Fully asymmetric small molecule donor (SMD-Asy) and preparation method and application thereof

Abstract

The present application relates to the field of organic solar cells, and provides a kind of full asymmetric small molecule donor SMD-Asy and its preparation method and application.The SMD-Asy is connected by Stille coupling from asymmetrically substituted conjugated BDTT core and acceptor unit, and the side chain and main chain structure are all asymmetrically distributed.The preparation of the small molecule donor includes: constructing thiophene and benzo dithiophene diketone BDTT intermediate, introducing long-chain alkoxy side chain under phase transfer catalysis condition, obtaining tin precursor by low-temperature lithiation, and then coupling with halogenated acceptor unit to obtain target molecule.Due to the simultaneous asymmetric design of main chain-side chain, SMD-Asy can regulate the phase separation scale and chain conformation of blended film as the third component in PM6:Y6 system, thereby improving the hole / electron transport balance and mechanical ductility, so that the device can ensure high photovoltaic performance while improving the cracking strain rate.The small molecule donor of the present application is suitable for flexible and stretchable organic solar devices.

Description

Technical Field

[0001] This invention relates to the field of organic solar cells, and more particularly to a fully asymmetric small molecule donor SMD-Asy with both the main chain and side chains being asymmetric, its preparation method, and its applications. Background Technology

[0002] Wearable electronics are increasingly integrating into daily life. For example, electronic devices with skin-like properties are not only skin-friendly and intelligent, but their functions are also constantly being upgraded. However, traditional planar power supplies occupy a large volume in portable or wearable devices, limiting the stretchability and integration of these devices, thus hindering the commercial application of next-generation wearable devices. Therefore, lightweight and stretchable organic solar cells (S-OSCs) have attracted widespread attention in textiles, artificial skin, and soft robotics due to their excellent performance. S-OSCs need to possess both good photovoltaic performance and mechanical stretchability, and the development of stretchability of the organic active layer remains a key factor limiting the performance improvement of S-OSCs.

[0003] In recent years, ternary organic solar cells (T-OSCs) have become an effective strategy for improving performance. T-OSCs typically consist of binary electron donors and electron acceptors as the main components, with the addition of a third component material. This third component can be a thermally insulating elastomer, a highly ductile polymer with long chains, or a small molecule donor. Among these, small molecule donors can significantly improve the power conversion efficiency (PCE) of ternary organic solar cells and also possess multiple advantages such as molecular designability, high purity, and reproducible synthesis. However, the typical strain range of human skin is between 10% and 30%, and low molecular weight small molecules are generally difficult to improve tensile properties, meaning it is difficult to simultaneously achieve both photovoltaic performance and tensile performance.

[0004] Therefore, designing a small molecule that can introduce a stretchable organic active layer and achieve excellent stretchability while ensuring that photovoltaic performance does not decrease significantly has become a key technical problem that urgently needs to be solved.

[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 designs and synthesizes a fully asymmetric small molecule with both asymmetric main chain and side chain. As the third component of the PM6:Y6 system, this molecule can significantly improve the photovoltaic performance and tensile properties of PM6:Y6, thereby meeting the application requirements of wearable devices on human body parts such as the back of the hand and arm.

[0007] A fully asymmetric small molecule donor, SMD-Asy, contains a BDTT core with a π-conjugated backbone, with rhodanine derivatives on both sides. The side chains and main chain structures are asymmetrically distributed, and its molecular structure is shown in formula (I). (I) A method for preparing a fully asymmetric small molecule donor SMD-Asy includes the following steps: (1) Construction of BDTT core: a Grignard reagent was prepared by reacting bromobenzene with magnesium shavings under an inert atmosphere, and the Grignard reagent was reacted with thiophenebenzodithiophene-4,9-dione by addition reaction, followed by hydrolysis and extraction to obtain BDTT intermediates; (2) Introducing asymmetric alkoxy substituents: The BDTT intermediate is reduced and activated under alkaline conditions, and then alkylated with long-chain haloalkanes under the action of a phase transfer catalyst to obtain BDTT-OR compounds with long-chain alkoxy substituents; (3) Construction of tin-modified precursor: The BDTT-OR compound was reacted with an organolithium reagent under an inert atmosphere and low temperature to form a lithiation intermediate, and then reacted with an organotin chloride reagent to introduce a trialkyltin group to obtain the tin-modified precursor BDTT-Asy; (4) Stille coupling: The BDTT-Asy was coupled with a rhodanine derivative halogenated acceptor unit in the presence of a palladium catalyst, and the fully asymmetric small molecule donor SMD-Asy was obtained by extraction and purification.

[0008] Preferably, the long-chain alkoxy group in step (2) is a branched or dibranched alkoxy group, and the phase transfer catalyst is tetrabutylammonium bromide.

[0009] Preferably, the organolithium reagent in step (3) is n-butyllithium.

[0010] Preferably, the palladium catalyst in step (4) is Pd(PPh3)4.

