Continuous gradient dyeing process for fiber flexible dye-sensitized cell photo-anode and application

Abstract

The application provides a continuous gradient dye sensitization process for a fibrous flexible dye-sensitized solar cell photoanode and application thereof, and comprises the following steps: S1. continuously unwinding fibers coated with a porous titanium dioxide coating on the surface; S2. the continuously unwound fibers are sequentially and continuously passed through multiple closed immersion tanks for gradient dyeing, and the concentration of dye solution in the multiple closed immersion tanks increases along the direction of fiber passing; S3. the fibers after completing the gradient dyeing are dried and wound. The application proposes a continuous gradient dye sensitization process for the technical bottleneck of uneven dye adsorption and poor performance consistency in the batch sensitization process of the fibrous flexible solar cell photoanode. By constructing a multi-stage closed concentration gradient system, the fiber electrode is repeatedly immersed in different concentrations of dye solution, the adsorption effect is enhanced layer by layer by using the cohesion of the dye, and uniform and controllable adsorption of the dye molecules on the surface of the TiO2 coating is realized.

Description

Technical Field

[0001] This invention belongs to the field of flexible dye-sensitized solar cell fabrication technology, and in particular to a continuous gradient impregnation sensitization process for the photoanode of a fibrous flexible dye-sensitized solar cell and its application. Background Technology

[0002] Flexible dye-sensitized solar cells (Flexible Dye-Sensitized Solar Cells, or Flexible DSSCs) are a new generation of photovoltaic devices with outstanding advantages such as light weight, flexibility, woven design, and excellent photoelectric conversion performance under low light conditions. They show broad application prospects in wearable electronic devices, smart fabrics, and portable energy systems. Among them, fibrous flexible dye-sensitized solar cells use one-dimensional metal wires as the conductive substrate, with a porous titanium dioxide (TiO2) film coated on its surface to form the photoanode. After dye sensitization treatment, it is assembled with the counter electrode to form a complete device, possessing both good mechanical flexibility and photoelectric conversion function. Currently, the core wire of the photoanode in fibrous flexible dye-sensitized solar cells is mostly made of titanium wire. After high-temperature annealing, a porous TiO2 coating that is firmly bonded to the metal substrate can be formed on the surface of the titanium wire. This coating has a large specific surface area, which can effectively adsorb dye molecules, thereby achieving light capture and electron injection. Because the titanium wire core wire provides the necessary mechanical support, and the annealed TiO2 coating is tightly bonded to the substrate, the photoanode has a certain degree of flexibility. However, it is crucial to ensure that the coating does not peel off or crack during the bending process. This places stringent requirements on the subsequent dye sensitization process, meaning that excessive mechanical stress or coating damage must not be applied to the photoanode during sensitization. In existing technologies, the dye sensitization of fibrous photoanodes typically employs a static, batch-based immersion method: the rolled-up fiber electrode is immersed entirely in a solution containing dye molecules, allowed to stand for a certain period (usually 12–48 hours) for adsorption, and then removed and dried. This traditional process reveals the following key technical shortcomings in mass production: (1) Poor uniformity of dye adsorption. During the static immersion process, the outer fibers of the rolled fibers preferentially contact the high-concentration dye solution and quickly complete the adsorption, while the inner fibers are tightly wrapped, and the dye molecules need to go through a longer diffusion path to reach their surface. As the immersion time increases, the dye concentration in the solution gradually decreases, resulting in a significant difference in the concentration environment of the inner and outer fibers, which ultimately leads to obvious color difference between the inner and outer electrodes of the batch and uneven dye loading. (2) Poor consistency of electrochemical performance. Due to the large differences in dye loading among different fibers, the assembled battery exhibits significant fluctuations in key parameters such as short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF), making it difficult to meet the requirements for industrial application in terms of photoelectric conversion efficiency consistency; (3) Low dye utilization. During the static dyeing process, dye molecules mainly migrate to the electrode surface by natural diffusion, resulting in low mass transfer efficiency. A large amount of dye is wasted because it cannot be effectively adsorbed, leading to high production costs. (4) It is difficult to achieve continuous production. Traditional static dyeing is an intermittent operation, which cannot form a continuous production line with the preceding and following processes (such as TiO2 coating preparation, drying, device assembly, etc.). The production efficiency is low, which seriously restricts the large-scale mass production of fibrous flexible dye-sensitized solar cells.

[0003] In summary, existing static batch dyeing techniques cannot effectively solve the problems of uneven dye adsorption, poor photoelectric performance consistency, and low production efficiency in fibrous photoanodes. Therefore, there is an urgent need in this field for a novel sensitization process that can achieve uniform dye adsorption, efficient utilization, and continuous operation. Summary of the Invention

[0004] The main objective of this invention is to address the technical pain points of existing technologies in the mass production of photoanodes for fibrous flexible solar cells, such as uneven dye adsorption, significant color differences between the inside and outside, poor consistency in electrochemical performance, low dye utilization, and inability to achieve continuous production. This invention provides a continuous gradient dyeing and sensitization process. Through the cyclic immersion and gradient progression of dyes of different concentrations in a closed bath, the dye cohesion is enhanced and the adsorption effect of the TiO2 coating is utilized to allow dye molecules to continuously accumulate on the electrode surface and gradually enhance the sensitization effect. Ultimately, this achieves highly uniform dye adsorption in batch photoanodes, a photoelectric conversion efficiency consistency exceeding 90%, and other performance indicators meeting industrialization requirements, providing reliable technical support for the large-scale mass production of fibrous flexible solar cells.

