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This content will become publicly available on February 8, 2017

Title: Harnessing Structure-Property Relationships for Poly(alkyl thiophene)-Fullerene Derivative Thin Filmsto Optimize Performance in Photovoltaic Devices

Nanoscale bulk heterojunction (BHJ) systems, consisting of fullerenes dispersed in conjugated polymers as the active component, have been actively studied over the last decades in order to produce high performance organic photovoltaics (OPVs). A significant role in device efficiency is played by the active layer morphology, but despite considerable study, a full understanding of the exact role that morphology plays and therefore a definitive method to produce and control an ideal morphology is lacking. In order to understand the BHJ phase behavior and associated morphology in these devices, we have used neutron reflection, together with grazing incidence X-ray and neutron scattering and X-ray photoelectron spectroscopy (XPS) to determine the morphology of the BHJ active layer in functional devices. We have studied nine model BHJ systems based on mixtures of three poly(3-alkyl thiophenes, P3AT) (A=butyl, hexyl, octyl) blended with three different fullerene derivatives, which provides variations in crystallinity and miscibility within the BHJ composite. In studying properties of functional devices, we show a direct correlation between the observed morphology within the BHJ layer and the device performance metrics, i.e., the short-circuit current (JSC), fill factor (FF), open-circuit voltage (VOC) and overall power conversion efficiency (PCE). Using these model systems, the effectmore » of typical thermal annealing processes on the BHJ morphology through the film thickness as a function of the polythiophene-fullerene mixtures and different electron transport layer interfaces has been determined. It is shown that fullerene enrichment occurs at both the electrode interfaces after annealing. The degree of fullerene enrichment is found to strongly correlate with JSC and to a lesser degree with FF. Finally, based on these findings we demonstrate that by deliberately adding a fullerene layer at the electron transport layer interface, JSC can be increased by up to 20%, resulting in an overall increase in PCE of 5%.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [2] ;  [2] ;  [2] ;  [4] ;  [1]
  1. Georgia Inst. of Technology, Atlanta, GA (United States)
  2. Univ. of Akron, Akron OH (United States)
  3. Science and Technology Facilities Council (STFC), Oxford (United Kingdom). Rutherford Appleton Lab. (RAL)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS)
Publication Date:
OSTI Identifier:
1257891
Grant/Contract Number:
FG02-10ER4779; AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Advanced Functional Materials
Additional Journal Information:
Journal Volume: 26; Journal Issue: 12; Journal ID: ISSN 1616-301X
Publisher:
Wiley
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS); Oak Ridge Leadership Computing Facility (OLCF)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE bulk heterojunctions; fullerenes; morphology; organic photovoltaics; polyalkylthiophenes