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Title: Acceptor Gradient Polymer Donors for Non-Fullerene Organic Solar Cells

Abstract

In organic solar cells, maximizing the open-circuit voltage ( V OC) via minimization of the ionization energy or electron affinity offsets of the blended donor and acceptor often comes at the expense of achieving a considerable amount of short-circuit current ( J SC). To explore a hypothesis for the design of materials that may circumvent this tradeoff, eight structurally similar polymers were synthesized consisting of a fluorinated/non-fluorinated benzothiadiazole (BTDF/BTD) strong acceptor moiety, a thiophene ester (TE) weak acceptor, and various donor units composed of bithiophene (T2), biEDOT, and benzodithiophene (BDT) to form six acceptor gradient and two nongradient polymers. The acceptor gradient motif was designed and theorized to induce more facile exciton dissociation in low driving force solar cells by creating a further separated intramolecular charge-transfer state between the strong BTD acceptor and various donor units through a bridging TE component. Solar cells were fabricated using the eight polymers blended with phenyl-C 71-butyric-acid methyl ester (PC 71BM) to reveal two top performing isomeric polymers, T2-BTDF-(TE2) and TE2-BTDF-(T2), which were further tested with several non-fullerene acceptors (NFAs): EH-IDTBR, ITIC, and ITIC- 4F. In order to fabricate optimally performing solar cells, a 0.2 eV ionization energy offset was found to be essentialmore » or the short-circuit current of the NFA cells diminished dramatically. Ultimately, optimized NFA solar cells were fabricated using ITIC-4F paired with each of the top performing polymers to produce an average PCE of 7.3% for TE2-BTDF-(T2) (nongradient) and 3.6% for T2-BTDF-(TE2) (gradient). The acceptor gradient effect was not shown to reduce the amount of charge recombination in NFA solar cells mainly due to the inability to fabricate solar cells, with minimal ionization energy or electron affinity offsets along with morphological complications. This work stresses the importance of acquiring accurate ionization energies and electron affinities when characterizing solar cell energetics, as differences as small as 0.1 eV in the offsets can make a significant impact on overall charge collection.« less

Authors:
 [1];  [1];  [2];  [1];  [1];  [3]; ORCiD logo [3]; ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [1]; ORCiD logo [1]
  1. Georgia Inst. of Technology, Atlanta, GA (United States)
  2. North Carolina State Univ., Raleigh, NC (United States)
  3. Stanford Univ., Menlo Park, CA (United States)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1591636
Grant/Contract Number:  
AC02-76SF00515; N00014-16-1-2520; N00014-17-1-2208; N00014-17-1-2242; N00014-17-1-2243
Resource Type:
Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 31; Journal Issue: 23; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Jones, Austin L., Zheng, Zilong, Riley, Parand, Pelse, Ian, Zhang, Junxiang, Abdelsamie, Maged, Toney, Michael F., Marder, Seth R., So, Franky, Brédas, Jean-Luc, and Reynolds, John R. Acceptor Gradient Polymer Donors for Non-Fullerene Organic Solar Cells. United States: N. p., 2019. Web. doi:10.1021/acs.chemmater.9b03327.
Jones, Austin L., Zheng, Zilong, Riley, Parand, Pelse, Ian, Zhang, Junxiang, Abdelsamie, Maged, Toney, Michael F., Marder, Seth R., So, Franky, Brédas, Jean-Luc, & Reynolds, John R. Acceptor Gradient Polymer Donors for Non-Fullerene Organic Solar Cells. United States. doi:10.1021/acs.chemmater.9b03327.
Jones, Austin L., Zheng, Zilong, Riley, Parand, Pelse, Ian, Zhang, Junxiang, Abdelsamie, Maged, Toney, Michael F., Marder, Seth R., So, Franky, Brédas, Jean-Luc, and Reynolds, John R. Wed . "Acceptor Gradient Polymer Donors for Non-Fullerene Organic Solar Cells". United States. doi:10.1021/acs.chemmater.9b03327.
@article{osti_1591636,
title = {Acceptor Gradient Polymer Donors for Non-Fullerene Organic Solar Cells},
author = {Jones, Austin L. and Zheng, Zilong and Riley, Parand and Pelse, Ian and Zhang, Junxiang and Abdelsamie, Maged and Toney, Michael F. and Marder, Seth R. and So, Franky and Brédas, Jean-Luc and Reynolds, John R.},
abstractNote = {In organic solar cells, maximizing the open-circuit voltage (VOC) via minimization of the ionization energy or electron affinity offsets of the blended donor and acceptor often comes at the expense of achieving a considerable amount of short-circuit current (JSC). To explore a hypothesis for the design of materials that may circumvent this tradeoff, eight structurally similar polymers were synthesized consisting of a fluorinated/non-fluorinated benzothiadiazole (BTDF/BTD) strong acceptor moiety, a thiophene ester (TE) weak acceptor, and various donor units composed of bithiophene (T2), biEDOT, and benzodithiophene (BDT) to form six acceptor gradient and two nongradient polymers. The acceptor gradient motif was designed and theorized to induce more facile exciton dissociation in low driving force solar cells by creating a further separated intramolecular charge-transfer state between the strong BTD acceptor and various donor units through a bridging TE component. Solar cells were fabricated using the eight polymers blended with phenyl-C71-butyric-acid methyl ester (PC71BM) to reveal two top performing isomeric polymers, T2-BTDF-(TE2) and TE2-BTDF-(T2), which were further tested with several non-fullerene acceptors (NFAs): EH-IDTBR, ITIC, and ITIC-4F. In order to fabricate optimally performing solar cells, a 0.2 eV ionization energy offset was found to be essential or the short-circuit current of the NFA cells diminished dramatically. Ultimately, optimized NFA solar cells were fabricated using ITIC-4F paired with each of the top performing polymers to produce an average PCE of 7.3% for TE2-BTDF-(T2) (nongradient) and 3.6% for T2-BTDF-(TE2) (gradient). The acceptor gradient effect was not shown to reduce the amount of charge recombination in NFA solar cells mainly due to the inability to fabricate solar cells, with minimal ionization energy or electron affinity offsets along with morphological complications. This work stresses the importance of acquiring accurate ionization energies and electron affinities when characterizing solar cell energetics, as differences as small as 0.1 eV in the offsets can make a significant impact on overall charge collection.},
doi = {10.1021/acs.chemmater.9b03327},
journal = {Chemistry of Materials},
number = 23,
volume = 31,
place = {United States},
year = {2019},
month = {11}
}

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This content will become publicly available on November 20, 2020
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