The interface between metals and organic semiconductors plays a central role in the physics of polymer light-emitting diodes.In addition

the asymmetry in the work function of the two electrodes is responsible for the polymer light-emitting diodes rectifying behavior and governs the injection of carriers in polymer.In order to fabricate efficient devices and to minimize injection barriers

the low work function cathodes and high work function anodes are desirable.Ideal electrode materials have been difficult to obtain

however

an incorporation of injectint inter-layers at electrode/polymer interfaces has been used as an alternative route towards enhanced carrier injection.The performance of polymer light-emitting diodes with inserting metal fluoride insulating layer between the metal cathode and active polymer was studied.As for the polymer light-emitting diodes

optimization of charge injection lies in the dominant factors for substantive improvement performance.Since it is minority carriers dominate the recombination thus the radiation

their injection takes priority over that of majority carriers.Generally in semiconducting polymers

holes are majority carriers while electron iniection.there are two commonly used stratagems in cathode fabrication.One is to employ low work function metals such as barium and calcium as cathode though they are susceptible to degradation upon water vapor and oxygen.The other choice is proposed to insert an insulating thin layer usually metal fluoride between polymer/electrode interfaces to build a bilayer cathode.Proper inserting of insulating layer would lead to improvement in the overall working perfomance.But the thickness of the insulating layer is a fatal factor that influences the enhancement effect.As show in the experiment result

the LiF/Al double-layer-cathode devices are capariable with Ba(Ca)/Al electrode devices in luminescence performance.Band bending and injection potential decrease of minority carrier caused by the inlay of metal fluoride insulating layer

are proposed to be responsible for the enhanced electron injection and improved performance in polymer light emitting diodes.