Increased Exciton Delocalization of Polymer upon Blending with Fullerene

Bhoj Gautam, Erik Klump, Xueping Yi, Iordania Constantinou, Nathan Shewmon, Amin Salehi, Chi Kin Lo, Zilong Zheng, Jean Luc Brédas, Kenan Gundogdu, John R. Reynolds, Franky So

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

Interfaces between donor and acceptor in a polymer solar cell play a crucial role in exciton dissociation and charge photogeneration. While the importance of charge transfer (CT) excitons for free carrier generation is intensively studied, the effect of blending on the nature of the polymer excitons in relation to the blend nanomorphology remains largely unexplored. In this work, electroabsorption (EA) spectroscopy is used to study the excited-state polarizability of polymer excitons in several polymer:fullerene blend systems, and it is found that excited-state polarizability of polymer excitons in the blends is a strong function of blend nanomorphology. The increase in excited-state polarizability with decreased domain size indicates that intermixing of states at the interface between the donor polymers and fullerene increases the exciton delocalization, resulting in an increase in exciton dissociation efficiency. This conclusion is further supported by transient absorption spectroscopy and time-resolved photoluminescence measurements, along with the results from time-dependent density functional theory calculations. These findings indicate that polymer excited-state polarizability is a key parameter for efficient free carrier generation and should be considered in the design and development of high-performance polymer solar cells.

Original languageEnglish (US)
Article number1801392
JournalAdvanced Materials
Volume30
Issue number30
DOIs
StatePublished - Jul 26 2018
Externally publishedYes

Keywords

  • Frenkel exciton
  • charge transfer states
  • electroabsorption
  • exciton delocalization
  • polarizability

ASJC Scopus subject areas

  • Materials Science(all)
  • Mechanics of Materials
  • Mechanical Engineering

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