Study On The Charge Transport And Electrical Properties In Organic Electronic Devices

In the past decade organic electronic devices have been extensively studied due totheir good properties and potential applications in many fields. However, their defects inpractical operation hamper progress toward the next step, such as the slow operationspeed, low work efficiency, short service life and so on. In order to slove these problem,people should synthesize better organic electronic materials and further improve thedevice structure. To achieve this purpose, people should understand the charge transportin organic electronic materials and devices properly. In this dissertation, we study thecharge transport and electrical properties in organic electronic materials and devices,and obtain some important results that allow the rational design of organic electronicmaterials and devices. Some important and valuable results which bring forth some newideas are listed as follows:1. A particular numerical method adopting the uneven discretization and NewtonIteration Method to solve the coupled equations describing the space-charge limitedcurrent (SCLC) in conjugated polymers is proposed. Based on this numerical methodand the extended Gaussian disorder model (EGDM), we calculate the current-voltage(J V) characteristics of MEH-PPV-based and P3HT-based hole-only devices, anddemonstrate that the numerical results are in good agreement with experimentalmeasurements. Furthermore, we calculate the variation of J Vcharacteristics withthe boundary carrier density and the distribution of charge-carrier density and electricfield with the distance to the interface. It is shown that the numerically calculated carrierdensity is a decreasing function of the distance and numerically calculated electric fieldis an increasing function of the distance. The maximum of carrier density and theminimum of electric field appear near the interface.2. Based on the extended Gaussian disorder model (EGDM) introduced by Pasveeret al, we propose an improved unified description of the dependence of the chargecarrier mobility on temperature, carrier density and electric field by considering theArrhenius temperature dependence ln()1/Tand non-Arrhenius temperaturedependenceln()1/T2together, and demonstrate the improved model can better describe the charge transport in organic electronic materials and devices, especially athigh carrier density and high electric field. In addition, we calculate the current-voltage(J V) characteristics of NRS-PPV-based, OC1C10-PPV-based and MEH-PPV-basedhole-only devices and demonstrate that the numerical results are in good agreement withexperimental measurements. These results indicate the improved model captures thephysical essence of the charge transport in organic electronic materials and devices, andis more applicable for organic electronic materials and devices than the original model.3. The devices based on the organic small molecule material NPB were fabricated,and the measured J Vcharacteristics were presented. It is demonstrated that theJ Vcharacteristics of various thickness at room temperature can be excellentlydescribed by the improved model only using a set of parameters. Furthermore, we studythe charge transport of PFO-based hole-only devices by using the improved model, anddemonstrate the temperature dependent and thickness dependent J Vcharacteristicscan be excellently described with a set of same parameters. Moreover, we further studythe charge transport of P3HT-based hole-only devices by using the improved model, anddemonstrate that the J Vcharacteristics can be better described by the improvedmodel than the original model. All the results indicate that the improved model isapplicable for various organic semiconductors.