2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole-based donor-acceptor type copolymers for photovoltaic cells

Eunjae Jeong, Gi Hwan Kim, In Hwan Jung, Pyeongsu Jeong, Jin Young Kim, Han Young Woo

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

Alternating donor-acceptor type copolymers, poly[{5,11-di(9′- heptadecanyl)indolo[3,2-b]carbazole}-alt-{2,5-di(thiophen-2-yl)thiazolo[5,4-d] thiazole-5,5′-diyl}] (PIC-TZ) and poly[{6,6′,12,12′- tetraoctylindeno[1,2-b]fluorene}-alt-{2,5-di(thiophen-2-yl)thiazolo[5,4-d] thiazole-5,5′-diyl}] (PIF-TZ), were synthesized and examined for applications in polymeric photovoltaic cells. The polymers have a fused coplanar main backbone with good planarity for intermolecular packing and high charge mobility. The indolocarbazole and indenofluorene units contain two or four binding sites for alkyl substituents that have pronounced solution processiblity compared to the carbazole and fluorene moieties. The number-average molecular weights (Mn) of the synthesized polymers were determined to be 11,000 g/mol (PDI = 2.27) for PIC-TZ, and 17,000 g/mol (PDI = 1.77) for PIF-TZ. The optical band gap of PIC-TZ and PIF-TZ in film was determined to be 2.14 eV and 2.21 eV, respectively, and an electrochemical study confirmed the desirable HOMO/LUMO levels of the copolymers, which enabled efficient electron transfer and a high open circuit voltage (VOC) when blending them with fullerene derivatives. The space charge limited current mobility measurements showed a hole mobility of 10-3 cm2 V-1 s -1 for the copolymers. When the polymers were blended with [6,6]phenyl-C61-butyric acid methyl ester (PCBM), PIC-TZ showed the best performance with VOC, short-circuit current and power conversion efficiency of 0.86 V, 4.16 mA/cm2 and 1.64%, respectively, under AM 1.5G illumination conditions (100 mW cm-2).

Original languageEnglish
Pages (from-to)11-16
Number of pages6
JournalCurrent Applied Physics
Volume12
Issue number1
DOIs
Publication statusPublished - 2012 Jan 1

Keywords

  • Low band gap polymers
  • Photovoltaic cells
  • Polymer solar cells

ASJC Scopus subject areas

  • Materials Science(all)
  • Physics and Astronomy(all)

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