Conjugated polymers as interfacial layer for efficiency improvement in fully solution-processable organic light-emitting diodes

Light sources based on organic emitters have already arrived to the market, however they are based on expensive and time consuming vacuum evaporation process. In order to employ fully possibilities that offer organic materials a passage to wet deposition techniques is required. The development of polymeric polyelectrolytes as charge injection layers (CIL) has significantly improved the performance of organic light emitting diodes (OLEDs) build from solutions. We have designed and synthesized a family of CIL compounds comprising a polyfluorene backbone with pendant polar or ionic groups, which increase alcohol/water solubility, hence providing a more environmentally friendly option to manufacture all-solution-processed multilayer OLEDs by using orthogonal solvents. We show that by CIL insertion a significant improvement of the performance of OLEDs based on phosphorescent compounds is achieved. As examples three devices based on iridium complexes emitting in green [1], red and near infrared (NIR) [2] spectral regions are presented. Thanks to application of polymer with polyethylene glycol lateral groups and the other one with polar and ionic pendant groups, external quantum efficiency (EQE) of the devices increases more than double for green, almost 30% for red and nearly 20% for NIR emitting OLEDs. CILs containing the polymers presented here pave the way to efficient, fully-solution-processed light sources.