[0011] Preferably, in step (4), BDTT-Asy is coupled to a rhodanine derivative-containing halogenated acceptor unit at a molar ratio of 1:2.5 to 1:3.

[0012] Application of a fully asymmetric small molecule donor, SMD-Asy, in the active layer of an organic solar cell.

[0013] Preferably, SMD-Asy is used as a third component in the PM6:Y6 active layer.

[0014] Preferably, the doping amount of SMD-Asy as the third component is 1~10%.

[0015] More preferably, the doping amount of SMD-Asy as the third component is 5%, and the PCE of the resulting PM6:SMD-Asy(5%):Y6 ternary device can reach 16.88%, and the cracking strain rate of the PM6:SMD-Asy:Y6 blend film is higher than 10%.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) Traditional small molecule donors often adopt symmetrical structures, which are prone to excessive stacking and brittleness. In this invention, both the conjugated backbone and the alkoxy side chain are designed as asymmetrical structures, which can destroy excessive π-π stacking and inhibit the crystallization and aggregation of large molecules, thereby improving the morphology, miscibility and stretchability of the blend film. At the same time, it does not simply destroy all ordered structures, but retains a large number of microcrystalline structures, forming an optimized stacking structure with close π-π distance, small grain size and uniform interpenetrating network. This structure also optimizes the charge transport and stress dissipation paths, thereby achieving a synergistic breakthrough in improving photovoltaic performance and mechanical properties. (2) The fully asymmetric small molecule donor SMD-Asy prepared in this invention, as a third component, can effectively regulate the donor-acceptor interface of the PM6:Y6 system, promote a more uniform distribution of donor and acceptor, and thus form a more uniform blending region. The regulated interface significantly improves the matching of hole mobility and electron mobility. Among them, the PM6:SMD-Asy(5%):Y6 mixture with a doping amount of 5% has the most balanced... μ h / μ e The value indicates that the hybrid thin film can form excellent electron transport channels to improve device efficiency; (3) Compared to symmetrical small molecules, the dual asymmetric structure of this invention fundamentally changes the mechanical behavior of the active layer film. By reducing the grain size and lowering the rigidity of the crystalline region, it allows stress to be uniformly distributed in the soft amorphous matrix, thereby significantly reducing local stress concentration. The results show that the cracking strain rate of the blend film based on this invention is significantly improved, and the prepared device can still maintain excellent photovoltaic function (PCE>16.5%) under tensile strain exceeding 10%. This characteristic makes it fully meet the common strain range of human skin in daily activities, laying a solid material foundation for the development of high-performance, high-reliability stretchable and wearable optoelectronic devices. Attached Figure Description

[0017] 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 Design for a stretchable photoactive layer; Figure 2 The synthetic route for small molecule SMD-Asy; Figure 3 For compound BDTT-1 1 H NMR spectrum; Figure 4 This is the mass spectrum of compound BDTT-1; Figure 5 For compound BDTT-2 1 H NMR spectrum; Figure 6 This is the mass spectrum of compound BDTT-2; Figure 7 For compound BDTT-OR1 1 H NMR spectrum; Figure 8 The mass spectrum of compound BDTT-OR1 is shown below. Figure 9 For compound BDTT-OR2 1 H NMR spectrum; Figure 10 This is the mass spectrum of compound BDTT-OR2; Figure 11 For compound BDTT-Asy1 1 H NMR spectrum; Figure 12 For the compound SMD-Asy 1 H NMR spectrum; Figure 13 For the compound BDT-LOR 1 H NMR spectrum; Figure 14 For the compound BDT-LOR-Sn 1 H NMR spectrum; Figure 15 For the compound BDT-OR 1 H NMR spectrum; Figure 16 Structure and optical properties of small molecule donors: (a) Chemical structure of the donor small molecule; (b) Normalized UV-Vis absorption spectra of the donor small molecule and polymer in the thin film (at room temperature); (c) Normalized UV-Vis absorption spectra of the donor small molecule and polymer in chloroform solution (at room temperature); (d) Energy level distribution of the donor; (e) Molecular geometry of SMD-Asy and SMD-OR simulated by density functional theory calculation; Figure 17 Comparison of absorption wavelengths of the donor thin film and the donor in solution: (a) PM6; (b) SMD-Asy; (c) SMD-Asy; Figure 18 Electrochemical cyclic voltammetry curves for the donor; Figure 19 Performance characterization of binary and ternary organic solar cell devices: (a) The best device JV (a) Curve; (b) Photoelectric efficiency (EQE) curve of OSCs; Figure 20 Charge transport characteristics of organic solar cells corresponding to blended thin films: (a) Hole mobility; (b) Electron mobility; Figure 21 For light-intensity dependent organic solar cells J SC Line graph; Figure 22 Microstructure characteristics of the optimal blend film: (a) Atomic force microscopy (AFM) height image (2×2 μm); (b) Transmission electron microscopy (TEM) image; (c) Two-dimensional wide-angle X-ray scattering (GIWAXS) spectrum; (d) GIWAXS one-dimensional distribution curve; Figure 23 AFM (2×2 μm) phase image of the optimal blend film; Figure 24 Optical microscope image of a blend film exhibiting good photovoltaic performance under strain conditions. Detailed Implementation

[0018] This invention proposes a fully asymmetric small molecule donor SMD-Asy, with both the main chain and side chains being asymmetric, along with its preparation method and 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.

