Potentiometry of Operating Perovskite-Based Devices with Kelvin Probe Force Microscopy

During the past decade, hybrid perovskite materials have attracted considerable attention for application in electronic devices due to the favorable properties their organic and inorganic structural elements grant them. Such devices include solar cells and field-effect transistors (FETs), which exhibit respectable performances with very low production costs. By employing Kelvin probe force microscopy (KPFM), we can scan a probe along the perovskite active area of such devices and quantitatively determine the evolution of potential across them, from one electrode to the other, in order to gain information about their charge transport and charge extraction characteristics. At the same time, we can subject our samples to conditions simulating real-life operation, i.e. application of a gate and source-drain voltage for FETs, or illumination and bias voltages in solar cells.<br/><br/>In this poster, we explain how in-situ nanoscale potentiometry in active devices can help understand the underlying working principles and performance bottlenecks. For example, mapping the potential distribution across the gate channel of FETs revealed that devices with better crystallinity exhibit fewer energetic barriers and a more uniform electric field. These results provide a microscopic explanation for their better performance, as estimated by current-voltage measurements of their transfer characteristics. For solar cells, the perovskite absorbing layer is covered by the layers deposited on top of it and is therefore not readily accessible for a scanning probe measurement. Therefore, a few extra steps are required in order to conduct the experiment: the device is initially cleaved in the direction perpendicular to its constituent layers and subsequently, the exposed cross-section is polished in order to eliminate cross-talk from a rough topography. Here, the potential profiles reveal the charge separating junctions on both sides of the perovskite absorbing layer, as well as the relative barriers for charge extraction at the interfaces with the electron and hole transport layers, which depend on the choice of these materials.