Fig. 1

Experiment setup and finite-element analysis. a Schematic diagram of the sample and the MIM setup with bottom illumination through the transparent glass substrate. Scanning is accomplished by moving the sample stage while fixing the laser beam and the probe tip, which are aligned before the experiment. The inset shows the scanning electron microscopy (SEM) image of a typical MIM tip. b Simulated MIM signals as a function of the MAPbI₃ conductivity σ. The quasi-static displacement-field distributions when σ is equal to 0.1, 10, and 1000 S m⁻¹ are displayed inside the blue, green, and red dash-dotted boxes, respectively