tuhin4u (Unstopable Lover + Mariana World DIAMOND member): During operation, a voltage is applied across the OLED such that the anode is positive with respect to the cathode. Anodes are picked based upon the quality of their optical transparency, electrical conductivity, and chemical stability. A current of electrons flows through the device from cathode to anode, as electrons are injected into the LUMO of the organic layer at the cathode and withdrawn from the HOMO at the anode. This latter process may also be described as the injection of electron holes into the HOMO. *05-10-14 - 05:15:35
tuhin4u (Unstopable Lover + Mariana World DIAMOND member): Electrostatic forces bring the electrons and the holes towards each other and they recombine forming an exciton, a bound state of the electron and hole. This happens closer to the emissive layer, because in organic semiconductors holes are generally more mobile than electrons. The decay of this excited state results in a relaxation of the energy levels of the electron, accompanied by emission of radiation whose frequency is in the visible region. *05-10-14 - 05:16:36
tuhin4u (Unstopable Lover + Mariana World DIAMOND member): The frequency of this radiation depends on the band gap of the material, in this case the difference in energy between the HOMO and LUMO. *05-10-14 - 05:17:22
tuhin4u (Unstopable Lover + Mariana World DIAMOND member): As electrons and holes are fermions with half integer spin, an exciton may either be in a singlet state 0r a triplet state depending on how the spins of the electron and hole have been combined. Statistically three triplet excitons will be formed for each singlet exciton. Decay from triplet states (phosphorescence) is spin forbidden, increasing the timescale of the transition and limiting the internal efficiency of fluorescent devices. *05-10-14 - 05:18:14
tuhin4u (Unstopable Lover + Mariana World DIAMOND member): Phosphorescent organic light- emitting diodes make use of spin–orbit interactions to facilitate intersystem crossing between singlet and triplet states, thus obtaining emission from both singlet and triplet states and improving the internal efficiency. *05-10-14 - 05:18:59