ECE Seminar Series: Emerging Designs for Polymer-Based Optoelectronics and Energy Storage

Abstract:

The shortwave infrared spectral region (SWIR: 1-3 m) is particularly powerful for health monitoring and medical diagnostics, because biological tissues show low absorbance and minimal SWIR auto-fluorescence, enabling greater penetration depth and improved resolution in comparison to visible light. However, conventional SWIR sensors are limited by complex die transfer and bonding processing. Here we are advancing SWIR photodiodes by using a new generation of semiconducting polymers that are processed by solution processing techniques and allow simple direct deposition. The bulk heterojunction photodiodes show photo-response spanning from the visible to 1.7 micron. We develop a physical model to pinpoint the origins of efficiency losses by decoupling the exciton dissociation efficiency and charge collection efficiency, and identify avenues that will improve sensor detectivity. Several demonstrations will show the various potential applications of organic SWIR photodiodes including blood pulse measurements, spectroscopic identification, and image reconstruction. In addition, the same infrared polymers present opportunities to create energy dense supercapacitors. Here we present promising n-type polymers that retained 90% of initial capacitance after 5000 charge-discharge cycles. Through current-voltage and spectroscopic measurements, we infer the mechanisms that lead to capacitance fade and suggests structural and electrochemical strategies to realize high endurance energy storage devices for flexible printed systems.

Bio:

Dr. Tse Nga Tina Ng is an Associate Professor in the Department of Electrical and Computer Engineering at University of California San Diego (UCSD), USA. Her research focuses on devices and fabrication methods for flexible printed electronics: http://flexible-electronics.ucsd.edu/ She received her PhD in Physical Chemistry under the supervision of Professor John Marohn at Cornell University. Subsequently she worked at Palo Alto Research Center before joining UCSD in 2015. Her work on printed systems has received the 2012 Innovation Award from Flextech Alliance, named Runner-up for the Wall Street Journal Technology Innovation Award, and received second place in the 2017 Bell Lab Prize and is named a Hartwell Investigator in 2017. She is on the Editorial Board of the journal Flexible Printed Electronics and ACS Applied Electronic Materials.