Tailoring donor-acceptor morphologies through melt-crystallization

This project is jointly funded by the DMR Polymers Program, and the Established Program to Stimulate Competitive Research (EPSCoR). NON-TECHNICAL SUMMARY

Organic photovoltaics (OPVs) made from conjugated (alternating single and double bond containing) polymers are promising materials for application as light-harvesting devices because they are lightweight, flexible, and can be made by easy, low-cost processing. Conjugated polymer-acceptor blends have great potential as active layers in OPVs. The final way the polymer-acceptor blends are organized is controlled by processing conditions and built-in molecular characteristics that dictate the final properties and performance of the critical, active layer.

Polymer-acceptor layers are typically made in a complicated process using organic solvents and thermal annealing; in contrast, melt-processing, a simpler, low-cost process which is used to make most inexpensive plastic parts, has remained largely unexplored, so its potential is virtually untapped for OPVs. This research project will enable novel melt-based processing methods of polymer-acceptor films for OPVs and has potential to achieve previously inaccessible morphologies and performance for light-harvesting applications.

This project will train graduate students for STEM jobs in both academic and industrial settings and will also educate undergraduate students through research and mentoring opportunities. Outreach efforts in preschool and K-5 will motivate young students and educate their teachers and will seek to broaden participation of underrepresented students in STEM, ultimately contributing to development of the future STEM workforce.

Results will be broadly disseminated through specialized journals, publications for broader audiences, at scientific conferences, and by making materials and publications available online. TECHNICAL SUMMARY

The objective of this project is to understand and direct morphology development in conjugated polymer-acceptor blends through melt-processing. The bulk heterojunction structure of semicrystalline polymer-acceptor films is determined by an intricate interplay between crystallization and phase separation, depends strongly on material components and processing conditions, and ultimately dictates final photoelectric, mechanical, and stability properties.

Polymer-acceptor blends are typically solution-processed and annealed to change structure and improve properties, but the fundamental mechanism of structure development during melt-processing has received little attention and remains poorly understood. This research project will investigate how manipulating melt-crystallization through material and processing parameters can be used to tailor the complex interaction with phase separation and, consequently, morphology development and final properties.

The significance of this research is two-fold. On one hand, it will generate fundamental knowledge in structure development of conjugated polymer-acceptor blends of interest for organic photovoltaics. On the other hand, this project will open up the way to rational design of new materials and processing methods to yield previously inaccessible morphologies and properties in polymer-based active layers.

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.