EP3008480A1 - A device, a method, and a computer program for testing of photovoltaic devices - Google Patents

A device, a method, and a computer program for testing of photovoltaic devices

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Publication number
EP3008480A1
EP3008480A1 EP14811679.1A EP14811679A EP3008480A1 EP 3008480 A1 EP3008480 A1 EP 3008480A1 EP 14811679 A EP14811679 A EP 14811679A EP 3008480 A1 EP3008480 A1 EP 3008480A1
Authority
EP
European Patent Office
Prior art keywords
photovoltaic device
output current
frequency
photocurrent
light sources
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP14811679.1A
Other languages
German (de)
French (fr)
Other versions
EP3008480A4 (en
Inventor
Jonas BERGQVIST
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Individual
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Publication of EP3008480A1 publication Critical patent/EP3008480A1/en
Publication of EP3008480A4 publication Critical patent/EP3008480A4/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S50/00—Monitoring or testing of PV systems, e.g. load balancing or fault identification
    • H02S50/10—Testing of PV devices, e.g. of PV modules or single PV cells
    • H02S50/15—Testing of PV devices, e.g. of PV modules or single PV cells using optical means, e.g. using electroluminescence
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S50/00—Monitoring or testing of PV systems, e.g. load balancing or fault identification
    • H02S50/10—Testing of PV devices, e.g. of PV modules or single PV cells
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21S—NON-PORTABLE LIGHTING DEVICES; SYSTEMS THEREOF; VEHICLE LIGHTING DEVICES SPECIALLY ADAPTED FOR VEHICLE EXTERIORS
    • F21S8/00—Lighting devices intended for fixed installation
    • F21S8/006—Solar simulators, e.g. for testing photovoltaic panels
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy

Definitions

  • the present invention relates to a device, a method, and a computer program for testing of photovoltaic devices.
  • PVDs photo voltaic devices
  • solar cells There are several different types of solar cells, such as silicon based solar cells, and the recently developed thin organic solar cells, e.g produced by means of printing.
  • Quality control is an essential step in the production process for photo voltaic devices, to ensure that the efficiency of the photo voltaic devices meet the desired requirements. This is important for both large scale and small scale production of photo voltaic devices. Quality control may also be important in the research and development of photovoltaic devices.
  • Testing of solar cells is at present commonly performed by either illuminating the entire solar cell at once or in a small area and scanning across the entire surface of the solar cell and measuring the output current generated by the solar cell.
  • US8239165 discloses an apparatus for measuring quantum efficiency, QE, of solar cells.
  • the apparatus includes a light source including an array of light emitting diodes, LEDs, that each emit light corresponding to a differing portion of a test spectrum and each LED is driven by a sinusoidal power supply that operates at a unique frequency.
  • the light source includes an optical coupling focusing the LED light into a test beam targeted on a solar cell, and a signal conditioner converts analog current signals generated by the solar cell into digital voltage signals.
  • a QE measurement module determines a QE value corresponding to each of the LEDs based on the digital voltage signals using a Fast Fourier Transform module that processes the digital voltage signals to generate values for each operating frequency.
  • the QE measurement module determines the QE values by applying a conversion factor to these values. Since all the LEDs can be power-modulated simultaneously and the corresponding cell responses to each of the LEDS can be analyzed simultaneously, the QE spectrum measurement time is greatly shortened as compared to conventional methods.
  • US2013/0021054 discloses an apparatus used for simulating spectrum of solar radiation and testing a photovoltaic device using the simulated spectrum of solar radiation.
  • the apparatus may include a light-source device configured to reproduce spectrum of solar radiation, the light-source device comprising a radiation plate divided into a plurality of cells, and each of the cells comprises a plurality of light-emitting diodes emitting at least two different wavelengths, and a substrate support disposed opposite to the light-source device.
  • the plurality of light-emitting diodes emit a wavelength that is selected from the group consisting of colours blue, green, yellow, red, a first and a second colour in infrared having different wavelengths with respect to each other.
  • Another testing method for photo voltaic devices is that of using a focused laser beam to scan across the surface of the photo voltaic device.
  • the laser beam is moved in at least two directions across the photo voltaic device, illuminating a small area of the cell at each measuring instance until the total area of the cell has been covered.
  • this testing method is slow and thus time consuming since the scanning of the cell is performed by a single laser beam and needs to be performed in at least two directions.
  • the technique further has the drawback of being expensive and complex since it involves delicate and intricate components to focus and control the laser beam.
  • An object of the invention is therefore to provide a device, a method, a system and a computer program for fast localisation of defects in a photovoltaic device.
  • a further object of the invention is to achieve said localisation in a cost effective manner.
  • a photocurrent testing device for testing photovoltaic devices such as solar cells.
  • This device includes a plurality of pulsating light sources and a signal generator which generates an individual driving frequency for each light source. This causes each light source to pulsate at an individual frequency corresponding to its individual driving frequency.
  • an amplifier unit which collects output current from the photovoltaic device and amplifies the output current at each individual frequency.
  • the photocurrent testing device further included in the photocurrent testing device are analysing means which analyse the amplitude of the output current at each individual frequency wherein the output current at each individual frequency originates from the light source pulsating at the same individual frequency, and where each light source illuminates a specific spot on the photovoltaic device.
  • the amplitude of the output current at each individual frequency is matched with a corresponding specific spot on the photovoltaic device.