[0005] To achieve the above objectives, the present invention provides a continuous gradient dyeing sensitization process for the photoanode of a fibrous flexible dye-sensitized solar cell, comprising the following steps: S1. Unwind the fiber coated with a porous titanium dioxide coating; S2. The continuously unwound fibers are sequentially and continuously passed through a multi-stage closed immersion tank for gradient dyeing, and the concentration of the dye solution in the multi-stage closed immersion tank increases along the direction in which the fibers pass. S3. After the gradient dyeing is completed, the fibers are dried and then wound up.

[0006] The reaction principle of this invention is as follows: The fibers are sequentially immersed in sealed immersion tanks from level 1 to level N (N≥3) for gradient dyeing. The dye concentration in each tank increases progressively according to a preset gradient, ensuring sufficient contact and adsorption of dye molecules onto the fibers. During this process, low-concentration dye first forms a uniform initial adsorption layer on the titanium dioxide surface. Subsequently, as the fiber enters a higher concentration zone, dye molecules continue to accumulate on top of the existing adsorption layer. Due to the cohesive forces between dye molecules, subsequently adsorbed molecules preferentially combine with already adsorbed molecules, thus forming a dense and uniform dye layer, effectively enhancing the interfacial bonding between the dye and the titanium dioxide coating. After gradient dyeing, the fibers are removed from the sealed tank system and dried, allowing the dye molecules to be firmly fixed on the titanium dioxide surface. They are then neatly wound up by a winding device, and samples are taken to test the dye loading, adsorption uniformity, and photoelectric performance of the assembled cells, ensuring consistent and compliant photoelectric conversion efficiency.

[0007] According to the first aspect of the present invention, at least the following beneficial effects are achieved: This invention employs a multi-stage, sealed immersion tank, with dye solutions of progressively increasing concentrations set along the fiber's direction of travel. Fibers coated with a porous titanium dioxide layer are repeatedly immersed in these concentration gradient zones after continuous unwinding. Dye molecules, aided by intermolecular cohesion, are adsorbed layer by layer onto the titanium dioxide coating surface, significantly improving the uniformity of dye adsorption. By rationally controlling the concentration gradient, the uniformity of immersion is effectively enhanced while ensuring no desorption of the titanium dioxide coating. Testing shows that the coefficient of variation of dye loading within a batch can be controlled within 3%, far lower than the variation level of over 15% in traditional static immersion dyeing processes, significantly eliminating color difference problems between the inner and outer layers of the wound fiber. Due to the uniform and sufficient dye loading, after batch photoanodes are assembled into batteries, the consistency of their photoelectric conversion efficiency reaches over 96%, with a coefficient of variation not exceeding 5%, significantly better than the approximately 80% consistency level of traditional processes; simultaneously, the photoelectric conversion efficiency is improved by approximately 15% to 25% compared to traditional static immersion dyeing processes. In addition, during the gradient dyeing process, the dye is fully adsorbed in each concentration tank, increasing the dye utilization rate by about 20% to 30% and effectively reducing production costs.

[0008] This invention achieves continuous operation throughout the entire process, from unwinding, gradient dyeing, drying to rewinding. The dyeing process time is significantly reduced from the traditional 12-48 hours to 2-4 hours, and it can be seamlessly connected with the preceding and following processes, increasing overall production efficiency by tens of times and fully meeting the needs of large-scale mass production. Throughout the entire process, the fiber operates under low tension, and the bending path is precisely controllable, preventing mechanical damage to the titanium dioxide coating. After a bending radius of 5mm and repeated bending 1000 times, the efficiency retention rate is still no less than 90%, fully maintaining the flexibility of the photoanode. In addition, by adjusting process parameters such as the number of immersion tank stages, concentration gradient differences, fiber travel speed, and number of immersions, it can flexibly adapt to the sensitization requirements of different types of dyes and photoanodes of different specifications, demonstrating strong process adaptability and a wide range of applications.

[0009] According to some embodiments of the present invention, before step S1, the method further includes dust removal and static electricity removal of fibers coated with a porous titanium dioxide coating.

[0010] According to some embodiments of the present invention, the number of stages N in the multi-stage sealed immersion tank is ≥3.

[0011] According to some embodiments of the present invention, the number of stages in the multi-stage sealed immersion tank is 3≤N≤5.

[0012] In some embodiments, the number of stages N in the multi-stage sealed immersion tank is greater than or equal to 3. The number of stages can be, for example, 3, 4, 5, or any integer value between 3 and 5.

