Electrical properties of organic light-emitting diodes using PECCP Langmuir–Blodgett films

Organic light-emitting diodes were fabricated using Langmuir–Blodgett (LB) technique with new emissive organic material. This new emissive organic material was synthesized and called PECCP [poly(3,6-N-2-ethylhexyl carbazolyl cyanoterephthalidene)], which has strong electron donor group and electron acceptor group in main chain repeated unit. This material has good solubility in common organic solvent and has a good stability in air. We made PECCP LB films and investigated current–voltage (I–V) characteristics in ITO/PECCP LB/Al and ITO/PECCP LB/Alq3/Al structures, and the Alq3 was used as an electron transport layer. We have observed that the peak in electroluminescent spectrum of ITO/PECCP LB/Alq3/Al device shifts to lower wavelength as the number of LB layer increases. The electroluminescent peaks are at about 507 nm, 505 nm, 503 nm, and 491 nm when the number of LB layers are 5, 7, 9, and 11 layers, respectively. From the I–V characteristics, the barrier height was obtained using Fowler–Nordheim analysis and it is in the range of 0.18 eV–0.26 eV.