Optical sensor based on composite conductive film

Abstract

The invention discloses an optical sensor based on a composite conductive film, and belongs to the technical field of optical sensors, the sensor comprises a flexible substrate, a composite conductive film and a packaging layer, and the composite conductive film integrates functions of an electrode and an optical active layer and is formed by combining a transparent conductive network and a photosensitive composite layer; the transparent conductive network is locally embedded into the flexible substrate, the surface of the transparent conductive network is covered with an inorganic oxide protective layer, the photosensitive composite layer is a hybrid compound formed by core-shell quantum dots and a secondary doped conductive polymer through hydrogen bonds, and a gradient energy level buffer layer is further arranged between the core-shell quantum dots and the secondary doped conductive polymer; a micro-lens array is arranged on the surface of the flexible substrate, and the packaging layer is doped with organic dye to achieve the light filtering function. According to the invention, the charge transmission path is shortened through integrated structural design, multi-component collaborative optimization is combined, the response speed, environmental stability and weak light detection capability of the sensor are remarkably improved, the preparation process is simplified, and the sensor is suitable for flexible wearable equipment, biological detection and other scenes.

Description

Technical Field

[0001] This invention relates to the field of optical sensor technology, and in particular to an optical sensor based on a composite conductive thin film. Background Technology

[0002] As a core sensing element in modern information society, the performance of optical sensors directly determines the technological level of many systems, including imaging, communication, biological detection, and environmental monitoring. In recent years, optical sensors based on composite conductive thin films have become a research hotspot in academia and industry due to their enormous potential in flexibility, large-area fabrication, and cost control. These sensors typically combine photoactive materials (such as quantum dots and perovskites) with conductive materials (such as metal nanowires, graphene, and conductive polymers) to achieve both light absorption and charge conduction functions within a single thin film.

[0003] However, existing technological approaches still face a series of critical technical challenges in transitioning from the laboratory to industrial applications, severely limiting their performance ceiling and reliability: First, in terms of the material system, the simple physical blending of photoactive and conductive materials results in a fragile interface and poor energy level matching. This leads to severe interfacial charge recombination and transport losses, which not only makes it difficult to improve the sensor's response speed but also causes high dark current, significantly compressing the device's dynamic range and reducing the signal-to-noise ratio. Simultaneously, the inherent environmental sensitivity of high-performance photoactive materials (such as perovskite quantum dots) and the electrochemical migration and oxidation problems of conductive materials (such as silver nanowires) during use together contribute to a serious lack of long-term device stability.

[0004] Secondly, in terms of device structure, the traditional stacked "sandwich" structure has inherent defects. The separation between the photoactive layer and the charge collection layer means that photogenerated charges need to travel a long lateral distance to be collected by the electrodes, resulting in a long path and low efficiency. The steep energy level barrier between the electrodes and the photosensitive layer further hinders efficient charge extraction and becomes a leakage channel for dark current. In addition, to achieve spectrally selective detection, traditional solutions have to rely on external filters that require precise alignment. This not only increases the complexity and cost of the process but also leads to an increase in the thickness of the sensor module, making it difficult to meet the stringent requirements for thinner and lighter devices in the consumer electronics field.

[0005] Finally, in flexible applications, multilayer thin film structures are prone to interface separation under mechanical stress, and transparent conductive networks are prone to breakage when repeatedly bent, leading to irreversible degradation of device performance and poor mechanical robustness.

[0006] Therefore, there is an urgent need in this field for a novel composite conductive thin-film optical sensor design that can fundamentally improve the stability of the material interface and charge transport efficiency without significantly increasing the manufacturing cost and process complexity, and integrate spectral selection function to achieve a balance of high response speed, low noise, long lifespan and excellent flexibility. Summary of the Invention

[0007] The main objective of this invention is to provide an optical sensor based on a composite conductive thin film, which can effectively solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A photosensitive sensor based on a composite conductive thin film, comprising: Flexible substrate; A composite conductive film formed on the flexible substrate, the composite conductive film serving as the electrode and photoactive layer of the device; And an encapsulation layer formed on the composite conductive film; The composite conductive film comprises a transparent conductive network and a photosensitive composite layer bonded together.

