Light Activated Charge-Ionic Transport in Cs₂AgBi₂I₉ for Self-Powered Synaptic Photodetection

Area of Science:

• Materials Science
• Condensed Matter Physics
• Device Engineering

Background:

• Self-powered optoelectronic and neuromorphic systems rely on materials with coupled electronic-ionic dynamics.
• The interplay between electronic and ionic processes under illumination is poorly understood in lead-free perovskite-inspired semiconductors.

Purpose of the Study:

• To elucidate the coupled electronic-ionic dynamics in Cs2AgBi2I9 thin films under illumination.
• To investigate the role of silver (Ag) incorporation on electronic connectivity and charge transport.
• To demonstrate the application of these materials in self-powered photodetectors and synaptic devices.

Main Methods:

• Solution-processed Cs2AgBi2I9 thin films were fabricated.
• Structural, optical, and density functional theory (DFT) analyses were performed.
• Photoexcited impedance spectroscopy, time-resolved photoresponse measurements, and Kelvin probe force microscopy (KPFM) were employed.

Main Results:

• Ag incorporation in Cs2AgBi2I9 enhances electronic connectivity via band edge delocalization.
• Photoexcited impedance spectroscopy quantified light-induced ionic transport and its coupling to electronic conduction.
• Distinct fast (carrier) and slow (ionic) relaxation processes were observed in time-resolved photoresponse.
• KPFM confirmed illumination-driven interfacial potential modulation due to ion accumulation.

Conclusions:

• Coupled charge-ion interactions are fundamental to the operation of Cs2AgBi2I9-based devices.
• Controlled manipulation of these interactions is key to regulating interfacial transport and temporal response.
• This work provides a pathway for designing advanced self-powered optoelectronic and neuromorphic devices.