Cadmium telluride thin film battery cadmium chloride spraying monitoring and control system and method

Abstract

The invention discloses a cadmium telluride thin film battery cadmium chloride spraying monitoring and control system and method. The system comprises a material preparation module used for preparing and storing a cadmium chloride solution containing a cadmium ion fluorescent probe; the spraying module is used for uniformly spraying the solution containing the probe to the surface of the cadmium telluride substrate to form a liquid film; the on-line detection module is used for collecting a liquid film fluorescence image through an optical detection unit and measuring the conductivity of the liquid film in a non-contact manner through a conductivity detection unit; and the data processing and control module is used for carrying out fusion analysis on the fluorescence image and the conductivity data, calculating the coverage rate, the uniformity and the cadmium chloride content of the liquid film in real time, and dynamically adjusting spraying parameters and probe injection parameters according to an analysis result, so as to realize closed-loop accurate control of the coating process. The problems that in the prior art, real-time performance is poor, blind areas exist in microcosmic distribution detection, and control precision is insufficient are effectively solved, and the consistency of the coating technology and the material utilization rate are improved.

Description

Technical Field

[0001] This invention relates to the field of cadmium telluride thin-film solar cell technology, and particularly to a monitoring and control system and method for cadmium chloride spraying in cadmium telluride thin-film solar cells. Background Technology

[0002] Among various photovoltaic technologies, cadmium telluride (CdTe) thin-film solar cells have become the most mature thin-film photovoltaic technology in industrialization due to their advantages such as high absorption coefficient, superior theoretical efficiency, low temperature coefficient, low manufacturing cost, and ability to be deposited over large areas. They play an important role in energy conservation and emission reduction in applications such as distributed power stations and building-integrated photovoltaics.

[0003] The cadmium chloride (CdCl2) heat treatment process is considered a key step in the preparation of high-efficiency cadmium telluride thin-film modules. Without this treatment, the cadmium telluride absorber layer has fine grains, high dislocation and grain boundary defect density, and a large number of non-radiative recombination centers, resulting in a short photogenerated carrier lifetime and a module conversion efficiency generally below 10%. After cadmium chloride heat treatment, the defects and recombination in the cadmium telluride absorber layer are significantly reduced, and the module efficiency can be stably improved to over 15%.

[0004] Currently, the mainstream method is to use wet coating processes (such as spraying, roller coating, and immersion) to deposit cadmium chloride solution onto the surface of cadmium telluride. Spraying is widely used due to its good coverage uniformity. However, existing wet spraying processes still face the following technical bottlenecks in large-scale production: ① Spray uniformity depends on operator experience, lacks real-time monitoring methods, and cannot adjust process parameters online; ② Traditional sampling and testing (such as EDS and XPS) takes too long, usually more than 2 hours; ③ Direct detection of chlorine (Cl) distribution is difficult, as its microscopic distribution is not visible.

[0005] Existing patented technologies mostly focus on improving the structure of coating equipment and solution formulations, failing to effectively solve the core problem of "real-time monitoring of cadmium chloride distribution uniformity". For example, patent CN111430476B discloses a cadmium chloride spraying device that improves the coating speed through multi-nozzle linkage, but does not integrate an online detection unit; patent CN109801994A optimizes solution wettability and reduces droplet aggregation by adding surfactants, but still relies on offline sampling and electrical performance feedback after heat treatment, and cannot achieve closed-loop control of the process.

[0006] There is an urgent need to develop a cadmium chloride spraying system that integrates real-time monitoring, intelligent feedback, and process control to achieve dynamic optimization of spray uniformity. Summary of the Invention

[0007] This invention addresses the problems of lack of real-time monitoring, unmeasurable microscopic distribution, and closed-loop control failure in the existing cadmium chloride spraying process for cadmium telluride thin-film solar cells. It proposes a monitoring and control system and method for cadmium chloride spraying in cadmium telluride thin-film solar cells. By utilizing cadmium ion fluorescent labeling technology to achieve dynamic imaging detection of cadmium chloride distribution, and combining it with a temperature-compensated conductivity-content intelligent conversion model, a real-time monitoring system for coverage, uniformity, and content is constructed. Furthermore, based on multi-parameter fusion feedback, an intelligent closed-loop control is established, achieving real-time feedback of cadmium chloride distribution characteristics during spraying, high-precision detection of microscopic distribution at the 50μm scale, and precise closed-loop control of coating quality, thus improving process consistency and material utilization. The technical solution provided by this invention is as follows: On one hand, the present invention provides a monitoring and control system for cadmium chloride spraying in cadmium telluride thin-film batteries, comprising: The material preparation module includes a cadmium chloride solution storage unit, a probe injection unit for injecting cadmium ion fluorescent probes into the cadmium chloride solution, and a solution temperature control unit for controlling the temperature of the cadmium chloride solution. A spraying module includes a spraying unit for spraying a cadmium chloride solution containing the cadmium ion fluorescent probe onto the surface of a cadmium telluride substrate to form a liquid film. The online detection module includes: An optical detection unit is used to excite and capture the fluorescence image of the liquid film; A conductivity detection unit is used for non-contact measurement of the conductivity of the liquid film; The data processing and control module is communicatively connected to the material preparation module, the spraying module, and the online detection module, and is configured as follows: The fluorescence image and conductivity data are received and processed to calculate the coverage, uniformity, and cadmium chloride content of the liquid film on the cadmium telluride substrate surface. Based on the deviations of the coverage, uniformity, and cadmium chloride content from the preset target values, the spraying parameters of the spraying unit and / or the injection parameters of the probe injection unit are dynamically adjusted.

[0008] Optionally, the cadmium ion fluorescent probe is selected from one or more of the following: Rhodamine derivative (Rhod-5N) probes, water-soluble porphyrin probes, dipyridine methylamine-functionalized porphyrin probes, and thiol-modified cadmium telluride quantum dot probes; the cadmium ion fluorescent probe and Cd 2+ Specific chelation forms a fluorescent complex.

[0009] Optionally, the cadmium ion fluorescent probe reacts with Cd in the cadmium chloride solution. 2+ The molar ratio is (15-100):1.

