The growth of molecular adlayers on solid substrates is reviewed with aspecial emphasis on molecules of relevance for organic electronics. In particular,we will consider planar molecules with extended π-systems, namely acenes (anthracene, tetracene, pentacene), perylene, coronenes, diindenoperylene, 3,4,9,10-perylene-tetracarboxylicacid-dianhydride, poly-phenylenes, oligothiophenes, and phthalocyanines. Special consideration is given to the importance of the formation of ordered molecular overlayers, which are compared with the structure of the corresponding bulk crystals. Whenever possible, aspects relevant for device fabrication (morphology of deposited films, mobilities of charge carriers) will be addressed.

The control of hybrid interfaces in polymer-based electronic devices may be enabling in many applications. The engineering of hybrid interface involves (requires) an understanding of the electronic structure of materials—one organic and one inorganic—that form the two halves of hybrid interfaces, as well as the electronic and chemical consequences of the coupling of the two. Although much literature exists describing the interfaces between vapor-deposited organic molecules and model molecules for polymers on the surfaces of clean metals in ultrahigh vacuum, few studies have been reported on spin-coated, semiconducting polymer films on realistic substrates. Spin coating in an inert atmosphere (or even air) is a central part of the process of the fabrication of polymer-based light-emitting devices and other modern polymer-based electronic components. Here, work on the electronic structure of semiconducting (conjugated) polymer films spin-coated onto selected inorganic substrates, carried out using ultraviolet photoelectron spectroscopy, is reviewed and summarized to generate a generalized picture of the hybrid interfaces formed under realistic device fabrication conditions.

Organic solar cell research has developed during the past 30 years, but especially in the last decade it has attracted scientific and economic interest triggered by a rapid increase in power conversion efficiencies. This was achieved by the introduction of new materials, improved materials engineering, and more sophisticated device structures. Today, solar power conversion efficiencies in excess of 3% have been accomplished with several device concepts. Though efficiencies of these thin-film organicdevices have not yet reached those of their inorganic counterparts (η ≈ 10–20%); the perspective of cheap production (employing, e.g., roll-to-roll processes) drives the development of organic photovoltaic devices further in a dynamic way. The two competitive production techniques used today are either wet solution processing or dry thermal evaporation of the organic constituents. The field of organic solar cells profited well from the development of light-emitting diodes based on similar technologies, which have entered the market recently. We review here the current status of the field of organic solar cells and discuss different production technologies as well as study the important parameters to improve their performance.

The organic thin-film transistor (OTFT) is now a mature device that has developed tremendously during the last twenty years. The aim of this paper is to update previous reviews on that matter that have been published in the past. The operating mode of OTFTs is analyzed in view of recent model development. This mainly concerns the distribution of charges in the conducting channel and problems connected with contact resistance. We also delineate what differentiates n- and p-type semiconductors, and show how this concept differs from what it covers in conventional semiconductors. In the chapter devoted to fabrication techniques, emphasis is placed on solution-based techniques and particularly printing processes. Similarly, soluble materials are given a prominent place in the section dedicated to the performance of devices. Finally, special attention is given to devices at the nanoscale level, which demonstrate a new route toward molecular electronics.

Printed organic circuits have the potential to revolutionize the spread of electronic applications. This will be enabled by inexpensive and fast fabrication with printing techniques using soluble organic materials. Two main challenges have to be mastered on the way towards printed electronics. First, the development of stable transistors and an adapted chip design for organic materials, and second, the development of a reliable fabrication process. We present our results on high performance polymer transistors, mainly based on poly-3alkylthiophene (P3AT) as semiconducting material. Fast circuits up to 200 kHz and stable circuits with operation lifetimes of more than 1000 h under ambient conditions without any encapsulation are shown. We also report on a fully printed, all organic ring oscillator.

