In organic-based (opto)electronic devices, charge injection into conjugated materials is governed to a large extent by the metal-organic interface dipole. Controlling the injection of charges requires a better understanding of the fundamental origin of the interface dipole. In this context, photoelectron spectroscopies and density functional theory calculations are used to investigate the interaction between para-phenylenediamine (PPDA), an electron donor, and a polycrystalline nickel surface. The interface dipole formed upon chemisorption of one PPDA monolayer strongly modifies the work function of the nickel surface from 5.10 to 3.55 eV. The work function decrease of 1.55 eV is explained by the electron-donor character of PPDA and the modification of the electronic density at the metal surface. PPDA monolayers are composed of tilted molecules interacting via the nitrogen lone-pair and PPDA molecules chemisorbed parallel to the surface via their π-electron density. Annealing the monolayer leads to dehydrogenation of PPDA activated by the nickel surface, as found for other amines.

In organic-based electronics, interfacial properties have a profound impact on device performance. The lineup of energy levels is usually dependent on interface dipoles, which may arise from charge transfer reactions. In many applications, metal-organic junctions are prepared under ambient conditions, where direct overlap of the organic system from the metal bands is prevented due to presence of oxides and/or hydrocarbons. We present direct experimental and theoretical evidence showing that the interface energetic for such systems is governed by exchange of an integer amount of electrons.

Transparent low-work-function indium tin oxide (ITO) electrode was obtained by using molecular scale interface engineering. The modified ITO surface may be used as electron injecting electrode in polymer light-emitting devices. ITO surfaces, exposed to TDAE molecules, were found to be stable upon exposure to air, and to mild annealing. Photoelectron spectroscopy measurements show that the low-work-function of the modified electrode remains upon exposure to air in gentle annealing.

Most interfaces in organic electronics consists of weakly interacting organic/(in)organic material interfaces where the interaction is limited to charge transfer via tunnelling. In order to optimize device structure and performance, it is of great importance to understand the rules that govern the energy level alignment at those interfaces. The integer charge transfer (ICT) model is a model used to explain and predict the interaction and energy level alignment behaviour from the so-called integer charge transfer energy, EICT values. In this paper we investigate two phenomena that could influence the absolute value of EICT at hybrid organic and organic-organic interfaces and provide experimentally-derived quantitative data on the strength of the effects.

The energy level alignment behavior of the widely used materials tris-(8-hydroxyquinoline)aluminum (Alq3) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) is investigated. The Integer Charge Transfer (ICT) model is successfully used to predict their overall behavior at weakly-interacting hybridorganic and organic-organic interfaces, including NTCDA/Alq3 bilayers. The E_ICT- of NTCDA is measured to be 4.35 eV and the E_ICT+ of Alq₃ is found to be 4.3 eV. The Alq₃ films furthermore feature an interface dipole in absence of charge transfer due to the intrinsic dipole of the molecule and ordering effects.