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Title: Peculiarity of two thermodynamically-stable morphologies and their impact on the efficiency of small molecule bulk heterojunction solar cells

Structural characteristics of the active layers in organic photovoltaic (OPV) devices play a critical role in charge generation, separation and transport. Here we report on morphology and structural control of p-DTS(FBTTh 2) 2:PC 71BM films by means of thermal annealing and 1,8-diiodooctane (DIO) solvent additive processing, and correlate it to the device performance. By combining surface imaging with nanoscale depth-sensitive neutron reflectometry (NR) and X-ray diffraction, three-dimensional morphologies of the films are reconstituted with information extending length scales from nanometers to microns. DIO promotes the formation of a well-mixed donor-acceptor vertical phase morphology with a large population of small p-DTS(FBTTh2)2 nanocrystals arranged in an elongated domain network of the film, thereby enhancing the device performance. In contrast, films without DIO exhibit three-sublayer vertical phase morphology with phase separation in agglomerated domains. Our findings are supported by thermodynamic description based on the Flory-Huggins theory with quantitative evaluation of pairwise interaction parameters that explain the morphological changes resulting from thermal and solvent treatments. Our study reveals that vertical phase morphology of small-molecule based OPVs is significantly different from polymer-based systems. Lastly, the significant enhancement of morphology and information obtained from theoretical modeling may aid in developing an optimized morphology to enhance devicemore » performance for OPVs.« less
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [1] ;  [3] ;  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Univ. of Tennessee, Knoxville, TN (United States)
  3. UNSW Australia, Sydney, NSW (Australia)
Publication Date:
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 5; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; nanoscale materials; solar cells; 36 MATERIALS SCIENCE
OSTI Identifier:
1259703
Alternate Identifier(s):
OSTI ID: 1333656

Herath, Nuradhika, Das, Sanjib, Keum, Jong K., Zhu, Jiahua, Kumar, Rajeev, Ivanov, Ilia N., Sumpter, Bobby G., Browning, James F., Xiao, Kai, Gu, Gong, Joshi, Pooran, Smith, Sean, and Lauter, Valeria. Peculiarity of two thermodynamically-stable morphologies and their impact on the efficiency of small molecule bulk heterojunction solar cells. United States: N. p., Web. doi:10.1038/srep13407.
Herath, Nuradhika, Das, Sanjib, Keum, Jong K., Zhu, Jiahua, Kumar, Rajeev, Ivanov, Ilia N., Sumpter, Bobby G., Browning, James F., Xiao, Kai, Gu, Gong, Joshi, Pooran, Smith, Sean, & Lauter, Valeria. Peculiarity of two thermodynamically-stable morphologies and their impact on the efficiency of small molecule bulk heterojunction solar cells. United States. doi:10.1038/srep13407.
Herath, Nuradhika, Das, Sanjib, Keum, Jong K., Zhu, Jiahua, Kumar, Rajeev, Ivanov, Ilia N., Sumpter, Bobby G., Browning, James F., Xiao, Kai, Gu, Gong, Joshi, Pooran, Smith, Sean, and Lauter, Valeria. 2015. "Peculiarity of two thermodynamically-stable morphologies and their impact on the efficiency of small molecule bulk heterojunction solar cells". United States. doi:10.1038/srep13407. https://www.osti.gov/servlets/purl/1259703.
@article{osti_1259703,
title = {Peculiarity of two thermodynamically-stable morphologies and their impact on the efficiency of small molecule bulk heterojunction solar cells},
author = {Herath, Nuradhika and Das, Sanjib and Keum, Jong K. and Zhu, Jiahua and Kumar, Rajeev and Ivanov, Ilia N. and Sumpter, Bobby G. and Browning, James F. and Xiao, Kai and Gu, Gong and Joshi, Pooran and Smith, Sean and Lauter, Valeria},
abstractNote = {Structural characteristics of the active layers in organic photovoltaic (OPV) devices play a critical role in charge generation, separation and transport. Here we report on morphology and structural control of p-DTS(FBTTh2)2:PC71BM films by means of thermal annealing and 1,8-diiodooctane (DIO) solvent additive processing, and correlate it to the device performance. By combining surface imaging with nanoscale depth-sensitive neutron reflectometry (NR) and X-ray diffraction, three-dimensional morphologies of the films are reconstituted with information extending length scales from nanometers to microns. DIO promotes the formation of a well-mixed donor-acceptor vertical phase morphology with a large population of small p-DTS(FBTTh2)2 nanocrystals arranged in an elongated domain network of the film, thereby enhancing the device performance. In contrast, films without DIO exhibit three-sublayer vertical phase morphology with phase separation in agglomerated domains. Our findings are supported by thermodynamic description based on the Flory-Huggins theory with quantitative evaluation of pairwise interaction parameters that explain the morphological changes resulting from thermal and solvent treatments. Our study reveals that vertical phase morphology of small-molecule based OPVs is significantly different from polymer-based systems. Lastly, the significant enhancement of morphology and information obtained from theoretical modeling may aid in developing an optimized morphology to enhance device performance for OPVs.},
doi = {10.1038/srep13407},
journal = {Scientific Reports},
number = ,
volume = 5,
place = {United States},
year = {2015},
month = {8}
}