Description of Research:

Topics of Interest:

1. Thin Film Nanocomposites

2. Thin Polymer Films

3. Organic Electronics

4. Polymer Dynamics

5. Electrorheological Fluids

Organic Electronics

 

We are investigating conjugated polymers, primarily in thin film configurations, for photovoltaic and other organic electronic applications. Conjugated polymers, whether independently or blended with other components, form complex morphologies with both ordered and disordered phases across a range of length scales. Structural characteristics (crystallinity, domain size, phase purity, molecular orientation, interfacial behavior, etc) play a critical role in fundamental physical processes of charge carrier generation and transport, which in turn influence the optoelectronic properties and device performance

 

By employing different deposition and post-processing strategies, we are able to control selective aspects of the morphology, which we can characterize using a broad range of techniques, including atomic force microscopy (AFM), transmission electron microscopy (TEM), spectroscopic ellipsometry (SE), and UV-vis spectroscopy. In tandem with structural characterization, we study carrier generation and transport using methods such as charge extraction with a linearly increasing voltage (CELIV), impedance spectroscopy (IS), and conductive and Kelvin probe variants of AFM. Combining these results with bulk device measurements, we obtain an understanding of the structure-property-function relationships in conjugated polymer systems, which enable us to formulate guidelines for the design/engineering of materials for specific applications.

Conjugated polymers' nanostructure and transport

Transport

 

In thin conjugated polymer films, the presence of an external interface influences the orientation of the domains. We have shown that morphology and transport strongly depend on the distance from the supporting substrate in conjugated polymers.

Morphology-performance correlation in organic solar cells

OPV

 

Supercritical CO2 annealing enhances local photocurrent and solar cell performance (left figures). Addition of a random copolymer (RCP) to a donor/acceptor blend promotes microphase separation, enhances phase purity and device performance (right figures).