Tue, 20 April, 2021
TWI has been working as one of 16 organisations on the EC-funded OLEDSOLAR project, which has been developing innovative manufacturing processes and in-line monitoring techniques for detecting defects in solar panels.
The aim is to use the new monitoring techniques in the OLED and thin film photovoltaic industries (CIGS and OPV), to improve the quality and yield of the fabricated devices as well as improving processing efficiency and sustainability.
The project recently saw the in-line implementation of TWI’s dark lock-in thermography (DLIT) system on a VTT pilot test line. The DLIT system applies a square wave modulated voltage to the sample while it is imaged using the infrared camera (see Figure 1).
An in-house designed relay circuit acts as a switch to turn the power supply on and off according to the square wave generated, 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.
Figure 1. The Dark Lock-in Thermography (DLIT) system developed at TWI
Laboratory testing detected scratches artificially introduced onto the sample provided by VTT to replicate defective printing. Figure 2 shows how the resulting signal amplitude and the scratched location is identified as a hotspot using the DLIT system.
Figure 2. Lab testing: Scratched VTT sample and DLIT amplitude image
Custom GUI software was developed at TWI for the inline implementation, including two modes of thermography data acquisition and DLIT processing. Figure 3 shows the DLIT amplitude image.
Figure 3. TWI’s in-house GUI software
The in-line implementation of TWI’s DLIT inspection system on VTT’s R2R TESLA line is currently under development. The TESLA line is equipped with a series of pins for electrical measurement. It can be configured to apply periodical voltage inputs for DLIT in-line inspection system. Figure 4 shows VTT’s R2R TESLA pilot line.
Figure 4. R2R TESLA test line at VTT