Conjugated Block Copolymers as Model Systems to Examine Mechanisms of Charge Generation in Donor–Acceptor Materials

Melissa P. Aplan, Christopher Grieco, Youngmin Lee, Jason M. Munro, Wonho Lee, Jennifer L. Gray, Zach D. Seibers, Brooke Kuei, Joshua H, Litofsky, S. Micheal Klbey II, Qing Wang, Ismaila Dabo, John B. Asbury, and Enrique D. Gomez, 2018

Image courtesy of Protochips

Abstract

Fully conjugated donor–acceptor block copolymers are established as model systems to elucidate fundamental mechanisms of photocurrent generation in organic photovoltaics. Using analysis of steady‐state photoluminescence quenching, exciton dissociation to a charge transfer state within individual block copolymer chains is quantified. By making a small adjustment to the conjugated backbone, the electronic properties are altered enough to disrupt charge transfer almost entirely. Strong intermolecular coupling of the electron donor is introduced by synthesizing block copolymer nanoparticles. Transient absorption spectroscopy is used to monitor charge generation in block copolymer isolated chains and nanoparticles. While efficient charge transfer is observed in isolated chains, there is no indication of complete charge separation. In the nanoparticles, long‐lived polarons are observed as early as ≈15 ns. Thus, aggregation of electron donors can facilitate efficient charge generation.

Impact Statement

LC-TEM was used to complement dynamic light scattering data to record size and aggregation of block copolymer nanoparticles in solution.