Organic Electronics & Materials Research Laboratory
Department of Physics & Astrophysics, University of Delhi, India
In the past few decades, organic light emitting diodes (OLEDs) have made a remarkable breakthrough in both research as well as in industries due to their potent applications in various areas. At present, OLED technology is used in multiple commercial applications such as displays for mobile phones and portable digital media player, car radios, digital cameras, smart watches, etc. In these devices, holes and electrons are injected into the organic thin film from opposite electrodes (anode and cathode). The holes and electrons migrate through the thin film which is the active layer, where they recombine to form the radiative excited states or excitons. The colour of the emission depends on HOMO-LUMO energy gap of emissive layer. The major advantage of OLEDs is the ability to tune the colour of the light. Another advantage of OLEDs is that they are current driven devices, where brightness can be varied over a wide dynamic range and they operate uniformly, without flicker. Compared to inorganic LEDs, organic LEDs have high emission efficiency in the visible spectrum, easy to process, robust, low power consumption, tunability of the colour and wide viewing angles. The components in the OLED structure differ according to the number of layers of the organic material.
There are mainly three classes of materials which have been used as effective emissive layers in OLEDs so far: conducting polymers, small molecules and dendrimers. Small molecules tend to have higher efficiency due to their phosphorescence nature. Metal complexes containing heavy transition metals (Ir, Os, Ru, Eu etc.) can serve as efficient phosphors in small molecule OLEDs. OLEDs based on fluorescent materials do not give triplet emission thus implies a 25% internal quantum efficiency. By doping OLEDs with these metal complexes, this singlet-triplet limitation can be eliminated. OLEDs prepared with these metal complexes are the most efficient ones with internal quantum efficiency greater than 75% and external quantum efficiencies of nearly 25%.
Here in our group, we are synthesizing organic molecules such as conducting polymers, metal ion complexes, etc., to develop highly efficient active layers for OLEDs.
There are mainly three classes of materials which have been used as effective emissive layers in OLEDs so far: conducting polymers, small molecules and dendrimers. Small molecules tend to have higher efficiency due to their phosphorescence nature. Metal complexes containing heavy transition metals (Ir, Os, Ru, Eu etc.) can serve as efficient phosphors in small molecule OLEDs. OLEDs based on fluorescent materials do not give triplet emission thus implies a 25% internal quantum efficiency. By doping OLEDs with these metal complexes, this singlet-triplet limitation can be eliminated. OLEDs prepared with these metal complexes are the most efficient ones with internal quantum efficiency greater than 75% and external quantum efficiencies of nearly 25%.
Here in our group, we are synthesizing organic molecules such as conducting polymers, metal ion complexes, etc., to develop highly efficient active layers for OLEDs.