Device physics of single layer organic light-emitting diodes

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 vinylene) 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.