Effects of Cs Doping on Ion Transport in MAPbI₃ Hybrid Perovskite Memristors

Hybrid perovskite materials have drawn a lot of attention recently for solar energy applications, but the instability of these materials makes long term efficiency a major issue that needs to be addressed. The weak bonding in methylammonium lead iodide (MAPbI₃) that enables ion migration can be leveraged for memristivie applications where ion migration needs to be controlled rather than eliminated. We show that in modeled structures, cesium (Cs) doping the MA site (A-site) can enable stronger local bonding with the iodine (I) ions allowing for weak bonding ion conductivity channels that can help control ion migration under applied bias. Cs doped MAPbI₃ films were spin coated on glass/ITO substrates to act as an active layer for memristive devices. Local IV measurements were conducted using an AFM tip and a DC bias was applied to the tip in contact mode in order to induce ion migration. Kelvin probe force microscopy (KPFM) was used to probe the resulting variation in surface potential. The chemical origins of the surface potential variations were investigated using specially resolved time-of-flight scanning ion mass spectroscopy.