A Unified Model for the Space Charge Limited Currents in Organic Materials Combining Field Dependent Mobility and Poole-Frenkel Detrapping

Abstract

We have calculated J-V characteristics of an organic conducting sample (containing traps) including the Poole-Frenkel Effect (PFE). Both shallow and exponentially distributed traps are considered. We show that our approach is equivalent to combining the effect of trapping and using the field dependent mobility in one unified model. For shallow single level or shallow Gaussian traps, inclusion of PFE or using the (well-known) field dependent mobility gives the same dependence of current on voltage at a given temperature. However the value of zero field mobility µ 0 comes out to be different. We have fabricated and measured the J-V curves of the ITO/MEH-OPV5/Al diodes. An extremely fast rise with voltage V is observed at small voltages, which can be interpreted either by the Schottky contact limited Shockley like current or by bulk space charge limited current with PFE. The correct mechanism can be determined by making J-V measurements at different temperatures.

Charge-Transport Networks via Small-Molecule Self-Assembly in Conjugated Polymer Bulk Heterojunctions

“…At higher positive bias, the current densities for both PHM/BAI blends follow voltage power laws with exponents greater than two. Thus, Child’s square-voltage law is not obeyed, which, within the space-charge-limited current formalism, implies that either (i) the charge mobility is a function of the electric field or (ii) there exists an energy-dependent electronic trap distribution. − Both models have previously been applied with reasonable success. We have chosen to model the device current–voltage behavior using the latter, since the physical network structure shown in our STEM-HAADF images can be reasonably expected to give rise to the formation of electronic traps due to site-energy disorder .…”