Incoherent charge separation dynamics in organic photovoltaics

Shyamal K.K. Prasad, Joseph K. Gallaher, Alex J. Barker, Han Young Woo, Mamatimin Abbas, Lionel Hirsch, Justin M. Hodgkiss

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

There is mounting evidence that long-range charge separation determines the efficiency of organic photovoltaic cells, yet different mechanisms remain under debate. One class of proposed mechanism is ultrafast coherent long-range charge separation, and another is a slower process whereby charges incoherently hop apart with a transiently enhanced mobility due to morphology and disorder. Here, we use transient absorption spectroscopy to probe incoherent charge separation dynamics in two different ways. First, we use a family of polymers whose backbone structures allows us to compare 2- phase donor-acceptor morphologies with 3-phase morphologies that feature an intermixed region. In the 3-phase system, we see pronounced spectral signatures associated with charges (holes) occupying the disordered intermixed region, and we track separation via biased charge diffusion to more ordered neat regions on the timescale of hundreds of picoseconds. Secondly, by resolving bimolecular charge recombination at high excitation density, we show that charge mobilities must be substantially enhanced on early timescales, which may be sufficient for separation to occur. Together, these measurements provide support for models of incoherent and relatively slow charge separation.

Original languageEnglish
Title of host publicationPhysical Chemistry of Interfaces and Nanomaterials XV
EditorsRobert Lovrincic, Artem A. Bakulin, Natalie Banerji
PublisherSPIE
ISBN (Electronic)9781510602373
DOIs
Publication statusPublished - 2016
EventPhysical Chemistry of Interfaces and Nanomaterials XV - San Diego, United States
Duration: 2016 Aug 282016 Aug 31

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
Volume9923
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X

Conference

ConferencePhysical Chemistry of Interfaces and Nanomaterials XV
CountryUnited States
CitySan Diego
Period16/8/2816/8/31

Keywords

  • Charge separation
  • Intermixed phase
  • Mobility relaxation
  • Organic photovoltaic
  • Three phase
  • Transient absorption

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering

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