Mobile Ion Concentration - A new Stability metric in Perovskite Solar Cells

Saivineeth Penukula1, Axel F. Palmstrom2, Muzhi Li1, Ross A. Kerner2, Min Chen2, Ian Sellers3, Joseph M. Luther2, Joseph J. Berry2, Nicholas Rolston1 1School of Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, AZ, United States /2National Renewable Energy Laboratory, Golden, CO, United States /3University of Buffalo, Buffalo, NY, United States

Mobile ion concentration (No) is the most direct method to quantify undesired ion migration that happens in perovskite solar cells (PSCs) and metal halide perovskites (MHPs). It is essential to understand how No changes with different device structures and properties of PSCs. Here, we show from our measurements that Ag metal ions diffuse into the perovskite lattice in p-i-n architectures that use a fullerene-based ETL, increasing the ion concentration of devices without any other stimulus other than a voltage bias of 0.8V for just 10ms, while C electrodes reduce the concentration. The use of Au or C-based electrodes or SnO2-based ALD barrier layers appears to prevent the diffusion of ions into and out of MHP layer. We determine the highest operating temperature and activation energy (EA) for various state-of-the-art device designs. We also show that ozone-nucleated SnO2 is the most effective barrier layer at preventing ion migration based on the suppression of ion concentration under thermal aging. Lastly, we show a correlation between fracture energy (Gc) and No, and the composition of perovskite and No. We believe that No is a metric that can be used for the design of operational and thermomechanically stable PSCs.