[0013] In some embodiments, along the direction of fiber passage, the multi-stage closed immersion tank is sequentially a first-stage closed immersion tank, a second-stage closed immersion tank, and subsequent closed immersion tanks; the molar concentration of the dye solution in the first-stage closed immersion tank is lower than the molar concentration of the dye solution in the second-stage closed immersion tank, and starting from the second-stage closed immersion tank, the molar concentration of the dye solution in the subsequent closed immersion tank increases by 10% to 30% relative to the molar concentration of the previous stage.

[0014] In some embodiments, the molar concentration of the dye solution in the first-stage closed immersion tank is lower than that in the second-stage closed immersion tank, and starting from the second-stage closed immersion tank, the molar concentration of the dye solution in each subsequent closed immersion tank increases by 10% to 30% compared to the previous stage. The increase is, for example, 10%, 15%, 20%, 25%, 30%, or any value between 10% and 30%.

[0015] In some embodiments, the molar concentration of the dye solution in the first-stage closed immersion tank is lower than the molar concentration of the dye solution in the second-stage closed immersion tank, and starting from the second-stage closed immersion tank, the molar concentration of the dye solution in the subsequent-stage closed immersion tank is 10% to 30% higher than that in the previous stage. The increase range is, for example, 10%, 10% to 12%, 28% to 30%, or any value between 10% and 30%.

[0016] In some embodiments, 5 stages of closed immersion tanks are arranged along the traveling direction of the fiber, and the N719 dye concentration of each stage increases sequentially. The dye concentration in the first-stage immersion tank is 0.20 to 0.35 mM, that in the second stage is 0.35 to 0.45 mM, that in the third stage is 0.45 to 0.50 mM, that in the fourth stage is 0.50 to 0.55 mM, and that in the fifth stage is 0.50 to 0.55 mM.

[0017] In some embodiments, 5 stages of closed immersion tanks are arranged along the traveling direction of the fiber, and the molar concentration of the N719 dye solution in each stage increases sequentially. The molar concentration of the dye solution in the first-stage immersion tank is 0.18 to 0.22 mM, that in the second stage is 0.33 to 0.37 mM, that in the third stage is 0.43 to 0.47 mM, that in the fourth stage is 0.48 to 0.52 mM, and that in the fifth stage is 0.53 to 0.57 mM.

[0018] In the present invention, the fibers sequentially enter the 1st to Nth stage immersion tanks (N≥3), and the dye concentration in each tank changes gradually according to a preset gradient. Taking N=5 as an example, the dye concentration gradient is designed as: the first-stage tank is a low-concentration zone (C1), the second-stage tank is a medium-low concentration zone (C2), the third-stage tank is a medium-concentration zone (C3), the fourth-stage tank is a medium-high concentration zone (C4), and the fifth-stage tank is a high-concentration zone (C5), where C1<C2<C3<C4<C5. Each tank is provided with a guide wheel set, which guides the fibers to be repeatedly immersed in the tank for 3 to 5 times, and the single immersion time is controlled at 10 to 30 seconds, so that the dye molecules are fully adsorbed.

[0019] According to some embodiments of the present invention, the dye solution includes at least one of ruthenium-based dyes and organic dyes.

[0020] According to some embodiments of the present invention, the solvent of the dye solution includes a mixed solvent of acetonitrile and tert-butanol.

[0021] According to some embodiments of the present invention, the solvent of the dye solution includes a mixed solvent of acetonitrile and tert-butanol, with a volume ratio of 1:0.5 to 2:1.

[0022] Under the above conditions, acetonitrile ensures that N719 is fully dissolved and maintains suitable diffusion capacity, while tert-butanol reduces solution polarity, inhibits dye stacking and aggregation, and improves the wettability of the solution on the porous titanium dioxide surface, making it easier for dye molecules to enter the depth of the pores rather than prematurely accumulating on the outer surface.

[0023] According to some embodiments of the present invention, in the multi-stage closed immersion tank, the concentration difference between adjacent closed immersion tanks is 10% to 30% of the relative concentration.

[0024] According to some embodiments of the present invention, except for the first stage, the dye concentration difference between adjacent sealed immersion tanks is controlled within 10% to 30% of the relative concentration. Specifically, an N-stage (3≤N≤5) increasing concentration gradient is set: along the fiber travel direction, the N719 dye concentration in each immersion tank increases progressively. This concentration difference range ensures that a uniform initial adsorption layer is fully formed in the low-concentration area, allowing dye molecules to preferentially penetrate deep into the pores of the titanium dioxide coating; it also allows dye molecules in the subsequent high-concentration area to be orderly superimposed layer by layer on the surface of the initial adsorption layer under the action of intermolecular cohesion, avoiding insufficient gradient effect due to too small a difference, or adsorption abrupt changes and local non-uniformity due to too large a difference. Through the above gradient setting, the uniformity and density of dye adsorption are significantly improved, achieving a batch-to-batch photoelectric conversion efficiency consistency of over 90%, while increasing dye utilization by approximately 20% to 30%, and enhancing the interfacial bonding force between the dye and the titanium dioxide coating.

