AMADEus Seminar - Pr. Harald Ade - Thursday 26 May 2016 - 10:00 am ENSCBP (Amphi 1)

Abstract
It is well established that the morphology of bulk heterojunction donor:acceptor blends is critical to performance and that actual morphologies comprise at least three phases in many systems, with mixed amorphous regions in addition to relatively pure, aggregated donor and acceptor domains. Understanding the role and controlling the mixed amorphous phase for maximum charge creation and minimum recombination remains a principal challenge. Optimizing performance continues to be a delicate balance of possibly competing factors and the volume fraction of the ideal morphology remains to be determined. Few efforts are aimed at understanding the morphology from a fundamental thermodynamic perspective. We argue that in an ideal morphology the amorphous mixed phase has a small volume fraction and a PCBM concentration near the percolation threshold. This should provide high performance, large processing window and long term thermal stability. We relate this hypothesized morphology to ?(T) and phase diagrams and discuss efforts to estimate the temperature dependence of ? in a number of systems. Numerous experimental indications support that ?(T) can likely be used to predict morphologies, relative performance, and help design optimum processing routes. We discuss our efforts to measure or estimate ?(T) and development of methods that would be widely available to the polymer solar cell community. Our overarching goal is to develop a predictive morphology paradigm.

Short bio:
Dr. Harald Ade obtained his Ph.D. in physics from SUNY@Stony Brook in 1990 and held appointments at NCSU since 1992. He is currently Distinguished Professor in Physics and coordinator of a Carbon Electronics cluster initiative. He is developing and using novel soft X-ray characterization tools, with a focus on the characterization of organic devices. H. Ade is recipient of several Awards and is a Fellow of the APS and the AAAS.