Rational Design of Conjugated Polymers with Cleavable Side Chains to Achieve Morphological Stability of Polymer Solar Cells

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NON-TECHNICAL SUMMARY:With the support of the Polymers Program in the Division of Materials Research, Professor Wei You of the University of North Carolina at Chapel Hill intends to explore rational design of conjugated polymers with cleavable side chains, aiming to enhance the stability of such conjugated polymer-based solar cells. The success of this project would significantly enhance the understanding of the function of side chains in balancing the solubility of conjugated polymers and the thermal stability of such polymer-based solar cells, and result in polymer solar cells of improved thermal stability and high efficiency. All participants in this project will have the opportunity for interdisciplinary learning from synthesis to device fabrication, as well as sophisticated characterization tools via a number of established collaborations. The PI's group will actively recruit and train students of diverse backgrounds, in addition to conducting outreach activities for the general public and K-12 students.TECHNICAL SUMMARY:Typically, conjugated polymers used in high efficiency solar cells often show low glass transition temperatures, leading to instability of such solar cells during operation by heat. Thermally removing cleavable side chains is an effective approach to offer the necessary solubility of conjugated polymers during solution processing, and re-gain the high glass transition temperature of conjugated polymers via thermal removal of side chains after the film formation. The You group recently proposed a balanced approach where some side chains would be cleaved to gain morphological stability while keeping other side chains to maintain the pre-established morphology to largely retain the efficiency. The objectives of this project are: (1) to design the synthesis of poly(thiophene)s with cleavable side chains and unsubstituted thiophene units to further improve the efficiency and stability, (2) to develop milder methods for cleaving alkyl chains to minimize the thermal impact on morphology, (3) to conduct morphological investigations to develop structure-morphology-stability-efficiency relationships within these model systems, and (4) to explore the cleavable side chains in high-performance conjugated polymers and small molecule acceptors to achieve high device efficiency and high morphological stability. The success of this project would lead to development of a low-temperature process to achieve the cleavage of side chains, achieving PSCs of high morphological stability and high efficiency, and elucidating the structure-morphology-stability-efficiency relationships.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.