Research On Preparation Of Organic Thin Film Transistor Active Layer

In recent decades, organic semiconductor materials have been received great attention. In this context, the research of organic thin film transistors (OTFTs) also has been started. With its potential advantages, solution-processed OTFTs have attracted considerable attention. Organic semiconductor materials play the main role in carrier transport, and the intrinsic and interface properties of semiconductor materials determines the nature of carrier transport speed, thereby determining the performance of OTFTs. In view of the advantages in carrier mobility, exciton diffusion length and emission efficiency, Rubrene as a small molecule organic semiconductor material, has been widely used in manufacturing OTFTs.The main contents include:(1) PEDOT film was manufactured by spin-coating method and the optical parameters of the film were measured by spectroscopic ellipsometry. Ohmic contact between the electrode and Rubrene film was formed by modifying electrode with PEDOT.(2) The effects of annealing temperature on the electrical properties of Rubrene film were studied. When the annealing temperature was 373 K, the conductive properties of the film were the best and the current density could be up to 0.93 A/cm" at 10 V bias voltage.(3) It was researched that the effects of the solvent boiling point on Rubrene film, which manufactured with anisole, chlorobenzene, toluene, and chloroform. The optical parameters of Rubrene film were obtained by spectroscopic ellipsometry and the electrical properties were gained by the space charge limited current method. The results indicated that, when using high boiling anisole as solvent, the maximum film refractive index was 1.78 at wavelength of 800 nm, the minimum thickness of roughness layers was 11.92 nm and the utmost mobility was 1.58×10-5cm2/(V·s). Then, the thinner film was prepared by adjusting the spin-coating speed and the current transfer characteristics were analyzed. It was found that Rubrene film had different current transmission characteristics when using different solvents. With the increase of bias voltage, the J-V curves of the devices in double-logarithmic scale existed different regions, where slopes are 1,2, larger than 3 and 2 successively. Using space charge limited current model, charge transport mechanisms in different regions were analyzed and the trap densities and hole mobilities were extracted. When using anisole as solvent, the minimum trap density of the Rubrene film was 2.43×1017 cm3 and the maximum hole mobility was 2.41×10-5 cm2/(V-s).(4) The effects of solvent vapor annealing treatment temperature on optical properties of Rubrene film were studied by Spectroscopic ellipsometry. Results indicated that, when the treatment temperature increased from 300 K to 310 K, the optical band gap of the film decreased from 2.14 eV to 2.09 eV and the thickness of roughness layers decreased from 29.2 nm to 27.4 nm at wavelength of 800 nm. However, when the treatment temperature reached 320 K, the quality of film was remarkably deteriorated, comparing to the quality of 310 K.