[0010] Optionally, the optical detection unit includes an excitation light source, a high-speed CMOS camera, and a filter; The emission wavelength of the excitation light source is 400-600 nm; The filter is positioned in front of the high-speed CMOS camera, and its transmission wavelength is 550-600 nm. The high-speed CMOS camera is used to acquire fluorescence images after being filtered by the filter, and to transmit the fluorescence images to the data processing and control module.

[0011] Optionally, the conductivity detection unit includes an eddy current probe, a temperature sensor, a signal processor, and a scanning mechanism; The scanning mechanism is configured to drive the eddy current probe to scan the surface of the cadmium telluride substrate along a predetermined path; The temperature sensor is configured to monitor the ambient temperature in real time to compensate for the temperature of the conductivity measurement. The signal processor is configured to receive and process signals from the eddy current probe and the temperature sensor, and output compensated conductivity data.

[0012] Optionally, the data processing and control module includes a data processing unit, a PID controller, a nozzle adjustment unit, and an injection pump adjustment unit; The data processing unit is configured to perform the calculations of coverage, uniformity, and cadmium chloride content, and generate control instructions based on the calculation results; The PID controller is communicatively connected to the data processing unit and is configured to receive the control command and output the corresponding adjustment signal. The nozzle adjustment unit is connected to the PID controller and is configured to adjust the spraying path, moving speed and spraying flow rate of the spraying unit according to the adjustment signal. The injection pump regulating unit is connected to the PID controller and is configured to adjust the injection volume of the fluorescent probe in the probe injection unit and the mixing ratio with the cadmium chloride solution according to the regulating signal.

[0013] On the other hand, the present invention also provides a method for monitoring and controlling cadmium chloride spraying in cadmium telluride thin-film batteries, the method comprising the following steps: Monitoring solution preparation steps: Inject cadmium ion fluorescent probes into cadmium chloride solution and mix to form the monitoring solution to be coated; Coating liquid film step: The monitoring solution is coated onto the surface of a cadmium telluride substrate to form a liquid film; Optical monitoring step: Excite and capture fluorescence images of the liquid film; Conductivity monitoring steps: Non-contact measurement of the conductivity of the liquid film; Data fusion analysis steps: The fluorescence image and conductivity data are fused and processed to calculate the coverage and uniformity of the liquid film on the cadmium telluride substrate surface, and the cadmium chloride content in the liquid film is calculated based on the pre-stored conductivity-cadmium chloride content relationship model. Closed-loop control steps: Based on the deviations of the coverage, uniformity, and cadmium chloride content from their respective preset target values, dynamically adjust the coating process parameters and / or the preparation parameters of the monitoring solution.

[0014] Optionally, in the data fusion analysis step, the calculation of coverage and uniformity includes the following process: The area division step is as follows: The surface of the cadmium telluride substrate is uniformly divided into M×N equal-area grids, and each grid constitutes an independent detection area; Coverage status determination step: Based on the fluorescence image data or conductivity data, obtain the measurement value of each detection area. When the measurement value of a certain detection area exceeds a preset threshold, the detection area is determined to be an effective coverage area. Coverage calculation steps: The coating coverage rate is calculated based on the formula Coverage Rate = (Number of effective coverage areas / Total number of areas) × 100%, where the number of effective coverage areas is the number of areas determined to be effective coverage areas, and the total number of areas is the total number of the M×N grids; Uniformity calculation steps: Extract the measurement values ​​of all effective coverage areas, calculate their average value μ and standard deviation σ, and determine the coating uniformity based on the formula uniformity = ±(σ / μ)×100%.

[0015] Optionally, the conductivity-cadmium chloride content relationship model is as follows: C CdCl2 = a · σ 2 + b · σ + c Among them, C CdCl2 σ represents the cadmium chloride content, σ is the measured conductivity value after temperature compensation, and a, b, and c are the fitting coefficients determined through calibration experiments. The temperature compensation is achieved by the following formula: σ Tref = σ T · [1 + α(T - T ref )] Where, σ T σ is the original conductivity measured at temperature T. Tref To convert to reference temperature T ref The standard conductivity is given below, where T is the actual temperature during measurement. ref The reference temperature is α, and the temperature coefficient of conductivity is α.

[0016] Optionally, the data fusion analysis step further includes calibrating and verifying the cadmium chloride content measured by the conductivity-cadmium chloride content relationship model based on the fluorescence intensity-concentration calibration model. The fluorescence intensity-concentration calibration model is expressed as follows: C CdCl2 = k × (I - I0) Among them, C CdCl2 denoted as cadmium chloride content, I as measured fluorescence intensity, I0 as background fluorescence intensity, and k as probe response coefficient; When the cadmium chloride content measured based on the fluorescence intensity-concentration calibration model and the conductivity-cadmium chloride content relationship model are inconsistent, the cadmium chloride content measured based on the conductivity-cadmium chloride content relationship model shall be taken as the standard.

[0017] By adopting the above technical solution, the cadmium chloride spraying monitoring and control system and method for cadmium telluride thin-film batteries provided by the present invention have the following beneficial effects: This invention utilizes cadmium ion fluorescent labeling technology and high-speed CMOS camera dynamic imaging to capture real-time images of CdCl2 distribution on the surface of a cadmium telluride substrate after spraying, and accurately calculates coverage and uniformity based on image algorithms. Simultaneously, through an intelligent conversion model of conductivity-cadmium chloride content (based on a fitting curve of calibrated solution conductivity and temperature compensation), the online conductivity data is accurately converted into CdCl2 deposition amount, and dual verification ensures the accuracy of the monitoring data.

[0018] Experimental verification shows that in the traditional open-loop process, the coverage of CdCl2 after spraying is only 75%~85%, and the distribution uniformity is poor (fluctuation range ±20%), which easily leads to insufficient or excessive film formation in local areas, causing battery interface defects or aggravated carrier recombination. However, the system of this invention can stably increase the coverage to 90%~98% (significantly higher than the traditional process) through real-time monitoring and dynamic feedback control, and strictly control the uniformity fluctuation within ±5% (far better than the traditional ±20%), effectively solving the technical problem of uneven film thickness.

