Analytical Evaluation of the Ratio Between Injection and Space-Charge Limited Currents in Single Carrier Organic Diodes

An analytical, complete framework to describe the current-voltage (I-V) characteristics of organic diodes without the use of previous approaches, such as injection or bulk-limited conduction is proposed. Analytical expressions to quantify the ratio between injection and space-charge-limited current from experimental I-V characteristics in organic diodes have been derived. These are used to propose a numerical model in which both bulk transport and injection mechanisms are considered simultaneously. This procedure leads to a significant reduction in computing time with respect to previous rigorous numerical models. In order to test the model, different diode structures based on two different polymers: poly(2-methoxy-5-{3´,7´-dimethyloctyloxy}-p-phenylenevinylene) (MDMO-PPV) and a derivative of the poly (2,7-fluorene phenylidene) [PFP:(CN)₂], have been fabricated. The present model is excellently fitted to experimental curves and yields the microscopic parameters that characterize the active layer.