The Research On Electrical Properties Of Organic Semiconductor Diodes

The research of the electrical transport properties in organic semiconductingpolymers has drawn intensive attention because of their potential applications in organicsemiconductor devices such as light-emitting diodes (PLEDs) and field-effecttransistors (FETs). Understanding their charge-carrier transport mechanism and electricproperties is also very useful to improve the device performances, design and synthesizebetter materials.In this thesis, the J-V characteristics are calculated by solving the drift-diffusionmodel in two kinds of organic semiconducting devices. In addition, a formula for acimpedance spectroscopy (IS) of the organic semiconducting diodes is derived.1. Based on recent experiment about applicability of the classical Einsteinrelationship, the nondegenarate expression of density of holes is used to solve thedrift-diffusion model for J-V characteristics in organic semiconducting layers. Amodified mobility model reported by Pasveer et al. is used; and the realistic contactcondition are considered. The results show that the drift-diffusion model combining theoptimized parameters can well describe the experimental J-V data for NRS-PPV andOC1C10-PPV devices. The parameters determined by Pasveer et al. ignoring thediffusion effects are used to estimate the relative contribution of diffusion effects. It isshown that the popular drift model ignoring the diffusion effects is not necessarily true.It is shown that the relative deviation of J-V curves with and without diffusion effects isabout20~30%for NRS-PPV device, but is about250~350%for OC1C10-PPV device. Itis proposed to use complete drift-diffusion model in researching organic semiconductordiodes. The distributions of potential, electric field and density of holes are calculatedand analyzed.2. A improved mobility factorizing parametrization scheme reported by Xue Bo etal. is used to solving the drift-diffusion equations. The results also show that thediffusion current is very important for total current contribution in researching organicsemiconductor devices3. The formula for ac IS of the organic semiconducting diodes is derived. The agreement of numerical results as mobility being constant with analytic formula inliterature verifies the correctness of our formula and program. The program is then usedto calculate IS of organic NRS-PPV diode based on the mobility model of Pasveer et al.as a function of temperature, electric field and charge carrier concentration.