[0019] 2. This invention integrates a dynamic control method, which adjusts spraying process parameters (such as solution flow rate, nozzle movement speed, atomizing pressure, etc.) in real time based on CdCl2 coverage, content, and uniformity data obtained from online monitoring, forming a closed-loop control cycle of "monitoring-analysis-feedback-adjustment". This method avoids the problems of "overspraying" or "insufficient coverage" caused by experience-based preset parameters in traditional open-loop control by accurately matching actual needs with process inputs.

[0020] Practical applications show that the system of this invention can save 15% to 20% of CdCl2 solution usage. At the same time, due to the optimization of process parameters, it reduces the ineffective energy consumption during the spraying process (such as redundant atomization gas pressure, heating maintenance, etc.), resulting in a 10% to 15% reduction in overall energy consumption. In addition, the improvement in coverage uniformity significantly reduces the number of defective batteries caused by film defects (such as short circuits, open circuits, or low efficiency), reducing the defect rate by 40% to 50% (the defect rate of traditional processes is relatively high, while this invention improves battery efficiency from 15.7% to 17.2% through precise control, and significantly reduces the defect rate).

[0021] 3. Unlike traditional offline sampling detection methods that rely on energy dispersive spectroscopy (EDS) or X-ray photoelectron spectroscopy (XPS) (which take >2 hours, have a response delay >30 minutes, and cannot obtain microscopic distribution information), this invention achieves precise "online, real-time, and microscopic" sensing of CdCl2 distribution through simultaneous real-time monitoring of fluorescence imaging and conductivity scanning. More importantly, the system response delay is only 200~500 ms (compared to >30 minutes for traditional methods), allowing for immediate adjustment of spraying parameters when abnormal coverage is detected (such as local coverage <95% or excessive uniformity). This reduces process adjustment time from "hours" to "milliseconds," completely solving the vicious cycle of "detection lag - adjustment delay - quality fluctuation" inherent in traditional processes. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0023] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. In the description of the invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in sequences other than those illustrated or described herein.

[0024] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein. For example, a specified range from “1 to 10” should be considered to include any and all subranges between the minimum value 1 and the maximum value 10. Exemplary subranges of the range 1 to 10 include, but are not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc.

[0025] This invention provides a monitoring and control system for cadmium chloride spraying in cadmium telluride thin-film batteries, comprising: The material preparation module includes a cadmium chloride solution storage unit, a probe injection unit for injecting cadmium ion fluorescent probes into the cadmium chloride solution, and a solution temperature control unit for controlling the temperature of the cadmium chloride solution. A spraying module includes a spraying unit for spraying a cadmium chloride solution containing cadmium ion fluorescent probes onto the surface of a cadmium telluride substrate to form a liquid film. The online detection module includes: An optical detection unit is used to excite and capture fluorescence images of the liquid film; Conductivity detection unit for non-contact measurement of the conductivity of liquid films; The data processing and control module is communicatively connected to the material preparation module, the spraying module, and the online detection module, and is configured as follows: Receive and process fluorescence images and conductivity data, and calculate the coverage, uniformity, and cadmium chloride content of the liquid film on the cadmium telluride substrate surface; Based on the deviations of coverage, uniformity, and cadmium chloride content from preset target values, the spraying parameters of the spraying unit and / or the injection parameters of the probe injection unit are dynamically adjusted.

[0026] Optionally, the cadmium ion fluorescent probe is selected from one or more of the following: rhodamine derivative (Rhod-5N) probes, water-soluble porphyrin probes (such as TMPyP type), dipyridine methylamine-functionalized porphyrin probes (PD series), and thiol-modified cadmium telluride quantum dot probes. These probes interact with Cd through specific coordinating groups (carboxyl, amino, pyridine nitrogen, thiol, etc.). 2+ Formation of stable complexes: Rhod-5N achieves rapid response (approximately 500 ms) through carboxyl-amino bidentate coordination; porphyrin probes achieve selective inclusion via macrocyclic cavities; PD series probes combine amino coordination with porphyrin cavities to synergistically enhance sensitivity; quantum dot probes utilize surface thiol groups and Cd... 2+Specific chelation enhances anti-interference properties. The probe interacts with Cd. 2+ Upon binding, it induces changes in molecular configuration and electronic transition states. Through mechanisms such as inhibiting photoinduced electron transfer or inducing intramolecular charge transfer, it generates quantitative signals such as enhanced fluorescence intensity, emission wavelength shift, or lifetime changes. Based on this, a Cd23434344444444444444444444444444444444444444444444444444444444444444445 ... 2+ Functional relationship between concentration and fluorescence characteristics.

[0027] Optionally, the cadmium ion fluorescent probe reacts with Cd in the cadmium chloride solution. 2+ The molar ratio is (15-100):1 (e.g., 15:1, 30:1, 50:1, 70:1, or 100:1, etc.). If the ratio is lower than 15:1, the probe will not be able to adequately label Cd. 2+ This will result in insufficient fluorescence signal intensity, affecting detection sensitivity and the accuracy of distribution identification; if the ratio is higher than 100:1, it is prone to triggering a concentration quenching effect, destroying fluorescence intensity and Cd. 2+ The linear relationship between concentrations may be observed, but probe molecule aggregation could interfere with the crystallization behavior of cadmium chloride and increase reagent costs. This optimized ratio range ensures that Cd... 2+ It is effectively labeled and generates sufficient fluorescence signal that can be captured by a high-speed CMOS camera, while maintaining good dispersion of the probe in the solution and avoiding detection deviation caused by aggregation.

[0028] Optionally, the optical detection unit includes an excitation source, a high-speed CMOS camera, and a filter; The excitation light source emits light at a wavelength of 400-600 nm, which can effectively excite the selected cadmium ion fluorescent probe (such as Rhod-5N, whose maximum excitation peak is about 532 nm), while avoiding photodamage to the cadmium telluride substrate.

[0029] The filter is positioned in front of the high-speed CMOS camera, with a transmission wavelength of 550-600 nm, effectively filtering out excitation light scattering and ambient stray light interference, thus improving the signal-to-noise ratio.

