Energy‐Level Alignment at Organic/Metal and Organic/Organic Interfaces

Abstract

In this Review, we summarize recent work on modeling of organic/metal and organic/organic interfaces. Some of the models discussed have a semiempirical approach, that is, experimentally derived values are used in combination with theory, and others rely completely of calculations. The models are categorized according to the types of interfaces they apply to, and the strength of the interaction at the interface has been used as the main factor. We explain the basics of the models, their use, and give examples on how the models correlate with experimental results. We stress that given the complexity of organic/metal and organic/organic interface formation, it is crucial to know the exact way in which the interface was formed before choosing the model that is applicable, as none of the models presented covers the whole range of interface interaction strengths (weak physisorption to strong chemisorption).

Widely Applicable Coinage Metal Window Electrodes on Flexible Polyester Substrates Applied to Organic Photovoltaics

“…For transition metal oxide holeextraction layers efficient hole extraction from an organic semiconductor is only achieved when the oxide work function is higher or comparable to the ionization potential of the adjacent organic semiconductor. 33 In this case, even for the highest MPA doping level tested, the work function of H y MoO 3−x :MPA should still be sufficiently large to ensure optimized interfacial energy level alignment with the HOMO of most donor-type organic semiconductors. 34 This conclusion is supported by the OPV device studies reported in a subsequent section of this paper.…”

Metal−Molecule Schottky Junction Effects in Surface Enhanced Raman Scattering

“…In fact the value of S was calculated to be 0.5 experimentally for Au and benzenethiol system [86]. Again the density of states D(E F ) of interfacial electronic states can be calculated using the relation, S = (1 + e 2 δD(E F )/ε) −1 , [85][86][87] where e, δ, and ε denote the elementary charge, width of the metal−molecule interface, and dielectric constant, respectively. Taking δ and ε to be 5.7 Å and 4.38 for benzenethiol [81] respectively, D (E F ) is estimated to be 4.2 × 10 13 states/(cm 2 ·eV), which is less than 20% of the density of states of Au at the Fermi level [88].…”

Fingerprint of Fractional Charge Transfer at the Metal/Organic Interface

“…Although organic/metal interfaces have been the focus of nearly two decades of investigations, [3][4][5][6][7] very recently the interest in this type of interface has enjoyed a renaissance with the flourishing of a body of work focused mainly on the interfaces between chemisorbed organic molecules and metals. [8][9][10][11] Photoemission features strongly depend on the strength of the molecule/substrate interaction, as demonstrated for a number of molecules on Ag(111). [9] These experiments show that the stronger the bond of the molecules with the substrate, the larger the effect of the charge transfer on photoemission is.…”

“…[8] The present "state of the art" in the interpretation of the organic/metal and organic/organic interfaces, is based on the interface interaction strength, considering the complete range of interactions from physisorption of noble gases to strong chemisorption of -conjugated molecules. [11] The case of physisorption with and without charge transfer is typically examined within the integer electron charge transfer model, stating that physisorption on organic and passivated metal surfaces is possible, while weak chemisorption, with possible fractional charge transfer, occurs on non-reactive clean metal surfaces. [11] These models, although extremely useful and detailed, do not explain all experimental results: Physisorption is a widely occurring phenomenon at the organic/metal interface, exhibiting different spectral characteristics that also depend on the strength of molecule/metal interaction.…”

“…[11] The case of physisorption with and without charge transfer is typically examined within the integer electron charge transfer model, stating that physisorption on organic and passivated metal surfaces is possible, while weak chemisorption, with possible fractional charge transfer, occurs on non-reactive clean metal surfaces. [11] These models, although extremely useful and detailed, do not explain all experimental results: Physisorption is a widely occurring phenomenon at the organic/metal interface, exhibiting different spectral characteristics that also depend on the strength of molecule/metal interaction. We here contribute to the understanding of the organic/metal interface by an experimental and theoretical multi-technique investigation, choosing 2,3,9,10-tetrafluoropentacene [12] (F4PEN, Figure 1), a fluorinated pentacene derivative, as a model system.…”