Revealing the Nanomorphology and Excited State Dynamics Behind the Ternary Advantage in Organic Photovoltaics

Washington State University, Pullman WA

Investigators

Abstract

Non-technical Description The emergence of low-cost, flexible, and biocompatible organic devices will have a game-changing impact on society. These devices could revolutionize how we interface with technology, transform our ability to renewably harvest and store energy, and advance healthcare. Printed solar panels have great potential, yet current technology still uses relatively low-performance materials or involves toxic lead-based materials. Organic solar cells require two different types of molecules to generate and transport charge from incident light. A recent breakthrough in the performance of organic solar cells uses a blend of three types of molecules. This suggests an opportunity for the next leap in a disruptive technology, but it is held back by a lack of scientific understanding of the phenomenon. Investigators will use X-ray probes to correlate the performance and nanostructure of these blends. They will also analyze charge generation dynamics to determine the processes responsible for performance gains. This work will reveal how to control the phenomenon to enable truly high-performance printed and lead-free photovoltaic modules to fully compete in the marketplace. Graduate students involved will benefit from the multidisciplinary nature of the work to gain critical experience and expertise in communicating in diverse collaborations. Their travel to major national laboratories for the work will provide new career opportunities and perspective. Students involved will bolster outreach activities of the WSU Science Ambassadors Program by traveling to area schools with educational activities and mentoring undergraduates in summer projects in the principal investigator’s Research Experience for Undergraduates program. Technical Description Multicomponent organic electronic systems are being increasingly explored to enhance properties and performance in devices for printable, flexible, and biocompatible applications. Recently, ternary and quaternary blends have been shown to enhance performance of organic photovoltaics to over 20% efficiencies. The high dimensionality of parameter space which are difficult to characterize, however, results in halting progress. In this project, a spectral analysis of resonant soft X-ray nanoprobes will uniquely enable definitive characterization of these complex three and four-component systems to reveal the precise morphological paradigms responsible for the ternary advantage. These nanostructure measurements will be combined with a holistic analysis of the fundamental charge generation dynamic process as well its energetics in device-relevant conditions to define the emergent excited state pathways responsible for the performance gains. The hypothesis is that mixing of guest molecules in strategic domains can tune charge transport and non-radiative losses, but collection of the guest molecules at donor-acceptor interfaces is key to lowering energetic barriers to enhance charge separation efficiencies. The aim is to establish the mechanisms of the ternary advantage and the thermodynamic and kinetic limits of these mechanisms to provide a model for further optimization through molecular design and device processing. 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.