Ultrathin buffer layer at organic/organic interface for managing the recombination profile in organic light-emitting diodes: Metal versus dielectric buffer

We report on the utilization of an ultrathin buffer layer at the organic/organic (O/O) interface to enhance device efficiency in organic light-emitting diodes. Two different kinds of buffer layers are examined: metal and dielectric. It is shown that employment of an ultrathin Ag layer with a thickness of 1-2 nm enhances the device performance, while a MgF2 dielectric buffer cannot affect the device properties considerably. In particular, the turn-on voltage of the device with an appropriate buffer layer is reduced about 3 V, its current efficiency increases by a factor of more than three, and the power efficiency increases by a factor of more than five in comparison to the control device when a Ag buffer layer is introduced at the O/O interface. By employment of the buffer layer at the interface, an accumulation of current carriers appears within the device that redistribute the recombination profile toward the interior part of the emissive layer. Also, morphological examinations reveal that distinguishable phase segregation occurs in the blend of the hole-transport layer. In particular, the polymer component remains at the surface and facilitates the hole transport into the successive layers. (C) 2016 Wiley Periodicals, Inc.