  • the photocurrent testing device will match differences in the amplitude of the output current of the photovoltaic device to a specific spot on the photovoltaic device, such that a plurality of defects can be localised simultaneously in a fast and cost effective manner.
  • the light sources are light emitting diodes, LEDs.
  • Light emitting diodes are inexpensive to buy and operate, and have a long lifetime.
  • the light sources are preferably adapted to have the same light emitting spectrum. This allows for a more efficient calibrating of the device.
  • the light sources are arranged in a single row.
  • the row of light sources covers the entire width of the photovoltaic device to be tested, allowing the device to scan the entire width of the solar cell in one run, thereby enabling a faster and continuous testing of photovoltaic devices arranged as solar panels.
  • the light sources are arranged in a matrix that illuminates the full solar cell or parts of the solar cell.
  • the light sources are arranged to move relative to the photovoltaic device in one direction.
  • the individual driving frequencies are evenly distributed within a predetermined frequency interval, thereby simplifying calculations performed in the analyzing means.
  • the amplifier unit is a lock-in amplifier unit.
  • the signal generator is comprised within the lock-in amplifier unit.
  • a method for testing a photovoltaic device comprises a first step of generating an individual driving frequency for each of a plurality of light sources.
  • each of the light sources is driven with its individual driving frequency such that each light source pulsates at an individual frequency corresponding to its driving frequency.
  • each light source illuminates a specific spot on the photovoltaic device.
  • output current from the photo voltaic device is collected and the current at each individual frequency is amplified.
  • the amplitude of the output current is analysed at each individual frequency, wherein the output current at each individual frequency originates from the light source pulsating at the same individual frequency.
  • the amplitude of the output current at each individual frequency is matched with a corresponding specific spot on the photovoltaic device.
  • a photocurrent map of the photovoltaic device is created, simplifying the further assessment of the data obtained.
  • the quality of the photovoltaic device is assessed.
  • the objects of the invention are also achieved in a system for testing photovoltaic devices comprising a photocurrent testing device and a computer program for controlling a method for testing a photovoltaic device.
  • Figure 1 shows a schematic layout of the inventive photocurrent testing device
  • Figure 2 shows a schematic layout of a part of an embodiment of the photocurrent testing device
  • Figure 3 shows a flow chart illustrating the method according to the invention.
  • Figure 4 shows examples of photocurrent maps produced with the system acco to the invention
  • Figure 5 shows the principles of quantum efficiency determination for a photovoltaic device.
  • FIG. 1 shows a schematic layout of a photocurrent testing device 100 according to the present invention.
  • the photocurrent testing device 100 is for testing a photovoltaic device 120, such as an organic solar cell or a silicon wafer solar cell.
  • the photocurrent testing device 100 comprises a plurality of light sources 110. There may be as few as two light sources 110, as many as one thousand, any number in between, or more than one thousand.
  • the light sources could be any kind of light sources, such as light emitting diodes, LED, lasers, or gas-discharge lamps.
  • the light emitting spectra of the light sources 110 should at least partially overlap with the absorption spectrum of the photovoltaic device 120 to be tested.
  • a preferred light emitting spectrum of the light sources 110 should lie within or at least have significant parts within the wavelength interval 350- 1100 nm, and more specifically within 400-700 nm. This is to maximise the current output from the photovoltaic device 120 for a given power of the illuminating light.
  • all the light sources 110 are adapted to have the same light emitting spectrum, since photovoltaic devices 120 normally responds differently to different wavelengths of incoming light. With all the light sources 110 having the same light emitting spectrum, no correction factor for the light spectrum has to be taken into account.
  • Each light source 110 emits a light cone 115 which illuminates a corresponding spot 116 on the photovoltaic device.
  • the light sources 110 are arranged such that their respective illuminated spots 116 on the photovoltaic device do not significantly overlap.
  • the light intensity in the overlapping part of two spots 116 is in one example of the invention kept one or more orders of magnitude lower than the light intensity in the non-overlapping parts of a spot 116.
  • the term spot 116 refers to a small area, typically circularly shaped.
  • One or more optical elements, such as lenses or filters, may be provided between the light sources 110 and the corresponding spots 116. This is for controlling or defining the size and shape of the corresponding spot 116, and for controlling and defining the spectrum of the illuminating light.
  • the light sources 110 are driven by a signal generator 130 which is connected to the light sources 110 via one or more cables 135.
  • the signal generator 130 generates for each light source 110 an individual driving frequency such that each light source 110 pulsates at an individual frequency corresponding to its individual driving frequency.
  • the signal generator is preferably able to produce many different driving frequencies, since the photovoltaic testing device 100 may comprise a large number of light sources 110, each light source 110 requiring its own individual driving frequency.
  • a multiplexing unit is provided between the signal generator 130 and the light sources 110.
  • the photovoltaic device 120 As the photovoltaic device 120 is illuminated by the light sources 110, it will generate a photocurrent. Every spot 116 will generate a pulsating photocurrent with the individual frequency equal to the individual frequency of the light source 110 illuminating that specific spot 116.
  • the total photocurrent generated by the photovoltaic device 120 is the sum of the photocurrents produced by each illuminated spot 116. Therefore, the total photocurrent comprises a frequency component for each of the individual driving frequencies of the light sources 110.
