José P. M. Serbena

Very high magnetocurrent in tris-(8-hydroxyquinoline) aluminum-based bipolar charge injection devices

Bipolar devices constructed using 60nm thick tris-(8-hydroxyquinoline) aluminum (Alq3) thin films sandwiched between a 200nm thick sulfonated polyaniline hole-injection electrode and Al∕Ca electron-injection electrode show very high (up to 103%) magnetocurrent values. True-hole-only and true-electron-only Alq3-based devices that make use of Si as charge carrier collecting electrode, and Al∕Ca as electron injecting electrode or Au as hole injecting electrode, are also proposed, prepared, and characterized. In these true-single-carrier devices magnetocurrent is not observed. This result provides strong evidence that bipolar injection is a necessary condition for very high magnetocurrent observation in Alq3.

Efficient organic light-emitting diodes with fluorine-doped tin-oxide anode and electrochemically synthesized sulfonated polyaniline as hole transport layer

In this work we report efficiency measurements on light-emitting diodes with electrochemically synthesized sulfonated polyaniline as hole transport layer. The anode used in our devices is fluorine-doped tin oxide, the blocking layer is electrochemically synthesized poly(9,9-dioctyl-1,4-fluorenylenevinylene) and the electron transporting material and emitter is tris-(8-hydroxyquinoline) aluminum. Sulfonated polyaniline based devices presented efficiency of 0.79 cd/A.

SeP hole injection layer for devices based on organic materials

Selenium : phosphour (SeP) thin films produced by thermal sublimation in vacuum are used as hole injection layers (HILs) in tris(8-hydroxyquinolinato) aluminum (Alq3) based devices. These devices are constructed in the sandwich structure substrate/HIL/Alq3/Al using three different substrate electrodes: fluorine doped tin oxide, Au, and indium tin oxide. The obtained electrical measurements indicate a better injection of positive charge carriers using the SeP layer. Syncrotron radiation x-ray photoelectron experiments allowed the determination of the work function of SeP. The obtained value (Φ = 5.6 eV) is close to the HOMO energy level of Alq3 and is consistent with the better positive charge injection. The thermionic injection process is suggested to be responsible for the charge injection from the different substrate electrodes into the SeP material. From transmittance measurements it was possible to calculate the refractive index and absorption coefficient as a function of wavelength, and to estimate the optical band gap (Eg = 1.9 eV). The latter and the measured work function were used in the construction of an energy level diagram of the SeP thin films used as HILs in organic devices. The hole injection efficiency of the produced films are compared with results using poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT : PSS).

Electronic and optical properties of amorphous GaSe thin films

The eletronic and optical properties of amorphous GaSe thin films produced by vacuum evaporation were investigated using X-ray photoemission spectroscopy (XPS) and transmittance spectroscopy techniques. XPS measurements allowed the determination of the valence band energy and showed the chemical bonding and the charge transfer between Se and Ga atoms. Transmittance measurements allowed the determination of the optical gap, refractive index and extinction coefficient in the low and high absorption regions. Using the Wemple and DiDomenico single oscillator model we also found the oscillator and the dispersive energies. From the valence band and optical gap energies, the conduction band was found and an energy level diagram for f-GaSe is proposed.