Improvement of organic light emitting diodes through molecular structure and radiative decay engineering

Organic-based light emitting diodes (OLEDs) have been the topic considerable research in the last 20 years, and this field has encompassed the 2000 Nobel Prize in Chemistry. The research presented herein focuses on the synthesis of organic and organometallic chromophores with the implementation into OLEDs. Organic chromophores were synthesized on the tetrahedral and binaphthyl molecular templates which force non-crystalline behavior in the solid state. Organometallic complexes based on iridium were synthesized to have high quantum yields, to minimize triplet-triplet annihilation which was achieved by ligand design, and to have non-crystalline behavior also facilitated by ligand design. The advantage of organometallic species over solely organic chromophores in OLED operation is that organometallic species can harvest both singlets and triplets thus having a theoretical electroluminescent performance of 100%, while solely organic molecules can only harvest singlets having a theoretical maximum electroluminescent performance of 25%. It was found that binaphthyl and tetrahedral chromophores produced with low efficiencies during OLED operation. Likewise, devices fabricated only with iridium based chromophores produced poor efficiencies. However, in blended devices, with a host polymer, device performance was improved for both solely organic and organometallic base chromophores. The improvement of the quantum yield of organometallic species was further sought through the acceleration of lifetime, minimization of triplet-triplet annihilation, and preventing chromophore saturation during device operation. This was achieved by radiative decay engineering of organometallic chromophores through the use of surface plasmon resonances of gold nanoparticles. It was determined that the quantum yield of organometallic species could be improved by adding gold nanoparticles to a film matrix that contained the organometallic chromophore. OLEDs fabricated with gold nanoparticles and organometallic chromophores were found to sustain higher current densities and efficiencies than OLEDs fabricated without gold nanoparticles.