Electroluminescence and photovoltaic effects using columnar mesogenic compounds

Columnar liquid crystals are useful for the construction of organic light emitting diodes (OLED) due to their high charge carrier mobility and their ability of developing defect-free superstructures. We investigated the electroluminescent properties of various mesogenic derivatives of triphenylene, pyrene, perylene, benzoperylene and hexa-peri-hexabenzocoronene (HBC) which combine good charge carrying properties and luminescence. The wavelengths of maximum electroluminescence range from about 400 nm to 720 nm, depending on the core and the substitution of the molecules. Nearly white emission can be obtained in samples containing two or more emitting layers. The perylene core is so efficient that even a single organic layer between an ITO anode and an aluminum cathode can give luminance values up to 100 cd/m². In addition to the electroluminescence, we present results on the photovoltaics in hetero junction structures of the compounds. Samples with two organic layers made of a HBC- and a perylene derivative show an open circuit voltage V_oc of about 0.8 V, a short circuit current I_sc of a few μA/cm², and a filling factor FF of approximately 31%.