Side chain and solvent direction of film morphology in small-molecule organic solar materials

Eric F. Manley, Tobias Harschneck, Nicholas D. Eastham, Matthew J. Leonardi, Nanjia Zhou, Joseph Strzalka, Robert P.H. Chang, Lin X. Chen, Tobin J. Marks

Research output: Contribution to journalArticle

Abstract

Film morphology control is essential to developing materials for efficient organic solar cells (OSCs). Unlocking methods to optimize the film morphology without changing the fundamental electronic characteristics can enable previously unacceptable materials to achieve high performance. Here, a series of acceptor/donor/acceptor small-molecule p-type OSC semiconductors having benzo[1,2-b:6,5-b0]dithiophene (bBDT) donor units and thiophene-capped diketopyrrolopyrrole (TDPP) acceptor units are examined, where the sole molecular design variation is the electronically inactive side chains. Four bBDT(TDPP)2 molecules with all possible combinations of either 2-ethylhexyl (EH) or 3,7-dimethyloctyl (DMO) side chains on the bBDT core and TDPP units are discussed. When processed from chloroform-only solutions, blend films of the molecules, with the PC71BM electron acceptor, exhibit similar thin-film properties and photovoltaic performance, regardless of the side chain composition. However, when the additive 1,8-diiodooctane (DIO) is included in the processing solution, the morphological properties and OSC performance diverge dramatically, with the side chain variations now dictating the film morphology, resulting in a >400% spread in power conversion efficiency. Donor molecules with a mixed side chain motif having the larger DMO side chain on the bBDT core unit deliver superior performance owing to greater donor/acceptor phase intermixing while maintaining contiguous and efficient charge transport pathways. In situ grazing incidence wide-angle X-ray scattering data acquired during spin-coating show that DIO extends crystallization times, thereby promoting more thermodynamically driven structures, where the side chain compositions have greater impact. Finally, general guidelines are presented for achieving morphological optimization via combined side chain engineering and processing additives.

Original languageEnglish
Pages (from-to)8308-8319
Number of pages12
JournalChemistry of Materials
Volume31
Issue number20
DOIs
Publication statusPublished - Oct 22 2019

Fingerprint

Thiophenes
Thiophene
Molecules
Spin coating
Chloroform
Chlorine compounds
Processing
Crystallization
X ray scattering
Chemical analysis
Conversion efficiency
Charge transfer
Semiconductor materials
Thin films
Direction compound
Electrons
Organic solar cells

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

Cite this

Side chain and solvent direction of film morphology in small-molecule organic solar materials. / Manley, Eric F.; Harschneck, Tobias; Eastham, Nicholas D.; Leonardi, Matthew J.; Zhou, Nanjia; Strzalka, Joseph; Chang, Robert P.H.; Chen, Lin X.; Marks, Tobin J.

In: Chemistry of Materials, Vol. 31, No. 20, 22.10.2019, p. 8308-8319.

Research output: Contribution to journalArticle

Manley, EF, Harschneck, T, Eastham, ND, Leonardi, MJ, Zhou, N, Strzalka, J, Chang, RPH, Chen, LX & Marks, TJ 2019, 'Side chain and solvent direction of film morphology in small-molecule organic solar materials', Chemistry of Materials, vol. 31, no. 20, pp. 8308-8319. https://doi.org/10.1021/acs.chemmater.9b01407
Manley EF, Harschneck T, Eastham ND, Leonardi MJ, Zhou N, Strzalka J et al. Side chain and solvent direction of film morphology in small-molecule organic solar materials. Chemistry of Materials. 2019 Oct 22;31(20):8308-8319. https://doi.org/10.1021/acs.chemmater.9b01407
Manley, Eric F. ; Harschneck, Tobias ; Eastham, Nicholas D. ; Leonardi, Matthew J. ; Zhou, Nanjia ; Strzalka, Joseph ; Chang, Robert P.H. ; Chen, Lin X. ; Marks, Tobin J. / Side chain and solvent direction of film morphology in small-molecule organic solar materials. In: Chemistry of Materials. 2019 ; Vol. 31, No. 20. pp. 8308-8319.
@article{cab6015a290b43938c1807fddfc151f2,
title = "Side chain and solvent direction of film morphology in small-molecule organic solar materials",
abstract = "Film morphology control is essential to developing materials for efficient organic solar cells (OSCs). Unlocking methods to optimize the film morphology without changing the fundamental electronic characteristics can enable previously unacceptable materials to achieve high performance. Here, a series of acceptor/donor/acceptor small-molecule p-type OSC semiconductors having benzo[1,2-b:6,5-b0]dithiophene (bBDT) donor units and thiophene-capped diketopyrrolopyrrole (TDPP) acceptor units are examined, where the sole molecular design variation is the electronically inactive side chains. Four bBDT(TDPP)2 molecules with all possible combinations of either 2-ethylhexyl (EH) or 3,7-dimethyloctyl (DMO) side chains on the bBDT core and TDPP units are discussed. When processed from chloroform-only solutions, blend films of the molecules, with the PC71BM electron acceptor, exhibit similar thin-film properties and photovoltaic performance, regardless of the side chain composition. However, when the additive 1,8-diiodooctane (DIO) is included in the processing solution, the morphological properties and OSC performance diverge dramatically, with the side chain variations now dictating the film morphology, resulting in a >400{\%} spread in power conversion efficiency. Donor molecules with a mixed side chain motif having the larger DMO side chain on the bBDT core unit deliver superior performance owing to greater donor/acceptor phase intermixing while maintaining contiguous and efficient charge transport pathways. In situ grazing incidence wide-angle X-ray scattering data acquired during spin-coating show that DIO extends crystallization times, thereby promoting more thermodynamically driven structures, where the side chain compositions have greater impact. Finally, general guidelines are presented for achieving morphological optimization via combined side chain engineering and processing additives.",
author = "Manley, {Eric F.} and Tobias Harschneck and Eastham, {Nicholas D.} and Leonardi, {Matthew J.} and Nanjia Zhou and Joseph Strzalka and Chang, {Robert P.H.} and Chen, {Lin X.} and Marks, {Tobin J.}",
year = "2019",
month = "10",
day = "22",
doi = "10.1021/acs.chemmater.9b01407",
language = "English",
volume = "31",
pages = "8308--8319",
journal = "Chemistry of Materials",
issn = "0897-4756",
publisher = "American Chemical Society",
number = "20",