[0030] High-speed CMOS cameras are used to acquire fluorescence images after they have been filtered by a filter and transmit these images to the data processing and control module. High-speed CMOS cameras (such as ORCA-Flash4.0 V3) capture filtered fluorescence images at a rate of at least 500 fps. Their high quantum efficiency ensures clear images even under weak fluorescence conditions, and the image data is transmitted to the data processing and control module in real time via a gigabit Ethernet interface.

[0031] Optionally, the conductivity detection unit includes an eddy current probe, a temperature sensor, a signal processor, and a scanning mechanism. The scanning mechanism employs a spraying robotic arm, which drives the eddy current probe to perform a non-contact scan of the cadmium telluride substrate surface along a preset spiral path, acquiring a set of data every 0.1 seconds to ensure the spatiotemporal continuity and real-time performance of the overall conductivity data. The temperature sensor is installed adjacent to the eddy current probe to monitor changes in ambient temperature in real time, utilizing a built-in temperature compensation model (σ... Tref = σ T · [1+α(TT ref The original conductivity value is dynamically corrected using a method where α is typically taken as 0.02 / ℃, effectively eliminating measurement deviations caused by temperature fluctuations. The signal processor, based on digital lock-in amplification technology, synchronously acquires the high-frequency response signal and temperature data from the eddy current probe. Combined with an adaptive filtering algorithm and a temperature compensation module, it outputs a standardized conductivity distribution map in real time. This conductivity detection unit achieves in-situ, rapid, and accurate measurement of liquid film conductivity during the spraying process through high-precision scanning positioning and multi-parameter fusion processing.

[0032] Optionally, the data processing and control module includes a data processing unit, a PID controller, a nozzle adjustment unit, and an injection pump adjustment unit. The data processing unit, based on real-time acquired fluorescence images and conductivity data, calculates the liquid film coverage through gridded analysis, evaluates distribution uniformity using statistical methods, and accurately calculates the cadmium chloride content using a conductivity-content fitting model. This data processing unit generates control commands through a multi-parameter fusion algorithm, ensuring a balance between detection accuracy and system response speed. The PID controller establishes real-time communication with the data processing unit, and upon receiving control commands, outputs a high-precision adjustment signal through a proportional-integral-derivative algorithm. Its fast response effectively eliminates system overshoot and steady-state errors. The nozzle adjustment unit dynamically adjusts the spraying path, moving speed, and spraying flow rate according to the PID signal, achieving precise control of the coating morphology. The injection pump adjustment unit synchronously receives PID commands, controlling the injection rate of the fluorescent probe and its mixing ratio with the cadmium chloride solution, ensuring the consistency and reliability of the fluorescent labeling process. This module, through multi-unit collaborative control, forms a closed-loop system integrating "sensing-decision-execution."

[0033] This invention also provides a method for monitoring and controlling cadmium chloride spraying in cadmium telluride thin-film batteries. This method achieves precise monitoring and process optimization of the liquid film deposition process through coordinated optical and electrical detection, multi-parameter fusion analysis, and real-time closed-loop control. Specifically, it includes the following steps: 1. Monitoring solution preparation steps A cadmium ion fluorescent probe (preferably Rhod-5N) was precisely injected into a cadmium chloride solution at a molar ratio of (15–100):1, and stirred under isothermal conditions to form a homogeneous and stable monitoring solution; wherein, Rhod-5N binds to Cd via a bidentate coordination mechanism between the carboxyl and amino groups. 2+ Specific chelation forms a fluorescently responsive complex, converting the invisible distribution of cadmium chloride into a fluorescent signal whose intensity is positively correlated with concentration.

[0034] 2. Liquid film coating step An ultrasonic atomization spraying process is used to uniformly coat the monitoring solution onto the surface of a preheated cadmium telluride substrate. By controlling the spraying speed (preferably 550-600 mm / s), solution flow rate (preferably 15-20 mL / min), atomization pressure (preferably 0.3-0.4 MPa), and nozzle-substrate distance (preferably 50-80 mm), a liquid film with a thickness of 50-120 nm is formed. This effectively solves the defects such as agglomeration, flow, and dry spots caused by the discrete droplet size distribution and uneven kinetic energy distribution in traditional spraying.

[0035] 3. Optical monitoring steps A 532 nm semiconductor laser is preferably used as the excitation source, and a high-speed CMOS camera (such as ORCA-Flash4.0 V3) equipped with a bandpass filter is used to capture the fluorescence image of the liquid film. This optical system utilizes spectral matching and spatial filtering techniques to effectively separate the excitation light and fluorescence signals, and can clearly identify Cd at the 50 μm scale. 2+ Distribution characteristics enable visual detection of the coverage area on the surface of cadmium telluride substrates.

[0036] 4. Conductivity Monitoring Procedure When using a non-contact eddy current probe (such as those from Eddydyne Technologies) to scan a liquid film on a substrate surface via a spiral path, the optimization of key scanning parameters has a decisive impact on the detection accuracy and reliability of ultrathin liquid films (50-120 nm). The scanning spacing is typically set within the range of 1-3 mm to ensure that more than 300 effective detection points are obtained on a 300 mm standard substrate, achieving the necessary spatial resolution. Too small a spacing leads to detection redundancy and reduced efficiency, while too large a spacing may fail to detect micro-area non-uniformity in the liquid film thickness. The scanning speed is preferably 400-800 mm / s. This range is designed to achieve dynamic synchronization with typical spraying speeds (550-600 mm / s), ensuring a speed difference of less than 150 mm / s, thereby avoiding detection signal distortion caused by relative motion lag. The probe lift height is preferably controlled between 0.5-2 mm. Too low a height may mechanically interfere with the extremely thin liquid film, while too high a height will cause significant attenuation of the eddy current signal (more than 50%). Therefore, close-range detection is crucial for maintaining high sensitivity. The preferred measurement frequency range is 500–2 MHz, with 1 MHz proven to provide optimal response sensitivity for liquid films with thicknesses ranging from 50–120 nm. This is because higher-frequency eddy currents can more effectively couple to the thin conductive film, enhancing the detection capability for minute changes in conductivity. By comprehensively optimizing these parameters, high-precision and high-efficiency online detection of the thickness and uniformity of this ultrathin liquid film can be achieved. A temperature sensor is integrated simultaneously to monitor the liquid film temperature in real time, and the temperature is compensated using the following formula: σ Tref = σ T · [1 + α(T - T ref )] Where: σ T The original conductivity (in mS / cm) was measured at temperature T; σ Tref To convert to reference temperature T ref Standard conductivity (mS / cm); T is the actual measured temperature (°C); T ref The reference temperature is ℃; α is the temperature coefficient of conductivity, usually taken as 0.02 / ℃.