[0019] Example 1 Preparation of the fully asymmetric small molecule donor SMD-Asy The synthetic route of the small molecule donor SMD-Asy is as follows: Figure 2 As shown, the target small molecule was obtained via a Stille coupling reaction using tetrakis(triphenylphosphine)palladium (Pd(PPh3)4) as a catalyst. All key compounds were obtained through... 1 Confirmed by 1H NMR and mass spectrometry. The specific synthesis steps are as follows.

[0020] 1. Synthesis of compounds BDTT-1 and BDTT-2: (1) Synthesis of compound BDTT-1 In THF (13 mL), bromobenzene (1.43 g, 9.12 mmol) was added dropwise to a mixture of magnesium shavings (0.27 g, 10.94 mmol) and one I2 grain (13 mL), and reflux was maintained under nitrogen. After addition, reflux was maintained for 3 h. Then, Grignard reagent was added dropwise to a solution of thiophene [1,2-b:4,5-b']benzodithiophene-4,9-dione (1.29 g, 4.56 mmol) in THF (60 mL) under an ice-water bath. Finally, the mixture was stirred for 40 h at room temperature under nitrogen. Subsequently, the mixture was hydrolyzed by the slow addition of water followed by the addition of 38% hydrochloric acid aqueous solution, and finally extracted with petroleum ether. The organic phase was dried on Na2SO4. After removing the solvent under vacuum, the residue was eluted with petroleum ether-dichloromethane by silica gel column chromatography to give a pale yellow solid compound, BDTT-1 (0.72 g, yield = 44%). 1 H NMR (600 MHz, CDCl3) δ(ppm) 7.58 (d, J = 5.0 Hz, 1H),7.51 (d, 1H), 7.45 (d, 2H), 7.32-7.28 (m, 3H), 7.22 (d, 1H), 7.09 (d, 1H),3.29 (s, 1H) ( Figure 3 Mass spectrometry: C 18 H 10 The theoretical value of O2S3 is [M]. + : 353.9843; Measured value: 354.9919 ( Figure 4 ); (2) Synthesis of compound BDTT-2 The synthesis steps were the same as those for compound BDTT-1, except that after removing the solvent under vacuum, the residue was eluted by silica gel column chromatography with petroleum ether-dichloromethane to give a slightly green solid compound, BDTT-2 (0.31 g, yield = 19%). 1 H NMR (600 MHz, CDCl3) δ (ppm) 7.56. (d, J = 6.0 Hz, 1H), 7.50-7.49 (m,3H), 7.34-7.30 (m, 3H), 7.27-7.28 (m, 2H), 3.27 (s, 1H) ( Figure 5 Mass spectrometry: C 18 H 10 The theoretical value of O2S3 is [M].+ : 353.9843; Measured value: 354.9916 ( Figure 6 ).

[0021] 2. Synthesis of compounds BDTT-OR1 and BDTT-OR2 Introducing asymmetric long-chain alkoxy groups onto BDTT yields BDTT-OR, providing substituents for the subsequent formation of asymmetric small molecules, which is a pretreatment at the molecular design level.

[0022] (1) Synthesis of compound BDTT-OR1 Under nitrogen protection, compound BDTT-1 (0.72 g, 2.03 mmol) and zinc powder (0.26 g, 4 mmol) were placed in a 100 mL flask, followed by the addition of an aqueous solution (40 mL) containing 3.2 g NaOH. The mixture was stirred thoroughly and refluxed for 3 hours. Then, 1-bromo-2-decyltetradecane (2.55 g, 6.1 mmol) and tetrabutylammonium bromide (1.9 g, 6.0 mmol) were added to the flask. After reflux overnight, the reaction mixture was poured into cold water and extracted with petroleum ether. The organic phase was dried over Na₂SO₄. After removing the solvent under reduced pressure, the residue was eluted with petroleum ether by silica gel column chromatography to give compound BDTT-OR1 as a pale yellow oil (1.16 g, yield = 85%). 1 H NMR (600 MHz, CDCl3) δ(ppm) 7.63 (d, J = 6.0 Hz,2H), 7.54-7.51 (m, 3H), 7.47-7.44 (m, 1H), 7.37 (d, 1H), 7.25-7.23 (m, 2H),4.36 (d, J = 6.0 Hz, 2H), 2.13-2.09 (m, 1H), 1.74-1.68 (m, 2H), 1.59-1.53 ​​(m,2H), 1.48-1.43 (m, 4H), 1.38-1.24 (m, 32H), 0.89-0.86 (m, 6H)( Figure 7 Mass spectrometry: C 42 H 58 The theoretical value of OS3 is [M]. + : 674.3650; Actual measurement: 675.3722 ( Figure 8 ).

