Organic light emitting diodes: Energy saving lighting technology-A review

This paper reflects the achievements and the challenges ahead in the field of organic light emitting diodes (OLEDs). The primary intention of this paper is to study different organic materials synthesized so far and the OLEDs fabricated for solid-state lighting. After deep review of literature we have synthesized and characterized rare earth based europium organic complexes Eu(TTA)(3)Phen, Eu(x)Y(1-x)(TTA)(3)Phen, and Eu(x)Tb(1-x)(TTA)(3)Phen, where x = 0.4 and 0.5 by solution technique maintaining stoichiometric ratio. Blended films of pure and doped Eu complexes that are molecularly doped into polymer resins namely polymethylmethacrylate (PMMA) and polystyrene (PS) are prepared according to weight percentage. Concentration effect on absorption and emission spectra of the blended films was studied for different weight percentages (10, 25, 50, 60%). All the complexes doped in PMMA showed an excellent transparency of 90-97% while the complexes doped in polystyrene showed a transparency of 85-90%, bit less than in PMMA. Energy gap of the synthesized complexes have been determined in PMMA and PS. Considering the facts that these complexes have good solubility in most of the organic solvents, the absorption spectra of Eu(TTA)(3)Phen. Eu0.5Y0.5(TTA)(3)Phen and Eu0.5Tb0.5(TTA)(3)Phen complexes are studied, and OLED devices having the structure ITO/m-MTDATA/alpha-NPD/TPBi:Eu(x)Y(1-x)(TTA)(3)Phen/Alq(3)/LiF:Al (where x = 0.4, 0.5) were fabricated and characterized. Significant red emission was observed from fabricated OLED devices at 612 nm when operated in a range of 10-18 V. Thus the synthesized rare earth based organic complexes are the best suitable candidates for fabrication of red OLED devices. The extensive review on OLEDS concludes that our present lighting system can be replaced with white OLEDS, recently developed energy saving lighting technology. (C) 2012 Elsevier Ltd. All rights reserved.