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Title: Stability of push–pull small molecule donors for organic photovoltaics: spectroscopic degradation of acceptor endcaps on benzo[1,2-b:4,5- b′]dithiophene cores

Abstract

High efficiency organic photovoltaic devices have relied on the development of new donor and acceptor materials to optimize opto-electronic properties, promote free carrier generation, and suppress recombination losses. With single junction efficiencies exceeding 15%, materials development must now target long-term stability. This work focuses on the photobleaching dynamics and degradation chemistries of a class of small molecule donors inspired by benzodithiophene terthiophene cores (BDT-3T) with rhodanine endcaps, which have demonstrated 9% efficiency in single junction devices and >11% in ternary cells. Density functional theory was used to design three additional molecules with similar synthetic pathways and opto-electronic properties by simply changing the electron accepting endcap to benzothiazoleacetonitrile, pyrazolone, or barbituric acid functional groups. This new class of semiconductors with equivalent redox properties enables systematic investigation into photobleaching dynamics under white light illumination in air. Degradation chemistries are assessed via unique spectroscopic signatures for the BDT-3T cores and the endcaps using photoelectron spectroscopies. We show that the pyrazolone undergoes significant degradation due to ring opening, resulting in complete bleaching of the chromophore. The barbituric and rhodanine endcap molecules have moderate stability, while the benzothiazoleacetonitrile group produces the most stable chromophore despite undergoing some oxidative degradation. Collectively, our results suggest the following:more » (i) degradation is not just dependent on redox properties; (ii) core group stability is not independent of the endcap choice; and (iii) future design of high efficiency materials must consider both photo and chemical stability of the molecule as a whole, not just individual donor or acceptor building blocks.« less

Authors:
 [1];  [1]; ORCiD logo [2];  [1];  [1]; ORCiD logo [2]; ORCiD logo [2]; ORCiD logo [2];  [2];  [2];  [2];  [3];  [3]
  1. Univ. of Arizona, Tucson, AZ (United States)
  2. National Renewable Energy Laboratory (NREL), Golden, CO (United States)
  3. University of Arizona
Publication Date:
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)
OSTI Identifier:
1567035
Alternate Identifier(s):
OSTI ID: 1557870
Report Number(s):
NREL/JA-5900-74173
Journal ID: ISSN 2050-7488; JMCAET
Grant/Contract Number:  
AC36-08GO28308; AC02-76SF00515
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Materials Chemistry. A
Additional Journal Information:
Journal Volume: 7; Journal Issue: 34; Journal ID: ISSN 2050-7488
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; organic photovoltaics; stability; degradation; small molecule

Citation Formats

Watts, Kristen, Nguyen, Trung, Tremolet de Villers, Bertrand J, Neelamraju, Bharati, Anderson, Michael, Braunecker, Wade A, Ferguson, Andrew J, Larsen, Ross E, Larson, Bryon W, Owczarczyk, Zbyslaw, Pfeilsticker, Jason, Pemberton, Jeanne, and Ratcliff, Erin. Stability of push–pull small molecule donors for organic photovoltaics: spectroscopic degradation of acceptor endcaps on benzo[1,2-b:4,5-b′]dithiophene cores. United States: N. p., 2019. Web. doi:10.1039/C9TA06310B.
Watts, Kristen, Nguyen, Trung, Tremolet de Villers, Bertrand J, Neelamraju, Bharati, Anderson, Michael, Braunecker, Wade A, Ferguson, Andrew J, Larsen, Ross E, Larson, Bryon W, Owczarczyk, Zbyslaw, Pfeilsticker, Jason, Pemberton, Jeanne, & Ratcliff, Erin. Stability of push–pull small molecule donors for organic photovoltaics: spectroscopic degradation of acceptor endcaps on benzo[1,2-b:4,5-b′]dithiophene cores. United States. doi:10.1039/C9TA06310B.
Watts, Kristen, Nguyen, Trung, Tremolet de Villers, Bertrand J, Neelamraju, Bharati, Anderson, Michael, Braunecker, Wade A, Ferguson, Andrew J, Larsen, Ross E, Larson, Bryon W, Owczarczyk, Zbyslaw, Pfeilsticker, Jason, Pemberton, Jeanne, and Ratcliff, Erin. Fri . "Stability of push–pull small molecule donors for organic photovoltaics: spectroscopic degradation of acceptor endcaps on benzo[1,2-b:4,5-b′]dithiophene cores". United States. doi:10.1039/C9TA06310B.
@article{osti_1567035,
title = {Stability of push–pull small molecule donors for organic photovoltaics: spectroscopic degradation of acceptor endcaps on benzo[1,2-b:4,5-b′]dithiophene cores},
author = {Watts, Kristen and Nguyen, Trung and Tremolet de Villers, Bertrand J and Neelamraju, Bharati and Anderson, Michael and Braunecker, Wade A and Ferguson, Andrew J and Larsen, Ross E and Larson, Bryon W and Owczarczyk, Zbyslaw and Pfeilsticker, Jason and Pemberton, Jeanne and Ratcliff, Erin},
abstractNote = {High efficiency organic photovoltaic devices have relied on the development of new donor and acceptor materials to optimize opto-electronic properties, promote free carrier generation, and suppress recombination losses. With single junction efficiencies exceeding 15%, materials development must now target long-term stability. This work focuses on the photobleaching dynamics and degradation chemistries of a class of small molecule donors inspired by benzodithiophene terthiophene cores (BDT-3T) with rhodanine endcaps, which have demonstrated 9% efficiency in single junction devices and >11% in ternary cells. Density functional theory was used to design three additional molecules with similar synthetic pathways and opto-electronic properties by simply changing the electron accepting endcap to benzothiazoleacetonitrile, pyrazolone, or barbituric acid functional groups. This new class of semiconductors with equivalent redox properties enables systematic investigation into photobleaching dynamics under white light illumination in air. Degradation chemistries are assessed via unique spectroscopic signatures for the BDT-3T cores and the endcaps using photoelectron spectroscopies. We show that the pyrazolone undergoes significant degradation due to ring opening, resulting in complete bleaching of the chromophore. The barbituric and rhodanine endcap molecules have moderate stability, while the benzothiazoleacetonitrile group produces the most stable chromophore despite undergoing some oxidative degradation. Collectively, our results suggest the following: (i) degradation is not just dependent on redox properties; (ii) core group stability is not independent of the endcap choice; and (iii) future design of high efficiency materials must consider both photo and chemical stability of the molecule as a whole, not just individual donor or acceptor building blocks.},
doi = {10.1039/C9TA06310B},
journal = {Journal of Materials Chemistry. A},
number = 34,
volume = 7,
place = {United States},
year = {2019},
month = {8}
}

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