Enhancing the performance of organic light emitting diodes by using nanostructured composite films
Source: International Journal of Nanotechnology, Volume 8, Numbers 3-5, 2011 , pp. 201-213(13)
Publisher: Inderscience Publishers
Abstract:Recent achievements on the use of nanocomposites such as nanostructured composites with a structure of nanoparticles embedded in polymers (NIP) and nanocomposites with a structure of polymers deposited on nanoporous thin films (PON) for OLEDs are presented in this report. The influence of nanooxides on the photoelectric properties of the NIPs is explained with regard to the fact that TiO<SUB align=right>2 particles usually form a type-II heterojunction with a polymer matrix, which essentially results in the separation of non-equilibrium electrons and holes. MEH-PPV luminescence quenching is strongly dependent on the nature of nanostructural particles embedded in polymer matrix. Actually, the higher quenching of the polymer fluorescence observed in the presence of titania nanoparticles proves that the transfer of the photogenerated electrons to the TiO<SUB align=right>2 is more efficient for rods. Characterisation of the nanocomposite films showed that both the current-voltage characteristics and the photoluminescent properties of the NIP nanocomposite materials were significantly enhanced in comparison with the standard polymers. OLEDs made from these layers demonstrate high photonic efficiency. For a PON-like hybrid layer of MEH-PPV/nc-TiO<SUB align=right>2, the photoluminescence enhancement was observed when the MEHPPV-PON films were excited by a 325 nm wavelength laser, and the excitation of a 470 nm wavelength light resulted in the strong polymer fluorescence quenching. Current-voltage characteristics of laminar layer devices with a structure of Ti/PON/Al-Ag in comparison with that of Ti/MEH-PPV/Al-Ag showed that the turn-on voltage of the devices was lowered considerably. Therefore, PONs are suitable for use in a reverse OLED, where the light goes out through a transparent or semi-transparent cathode; moreover, it is much easier to make ohmic contact to the metallic Ti electrode.
Document Type: Research article
Affiliations: 1: University of Engineering and Technology, VNU Hanoi, No. 144 Xuan Thuy Road, Cau Giay District, Hanoi, Vietnam. 2: College of Natural Science, Vietnam National University, Ho Chi Minh, No. 227 Nguyen Van Cu Road, District 5, Ho Chi Minh City, Vietnam
Publication date: 2011-01-01