  • the photovoltaic device 120 is defect in a specific spot 116, the amount of current generated in that spot 116 will be lower than in a non-defect spot.
  • the term defect refers to any deviation from the optimal functioning of the photovoltaic device 120, such as total dysfunction, degradation or any other impaired operational characteristics. Consequently, the contribution to the total photocurrent at the frequency corresponding to the defect spot will be lower than from a non-defect spot.
  • Said total photocurrent constitutes the output current from the photovoltaic device 120.
  • the output current is collected by an electrical cable 145 connecting the photovoltaic device 120 to an amplifier unit 140.
  • the amplifier unit 140 transfers the output current signal from the time domain to the frequency domain by means of a Fourier transform or a Fast Fourier Transform, FFT, and amplifies the output current at each individual driving frequency of the light sources 110.
  • the current component at each individual frequency is typically very small since it originates from a corresponding, typically very small spot 116 on the photovoltaic device. Amplification of these small current components is thus advantageous in order to more easily distinguish them from white noise.
  • the driving frequencies generated by the signal generator 130 are also directly input to the amplifying unit 140 to enable amplification at exactly these frequencies. This can for example be achieved by a lock-in amplifier.
  • the amplifying unit 140 is a signal analyser with combined lock-in amplifier.
  • the signal generator 130 and the amplifier unit 140 are comprised within the same unit.
  • the amplitude of the output current at each individual frequency is analysed by analysing means 150.
  • the analysing means 150 is preferably constituted by a computer.
  • the driving frequencies, which individual driving frequency corresponds to which light source 110, and the physical position of each spot 116 are preferably predetermined and known to the analysing means 150. Since illuminating the photovoltaic device 100 with the individual frequency of the light source results in the generation of a current pulsating with the same individual frequency, the analysing means 150 can match each of the output current amplitudes with a specific light source 110, via their common pulsating frequency. Since each light source 110 is responsible for illuminating a specific spot 116 on the photovoltaic device 120, each output current amplitude component can be paired with the specific spot 116 in which it was generated.
  • the driving frequencies of the light sources 110 are equally distributed in a frequency interval.
  • the difference in driving frequencies between two light sources 110 are multiples of 1000 Hz, such that one light source 110 is driven with 1000 Hz, another with 2000 Hz, yet another with 4000 Hz and so on.
  • the differences in driving frequencies are multiples of 100 Hz.
  • the output current of the photovoltaic device 120 has to be inputted to the amplifying unit for at least one full period of the differences in driving frequencies , i.e., for example for at least 10 ms when the differences in driving frequencies is 100 Hz and the lowest driving frequency is at least 100 Hz and for at least 1 ms when the differences in driving frequencies is 1000 Hz and the lowest driving frequency is at least lOOOHz.
  • This is to assure that at least one period of the lowest driving frequency can be integrated in the Fourier transform or the FFT and to assure that the differences in frequency are detected.
  • measuring the phase from the FFT will enable two light sources driven at the same frequency, as they can be separated by a phase difference.
  • the analysing means 150 may comprise a computer program which controls the signal generator 130, and the amplifier unit 140 during the testing of the photovoltaic device 120, as well as the positioning of the light sources 110 relative to the photovoltaic device 120. In one example, the analysing means 150 also processes the data obtained during the testing, for example creates a photocurrent map 400, 450 over the tested photovoltaic device 120 and/or uses an algorithm in which the current amplitudes are compared with a predefined model in order to assess the quality of the tested photovoltaic device 120.
  • Figure 2 shows a schematic layout of a part of an embodiment of the photocurrent testing device.
  • the light sources 110 are arranged in a single row in a list 111, wherein the list covers the entire width of the photovoltaic device 120.
  • a strip 112 covering the entire width of the photovoltaic device can be illuminated and thus tested simultaneously.
  • Letting the list 111 scan the photovoltaic device in a direction perpendicular to said strip 112 enables progressive testing of further strips of the photovoltaic device. Consequently, the entire or part of the area of the photovoltaic device may be tested in a continuous testing procedure.
  • said scanning is realized by moving the photovoltaic device relative to the list 111 of light sources 110 in a direction 121 perpendicular to the list.
  • the list 111 is kept in a fixed position and only the photovoltaic device 120 moves, or the photovoltaic device 120 is kept in a fixed position and only the list 111 moves, or both the list 111 and the photovoltaic device 120 are arranged to move.
  • the photovoltaic device 120 is transported on a conveyor belt and the list 111 is fixedly mounted above said conveyor belt.
  • the speed at which the photovoltaic device 120 can be moved relative to the list 111 of light sources 110 is limited by the integration time as described in connection with the Fourier. This is due to that the resolution in the direction of the move of the photovoltaic device 120 will be limited by how much the photovoltaic device 120 moves under the integration time.
  • Figure 3 shows a flowchart 300 describing a method for testing a photocurrent device.
  • the method comprises a first step 305 of generating an individual driving frequency for each of a plurality of light sources 110.
  • the method further comprises an additional step 310 of driving each of the light sources 110 with its individual driving frequency, causing each light source 110 to pulsate at an individual frequency corresponding to its driving frequency.
  • the next step 315 comprises illuminating for each light source 110 a specific spot on the photovoltaic device 120.
  • the next step 320 comprises collecting output current from the photovoltaic device 120 and amplifying the current at each individua l frequency.
