A liquid crystalline phthalocyanine semiconductor, 1, 4, 8, 11, 15, 18, 22, 25-hexahexylphthalocyanine (C6PcH2) was studied on the drift mobility of charged carriers by a Time-Of-Flight (TOF) method. It was found that this compound exhibits an ambipolar nature for charge transport and the hole and electron mobilities were determined to be in the order of 10^-1 cm² V^-1 s^-1 for polydomain films of the hexagonal disordered columnar (Colh_d) mesophase. This is comparable to that of the octyl homologue (C8PcH₂) reported by Hanna et al. However, C6PcH₂ did not show any tendency to form the homeotropic alignment between ITO-coated glass substrates, though C8PcH₂ so clearly and easily does. Clear decay curves of the transient photocurrents could be obtained in TOF measurements even for polydomain films of the crystalline solid phase to give a strongly temperature-dependent mobility of holes which reaches to 1.1 cm² V^-1 s^-1 at room temperature (RT) as the temperature goes down, whilst the electron mobility slightly increases to be 0.5 cm² V^-1 s^-1at RT. This compound could easily form thin films by spin-coating technique with the toluene solution and a simple bulk-heterojunction thin film solar cell was fabricated to give a good performance such as 3.1 % of power conversion efficiency and > 70 % of external quantum efficiency.

Date Published: 2 February 2011
PDF: 8 pages
Proc. SPIE 7955, Emerging Liquid Crystal Technologies VI, 795505 (2 February 2011); doi: 10.1117/12.873717

Published in SPIE Proceedings Vol. 7955:
Emerging Liquid Crystal Technologies VI
Liang-Chy Chien; Hiroshi Yokoyama, Editor(s)