Nanoestruturas de carbono: sínteses, caracterizações e aplicações em dispositivos optoeletrônicos

Abstract

In this work, graphene and amorphous carbon pure (𝑎-C) and doped with nitroge n (𝑎-CNx) thin films were grown, characterized and employed in the fabrication of optoelectronic devices. Thin Films of 𝑎-C and 𝑎-CNx were employed as electroluminescent layer in light- emitting devices. These films were grown employing the technique of RF Magnetron Sputtering in three series of depositions where were optimized the N 2 gas flow, the power of deposition and the films thickness. After the growth, this films were structura lly, compositionally and optically characterized employed the technical of X-ray diffract io n, X-ray photoelectron (XPS) and optical absorption spectroscopy in the UV-Vis region. The results obtained with these characterizations were related with the efficiency and luminescence of the light-emitting devices fabricated from these films that, for this purpose, were grown on ITO substrates, employed as anode, and below a film of aluminum of 120 nm, employed as cathode. The best device exhibited an electroluminescence spectrum that covers practically all the visible region, with a maximum luminescence of 206 cd/m2 at 9.86 V and current efficiency of 1.31x10-2 cd/A at 15.62x10-4 mA/cm2. These values are about three orders of magnitude greater than other similar devices found in literature. Graphene films were grown by CVD technical and employed as anode in the fabrication of OLEDs with the following architecture: Graphene/CuPc/𝛽-NPB/Alq3/ A l. The graphene films were electrically, optically and structurally characterized employed the technical of Hall effect, UV-Vis optical absorption spectroscopy and Raman spectroscopy, respectively. The graphene films exhibits sheet resistance of 500 Ω/square , high optical transmittance in the visible region of about 90% in 550 nm and high degree of crystallinity, besides great uniformity in large areas. The graphene OLED (G-OLED) turn on with an applied voltage of 2.75 V much earlier than reference OLED fabricated employed commercial ITO as anode, (I-OLED), that turn on with a voltage of 3.80 V. The I-OLED exhibited the maximum of current efficiency of 0.95 cd/A in a luminesce nce of 1400 cd/m2, much smaller than exhibited by G-OLED, that for the same luminesce nce exhibited a current efficie ncy of 9.67 cd/A, reaching a maximum of 19.26 cd/A in 6352 cd/m2. The power efficiency of G-OLED is one order of magnitude greater than I-OLEDof 4.9x10-2 lm/W in 0.27 cd/m2. Furthermore, the maximum of electroluminesce nce exhibited by G-OLED of 6351 cd/m2 in 11.20 V is higher than I-OLED of 5863 cd/m2 in 10.75 V