  • the next step 325 comprises measuring the amplitude of the output current at each individual frequency, wherein the output current at each individual frequency originates from the light source pulsating at the same individual frequency.
  • the next step 330 comprises matching the measured amplitude of the output current at each individual frequency with a corresponding specific spot 116 on the photovoltaic device 120.
  • step 340 further spots on the photovoltaic device 120 are to be measured, the light sources 110 are moved a predetermined distance relative to the photovoltaic device 120.
  • the photovoltaic device 120 may be moved relative to the light sources 110. The movement can be executed in a step-wise manner, or continuously throughout the testing.
  • An optional further step 345 comprises creating a photocurrent map 400, 450.
  • This map 400, 450 can be a visualization of the measured current amplitudes matched to specific spots 116 on the photovoltaic device, or a data set of such a matching.
  • An optional further step 350 comprises assessing the quality of the photovoltaic device. This assessment 350 can be made using the photocurrent map 400, 450 through a visual assessment or other means such as a computer 160 performing calculations on the photocurrent map 400, 450.
  • Figure 4 shows examples of photocurrent maps produced with the system according to the present invention. The map in Figure 4a illustrates a photocurrent map 400 in which the photocurrent across a solar cell is illustrated 410.
  • the photocurrent at different areas of the solar cell is in this example illustrated using gray scale 405, and associating different values of the photocurrent to different shades of gray.
  • Defects 415 can in this way be identified as areas of the solar cell that give rise to photocurrents outside a preferred predetermined photocurrent range or value.
  • the map in Figure 4b shows a photocurrent map in the form of a matrix 450.
  • the matrix 450 comprises a number of cells 480 arranged in columns 470 and rows 460 wherein each cell 480 corresponds to a specific spot 116 on the photo voltaic devices.
  • An area of the photo voltaic device 120 is illuminated by a light source 110 with a specific frequency and the photocurrent with corresponding frequency is isolated and amplified and the value of the photocurrent is presented in the correct cell 480 in the matrix 450.
  • the amount of cells 480 may be increased or decreased depending on the desired speed of the production of and resolution of the photocurrent map.
  • the data acquired in the assessment may be retrieved as raw data.
  • the data acquired in the assessment may be presented on a display.
  • the data acquired in the assessment may be printed as a raw data, a photocurrent map and/or a matrix.
  • the data may further be presented as a three dimensional plot.
  • the presentation of data is however not limited to the above described forms.
  • An operator may assess the presented data.
  • the presented data may further be automatically assessed.
  • Figure 5 discloses principles of quantum efficiency determination for a photovoltaic device.
  • a light source 510 such as a light emitting diode, LED, illuminates a photovoltaic device.
  • the reflectance from the photo voltaic device is measured in a first photo detector 530.
  • transmittance of the photovoltaic device is determined in a second photo detector 540.
  • external quantum efficiency, EQE can be determined from the photocurrent for the wavelength of the illuminating light.
  • IQE can be determined when the reflectance and/or transmittance of the photovoltaic device has been established.
  • the photovoltaic testing device includes first and/or second photo detectors for determining reflectance and/or transmittance of the photoelectric device.
  • the analysing means are in accordance with this aspect of the invention, arranged to perform the analysis to determine EQE as well as IQE.

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  • Photovoltaic Devices (AREA)

Abstract

The present invention relates to a photocurrent testing device (100) for testing photovoltaic devices (120) such as solar cells. This device (100) includes a plurality of pulsating light sources (110) and a signal generator (130) which generates an individual driving frequency for each light source(110). This causes each light source (110) to pulsate at an individual frequency corresponding to its driving frequency. Also included in the photocurrent testing device (100) is an amplifier unit (140) which collects output current from the photovoltaic device (120) and amplifies the output current at each individual frequency. Further included in the photocurrent testing device (100) are analysing means (150) which analyse the amplitude of the output current at each individual frequency wherein the output current at each individual frequency originates from the light source pulsating at the same individual frequency, and where each light source (110) illuminates a specific spot(116) on the photovoltaic device. The amplitude of the output current at each individual frequency is matched with a corresponding specific spot(116) on the photovoltaic device.

Description

A DEVICE, A METHOD, AND A COMPUTER PROGRAM FOR TESTING OF PHOTOVOLTAIC DEVICES
TECHNICAL FIELD
The present invention relates to a device, a method, and a computer program for testing of photovoltaic devices.
BACKGROUND
With diminishing fossil fuels and increased awareness of the climate change, there is a global increase in the demand for renewable energy sources. Solar energy is being viewed as one of the most available and reliable renewable energy sources. The use of photo voltaic devices, PVDs, such as solar cells is important in the harvesting of solar energy. There are several different types of solar cells, such as silicon based solar cells, and the recently developed thin organic solar cells, e.g produced by means of printing.
Quality control is an essential step in the production process for photo voltaic devices, to ensure that the efficiency of the photo voltaic devices meet the desired requirements. This is important for both large scale and small scale production of photo voltaic devices. Quality control may also be important in the research and development of photovoltaic devices.
Testing of solar cells is at present commonly performed by either illuminating the entire solar cell at once or in a small area and scanning across the entire surface of the solar cell and measuring the output current generated by the solar cell.
