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 metal–semiconductor interface determines the efficiency of charge carrier injection into any organic electronics device. Control of this interface, its structure, and its morphology is therefore essential for device improvement. In this study, we analyze the approach of controlling semiconductor morphology at this interface by insertion of a copper phthalocyanine (CuPc) monolayer as a primer between Ag(111), Au(111), and Cu(100) surfaces and the organic semiconductor pentacene (PEN). Controlled monolayer formation is facilitated by thermal desorption of excess multilayers, monitored via thermal desorption spectroscopy (TDS), X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM), and the growth of PEN on the resultant monolayer primers is investigated by near-edge X-ray absorption spectroscopy (NEXAFS), atomic force microscopy (AFM) and STM. While well-ordered CuPc monolayers with flat-lying molecules are formed on Au(111) and Ag(111), no long-range order is observed on Cu(100). Subsequently deposited PEN molecules initially adopt a recumbent orientation with their long axis oriented parallel to the surface, while upon further deposition this structure is metastable as molecules adopt an upright orientation beyond the bilayer and form (001) oriented films. Although the recumbent orientation of the CuPc primer layer is not transferred to thicker PEN films, which is attributed to the geometrical inequality of the two molecules, a distinct dewetting, as found for PEN films grown on bare metal surfaces, is efficiently suppressed. This effect is reproducible even for polycrystalline Au surfaces, which resemble the situation of metal contacts in devices.

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To benefit from the many advantages of organic semiconductors like flexibility, transparency, and small thickness, electronic devices should be entirely made from organic materials. This means, additionally to organic LEDs, organic solar cells, and organic sensors, we need organic transistors to amplify, process, and control signals and electrical power. The standard lateral organic field effect transistor (OFET) does not offer the necessary performance for many of these applications. One promising candidate for solving this problem is the vertical organic field effect transistor (VOFET). In addition to the altered structure of the electrodes, the VOFET has one additional part compared to the OFET – the source-insulator. However, the influence of the used material, the size, and geometry of this insulator on the behavior of the transistor has not yet been examined. We investigate key-parameters of the VOFET with different source insulator materials and geometries. We also present transmission electron microscopy (TEM) images of the edge area. Additionally, we investigate the charge transport in such devices using drift-diffusion simulations and the concept of a vertical organic light emitting transistor (VOLET). The VOLET is a VOFET with an embedded OLED. It allows the tracking of the local current density by measuring the light intensity distribution.We show that the insulator material and thickness only have a small influence on the performance, while there is a strong impact by the insulator geometry – mainly the overlap of the insulator into the channel. By tuning this overlap, on/off-ratios of 9x105 without contact doping are possible.