Ultrafast excited state dynamics of a bithiophene-isoindigo copolymer obtained by direct arylation polycondensation and its application in indium tin oxide-free solar cells

Newayemedhin A. Tegegne, Zelalem Abdissa, Wendimagegn Mammo, Mats R. Andersson, Derck Schlettwein, Heinrich Schwoerer

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

A low band gap copolymer, P2TI (Eg = 1.6.eV), with bithiophene as donor and isoindigo as acceptor units is designed and synthesized by the direct arylation polycondensation (DAP) method. Absorbance of the polymer spans from 300 to 780 nm. It exhibits an absorption coefficient (ε) of 96 L/g cm in solution at its maxima. A HOMO level of −5.42 eV and LUMO level of −3.72 eV is measured by square wave voltammetry. ITO-free solar cells fabricated using a P2TI:PCBM71 bulk heterojunction shows a moderate efficiency of 1.02% with a high open circuit voltage of 0.81 V. An intramolecular charge transfer state is found in the relaxation of P2TI in solution, which is generated with a time constant of 2 ps as measured by femtosecond-transient absorption spectroscopy. Charge carriers were generated in <250 fs in P2TI:PCBM71 films.

Original languageEnglish
Pages (from-to)1475-1483
Number of pages9
JournalJournal of Polymer Science Part B: Polymer Physics
Volume56
Issue number21
Early online date8 Oct 2018
DOIs
Publication statusPublished - 1 Nov 2018
Externally publishedYes

Keywords

  • charge transfer
  • copolymer

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