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

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. In conclusion, 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.
 [1] ;  [2] ;  [1] ;  [3] ; ORCiD logo [2] ; ORCiD logo [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. Indian Association for the Cultivation of Science, Kolkata (India)
  3. Univ. of Colorado, Boulder, CO (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 2380-8195
Grant/Contract Number:
Accepted Manuscript
Journal Name:
ACS Energy Letters
Additional Journal Information:
Journal Volume: 2; Journal Issue: 7; Journal ID: ISSN 2380-8195
American Chemical Society (ACS)
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
Country of Publication:
United States
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; processing additives; scanning tunneling spectroscopy; organic photovoltaics; morphology and nanoscale electronic properties
OSTI Identifier: