Benzisoindole compound with conjugated polycyclic structure and application of benzisoindole compound

Abstract

The invention relates to the technical field of solar cell preparation, in particular to a benzisoindole compound with a conjugated polycyclic structure and application of the benzisoindole compound. The structural general formula of the compound is as shown in formula I, wherein R1 is benzene ring, thiophene, furan, pyridine, 2-phenyl thiophene, 2-phenyl furan and / or biphenyl, bithiophene and bifuran substituent, and R2 is benzene ring and / or hydrogen. In conclusion, the invention provides a novel material system with high efficiency, high stability and low cost for the exciton splitting type photovoltaic cell, which is hopeful to accelerate breakthrough of the limit of the Porcley-Quinisseria theory and promote the practical development of the third generation solar cell technology.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cell preparation, and more particularly to a benzisoindole compound with a conjugated polycyclic structure and applications thereof. Background Art

[0002] As global energy demand continues to grow, solar energy, one of the most promising clean energy sources, has drawn significant attention for its photovoltaic conversion technology. Despite years of development, photovoltaic devices that convert solar energy into electricity are limited by various energy loss pathways, such as thermalization of high-energy photons. Single-junction solar cells face a Shockley-Queisser limit of 33%, presenting fundamental challenges in increasing their efficiency. With the efficiency of single-junction solar cells, such as those based on perovskites and silicon, approaching the theoretical limit in recent years, overcoming this efficiency bottleneck requires the development of a new generation of photovoltaic conversion technologies.

[0003] In third-generation photovoltaic cells, multi-junction tandem cells can broaden the spectral response through energy-level gradient absorption, but the complex heterojunction growth process leads to high costs. In contrast, exciton engineering strategies based on carrier multiplication are more cost-effective. Singlet fission (SF) technology, in particular, dissociates singlet excitons converted from high-energy photons into two triplet excitons, theoretically raising the upper limit of photoelectric conversion efficiency to 45%. This process effectively suppresses high-energy photon thermal losses through the generation of multiple excitons, while simultaneously multiplying the device photocurrent, providing a new path for single-junction solar cells to break through the Shockley-Queisser theoretical limit. However, existing exciton fission material systems (such as tetracene / pentacene derivatives) suffer from poor photochemical stability and insufficient environmental tolerance, severely limiting device lifespan and industrial application. Developing new organic semiconductor materials that combine efficient exciton fission with excellent stability has become a key scientific challenge in the photovoltaic field. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, one aspect of the present invention is to provide a benzisoindole compound having a conjugated polycyclic structure, the structural formula of which is shown in Formula I below: Formula I; Wherein, R1 is a benzene ring, thiophene, furan, pyridine, 2-phenylthiophene, 2-phenylfuran and / or a biphenyl group, bithiophene, or bifuran substituent, and R2 is a benzene ring and / or hydrogen.

[0005] The compound is any one of the following: .

[0006] Another aspect of the present invention is to provide an application of a benzisoindole compound with a conjugated polycyclic structure, wherein the compound is used to prepare a thin film.

[0007] Preferably, the film is applied to an active layer of a solar cell.

[0008] Preferably, the solar cell structure is ITO / PEDOT:PSS / P3HT / active layer / C60 / Ag.

[0009] Preferably, the film is prepared by vacuum vapor deposition.

[0010] Preferably, the vacuum vapor deposition method is a method of preparing the substrate by vacuum vapor deposition on a sapphire or quartz substrate under vacuum conditions at a constant temperature and deposition rate.

[0011] Preferably, the vacuum pressure is 1×10 −4 ~3×10 −4 Pa.

[0012] Preferably, the constant temperature is 100-200°C, and the deposition rate is 0.3-1 Å / s.

[0013] Preferably, the film thickness is 80-100 nm.

[0014] The beneficial effects of the present invention are as follows: Breaking through the theoretical efficiency limit: High-energy photons are converted into two triplet excitons through exciton splitting technology, effectively suppressing the thermal loss of high-energy photons and doubling the device photocurrent. The theoretical upper limit of photoelectric conversion efficiency is increased to 45%, providing a practical path for a substantial improvement in single-junction solar cell devices.

[0015] Excited state energy level design: The designed organic compound has a unique excited state energy level relationship, that is, the singlet state energy level is approximately equal to the triplet state energy level ( E (S1) ≈ 2 E (T1)), ensuring that singlet excitons can efficiently split into triplet excitons in a very short time (~ps), satisfying the thermodynamic spin-allowed conditions and significantly improving the utilization rate of light energy.

[0016] Material stability optimization: To address the poor photochemical stability of existing exciton fission materials (such as tetracene / pentacene derivatives), new organic semiconductor materials have been developed that combine high exciton fission efficiency with excellent environmental tolerance, laying the foundation for long-term stable operation and industrial application of devices.

