Photocurrent transient measurements in MAPbI₃ thin films

Methylammonium lead iodide (CH₃NH₃PbI₃ or MAPbI₃) is one of the hybrid perovskite materials most widely used in high performing perovskite solar cells. In this work, the charge carrier recombination process of MAPbI₃ perovskite thin-film fabricated on corning 1737 glass substrate is studied by means of transient photocurrent measurements and the current decay curves after turning off the lights. The influences of temperature (25–70 °C), illumination time (30–90 s) and intensity of illumination (100–1000 W m⁻²) on the photocurrent response are studied. The photocurrent measurements are taken in vacuum to avoid the effect of atmospheric air and moisture, at an applied field of 100 V cm⁻¹. The MAPbI₃ film shows good photosensitivity with two orders of magnitude change in current when exposed to full intensity of light. As soon as the light is turned on, the current increases rapidly; however, a small decrease is observed before a stabilized current is achieved. The stabilized value of current does not depend upon exposure time. The current falls abruptly as soon as the light is turned off and then slowly reaches back the dark current value. The fast decay of photocurrent can be attributed to fast recombination of free electrons and hole having decay time constant approximately 100 ms and the slow decay corresponds to slow re-emission of trapped carriers which has at least 3–4 times higher decay time constants compared to the fast decay. Intensity-dependent photocurrent follows a power law (I_ph ~ Φ ^γ), indicating predominantly bimolecular recombination process. The activation energy (E_a) estimated from the temperature-dependent dark current measurement is found to be ~ 210 meV.