Abstract:
In this thesis, the layers of MEH-PPV was fabricated and examined for electrical and optical characteristics. The layer was prepared by spin-coating on glass slides and then had Indium Tin Oxide (ITO) coated on the glass substrates. The optical absorption of MEH-PPV films on glass slides showed the maximum absorption at a wavelength of 514.8 nm. A photo-luminescence of yellow-orange color at a wavelength of 567.4 nm can be observed under ultra-violet illumination. In order to measure the electrical properties, the top electrode of aluminum was coated by evaporation in the vacuum chamber with the pressure below 10('-4) Torr. Then the single layer devices were studied at three MEH-PPV concentrations of 8, 10, and 12 mg/ml with spin-coating speeds of 2000, 4000, 6000 and 8000 rpm. The current-voltage characteristic of the single layered device in vacuum exhibited an exponential curve with an anti-symmetry between forward and reverse bias voltages. The devices can emit visible light which was observed by eye at voltage range 7.0-8.0 V. Multi-layered devices were fabricated by adding spin-coating of the hole transport layer at TPD concentrations to 0.75 and 0.85 by percentage weight. These devices emit visible light under the bias voltage range 7.0-9.0 V. As for current-voltage characteristics in vacuum, the trap charge characteristic was observed in the reverse bias. By adding the electron transport layer of Alq3 by thermal evaporation in the same chamber of aluminum evaporation, a trap charge characteristic was observed in the reverse bias region of 0-0.75 V. However electro-luminescence cannot be observed in this device.