[0037] Temperature compensation is applied to conductivity data, achieving an accuracy of ±0.3% after compensation. This effectively suppresses measurement errors introduced by ambient temperature fluctuations and ensures the reliability of conductivity data.

[0038] 5. Data fusion and analysis steps: (a) Determination of effective coverage area: The surface of the cadmium telluride substrate is divided into M×N equal-area grid units (e.g., the standard size of each grid is 1 mm × 1 mm), and each grid is used as an independent detection area; the fluorescence imaging signal and conductivity detection data of each grid are collected simultaneously. Based on the background signal intensity of the clean (uncovered) substrate measured in the pre-experiment, the fluorescence intensity threshold 3I0 and the conductivity threshold 3σ0 are set (I0 is the fluorescence background value, and σ0 is the conductivity background value); if the fluorescence intensity of any grid is ≥3I0 or the conductivity is ≥3σ0, it is determined to be an effective coverage area; when the fluorescence and conductivity results conflict, the conductivity data is given priority (because it is less affected by the uneven distribution of probes and can better reflect the actual coverage status).

[0039] (b) Coverage calculation: based on the formula: Coverage rate = (Number of effective coverage areas / Total number of areas) × 100% The effective coverage area is defined as the number of grid cells that meet the requirements of fluorescence ≥ 3I0 or conductivity ≥ 3σ0, i.e., the total number of grid cells that are determined to be effective coverage areas. The total number of areas is the total number of grid cells divided on the entire substrate surface, i.e., M×N. The coverage degree of the substrate surface is quantified by statistically counting the number of grid cells that meet the threshold conditions. A cross-validation mechanism for fluorescence and conductivity signals is established: when the quantification results of the two signals deviate by more than 12%, the cause analysis and area labeling will be performed automatically. Specifically, if the fluorescence signal of a certain area meets the standard (≥ 3I0) but the conductivity does not meet the standard (< 3σ0), it is judged as "probe surface aggregation, liquid film discontinuity", and this area is marked as false positive coverage caused by probe aggregation; if the conductivity of a certain area meets the standard (≥ 3σ0) but the fluorescence does not meet the standard (< 3I0), it is judged as "liquid film exists but probe distribution is significantly uneven or concentration is insufficient", and this area is marked as sub-healthy coverage that needs attention. Due to stringent quality control principles, it is not included in the regular statistics of effective coverage area, but it can be analyzed separately to guide adjustments to probe mixing uniformity. This mechanism effectively distinguishes between apparent signals and actual coverage status, improving the accuracy of detection and judgment.

[0040] (c) Uniformity calculation: based on the formula: Uniformity = ±(σ / μ) × 100% Where μ is the arithmetic mean of all measurements in the effective coverage area, and its calculation formula is: μ=Σx i / N Where Σ is the summation symbol, indicating that the measurements of all effective coverage areas are summed, and x iLet N be the measured value of the i-th effective coverage area (such as fluorescence intensity or conductivity value), and N be the total number of effective coverage areas, that is, the number of grid cells that meet the judgment conditions (such as fluorescence intensity ≥ 3I0 or conductivity ≥ 3σ0). σ is the standard deviation of measurements across all effective coverage areas, used to measure the dispersion of measurements from one area to the mean. Its calculation formula is typically as follows:

[0041] Where, N 1 represents the Bessel correction factor, which is used to achieve an unbiased estimate of the variance when calculating the sample standard deviation, thereby improving statistical accuracy. Uniformity is expressed as a percentage, calculated by multiplying the standard deviation by the mean (σ / μ) by 100%, representing the relative fluctuation or consistency of measurements at each detection point within the effective coverage area. The "±" in the formula indicates the degree of dispersion (range of fluctuation) around the mean; a smaller value indicates more concentrated measurements and better uniformity within the coverage area, while a larger value indicates poorer uniformity. By calculating this uniformity index, the distribution consistency, process stability, and measurement repeatability within each effective coverage area on the cadmium telluride substrate surface can be quantitatively assessed.

[0042] (d) Calculation of cadmium chloride content: Based on the temperature-compensated conductivity σ, using a pre-calibrated conductivity-content relationship model: C CdCl2 = a · σ 2 + b · σ + c Among them, C CdCl2 Cadmium chloride content (unit: g / m³) 2 The conductivity value is σ (or mol / L), where σ is the temperature-compensated conductivity measurement (unit: mS / cm). Coefficients a, b, and c are determined by fitting measured data of CdCl2 standard solutions of different concentrations (e.g., 0.1, 0.5, 1.0, 1.5, 2.0 mol / L) using the least squares method. This model can convert conductivity values ​​into solute content, enabling quantitative monitoring of solute distribution in the liquid film and rapid determination of whether a continuous and effective cadmium chloride liquid film has formed, effectively avoiding false coverage caused by dry spots, volatilization, or uneven distribution.

[0043] To improve the reliability and accuracy of detection, the fluorescence intensity obtained through the optical monitoring step is validated based on a pre-calibrated fluorescence intensity-concentration calibration model, the expression of which is: C CdCl2 = k · (I I0) Where I is the fluorescence intensity, I0 is the background fluorescence intensity, and k is the probe response coefficient.

[0044] When the calculation results of the two models are inconsistent, the results of the conductivity model shall be given priority because it is less affected by uneven probe distribution, optical interference, etc., and has higher stability.

[0045] To ensure the accuracy and applicability of the k value under ultra-thin liquid film conditions, this invention employs an "in-situ spraying calibration method," the specific steps of which are as follows: Step 1: Preparation of a series of standard solutions. Prepare a set of cadmium chloride standard solutions with known concentrations covering the process range, such as concentration gradients of 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, and 1.6 mol / L. In each standard solution, strictly maintain the Rhod-5N probe and Cd... 2+ The molar ratio was 50:1 (this ratio is optimized for 50-120 nm thin films). Stir for 30 min using a thermostatic magnetic stirrer (25 ± 0.5℃), ensuring the probe and Cd... 2+ Fully chelate to form a homogeneous and stable monitoring solution.

