摘要： Organometallic halide perovskites attract strong interests for their high photoresponsivity and solar cell efficiency. However, there was no systematic study of their power and frequency dependent photoresponsivity. We identified two different power-dependent photoresponse types in methylammonium lead iodide perovskite (MAPbI3) photodetectors. In the first type, photoresponse remains constant from 5 Hz to 800 MHz. In the second type, absorption of a single photon can generate a persistent photoconductivity of 30 pA under an applied electric field of 2.5×104 V/cm. Additional absorbed photons, up to 8, linearly increase the persistent photoconductivity, which saturates with absorption of more than 10 photons. This is different than single photon avalanche detectors (SPADs) because the single photon response is persistent as long as the device is under bias, providing unique opportunities for novel electronic and photonic devices such as analog memories for neuromorphic computing. We propose an avalanche-like process for iodine ions and estimate that absorption of a single 0.38 aJ photon triggers motion of 108-9 ions, resulting in accumulations of ions and charged vacancies at the MAPbI3/electrode interfaces to cause band bending and change of material electric properties. We have made the first observation that single-digit photon absorption can alter the macroscopic electric and optoelectronic properties of a perovskite thin film.