A solution-processed organometallic halide perovskite-based bulk heterojunction (BHJ) memory device with a configuration of indium-doped tin oxide (ITO)/CH₃NH₃PbI₃:PVK/Al has been successfully fabricated. Under a threshold voltage of −1.57 V, this device shows a nonvolatile write-once read-many-times (WORM) memory effect, with a maximum ON/OFF current ratio exceeding 10³. In contrast, the ITO/CH₃NH₃PbI₃/Al device showed only conductor characteristics, while the PVK-based device exhibited insulator behavior. Upon being subjected to voltages, an interesting filamentary nature of the CH₃NH₃PbI₃:PVK film was also observed in situ at the microscopic nanometer level using a conductive atomic force microscopy (C-AFM) technique with a device configuration of Si/Pt/CH₃NH₃PbI₃:PVK/Pt. The mechanism associated with the memory effect is discussed. The electric-field-induced intermolecular charge transfer effect between CH₃NH₃PbI₃ and PVK, and the possible conformational ordering of the PVK side-chains/backbone under an applied bias voltage, may cause the electrical conductivity switching and WORM effect in the reported BHJ device.