[0017] Significant cost-effectiveness: Compared with the complex heterojunction growth process of multi-junction stacked cells, the exciton engineering strategy can achieve spectral response broadening through molecular design, greatly reducing preparation costs and having greater commercial potential.

[0018] Strong technical compatibility: This material system can be adapted to the structure of single-junction solar cells and can achieve efficiency leaps without the need for multi-layer stacking, providing an innovative solution for the next generation of high-efficiency, lightweight photovoltaic devices.

[0019] In summary, the present invention provides a new material system for exciton-splitting photovoltaic cells that combines high efficiency, high stability and low cost, which is expected to accelerate the breakthrough of the Shockley-Queisser theoretical limit and promote the practical development of third-generation solar cell technology.

[0020] Additional aspects and advantages of the invention will become apparent from the description which follows, or may be learned by practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which: Figure 1 The absorption and emission spectrum of the molecular solution and the thin film absorption spectrum of the structural formula 11 in Example 3 of the present invention are shown; Figure 2 is the transient absorption spectrum of the molecule of structural formula 11 in solution in Example 3 of the present invention; Figure 3 is the transient absorption spectrum of the molecular film of structural formula 11 in Example 3 of the present invention; Figure 4 This is the triplet absorption spectrum of Example 3 of the present invention. DETAILED DESCRIPTION

[0022] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0023] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from the description. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0024] Example 1: Thin film preparation and characterization of the molecule of structural formula 1: Preparation of benzisoindole molecular film: at 1×10 −5 Under vacuum conditions of 0.1 mbar, a molecular film of structure 1 was prepared by vacuum vapor deposition on a sapphire or quartz substrate at a rate of 0.3 Å / s. The thickness of the evaporated molecular film was 80-100 nm according to the step profiler.

[0025] Example 2: Thin film preparation and characterization of the molecule of structural formula 2: Preparation of benzisoindole molecular film: at 1×10 −5 Under vacuum conditions of 0.1 mbar, a molecular film of structure 2 was prepared by vacuum vapor deposition on a sapphire or quartz substrate at a rate of 0.3Å / s. The step profiler detected that the evaporated molecular film was 80-100nm.

[0026] Example 3: Thin film preparation and characterization of the molecule of structural formula 11: Preparation of benzisoindole molecular film: at 1×10 −5 Under vacuum conditions of 0.1 mbar, a molecular film of structural formula 11 was prepared by vacuum vapor deposition on sapphire or quartz substrates at a rate of 0.3 Å / s. The step profiler detected that the evaporated molecular film was 80-100 nm.

[0027] like Figure 1 As shown, the absorption and emission spectra of the solution and film of the molecule of Structural Formula 11 show that the maximum absorption peak of the molecule of Structural Formula 11 in solution is at 536 nm, and the maximum emission peak is at 575 nm. The maximum absorption peak of the film of the molecule of Structural Formula 11 is significantly red-shifted compared to the solution, with an absorption band edge at 590 nm and an optical band gap of approximately 2.10 eV.

[0028] The transient absorption spectra of the molecule of structural formula 11 in solution and film are as follows: Figure 2 As shown, the molecule of structure 11, dissolved in dichloromethane, was photoexcited at 450 nm. A ground-state bleaching signal (GSB) was observed near 545 nm, along with an excited-state absorption band (ESA) at 650-820 nm. This initial signal decayed over time, but its peak shape remained unchanged until the time window was reached, at which point the excited-state absorption signal shifted. Global fitting analysis revealed that the decay process in solution was primarily due to radiative deactivation of singlet excitons.

[0029] like Figure 3As shown, the transient absorption spectrum of a thin film of the molecule of formula 11 differs from the solution spectrum. A ground-state bleaching signal appears at 600 nm, followed by an excited-state absorption signal in the near-infrared region between 650 and 890 nm. This signal is characterized by the rapid decay of the excited singlet state, with a lifetime of less than 100 ps, ​​significantly shorter than the 4.1 ns lifetime in solution. Over time, a new excited-state absorption signal appears at 558 nm, extending beyond the 5.0 ns detection window. Nanosecond transient absorption spectroscopy measurements were performed using parallel samples to track the decay dynamics of long-lived transient species. The signal line shape in the nanosecond transient spectrum overlaps well with the femtosecond transient absorption spectrum, and the signal persists into the microsecond timescale, indicating that the primary terminal species formed by photoexcitation is a triplet exciton. Compared to solution, the singlet excited-state lifetime in the thin film is significantly shortened, and no significant fluorescence emission is observed, suggesting the presence of a more efficient non-radiative deactivation process. Comprehensive characterization and analysis led to the conclusion that these benzisoindole derivatives mainly undergo singlet exciton fission in the thin film state to generate long-lived triplet states, and the measured triplet lifetime reaches 2.3µs.

