Promoting Morphology with a Favorable Density of States Using Diiodooctane to Improve Organic Photovoltaic Device Efficiency and Charge Carrier Lifetimes

Wade Braunecker, Bryon Larson, Abhijit Bera, David Ostrowski, Amlan Pal, Logan Garner

Research output: Contribution to journalArticlepeer-review

19 Scopus Citations

Abstract

Due to the inherent challenges in probing nanoscale properties within bulk heterojunction (BHJ) active layers of organic photovoltaic (OPV) devices, the relationship between morphology and nanoscale electronic structure is not well understood. Here, we employ scanning tunneling microscopy (STM) dI/dV imaging and localized density of states (DOS) spectra to investigate the influence of additives on morphology in a high-performance OPV system. In short, we are able to correlate the use of diiodooctane (DIO) additive with significant changes to the distribution of the localized DOS, most notably a broader distribution of PCE10 polymer HOMO levels and PC70BM fullerene LUMO levels, as well as significantly smaller domain sizes and significantly higher overall device efficiencies. We further correlate this data with a nearly 3-fold increase in charge carrier lifetimes in the active layer when DIO is employed, determined by time-resolved microwave conductivity (TRMC) measurements. The results are consistent with the growing body of literature evidence that DIO promotes the formation of a polymer/fullerene mixed phase and therefore highlight the unique information that this combination of techniques can provide when investigating OPV active layer morphology.

Original languageAmerican English
Pages (from-to)1556-1563
Number of pages8
JournalACS Energy Letters
Volume2
Issue number7
DOIs
StatePublished - 14 Jul 2017

Bibliographical note

Publisher Copyright:
© 2017 American Chemical Society.

NREL Publication Number

  • NREL/JA-5900-68311

Keywords

  • morphology and nanoscale electronic properties
  • organic photovoltaics
  • processing additives
  • scanning tunneling spectroscopy

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