Structural and morphological tuning of dithienobenzodithiophene-core small molecules for efficient solution processed organic solar cells

Minwoo Jung, Dongkyun Seo, Kyungwon Kwak, Ajeong Kim, Wonsuk Cha, Hyunjung Kim, Youngwoon Yoon, Min Jae Ko, Doh Kwon Lee, Jin Young Kim, Hae Jung Son, Bong Soo Kim

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)

Abstract

The fused dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene (DTBDT) structure was coupled with diketopyrrolopyrrole (DPP) moieties to generate highly planar bis(2,5-bis(2-ethylhexyl)-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione)dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene (DTBDTDPP-EH) and bis(2,5-bis(2-butyloctyl)-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione)dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene (DTBDTDPP-BO) molecules, where the EH and BO stands for 2-ethylhexyl and 2-butyloctyl groups respectively. The morphology of the DTBDTDPP-EH alone or DTBDTDPP-EH:[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend film was controlled using post-thermal annealing at 130°C or addition of 1,8-diiodooctane (DIO) additives. The DIO-additive treatment was more effective than thermal annealing at increasing crystallinity; the DIO-additives promoted the formation of nanoscopically well-connected molecular crystalline domains in the blend films. This observation well explained the ordering of the photovoltaic properties of DTBDTDPP-EH:PCBM devices: from worst to best, as-cast, thermally treated, and DIO-treated photoactive films. The DTBDTDPP-BO:PCBM device followed the similar trend with lower performances due to the presence of irregularly overgrown domains. Overall, we demonstrate that it is critical to optimize nanoscale film morphologies by engineering alkyl chains and selecting an appropriate processing method.

Original languageEnglish
Pages (from-to)23-34
Number of pages12
JournalDyes and Pigments
Volume115
DOIs
Publication statusPublished - 2015 Apr
Externally publishedYes

Keywords

  • Conjugated small molecules
  • Crystallinity
  • Nanoscale phase separation
  • Organic semiconductors
  • Organic solar cells
  • Power conversion efficiency

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Process Chemistry and Technology

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