Ideal organic homojunction diode obtained using controlled alignment of localized density of states across doped/undoped interface

We show that for organic semiconductors, it is sufficient to have a doped/undoped homojunction to obtain a near ideal diode with exponential dependence of current density (J) on voltage (V), though the physics is very different from the ideal Shockley equations for conventional p-n junction. Unlike Shockley diodes, the slope of the semi-log plot in this regime is independent of temperature, and is related to the broadening parameters of Gaussian density of states (DOS). We show that physics of transport in the regime is controlled by alignment through local DOS and tunneling across the interface. The mechanism sets in beyond a newly identified threshold voltage (Vth) which decreases linearly with temperature and corresponds to offset in energy of localized DOS at the interface at which overlap begins to occur. The temperature dependence of all other significant features is shown to be consistent with localized Gaussian density of states model of disordered solids. (C) 2012 Elsevier B.V. All rights reserved.