US8239165 discloses an apparatus for measuring quantum efficiency, QE, of solar cells. The apparatus includes a light source including an array of light emitting diodes, LEDs, that each emit light corresponding to a differing portion of a test spectrum and each LED is driven by a sinusoidal power supply that operates at a unique frequency. The light source includes an optical coupling focusing the LED light into a test beam targeted on a solar cell, and a signal conditioner converts analog current signals generated by the solar cell into digital voltage signals. A QE measurement module determines a QE value corresponding to each of the LEDs based on the digital voltage signals using a Fast Fourier Transform module that processes the digital voltage signals to generate values for each operating frequency. The QE measurement module determines the QE values by applying a conversion factor to these values. Since all the LEDs can be power-modulated simultaneously and the corresponding cell responses to each of the LEDS can be analyzed simultaneously, the QE spectrum measurement time is greatly shortened as compared to conventional methods.
US2013/0021054 discloses an apparatus used for simulating spectrum of solar radiation and testing a photovoltaic device using the simulated spectrum of solar radiation. The apparatus may include a light-source device configured to reproduce spectrum of solar radiation, the light-source device comprising a radiation plate divided into a plurality of cells, and each of the cells comprises a plurality of light-emitting diodes emitting at least two different wavelengths, and a substrate support disposed opposite to the light-source device. In one example, the plurality of light-emitting diodes emit a wavelength that is selected from the group consisting of colours blue, green, yellow, red, a first and a second colour in infrared having different wavelengths with respect to each other.
Another testing method for photo voltaic devices is that of using a focused laser beam to scan across the surface of the photo voltaic device. The laser beam is moved in at least two directions across the photo voltaic device, illuminating a small area of the cell at each measuring instance until the total area of the cell has been covered. However, this testing method is slow and thus time consuming since the scanning of the cell is performed by a single laser beam and needs to be performed in at least two directions. The technique further has the drawback of being expensive and complex since it involves delicate and intricate components to focus and control the laser beam. The methods and apparatus disclosed in US8239165 and US2013/0021054 can be used for testing the overall performance of the photo voltaic device, but cannot be used to localise defects in a photo voltaic device. Therefore, there is a need in the art for a device, a method, a system and a computer program that enables fast localisation of defects. SUMMARY OF INVENTION
An object of the invention is therefore to provide a device, a method, a system and a computer program for fast localisation of defects in a photovoltaic device. A further object of the invention is to achieve said localisation in a cost effective manner. The invention is set forth and characterized in the main claims, while the dependent claims describe additional aspects of the invention.
The objects of the invention are achieved by a photocurrent testing device for testing photovoltaic devices such as solar cells. This device includes a plurality of pulsating light sources and a signal generator which generates an individual driving frequency for each light source. This causes each light source to pulsate at an individual frequency corresponding to its individual driving frequency. Also included in the photocurrent testing device is an amplifier unit which collects output current from the photovoltaic device and amplifies the output current at each individual frequency.
Further included in the photocurrent testing device are analysing means which analyse the amplitude of the output current at each individual frequency wherein the output current at each individual frequency originates from the light source pulsating at the same individual frequency, and where each light source illuminates a specific spot on the photovoltaic device. The amplitude of the output current at each individual frequency is matched with a corresponding specific spot on the photovoltaic device. In accordance with the present invention, the photocurrent testing device will match differences in the amplitude of the output current of the photovoltaic device to a specific spot on the photovoltaic device, such that a plurality of defects can be localised simultaneously in a fast and cost effective manner.
In a further aspect of the invention the light sources are light emitting diodes, LEDs. Light emitting diodes are inexpensive to buy and operate, and have a long lifetime. The light sources are preferably adapted to have the same light emitting spectrum. This allows for a more efficient calibrating of the device. In a further aspect of the invention the light sources are arranged in a single row.
In a further aspect of the invention the row of light sources covers the entire width of the photovoltaic device to be tested, allowing the device to scan the entire width of the solar cell in one run, thereby enabling a faster and continuous testing of photovoltaic devices arranged as solar panels.
In a further aspect of the invention the light sources are arranged in a matrix that illuminates the full solar cell or parts of the solar cell.
In a further aspect of the invention the light sources are arranged to move relative to the photovoltaic device in one direction. In a further aspect of the invention the individual driving frequencies are evenly distributed within a predetermined frequency interval, thereby simplifying calculations performed in the analyzing means.
In a further aspect of the invention the amplifier unit is a lock-in amplifier unit.
In a further aspect of the invention the signal generator is comprised within the lock-in amplifier unit.
A method for testing a photovoltaic device according to the invention comprises a first step of generating an individual driving frequency for each of a plurality of light sources. In a next step, each of the light sources is driven with its individual driving frequency such that each light source pulsates at an individual frequency corresponding to its driving frequency. In a next step, each light source illuminates a specific spot on the photovoltaic device.
In a next step output current from the photo voltaic device is collected and the current at each individual frequency is amplified. In a next step, the amplitude of the output current is analysed at each individual frequency, wherein the output current at each individual frequency originates from the light source pulsating at the same individual frequency. In a next step, the amplitude of the output current at each individual frequency is matched with a corresponding specific spot on the photovoltaic device.
In an optional further step a photocurrent map of the photovoltaic device is created, simplifying the further assessment of the data obtained.
In an optional further step the quality of the photovoltaic device is assessed.
The objects of the invention are also achieved in a system for testing photovoltaic devices comprising a photocurrent testing device and a computer program for controlling a method for testing a photovoltaic device.