[0009] The above structure revolutionizes the traditional "electrode-separated photosensitive layer-electrode" sandwich structure into an integrated composite thin film in terms of both physical space and function, where the electrode and photoactive layer are combined. This design significantly shortens the path of photogenerated charge from generation to collection, solving the inherent problems of long lateral charge transport distance and high loss in layered structures.

[0010] Preferably, the transparent conductive network is a silver nanowire network or metal mesh partially embedded in the surface of the flexible substrate, and the surface of the transparent conductive network is covered with an inorganic oxide protective layer.

[0011] Local embedding effectively anchors the silver nanowires, preventing them from detaching or experiencing a sharp increase in resistance during bending, thus ensuring mechanical flexibility. The surface inorganic oxide protective layer (such as Al2O3) acts like a "protective suit" for the silver nanowires, effectively isolating them from water and oxygen and inhibiting electrochemical migration, fundamentally improving the environmental stability and lifespan of the electrode.

[0012] Preferably, the inorganic oxide protective layer is made of alumina or titanium dioxide, with a thickness of 10-30 nanometers. Alumina or titanium dioxide is chosen because they can form dense, pinhole-free thin films through low-temperature atomic layer deposition and possess excellent chemical inertness and insulation. Controlling the thickness within the 10-30 nanometer range ensures the formation of a continuous and complete protective layer while minimizing impact on the electrode's transmittance and in-plane conductivity due to their ultra-thin characteristics, thus achieving an optimal balance between protective function and photoelectric performance.

[0013] Preferably, the photosensitive composite layer comprises a photoactive material and a conductive polymer, wherein the photoactive material is a core-shell structured quantum dot, and its surface ligands interact with the conductive polymer through hydrogen bonding to form a hybrid complex.

[0014] Core-shell quantum dots (such as CdSe / ZnS) offer high fluorescence quantum efficiency and environmental stability. By designing surface ligands to form hydrogen-bonded hybridization networks with conductive polymers (such as PEDOT:PSS), a robust point-to-surface contact interface is created, replacing simple physical blending. This strong interaction not only prevents phase separation but also establishes efficient charge transfer channels, which is crucial for achieving fast photoelectric response and high gain.

[0015] Preferably, the core-shell quantum dot is a CdSe quantum dot wrapped with ZnS, and the ligands on its surface are terminal with carboxyl or amino groups; The conductive polymer is PEDOT:PSS, which has been doped twice.

[0016] The ZnS shell provides optimal protection for the CdSe core, which is a prerequisite for stability. Designing the ligand ends as carboxyl or amino groups allows for the strongest hydrogen bonding with PEDOT:PSS (rich in hydroxyl groups) treated with secondary dopants such as sorbitol. This secondary doping not only improves the conductivity of PEDOT:PSS but also enhances its hydrophilicity, promoting uniform recombination with modified quantum dots and ensuring consistent film quality and performance of the hybrid composite.

[0017] Preferably, a gradient energy level buffer layer is further provided between the transparent conductive network and the photosensitive composite layer; the gradient energy level buffer layer is a composite film composed of two or more metal oxide nanoparticles, and its work function changes continuously in a gradient from the transparent conductive network to the photosensitive composite layer.

[0018] By mixing two types of nanoparticles with different work functions (such as MoO3 with a high work function and ZnO with a low work function) in a certain proportion, a composite film with a continuous transition in work function is formed. This gradient structure physically creates a built-in electric field, which is like laying a "barrier-free slide" for photogenerated charges, realizing ohmic contact, thereby greatly improving charge extraction efficiency and reducing turn-on voltage and dark current.

[0019] Preferably, when the sensor is an electron-collecting type, the gradient energy level buffer layer is composed of a mixture of zinc oxide nanoparticles and molybdenum oxide nanoparticles, and its work function gradually decreases along the direction from the transparent conductive network to the photosensitive composite layer; When the sensor is a hole-collecting type, the gradient energy level buffer layer is composed of a mixture of PEDOT:PSS and molybdenum oxide nanoparticles, and its work function gradually increases along the direction from the transparent conductive network to the photosensitive composite layer.

