CsCl Induced Grain Size Control and Performance Enhancement of MA-Based Perovskites Film for High-Performance Memristive Devices

Recently, a new class of organic-inorganic hybridized perovskites (OIHPs) materials with various functionalities such as dielectric, semiconducting, and photosensitive properties have proven to be very promising for resistance switching (RS) memory applications. Due to the atmospheric instability of OIHPs materials, defects or pinholes can appear on the film surface during the manufacturing process. Some literature discusses the posttreatment process for improving defects. In this study, we purpose that the CsCl of the double-site repair mechanism not only passivates defects but also improves the electrical properties of the RS memory device due to the reduction of grain boundaries and grain size enlargement. The MAPbI₃ perovskite precursor was prepared by dissolving MAI and PbI₂ powder into the mixed solvent of GBL and DMSO. The CsCl solutions were prepared in methanol and ethanol; the concentrations were 0.5, 1 and 1.5 mg mL^-1, labeled as CsCl-0.5, CsCl-1 and CsCl-1.5, respectively. The untreated film is labeled as CsCl-0.<br/>The pristine OIHPs films and the film with CsCl posttreatment both exhibit intense diffraction peaks at 13.9°, 20.2°, 21.4°, 28.5°, and 31.9°, corresponding to the (110), (200), (211), (220), and (310) MAPbI₃ tetragonal crystal planes. The XRD patterns result indicated that there is no significant peak shift. The UV-Vis absorption spectra showed a blue shift in the absorption edge after the addition of CsCl doping, indicating that some Cs substitution occurred on the OIHPs surface and most of MAPbI₃was retained. The PL response spectra showed the same trend, with the highest intensity for the CsCl-1.5 film. It indicated a reduction of defects and pinholes in the film, which can be attributed to the higher concentration, resulting in more surface replacement effects. In addition, the average grain size of the OIHPs films was increased from ~339.2 nm (CsCs-0) to ~658.1 nm (CsCl-1.5) by raising the amount of CsCl doping. The MAPbI₃ films treated with CsCl exhibited signs of remodeling, resulting in grain size increase and grain boundary reduction. Control and moderate increases in grain size can affect the electrical characteristics of OIHPs memory devices. Thus, to achieve high-performance memory devices using OIHPs film, we realize the control of grain size in the film by CsCl facial treatment.<br/>Herein, we reported the bipolar RS behavior of the organic-inorganic hybrid Cs_xMA_1-xPbI_3-yCl_y perovskite memory device. The switching behavior of the OIHPs RS device in Al/PMMA/Cs_xMA_1-xPbI_3-yCl_y/ITO configuration was studied under a direct current (DC) at ambient air conditions with high humidity between 50% and 70%. The top electrode (TE) Al is biased, and the bottom electrode (BE) ITO is grounded using a typical linear I-V sweep in the order 0V→-3V→0V→3V→0V at the bias voltage. To ensure the RS behavior and conductive filament were from the OIHPs layer, no significant switching behavior was observed for Al/PMMA/ ITO. All the RS memory devices exhibited stable hysteresis I-V curves with bipolar resistive switching behavior. To prevent the RS memory device from being damaged during the measurement, a compliance current of 1 mA was applied. When an external voltage is swept from -3 to 0 V, the resistance transition from a high-resistance state (HRS) to a low-resistance state (LRS) was observed at 1.1 V, which means the set process occurs. The Al/PMMA/Cs_xMA_1-xPbI_3-yCl_y/ITO device was maintained at LRS state when voltage was reversed from 3 to 0 V, corresponding to the reset process. The on/off current ratio of the CsCl-0 device reached about 10², 10³ for CsCl-0.5, 10³ for CsCl-1, and 10⁴ for the CsCl-1.5 device, respectively. Compared to untreated OIHPs devices, RSM devices with MAPbI₃ treated with CsCl-1.5 device are improved by two orders of magnitude. The results demonstrated the high-performance electronic applications of CsCl-induced OIHPs in resistive switching memories.