Charge-carrier transport in amorphous organic semiconductors

Organic semiconductors have been extensively studied ever since the successful fabrication of organic light-emitting diodes (OLED).4 2-44 Due to their success, it is becoming increasingly important to understand the theory behind the properties of organic materials. In order to exploit all the advantages of implementing organic materials to construct devices, a detailed understanding of charge-carrier transport in these materials is necessary to obtain optimal efficiency for device operation. In the interface-limited model,45 transport is heavily dependent on the characteristics of the interface. One important property is the distribution of energy states at the interface. Thin organic films grown from thermal vapor deposition seldom form a smooth interface but rather diverse morphologies. In here, we analyze the effect of the rough metal/organic interface on the density of states, aiding in the study of interface-limited charge transport. We find that the energy distribution due to the electrostatic potential of the metal/organic charge separation is broad in the interface and gets narrower further into the bulk. Therefore, we have a broad distribution of states at the interface compared to the bulk. Charges are trapped in the tail of the broad density of states and hopping from these interface states into the bulk limits charge transport. Thesis Supervisor: Marc Baldo Title: Professor