[0020] For electron-collecting types, a structure with a gradually decreasing work function effectively drives electrons to the electrodes while blocking holes, achieving unidirectional conduction. For hole-collecting types, a structure with a gradually increasing work function facilitates hole outflow and blocks electrons. This directional design allows for flexible application in optoelectronic devices of different polarities (such as photoconductive and photovoltaic sensors), providing broad application adaptability.

[0021] Preferably, the surface of the flexible substrate in contact with the composite conductive film has a microprism or microlens array structure. The microlens / microprism structure can refocus scattered light incident at large angles and guide it into the photosensitive layer, effectively increasing the optical path and thus significantly enhancing the absorption capacity for weak light. This is a purely physical optics enhancement strategy decoupled from electronic device design, which can directly improve the sensitivity and responsivity of the sensor at a lower cost.

[0022] Preferably, the encapsulation layer is a polymer layer doped with organic dyes, which enable the encapsulation layer to filter light in a specific wavelength band. By directly incorporating organic dyes (such as the Rhodamine series) of a specific wavelength band into the encapsulation epoxy resin or polymer, the encapsulation layer itself possesses filtering functionality. This method eliminates the complex steps of independently cutting and bonding filters in traditional processes, significantly reducing manufacturing costs, simplifying the pixelation process, and avoiding the negative impacts of multi-layer bonding on device thinness and mechanical flexibility. It is particularly suitable for RGB color sensing or spectral analysis applications.

[0023] Compared with the prior art, the present invention has the following beneficial effects: This invention designs a photosensor based on a composite conductive thin film. By employing a synergistic design of a hydrogen-bonded hybrid core-shell quantum dot / conductive polymer composite photosensitive layer, an oxide-protected embedded silver nanowire electrode, a gradient energy level buffer layer, and a microlens structure, the device's response speed, environmental stability, and spectral selectivity are significantly improved while maintaining compatibility with traditional processes. It also effectively reduces dark current, providing a reliable solution for high-performance flexible photosensing. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of an optical sensor based on a composite conductive thin film according to the present invention. Detailed Implementation

[0025] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0026] This embodiment features a light sensor based on a composite conductive thin film (such as...). Figure 1 As shown, the device employs a three-layer core architecture of "flexible substrate - composite conductive film - encapsulation layer," where the composite conductive film integrates the electrode and photoactive layer functions of traditional devices, achieving integration in both physical space and function. The specific structure, from top to bottom, consists of: a 125μm thick polyethylene terephthalate (PET) flexible substrate with a microlens array fabricated on its surface; a locally embedded silver nanowire transparent conductive network covered with a 20nm alumina protective layer; a 50nm thick zinc oxide / molybdenum oxide gradient energy level buffer layer; an 80nm thick ZnS-encapsulated CdSe quantum dot / PEDOT:PSS photosensitive composite layer; and a 30μm thick polyimide encapsulation layer doped with Rhodamine B.

[0027] This architecture, through its integrated design, shortens the lateral transport distance of photogenerated charges in the traditional "electrode-photosensitive layer-electrode" sandwich structure from 10-50μm to 1-5μm, significantly reducing charge transport loss. At the same time, it eliminates the step of bonding the independent electrode layer and photosensitive layer, keeping the total thickness of the device within 200μm and the bending radius up to 5mm, thus meeting the application requirements of flexible electronic devices.

[0028] I. Component Preparation and Parameter Details (I) Preparation of flexible substrate Substrate material selection: A 125μm thick biaxially oriented PET film, model SKCPET-A4300, was selected. It has a light transmittance of 92%, an elongation at break of 15%, a glass transition temperature of 78℃, and can withstand subsequent hot pressing at 80℃ and sintering at 120℃. It also has excellent dimensional stability in an environment of -40℃ to 85℃ and a thermal shrinkage rate of <0.5%, making it suitable as a support substrate for flexible devices.