BRIEF DESCRIPTION OF DRAWINGS
Further objects, features, and advantages of the present invention will appear from the following detailed description, wherein some aspects of the disclosure will be described in more detail with reference to the accompanying drawings, in which:
Figure 1 shows a schematic layout of the inventive photocurrent testing device,
Figure 2 shows a schematic layout of a part of an embodiment of the photocurrent testing device,
Figure 3 shows a flow chart illustrating the method according to the invention, and
Figure 4 shows examples of photocurrent maps produced with the system acco to the invention, and
Figure 5 shows the principles of quantum efficiency determination for a photovoltaic device.
DETAILED DESCRIPTION
Various aspects of the invention will hereinafter be described in conjunction with the appended drawings to illustrate, but not to limit the invention. Like designations denote like elements, and variations of the inventive aspects are not restricted to the specifically shown embodiment, but are applicable on other variations of the invention.
Figure 1 shows a schematic layout of a photocurrent testing device 100 according to the present invention. The photocurrent testing device 100 is for testing a photovoltaic device 120, such as an organic solar cell or a silicon wafer solar cell. The photocurrent testing device 100 comprises a plurality of light sources 110. There may be as few as two light sources 110, as many as one thousand, any number in between, or more than one thousand. The light sources could be any kind of light sources, such as light emitting diodes, LED, lasers, or gas-discharge lamps. The light emitting spectra of the light sources 110 should at least partially overlap with the absorption spectrum of the photovoltaic device 120 to be tested. The reason for this is that at least part of the light emitted by the light sources 110 has to be absorbed by the photovoltaic device 120 in order for the photovoltaic device 120 to produce a current, said current being a prerequisite for the photocurrent testing device 100 to function. For an organic photovoltaic device, a preferred light emitting spectrum of the light sources 110 should lie within or at least have significant parts within the wavelength interval 350- 1100 nm, and more specifically within 400-700 nm. This is to maximise the current output from the photovoltaic device 120 for a given power of the illuminating light. Preferably, all the light sources 110 are adapted to have the same light emitting spectrum, since photovoltaic devices 120 normally responds differently to different wavelengths of incoming light. With all the light sources 110 having the same light emitting spectrum, no correction factor for the light spectrum has to be taken into account.
Each light source 110 emits a light cone 115 which illuminates a corresponding spot 116 on the photovoltaic device. In an example of the invention, the light sources 110 are arranged such that their respective illuminated spots 116 on the photovoltaic device do not significantly overlap. The light intensity in the overlapping part of two spots 116 is in one example of the invention kept one or more orders of magnitude lower than the light intensity in the non-overlapping parts of a spot 116. The term spot 116 refers to a small area, typically circularly shaped. One or more optical elements, such as lenses or filters, may be provided between the light sources 110 and the corresponding spots 116. This is for controlling or defining the size and shape of the corresponding spot 116, and for controlling and defining the spectrum of the illuminating light.
The light sources 110 are driven by a signal generator 130 which is connected to the light sources 110 via one or more cables 135. The signal generator 130 generates for each light source 110 an individual driving frequency such that each light source 110 pulsates at an individual frequency corresponding to its individual driving frequency. The signal generator is preferably able to produce many different driving frequencies, since the photovoltaic testing device 100 may comprise a large number of light sources 110, each light source 110 requiring its own individual driving frequency. In one example, a multiplexing unit is provided between the signal generator 130 and the light sources 110.
As the photovoltaic device 120 is illuminated by the light sources 110, it will generate a photocurrent. Every spot 116 will generate a pulsating photocurrent with the individual frequency equal to the individual frequency of the light source 110 illuminating that specific spot 116. The total photocurrent generated by the photovoltaic device 120 is the sum of the photocurrents produced by each illuminated spot 116. Therefore, the total photocurrent comprises a frequency component for each of the individual driving frequencies of the light sources 110.
If the photovoltaic device 120 is defect in a specific spot 116, the amount of current generated in that spot 116 will be lower than in a non-defect spot. The term defect refers to any deviation from the optimal functioning of the photovoltaic device 120, such as total dysfunction, degradation or any other impaired operational characteristics. Consequently, the contribution to the total photocurrent at the frequency corresponding to the defect spot will be lower than from a non-defect spot.
Said total photocurrent constitutes the output current from the photovoltaic device 120. The output current is collected by an electrical cable 145 connecting the photovoltaic device 120 to an amplifier unit 140. The amplifier unit 140 transfers the output current signal from the time domain to the frequency domain by means of a Fourier transform or a Fast Fourier Transform, FFT, and amplifies the output current at each individual driving frequency of the light sources 110. The current component at each individual frequency is typically very small since it originates from a corresponding, typically very small spot 116 on the photovoltaic device. Amplification of these small current components is thus advantageous in order to more easily distinguish them from white noise. Preferably, the driving frequencies generated by the signal generator 130 are also directly input to the amplifying unit 140 to enable amplification at exactly these frequencies. This can for example be achieved by a lock-in amplifier. In one example the amplifying unit 140 is a signal analyser with combined lock-in amplifier. In one example of the invention, the signal generator 130 and the amplifier unit 140 are comprised within the same unit.