[0025] According to some embodiments of the present invention, the immersion tank is provided with a set of guide wheels arranged alternately in the upper and lower parts to guide the fiber to be repeatedly immersed in the tank 3 to 5 times.

[0026] According to some embodiments of the present invention, the linear velocity of the fiber is 0.5 to 5 m / min.

[0027] According to some embodiments of the present invention, the drying process includes hot air or infrared heating at a temperature of 60–80°C for 2–5 minutes.

[0028] According to some embodiments of the present invention, in the fiber unwinding step, the unwinding tension is 0.3 to 1.0 N.

[0029] Under the above conditions, the tension window keeps the fiber running straight during unwinding, grooving, and winding, preventing slack slippage and wrinkling around the guide rollers, and also preventing excessive tension from tearing the porous titanium dioxide coating or peeling it off from the titanium wire substrate.

[0030] The present invention also proposes a fibrous flexible dye-sensitized solar cell photoanode, which is prepared by the process described above.

[0031] The technological innovations of this invention are mainly reflected in the following aspects: Firstly, at the process level, this invention proposes for the first time a continuous gradient immersion sensitization process, completely breaking the inherent mode of traditional static single-concentration immersion dyeing. By setting up a closed immersion tank with multiple levels of progressively increasing concentrations, the fibrous photoanode is sequentially passed through dye solutions of different concentrations, achieving layer-by-layer superposition and uniform adsorption of dye molecules on the fiber surface, fundamentally solving the industry problem of uneven adsorption between inner and outer layers during batch immersion dyeing.

[0032] Secondly, regarding the adsorption mechanism, this invention fully utilizes the cohesive forces between dye molecules. The initial adsorption layer formed in the low-concentration region can serve as a seed layer for subsequent high-concentration adsorption, making subsequent dye molecules more inclined to grow and stack on existing adsorption sites rather than randomly scattering, thereby forming a dense and uniform dye layer, which significantly enhances the binding force between dye molecules and the porous titanium dioxide coating.

[0033] Furthermore, in terms of system control, this invention designs a closed multi-stage material tank system, and with the help of an online concentration monitoring and automatic liquid replenishment control unit, it realizes precise gradient control of dye concentration and long-term stable operation, effectively avoiding the problem of decreased adsorption effect caused by the continuous decay of dye concentration in the traditional dyeing process.

[0034] Furthermore, this invention enables continuous operation of the entire process of photoanode from continuous unwinding, gradient dyeing, drying to rewinding, which can be seamlessly connected with the preceding and following processes, greatly improving production efficiency and meeting the needs of large-scale mass production.

[0035] Finally, in terms of flexibility, the fiber maintains low tension throughout the entire process, and the bending path is precisely controlled by the guide wheel assembly, which avoids mechanical damage to the titanium dioxide coating and perfectly matches the flexibility requirements of the bendable photoanode.

[0036] According to some embodiments of the present invention, the fibrous flexible dye-sensitized solar cell photoanode comprises a fiber matrix and a porous titanium dioxide coating formed on the surface of the fiber matrix. The porous titanium dioxide coating has a thickness of 30–35 μm and adsorbs dye, wherein the dye loading is 0.28–0.32 μmol / cm³. 2 . Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the overall structure of the continuous gradient sensitization system of the present invention; reference numerals: 1. Pay-off device; 2. Guide roller; 3. Pressure roller; 4. Dye tank; 5. Temperature control device; 6. Light-proof box; 7. Drying oven; 8. Tension adjustment device; 9. Take-up device; Figure 2This is a schematic diagram of the concentration gradient distribution in the multi-stage closed material tank of the present invention; Figure 3 This is a schematic diagram of the adsorption mechanism of enhanced cohesive forces of dye molecules in this invention; Figure 4 This is a comparison diagram of the dye adsorption uniformity of the embodiments and comparative examples of the present invention. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0040] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of this invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to those described, used, or made of materials in the embodiments of this invention.

[0041] The following are specific examples of the present invention: Example 1 This embodiment provides a continuous gradient dyeing sensitization process for the photoanode of a fibrous flexible dye-sensitized solar cell, specifically as follows: S1. Take a titanium wire photoanodic fiber with a length of 100m, a diameter of 150μm, a surface coated with a porous titanium dioxide coating with a thickness of about 30~35μm and annealed, load it into the unwinding device, adjust the unwinding tension to 0.5N, and continuously unwind it at a constant linear speed of 3.0m / min. S2. Fibers sequentially enter five stages of sealed immersion tanks arranged along the direction of travel, with adjacent tanks separated by a sealed transition zone. Each immersion tank is filled with N719 dye solution (acetonitrile / tert-butanol mixed solvent, volume ratio 1:1) of progressively increasing concentration, with concentration gradients of 0.20 mM, 0.35 mM, 0.45 mM, 0.50 mM, and 0.55 mM. Each immersion tank is equipped with alternating guide rollers to guide the fibers through four immersions, with each immersion lasting 30 seconds. During the dyeing process, online concentration monitoring sensors, replenishment pumps, and a control system maintain a stable dye concentration in each tank in real time, with a control accuracy of ±0.01 mM. S3. After gradient dyeing is completed, the fiber enters the drying device and is dried for 3 minutes under 70°C hot air conditions to fully fix the dye molecules on the surface of the titanium dioxide coating. Then, it is neatly wound up by the winding device.

