报告题目: Molecular Engineering of Conjugated Polymers and Non-Fullerene Acceptors for Organic Photovoltaics

报告人： Prof. Wei You  Department of Chemistry,University of North Carolina at Chapel Hill

报告地点：麦氏楼二楼圆锥报告厅

报告时间：2019年06月24日下午2:30（星期一）

邀请人： 陈峥

Short Bio:

Wei You was born in a small village outside of Chuzhou in Anhui Province of China and grew up in Hefei, the provincial capital of Anhui. After receiving a B.S. degree in Polymer Chemistry from University of Science and Technology of China in 1999, he attended the graduate program of chemistry at the University of Chicago, where he obtained his Ph.D. in 2004 under the guidance of Professor Luping Yu. He then moved west and finished his postdoctoral training at Stanford University in 2006 with Professor Zhenan Bao.

In July 2006, he joined the University of North Carolina at Chapel Hill as an Assistant Professor in Chemistry. He was promoted to the rank of Associate Professor in 2012 and then Full Professor in 2017. He has published over 100 papers in premier journals such as Nature Photonics, JACS, Angew. Chem., Int. Ed., Macromolecules, Advanced Materials, among others, and has been an Associate Editor for Polymer Chemistry (RSC) since July 2013. He is also on the advisory board for Macromolecules (ACS)and ACSAppliedEnergy Materials (ACS). He has received DuPont Young Professor Award (2008), NSF CAREERAward (2010), CamilleDreyfus Teacher-Scholar Award (2011), Tanner Award for Excellence in Undergraduate Teaching (2011), CAPA Distinguished Junior Faculty Award (2012), Ruth and Phillip Hettleman Prize for Artistic and Scholarly Achievement (2013), and Fellow of Royal Society of Chemistry (FRSC) (2017).

His group is currently investigating organic solar cells, organic/inorganic hybrid 2D perovskites, molecular spintronics/electronics and devices, bio-inspired materials for biomedical applications, and new polymerization methodologies.

Molecular Engineering of Conjugated Polymers and Non-Fullerene Acceptors for Organic Photovoltaics

Jeromy J. Rech, Nicole Bauer, and Wei You*

Department of Chemistry

University of North Carolina at Chapel Hill

Chapel Hill, North Carolina 27599-3290 USA

*Corresponding author (wyou@unc.edu)

The continued improvement in efficiency for organic photovoltaics (OPVs) is due in part to the development of new conjugated polymeric materials. We have reported a fluorination technique which yields a high efficiency polymer, PBnDT-FTAZ, (~7%) with phenyl-C61-butyric acid methyl ether (PCBM) and even higher efficiencies (13.6%) when paired with non-fullerene acceptors. The addition of the fluorine substituent on the acceptor benzotriazole (TAZ) moiety increased all three major device characteristics (Voc, Jsc, and FF). In this presentation, I will first discuss a new design motif to incorporate fluorine substituents into conjugated polymers using the common thiophene linkers which connect the donor and acceptor moieties of the polymer, rather than fluorinating directly on the acceptor moiety. This new design motif will allow for materials, previously with no fluorination location, to enjoy the benefits attributed to fluorination. Specifically, we introduce a difluorinated thiophene (dFT) linker into the BnDT-TAZ system to create a new polymer, PBnDT-dFT-HTAZ. Compared with the nonfluorinated counterpart (PBnDT-HTAZ), a 50% improvement in the efficiency is seen when using the dFT linker.

Next, newly developed fused-ring electron acceptors (FREAs) have proven to be an effective class of materials for extending the absorption window and boosting the efficiency of OPVs. Of the high efficiency electron acceptors reported, the vast majority utilize derivatives of 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (INCN) as the acceptor moiety. It has been postulated that the high electron mobility exhibited by FREA molecules with INCN end groups is a result of close π-π stacking between the neighboring planar INCN groups, forming an effective charge transport pathway. To explore this as a design rationale for electron acceptors, we synthesized a new fused-ring electron acceptor, IDTCF, which has methyl substituents out of plane to the conjugated acceptor backbone. These methyl groups hinder packing and expand the π-π stacking distance by ~ 1 Å, but this change doesn’t affect the optical or electrochemical properties of the individual acceptor molecule. Our results show that intermolecular interactions (especially π-π stacking between end groups) play a crucial role in performance of FREAs. We demonstrated that the planarity of the acceptor unit is of paramount importance as even minor deviations in end group distance are enough to disrupt crystallinity and cripple device performance.