Infrared Organic Optoelectronics

Low-energy (IR) photon detection forms the foundation for industrial, scientific, energy, medical, and defense applications. State-of-the-art technologies remain dependent on epitaxially grown, lattice-matched, crystalline inorganic devices.

These suffer from limited modularity, intrinsic fragility, low speed, high-power consumption, require cryogenic cooling, and are largely incompatible with integrated circuit technologies.

Photoexcitation of organic semiconductors (OSCs), does not lead to substantial instantaneous free carrier generation as in inorganics, and instead results in bound electron-hole pairs (excitons).

Excitons are crucial intermediates for energy transduction in these systems, are the basis for energy efficient solid-state lighting, photoresponsive technologies (photovoltaics, photodetectors), and emergent functionalities (singlet fission, coherence, quantum processes, etc.) that are studied within the group. 

Through the development of modular synthetic approaches, we have demonstrated precise control of the properties of donor-acceptor (DA) conjugated polymers (CPs) in the short-wavelength infrared (SWIR: 1.4-3 μm).

Building on this expertise, we developed new materials, soft matter systems, and device paradigms enabling optical to electrical transduction of SWIR light. We discovered that charge generation assisted by polymer aggregation is essential to compensate for the energy gap law, which dictates that excited state lifetimes decrease as the bandgap narrows.

Fundamental investigations of polymer and device physics have resulted in improving performance to levels now matching commercial inorganic photodiodes. We have integrated these photodetectors within a wide range of systems such as wearable physiological monitors and SWIR spectroscopic imagers that enable compositional analysis for food, water quality monitoring, imaging, and medical and biological studies.

These studies are the first of their kind that detail general design rules for incorporating CPs into high performing IR optoelectronics, articulate specific challenges associated with these materials, and that connect intrinsic properties with device performance. 

The conversion of IR photons to electrons requires coordination of multiple steps, each carried out by customized materials with designed electronic and nanoscale structures.

Such advanced materials must be designed and fabricated to exacting standards using principles revealed by basic science.

This program provides a fundamental understanding of the how organic molecules interact with light in the IR spectral regions.

Systematically controlling the properties of these materials and developing an understanding of fundamental properties will support the basic knowledge necessary to bring to reality new technologies and extend the utility of organics into a field now completely dominated by inorganic materials.