[0029] Surface microlens array fabrication: A microlens array is fabricated on the surface of a PET substrate using ultraviolet nanoimprint lithography. The specific steps are as follows: Pretreatment: The PET substrate is ultrasonically cleaned in isopropanol for 15 minutes to remove surface oil and dust, and then dried in an oven at 120°C for 30 minutes to eliminate internal stress in the substrate; Imprinting adhesive coating: Using a spin-coating process, UV-curable imprinting adhesive is coated on the PET surface at a speed of 3000 rpm for 30 seconds to form a uniform adhesive layer with a thickness of 5 μm. Nanoimprinting: Align a quartz imprinting template with a microlens array pattern with a coated PET substrate. The lenses are 10 μm in diameter, 3 μm in height, and 12 μm apart. Apply a pressure of 50 N / cm² and simultaneously irradiate with 365 nm ultraviolet light for 30 seconds to allow the imprinting adhesive to fully cure. Demolding and post-processing: The quartz template and PET substrate are slowly separated to obtain a flexible substrate with a microlens array on the surface. Finally, the substrate is annealed in an oven at 150°C for 10 minutes to improve the mechanical strength of the microlens structure.

[0030] The function of the microlens array is to focus scattered light incident at a large angle (such as diffuse reflection light in an indoor environment) onto the photosensitive composite layer below through optical refraction, effectively increasing the optical path by more than 30%, thereby improving the absorption efficiency of the photosensitive layer for weak light (light intensity <10μW / cm²) in the 500-650nm wavelength band by 45%, and significantly enhancing the sensor's weak light detection capability.

[0031] (II) Fabrication of transparent conductive networks Silver nanowire ink preparation: Silver nanowires with a diameter of 50 nm and a length of 20 μm were selected and dispersed in a water / ethanol mixed solvent at a volume ratio of 1:1. 0.5 wt% polyvinylpyrrolidone (PVP) with a molecular weight of 10,000 was added as a dispersant. The mixture was magnetically stirred for 2 hours and ultrasonically treated for 30 minutes at an ultrasonic power of 300 W to prepare silver nanowire ink with a concentration of 5 mg / mL. The ink viscosity was controlled at 5-8 cP to ensure uniform coating.

[0032] Transparent conductive network precursor coating: Silver nanowire ink was coated on a PET substrate modified with a microlens array using a slit coating process. The coating speed was 5 mm / s, the coating gap was 100 μm, and the wet film thickness was 20 μm. Then, it was pre-dried in an 80℃ hot air oven for 10 minutes to remove the solvent and form a silver nanowire transparent conductive network precursor. At this time, the sheet resistance of the precursor was about 200 Ω / sq.

[0033] Hot-press embedding and sintering: The pre-dried substrate is placed in a hot-pressing device, with a hot-pressing temperature of 80℃, a pressure of 10MPa, and a holding time of 5 minutes, so that the silver nanowire precursor is partially embedded in the PET substrate surface. The embedding depth is about 1 / 3 of the diameter of the silver nanowire, which effectively anchors the silver nanowire and prevents it from falling off when bent. Subsequently, photo-sintering is performed. The substrate surface is scanned with a laser with a wavelength of 532nm, a laser power of 5W, and a scanning speed of 10mm / s. The photothermal effect of the laser forms good ohmic contact between the silver nanowires. After sintering, the resistance drops to 15Ω / sq, and the transmittance in the 550nm band remains above 88%.

[0034] The advantages of local embedding design are: when the device is bent 180° with a bending radius of 5mm, after 1000 times, the surface resistance increases by only 12%, which is much lower than that of the non-embedded structure, which increases by more than 80%, significantly improving mechanical flexibility; at the same time, the embedded structure reduces the direct contact between the silver nanowires and the external environment, providing a smooth surface for subsequent protective layer deposition.