[0042] The performance of the obtained sensitized photoanode was tested, and the results showed that the average dye loading was 0.32 μmol / cm², and the intra-batch coefficient of variation (CV) was [missing information]. DL =2.5%; it was assembled with a counter electrode made of 0.20 mm diameter titanium wire coated with CNTs to form a 2 cm test cell (using I - / I3 - After electrolysis, the average photoelectric conversion efficiency (8.58%, maximum 8.76%, minimum 8.44%) was obtained by using a solar simulator at 25℃ and 100mW / cm². The coefficient of variation (CV) of the photoelectric conversion efficiency of 40 fibers in the batch was 2.9%, with a consistency of 97.1%. After repeated bending 1000 times at a bending radius of 5mm, the photoelectric conversion efficiency retention rate was 91.3%.

[0043] Figure 1 The process flow for continuous gradient dyeing is presented. The fiber is released by the unwinding device, passes through guide rollers and pressure rollers into a light-proof, temperature-controlled multi-stage dye bath, completes the dyeing process, enters the drying oven, and is finally wound up by the tension regulating device.

[0044] Figure 2 The given information describes the concentration distribution of a multi-stage closed feed trough along the wire feeding direction, with the first stage having the lowest concentration and subsequent stages increasing in concentration, C1 < C2 < C3 < ... < C N The gradient is the difference in dye concentration between different tanks.

[0045] Figure 3 This is a schematic diagram of the adsorption mechanism. The fiber first passes through a low-concentration region, where the dye enters the titanium dioxide pores and forms an initial adsorption layer. When it enters a high-concentration region, subsequent molecules are superimposed on the existing adsorption layer by means of intermolecular cohesive forces, rather than being randomly stacked on the surface.

[0046] Example 2 S1. Take a titanium wire photoanodic fiber with a length of 100m, a diameter of 150μm, a surface coated with a porous titanium dioxide coating with a thickness of about 30~35μm and annealed, load it into the unwinding device, adjust the unwinding tension to 0.5N, and continuously unwind it at a constant linear speed of 3.0m / min. S2. Fibers sequentially enter three stages of sealed immersion tanks arranged along the direction of travel, with adjacent tanks separated by a sealed transition zone. Each immersion tank is filled with N719 dye solution (acetonitrile / tert-butanol mixed solvent, volume ratio 1:1) of progressively increasing concentration, with concentration gradients of 0.20 mM, 0.45 mM, and 0.55 mM. Each immersion tank is equipped with alternating guide rollers to guide the fibers through three repeated immersions, with each immersion lasting 15 seconds. During the dyeing process, online concentration monitoring sensors, replenishment pumps, and a control system maintain a stable dye concentration in each tank in real time, with a control accuracy of ±0.01 mM. S3. After gradient dyeing is completed, the fiber enters the drying device and is dried for 3 minutes under 70°C hot air conditions to fully fix the dye molecules on the surface of the titanium dioxide coating. Then, it is neatly wound up by the winding device.

[0047] The performance of the obtained sensitized photoanode was tested under the same conditions as in Example 1. The results showed that the average dye loading was 0.28 μmol / cm², and the intra-batch coefficient of variation (CV) was [missing information]. DL =12.1%; after assembling it with CNT counter electrodes into a battery, the average photoelectric conversion efficiency was 7.27% (highest 7.91%, lowest 6.56%), the coefficient of variation of photoelectric conversion efficiency CV=9.6%, and the consistency reached 90.4%. Compared with Example 1, due to the large concentration step and lack of a smooth transition stage, the initial adsorption layer in the low concentration region did not spread sufficiently and uniformly before entering the high concentration region prematurely. The dye molecules were forced to stack rapidly and disorderly at high concentrations, and could not achieve orderly and dense accumulation layer by layer by intermolecular cohesion. This resulted in insufficient deep penetration of the titanium dioxide porous coating and premature saturation of the surface adsorption, so the absolute value of the efficiency was slightly reduced. However, the consistency still met the industrialization requirements of more than 90%. After repeated bending 1000 times under a bending radius of 5mm, the photoelectric conversion efficiency was maintained at 83.1%.