[0023] (2) Synthesis of compound BDTT-OR2 Under nitrogen protection, compound BDTT-2 (0.31 g, 0.87 mmol) and zinc powder (0.17 g, 1.74 mmol) were placed in a 50 mL flask, followed by the addition of 20 mL of an aqueous solution containing 1.6 g of NaOH. The mixture was stirred thoroughly and refluxed for 3 hours. Then, 1-bromo-2-decyltetradecane (1.09 g, 2.60 mmol) and tetrabutylammonium bromide (0.77 g, 2.4 mmol) were added to the flask. After reflux overnight, the reaction mixture was poured into cold water and extracted with petroleum ether. The organic phase was dried over Na₂SO₄. After removing the solvent under reduced pressure, the residue was purified by silica gel column chromatography with petroleum ether to give BDTT-OR2 as a white solid (100 mg, yield = 17%). Due to insufficient yield, subsequent steps were difficult to perform. 1 H NMR (600 MHz, CDCl3) δ(ppm) 7.62-7.55(m, 6H), 7.39 (d, J = 6.0 Hz, 1H), 7.32(d, 1H), 7.25 (d, 1H), 4.28 (d, J = 6.0Hz, 2H), 1.94-1.90 (m, 1H), 1.70-1.65 (m, 2H), 1.53-1.50 (m, 2H), 1.47-1.42(m, 4H), 1.37-1.26 (m, 32H), 0.89-0.86 (m, 6H) ( Figure 9 Mass spectrometry: C 42 H 58 The theoretical value of OS3 is [M]. + : 674.3650; Measured value: 675.3718 ( Figure 10 ).

[0024] 3. Synthesis of compound BDTT-Asy1 BDTT-OR was lithiated and a trialkyltin group was introduced to obtain the tin-modified precursor BDTT-Asy, which is a tin-modified fragment for cross-coupling (Stille).

[0025] Under nitrogen protection, a 1.4 mL n-butyllithium solution (3.45 mmol, n-hexane solution concentration 2.4 mol / L) was prepared. -1The BDTT-OR1 compound (0.92 g, 1.38 mmol) solution dissolved in tetrahydrofuran (50 mL) at -78 °C was slowly added dropwise. The mixture was stirred at -78 °C for 1 hour, then heated to room temperature for 0.5 hours. After cooling back to -78 °C, trimethyltin chloride (4.14 mL, 4.14 mmol, n-hexane solution concentration 1 mol L) was added in a single batch. -1 The mixture was heated to room temperature and stirred overnight. Water was added to the reaction mixture, and the mixture was extracted with petroleum ether. The combined organic extracts were dried over Na2SO4 and the solvent was removed under reduced pressure. The residue was recrystallized from ethanol to give a white solid compound, BDTT-Asy1 (981 mg, yield = 70%). 1 H NMR(500 MHz, CDCl3) δ(ppm) 7.69-7.367 (m, 2H), 7.60-7.56 (m, 2H), 7.51 (d, J =10.0 Hz, 1H), 7.30 (d, 2H), 4.41 (d, J = 5.0 Hz, 2H), 2.14-2.10 (m, 1H), 1.79-1.73 (m, 2H), 1.63-1.59 (m, 2H), 1.53-1.48 (m, 4H), 1.37-1.27 (m, 32H), 0.92-0.88 (m, 6H), 0.49-0.39 (m, 18H) ( Figure 11 ).

[0026] 4. Synthesis of compound SMD-Asy The tin-modified BDTT-Asy was coupled with a rhodanine derivative-containing halogenated acceptor unit at a molar ratio of approximately 1:3 (central donor:acceptor), using Pd(PPh3)4) as a catalyst, to obtain a discrete small molecule SMD-Asy with an A-π-D-π-A conjugated structure with rhodanine end groups.

[0027] Compound BDTT-Asy1 (100 mg, 0.1 mmol) and trithiophene-rhodaninyl (225 mg, 0.3 mmol) were dissolved in dry toluene (10 mL), degassed several times under nitrogen, and then Pd(PPh3)4 (15 mg) was added. After stirring at 110 °C for 24 hours under a nitrogen atmosphere, the mixture was poured into water and extracted with CHCl3. The residue was purified by silica gel chromatography and eluted with a mixture of petroleum ether and dichloromethane (2:1 v / v) to give a black solid compound SMD-Asy (64 mg, yield = 32%). 1H NMR (500MHz, CDCl3) δ(ppm) 7.77. (s, 2H), 7.66 (d, J = 5.0 Hz, 2H), 7.61-7.58 (m, 2H),7.54-7.51 (m, 1H), 7.24-7.20 (m, 4H), 7.15-7.10 (m, 4H), 7.09-7.05 (m, 1H)4.39 (d, J = 5.0 Hz, 2H), 4.13-4.09 (m, 4H), 2.84-2.77 (m, 8H), 2.23-2.20 (m,1H), 1.73-1.66 (m, 12H), 1.34-1.21 (m, 84H), 0.98-0.95 (m, 6H), 0.90-0.81 (m,24H)( Figure 12 ).

