The relevance of correct injection model to simulate electrical properties of organic semiconductors Francesco Santoni a,⇑ , Alessio Gagliardi a,b , Matthias Auf der Maur a , Aldo Di Carlo a a Department of Electronic Engineering, University of Rome ‘‘Tor Vergata’’, 00133 Rome, Italy b Technische Universität München, Electrical Engineering and Information Tech., Arcisstr. 21, 80333 München, Germany article info Article history: Received 18 February 2014 Received in revised form 14 April 2014 Accepted 18 April 2014 Available online 5 May 2014 Keywords: Organic semiconductors Current injection Hopping Interfaces Organic devices Oled abstract In this work we demonstrate how a full comprehensive model can be used to understand the electrical behavior of actual organic devices. We address all the aspects which need to be taken into account for realistic simulations of a wide range of device structures and con- figurations. In particular we stress the relevance of the correct modeling of contact/organic interfaces. The model is applied to perform predictive simulations of organic light-emitting diodes and to deduce how a full experimental characterization of an organic device should be performed in order to completely grasp its electrical behavior. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Organic electronics is a continuously growing field and in the last decades it has been recognized that organic semiconductors [12] can have an important role in the fab- rication of a wide variety of electronic devices. Several applications have been intensively studied and developed, such as organic light emitting diodes (OLED) [37], organic photovoltaics (OPV) [10], organic field effect transistors (OFET) [4]. Research efforts are motivated by the fact that organic devices are cheaper, easier to fabricate and suitable for new applications. Moreover, chemistry offers much control on the tuning of material properties. From a theoretical point of view, all these kinds of devices require a correct understanding of several aspects: charge injection and transport, energy structure of the organic semiconductors, energy levels alignment at the interface between different materials, the role of trap states, charge recombination and generation. A compre- hensive model would be of great help for devices develop- ment and optimization. The key problem is to understand the basic mechanisms of charge conduction and injection in organic semiconductors [6]. The conduction model should correctly account for (1) the energy structure of the organic material and (2) the charge transport mecha- nism. In Section 2 we will review all the relevant theory and explain how we developed an effective drift–diffusion model that can be used to simulate many kinds of device structures within the framework of the finite element method. We will also show how trap states, charge recom- bination and generation can be straightforwardly inserted in the model. Charge injection in the organic is a critical issue. Organic semiconductors have large band gaps (1.5 to 3.0 eV) – they are almost insulators – and low mobility (10 5 —10 3 cm 2 V 1 s 1 , for comparison, silicon mobility is  10 3 cm 2 V 1 s 1 [22]), thus currents in organic devices are essentially injection controlled. It is then very impor- tant to correctly model contact interfaces. Metal/organic http://dx.doi.org/10.1016/j.orgel.2014.04.023 1566-1199/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +39 0672597777. E-mail address: francesco.santoni@uniroma2.it (F. Santoni). Organic Electronics 15 (2014) 1557–1570 Contents lists available at ScienceDirect Organic Electronics journal homepage: www.elsevier.com/locate/orgel