[0030] Compared with the solution, the lifetime of the singlet excited state in the thin film state is greatly shortened, and there is no fluorescence, which indicates the existence of other more effective non-radiative deactivation processes. Comprehensive characterization and analysis lead to the conclusion that these isoindole compound derivatives mainly undergo singlet exciton fission process in the thin film state to generate long-lived triplet states, and the measured triplet lifetime reaches 2.3µs.

[0031] The triplet yield of the derivative film was estimated by quantifying the ground-state bleaching signal in the nanosecond transient spectroscopy data and correlating this exciton density with the exciton density calculated due to laser power, spot size, film thickness, and absorption, as follows: Calculate the excitation density:

[0032] Examine the actual ground-state bleaching signal required to generate a triplet absorption spectrum from the spectrum and compare it to the calculated ground-state bleaching signal. To more rigorously quantify this analysis, we can focus on regions where the ground-state bleaching spectrum has strong features that would yield plausible triplet absorption spectra (e.g. Figure 4 (as shown). This approximate measurement of the ground-state bleaching signal required for triplet absorption spectroscopy provides the triplet yield. Using this method, the triplet yield of the molecule of formula 11 was estimated to be 174%, a high triplet yield that paves the way for the successful fabrication of organic photovoltaic devices based on singlet exciton fission.

[0033]

[0034] This material was applied to the active layer of a solar cell with a device structure of ITO / PEDOT:PSS / P3HT / active layer / C60 / Ag. The anode system comprises a transparent conductive electrode, ITO, and a work-function-matched hole-transport layer, PEDOT:PSS. Among the key functional layers, P3HT serves as an exciton blocker with a triplet energy of 1.5 eV, and the active layer utilizes SF materials for exciton multiplication. C60 serves as an electron acceptor material, while the cathode system comprises a metal electrode, Ag, to collect electrons. By combining this active layer with acceptor materials such as C60 to create a photovoltaic device, efficient triplet exciton dissociation is achieved.

[0035] Using the calculated experimental values, the triplet yield can be estimated. Using this method, the triplet yield of the molecule of structural formula 11 can be estimated to be 174%, which is a relatively high triplet yield, providing the possibility for organic photovoltaic devices based on singlet exciton fission.

[0036] This invention also provides a framework for designing and synthesizing exciton-splitting material performance, and its molecular extension. Its key characteristic is that its singlet excited state energy (2.2-2.5 eV) is significantly higher than twice its triplet excited state energy (~1.0 eV). This unique energy level relationship is the thermodynamic basis for the spin-allowed singlet fission process, ensuring that incident high-energy photons can efficiently split into two triplet excitons within an extremely short time (~ps). Due to the suitable triplet energy level, high stability, and high triplet yield, it is expected to break the Shockley-Queisser theoretical limit, increasing the photoelectric conversion efficiency of single-junction solar cells from 33% to 45%, paving the way for the development of exciton-splitting photovoltaic cells.

[0037] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A benzisoindole compound having a conjugated polycyclic structure, characterized in that: The general structural formula of the compound is shown in Formula I below: Formula I; Wherein, R1 is a benzene ring, thiophene, furan, pyridine, 2-phenylthiophene, 2-phenylfuran and / or a biphenyl group, bithiophene, or bifuran substituent, and R2 is a benzene ring and / or hydrogen.

2. The benzisoindole compound having a conjugated polycyclic structure according to claim 1, wherein: The compound is any one of the following: 。 3. The use of a conjugated polycyclic benzisoindole compound according to claim 1, characterized in that: The compound is used for preparing a thin film.

4. The use of a conjugated polycyclic benzisoindole compound according to claim 3, characterized in that: The film is applied to the active layer of a solar cell.

5. The use of a conjugated polycyclic benzisoindole compound according to claim 4, characterized in that: The solar cell structure is ITO / PEDOT:PSS / P3HT / active layer / C60 / Ag.

6. The use of a conjugated polycyclic benzisoindole compound according to claim 3, characterized in that: The film is prepared by vacuum vapor deposition.

7. The use of a conjugated polycyclic benzisoindole compound according to claim 6, characterized in that: The vacuum vapor deposition method is to prepare the product by vacuum vapor deposition on a sapphire or quartz substrate under vacuum conditions at a constant temperature and deposition rate.

8. The use of a conjugated polycyclic benzisoindole compound according to claim 7, characterized in that: The vacuum pressure is 1×10 −4 ~3×10 −4 Pa.

9. The use of a conjugated polycyclic benzisoindole compound according to claim 7, characterized in that: The constant temperature is 100-200° C., and the deposition rate is 0.3-1 Å / s.

10. The use of a conjugated polycyclic benzisoindole compound according to claim 3, characterized in that: The film thickness is 80-100 nm.

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