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

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> An analytical, complete framework to describe the current–voltage (<emphasis emphasistype="italic"> I–V</emphasis>) 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 <emphasis emphasistype="italic">I–V</emphasis> 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<formula formulatype="inline"><tex>$^\prime$</tex></formula>,7 <formula formulatype="inline"><tex>$^\prime$</tex></formula>-dimethyloctyloxy}-<formula formulatype="inline"><tex>$p$ </tex></formula>-phenylenevinylene) (MDMO-PPV) and a derivative of the poly(2,7-fluorene phenylidene) [PFP:(CN) <formula formulatype="inline"><tex>$_{2}$</tex></formula>], have been fabricated. The present model is excellently fitted to experimental curves and yields the microscopic parameters that characterize the active layer. </para>