[0028] Comparative Example 1 Preparation of SMD-OR with symmetrical alkoxy chains and backbone 1. Synthesis of compound BDT-LOR Under nitrogen protection, compound BDT (740 mg, 3.36 mmol) and zinc powder (553 mg, 8.4 mmol) were placed in a 100 mL flask, followed by the addition of 30 mL of an aqueous solution containing 2.4 g of NaOH. The mixture was stirred thoroughly and refluxed for 3 hours. Then, 1-bromo-2-decyltetradecane (3.5 g, 8.4 mmol) and a catalytic amount of tetrabutylammonium bromide (3.2 g, 10.0 mmol) were added to the flask. After reflux overnight, the reaction mixture was poured into cold water and extracted with petroleum ether. The organic phase was dried over Na₂SO₄. After removing the solvent under reduced pressure, the residue was eluted with petroleum ether by silica gel column chromatography to give compound BDT-LOR as a colorless oil (2.5 g, yield = 85%). ¹H NMR (500 MHz, CDCl₃) δ(ppm) 7.47. (d, J = 5.0 Hz,2H), 7.36 (d, 2H), 4.16 (d, J = 10.0 Hz, 4H), 1.88-1.82 (m, 2H), 1.68-1.48 (m,8H), 1.40-1.25 (m, 72H), 0.90-0.86 (m, 12H) ( Figure 13 ).

[0029] 2. Synthesis of compound BDT-LOR-Sn Under nitrogen protection, a 5.7 mL n-butyllithium solution (9.15 mmol, n-hexane solution concentration 1.6 mol L) was prepared. -1 The compound BDT-LOR (2.5 g, 2.85 mmol) was slowly added dropwise to a solution dissolved in tetrahydrofuran (70 mL) at -78 °C. The mixture was stirred at -78 °C for 1 hour, then heated to room temperature for 0.5 hours. After cooling back to -78 °C, trimethyltin chloride (10 mL, 9.98 mmol, 1 mol / L hexane solution) was added in a single batch. -1 The mixture was heated to room temperature and stirred overnight. Water was added to the reaction mixture, and the mixture was extracted with petroleum ether. The organic extracts were combined, dried over Na₂SO₄, and the solvent was removed under reduced pressure. The residue was recrystallized from ethanol to give a white solid compound BDT-LOR-Sn (2.6 g, yield = 76%). ¹H NMR (500 MHz, CDCl₃) δ (ppm) 7.54–7.45 (m, 2H), 4.18 (d, J = 5.0 Hz, 4H), 1.88-1.83 (m,2H), 1.69-1.61 (m, 5H), 1.54-1.21 (m, 88H), 0.90-0.85 (m, 12H), 0.50 (d, 1H), 0.45 (d, 13H), 0.39 (d, 1H) ( Figure 14 ).

[0030] 3. Synthesis of compound SMD-OR Compound SMD-LOR-Sn (122.19 mg, 0.1 mmol) and trithiophene-rhodaninyl (225 mg, 0.3 mmol) were dissolved in dry toluene (10 mL), degassed several times with nitrogen, and then Pd(PPh3)4 (15 mg) was added. After stirring at 110 °C for 24 hours under argon protection, the mixture was poured into water and extracted with CHCl3. The residue was purified by silica gel chromatography using petroleum ether and dichloromethane (3:1 v / v) as eluent to give a black solid compound SMD-OR (65 mg, yield = 29%). ¹H NMR (500 MHz, CDCl3) δ (ppm) 7.78 (s, 2H), 7.48 (s, 2H), 7.24 (d, 2H), δ (ppm) J= 5.0 Hz 4H),7.17-7.14 (m, 4H), 4.19 (d, J = 5.0 Hz, 4H), 4.13-4.10 (m, 4H), 2.85-2.80 (m,8H), 1.90-1.87 (m, 2H), 1.73-1.67 (m, 12H), 1.41-1.20 (m, 124H), 0.98-0.95(m, 6H), 0.89-0.83 (m, 24H) ( Figure 15 ).

[0031] Performance Characterization 1. Photovoltaic performance (1) Ultraviolet-Visible Absorption Spectroscopy Test Figure 16 b and Figure 16 c shows the normalized UV-Vis absorption spectra of the three donors in the thin film and chloroform solution, namely PM6, SMD-OR and SMD-Asy. The corresponding absorption characteristics are summarized in Table 1.

[0032] like Figure 16 As shown in b, in solid films, compared with polymer PM6, the maximum absorbance values ​​of SMD-OR and SMD-Asy show a trend of enhanced (0-0) absorption peak and weakened (0-0) absorption peak. This (0-0) absorption peak is generally attributed to intermolecular stacking, indicating that the fully asymmetric strategy can effectively suppress molecular aggregation.

