Developing in operando structure-property-function guidelines for small molecule organic electron acceptors and its implication on device performance and charge carrier mobility

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Organic photovoltaic (OPV) technology has the potential for significant economic impact due to unique features such as flexibility, low weight, and short energy payback time (i.e. the time needed to produce the energy that was required for its production). To achieve greater commercial application, OPVs need to overcome technology challenges in efficiency, stability, durability, and safe and sustainable production. This project will investigate the processes responsible for the limited lifetime and efficiency of OPVs under operating conditions. These studies will be carried out using a suite of in-house and synchrotron diffraction and spectroscopy tools coupled with device fabrication. The project team will engage the Salt Lake City community in energy and organic electronic topics through an innovative education and outreach effort involving high school teachers. Also, the project team will provide professional mentoring and short research activities in STEM to economically disadvantaged young female students in the Valley through the Young & WISE (Women in Science and Engineering) outreach effort.The rational design and investigation of the physical and chemical properties of well-controlled non-fullerene electron acceptors are critical for enabling high efficiency, flexible, and solution processable organic photovoltaics (OPVs). Although, power conversion efficiencies are approaching 15% for OPVs comprising a p-type donor polymer and an n-type small molecule acceptor in a conventional bulk-heterojunction architecture, there are still major fundamental knowledge gaps (i.e., morphology changes, appropriate donor-acceptor coupling, energy level mismatches) that impede their accelerated development and commercialization. Furthermore, there is little to no fundamental knowledge on how morphology, donor-acceptor interfaces, energy level alignments, and device characteristics evolve under operando conditions and bias stress effects. In this fundamental research project, the research team will 1) design a model system based on thionated contorted quaternary perylene diimide propellers as efficient electron acceptors; 2) develop diffraction and spectroscopy characterization approaches to elucidate energy level alignment, molecular orientation, and morphology of electron acceptors when interfaced with other molecules under operating conditions; and 3) investigate exciton interactions and spin processes that could enhance power conversion efficiencies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.