Advancing the State of Knowledge
RFA1 will develop the fundamental chemistry and physics to produce new materials, soft matter systems, and device paradigms enabling optical to electrical transduction of infrared (IR) light using organic semiconductors (OSCs). Through the development of modular synthetic approaches, we demonstrated the first example of precise control of conjugated polymers in the IR spectral regions. Such synthetic control has also resulted in the development of materials with complex and tunable electronic structures, varying magnitudes of intramolecular electron-electron pairing, cooperative electronic properties based on π-electrons, and controlled spin alignments; design paradigms which underlie the development of next generation optoelectronic technologies. The discontinuity in the structure and dynamics of these materials as the bandgap continues to narrow is a manifestation of increasing electron correlations and, similar to their inorganic counterparts, leads to new emergent properties. Furthermore, these materials are multiscale in their characteristic energy, length, and time scales and fundamental excitations span the ultraviolet-visible-IR (intra- and intermolecular excited state transitions) and microwave (between different spin states). A lack of IR-absorbing polymers has precluded in-depth investigations of various phenomena in low bandgap systems and excluded the use of conjugated polymers (CPs) beyond the NIR. It is critical that the properties of these materials are carefully controlled and investigated in order to enable the desired optoelectronic functionality. These studies will be the first of their kind that detail general design rules for incorporating CPs into IR optoelectronics, articulate specific challenges associated with these materials, and that connect intrinsic properties with device performance.
IR photoresponsive OSCs will exhibit completely new properties in relation to existing semiconductor materials. Extending the photoresponse of OSCs into new spectral regions will enable new technologies. IR photoresponsive devices based on OSCs will serve as the basic building blocks for more advanced optoelectronic technologies, supersede traditional IR photodetection and energy conversion paradigms with lower cost, higher performing devices that use excitons (bound state of an electron and hole) to mediate the flow of energy. Research objectives and tasks (defined below) have been developed to address the following research questions:
1.1 What are the electronic and physical interactions, determined by orientation, interchain packing, and ensemble structure that will enable bandgap and electronic structure control in the IR in diverse materials sets?
1.2 Using a combination of theory-guided chemical design, synthesis, and characterization, how do we establish a fundamental understanding of the interrelation between molecular and solid-state structure on exciton formation, lifetime, dissipation, and coherence?
1.3 What are the underlying physical and chemical principles of function and how can we establish conceptual designs for new molecules and materials?
1.4 Using our established design rules and systematic approaches is it possible to enable efficient charge photogeneration in progressively narrow bandgap and strongly correlated organic materials?
1.5 How do OSCs fundamentally interact with IR light? What new photophysical phenomena and properties are available and how can they be translated into devices?
Goals and Objectives
Goal 1: Develop narrow bandgap and infrared photoresponsive organic semiconductors and fabricate and engineer photoresponsive devices that operate in various infrared spectral regions.
Objective 1.1: Synthesize Materials: Establish Energy Level & Bandgap Control
Objective 1.2: Carry out Photophysical Investigations & Engineer Excited State Properties
Objective 1.3: Fabricate & Engineer Infrared Photoresponsive Devices