[0035] (III) Preparation of Inorganic Oxide Protective Layer An aluminum oxide (Al2O3) protective layer was deposited on the surface of a silver nanowire network using atomic layer deposition (ALD) technology. Specific parameters are as follows: Deposition equipment: Picosun R-200 Advanced ALD system from Finland; Precursor: Trimethylaluminum (TMA) and deionized water, TMA purity 99.999%, deionized water purity 18.2 MΩ·cm; Deposition temperature: 100℃, lower than the glass transition temperature of the PET substrate, to avoid substrate deformation; Deposition cycle: Each ALD cycle includes a 0.1s TMA pulse, a 5s nitrogen purging, a 0.1s water pulse, and a 5s nitrogen purging, for a total of 200 cycles, to prepare an Al2O3 protective layer with a thickness of approximately 20nm; Thin film properties: Root mean square roughness (RMS) of the protective layer < 1 nm, water vapor transmission rate (WVTR) < 1 × 10⁻ 6 g / (m²・day), which can effectively isolate water and oxygen.

[0036] The reasons for choosing alumina as the protective layer are: compared to titanium dioxide, alumina has stronger chemical inertness, is stable in both acidic environments (pH 3-7) and alkaline environments (pH 7-11), and can form a dense film without pinholes through the ALD process; the 20nm thickness design is the optimal value verified by multiple experiments—a thickness of less than 10nm cannot form a continuous protective layer and is prone to pinholes; a thickness of more than 30nm will lead to a significant increase in sheet resistivity (increase >30%), while reducing light transmittance (decrease >5%).

[0037] (iv) Preparation of gradient energy level buffer layer In this embodiment, an electron-collecting sensor is fabricated. Therefore, a gradient energy level buffer layer is formed by mixing zinc oxide (ZnO) nanoparticles and molybdenum oxide (MoO3) nanoparticles. The specific steps are as follows: Nanoparticle preparation: ZnO nanoparticles: The sol-gel method was used to mix 0.1 mol / L zinc acetate ethanol solution and 0.1 mol / L sodium hydroxide ethanol solution at a molar ratio of 1:2 and stir at 60°C for 2 hours to form ZnO sol. The sol was then dried at 80°C for 24 hours, ground, and calcined in a muffle furnace at 400°C for 2 hours to obtain ZnO nanoparticles with a particle size of 20 nm. MoO3 nanoparticles: Using a hydrothermal method, a 0.05 mol / L ammonium molybdate solution and a 0.1 mol / L nitric acid solution were mixed at a volume ratio of 1:1 and transferred to a high-pressure reactor. The mixture was reacted at 180°C for 12 hours. After cooling, the mixture was centrifuged, washed three times with deionized water, and dried at 100°C for 12 hours to obtain MoO3 nanoparticles with a particle size of 30 nm.

[0038] Gradient mixed solution preparation: ZnO nanoparticles and MoO3 nanoparticles were separately dispersed in ethanol to prepare single-component dispersions with a concentration of 10 mg / mL; then, nine mixed dispersions were prepared according to volume ratios of 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, and 9:1. 0.2 wt% polyethylene glycol (PEG) was added as a binder to each mixture. The mixtures were ultrasonically treated for 30 minutes to ensure uniform dispersion of the nanoparticles.

[0039] Gradient layer coating: A layer-by-layer spin-coating process is used to coat the gradient mixed solution, starting with ZnO:MoO3=1:9, on the side close to the transparent conductive network, with a work function of approximately 5.2 eV. The coating speed for each layer is 2000 rpm and the coating time is 30 seconds. After coating, the solution is dried at 120°C for 5 minutes. Nine layers of the mixed solution are coated sequentially to form a gradient energy level buffer layer with a thickness of 50 nm. The ZnO:MoO3=9:1 layer is close to the photosensitive composite layer, with a work function of approximately 4.3 eV on this side. The work function changes continuously along the vertical direction, decreasing from 5.2 eV to 4.3 eV.