[0033] like Figure 16 As shown in c, in solution, the maximum absorption wavelengths of SMD-Asy and SMD-OR show a significant blue shift from 622 nm and 614 nm to 506 nm, respectively. Compared to the polymer donor PM6 (612 nm), their maximum absorption wavelengths both show a significant blue shift. However, the maximum absorption value of SMD-Asy still shows a blue shift compared to its thin film. Figure 17 This indicates that SMD-Asy effectively inhibits intermolecular aggregation. Based on formula (1) and combined with the determination of the thin film absorption initiation point, the optical band gaps of donors PM6, SMD-OR, and SMD-Asy ( E g opt The values ​​were estimated to be 1.80, 1.77, and 1.75 eV, respectively.

[0034] (1) (2) Electrochemical cyclic voltammetry The electrochemical properties of the donor were investigated using electrochemical cyclic voltammetry (CV). The cyclic voltammetry curves are shown below. Figure 18 As shown. The results are summarized in Table 1. Figure 16As shown in d, the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels of the small molecule donors (SMD-OR and SMD-Asy) are slightly higher than those of the benchmark polymer PM6.

[0035] (3) Fabrication and device performance of organic solar cells Binary and ternary devices are fabricated using conventional structures. The conventional layered structure is ITO / PEDOT:PSS / active layer / PDINN / Ag. Specifically, in this embodiment, the active layer is PM6:Y6, PM6:SMD-Asy:Y6, or PM6:SMD-OR:Y6.

[0036] Current density-voltage (NDV) in binary and ternary systems JV The curves and their corresponding photovoltaic parameters are as follows: Figure 19 As shown in a and Table 2. After optimization, the optimal mass ratio of SMD-Asy in the PM6:Y6 system for constructing the active layer was determined to be 0.95:0.05:1.2 (i.e., PM6:SMD-Asy:Y6). The binary organic solar cell based on the reference PM6:Y6 active layer exhibited a PCE of 15.57% and a short-circuit current density (…). J SC The value is 25.33 mA cm. -2 Open circuit voltage ( V OC The voltage is 0.86 V, and the fill factor (FF) reaches 71.69%. In PM6:SMD-OR:Y6-based ternary devices, whether 5% or 10% of the small molecule is added, it has an effect on... J SC , V OC The improvement in FF value is very limited, and when the doping concentration reaches 10%, its performance is even lower than that of binary devices. In contrast, the optimized PM6:SMD-Asy(5%):Y6 ternary device exhibits a higher JSC (26.23 mA cm⁻¹). -2 The device achieves higher PCE (16.88%) by increasing the FF (75.93%) and FF (75.93%). The corresponding external quantum efficiency (EQE) of the device is as follows: Figure 19 As shown in b.

[0037] Table 1 Basic properties of donor molecules

[0038] Note: a) Calculated based on the absorption initiation wavelength of the compound in the thin film; b) Determined by electrochemical cyclic voltammetry; c) Calculated based on the highest unoccupied molecular orbital energy level and optical band gap.

[0039] Table 2 Photovoltaic performance characteristics

[0040] Note: a) Values ​​for the highest PCE device, the average of the 10 devices listed in parentheses; b) Values ​​derived from EQE spectral integration.

[0041] To determine the impact of small molecule introduction on carrier mobility in organic solar cells, the charge transport characteristics of organic solar cells were evaluated using the space charge confinement current method. Figure 20 The hole mobility was calculated. μ h ) and electron mobility ( μ e ), PM6:Y6, PM6:SMD-OR(5%):Y6, SMD-OR(10%):Y6, PM6:SMD-Asy(5%):Y6 and PM6:SMD-Asy(10%):Y6 μ h The values ​​are 3.72 × 10 -4 3.76×10 -4 3.74×10 -4 3.26×10 -4 and 3.11×10 - 4 cm 2 V -1 s -1 . PM6:Y6, PM6:SMD-OR(5%):Y6, SMD-OR(10%):Y6, PM6:SMD-Asy(5%):Y6 and PM6:SMD-Asy(10%):Y6 μ e The values ​​are 2.74 × 10 -4 3.45×10 -4 2.20×10 -4 3.10×10 -4 and 2.29×10 -4 cm 2 V -1 s -1 . PM6:Y6, PM6:SMD-Asy(5%):Y6, PM6:SMD-Asy(10%):Y6, PM6:SMD-OR(5%):Y6 and PM6:SMD-OR(10%):Y6 μ h / μ e The values ​​were 1.36, 1.09, 1.70, 1.05, and 1.40, respectively. Among them, the PM6:SMD-Asy(5%):Y6 mixture had the most balanced... μ h / μ e The value indicates that the hybrid thin film can form an excellent electron transport channel to improve device efficiency.