Techniques for manufacturing organic electronic devices [organic light-emitting diodes (OLEDs), photovoltaic cells, transistors, and solid-state memory] are reviewed and analyzed with respect to cost and market fitness in comparison to competitive approaches based on silicon electronics. The conclusions are (i) OLED displays will be successful using infrastructure largely borrowed from liquid crystal displays, because they provide fundamental customer value not dependent on lower cost; (ii) OLEDs for general lighting and organic–inorganic hybrid photovoltaic cells currently confront substantial barriers in cost and efficiency, but solutions appear feasible and would lead to very large volume businesses; (iii) organic crossbar memories are promising, but require innovations in driver architecture and interconnection; and (iv) organic transistors have not yet found a viable major market, but have great promise for highly customized, small-volume product runs using digital patterning techniques.

Hybrid bulk heterojunction composites are promising material for low-cost organic solar cells. Fundamental measurements with CdTe nanocrystal/MEH-PPV poly [2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] composites and the first realization of a solar cell based on this material are presented. Optical and electrochemical properties are discussed as well as the current voltage characteristic of the resulting cell. It was found, that CdTe nanocrystal/MEH-PPV composites are well suited for an organic solar cell, even though the technological realization needs to be improved.

We report properties of devices made by the adhesion of semiconductor crystals, including several tetracene specimens, to polymer gate dielectrics along with measurements of tetracene crystals on conventional Si/SiO2 dielectric surfaces. For the best tetracene, pentacene, and alpha-6T devices, mobilities exceeding 0.1 cm2/V were measured, correlating well with expectations based on the literature, and in the case of tetracene and alpha-6T, exceeding the thin film mobility value. The devices were prepared in the open laboratory using simpler crystal handling techniques than had been thought necessary.

This article reports degradation experiments on organic thin film transistors using the small organic molecule pentacene as the semiconducting material. Starting with degradation inert p-type silicon wafers as the substrate and SiO2 as the gate dielectric, we show the influence of temperature and exposure to ambient air on the charge carrier field-effect mobility, on-off-ratio, and threshold-voltage. The devices were found to have unambiguously degraded over 3 orders of magnitude in maximum on-current and charge carrier field-effect mobility, but they still operated after a period of 9 months in ambient air conditions. A thermal treatment was carried out in vacuum conditions and revealed a degradation of the charge carrier field-effect mobility, maximum on-current, and threshold voltage.

A study comparing the morphology and electrical transport properties of pentacene films on underlayers of different self-assembled monolayers (SAMs) is presented. The SAMs studied as underlayers were phenyltrichlorosilane, n-octadecyltrichlorosilane, and t-butyldiphenylchlorosilane. Pentacene thin films were grown by vacuum sublimation on SiO2 surfaces treated with self-assembled monolayers. During deposition, substrates were held at a temperature of 70 °C. The morphologies of the films at different stages of deposition were studied by atomic force microscopy, and the transport properties of the films were characterized by I-V measurements in a simple field-effect transistor (FET) structure. The SAM underlayers strongly influence the film morphology in the first few molecular layers and hence significantly impact the electrical transport in the resulting FETs.

Thin films of perfluorinated vanadyl phthalocyanine F16PcVO were prepared by physical vapor deposition in high vacuum on KBr and fused silica substrates. The absorption spectra in the visible region show that the films on different substrates have different structure. The optical constants for F16PcVO films were obtained in the spectral range of 0.7–4.5 eV from the simulation of ellipsometry spectra with an anisotropic uniaxial model. From the difference between the in-plane and out-of-plane components of the extinction coefficient the average tilt angle of the F16PcVO molecular planes with respect to the substrate plane was found to be 56° for fused silica substrates and between 0° and 3° for KBr substrates.