[0046] Step 2: Simulated spraying and standard sample preparation. Multiple clean 300 mm × 300 mm cadmium telluride substrates were used for ultrasonic spraying with parameters identical to those in formal production, including: nozzle movement speed 600 mm / s, solution flow rate 20 mL / min, atomization pressure 0.4 MPa, nozzle-substrate distance 50 mm, and substrate preheating temperature 60℃. Standard solutions of different concentrations were sprayed onto different substrates to form a series of standard liquid film samples with known concentrations and uniform film thickness (approximately 80 nm).

[0047] Step 3: Synchronous Measurement and Data Acquisition Within 5 seconds of liquid film formation (to prevent evaporation and drying), each standard sample is measured simultaneously: Optical measurement: The fluorescence intensity I at 9 points (3×3 matrix) in the central region of the liquid film was measured using an optical detection unit (532 nm laser excitation, 570 ± 10 nm filter acquisition) and the average value was taken.

[0048] Background measurement: The fluorescence intensity was measured under the same conditions on another clean, uncoated cadmium telluride substrate and recorded as the background fluorescence intensity I0.

[0049] Step 4: Data processing and coefficient determination. Calculate the net fluorescence intensity corresponding to each concentration point: ΔI = I - I0.

[0050] With CdCl2 concentration C CdCl2 Using ΔI as the x-axis and net fluorescence intensity ΔI as the y-axis, a linear regression analysis is performed, and the slope of the resulting straight line is the probe response coefficient k.

[0051] Step 5: Validation and cross-calibration. Substitute the calibrated k value into the system, randomly select a newly prepared sample, calculate its CdCl2 content using fluorescence method, and simultaneously measure it using conductivity detection unit and calculate its content using conductivity-cadmium chloride content relationship model.

[0052] If the difference between the results from the two methods remains less than 3%, the k-value calibration is considered successful. Otherwise, the calibration process or equipment status needs to be checked.

[0053] 6. Closed-Loop Control Steps: Closed-loop control is designed based on the fundamental differences in various process parameters: Coverage adjustment focuses on flow rate and speed, as its core function is to ensure the spatial continuity of the liquid film on the substrate, i.e., solving the "present" or "absent" problem. Under the premise of good atomization, the solution deposition volume per unit area is directly determined by the formula "flow rate / (speed × scanning interval)", therefore, adjusting the flow rate and speed can most effectively affect the coverage effect. Uniformity adjustment focuses on motion control and atomization quality, essentially optimizing the "uniformity" of thickness distribution. It is affected by the smoothness of mechanical motion, path overlap accuracy, droplet size distribution (affected by air pressure), and substrate surface wetting consistency (affected by temperature), therefore, all related adjustments revolve around these factors. Content deviation is a quantitative indicator, and its systematic error must be traced back to the input source, i.e., the actual concentration of the solution and the probe marking ratio. Therefore, the fundamental method of correction lies in adjusting the probe injection volume and compensating for the solution concentration.

[0054] Specifically, coverage reflects the continuity of the liquid film space, and the core adjustment is the amount of solution deposited per unit area. When the system detects that the coverage is lower than the preset target (≥95%), the system automatically adjusts the core parameter, the amount of solution deposited per unit area, according to the degree of deviation. For slight deviations (coverage between 90% and 95%), compensation is mainly achieved by increasing the solution flow rate by 5%–8% (i.e., from the baseline value of 20 mL / min to 21–21.6 mL / min). This is the most direct and linear fine-tuning method, which can supplement the deposition amount while minimizing interference with the atomization state. If a moderate deviation occurs (coverage between 80% and 90%), the system will simultaneously increase the flow rate by 10%–15% (to 22–23 mL / min) and reduce the nozzle movement speed by about 10% (e.g., from 600 mm / s to 540 mm / s). By synergistically increasing the discharge volume per unit time and the deposition time per unit area, the coverage effect is enhanced, while avoiding excessive droplet size due to simply increasing the flow rate. When a serious deviation occurs (coverage below 80%), the system will activate the "coverage enhancement mode" to implement a multi-parameter collaborative reset: increase the flow rate by 15%–20%, reduce the nozzle movement speed by 15%–20%, and check or increase the atomizing air pressure by about 0.05 MPa to quickly correct the seriously deviated spraying process state and rebuild effective liquid film coverage.

[0055] Uniformity reflects the consistency of liquid film thickness distribution, and the core adjustment focuses on the spray trajectory and atomization quality. When the system detects that the uniformity of the liquid film thickness distribution deviates from the preset target (within ±3%), it will optimize and adjust the spray trajectory and atomization quality according to the degree of deviation. For slight deviations (uniformity deviation between ±3% and ±5%), while ensuring coverage meets the target, the system will fine-tune the nozzle movement speed by approximately ±5%, and initially optimize slight streaks or unevenness caused by mechanical scanning speed instability by changing the path overlap rate. When a moderate deviation occurs (deviation between ±5% and ±8%), the system will collaboratively increase the path overlap rate (e.g., from the baseline value of 30% to 40%) and fine-tune the atomization pressure by approximately ±0.02MPa to simultaneously improve the coverage smoothness of the scanning path and the uniformity of droplet size distribution. If a serious deviation occurs (uniformity deviation exceeds ±8%), the system will comprehensively increase the substrate preheating temperature by 5–10°C to enhance solution wetting and spreading uniformity, and perform dynamic replenishment spraying on low-thickness areas identified by the software (such as reducing the scanning speed of the area by 20%), thereby accurately compensating for thickness differences caused by uneven temperature or fixed airflow interference based on real-time image feedback.