}

TY - JOUR

T1 - Side chain and solvent direction of film morphology in small-molecule organic solar materials

AU - Manley, Eric F.

AU - Harschneck, Tobias

AU - Eastham, Nicholas D.

AU - Leonardi, Matthew J.

AU - Zhou, Nanjia

AU - Strzalka, Joseph

AU - Chang, Robert P.H.

AU - Chen, Lin X.

AU - Marks, Tobin J.

PY - 2019/10/22

Y1 - 2019/10/22

N2 - Film morphology control is essential to developing materials for efficient organic solar cells (OSCs). Unlocking methods to optimize the film morphology without changing the fundamental electronic characteristics can enable previously unacceptable materials to achieve high performance. Here, a series of acceptor/donor/acceptor small-molecule p-type OSC semiconductors having benzo[1,2-b:6,5-b0]dithiophene (bBDT) donor units and thiophene-capped diketopyrrolopyrrole (TDPP) acceptor units are examined, where the sole molecular design variation is the electronically inactive side chains. Four bBDT(TDPP)2 molecules with all possible combinations of either 2-ethylhexyl (EH) or 3,7-dimethyloctyl (DMO) side chains on the bBDT core and TDPP units are discussed. When processed from chloroform-only solutions, blend films of the molecules, with the PC71BM electron acceptor, exhibit similar thin-film properties and photovoltaic performance, regardless of the side chain composition. However, when the additive 1,8-diiodooctane (DIO) is included in the processing solution, the morphological properties and OSC performance diverge dramatically, with the side chain variations now dictating the film morphology, resulting in a >400% spread in power conversion efficiency. Donor molecules with a mixed side chain motif having the larger DMO side chain on the bBDT core unit deliver superior performance owing to greater donor/acceptor phase intermixing while maintaining contiguous and efficient charge transport pathways. In situ grazing incidence wide-angle X-ray scattering data acquired during spin-coating show that DIO extends crystallization times, thereby promoting more thermodynamically driven structures, where the side chain compositions have greater impact. Finally, general guidelines are presented for achieving morphological optimization via combined side chain engineering and processing additives.

AB - Film morphology control is essential to developing materials for efficient organic solar cells (OSCs). Unlocking methods to optimize the film morphology without changing the fundamental electronic characteristics can enable previously unacceptable materials to achieve high performance. Here, a series of acceptor/donor/acceptor small-molecule p-type OSC semiconductors having benzo[1,2-b:6,5-b0]dithiophene (bBDT) donor units and thiophene-capped diketopyrrolopyrrole (TDPP) acceptor units are examined, where the sole molecular design variation is the electronically inactive side chains. Four bBDT(TDPP)2 molecules with all possible combinations of either 2-ethylhexyl (EH) or 3,7-dimethyloctyl (DMO) side chains on the bBDT core and TDPP units are discussed. When processed from chloroform-only solutions, blend films of the molecules, with the PC71BM electron acceptor, exhibit similar thin-film properties and photovoltaic performance, regardless of the side chain composition. However, when the additive 1,8-diiodooctane (DIO) is included in the processing solution, the morphological properties and OSC performance diverge dramatically, with the side chain variations now dictating the film morphology, resulting in a >400% spread in power conversion efficiency. Donor molecules with a mixed side chain motif having the larger DMO side chain on the bBDT core unit deliver superior performance owing to greater donor/acceptor phase intermixing while maintaining contiguous and efficient charge transport pathways. In situ grazing incidence wide-angle X-ray scattering data acquired during spin-coating show that DIO extends crystallization times, thereby promoting more thermodynamically driven structures, where the side chain compositions have greater impact. Finally, general guidelines are presented for achieving morphological optimization via combined side chain engineering and processing additives.

UR - http://www.scopus.com/inward/record.url?scp=85073036108&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85073036108&partnerID=8YFLogxK

U2 - 10.1021/acs.chemmater.9b01407

DO - 10.1021/acs.chemmater.9b01407

M3 - Article

AN - SCOPUS:85073036108

VL - 31

SP - 8308

EP - 8319

JO - Chemistry of Materials

JF - Chemistry of Materials

SN - 0897-4756

IS - 20

ER -