Device physics of single layer organic light-emitting diodes

Abstract

We present experimental and device model results for electron only, hole only, and bipolar organic light-emitting diodes fabricated using a soluble poly ͑p-phenylene vinylene͒ based polymer. Current-voltage (I -V) characteristics were measured for a series of electron only devices in which the polymer thickness was varied. The I -V curves were described using a device model from which the electron mobility parameters were extracted. Similarly, the hole mobility parameters were extracted using a device model description of I -V characteristics for a series of hole only devices where the barrier to hole injection was varied by appropriate choices of hole injecting electrode. The electron and hole mobilities extracted from the single carrier devices are then used, without additional adjustable parameters, to describe the measured current-voltage characteristics of a series of bipolar devices where both the device thickness and contacts were varied. The model successfully describes the I -V characteristics of single carrier and bipolar devices as a function of polymer thickness and for structures that are contact limited, space charge limited, and for cases in between. We find qualitative agreement between the device model and measured external luminance for a thickness series of devices. We investigate the sensitivity of the device model calculations to the magnitude of the bimolecular recombination rate prefactor.

Electro-optical properties of a polymer light-emitting diode with an injection-limited hole contact

“…5,6 In a recent experimental study, however, it has been demonstrated that hole currents from silver and aluminum into OC 1 C 10 -PPV exhibit a very weak temperature dependence, in spite of the presence of a large injection barrier of 1 eV. 7 This behavior is in contrast with the thermionic emission model which predicts a strong thermal activation, dominated by the large injection barrier.…”

Gate-bias assisted charge injection in organic field-effect transistors

“…The current in an organic light-emitting diode (OLED) strongly depends on the charge injection barrier [1][2][3][4][5]. The injection barrier is taken as the energy difference between the workfunction of the electrode and the highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO) energy of the organic semiconductor.…”

Non-Equilibrium Charge Transport in Disordered Organic Films

“…The delay time, i.e., the time lag between applying a rectangular voltage pulse to the device and the first appearance of electroluminescence (EL), is identified as the time until the two leading fronts of injected carriers-holes and electrons-meet in the device. Zone of the most intensive EL is typically a narrow sheet (several nanometers in thickness) in proximity to one of the electrodes because of strong asymmetry of hole and electron mobilities (Crone et al, 1999;Friend et al. 1999).…”