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Crystallization-Induced Charge-Transfer Change in TiOPc Thin Films Revealed by Resonant Photoemission Spectroscopy

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Author

  • Shun Yu
  • Sareh Ahmadi
  • Chenghua Sun
  • Karina Schulte
  • Annette Pietzsch
  • Franz Hennies
  • Marcelo Zuleta
  • Mats Gothelid

Summary, in English

Organic semiconductors usually demonstrate crystal structure dependent electronic properties, and through precise control of film structure, the performance of novel organic electronic devices can be greatly improved. Understanding the crystal structure dependent charge-transfer mechanism thus becomes critical. In this work, we have prepared amorphous titanyl phthalocyanine films by vacuum molecular beam evaporation and have further crystallized them through vacuum annealing. In the crystalline phase, an excited electron is rapidly transferred into neighboring molecules; while in the amorphous phase, it is mainly localized and recombines with the core hole as revealed by resonant photoemission spectroscopy (RPES). The fast electron transfer time is determined to be around 16 fs in the crystalline film, which is in good agreement with the charge-transfer hopping time estimated from the best device performance reported. The crystallized film shows more p-type characteristics than the amorphous with all the energy levels shifting toward the vacuum level. However, the greatly improved charge transfer is assigned to the molecular orbital coupling rather than this shift. From density functional theory and RPES, we specify the contribution of two differently coordinated nitrogen atoms (N2c and N3c) to the experimental results and illustrate that the N3c related orbital has experienced a dramatic change, which is keenly related to the improved charge transfer.

Department/s

Publishing year

2011

Language

English

Pages

14969-14977

Publication/Series

Journal of Physical Chemistry C

Volume

115

Issue

30

Document type

Journal article

Publisher

The American Chemical Society (ACS)

Topic

  • Natural Sciences
  • Physical Sciences

Status

Published

ISBN/ISSN/Other

  • ISSN: 1932-7447