Figure 1.

Optical dynamic images of perovskite film under electric poling and illumination of various intensities in ambient air at room temperature. (a) The film shows little change under dark conditions at a 100-V bias (2 V μm⁻¹ high electric field). The scale bar represents 20 μm. (b) Under 5 mW cm⁻² illumination, the film shows black threads at the cathode, with black dots expanding at the anode after 10 s of high-field poling. (c) Under 20 mW cm⁻² illumination, the film shows black threads and plane-dendrite structures forming at the cathode and expanding from the cathode to the anode after 10 s of poling. (d) Schematic illustration of the migration of I⁻ anions and MA⁺ cations through the film. The temperature of the perovskite film under light illumination was monitored with a precision of 1 °C by an infrared thermometer.