CAREER: Morphology Control Through a Mechanistic Understanding of Structural Evolution in Organic Semiconductor Mixtures

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TECHNICAL SUMMARY:This award aims to examine the active-layer morphology of polymer solar cells in unprecedented detail to develop a basic understanding of the structure formation process. Energy-filtered transmission electron microscopy will enable elemental mapping at nanometer length scales, while grazing-incidence X-ray scattering will provide statistical measures of the morphology. The combination of these complementary techniques makes the identification of the critical material parameters governing non-equilibrium structural evolution possible. It is hypothesized that polymer semiconductor/fullerene mixtures can be described as polymer solutions; thus, the crystallization kinetics of conjugated polymers in concentrated solutions will be studied as model experiments. Insights from the combination of structural data and device data will lead to structure-function relationships relevant to polymer solar cells. Furthermore, methodologies to promote anisotropic crystal growth and control nucleation will be explored as strategies to control the morphology. The combination of basic knowledge regarding the morphological evolution and widely-applicable strategies for mesostructure control will enable the development of high-performance devices by easing the implementation of novel materials in polymer solar cells.NON-TECHNICAL SUMMARY:Plastics, or polymers, are ubiquitous in society. This is a result of the many intriguing properties of polymers. The proposed work aims to take advantage of some of these properties: the ability to absorb light, conduct charges, and spontaneously form an internal structure at nanometer length scales, or about 1/10,000 the width of a human hair. The combination and optimization of these properties will enable sunlight to electricity conversion and the fabrication of polymer-based solar cells. The strategy for achieving the proposed work is centered on developing a basic understanding of the polymer properties which govern the structure-formation process and ordering phenomena. Integrated undergraduate research and educational activities are proposed to improve retention of undergraduate students and encourage the pursuit of advanced degrees. An emphasis will be placed on underrepresented groups to improve diversity in both undergraduate and graduate student populations. This includes developing new interactions with Penn State satellite campuses, which in some cases lack post-bachelor degrees but boast diverse student populations, in an effort to highlight undergraduate research opportunities.