The amplitude of the output current at each individual frequency is analysed by analysing means 150. The analysing means 150 is preferably constituted by a computer. The driving frequencies, which individual driving frequency corresponds to which light source 110, and the physical position of each spot 116 are preferably predetermined and known to the analysing means 150. Since illuminating the photovoltaic device 100 with the individual frequency of the light source results in the generation of a current pulsating with the same individual frequency, the analysing means 150 can match each of the output current amplitudes with a specific light source 110, via their common pulsating frequency. Since each light source 110 is responsible for illuminating a specific spot 116 on the photovoltaic device 120, each output current amplitude component can be paired with the specific spot 116 in which it was generated.
In a preferred example the driving frequencies of the light sources 110 are equally distributed in a frequency interval. For example, the difference in driving frequencies between two light sources 110 are multiples of 1000 Hz, such that one light source 110 is driven with 1000 Hz, another with 2000 Hz, yet another with 4000 Hz and so on. I n another example, the differences in driving frequencies are multiples of 100 Hz. Before performing the Fourier transform or the FFT the output current of the photovoltaic device 120 has to be inputted to the amplifying unit for at least one full period of the differences in driving frequencies , i.e., for example for at least 10 ms when the differences in driving frequencies is 100 Hz and the lowest driving frequency is at least 100 Hz and for at least 1 ms when the differences in driving frequencies is 1000 Hz and the lowest driving frequency is at least lOOOHz. This is to assure that at least one period of the lowest driving frequency can be integrated in the Fourier transform or the FFT and to assure that the differences in frequency are detected. Also measuring the phase from the FFT will enable two light sources driven at the same frequency, as they can be separated by a phase difference. The analysing means 150 may comprise a computer program which controls the signal generator 130, and the amplifier unit 140 during the testing of the photovoltaic device 120, as well as the positioning of the light sources 110 relative to the photovoltaic device 120. In one example, the analysing means 150 also processes the data obtained during the testing, for example creates a photocurrent map 400, 450 over the tested photovoltaic device 120 and/or uses an algorithm in which the current amplitudes are compared with a predefined model in order to assess the quality of the tested photovoltaic device 120.
Figure 2 shows a schematic layout of a part of an embodiment of the photocurrent testing device. Here, the light sources 110 are arranged in a single row in a list 111, wherein the list covers the entire width of the photovoltaic device 120. Hence, a strip 112 covering the entire width of the photovoltaic device can be illuminated and thus tested simultaneously. Letting the list 111 scan the photovoltaic device in a direction perpendicular to said strip 112 enables progressive testing of further strips of the photovoltaic device. Consequently, the entire or part of the area of the photovoltaic device may be tested in a continuous testing procedure. Preferably, said scanning is realized by moving the photovoltaic device relative to the list 111 of light sources 110 in a direction 121 perpendicular to the list. Either the list 111 is kept in a fixed position and only the photovoltaic device 120 moves, or the photovoltaic device 120 is kept in a fixed position and only the list 111 moves, or both the list 111 and the photovoltaic device 120 are arranged to move. In one example, the photovoltaic device 120 is transported on a conveyor belt and the list 111 is fixedly mounted above said conveyor belt.
The speed at which the photovoltaic device 120 can be moved relative to the list 111 of light sources 110 is limited by the integration time as described in connection with the Fourier. This is due to that the resolution in the direction of the move of the photovoltaic device 120 will be limited by how much the photovoltaic device 120 moves under the integration time.
Figure 3 shows a flowchart 300 describing a method for testing a photocurrent device. The method comprises a first step 305 of generating an individual driving frequency for each of a plurality of light sources 110. The method further comprises an additional step 310 of driving each of the light sources 110 with its individual driving frequency, causing each light source 110 to pulsate at an individual frequency corresponding to its driving frequency. The next step 315 comprises illuminating for each light source 110 a specific spot on the photovoltaic device 120. The next step 320 comprises collecting output current from the photovoltaic device 120 and amplifying the current at each individua l frequency. The next step 325 comprises measuring the amplitude of the output current at each individual frequency, wherein the output current at each individual frequency originates from the light source pulsating at the same individual frequency. The next step 330 comprises matching the measured amplitude of the output current at each individual frequency with a corresponding specific spot 116 on the photovoltaic device 120.
In an optional further step 340, further spots on the photovoltaic device 120 are to be measured, the light sources 110 are moved a predetermined distance relative to the photovoltaic device 120. Alternatively the photovoltaic device 120 may be moved relative to the light sources 110. The movement can be executed in a step-wise manner, or continuously throughout the testing.
