced with compound C4 (0.19 g, 0.51 mmol), the amount of N-bromosuccinimide (0.38 g, 2.15 mmol) was changed to (0.19 g, 1.07 mmol), and the ratio of acetone to chloroform in the eluent was changed to 1:1, finally yielding a white powder compound C4-Br (0.19 g, yield 72.4%). 1 H NMR (500 MHz, CDCl3): δ(ppm) 6.88 (d, J =3.5 Hz, 2H), 6.60 (d, J =3.5 Hz, 2H), 5.86-5.75 (m, 2H), 3.54-3.44 (m, 4H), 3.00-2.90 (m,4H), 2.24-2.14 (m, 4H) 1.69-1.55 (m, 4H) ( Figure 7 ).

[0031] (3) Synthesis of D18-C4 Similar to step (3) of Example 1, except that C6-Br is replaced with C4-Br to obtain black solid D18-C4 with a yield of 64%. HT-GPC: M n =65.08 kDa, =1.80. Td =421 ℃.

[0032] Comparative Example 3 The preparation of D18-C8 includes the following steps: (1) Synthesis of compound C8 Similar to step (1) of Example 1, except that 1,8-dioctanoyl chloride (1.05 g, 5 mmol) was replaced with sebacate chloride (1.20 g, 5 mmol), and the ratio of acetone to chloroform in the eluent was changed to 1:2, finally yielding white powder compound C8 (1.68 g, yield 80.0%). 1 H NMR (500 MHz, CDCl3): δ(ppm) 7.17 (d, J =5.1 Hz,2H), 6.97-6.93 (m, 2H), 6.83 (d, J =2.7 Hz, 2H), 5.67-5.56 (m, 2H), 3.55-3.50(m, 4H), 3.05-3.01 (m, 4H), 2.15-2.11 (m, 4H), 1.62-1.57 (m, 4H), 1.30-1.26(m, 8H) ( Figure 8 ).

[0033] (2) Synthesis of compound C8-Br Similar to step (2) of Example 1, except that compound C6 (0.41 g, 1.02 mmol) was replaced with compound C8 (0.34 g, 0.11 mmol), the amount of N-bromosuccinimide (0.38 g, 2.15 mmol) was changed to (0.30 g, 1.70 mmol), and the ratio of acetone to chloroform in the eluent was changed to 2:1, finally yielding a white powder compound C8-Br (0.38 g, yield 82.0%). 1 H NMR (500 MHz, CDCl3): δ(ppm) 6.88 (d, J =3.5 Hz, 2H), 6.59 (d, J =3.5 Hz, 2H), 5.70-5.56 (m, 2H), 3.53-3.44 (m, 4H), 3.04-2.92 (m,4H), 2.23-2.11 (m, 4H), 1.64-1.59 (m, 4H), 1.32-1.24 (m, 8H) ( Figure 9 ).

[0034] (3) Synthesis of D18-C8 Similar to step (3) of Example 1, except that C6-Br is replaced with C8-Br to obtain black solid D18-C8 with a yield of 60%. HT-GPC: M n =75.38 kDa, =1.63. T d =423 ℃.

[0035] Comparative Example 4 The preparation of D18 includes the following steps: Similar to step (3) in Example 1, except that the amount of DTBT-Br added is 0.1 mmol, and C6-Br is not added, resulting in black solid D18 with a yield of 51%. HT-GPC: M n =59.78 kDa, =1.75. T d =396 ℃.

[0036] Performance Characterization 1. Basic material properties The donor polymer was characterized by high-temperature gel permeation chromatography (HT-GPC) to determine its number-average molecular weight. M n The synthesis method described above is already described. The decomposition temperature of the donor polymer was determined by thermogravimetric analysis (TGA). T d (5% weight loss) up to 396~425℃ ( Figure 10 ), T d The high thermal stability at temperatures above 400°C indicates that all donor polymers exhibit excellent thermal stability, and the incorporation of amide units does not negatively affect their thermal properties.

