Room-temperature stable CsPbI3 perovskite quantum dots prepared by layer-by-layer assembly for photonic synapse

Abstract

CsPbX3 (X = I, Br, or Cl) perovskite materials have attracted great interest due to versatile and excellent photoelectric properties, applicable to various devices ranging from memory to solar cells. In particular, the cubic phase of CsPbI3 perovskite has a band gap of 1.73 eV, absorbing most of the visible region. However, despite excellent material properties, it is still difficult to apply to devices due to the unstable crystalline phase of CsPbI3 at room temperature. To overcome this shortcoming, we fabricated a cubic CsPbI3 perovskite quantum dots (CsPbI3-PQDs) thin film using in-situ ligand exchange layer-by-layer self-assembly (LbL SA). These room-temperature stable CsPbI3-PQDs thin films could control not only the thickness in nano-scale, but also the electrical properties. For device application, CsPbI3-PQD was formed on the fluorine doped tin oxide (FTO) substrate by LbL SA method, and W/CsPbI3-PQD/FTO photonic synapse was fabricated and evaluated. This photonic synapse exhibited photo-sensitive current-voltage characteristics under various UV stimuli such as intensity, exposure time, and interval. Furthermore, we successfully emulated the essential synaptic behaviors induced by photonic stimulus including short term plasticity, long term plasticity, and paired pulse facilitation. The CsPbI3-PQD-based device exhibited resistive switching characteristics with Ron/Roff of 103, stable endurance (103 cycles) and retention time (∼ 9 ×103 s). Additionally, we fabricated a heterojunction CsPbI3-PQD/a-IGZO based synaptic device and improved synaptic behaviors under various visible stimuli by enhancing the maintenance capability of photogenerated charge carriers through energy band engineering.