Orientation Of The Discotic Liquid Crystals And Their Application In The Optoelectronic Device

Discotic liquid crystal with electron-rich cores can be self-assembled into columuar mesophase via intermolecular interaction. The columns arrange in order,which causes a high charge transporting property. It has found their potentials to be used in photoconductive devices, organic light emitting diodes, solar cells.In this paper the two triphenylene derivatives, 2,3,6,7,10,11-hexapentyloxytriphenylene (HAT5) and 2,6,10-tricarbetboxy-3,7,11 -tripentyloxytriphenylene (TPE) were thermally treated aimed to get the moleculars reorientated. In this study, the thickness of the films and the cooling rate of the annealing were the factors affect the alignment behavior most. In order to get a uniform alignment, it is necessary to prepare the specimens onto the substrate with a uniform thickness and then annealed at very slow-rate cooling condition. Spontaneous homeotropic alignments of the triphenylene derivates on the variety of substrates were obtained through a controlled thermal annealing method, such as glass, quartz, and indium tin oxide (ITO)-coated glass substrates. The texture formed by annealing was observed using a cross polarized microscope. The self-organization of these triphenylene derivatives were investigated using wide-angle X-ray scattering. Both of the triphenylene derivates would align in a hexagonal way.Double layer photovoltaic devices based on triphenylene derivate (HAT5) comprising small molecule material N,N' -ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C₁₃) were constructed for further investigation. The device demonstrated an open circuit voltage up to 0.75V under monochromatic illumination, which depended strongly on the thickness of the PTCDI-C₁₃ layer. In order to study the influence of thermal treatment on the device performance, devices using thermally annealed HAT5 materials were fabricated for comparison. The device made of annealed HAT5 showed almost an 100% improvement in fill factor when compared to the devices without annealing. However, the V_oc of device made with annealed HAT5 was unfortunately reduced to 0.36V This work demonstrated that organic/organic interface is the key in generation of photovoltaic effect.