[0037] The normalized UV-Vis absorption spectra of the polymer in the thin film and chloroform solution at room temperature are as follows: Figure 11 As shown in a and 11b, detailed optical performance parameters are listed in Table 1. These donor polymers exhibit absorption spectra complementary to the acceptor PY-IT, enabling a wider solar spectral coverage and higher light collection efficiency. In the solution UV-Vis absorption spectra at room temperature, all polymers exhibit similar 0-0 absorption peaks (…). λ 0-0 () Figure 11a) This indicates that the introduction of amide units has only a small effect on the aggregation behavior of polymers in solution. In thin films, polymers containing amide units with flexible alkyl segments of different lengths (D18-C2, D18-C4, D18-C6, and D18-C8) show reduced 0-0 absorption peaks compared to the reference polymer D18. λ 0-0 () Figure 11 (b) indicates that the introduction of amide units has a negative impact on the aggregation of polymer films. This suggests that the introduction of amide units inhibits aggregation in polymer films, thereby improving the stretchability of the polymer. The optical band gaps of the donor polymers (D18, D18-C2, D18-C4, D18-C6, and D18-C8) are shown. E g opt The equation is used to determine the initial wavelength of the thin film. E g opt =1240 / λ The estimated values ​​are 1.98, 1.99, 2.00, 2.00, and 2.00 eV, respectively.

[0038] Table 1 Basic Characterization of Polymers

[0039] Note: a Thin film state; b Calculated based on the initial absorption of the thin-film polymer; c Electrochemical cyclic voltammetry determination; d Calculated based on HOMO energy level and optical band gap.

[0040] The electrochemical properties of the polymer were determined using electrochemical cyclic voltammetry (CV). The corresponding CV curves and obtained electrochemical parameters are shown below. Figure 12 As shown in Table 1, among the donor polymers, the highest occupied molecular orbital (HOMO) energy levels of the four polymers with amide units (D18-C2, D18-C4, D18-C6, and D18-C8) are slightly higher than those of the reference polymer D18. Furthermore, Table 1 summarizes the lowest unoccupied molecular orbital (LUMO) energy levels calculated based on the corresponding HOMO values ​​and optical band gaps. All donor polymers exhibit HOMO and LUMO energy levels that are well matched to the acceptor polymer PY-IT, indicating sufficient driving force for effective exciton dissociation in the blend film.

[0041] 2. Photovoltaic performance Photovoltaic performance is evaluated using devices with a conventional structure, which is a standardized organic photovoltaic device architecture consisting of ITO / PEDOT:PSS / active layer / PDINN / Ag stacked sequentially.

[0042] Under AM 1.5G illumination (100 mW cm⁻¹) -2 (Pass) J - V Measurements characterized the photovoltaic performance of the optimized device, as follows: Figure 13 As shown in a and Table 2, the organic solar cell device based on the reference D18:PY-IT mixture exhibits a PCE of 13.33% and an open-circuit voltage ( ). V OC The voltage is 0.96 V, and the short-circuit current density is ( J SC The value is 23.24 mA cm. -2 The fill factor (FF) was 59.43%. In contrast, devices fabricated using the D18-C6:PY-IT blend exhibited a higher PCE of 14.67%, primarily due to... J SC Increased to 24.14 mA cm -2 At the same time, it maintained a voltage of 0.96 V. V OC However, devices based on mixtures of D18-C2:PY-IT and D18-C4:PY-IT exhibited reduced PCE. These significant differences in device performance highlight the crucial role of alkyl segment length in the donor polymer containing amide units in modulating the photovoltaic performance of solar cells. External quantum efficiency (EQE) spectra are shown below. Figure 13 As shown in b. The integrals derived from these spectra. J SC Value and J - V The measured values ​​showed good consistency, with deviations within 5% (Table 2). All polymer blends exhibited strong responses in both the donor polymer absorption range (400–600 nm) and the acceptor polymer range (650–850 nm), indicating that charge generation can be effectively achieved in blends containing amide units and flexible alkyl segments of varying lengths.

