The importance of gap states for energy level alignment at hybrid interfaces

Abstract

Energy level alignment and electronic structure at organic semiconductor interfaces must be controlled to ensure efficient carrier harvesting or injection in next-generation organic optoelectronic technologies. In this context, hybrid organic/inorganic semiconductor interfaces exhibit particularly rich physics. Here, we show that states in the band gap of the inorganic layered van der Waals dichalcogenide SnS 2 play an important role in determining energy level alignment at the hybrid interface with copper phthalocyanine (CuPc). By taking advantage of the closely related CuPc film growth on SnS 2 and the well-studied interface of CuPc/HOPG, we are able to trace spectroscopic differences to the fundamentally different electronic interactions across the two interfaces. We provide a detailed picture of the role of gap states at the hybrid interface and shed light on the electronic properties of inorganic semiconductors in general and metal dichalcogenides in particular.

Anisotropic attosecond charge carrier dynamics and layer decoupling in quasi-2D layered SnS2

“…Here we address this open question by investigating the ultrafast carrier dynamics in the layered semiconductor SnS 2 23 – 25 . Using core–hole clock spectroscopy 26 , we observe spin-dependent anisotropic charge transfer on attosecond timescales in quasi-2D bulk SnS 2 , and show that already in bulk crystals individual layers are indeed strongly decoupled and essentially 2D.…”

Valence and conduction band structure of the quasi-two-dimensional semiconductorSnS2

“…The localization behavior implied by the unique dispersion of these bands suggests that they may in fact originate from small populations of crystal defects, also supported by their low photoemission intensity ( Figure 1). Point defects such as sulfur vacancies have been recently observed indirectly in the nearsurface region [27,28], and have also been suggested to be responsible for the intrinsic n-type character of SnS 2 [49]. We will return to this interpretation in the next section.…”

“…eV [28]. For photon energies up to 4.8 eV, the spectra can be fit well with two overlapping Gaussian features, supported on a linear background to represent the slope of the secondary electron cut-off and with a full-width-half-maximum of ~400 meV each (blue and black features in Figure 3a).…”

“…SnS 2 crystals of the 4H polymorph were prepared according to methods described previously [22,27,28]. Briefly, SnS 2 was grown by the Bridgman method, and n-doped with a carrier concentration of 2.3(1)×10 17 cm -3 , as determined by the van der Pauw method [34].…”

“…SnS 2 has attracted long-standing interest for energy harvesting, storage and photocatalytic water splitting applications both at the bulk and the nanoparticle level [2,[23][24][25][26], driven in part by the earth abundance of both Sn and S. To take full advantage of the unique electronic properties in the single and few-layer limit, Huang et al investigated carrier transport in field effect transistors, achieving mobilities in excess of 5 cm 2 /Vs [22]. Recently, hybrid organic semiconductor / SnS 2 structures were investigated as well, highlighting the role of defects in controlling electronic interactions in the interfacial region [27,28]. In order to understand and tailor these properties more comprehensively, it is essential to accurately map the electronic structure of SnS 2 .…”