MAT Seminar

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Dr. Hakan Usta, Project Leader

Polyera Corporation, Illinois Science & Technology Park, Skokie, IL, USA
Northwestern University, Evanston, IL, USA

During the past two decades, design, synthesis and characterization of functional materials based on organic ?-conjugated small molecules and polymers received major scientific and technological attention. Thin films prepared by these materials form favorable nanostructures, which can be used in a variety of optoelectronic applications such as organic photovoltaic cells (OPVs), thin-film transistors (OTFTs), and organic light-emitting transistors (OLETs). Compared to inorganic-based electronics, these materials enable proper ink formulations for low-cost, high-throughput printing processes on large-area, light-weight, and flexible plastic substrates. Owing to their unique features, they are envisioned as essential components of next-generation optoelectronic devices such as flexible displays, low-cost solar panels, electronic papers, printable RFID tags, and sensors. These new technologies will revolutionize the role of electronics in our daily lives and compliment current inorganic-based optoelectronic devices, which greatly impacted our society starting from the second half of the 20th century. This study demonstrates theory-aided rational design, synthesis, and characterization of a "library" of functional organic materials as novel n-type, p-type, and ambipolar semiconductors. Solution-processed thin films of these semiconductors yield OTFTs with high hole/electron mobilities of 0.2-2.0 cm2/V·s and Ion/Ioff ratios of >106, one of the highest device performance reported to date. We also report the first examples of polymeric and molecular ambipolar semiconductors in the literature to function in air. Furthermore, organic light-emitting transistors (OLETs) with breakthrough efficiencies of ~5% are demonstrated through a p-channel/emitter/n-channel trilayer heterostructure architecture. OLETs are alternative light sources combining switching mechanism of a thin-film transistor and an electroluminescent device in the same architecture. Significant correlations are established between molecular/polymeric structures, physicochemical properties, and device performances, providing detailed insight into charge transport characteristics and ambient stability. The advances we have made toward realizing truly high-performance and air-stable optoelectronic devices affirm the possibility of achieving low-cost microelectronic devices through rational materials development.