Unraveling hole interlayer-dependent interfacial energetics of LEDs

To fundamentally understand the underlying interfacial physics of hole transporting layer is a key to rotationally engineer high-performance light-emitting diodes (LEDs). Here, we unravel the hole interlayer-dependent interfacial energetics of LEDs via combining imaged contact potential/polarization difference, and multi-time scale capacitance/voltage response. A universally existing but undesired stagnation of current density with voltages, under the direct contact of light-emitting Poly-TPD with electrodes, was proved to be rooted from the alternant dominance of capacitance/resistance behaviors with alternating strong/weak polarizations of Poly-TPD. The introduction of hole interlayer (PEDOT:PSS) with more disordered polarization direction and greater intensity can build plentiful carrier hopping channels and ensure the rapidly dynamic charge transfer from electrodes to Poly-TPD, conducing to the increased capacitive reactance contribution at low voltages and inductive effects at high voltages. Also, we clarify its frequency-response difference for emerging high-speed modulation application. This discovery might enable us to explore the next-generation high-efficiency display and optical data-communication.