[0048] Example 3 S1. Take a titanium wire photoanodic fiber with a length of 100m, a diameter of 150μm, a surface coated with a porous titanium dioxide coating with a thickness of about 30~35μm and annealed, load it into the unwinding device, adjust the unwinding tension to 0.5N, and continuously unwind it at a constant linear speed of 3.0m / min. S2. Fibers sequentially enter five sealed immersion tanks arranged along the direction of travel, with adjacent tanks separated by a sealed transition zone. Each immersion tank is filled with N719 dye solution (acetonitrile / tert-butanol mixed solvent, volume ratio 1:1) of progressively increasing concentration, with concentration gradients of 0.20 mM, 0.30 mM, 0.40 mM, 0.50 mM, and 0.60 mM. Each immersion tank is equipped with alternating guide rollers to guide the fibers through three repeated immersions, with each immersion lasting 15 seconds. During the dyeing process, online concentration monitoring sensors, replenishment pumps, and a control system maintain a stable dye concentration in each tank in real time, with a control accuracy of ±0.01 mM. S3. After gradient dyeing is completed, the fiber enters the drying device and is dried for 3 minutes under 70°C hot air conditions to fully fix the dye molecules on the surface of the titanium dioxide coating. Then, it is neatly wound up by the winding device.

[0049] The performance of the obtained sensitized photoanode was tested, and the results showed that the average dye loading was 0.30 μmol / cm², and the intra-batch coefficient of variation (CV) was [missing information]. DL =8.5%; after assembling it with CNT counter electrodes into a battery, the average photoelectric conversion efficiency was 7.44% (maximum 8.20%, minimum 6.96%), the coefficient of variation of photoelectric conversion efficiency CV=7.6%, and the consistency reached 92.4%. The uniform gradient concentration steps were not fine enough in the high concentration section and the final stage was too high, which led to disordered dye stacking and uneven adsorption. After repeated bending 1000 times under the condition of bending radius of 5mm, the photoelectric conversion efficiency was retained at 87.5%.

[0050] Example 4 S1. Take a titanium wire photoanodic fiber with a length of 100m, a diameter of 150μm, a surface coated with a porous titanium dioxide coating with a thickness of about 30~35μm and annealed, load it into the unwinding device, adjust the unwinding tension to 0.5N, and continuously unwind it at a constant linear speed of 3.0m / min. S2. Fibers sequentially enter five sealed immersion tanks arranged along the direction of travel, with adjacent tanks separated by a sealed transition zone. Each immersion tank is filled with N719 dye solution (acetonitrile / tert-butanol mixed solvent, volume ratio 1:1) of progressively increasing concentration, with concentration gradients of 0.20 mM, 0.26 mM, 0.34 mM, 0.44 mM, and 0.57 mM. Each immersion tank is equipped with alternating guide rollers to guide the fibers through three repeated immersions, with each immersion lasting 15 seconds. During the dyeing process, online concentration monitoring sensors, replenishment pumps, and a control system maintain a stable dye concentration in each tank in real time, with a control accuracy of ±0.01 mM. S3. After gradient dyeing is completed, the fiber enters the drying device and is dried for 3 minutes under 70°C hot air conditions to fully fix the dye molecules on the surface of the titanium dioxide coating. Then, it is neatly wound up by the winding device.

[0051] The performance of the obtained sensitized photoanode was tested, and the results showed that the average dye loading was 0.31 μmol / cm², and the intra-batch coefficient of variation (CV) was [missing value]. DL =7.1%; after assembling it with CNT counter electrodes into a battery, the average photoelectric conversion efficiency was 7.64% (maximum 8.33%, minimum 7.09%), the coefficient of variation of photoelectric conversion efficiency CV=5.7%, and the consistency reached 94.3%. The uniform gradient concentration steps lacked a smooth transition and fine superposition, resulting in premature saturation of the dye surface and slightly insufficient deep penetration. After repeated bending 1000 times under a bending radius of 5mm, the photoelectric conversion efficiency retention rate was 89.6%.

[0052] Comparative Example 1 S1. Take titanium wire photoanode fibers with a length of 100m, a diameter of 150μm, a surface coated with a porous titanium dioxide coating of about 30-35μm thickness and annealed, from the same batch as in Example 1, roll them up and load them as a whole for later use. S2. Immerse the rolled photoanodized fibers in a 0.45mM N719 dye solution (the solvent is a mixture of acetonitrile and tert-butanol, volume ratio 1:1) and let it stand for 48 hours at room temperature in the dark. S3. After the dyeing process is complete, remove the fiber and place it in a drying device. Dry it for 3 minutes under 70°C hot air conditions to fix the dye molecules on the surface of the titanium dioxide coating. Then, roll it up for later use.

[0053] Testing showed that the photoanode prepared using the traditional static dyeing process in Comparative Example 1 had an average dye loading of 0.25 μmol / cm², and an intra-batch coefficient of variation (CV) of [missing value]. DL =15.8%. After assembly into a battery, the average photoelectric conversion efficiency was 6.53% (reaching a maximum of 7.07% and a minimum of only 5.55%). The consistency of photoelectric conversion efficiency was poor, with a coefficient of variation (CV) of 17.6% and an overall consistency of only about 82.4%. In addition, the dye loading of the outer fiber (closer to the solution side) was significantly higher than that of the inner fiber, and a significant color difference could be observed with the naked eye. After repeated bending 1000 times under a bending radius of 5mm, the photoelectric conversion efficiency retention rate was 86.3%.

