Our research interests are centered around a common theme of interfacial interactions and energetics, with an application oriented approach targeting the development and understanding of interfaces in organic electronics, perovskite based solar cells, organic-inorganic composites, and thermoelectrics.  In all of these application areas the various heterointerfaces play a major role in shaping the material properties or device performance.

In organic electronic devices, such as organic photovoltaics (OPVs), organic light emitting diodes (OLEDs), and organic field effect transistors (OFETs), the various interfaces present have a major influence on device performance.  These interfaces include the organic-organic interface, which for example plays a critical role in charge separation in OPVs, as well as the organic-inorganic interface, where charge injection or extraction occurs.  The energetic landscape at these interfaces, which is determined both by intermolecular interactions and interfacial molecular conformations, can drastically influence charge transport or charge separation dynamics.   To ultimately improve device level properties through obtaining a fundamental scientific understanding we aim to controllably tune interfacial properties, use various analytical techniques to probe the interface, and test the impact on device performance.

In any solar cell technology, such as the recently developed methyl ammonium lead iodide (CH3NH3)PbI3 perovskite system, the interface between the active layer and electrodes must be optimized to minimize performance losses.  For example, low energy defect states at the surface can serve as recombination centers while improper energy level alignment can result in barriers to charge collection or energetic losses during charge collection, all of which reduce the power conversion efficiency of the solar cell.  We seek to generate a better understanding of these interfaces and how they impact device performance through utilizing various optical and photoelectron spectroscopies to probe these interfaces.  Through tuning interfacial properties and comparing with solar cell performance we will be able to draw relationships between surface chemistry, interfacial energetics, and solar cell performance.

Organic-inorganic composites provide promising opportunities for a large suite of applications, including materials with novel combinations of electronic, optical, and mechanical properties.  To control these properties the surface chemistry of the inorganic-organic interface can be tuned.  For example, in a polymer-nanoparticle blend the surface chemistry of the nanoparticle may be altered such that it interacts more strongly with the polymer and thus nanoparticle aggregation will be reduced.  Furthermore, the interfacial energetics at the polymer-nanoparticle blend may be adjusted such that charges move more freely between polymer and nanoparticle.  Here we aim to understand these interfacial interactions and how they effect material properties, followed by using these interfaces to create composite materials with improved properties (such as transparent electrodes or thermoelectrics).

A major tool and analytical focus of the group is the application of various photoelectron spectroscopies to thoroughly probe the nature of the various interfaces highlighted above.  These include ultraviolet photoelectron spectroscopy to probe the valence band or ionization potentials, X-ray photoelectron spectroscopy to probe the chemical nature of the interface, and inverse photoelectron spectroscopy to probe the conduction band or electron affinities.

Analytical and Materials Chemistry