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TWI Joins OLEDSOLAR Project for Solar Panel Defect Detection

TWI is one of 16 organisations participating in the EC-funded OLEDSOLAR project to develop innovative manufacturing processes and in-line monitoring techniques to detect defects in solar panels. These processes and monitoring techniques would be used for the OLED and thin film photovoltaic industries (CIGS and OPV), with a particular focus on not only improving the quality and yield of the fabricated devices, but also improving processing efficiency and sustainability.

The participants in the project are working together to create robust and scalable, high yield manufacturing and control processes that will be tested on pilot lines before being implemented on existing solar panel production lines. Advanced sensors will provide a combination of quality control, inspection and functional testing and measurements, while new recycling strategies will reduce costly product waste. The entire process will be monitored by automated processing software to control roll-to-roll and sheet-to-sheet manufacture.

Industry Benefits

As opto-electronic devices open up new and exciting applications, with new display options using pliable substrates such as plastic and flexible glass, OLED manufacturers are delivering a range of new applications for lighting and different displays. In addition, as thin-film technologies emerge in the solar market, new applications ranging from installations on curved surfaces to building integrated PV has become possible.

However, the industry requirements for mass production mean that challenges need to be addressed to meet cost requirements as well as manufacturing volumes and efficiency. These will allow scale up for OPV, OLED and CIGs solar cells from laboratory level to mass production. The development of manufacturing processes, inspection, control and measurement techniques will meet the demands of industrial production of these opto-electronic devices.

Figure 1. The Dark Lock-in Thermography (DLIT) system developed at TWI
Figure 1. The Dark Lock-in Thermography (DLIT) system developed at TWI
Figure 2. Scratched VTT sample and amplitude image
Figure 2. Scratched VTT sample and amplitude image

Laboratory Testing

TWI has already begun work on the project by completing laboratory-based non-destructive testing for OLEDs and solar cells. Working alongside project coordinator, Teknologian tutkimuskeskus VTT Oy (VTT), TWI developed an innovative in-line inspection application for thin films using dark lock-in thermography (DLIT).

Figure 1 shows the DLIT set-up, which applies a square wave modulated voltage to the sample while being imaged using an infrared camera. An in-house designed relay circuit acts like a switch to turn the power supply on and off according to the square wave generated, thereby enabling high voltages to be applied using a low voltage signal. Along with thermal images, the camera also records the synchronised square wave reference signal that is generated using a signal generator.

For the laboratory tests, scratches were artificially induced on a sample to replicate a defected print. You can see the resulting amplitude from this sample in Figure 2, with the scratched location showing as a hotspot that is clearly identifiable using the DLIT system.

 

Next Steps

With the laboratory scale tests now complete, in-line implementation is now to be developed at VTT’s electrical measurement line (see the TESLA Line in figure 3).

The TESLA Line has 400 test pins that are traditionally used to measure the I-V characteristics of each line in stop-and-go mode. These pins can be configured to apply the voltage necessary for DLIT, with stop-and-go operation being the ideal mode since the voltage is usually applied as square waveforms for a short period of time (less than 5 seconds), which offers the optimum results from DLIT. Lock-in thermography enables the TESLA line to have the capability to find problem zones within the sample.

Upon successful completion, in-line DLIT would enable the detection of problem zones (hot spots) and also provide a measure of the quality of the printed lines.

Work on the in-line implementation has now initiated following the successful completion of the lab scale tests and algorithm development work. The software development required for the in-line testing is now nearing completion. This in-house developed software comprises data acquisition, data visualisation, and lock-in post processing and data analysis capabilities integrated to a single package.  The screenshots of the user interface when performing various functions are shown in Figure 4. Other aspects of the work that are currently being finalised include the set-up of the system on the TESLA Line (see Figure 5) where the potential location of the camera has been identified – below the test area where there is free space.

It is expected that the work will be completed by the end of January 2021.

Project Partners

Alongside TWI, the OLEDSOLAR Project partners include Teknologian tutkimuskeskus VTT Oy (VTT), Fraunhofer Gesellschaft (FhG), Nederlandse Organisatie voor Toegepast Narrturwetenschappelijk Onderzoek (TNO), INNOVACIO I RECERCA INDUSTRIAL I SOSTENIBLE SL (IRIS), ARMOR solar power films GmbH), Centre Suisse D’Electronique Et De Microtechnique SA (CSEM), Solibro Hi-Tech GmbH (Solibro), Smit TS & Smit Thermal Solutions, Brunel University London (BUL), Acondicionamiento Tarrasense Associacion (LEITAT), Coatema Coating Machinery GmbH (Coatema), DuPont Teijin Films UK Ltd (DTF), Silicon Austria Labs GmbH (SAL), ADVANCED ENERGY TECHNOLOGIES S.A. (Advent), and INURU GmbH. (INURU).

 

This OLEDSOLAR project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 820789

Figure 3. Automated R2R functional testing equipment at VTT (TESLA line)
Figure 3. Automated R2R functional testing equipment at VTT (TESLA line)
Figure 4. View of the GUI with actual sample data
Figure 4. View of the GUI with actual sample data
Figure 5. Plan of DLIT implementation on TESLA line
Figure 5. Plan of DLIT implementation on TESLA line
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