[0054] The comparative example used a traditional static roll-and-soak method, where the fibers were tightly wound. The outer layer preferentially contacted and rapidly adsorbed the high-concentration dye, while the inner layer mainly relied on slow diffusion, resulting in a significant difference in dye loading between the inner and outer layers. Simultaneously, the solution concentration continuously decreased during prolonged soaking, further exacerbating the uneven adsorption. Therefore, the dye loading was low and inconsistent, ultimately leading to low photoelectric conversion efficiency, large batch performance fluctuations, and noticeable color differences.

[0055] Comparative Example 2 S1. Take a titanium wire photoanodic fiber with a length of 100m, a diameter of 150μm, a surface coated with a porous titanium dioxide coating with a thickness of about 30~35μm and annealed, load it into the unwinding device, adjust the unwinding tension to 0.5N, and continuously unwind it at a constant linear speed of 3.0m / min. S2. Fibers sequentially enter five sealed immersion tanks arranged along the direction of travel, with adjacent tanks separated by a sealed transition zone. Each immersion tank is filled with N719 dye solution (acetonitrile / tert-butanol mixed solvent, volume ratio 1:1) of progressively increasing concentration, with concentration gradients of 0.55mM, 0.50mM, 0.45mM, 0.35mM, and 0.20mM. Each immersion tank is equipped with alternating guide rollers to guide the fibers through four immersions, with each immersion lasting 30 seconds. During the dyeing process, online concentration monitoring sensors, replenishment pumps, and a control system maintain a stable dye concentration in each tank in real time, with a control accuracy of ±0.01mM. S3. After gradient dyeing is completed, the fiber enters the drying device and is dried for 3 minutes under 70°C hot air conditions to fully fix the dye molecules on the surface of the titanium dioxide coating. Then, it is neatly wound up by the winding device.

[0056] The performance of the obtained sensitized photoanode was tested, and the results showed that the average dye loading was 0.22 μmol / cm², and the intra-batch coefficient of variation (CV) was [not specified]. DL =21.3%; it was assembled with a counter electrode made of 0.20 mm diameter titanium wire coated with CNTs to form a 2 cm test cell (using I - / I3 -After electrolysis, the average photoelectric conversion efficiency (PVC) under a solar simulator at 25°C and 100 mW / cm² was 5.24% (maximum 6.19%, minimum 4.53%). The coefficient of variation (CV) of the PPC for 40 fibers in the batch was 22.9%, with a consistency of 77.1%. After repeated bending 1000 times at a bending radius of 5 mm, the PPC retention rate was 61.3%. The reverse dyeing process, starting with a high concentration and then decreasing it, resulted in disordered molecular stacking and failure of cohesive densification due to the excessively high initial dye concentration, leading to reverse desorption upon entering the low concentration region. Simultaneously, the high-concentration solvent intensified the erosion of the porous titanium dioxide coating, and the internal stress generated by the drying shrinkage of the excessively thick adsorption layer also induced localized peeling of the coating. The combined effect of these multiple factors reduced the uniformity of dye adsorption, the effective adsorption capacity, and the stability of the coating structure, resulting in PPC performance and batch-to-batch consistency that were significantly worse than the concentration gradient process.

[0057] Table 1 shows the performance parameters of the embodiments and comparative examples of the present invention. Table 1 presents the photoelectric parameters of the test cells in each embodiment and comparative example. The data for Voc, Isc, Jsc, PCE, FF, and maximum power point in the table correspond to values ​​at 25°C and 100 mW / cm². 2 Open-circuit voltage, short-circuit current, short-circuit current density, photoelectric conversion efficiency, fill factor, and maximum power measured under standard illumination; the last column shows CV. DL It is the coefficient of variation of the total dye loading, used to measure the uniformity of adsorption.

[0058] The increasing concentration gradient breaks down adsorption into two steps: nucleation and growth. Fibers first enter the low-concentration region, where the driving force for dye molecule diffusion is moderate, allowing them to penetrate deep into the pores and form a relatively complete initial adsorption layer; this layer then serves as the growth site for subsequent adsorption. Upon entering a higher concentration region, the dye in the solution tends to stack orderly on the existing adsorption layer through intermolecular cohesion, rather than randomly accumulating on the outer surface. When the concentration steps are dense (Example 1), each step can complete a sufficient penetration and spreading, and deep loading and surface coverage can be established simultaneously, resulting in high dye loading, small batch dispersion, and the highest photoelectric conversion efficiency. When the steps are too wide (Example 2), the initial layer has not yet spread evenly before entering the high-concentration region, the surface layer quickly becomes saturated and closes the pores, internal penetration is insufficient, and efficiency and uniformity decrease accordingly, but the adsorption direction remains correct, so overall it is still superior to the control. Comparative Example 1 uses static roll soaking with a single concentration. Fibers outside the roll are directly exposed to a higher concentration solution and preferentially saturate, while fibers inside the roll can only rely on long-range diffusion; simultaneously, the solution concentration continuously decreases with soaking time, and the inner and outer fibers are always in different concentration fields. The result was low loading, significant internal and external color differences, and large batch-to-batch fluctuations in photoelectric parameters. Comparative Example 2 used a decreasing concentration approach. With an excessively high initial concentration, the dye rapidly and randomly deposited on the surface, prematurely clogging the pore inlets; subsequently, when entering the low-concentration zone, the concentration difference at the solid-liquid interface reversed, causing partial desorption of adsorbed molecules. The swelling and erosion of the porous layer by the high-concentration organic solvent, along with the internal stress generated by the drying shrinkage of the excessively thick adsorption layer, further damaged the coating integrity. Therefore, this pathway simultaneously resulted in losses in adsorption capacity, uniformity, and mechanical stability, with all indicators being the worst.