An optional further step 345 comprises creating a photocurrent map 400, 450. This map 400, 450 can be a visualization of the measured current amplitudes matched to specific spots 116 on the photovoltaic device, or a data set of such a matching. An optional further step 350 comprises assessing the quality of the photovoltaic device. This assessment 350 can be made using the photocurrent map 400, 450 through a visual assessment or other means such as a computer 160 performing calculations on the photocurrent map 400, 450. Figure 4 shows examples of photocurrent maps produced with the system according to the present invention. The map in Figure 4a illustrates a photocurrent map 400 in which the photocurrent across a solar cell is illustrated 410. The photocurrent at different areas of the solar cell is in this example illustrated using gray scale 405, and associating different values of the photocurrent to different shades of gray. Defects 415 can in this way be identified as areas of the solar cell that give rise to photocurrents outside a preferred predetermined photocurrent range or value. The map in Figure 4b shows a photocurrent map in the form of a matrix 450. The matrix 450 comprises a number of cells 480 arranged in columns 470 and rows 460 wherein each cell 480 corresponds to a specific spot 116 on the photo voltaic devices. An area of the photo voltaic device 120 is illuminated by a light source 110 with a specific frequency and the photocurrent with corresponding frequency is isolated and amplified and the value of the photocurrent is presented in the correct cell 480 in the matrix 450. The amount of cells 480 may be increased or decreased depending on the desired speed of the production of and resolution of the photocurrent map. The data acquired in the assessment may be retrieved as raw data. The data acquired in the assessment may be presented on a display. The data acquired in the assessment may be printed as a raw data, a photocurrent map and/or a matrix. The data may further be presented as a three dimensional plot. The presentation of data is however not limited to the above described forms. An operator may assess the presented data. The presented data may further be automatically assessed.
Figure 5 discloses principles of quantum efficiency determination for a photovoltaic device. A light source 510, such as a light emitting diode, LED, illuminates a photovoltaic device. The reflectance from the photo voltaic device is measured in a first photo detector 530. When the photovoltaic device is partly transparent, transmittance of the photovoltaic device is determined in a second photo detector 540. When the illumination power from the light source 510 is known, external quantum efficiency, EQE, can be determined from the photocurrent for the wavelength of the illuminating light. IQE, can be determined when the reflectance and/or transmittance of the photovoltaic device has been established.
According to an aspect of the invention, the photovoltaic testing device, as illustrated in Figure 1, includes first and/or second photo detectors for determining reflectance and/or transmittance of the photoelectric device. The analysing means are in accordance with this aspect of the invention, arranged to perform the analysis to determine EQE as well as IQE.
In the drawings and specification, there have been disclosed exemplary aspects of the invention. However, many variations and modifications can be made to these aspects without substantially departing from the principles of the present invention. Thus, the disclosure should be regarded as illustrative rather than restrictive, and not as being limited to the particular aspects discussed above. Accordingly, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. A photocurrent testing device (100) for testing photovoltaic devices (120) such as solar cells, comprising:
- a plurality of pulsating light sources (110),
- a signal generator (130) which generates for each light source (110) an
individual driving frequency, such that each light source (110) pulsates at an individual frequency corresponding to its driving frequency,
- an amplifier unit (140) which collects output current from the photovoltaic device (120) and amplifies the output current,
- analysing means (150) for analysing the amplitude of the output current at each individual frequency, wherein the output current at each individual frequency originates from the light source pulsating at the same individual frequency,
characterised in that each light source (110) illuminates a specific spot (116) on the photovoltaic device, such that the amplitude of the output current at each individual frequency is matched with a corresponding specific spot (116) on the photovoltaic device.
2. The photocurrent testing device according to claim 1, wherein the light sources (110) are light emitting diodes (LED).
3. The photocurrent testing device according to any of the preceding claims, wherein the light sources (110) are adapted to have the same light emitting spectrum.
4. The photocurrent testing device according to any of the preceding claims, wherein the light sources (110) are arranged in a single row.
5. The photocurrent testing device according to claim 4, wherein the row of light sources covers the entire width of the photovoltaic device to be tested.
6. The photocurrent testing device according to any of the preceding claims, wherein the light sources (110) are arranged in a matrix that illuminates the full solar cell or parts of the solar cell.
7. The photocurrent testing device according to any of the preceding claims, wherein the light sources (110) are arranged to move relative to the photovoltaic device (120) in one direction.
8. The photocurrent testing device according to any of the preceding claims, wherein the individual driving frequencies are evenly distributed within a predetermined frequency interval.
9. The photocurrent testing device (100) according to any of the preceding claims, wherein the amplifier unit (140) is a lock-in amplifier unit.
10. The photocurrent testing device according to any of the preceding claims, further including first and/or second photo detectors (530, 540) for determining the reflectance and/or transmittance of the photovoltaic device, and wherein the analysing means (150) is arranged to receive input on the reflectance and/or transmittance of the photovoltaic device and to determine external quantum efficiency, EQE, and/ or internal quantum efficiency, IQE, based on this input.
11. A method for testing a photovoltaic device, comprising the steps of:
- generating an individual driving frequency for each of a plurality of light
sources,
- driving each of the light sources with its individual driving frequency such that each light source pulsates at an individual frequency corresponding to its driving frequency,
- illuminating the photovoltaic device such that each light source illuminates a specific spot on the photovoltaic device, - collecting output current from the photovoltaic device and amplifying the current,
- analysing the amplitude of the output current at each individual frequency, wherein the output current at each individual frequency originates from the light source pulsating at the same individual frequency, and
- matching the amplitude of the output current at each individual frequency with a corresponding specific spot on the photovoltaic device.
12. The method according to claim 11, further comprising the step of creating a photocurrent map of the photovoltaic device.
13. The method according to claim 11 or 12, further comprising the step of assessing the quality of the photovoltaic device.
14. The method according to any of claims 11-13, further comprising the step of determining external quantum efficiency and/or internal quantum efficiency of the photovoltaic device.
15. Computer program for executing the steps of the method according to claims 11-14.
EP14811679.1A 2013-06-11 2014-06-05 A device, a method, and a computer program for testing of photovoltaic devices Withdrawn EP3008480A4 (en)

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