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Title: Tuning domain size and crystallinity in isoindigo/PCBM organic solar cells via solution shearing

Despite having achieved the long sought-after performance of 10% power conversion efficiency, high performance organic photovoltaics (OPVs) are still mostly constrained to lab scale devices fabricated by spin coating. Efforts to produce printed OPVs lag considerably behind, and the sensitivity to different fabrication methods highlights the need to develop a comprehensive understanding of the processing-morphology relationship in printing methods. Here we present a systematic experimental investigation of a model low bandgap polymer/fullerene system, poly-isoindigo thienothiophene/PC 61BM, using a lab-scale analogue to roll-to-roll coating as the fabrication tool in order to understand the impact of processing parameters on morphological evolution. We report that domain size and polymer crystallinity can be tuned by a factor of two by controlling the temperature and coating speed. Lower fabrication temperature simultaneously decreased the phase separation domain size and increased the relative degree of crystallinity in those domains, leading to improved photocurrent. We conclude that domain size in isoindigo/PCBM is dictated by spontaneous phase separation rather than crystal nucleation and growth. Moreover we present a model to describe the temperature dependence of domain size formation in our system, which demonstrates that morphology is not necessarily strictly dependent on the evaporation rate, but rather on the interplaymore » between evaporation and diffusion during the printing process.« less
Authors:
ORCiD logo [1] ;  [1] ;  [2] ;  [2] ;  [3] ;  [1] ;  [4] ;  [5] ; ORCiD logo [1]
  1. Stanford Univ., Stanford, CA (United States)
  2. Stanford Univ., Stanford, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
  3. Univ. of Illinois at Urbana-Champaign, Urbana, IL (United States)
  4. Iowa State Univ., Ames, IA (United States)
  5. SLAC National Accelerator Lab., Menlo Park, CA (United States)
Publication Date:
Grant/Contract Number:
N00014-14-1-0142; 1434799; 1435587; 1149365; AC02-05CH11231; AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Organic Electronics
Additional Journal Information:
Journal Volume: 40; Journal Issue: C; Journal ID: ISSN 1566-1199
Publisher:
Elsevier
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 14 SOLAR ENERGY; Organic photovoltaics; Isoindigo; Phase separation; Morphology evolution; X-ray scattering
OSTI Identifier:
1361161
Alternate Identifier(s):
OSTI ID: 1398694

Gu, Kevin L., Zhou, Yan, Gu, Xiaodan, Yan, Hongping, Diao, Ying, Kurosawa, Tadanori, Ganapathysubramanian, Baskar, Toney, Michael F., and Bao, Zhenan. Tuning domain size and crystallinity in isoindigo/PCBM organic solar cells via solution shearing. United States: N. p., Web. doi:10.1016/j.orgel.2016.10.033.
Gu, Kevin L., Zhou, Yan, Gu, Xiaodan, Yan, Hongping, Diao, Ying, Kurosawa, Tadanori, Ganapathysubramanian, Baskar, Toney, Michael F., & Bao, Zhenan. Tuning domain size and crystallinity in isoindigo/PCBM organic solar cells via solution shearing. United States. doi:10.1016/j.orgel.2016.10.033.
Gu, Kevin L., Zhou, Yan, Gu, Xiaodan, Yan, Hongping, Diao, Ying, Kurosawa, Tadanori, Ganapathysubramanian, Baskar, Toney, Michael F., and Bao, Zhenan. 2016. "Tuning domain size and crystallinity in isoindigo/PCBM organic solar cells via solution shearing". United States. doi:10.1016/j.orgel.2016.10.033. https://www.osti.gov/servlets/purl/1361161.
@article{osti_1361161,
title = {Tuning domain size and crystallinity in isoindigo/PCBM organic solar cells via solution shearing},
author = {Gu, Kevin L. and Zhou, Yan and Gu, Xiaodan and Yan, Hongping and Diao, Ying and Kurosawa, Tadanori and Ganapathysubramanian, Baskar and Toney, Michael F. and Bao, Zhenan},
abstractNote = {Despite having achieved the long sought-after performance of 10% power conversion efficiency, high performance organic photovoltaics (OPVs) are still mostly constrained to lab scale devices fabricated by spin coating. Efforts to produce printed OPVs lag considerably behind, and the sensitivity to different fabrication methods highlights the need to develop a comprehensive understanding of the processing-morphology relationship in printing methods. Here we present a systematic experimental investigation of a model low bandgap polymer/fullerene system, poly-isoindigo thienothiophene/PC61BM, using a lab-scale analogue to roll-to-roll coating as the fabrication tool in order to understand the impact of processing parameters on morphological evolution. We report that domain size and polymer crystallinity can be tuned by a factor of two by controlling the temperature and coating speed. Lower fabrication temperature simultaneously decreased the phase separation domain size and increased the relative degree of crystallinity in those domains, leading to improved photocurrent. We conclude that domain size in isoindigo/PCBM is dictated by spontaneous phase separation rather than crystal nucleation and growth. Moreover we present a model to describe the temperature dependence of domain size formation in our system, which demonstrates that morphology is not necessarily strictly dependent on the evaporation rate, but rather on the interplay between evaporation and diffusion during the printing process.},
doi = {10.1016/j.orgel.2016.10.033},
journal = {Organic Electronics},
number = C,
volume = 40,
place = {United States},
year = {2016},
month = {11}
}