Multimodal x-ray imaging of grain-level properties and performance in polycrystalline solar cells
Michael E. Stuckelberger1,2, Stephan O. Hruszkewycz3, Martin V. Holt4, Megan O. Hill5, Irene Calvo Almazan3, Maddali Siddharth3, Nathan Rodkey1, Xiaojing Huang6, Hanfei Yan6, Evgeny Nazaretski6, Yong S. Chu6, Lincoln J. Lauhon5, Mariana Bertoni1, Andrew Ulvestad3
1Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, AZ, United States
/2Photon Science, Deutsches Elektronen-Synchrotron, Hamburg, Germany
/3Materials Science Division, Argonne National Laboratory, Argonne, IL, United States
/4Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL, United States
/5Department of Materials Science and Engineering, Northwestern University, Evanston, IL, United States
/6National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY, United States

We present the latest developments in x-ray microscopy for the nanoscale characterization of thin-film solar cells. In a twofold approach, we give first an overview over the development of multi-modal operando and in-situ measurements at different synchrotron nanoprobes in the US and in Europe. In particular, we discuss challenges and opportunities realizing multi-modal measurements that include x-ray beam induced current (XBIC) and voltage (XBIV), x-ray diffraction (XRD), x-ray fluorescence (XRF), x-ray excited optical luminescence (XEOL), and ptychography. This combination allows to measure at the same time electrical performance, lattice strain and tilt, composition, optical performance, and structure at sub-100-nm resolution.
Second, we showcase two experiments where we have achieved milestones for correlative X-ray microscopy. First, we have investigated single grains in a fully operational industrial Cu(In,Ga)Se2 solar cell with sensitivity to local structural, chemical, and electrical performance. We have achieved this by integrating for the first time Bragg diffraction as a new mode of structural contrast (lattice strain and tilt), expanding upon the previous capabilities with XRF spectra (composition) and XBIC (charge collection efficiency). This allowed us to map heterogeneities in these quantities and to correlate them within grain cores and grain boundaries. For the second experiment, we have developed a new XEOL instrument for the simultaneous measurement of the optical solar cell properties with XBIV, XRF, and ptychography, and we show first results. This paves the way towards a more complete picture of the local structure-property relationship of CIGS specifically, and of polycrystalline thin film PV materials more generally. Finally, we present an outlook to new experiments that will be enabled by the 4th generation synchrotron sources that are being built worldwide.