Enhanced Orientation of 1,3,5-Tris(1-Phenyl-1H-Benzimidazole-2-yl)Benzene by Light Irradiation during Its Deposition Evaluated by Displacement Current Measurement

Yuya TANAKA  Yuki TAZO  Hisao ISHII  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E104-C   No.6   pp.176-179
Publication Date: 2021/06/01
Publicized: 2020/12/08
Online ISSN: 1745-1353
DOI: 10.1587/transele.2020OMS0009
Type of Manuscript: BRIEF PAPER
Category: 
Keyword: 
organic electronics,  energy harvesting,  electret,  polar molecule,  orientation polarization,  

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Summary: 
In vacuum-deposited film composed of organic polar molecules, polarization charges appear on the film surface owing to spontaneous orientation of the molecule. Because its density (σpol) determines an amount of accumulation charge (σacc) in organic light-emitting diodes and output power in polar molecular-based vibrational energy generators (VEGs), control of molecular orientation is highly required. Recently, several groups have reported that dipole-dipole interaction between polar molecules induces anti-parallel orientation which does not contribute to σpol. In other words, perturbation inducing the attenuation of the dipole interaction is needed to enhance σpol. In this study, to investigate an effect of light irradiation on σpol, we prepared 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) film under illumination during its deposition, and evaluated the σacc in TPBi-based bilayer device, which equals to σpol. We found that the σacc was increased by light irradiation, indicating that average orientation of TPBi is enhanced. These results suggest that light irradiation during device fabrication is promising process for organic electronic devices including polar molecule-based VEGs.