A group of researchers at the Institute of Microstructure Technology, Light Technology Institute & Thin Film Technology (TFT) at Karlsruhe Institute of Technology has published an RRL Solar article "Correlative In Situ Multichannel Imaging for Large-Area Monitoring of Morphology Formation in Solution-Processed Perovskite Layers" highlighting a novel method for measuring the quality of large-area thin films in a threefold manner: Reflectance, Photoluminescence (PL) intensity and PL emission wavelength in a fast and simultaneous way.
"Optical (or IR) techniques have the advantages that they can be easily used for monitoring common solution processing methods such as spin coating or blade coating and that they can provide large-area information at low cost using cameras as imaging detectors, while the necessary large-area excitation can be provided by high-power light-emitting diodes. Luminescence and reflectance imaging on large areas—established already in other PV technologies as silicon, GaAs, CdTe, and CIGS—as well as luminescence microscopy, demonstrated to yield critical information on the perovskite thin-film quality and the performance of devices incorporating these films. However, to the best of our knowledge, there is currently no technique available combining both imaging capability on large areas and rapid real-time operation for analyzing the dynamics of the perovskite formation."
"In response, we developed an in situ monitoring technique based on a commercially available scientific camera, an inexpensive ring light source, and a 3D printed rapidly rotating filter wheel that is able to generate sequences of images of reflectance, photoluminescence (PL) intensity, and an estimation of the central PL emission wavelength at a “frame-rate” of 3 fps each. This technique, which we call in situ multichannel imaging (IMI), enables the dynamic stages, I–IV, to be tracked in both space and time. To provide idealized conditions for testing the capability of IMI, we maintain full control of the airflow and temperature over the sample. With this idealized reference at hand, we will demonstrate that IMI would be useful in industrial-scale coating lines."