[0059] Figure 4 Two sets of key parameters are provided to compare the dye adsorption levels and batch uniformity of the various photoanodes. The first set is the dye adsorption capacity, expressed in μmol / cm³. 2 This indicates the actual amount of N719 carried per unit area of ​​the titanium dioxide coating. Examples 1 to 4 show amounts of 0.32, 0.28, 0.30, and 0.31 μmol / cm², respectively, while Comparative Examples 1 and 2 show amounts of 0.25 and 0.22 μmol / cm², respectively. 2 The adsorption amounts of the forward increasing gradient were all higher than those of static whole-roll immersion and reverse gradient, with Example 1 showing the highest amount, indicating that when a low-concentration base is followed by dense step-by-step stacking, the pores are utilized more fully. Comparative Example 2 showed the lowest amount, consistent with the phenomenon that a high-concentration-then-low-concentration gradient leads to surface blockage and reverse desorption. The second set is the coefficient of variation (CV) of the adsorption amount, given as a percentage in the figure, corresponding to the CV in the main text. DLThe coefficient of variation (CV) is used to measure the dispersion of the load among fibers in the same batch; the smaller the value, the more uniform the fiber. Examples 1 to 4 have CVs of 2.5%, 12.1%, 8.5%, and 7.1%, respectively, while Comparative Examples 1 and 2 have CVs of 15.8% and 21.3%, respectively. Example 1 has the gentlest gradient, the most thorough immersion, and the best uniformity; Example 2 has a CV of 12.1% due to an excessively large concentration gradient; Comparative Example 1 has a CV of 15.8% due to different mass transfer conditions inside and outside the roll; Comparative Example 2 has the worst reverse-order dyeing, with a CV of 21.3%.

[0060] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A continuous gradient impregnation sensitization process for the photoanode of a fibrous flexible dye-sensitized solar cell, characterized in that, Includes the following steps: S1. Continuously unwind the fiber coated with a porous titanium dioxide coating; S2. The continuously unwound fibers are sequentially and continuously passed through a multi-stage closed immersion tank for gradient dyeing, and the concentration of the dye solution in the multi-stage closed immersion tank increases along the direction in which the fibers pass. S3. After the gradient dyeing is completed, the fibers are dried and then wound up.

2. The continuous gradient sensitization process according to claim 1, characterized in that, The number of stages N in the multi-stage sealed immersion tank is ≥3.

3. The continuous gradient sensitization process according to claim 1, characterized in that, Along the direction of fiber passage, the multi-stage closed immersion tanks are sequentially a first-stage closed immersion tank, a second-stage closed immersion tank, and subsequent closed immersion tanks. The molar concentration of the dye solution in the first-stage closed immersion tank is lower than that in the second-stage closed immersion tank, and starting from the second-stage closed immersion tank, the molar concentration of the dye solution in the subsequent closed immersion tank increases by 10% to 30% compared to the previous stage.

4. The continuous gradient sensitization process according to claim 1, characterized in that, The immersion tank is equipped with a set of guide wheels arranged alternately up and down to guide the fiber to be repeatedly immersed in the tank 3 to 5 times.

5. The continuous gradient sensitization process according to claim 4, characterized in that, The fiber is immersed for 10 to 30 seconds in each immersion tank.

6. The continuous gradient sensitization process according to claim 5, characterized in that, The linear velocity of the fiber is 0.5 to 5 m / min.

7. The continuous gradient sensitization process according to claim 1, characterized in that, The drying process includes hot air or infrared heating at a temperature of 60–80°C for 2–5 minutes.

8. The continuous gradient sensitization process according to claim 1, characterized in that, In the fiber unwinding step, the unwinding tension is 0.3 to 1.0 N.

9. A fibrous flexible dye-sensitized solar cell photoanode, characterized in that, The fibrous flexible dye-sensitized solar cell photoanode is prepared by any one of claims 1 to 8 using a continuous gradient dyeing sensitization process.

10. The fibrous flexible dye-sensitized solar cell photoanode according to claim 9, characterized in that, It includes a fiber matrix and a porous titanium dioxide coating formed on the surface of the fiber matrix, wherein the thickness of the porous titanium dioxide coating is 30–35 μm. The porous titanium dioxide coating adsorbs dye, and the dye loading is 0.28–0.32 μmol / cm³. 2 .

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