Small Organic Molecules

Abstract

In order to improve devices based on organic thin films like organic light emitting diodes (OLEDs) and organic photo voltaic (OPV) cells, the molecular orientation has to be determined and optimized to increase the carrier mobility and the light emission and absorption within the layers. As many of the organic molecules possess an intrinsic molecular anisotropy, molecular ordering will induce optical and electrical anisotropy in the films.The optical anisotropy can be used to determine the average molecular orientation by modeling the anisotropic dielectric function using ellipsometric measurements. An overview of the procedure, valid for planar molecules, will be given in the first part of this chapter, with the main focus on the Phthalocyanine molecular class. The second part of the chapter focuses on vacuum ultra violet (VUV) ellipsometric measurements and the sensitivity gain at ultra-low coverages. Here the discussion will be restricted to optically isotropic films. IntroductionOrganic molecules, which in solid form exhibit semiconducting properties, were long hailed as candidates for cheap, roll to roll electronics. As of today, organic electronics is not anymore a faraway promise, as the huge success and growth of the smartphones market is powered by innovations like organic light emitting diodes (OLEDs). The recent launch of OLED TVs indicates that the OLED technology already reached a maturation state which ensures the long life time needed in television displays. Even in organic photo voltaic (OPV) applications, higher efficiencies than the limit predicted by the exciton dissociation energy were reached. Plastic electronics using organic field effect transistors (OFETs) is another field where huge progress was made in the past decade, and probably soon we will see commercial organic based radio frequency identification tags (ORFIDs). Compared to OPVs, OFETs, and especially to the already commercial OLEDs, molecular spintronics

Temperature-Dependent Spectroscopic Ellipsometry of Thin Polymer Films

“…100 For isotropic bulk materials, a simple relationship, α h ≈ (1/3)α V , is fulfilled. 101 However, for thin polymer films, volume thermal expansion may be highly anisotropic and dependent on the polymer−substrate interaction character. 99,102 Wide areas of polymer applications have been stimulating intensive research into polymer thermo-optical properties for many years.…”