Speaker: Harald Ade, Physics Department

Speaker: Dr. Harald Ade

Affiliation: Physics Department

Abstract:

Organic solar cells (OSCs) are one of the most promising cost-effective options for utilizing solar energy in high energy- per-weight or semi-transparent applications. Recently, the OSC field has been revolutionized through synthesis and processing advances, primarily through the development of numerous novel non-fullerene small molecular acceptors with efficiencies now reaching >18% when paired with suitable donor polymers. The device stability and mechanical durability of these non-fullerene OSCs have received less attention and developing devices with both high performance and long-
term stability remains challenging, particularly if the material choice is restricted by roll-to-roll and benign solvent processing requirements and desirable ductility requirements. Yet, morphological and mechanical stability is a prerequisite for OSC commercialization. Here, we discuss our current understanding of the phase behavior of OSC donor:acceptor mixtures and the relation of phase behavior to performance, processing needs (e.g., kinetic quenches), and morphological stability via meta-stability or vitrification. Characterization methods range from SIMS and DSC measurements to delineate phase diagrams and miscibility to x-ray scattering to determine critical morphology parameters and molecule packing. A large range of miscibility of the non-fullerene acceptor in the donor polymer (from hyper miscibility to strong hypo-miscibility) is observed, including complex temperature dependence that can be a mixture of upper- and lower critical solution temperature behavior for both the binodal and the liquidus. The results presented and its ongoing evolution are intended to uncover fundamental molecular structure-function relationships that would allow predictive guidance on how desired phase behavior and vitrification properties can be targeted by specific chemical design. The understanding gained also allows to predict how unstable binary systems can be stabilized with a ternary compound that has a favorable miscibility.

BioSketch:

A gradute of Stony Brook University, H. Ade has been a faculty member at NCSU since Nov. 1992, rising through the ranks to Full Professor by 2001, and been named Distinguished Professor of Physics in 2014 and Goodnight Innovation Distinguished Professor in 2017. He has had an active and continually funded research program and served as Director of Graduate Program in Physics from 2006-2013. Recognitions include R&D100 Award, NSF Young Investigator Award, APS Fellow, AAAS Fellow, Alumni Outstanding Research Award (twice, NCSU), Holladay Medal (NCSU), K. F. J. Heinrich Award, and Shirley Price for Outstanding Science and Halbach Award of Innovative Instrumentation (both at the Advanced Light Source). He is a Clarivate Analytics WoS Highly Cited Researcher in the field of Matearials Science since 2017. Some of his external engagements include serving on the Scientific Advisory Committee of the Advanced Light Source (2011- 2019) and the BESSY-II Synchrotron Facility in Berlin, Germany (2006-2009), as well as the Scientific Advisory Council of the Helmholz Zentrum Berlin, Germany (2009 – 2012).