[0056] Cadmium chloride (CdCl2) content deviation reflects systematic errors in the overall deposition amount or probe labeling rate, and the core adjustment is the calibration input concentration. When the system detects that the CdCl2 content deviates from the preset target (within ±2%), it will perform graded corrections based on the calibration input concentration. For slight deviations (between ±2% and ±3%), the system adjusts the probe injection rate by ±3%–5% according to the direction of the deviation to directly correct minor drifts in fluorescence labeling efficiency that may be caused by batch differences in probes. This is the preferred light adjustment method when there is a slight inconsistency between conductivity and fluorescence detection results. If a moderate deviation occurs (between ±3% and ±5%), concentrated CdCl2 mother liquor or deionized water is added to the main liquid path by controlling the preparation module to adjust the overall solution concentration by ±5%, thereby fundamentally correcting the systematic deposition amount deviation and ensuring the accuracy of the input substance concentration. When a severe deviation occurs (deviation exceeding ±5%), it indicates that the process may be in an unreliable state due to sensor drift, probe contamination, or actuator failure. The system will immediately suspend production and initiate a system-level recalibration process, including flushing the pipeline with a standard solution and recalibrating the conductivity probe and optical system to completely restore the baseline accuracy of measurement and execution.

[0057] This method leverages the complementary advantages of optical and electrical detection to establish a comprehensive quality assessment system. By combining the intuitiveness of fluorescence imaging with the quantitative nature of conductivity measurement, it significantly improves detection reliability. Practical applications show that this method can stabilize coating coverage at 90%-98% and control uniformity within ±5%, effectively solving industry problems such as lagging quality control and significant material waste in traditional processes.

[0058] To verify the practical effectiveness of the monitoring and control system of this invention, the cadmium chloride spraying process in the preparation of cadmium telluride thin-film batteries was selected and compared with a traditional open-loop control system under the same production environment. The experiment was conducted from two dimensions: process control effect, response time, and detection accuracy, as detailed below: Example 1: Verification of Process Control Effectiveness A 300×300mm cadmium telluride substrate was used, and CdCl2 spraying was performed using both a conventional open-loop control system and the online monitoring and control system for cadmium chloride coating quality of cadmium telluride thin-film batteries proposed in this invention. The system performance was evaluated by comparing the CdCl2 coverage uniformity, material consumption, and final battery efficiency under the two processes.

[0059] Test conditions: The CdCl2 solution concentration was 1.2 mol / L, the molar ratio of the fluorescent probe Rhod-5N to Cd2+ was 50:1, the spraying temperature was controlled at 25±2 ℃, the nozzle moving speed was 600 mm / s, the flow rate was 15 mL / min, the atomizing gas pressure was 0.4 MPa, and the nozzle-substrate distance was 50 mm. The system divided the substrate area into 1 mm × 1 mm grids and calculated the coverage and uniformity in real time.

[0060] Test results show that when using traditional open-loop control, the cadmium chloride coverage is 83.2%, and the uniformity is poor (fluctuation range of ±6.7%). The cadmium chloride consumption per unit area is 1.85 g / m², and the final battery efficiency is 15.7%.

[0061] After adopting the system of this invention, the cadmium chloride coverage was significantly improved to 97.5%, uniformity was greatly improved (fluctuation range was only ±1.2%), cadmium chloride consumption was reduced to 1.32 g / m², a decrease of 28.6%, and battery efficiency was improved to 17.2%. Specific data comparisons are shown in the table below:

[0062] Example 2: Comparison Experiment of Response Time and Detection Accuracy To evaluate the improvements of the system of the present invention in terms of response speed and detection sensitivity compared with traditional methods, a control experiment was set up as follows: Traditional methods (detection of open-loop control dependencies): Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were used to sample and test the substrate after spraying to analyze the distribution and content of Cd. Each test required sampling, vacuuming, testing, and data processing, with an average time of >2 hours, a response delay of over 30 minutes, and the inability to obtain distribution information with a spatial resolution of <100 μm.

[0063] The system of this invention: Fluorescence imaging and conductivity scanning are performed simultaneously during the spraying process. The system collects data every 0.1 seconds and generates Cd values ​​in real time. 2+ The system automatically calculates coverage and uniformity using distribution and conductivity maps, and adjusts spraying parameters in real time when anomalies are detected, with a response delay controlled within 200–500 ms. Specific performance comparisons are shown in the table below:

[0064] The system of this invention uses synchronous real-time monitoring of fluorescent probes and conductivity to detect Cd. 2+ The detection sensitivity has been improved to 0.5 μg / cm. 2(Reducing costs by 20 times compared to traditional methods), achieving a spatial resolution of 30–50 μm (capable of identifying micron-level coverage defects), and controlling response latency to the millisecond level (200–500 ms), this represents a leap from "offline sampling inspection + post-event adjustment" to "online real-time monitoring + instant feedback." It solves the problem of over- / under-adjustment of process parameters caused by detection lag in traditional open-loop control, improving the accuracy of the CdCl2 spraying process and the efficiency of battery fabrication.

[0065] Comparative experiments show that the monitoring and control system of this invention is superior to traditional open-loop control in both process control effect (coverage, uniformity, material consumption, battery efficiency) and real-time monitoring capability (response speed, detection accuracy), verifying its practical value and technological advancement in the preparation of cadmium telluride thin-film batteries.

[0066] In summary, through verification of the system's process control effects and comparison of real-time monitoring performance, it is fully demonstrated that the cadmium chloride spraying monitoring and control system for cadmium telluride thin-film batteries proposed in this invention significantly outperforms traditional open-loop control methods in terms of process accuracy, material utilization, and battery performance. This system achieves online real-time monitoring from offline sampling detection, not only increasing cadmium chloride coverage to 97.5% and reducing material consumption by 28.6%, but also improving battery efficiency to 17.2%. Simultaneously, it achieves precise monitoring with millisecond-level response and micron-level spatial resolution, effectively solving the problem of parameter inaccuracy caused by detection lag in traditional processes.