[0043] Table 2 Polymer Photovoltaic Performance

[0044] 3. Tensile properties The blend membrane was tested using GIWAXS. Figure 14 Table 3 summarizes the corresponding crystallographic parameters obtained from the GIWAXS profile. All blend films exhibit face-on orientation, as evidenced by the (100) layered diffraction peaks in the in-plane direction and the (010) π-π stacking peaks in the out-of-plane direction. The layered stacking distance was calculated using the Bragg equation. d 100) and π-π stacking distance ( d 010 The blended films of D18:PY-IT, D18-C2:PY-IT, D18-C4:PY-IT, D18-C6:PY-IT, and D18-C8:PY-IT exhibited the same layered stacking distance. d 100 (19.63 Å). The corresponding π-π stacking distances of these blend films ( d 010 The values ​​were 4.00, 4.00, 3.97, 3.97, and 3.95 Å, respectively. These results indicate that the introduction of amide units containing appropriately long alkyl segments has little effect on the molecular packing distance. To evaluate crystal properties, rDoC and α, β, and β were calculated based on GIWAXS data. L c rDOC and are calculated from the (010) peak in the out-of-plane direction using the Scherrer equation. L c As shown in Table 3, all four blends containing amide units with flexible alkyl segments of different lengths had lower rDoC values ​​compared to the reference D18:PY-IT blend. The decrease in crystallinity is related to the enhanced stretchability of these blend films. Furthermore, the coherence lengths of the D18-C2:PY-IT and D18-C4:PY-IT blends were decreased compared to the D18:PY-IT reference. The increased coherence length of the D18-C6:PY-IT blend, however, confirmed the formation of larger grains, which contributes to its enhanced photovoltaic performance. Generally, introducing flexible units into conjugated polymers disrupts the regularity and close packing of the main chain, leading to decreased crystallinity and... L c The reduction was observed. However, D18-C6 was an exception. Among all blended films, its blends achieved the highest reduction. L c (28.52 Å), even exceeding the reference polymer D18 (26.74 Å), indicating that the C6 chain length may have reached an optimal point in terms of steric hindrance and molecular chain mobility, maximizing the effect of hydrogen bonding and minimizing rigidity.

[0045] Table 3 Detailed parameters of the blended membranes obtained by GIWAXS

[0046] After confirming that amide units with flexible alkyl segments of different lengths affect the morphology of the blend film, further analysis was conducted to determine how these morphological changes affect mechanical properties. Crack propagation under strain hinders charge transport between electrodes, degrading device performance. Therefore, developing an active layer with high COS is crucial for realizing high-performance stretchable polymer solar cells. The COS of the blend polymer film was measured to evaluate its stretchability. Figure 15 As shown, compared to the reference D18:PY-IT blend film, four blend films (D18-C2:PY-IT, D18-C4:PY-IT, D18-C6:PY-IT, and D18-C8:PY-IT) containing amide units with flexible alkyl segments of different lengths exhibit higher COS values. Notably, the COS value of the D18-C6:PY-IT blend film is 30%, a significant improvement over the reference blend. These results further confirm that introducing amide units with alkyl segments of different lengths successfully reduces crystallinity and improves stretchability. Furthermore, fine-tuning the length of the flexible alkyl segments in the amide units provides an effective method for improving mechanical properties.