[0042] To determine the charge recombination characteristics, the short-circuit current density in organic solar cells was compared ( J SC ) on light intensity ( P light Dependence on ). For example, Figure 21 As shown, PM6:Y6, PM6:SMD-OR(5%):Y6, SMD-OR(10%):Y6, PM6:SMD-Asy(5%):Y6 and PM6:SMD-Asy(10%):Y6 The values ​​were 0.93, 0.94, 0.94, 0.98, and 0.92, respectively. Among them, PM6:SMD-Asy(5%):Y6 The value is the largest among these hybrid films, indicating that the addition of SMD-Asy can effectively suppress charge recombination. These results strongly confirm the aforementioned findings regarding the improvement of short-circuit current density (…). J SC The conclusions regarding the fill factor (FF) and the fill factor (FF).

[0043] 2. Tensile properties (1) Density Functional Theory (DFT) Analysis Density functional theory (DFT) analysis at the B3LYP(6-31G(d,p)) level was performed using the Gaussian 16 program, revealing the optimized geometries of the small molecule donors (SMD-OR and SMD-Asy) (e.g. Figure 16 (See e). To simplify calculations, all long alkyl chains were substituted with methyl groups. Compared to SMD-OR, each dihedral angle between thiophene rings in SMD-Asy was significantly increased. Larger dihedral angles between thiophene rings are beneficial for reducing molecular aggregation, indicating that SMD-Asy is more likely to improve the morphology, miscibility, and stretchability of the blend film compared to SMD-OR. This result is consistent with the trend of reduced aggregation shown by UV-Vis spectroscopy, and the improved morphology of the blend film can be further verified by grazing incidence wide-angle X-ray scattering (GIWAXS), atomic force microscopy (AFM), and transmission electron microscopy (TEM).

[0044] (2) Microscopic morphological characteristics of blended films The effects of asymmetric side chains and main chains on the microstructure of the active layer were analyzed using atomic force microscopy (AFM), transmission electron microscopy (TEM), and GIWAXS measurements (e.g., Figure 22 , Figure 23 (As shown in Table 3). AFM height image ( Figure 22 a) shows that the surface roughness values ​​of the ternary PM6:SMD-OR:Y6 and PM6:SMD-Asy:Y6 films are 1.04 and 0.97 nm, respectively, which are higher than those of the binary PM6:Y6 film (0.88 nm), indicating that SMD-Asy, as the third component, is more conducive to the formation of smooth blend films than SMD-OR. The corresponding transmission electron microscope images (…) Figure 22 b) Similarly, it is shown that the ternary PM6:SMD-Asy:Y6 hybrid film is superior to PM6:SMD-OR:Y6 and PM6:Y6 films in reducing phase separation and improving the miscibility of the active layer. This indicates that SMD-Asy, with its asymmetric side chains and main chain, can improve D / A compatibility and promote a more uniform distribution of donor and acceptor compared to the symmetric SMD-OR, thus forming a more uniform blend region. These results help enhance the mechanical properties of the blend film, promote exciton dissociation and charge transfer, and thus increase the open-circuit voltage ( ). J SC ) and fill factor (FF).

[0045] Table 3 Detailed parameters obtained by wide-angle X-ray scattering (GIWAXS)

[0046] Measurement by wide-angle incident X-ray scattering (GIWAXS) Figure 22 c and Figure 22 d) The crystal structure and microstructure of the blended thin films were studied to gain a deeper understanding of SMD-Asy materials with asymmetric side chain and main chain effects. Figure 22 c and Figure 22 Figure d shows the two-dimensional GIWAXS spectra and their corresponding one-dimensional line profile spectra. In the two-dimensional GIWAXS spectra, all three blend films exhibit (010) π-π diffraction patterns in both the in-plane (IP) and out-of-plane (OOP) directions, while maintaining an upward-facing stacked structure. The crystallinity of the PM6:SMD-Asy:Y6 blend film is significantly lower than that of the other blend films, which can be verified by the scattering peaks in the OOP direction. The coherence length of the (010) peak in the OOP direction is calculated using the Scherrer equation. L c The relative grain sizes of the three hybrid films were compared, and the results are shown in Table 3.

[0047] Compared to PM6:SMD-Asy:Y6, PM6:Y6 blend films have... L c(010) The value increased significantly; however, after introducing SMD-Asy with asymmetric side chains and main chains, the ternary blends showed a significant increase. L c(010)The value further decreased, indicating that the introduction of SMD-Asy can reduce grain size and improve the morphology of the blend film. The three blend films... d 010 The similar values ​​(≈3.84 Å) indicate that the PM6:SMD-Asy:Y6 system with close intermolecular packing can enhance π-π packing, thereby promoting charge generation and transport. These results demonstrate that introducing SMD-Asy with asymmetric side chains and a main chain can effectively disrupt molecular packing to improve the morphology of the blend film, while retaining a large amount of microcrystalline structure to enhance π-π packing, thus improving the photovoltaic performance and mechanical properties of the blend film.

