The energy level alignment between organic semiconductors (OSCs) and the respective (metal) electrodes in organic electronic devices is of key importance for efficient charge carrier injection. For many years, researchers have attempted to control this energy level alignment by means of functional self‐assembled monolayers or the insertion of thin injection layers (made, e.g., of doped OCSs or pure dopants). The present work demonstrates an alternative to these approaches, namely the use of phthalocyanine monolayers as contact primers, which are deposited onto noble metal electrodes by means of vacuum deposition. It is shown that polar as well as non‐polar phthalocyanines modify the work functions of clean Au(111) and Ag(111) surfaces as a function of their coverage and thus enable quantitative control of the metal work functions. This behavior is successfully replicated for the respective polycrystalline metal surfaces and it is found that full monolayers can even withstand air exposure when protected by sacrificial multilayers, which are afterward removed by thermal desorption.

The fabrication of smooth organic semiconductor films with homogeneous thickness is of key importance for the improvement of organic electronic devices and realization of well-defined molecular heterostructures. Although many π-conjugated molecular materials form highly ordered monolayers on (single) crystalline metal substrates, further deposition typically obeys a Stranski–Krastanov growth and results in considerable layer roughness. Here, we examine the evolution of titanylphthalocyanine (TiOPc) films on Ag(111) for thicknesses ranging from an initial seed layer to thick multilayers (200 nm) by combining scanning probe microscopy [scanning tunneling microscopy (STM) and atomic force microscopy (AFM)] with X-ray diffraction and synchrotron-based photoelectron spectroscopy [X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption spectroscopy (NEXAFS)]. While the crystallinity of the TiOPc films increases with substrate temperature during growth, even at temperatures close to the onset of desorption, extended and molecularly flat islands are formed, which cover more than 80% of the substrate area resulting in exceptional smooth layers. The crystalline TiOPc films exclusively exhibit the phase I polymorph where molecular planes are oriented nearly parallel to the substrate surface and adopt an alternating (up/down) stacking of their titanyl groups forming stable bilayer units. Similar to the first bilayer, TiOPc multilayers are also epitaxially aligned with respect to the substrate. STM and AFM data further show that the macroscopic film roughness is essentially due to rotational domain boundaries in the seed layer which are not overgrown and result in characteristic macroscopic trenches. The high crystalline ordering and exceptional smoothness make this metal/organic heterosystem particularly suitable as a molecular spacer layer and allows for thickness-dependent studies of optoelectronic excitations and their dynamics.

A photo-electrochemical sensor for the specific detection of guanosine monophosphate (GMP) is demonstrated, based on three enzymes combined in a coupled reaction assay. The first reaction involves the adenosine triphosphate (ATP)-dependent conversion of GMP to guanosine diphosphate (GDP) by guanylate kinase, which warrants substrate specificity. The reaction products ADP and GDPare co-substrates for the enzymatic conversion of phosphoenolpyruvate to pyruvate in a second reaction mediated by pyruvate kinase. Pyruvate in turn is the co-substrate for lactate dehydrogenase that generates lactate via oxidation of nicotinamide adenine dinucleotide (reduced form) NADH to NAD(+). This third enzymatic reaction is electrochemically detected. For this purpose a CdS/ZnS quantum dot (QD) electrode is illuminated and the photocurrent response under fixed potential conditions is evaluated. The sequential enzyme reactions are first evaluated in solution. Subsequently, a sensor for GMP is constructed using polyelectrolytes for enzyme immobilization.

BN-substituted nanographene molecules are currently the focus of interest because the substitution of C–C units by isoelectronic and isosteric BN units is a straightforward way of changing the electronic properties of nanographenes. Another parameter influencing the electronic structure, orientation, and growth mode of nanographene molecules is the planarity of the molecules. The electronic structure, orientation, and film growth of the related molecules B3N3-hexa-peri-hexabenzocoronene (BN-HBC), B3N3-hexabenzotriphenylen (BN-HBP), and B3N3-hexabenzotriphenylen-2H (BN-HBP-2H) on Au(111) have been studied by photoelectron spectroscopy (PES), X-ray absorption spectroscopy (XAS), atomic force microscopy (AFM), and scanning tunneling microscopy (STM). XA spectra were simulated using time-dependent density functional theory (TDDFT). The calculation of C 1s excitation spectra allows the assignment of individual transitions and the examination of the degree of cross-linking between biphenyl units. It is shown that the planarity of the molecules distinctly affects the electronic structure, interface properties, as well as growth in thin films.

Contact engineering is an important issue for organic electronics as it allows to reduce charge carrier injection barriers. While the use of molecular contact primer layers to control the energy level alignment is demonstrated in many concept studies, mainly using (single crystalline) model substrates, the processability of electrodes and their robustness must also be considered in real devices. Although silver electrodes can be printed using silver ink, their low work function and sensitivity to oxidation severely limits their use for printable organic electronics. The present study demonstrates that mono layers of F 4 TCNQ and F 6 TCNNQ provide a reliable approach to engineer high work function silver electrodes, which is examined for Ag(111) as well as polycrystalline and silver ink substrates. Notably, upon multilayer growth, a pronounced intercalation of silver into the molecular adlayer occurs, yielding thermally stabilized organometallic interphases extending over the entire adlayer. It is shown that heating allows their controlled desorption leaving behind a well-defined monolayer that is further stabilized by additional charge transfer. Especially F 6 TCNNQ contact primer layers can also be prepared on oxidized silver electrodes yielding work functions of 5.5-5.6 eV, which can even withstand air exposure. Such contact primers show no interdiffusion into subsequently deposited layers of the prototypical p-type organic semiconductor pentacene, hence validating their use for organic electronic devices.