[0047] In summary, the performance improvement resulting from introducing an appropriately long C6 alkyl chain segment is comparable to the performance improvement resulting from a simple alkyl chain reducing crystallinity and... L c This differs significantly from conventional understanding. Introducing C6 effectively inhibits excessive polymer aggregation, reduces relative crystallinity, and synergistically improves mechanical properties through hydrogen bonding. Furthermore, the introduction of this length of alkyl segment unexpectedly increases... L c This promotes charge transport and ultimately improves the photovoltaic performance of the device. Specifically, organic solar cells based on D18-C6:PY-IT enhance... J SC Under these conditions, a PCE of 14.67% was achieved. The D18-C6:PY-IT blend membrane exhibited excellent mechanical properties and a COS value of 30%. Compared with most existing technologies that require ternary blending or complex molecular engineering to achieve similar performance balance, this invention provides a simpler and more fundamental solution, highlighting the effectiveness and advancement of its molecular design strategy.

[0048] The embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A stretchable donor polymer, characterized in that: The main chain of the polymer is composed of alternating electron-donating and electron-accepting units, wherein the electron-donating unit is a benzodithiophene unit and the electron-accepting unit is a dithienothiazole unit. The main chain of the polymer introduces amide structural units containing C6 alkyl chains in a random copolymerization manner, and the molecular structure of the amide structural units is shown in formula (I). (I).

2. The stretchable donor polymer according to claim 1, characterized in that: The amide structural units form weak interactions between polymer chains through hydrogen bonding, which increases the crystal coherence length while reducing the overall crystallinity of the polymer.

3. The stretchable donor polymer according to claim 1, characterized in that: The amide structural unit is a third comonomer embedded in the main skeleton repeating unit.

4. A method for preparing the stretchable donor polymer as described in claim 1, characterized in that, Includes the following steps: (1) Preparation of amide monomer C6: Chloride with C6 alkyl chain and thiophene ethylamine compound were dissolved in dichloromethane respectively. Under alkaline and low temperature conditions, the dissolved thiophene ethylamine compound was added dropwise to the dissolved chloride and stirred to react. After the reaction was completed, the amide monomer C6 was obtained by washing with water, drying and purification. (2) Bromination of amide monomer C6: The amide monomer C6 is dissolved in a mixed system containing a polar co-solvent. N-bromosuccinimide is used as the bromine source. The bromine source is added in batches under low temperature and the reaction is stirred. After the reaction is completed, the bromoamide monomer C6-Br is obtained by extraction, drying and purification. (3) Synthesis of the target polymer D18-C6: Under an inert atmosphere, tin-terminated monomer Sn-BDT-Sn, dibromo-terminated block monomer DTBT-Br, and the bromoamide monomer C6-Br were fed into the reactor, along with Pd2(dba)3 and P( o The catalyst (-tol)3 was heated to 130-150℃ in an aromatic solvent to carry out Stille coupling polymerization for 20-30 hours. After polymerization, the temperature was lowered, the reactants were precipitated in methanol, and purified by Soxhlet extraction. The reactants were washed successively with methanol, acetone, n-hexane and chloroform, and finally collected with chlorobenzene. The chlorobenzene solution was concentrated and precipitated in methanol. The solid was collected and dried under vacuum to obtain the target polymer D18-C6.

5. The preparation method according to claim 4, characterized in that: The mixed system described in step (2) is a mixed solution of chloroform and N,N-dimethylformamide.

6. The preparation method according to claim 4, characterized in that: The molar ratio of Sn-BDT-Sn, DTBT-Br and C6-Br in step (3) is 1.00:0.95:0.

05.

7. The preparation method according to claim 4, characterized in that: The aromatic solvent mentioned in step (3) is o-xylene.

8. An organic photovoltaic active layer material, characterized in that: The material includes a binary blend of the donor polymer as described in any one of claims 1 to 7 and a non-fullerene acceptor material, wherein the acceptor material is PY-IT.

9. A stretchable organic solar cell, characterized in that: The binary blend material described in claim 8 is used as the active layer and is stacked with a stretchable electrode, a stretchable substrate and a stretchable encapsulation layer.

10. The stretchable organic solar cell according to claim 9, characterized in that: The crack initiation strain (COS) of the active layer reaches 30%, and the power conversion efficiency (PCE) of the stretchable organic solar cell is ≥14.5%.

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