Long-Term Stability of Unencapsulated Lead-Free CsBi₃I₁₀ in Ambient Air for Perovskites-Based Memory Devices

In recent years, organic–inorganic hybrid perovskites (OIHPs) materials have been widely studied in solar cells, resistive memory (ReRAM), field-effect transistors (FETs), due to their excellent carrier mobility, low cost of fabrication, and adjustable energy bands. However, the organic functional group is structurally unstable and thermally unstable and sensitive to humidity and oxygen in the air, which limits its application. Elemental lead is also an issue of environmental pollution and sustainable development. Therefore, developing inorganic lead-free perovskite crystals is very important to improve the stability of the components and is also very friendly to the environment. Bismuth is a non-hazardous and non-radioactive element. Bismuth-based lead-free perovskites exhibit excellent humidity resistance in solar cells, showing good stability in an unencapsulated high-humidity environment. In this study, CsBi₃I₁₀ has been studied for resistive switching memory applications to have a reliable bipolar resistive conversion, sufficient on/off ratio, and low operating voltage, along with excellent endurance and memory retention, which also demonstrates its potential for use in ReRAM applications.<br/>The dissolution solution was fixed at 1 ml and different ratios of DMSO and GBL were used to test the solubility of the precursor. 20 ml of DMSO and 80 ml of GBL were the optimal combination for the dissolution of the precursor. The CsBi₃I₁₀ films are prepared by spin-coating the precursor and antisolvent. The XRD pattern and SEM results were compared with the reference literature, and the XRD results show that there were obvious peaks in the directions of (003), (006), and (300). The XRD pattern showed a more obvious crystal structure in the (003) direction with the addition of ethyl acetate as the antisolvent, while it was more obvious in the (006) direction with the addition of ethyl acetate and chlorobenzene mixed with the antisolvent. The SEM image results showed that the average particle size was 85.2 nm. The UV-visible spectra of CsBi₃I₁₀ films showed enhanced absorption up to 685 nm. XRD spectra after one month in ambient air at a room temperature of 25°C and 65% relative humidity showed no significant change in the physical properties of the CsBi₃I₁₀films, indicating that the material remained stable without encapsulation.<br/>The bipolar RS behavior of the CsBi₃I₁₀perovskite memory device. The switching behavior of the OIHPs RS device in the CsBi₃I₁₀ configuration was studied under a direct current (DC) at ambient air conditions with high humidity between 50% and 70%. The top electrode (TE) of Au was biased and the bottom electrode (BE) ITO is grounded using a typical linear I-V sweep in a sequence of bias voltages of 0V→-3V→0V→3V→0V. All RS memories exhibited stable hysteresis I-V curves and bipolar resistor switching behavior. Apply a compliance current of 1 mA. When the applied voltage was swept from 0 V to 3 V, the transition of the resistance from the high resistance state (HRS) to the low resistance state (LRS) is observed at 0.76 V, which means that the SET process has occurred. When the voltage is switched from 0 V to -3 V, the device returns from the LRS state to HRS at 1.9 V, indicating that the conductive filaments (CFs) were broken, which corresponds to the RESET process. The on/off current ratio of the CsBi₃I₁₀memory device reached about 10³, and endurance was more than 200 cycles. The switching ratio of the unpacked CsBi₃I₁₀RSM device was two orders of magnitude, as measured by the device stored in the air for one month and is similar to the results of the XRD patterns. The results show that unpackaged CsBi₃I₁₀RSM devices can be used in resistive switching memories for high performance and long-term stability.