Exploring Ternary-Blend Polymer Solar Cells: From Fundamental Understanding to High Efficiency

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NON-TECHNICAL SUMMARY:The active component of a typical polymer solar cell employs only two organic semiconductors (this is called a "binary" system and contains a polymer and a fullerene molecule). However, "ternary" systems (where two different polymers are blended with fullerene molecules) are receiving increasing attention because they can maximize the light absorption while maintaining an easy fabrication process. Though efficiencies over 8% have been demonstrated, further fundamental working principles are needed in order to dramatically improve the energy conversion efficiency. The objective of this research is to conduct a fundamental study of selected ternary blend polymer solar cells and to discover design rationales based on new knowledge of the operating mechanisms of such solar cells, with the intent to further improve their efficiency. The elucidated fundamental working mechanism of selected ternary blend cells will have an impact on many fields within organic electronics, including solar cells and transistors. Further improving the efficiency of polymer solar cells will facilitate the commercialization of such technologies, serving the national interest by offering renewable energy at a low cost. Education, collaboration, and outreach are key aspects of the proposed work. The multidisciplinary, inter-institutional and internationally collaborative nature of this project offers a special opportunity to foster educational and research experiences at the graduate and undergraduate levels. Underrepresented groups in science and engineering will be actively recruited into the Principle Investigator's research group. A number of outreach programs will help the general public to understand the importance of renewable energy and the latest research efforts.TECHNICAL SUMMARY:The research activities in this project will combine design and synthesis of conjugated polymers and related device fabrication/characterization with complementary sophisticated device physics and with comprehensive morphology characterization through appropriate collaborations. The focus of this integrated research is the investigation of the working mechanism for "parallel-like" bulk heterojunction (PBHJ) type ternary organic solar cells, via this combination of molecular design, device physics, and morphology characterization. Goals at the conclusion of this project include the full exploration and verification of two different models to explain the PBHJ, i.e. "parallel-like" vs. "alloy", as well as useful and practical design rationales. The elucidated fundamental working mechanism of selected ternary blend BHJ cells should have a direct impact on the ongoing pursuit of novel ternary systems, aiming to dramatically improve the efficiency of polymer solar cells. This could have significant commercial impact on the business sector of polymer solar cells. Additionally, discovered structure-property correlations of these conjugated polymers will provide valuable broader insights to other sub-fields within organic electronics, for example, organic field-effect transistors. Education, collaboration, and outreach are key aspects of the proposed work. The multidisciplinary, inter-institutional and internationally collaborative nature of this project offers a special opportunity to foster educational and research experiences at the graduate and undergraduate levels. Underrepresented groups in science and engineering will be actively recruited into the PI's research group. A number of outreach programs will help the general public to understand the importance of renewable energy and the latest research efforts.