[0040] The working principle of the gradient energy level buffer layer: In traditional devices, the work function of the transparent conductive network is about 4.8 eV, and there is a 0.3 eV energy level barrier between it and the work function of the photosensitive composite layer (about 4.5 eV). This makes it difficult for photogenerated electrons to cross the barrier and be collected by the electrodes, and easily forms a dark current channel. However, the gradient buffer layer in this embodiment eliminates the energy level barrier through a continuous transition of the work function, forming an "unobstructed" electron transport channel, which improves the charge extraction efficiency by 60% and reduces the dark current from 1×10⁻⁻⁶. 8 A decreases to 5 × 10⁻¹ 0 A.

[0041] (V) Preparation of photosensitive composite layer Preparation of core-shell quantum dots: ZnS-encapsulated CdSe quantum dots (CdSe / ZnSQDs) were prepared using a hot-injection method. The specific steps are as follows: CdSe core preparation: Under nitrogen protection, 0.5 mmol of selenium powder was dissolved in 5 mL of trioctylphosphine TOP to form a selenium-TOP solution; 0.5 mmol of cadmium chloride, 1 mmol of oleic acid OA, and 20 mL of octadecene ODE were mixed, heated to 150 °C, and kept at that temperature for 30 minutes to remove moisture and oxygen; then the temperature was raised to 300 °C, and the selenium-TOP solution was rapidly injected, and the reaction was carried out for 5 minutes to obtain CdSe cores with an emission wavelength of 580 nm; ZnS shell coating: 0.2 mmol of zinc chloride, 0.4 mmol of OA and 10 mL LODE were mixed and heated to 120 °C and held for 20 minutes; then it was slowly added dropwise to a CdSe core solution at a dropping rate of 1 mL / min, the temperature was increased to 220 °C and the reaction was carried out for 30 minutes to form a ZnS shell; after the reaction was completed, the quantum dots were precipitated with ethanol, centrifuged at 8000 rpm for 10 minutes, and redispersed with n-hexane. This process was repeated 3 times to obtain CdSe / ZnS quantum dots with a particle size of 10 nm. Surface ligand modification: CdSe / ZnS quantum dots were dispersed in n-hexane, and 0.1 mmol of mercaptoacetic acid (MGA) containing carboxyl-terminated ligands was added. The mixture was stirred at room temperature for 12 hours to convert the ligands on the quantum dot surface to carboxyl groups through a ligand exchange reaction. Subsequently, the quantum dots were precipitated with ethanol and centrifuged to obtain carboxyl-modified CdSe / ZnS quantum dots.

[0042] Preparation of secondary doped PEDOT:PSS: A 1.3 wt% PEDOT:PSS aqueous solution (purchased from Heraeus Clevios PVPAI 4083) was taken and 5 wt% sorbitol was added as a secondary dopant. The solution was magnetically stirred for 2 hours and ultrasonically treated for 15 minutes. Then, it was filtered through a 0.22 μm aqueous filter membrane to remove impurities, resulting in a secondary doped PEDOT:PSS solution. After secondary doping, the conductivity of PEDOT:PSS increased from 0.1 S / cm to 10 S / cm, and the hydrophilicity was enhanced, with the contact angle decreasing from 70° to 45°, which is beneficial for recombination with carboxyl-modified quantum dots.

[0043] Photosensitive composite layer coating: Carboxyl-modified CdSe / ZnS quantum dots were dispersed in a secondary-doped PEDOT:PSS solution at a concentration of 20 mg / mL. The mixture was stirred at room temperature for 4 hours, and a hybrid complex was constructed by hydrogen bonding between the carboxyl groups on the quantum dot surface and the hydroxyl groups in the PEDOT:PSS. Subsequently, this mixed solution was coated onto a gradient energy level buffer layer using a spin-coating process at 2500 rpm for 30 seconds, followed by drying at 100°C for 15 minutes to form a photosensitive composite layer with a thickness of 80 nm. The absorption spectrum of the composite layer covered the 400-700 nm wavelength range, with an absorption coefficient of 1 × 10⁻⁶ at 580 nm. 5 cm⁻¹.

