(Invited) Emerging Designs for Polymer-Based Energy Storage Devices and Sensors

Abstract

Conducting polymers are an important class of Faradaic materials for energy storage, as they present opportunities to create energy dense supercapacitors. The vast majority of conducting polymers are p-type cathodes and already operating at or close to the upper voltage limit of non-aqueous electrolytes. On the other hand, it is generally safe for electrolytes to operate down to -2 V vs Standard Hydrogen Electrode. Therefore, extending the operational voltage in the negative range is an attractive route to increase energy density. Here we present promising n-type polymers that retained 90% of initial capacitance after 1000 charge-discharge cycles. We measure in operando the electronic and ionic transport in conducting polymers by current-voltage and spectroscopic measurements, where spatial variations of film absorption would be mapped to discern electronic versus ionic degradation. We infer the mechanisms that lead to capacitance fade and suggests structural and electrochemical strategies to realize high-endurance energy storage devices for wearable systems. In addition, organic polymers responsive to the short wavelength infrared (SWIR) spectra are used to realize photodetectors that is relevant to a variety of applications including environmental monitoring and medical diagnosis. Here we show novel donor-acceptor polymers with narrow bandgap responsive in the SWIR region, and the polymers are processed into bulk heterojunction photodiodes with photoresponse up to wavelength of 1.7 micron. The performances of devices with different polymer structures were compared through metrics including detectivity, quantum efficiency, response time and rectification ratio. Example applications including hemodynamics and tissue composition measurements will be demonstrated.