Investigation into the Gaussian density of states widths of organic semiconductors

Abstract

The determination of the Gaussian density of states (DOS) width and its influence on charge injection/extraction across an interface are of critical importance for the accurate physical understanding of the optoelectronic properties of organic electronics. A new technique is developed here, whereby the DOS width is extracted by numerical fitting of experimental band-bending observed across an interface. This is done by exploiting the fact that the band-bending can be influenced by the disordered nature of energetic sites that are involved in charge transfer across an interface. This technique is applied on a single component and blended mixture of materials. This approach is successfully tested on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), poly(N-vinylcarbazole) (PVK), 2,7-bis(diphenylphosphoryl)-9,9'-spirobifluorene (SPPO13) and poly(3-hexylthiophene-2,5-diyl) (P3HT) in a number of interfaces. The DOS width of PEDOT:PSS, PVK, SPPO13 and P3HT were calculated to be 105 meV, 144 meV, 178 meV and 80 meV respectively. The impact of DOS width on the interface between two materials is investigated. The Fermi level pinning model used to describe the hole barrier between an inorganic electrode and an organic semiconductor fails when applied to the interface between two organic semiconductors. Their energetic barriers are very highly dependent on the DOS of the materials.