Ion migration induced bipolar diode effect and ferroelectricity modulation in CuInP2S6

The coupling between ferroelectricity and ion conductivity always presents unique physical and chemical properties, making it crucial to understand their correlation for the development of advanced functional devices. CuInP2S6 (CIPS), a van der Waals “ferroionic” material, serves as an excellent platform to investigate their intercoupling. In this study, we observe a bipolar diode-like rectification behavior in a vertical Pt/CIPS/In capacitor by controlling the migration of Cu ions. The non-uniform distribution of mobile Cu ions is coupled with ferroelectricity, resulting in a switchable imprint field and an enhanced saturation polarization about 12 μC/cm2 in CIPS. Additionally, CIPS exhibits a significant photovoltaic response due to its robust built-in electric field caused by the unbalanced distribution of Cu ions. This work demonstrates a controllable Cu ions migration and its manipulation on the electrical transport and ferroelectricity in CIPS. The dynamically tunable bipolar diode effect, closely coupled with ferroelectricity in CIPS, has promising prospects in self-powered photodetectors, memristors, and neuromorphic computing.