Non-Destructive Steady-State and Time-Resolved Photoluminescence Characterization of Photovoltaic Devices

Over the years, luminescence spectroscopy has become one of the fundamental methods for analyzing the photophysical properties of a wide variety of samples, ranging from organic molecules to semiconductor materials and photovoltaic (PV) devices. It should be emphasized that detection sensitivity is a key parameter to meet today's requirements for handling weakly luminescent samples and for short measurement times in the optical evaluation of PV devices. The introduction of single-photon counting based data acquisition has proven to provide a significant increase in sensitivity and a very high dynamic range – it is the ideal method for measuring weak photoluminescence (PL).<br/>The commonly used steady-state luminescence spectroscopy methods provide valuable insight into the photophysics of a sample. However, such results offer only a partial picture of the sample’s behavior after photoexcitation. Another piece of the puzzle is often revealed by performing time-resolved PL spectroscopy, which provides deeper insights into the photophysical processes occurring in the sample under investigation. An even more comprehensive picture is gained by incorporating spatial information. Acquiring time-resolved spectroscopic data at regions of interest (ROI) in the sample can help to infer structural-to-photophysical relationships in PV materials. Gathering such information is an important step towards optimizing the structure as well as the preparation process of such materials in order to increase the performance of PV devices.<br/>Herein, we will demonstrate that the combination of time-resolved microscopy and PL spectroscopy provides a powerful tool for the characterization and analysis of various PV materials, providing spectral, spatial and temporal information on semiconductor samples studied by PL emission. This combination allows the mapping of a broad range of phenomena including time-resolved PL, carrier diffusion, wavelength and power dependent emission with high spatial resolution. We will also discuss the advantages of the MicroTime 100 confocal photoluminescence lifetime microscope combined with the FlexWave software controlled wavelength selection unit for time-resolved imaging of very weakly emitting PV materials such as perovskites up to 1000 nm.