Claims

1. A monitoring and control system for cadmium chloride spraying in cadmium telluride thin-film batteries, characterized in that, include: The material preparation module includes a cadmium chloride solution storage unit, a probe injection unit for injecting cadmium ion fluorescent probes into the cadmium chloride solution, and a solution temperature control unit for controlling the temperature of the cadmium chloride solution. A spraying module includes a spraying unit for spraying a cadmium chloride solution containing the cadmium ion fluorescent probe onto the surface of a cadmium telluride substrate to form a liquid film. The online detection module includes: An optical detection unit is used to excite and capture the fluorescence image of the liquid film; A conductivity detection unit is used for non-contact measurement of the conductivity of the liquid film; The data processing and control module is communicatively connected to the material preparation module, the spraying module, and the online detection module, and is configured as follows: The fluorescence image and conductivity data are received and processed to calculate the coverage, uniformity, and cadmium chloride content of the liquid film on the cadmium telluride substrate surface. Based on the deviations of the coverage, uniformity, and cadmium chloride content from the preset target values, the spraying parameters of the spraying unit and / or the injection parameters of the probe injection unit are dynamically adjusted.

2. The system according to claim 1, characterized in that, The cadmium ion fluorescent probe is selected from one or more of the following: Rhodamine derivative (Rhod-5N) probes, water-soluble porphyrin probes, dipyridine methylamine-functionalized porphyrin probes, and thiol-modified cadmium telluride quantum dot probes; the cadmium ion fluorescent probe and Cd 2+ Specific chelation forms a fluorescent complex.

3. The system according to claim 2, characterized in that, The cadmium ion fluorescent probe reacts with Cd in the cadmium chloride solution. 2+ The molar ratio is (15-100):

1.

4. The system according to claim 1, characterized in that, The optical detection unit includes an excitation light source, a high-speed CMOS camera, and a filter; The emission wavelength of the excitation light source is 400-600nm; The filter is positioned in front of the high-speed CMOS camera, and its transmission wavelength is 550-600nm. The high-speed CMOS camera is used to acquire fluorescence images after being filtered by the filter, and to transmit the fluorescence images to the data processing and control module.

5. The system according to claim 1, characterized in that, The conductivity detection unit includes an eddy current probe, a temperature sensor, a signal processor, and a scanning mechanism. The scanning mechanism is configured to drive the eddy current probe to scan the surface of the cadmium telluride substrate along a predetermined path; The temperature sensor is configured to monitor the ambient temperature in real time to compensate for the temperature of the conductivity measurement. The signal processor is configured to receive and process signals from the eddy current probe and the temperature sensor, and output compensated conductivity data.

6. The system according to claim 1, characterized in that, The data processing and control module includes a data processing unit, a PID controller, a nozzle adjustment unit, and an injection pump adjustment unit; The data processing unit is configured to perform the calculations of coverage, uniformity, and cadmium chloride content, and generate control instructions based on the calculation results; The PID controller is communicatively connected to the data processing unit and is configured to receive the control command and output the corresponding adjustment signal. The nozzle adjustment unit is connected to the PID controller and is configured to adjust the spraying path, moving speed and spraying flow rate of the spraying unit according to the adjustment signal. The injection pump regulating unit is connected to the PID controller and is configured to adjust the injection volume of the fluorescent probe in the probe injection unit and the mixing ratio with the cadmium chloride solution according to the regulating signal.

7. A monitoring and control method for implementing an online monitoring and control system for the cadmium chloride coating quality of cadmium telluride thin-film batteries according to any one of claims 1 to 6, characterized in that, The method includes the following steps: Monitoring solution preparation steps: Inject cadmium ion fluorescent probes into cadmium chloride solution and mix to form the monitoring solution to be coated; Coating liquid film step: The monitoring solution is coated onto the surface of a cadmium telluride substrate to form a liquid film; Optical monitoring step: Excite and capture fluorescence images of the liquid film; Conductivity monitoring steps: Non-contact measurement of the conductivity of the liquid film; Data fusion analysis steps: The fluorescence image and conductivity data are fused and processed to calculate the coverage and uniformity of the liquid film on the cadmium telluride substrate surface, and the cadmium chloride content in the liquid film is calculated based on the pre-stored conductivity-cadmium chloride content relationship model. Closed-loop control steps: Based on the deviations of the coverage, uniformity, and cadmium chloride content from their respective preset target values, dynamically adjust the coating process parameters and / or the preparation parameters of the monitoring solution.

8. The method according to claim 7, characterized in that, In the data fusion analysis step, the calculation of coverage and uniformity includes the following process: The area division step is as follows: The surface of the cadmium telluride substrate is uniformly divided into M×N equal-area grids, and each grid constitutes an independent detection area; Coverage status determination step: Based on the fluorescence image data or conductivity data, obtain the measurement value of each detection area. When the measurement value of a certain detection area exceeds a preset threshold, the detection area is determined to be an effective coverage area. Coverage calculation steps: The coating coverage rate is calculated based on the formula Coverage Rate = (Number of effective coverage areas / Total number of areas) × 100%, where the number of effective coverage areas is the number of areas determined to be effective coverage areas, and the total number of areas is the total number of the M×N grids; Uniformity calculation steps: Extract the measurement values ​​of all effective coverage areas, calculate their average value μ and standard deviation σ, and determine the coating uniformity based on the formula uniformity = ±(σ / μ)×100%.

9. The method according to claim 7, characterized in that, The conductivity-cadmium chloride content relationship model is as follows: C CdCl2 =a·s 2 +b·s+c Among them, C CdCl2 σ represents the cadmium chloride content, σ is the measured conductivity value after temperature compensation, and a, b, and c are the fitting coefficients determined through calibration experiments. The temperature compensation is achieved by the following formula: s Tref =s T ·[1+α(TT ref )] Where, σ T σ is the original conductivity measured at temperature T. Tref To convert to reference temperature T ref The standard conductivity is given below, where T is the actual temperature during measurement. ref The reference temperature is α, and the temperature coefficient of conductivity is α.

10. The method according to claim 9, characterized in that, The data fusion analysis step also includes calibrating and verifying the cadmium chloride content measured by the conductivity-cadmium chloride content relationship model based on the fluorescence intensity-concentration calibration model. The fluorescence intensity-concentration calibration model is expressed as follows: C CdCl2 =k×(I-I0) Among them, C CdCl2 denoted as cadmium chloride content, I as measured fluorescence intensity, I0 as background fluorescence intensity, and k as probe response coefficient; When the cadmium chloride content measured based on the fluorescence intensity-concentration calibration model and the conductivity-cadmium chloride content relationship model are inconsistent, the cadmium chloride content measured based on the conductivity-cadmium chloride content relationship model shall be taken as the standard.

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