ABSTRACT
Extensive research in the last few decades has brought to light the fact that organic solids that allow respectable charge mobilities can indeed be designed and synthesized.2 Unfortunately, the light emission from a single layer device-constructed from organic materials with good charge carrier properties-via electron-hole recombination under an applied voltage is fraught by a serious disadvantage of different mobilities of the charges, namely electrons and holes.3a This imbalance in the charge carrier properties is undesirable from the point of view of device functioning. The higher hole mobility compared to that of the electron often results in annihilation of holes at the cathode and edge emission closer to the cathode.3 Further, the excitons formed by the recombination of holes and electrons may also get quenched by the cathode without significant light emission.3 This problem is remedied by multilayer-device construction.4 In the latter, the organic lightemitting material (EM) is deposited in such a manner that it is sandwiched between electron-and hole-transporting materials (ETMs and HTMs).4 These layers are meant to modulate hole and electron mobilities in such a way that their recombination is selectively maneuvered within the emitting layer.1,2 The electron transport layer may not only facilitate the mobility of electrons, but also help in blocking the holes since the ETMs generally possess very high ionization potentials.5 Thus, the multilayer device construction-although disadvantageous from the point of view of technical complexity and cost-effectiveness-is the best alternative toward the emergent technology that is fast replacing the existing mechanisms of lighting.
