CsBr Immersion for Organic-Inorganic Hybrid Perovskite-Based Memristors: Controllable Grain, Poole-Frenkel Emission, and Electrical Properties

Organic-inorganic hybrid perovskites (OIHPs) have emerged as potential candidates for active layers in resistive switching memory (RSM) devices and have recently attracted much interest in academia and industry. In RSM devices based on the OIHPs, grain boundaries play an important role in the formation of resistive switching paths because the grain boundary regions contain many defects that favor the formation of conducting filaments. In this study, the effect of methylammonium lead iodide (MAPbI₃)/indium tin oxide (ITO) substrates with various post-treatments on RSM devices is demonstrated. To reduce the defect density, variation of the immersion time of the MAPbI₃ surface in CsI, MABr, and CsBr solutions promotes grain size enlargement and decreases the number of grain boundaries. The largest average grain size of the OIHP film obtained with 10 s of CsBr solution immersion (CsBr-10 s) for RSM devices is 1386.5 nm, and the corresponding photoluminescence (PL) intensity demonstrates the highest signal. The grain size can be well controlled by varying the immersion time in the ionic solution, and the appropriate post-treatment time is 10 s. Compared to untreated OIHP devices (on/off current ratio ∼10²), perovskite film (MAPbI₃)-based RSM devices with CsBr-10 s achieve a > 10⁵ on/off current ratio and >10⁴ s data retention. The conduction mechanism of the RSM devices with proper immersion treatment switches from the space-charge-limited current (SCLC) mechanism to Poole-Frenkel (PF) emission. This observation confirms that a low density of defects from fewer grain boundaries for RSM devices makes the conducting filaments in the memristors more susceptible to activation. Most OIHP-based devices suffer from humidity damage issues; however, the device fabrication and storage in our experiment are performed in ambient air. The results indicate that perovskite memory based on suitable ionic solution immersion exhibits great potential for use in future high-performance memristors.