Polarization and depolarization effects are shown to play virtually no role for the level alignment in a mixed SAM at 1 1 mixing ratio.
In the latter case, this shifts the eigenstates of the −NH2 substituted molecules up in energy and those of the −CN substituted molecules down, resulting in the peculiar level alignment discussed above.
This has led the community to acknowledge that minimizing these barriers/losses and, in a broader sense, controlling interfacial energy level alignment in general, is a key factor for improving device performance18,20,21,22,23,24,25,26,27,28,29. Figure 1: Sketch of the energy level alignment at organic/electrode interfaces.
In conclusion, inserting a SAM allows controlling the energy level alignment between an electrode and an organic semiconductor over a certain range in which vacuum-level alignment occurs between the SAM and the OSC.
BDT-C1 shows high hole mobility and high conductivity in its pristine form, in combination with appropriate energy level alignment with respect to [CH3NH3]PbI3 and PC70BM, qualifying the material as a good candidate for application both in perovskite solar cells (PSCs) as dopant-free hole transport material (HTM) and in OSCs as donor material.
This noteworthy result rationalizes the success of the induced density of interface state model in correctly reproducing the interfacial energy level alignment in the limiting case of atomically clean metals with intermediate work functions, despite it considering only monolayer coverage.
The maximum changes in energy level alignments due to both kinds of variation were <0.05 eV for all SAM head groups.
I will discuss metal organic interface dipole formation, charge transfer, chemical reaction, energy level alignment, in-diffusion, quenching of luminescence and possible recovery of it.
Our results thus provide a solid theoretical basis for past and present efforts in optimizing the interfacial energy level alignment at organic semiconductor/electrode contacts and will, hopefully, inspire future work.
This modification induces shifts in the vacuum level and work function over ∼1.0 eV depending on the molecular dipole moment of the PA, which in turn modifies the electronic level alignment across the organic heterojunction interface by up to 0.5 eV.
Nevertheless, also in the latter case, the level alignment at the organic/organic interface is markedly different from the situation encountered when the metal is present; that is, ΔΦ2P is reduced from −2.84 to −1.39 eV (cf. 2 and 4).