[0044] Advantages of hydrogen-bonded hybrid structures: Compared with simple physical blending, hydrogen bonding makes quantum dots more uniformly dispersed in PEDOT:PSS, with no obvious agglomeration and tighter interfacial bonding; when the device is subjected to mechanical bending, hydrogen bonds can act as "elastic bonds" to reduce interfacial separation, so that the photocurrent attenuation rate of the photosensitive composite layer is only 8% after 1000 bending cycles, which is much lower than that of physical blending structures, where the attenuation rate is >35%.

[0045] (vi) Preparation of encapsulation layer Preparation of the filter encapsulation solution: Polyimide (PI) was selected as the encapsulation matrix material, model KaptonHN. PI powder was dissolved in N,N-dimethylformamide (DMF) to prepare a 15wt% PI solution. 0.5wt% of Rhodamine B (an organic dye with a maximum absorption wavelength of 550nm) was added as a filter agent. The solution was magnetically stirred for 3 hours and ultrasonically treated for 20 minutes to ensure uniform dispersion of Rhodamine B. Subsequently, it was filtered through a 0.45μm organic filter membrane to remove impurities.

[0046] Encapsulation layer coating and curing: A filter encapsulation solution was coated onto the photosensitive composite layer using a doctor blade coating process, with a coating thickness of 30 μm. This was followed by a stepped curing process: drying at 80℃ for 30 minutes to remove the solvent; initial curing at 150℃ for 1 hour; and complete curing at 200℃ for 2 hours. The cured encapsulation layer exhibited a transmittance of 15% at 550 nm, achieving its filtering function; at other wavelengths such as 450 nm and 650 nm, the transmittance was >80%, and the water vapor transmittance was <5 × 10⁻⁻⁻⁶. 5 g / (m²・day) can effectively protect internal components from water and oxygen corrosion.

[0047] Advantages of integrated filtering function: Traditional sensors require additional independent filters after packaging, with a filter thickness of about 50μm. This not only increases the number of process steps but also leads to increased device thickness and cost. In this embodiment, organic dyes are directly doped into the packaging layer, integrating the packaging and filtering functions. The total device thickness is reduced by 50μm, and the cost is reduced by 30%. Furthermore, there is no gap between the filter and the packaging layer, avoiding the impact of dust or moisture in the gap on device performance.

[0048] II. Device Performance Testing and Results (a) Photoelectric performance testing Test conditions: A xenon lamp was used as the light source with a light intensity of 100mW / cm² to simulate AM1.5G sunlight. The current-voltage (IV) characteristics of the device were measured using a Keithley 2400 source meter. Test results: Dark current: 5 × 10⁻¹ 0 A, bias voltage 1V; Photocurrent: 2×10⁻ 4 A, bias voltage 1V; Light-to-dark current ratio: 4×10 5 ; Response speed: Rise time is 200 μs, which refers to the rise from 10% to 90% of the photocurrent; fall time is 300 μs, which refers to the fall from 90% to 10% of the photocurrent. Responsivity: The responsivity reaches 8 A / W in the 580nm band. 580nm is the emission wavelength of quantum dots, which is much higher than that of traditional silicon-based optical sensors, whose responsivity is about 0.5 A / W.

[0049] (ii) Environmental stability test Test conditions: The device was placed in a constant temperature and humidity chamber, with the temperature set at 60℃ and the relative humidity at 90%, and the test was conducted continuously for 30 days. Test results: After 30 days, the photocurrent of the device decreased by 10% and the surface resistance increased by 15%, indicating that the device has excellent environmental stability. This is due to the water and oxygen barrier effect of the alumina protective layer and the protective effect of the ZnS shell on the quantum dots.

[0050] (III) Mechanical flexibility test Test conditions: A bending tester was used, with a bending radius of 5mm, and 180° reciprocating bends were performed. The device performance was tested once every 100 bends. Test results: After 1000 bends, the surface resistivity of the device increased from 15Ω / sq to 16.8Ω / sq, an increase of 12%; the photocurrent increased from 2×10⁻ 4 A decreased to 1.84 × 10⁻ 4A. The attenuation rate is 8%, with no obvious delamination or breakage, meeting the long-term use requirements of flexible electronic devices.

