Nanostructure-dependent vertical charge transport in MEH-PPV films

Yi-Fang Huang, Jesuraj Inigo, Chia-Chen Chang, Kang-Chuang Li, Chiao-Tan Liang, Chan-Wei Chang, Tsong-Shin Lim, Su-Hua Chen, Jonathon David White, U-Ser Jeng, An-Chung Su, Ying-Sheng Huang, Kang-Yung Peng, Show-An Chen, Woei-Wu Pai, Chen-Hong Lin, Lexey R. Tameev, Sergey V. Novikov, Anatoly V. Vannikov, Wun-Shain Fann

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

The correlation between morphology and charge-carrier mobility in the vertical direction in thin films of poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) is investigated by a combination of X-ray reflectivity (XRR), field-emission scanning electron microscopy (FESEM), atomic force rnicroscopy (AFM), fluorescence optical microscopy (FOM), photoluminescence spectroscopy (PL), photoluminescence excitation spectroscopy (PLE), as well as time-of-flight (TOF) and transient electroluminescence (TrEL) techniques. The mobility is about two orders of magnitude greater for drop-cast films than for their spin-cast counterparts. Drop-casting in the presence of a vertical static electric field (E-casting) results in films with an additional increase in mobility of about one order of magnitude. While PL and PLE spectra vary with the method of film preparation, there is no correlation between emission spectra and charge-carrier mobility. Our XRR measurements on spin-cast films indicate layering along the film depth while no such structure is found in drop-cast or E-cast films, whereas FESEM examination indicates that nanodomains within drop-cast films are eliminated in the E-cast case. These observations indicate that carrier transport is influenced by structure on two different length scales. The low mobility observed in spin-cast films is a direct result of a global layered structure with characteristic thickness of ca. 4 nm: in the absence of this layered structure, drop-cast films with inherent nanoscale heterogeneities (ca. 20 nm in size) exhibit much better hole mobility. Elimination of nanodomains via electric-field alignment results in further improved charge mobility.

Original languageEnglish
Pages (from-to)2902-2910
Number of pages9
JournalAdvanced Functional Materials
Volume17
Issue number15
Early online date28 Aug 2007
DOIs
Publication statusPublished - 15 Oct 2007

Keywords

  • Poly(p-phenylene vinylene)s
  • interchain interactions
  • electric-field
  • electroluminescence
  • hole transport
  • carrier mobility
  • device performance
  • light-emitting-diodes
  • morphology
  • conjugated polymers

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