[0048] (3) Mechanical properties of the active layer Cracking strain rate was used to evaluate the mechanical properties of blended films, such as... Figure 24 As shown, the blended thin film was stretched onto a polydimethylsiloxane (PDMS) substrate, and crack formation was observed under an optical microscope as strain increased. Crack propagation and strain hinder charge transfer between electrodes, thus negatively impacting device performance. Therefore, a high crack initiation strain rate is crucial for high-performance stretchable organic solar cells.

[0049] The results show that the superior morphology and structure significantly improve the mechanical properties of the blend film. The crack initiation strain of the PM6:SMD-Asy:Y6 blend film is significantly higher than that of the control groups PM6:Y6 and PM6:SMD-OR:Y6 blend films, which is attributed to the reduced grain size and crystallinity. The stretchability of this blend film is similar to... L c(010) The crystal orientation values ​​show the opposite trend, indicating that excessively large grain size and reduced crystallinity not only hinder the formation of good morphology, but also weaken the mechanical properties of the blend film. Smaller grains are more evenly distributed in the amorphous region, thus more effectively offsetting tensile stress during stretching.

[0050] In summary, this invention designed and synthesized a fully asymmetric small molecule donor, SMD-Asy, with asymmetric side chains and a main chain. This SMD-Asy was used as the third component in the PM6:Y6 active layer of T-OSCs. SMD-Asy effectively improved morphology and suppressed intermolecular aggregation, resulting in a smooth blend film. Simultaneously, it reduced grain size while maintaining a certain degree of crystallinity. Compared to PM6:Y6 devices (15.57%), the SMD-Asy-based ternary device exhibited higher PCE (16.88%) and better performance. J SCCompared with PM6:Y6 blend film, the SMD-Asy blend film PM6:SMD-Asy:Y6 significantly improved the morphology and crystal size, allowing small molecules to be distributed in the amorphous region, thereby significantly enhancing the stretchability of the blend film. The cracking strain rate of PM6:SMD-Asy:Y6 blend film is higher than 10%.

[0051] 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 fully asymmetric small molecule donor, SMD-Asy, characterized in that: The molecule contains a BDTT core with a π-conjugated backbone, with rhodanine derivatives on both sides. The side chains and main chain structures are asymmetrically distributed, and its molecular structure is shown in formula (Ⅰ). （Ⅰ）。 2. A method for preparing the fully asymmetric small molecule donor SMD-Asy as described in claim 1, characterized in that, Includes the following steps: (1) Construction of BDTT core: a Grignard reagent was prepared by reacting bromobenzene with magnesium shavings under an inert atmosphere, and the Grignard reagent was reacted with thiophenebenzodithiophene-4,9-dione by addition reaction. The BDTT intermediate was obtained by hydrolysis and extraction. The molecular structure of the BDTT intermediate is shown in formula (II). （Ⅱ） (2) Introducing asymmetric alkoxy substituents: The BDTT intermediate is reduced and activated under alkaline conditions, and then alkylated with long-chain haloalkanes under the action of a phase transfer catalyst to obtain BDTT-OR compounds with long-chain alkoxy substituents. The molecular structure of the BDTT-OR compound is shown in formula (III). （Ⅲ） (3) Construction of tin-modified precursor: The BDTT-OR compound was reacted with an organolithium reagent under an inert atmosphere and low temperature to form a lithiation intermediate, and then reacted with an organotin chloride reagent to introduce a trialkyltin group to obtain the tin-modified precursor BDTT-Asy. The molecular structure of the BDTT-Asy is shown in formula (IV). （Ⅳ） (4) Stille coupling: The BDTT-Asy was coupled with a rhodanine derivative halogenated acceptor unit in the presence of a palladium catalyst, and the fully asymmetric small molecule donor SMD-Asy was obtained by extraction and purification.

3. The preparation method according to claim 2, characterized in that: The phase transfer catalyst mentioned in step (2) is tetrabutylammonium bromide.

4. The preparation method according to claim 2, characterized in that: The organolithium reagent mentioned in step (3) is n-butyllithium.

5. The preparation method according to claim 2, characterized in that: The palladium catalyst mentioned in step (4) is Pd(PPh3)4.

6. The preparation method according to claim 2, characterized in that: In step (4), BDTT-Asy is coupled to a rhodanine derivative-containing halogenated acceptor unit at a molar ratio of 1:2.5 to 1:

3.

7. An application of a fully asymmetric small molecule donor, SMD-Asy, characterized in that: The SMD-Asy described in claim 1 is doped as a third component into the active layer composed of polymer donor PM6 and non-fullerene acceptor Y6 to form a PM6:SMD-Asy:Y6 ternary active layer.

8. The application according to claim 7, characterized in that: The doping amount of the SMD-Asy is 1~10% by mass.

9. An electronic device, characterized in that: The electronic device comprising the PM6:SMD-Asy:Y6 ternary active layer as described in claim 7 has a PCE higher than 16.5%.

10. A blended thin film, characterized in that: The blended film includes PM6, Y6 and the SMD-Asy of claim 1, and the cracking strain rate of the blended film is higher than 10%.

Images