[0051] The optical sensor in this embodiment can be applied to flexible wearable health monitoring devices, such as the heart rate and blood oxygen monitoring module of a smart bracelet. Its specific advantages are as follows: Flexible design: With a bending radius of 5mm, it can closely conform to the skin of the human wrist, improving wearing comfort; Low-light detection capability: The microlens array improves the absorption efficiency of the sensor for low-light conditions such as 660nm red light and 940nm near-infrared light required for blood oxygen monitoring by 45%, ensuring the accuracy of heart rate and blood oxygen data. Fast response: A response speed of 200μs enables real-time monitoring, with a sampling rate of up to 500Hz; Long-term stability: Under human sweat and body temperature conditions (pH 4.5-7.0, body temperature 37℃), the performance degradation rate is less than 10% within 30 days, eliminating the need for frequent sensor replacements.

[0052] Furthermore, by adjusting the type of organic dye in the encapsulation layer, such as replacing it with sodium copper chlorophyllin, which absorbs light at a wavelength of 670 nm, selective detection of light in specific wavelength bands can be achieved, extending to fields such as plant growth status monitoring and spectral analysis.

[0053] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A photosensitive sensor based on a composite conductive thin film, characterized in that: include: Flexible substrate; A composite conductive film formed on the flexible substrate, the composite conductive film serving as the electrode and photoactive layer of the device; And an encapsulation layer formed on the composite conductive film; The composite conductive film comprises a transparent conductive network and a photosensitive composite layer bonded together.

2. The optical sensor based on a composite conductive thin film according to claim 1, characterized in that: The transparent conductive network is a silver nanowire network or metal mesh partially embedded in the surface of the flexible substrate, and the surface of the transparent conductive network is covered with an inorganic oxide protective layer.

3. A photosensitive sensor based on a composite conductive thin film according to claim 2, characterized in that: The inorganic oxide protective layer is made of aluminum oxide or titanium dioxide and has a thickness of 10-30 nanometers.

4. The optical sensor based on a composite conductive thin film according to claim 1, characterized in that: The photosensitive composite layer comprises a photoactive material and a conductive polymer. The photoactive material is a core-shell structured quantum dot, and its surface ligands interact with the conductive polymer through hydrogen bonding to form a hybrid complex.

5. A photosensitive sensor based on a composite conductive thin film according to claim 4, characterized in that: The core-shell structured quantum dots are CdSe quantum dots wrapped in ZnS, with carboxyl or amino groups at the end of their surface ligands; The conductive polymer is PEDOT:PSS, which has been doped twice.

6. A photosensitive sensor based on a composite conductive thin film according to any one of claims 1-5, characterized in that: Between the transparent conductive network and the photosensitive composite layer, a gradient energy level buffer layer is also provided; the gradient energy level buffer layer is a composite film composed of two or more metal oxide nanoparticles, and its work function changes continuously in a gradient from the transparent conductive network to the photosensitive composite layer.

7. A photosensitive sensor based on a composite conductive thin film according to claim 6, characterized in that: When the sensor is an electron-collecting type, the gradient energy level buffer layer is composed of a mixture of zinc oxide nanoparticles and molybdenum oxide nanoparticles, and its work function gradually decreases along the direction from the transparent conductive network to the photosensitive composite layer. When the sensor is a hole-collecting type, the gradient energy level buffer layer is composed of a mixture of PEDOT:PSS and molybdenum oxide nanoparticles, and its work function gradually increases along the direction from the transparent conductive network to the photosensitive composite layer.

8. A photosensitive sensor based on a composite conductive thin film according to claim 1, characterized in that: The surface of the flexible substrate that contacts the composite conductive film has a microprism or microlens array structure.

9. A photosensitive sensor based on a composite conductive thin film according to claim 1, characterized in that: The encapsulation layer is a polymer layer doped with organic dyes, which are used to make the encapsulation layer filter light.

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