45732-G10
One-Dimensional Exciton Diffusion in Perylene Based Solar Cell Materials
The PI, Ling Zang, moved to University of Utah in august 2008. This first-year report was made based on his group’s work performed at SIUC.
Under this PRF-G support scientists at Southern Illinois University (led by Ling Zang) have been working to fabricate well-defined nanofibers from a variety of planar rigid organic semiconductor molecules. Through integrated molecular design, synthesis and engineering, the molecular packing organization and the size and length of the nanofibers can be feasibly controlled to achieve desirable optoelectronic properties, particularly the one-dimensional confined exciton migration and polarized emission.
Results recently obtained at SIUC demonstrate the feasibility of controlling the morphology and molecular organization of organic nanofibers. Two types of molecules are employed to explore the nanofibril fabrication and the optoelectronic properties: one is perylene tetracarboxylic diimide (PTCDI, n-type) and the other is arylene ethynylene macrocycle (AEM, p-type). Particularly for PTCDI, ultralong (millimeter) nanofibers have been fabricated for the first time using a new developed, seeded self-assembling method. Long nanofibers will enable easy construction of nanodevices, for which deposition of a single-nanowire across multiple electrodes is usually needed, as envisioned with carbon nanotubes.
Because of the one-dimensionally dominant stacking of the molecules, the nanowires thus fabricated demonstrate uniaxial optical properties like linear polarized emission and self-waveguided emission. The latter particularly demands a single-crystalline phase throughout the whole nanowire, which in turn requires highly controlled fabrication process for the nanowires, in combination with the optimized thermodynamics and structure of the building block molecules. Indeed, the nanowires fabricated from the cyclohexyl-substituted PTCDI showed polarized emission with polarization factor as high as ca. 85%, even larger than the inorganic single-crystalline CdSe nanowires, which have widely been used in photovoltaic devices. The same PTCDI nanowires also demonstrated highly efficient waveguided emission, which is bending persistent, making them ideal for application in the solar cells, where flexible, conformal materials in accommodating with the device geometry is often demanded. The one-dimensional arrangement of the molecular stacking within the extended single crystalline phase of the nanowire is expected to enable linear enhancement of the exciton migration, which is currently in the process of characterization through different typed of investigations.
