Center for Excitonics


Polymer-Acceptor Bulk Heterojunction Solar Cells: From Chemical Structure to Packing and Efficiency

April 17, 2018 at 2:45pm/36-428

Jean-Luc Bredas
Department of Chemistry and Biochemistry, Georgia Tech

The morphology of the active layer of a bulk heterojunction (BHJ) solar cell, made of a blend of an electron-donating polymer and an electron-accepting fullerene or nonfullerene derivative, is known to play a determining role in device performance.  Here, based on the results of molecular dynamics simulations and long-range corrected density functional theory calculations, we first describe the nature of the binding interactions at the donor–acceptor interfaces, the molecular-level packing in the pure phases as well as at these interfaces, and the impact of the system dynamics on the interfacial electronic structure.

We then discuss how even minor changes in the chemical structure of the polymer backbone have been shown experimentally to change substantially the blend morphology and the resulting solar-cell efficiency. Taking a series of representative systems based on benzothiadiazole-quaterthiophene polymers and PC71BM, we elucidate the impact of the chemical changes on the ″local″ morphology. We focus on the extent of polymer-fullerene mixing, on their packing, and on the characteristics of the fullerene-fullerene connecting network in the mixed regions, which are all aspects that are difficult to access experimentally. We are able to rationalize the evolutions in power conversion efficiencies within the polymer series.  Finally, we address the peculiarities observed in the PIPCP-fullerene blends.

This work is supported by the Office of Naval Research, namely in the framework of the MURI Center on Advanced Organic Photovoltaics.

Jean-Luc Brédas is a Belgian chemist and currently at Georgia Tech. He was a Distinguished Professor of Material Science and Engineering in the Physical Science and Engineering Division at KAUST, and at the Université de Mons-Hainaut Belgium. He studied Chemistry (B.S. 1976) and obtained a PhD in 1979 at the Facultés Universitaires Notre-Dame de la Paix (University of Namur), Belgium. His research deals with the structural, electronic, and optical properties of novel organic and nanomaterials with promising characteristics in the field of electronics, photonics, and information technology.

Brédas is among the top 100 most cited chemists in the world, and is included in the list of the Highly Cited Researchers for Chemistry [2]. He is the Director of International Programs at the Center for Organic Photonics and Electronics at Georgia Tech. He is a member of the International Academy of Quantum Molecular Science (2011).[1] He is a Fellow of the American Association for the Advancement of Science, the American Chemical Society, the American Physical Society, and the Optical Society of America.