Numerical simulations of organic field-effect transistors (OFET) of bottom and top contact (BOC, TOC) design with different source/drain contacts were carried out considering an exponential distribution of trap states in the gap of the active layer (a-Si model). For ohmic contacts, the current-voltage characteristics are similar to the trap-free case and there is not much difference between the two designs. However, the currents are lower due to immobile trapped charges, the threshold voltage is shifted, and the inverse subthreshold slope increases due to trap recharging. An analytical approximation for the effective mobility deviates from the simulation up to 20%. For low source/drain work function, there occur particular dependencies of the current on the gate voltage for the two designs, which are explained with the internal concentration and field profiles. A series resistance between source and channel causes in the TOC structure an abrupt transition from the gate voltage independent active region into saturation. In the BOC case, the reverse-biased Schottky-type source contact dominates the current. Through simulation of measured characteristics of prepared OFETs based on a modified poly-(phenylene-vinylene), the observed hysteresis is analyzed.

Organic semiconductors on single-crystalline metal surfaces are model systems for injection contacts in organic field-effect transistors (OFET) and light-emitting diodes. They allow us to classify possible metal–organic interaction scenarios and to elucidate general tendencies, which most likely will also be found at metal–organic interfaces in real devices. In this contribution, we report a comprehensive investigation of the interface of perylene, a promising material for OFETs, with the close-packed noble metal surface Ag(111), using high-resolution electron energy loss spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy as surface analytical techniques. The most important findings are: In the monolayer, molecules are oriented flat and form an incommensurate, most probably fluid overlayer. The molecules interact electronically with the substrate and become weakly metallic. Scanning tunneling microscopy reveals a propensity of perylene molecules toward a specific adsorption site on Ag(111), if the influence of intermolecular interactions is inhibited. Film growth at room temperature is similar to Stranski–Krastanov type. Finally, co-planar adsorption of perylene on Ag(111) is metastable, and annealing the monolayer at 420 K leads to a structural transformation of the film. The perylene–Ag(111) interface can therefore be classified as weakly interacting.

Thin films of the perfluorinated phthalocyanines F16PcVO and F16PcCu were grown on insulator substrates by physical vapor deposition under high vacuum conditions to study their growth and electrical properties, analyzing them as possible candidates for n-type channel materials in organic field effect transistors. As insulator substrates, mica, amorphous SiO2, poly(styrene), poly(vinylchloride), poly(vinylcarbazole), poly(methylmetacrylate) and poly(vinylidenefluoride) were chosen, offering chemically different interactions with the molecules, degrees of order, and tribological characteristics. Optical absorption spectroscopy was used to analyze the alignment of the molecules relative to the substrates and the electronic coupling to adjacent molecules in the films. Electrical conduction measurements served to analyze the electronic coupling of the molecules parallel to the insulating substrates and to discuss the growth mode of films. Atomic force microscopy and scanning electron microscopy were chosen to study the morphology of the films. An inclined orientation at an average surface angle between 58° and 86° dependent on the different substrates was found for both F16Pc. In particular, on mica, thin conductive channels of the organic n-semiconductors could be formed at an average film thickness well below 10 nm at conductivities of up to 1.3 × 10-2 S cm-1. Conductive channels could also be formed on the different polymer substrates at, however, at least an order of magnitude smaller conductivity. Before these layers were formed on the polymers, semiconductor material diffused into the polymer substrates, dependent upon the substrate temperature during deposition relative to the glass transition temperature of the polymers. An influence of the viscous state of the polymer substrates was also seen on the intermolecular coupling detected in optical spectra. Based on these results, implications for the applicability of F16Pc as organic n-channels in organic field effect transistors are discussed.

The growth of the polycyclic aromatic hydrocarbon perylene on (110) oriented copper substrates has been studied by means of x-ray photoelectron spectroscopy, near-edge x-ray absorption spectroscopy, and atomic force microscopy. In the monolayer regime, the molecules are orientated with their molecular plane parallel to the substrate, whereas they adopt a tilted arrangement in multilayer films. For multilayers with thicknesses exceeding 10 nm, the molecules grow in a bulk-like structure with their long axes orientated upright to the substrate surface.

We demonstrate polymeric electrically programmable read-only-memory elements based on camphorsulfonic-acid–doped polyaniline lines. Their working mechanism relies on irreversible reduction of the electrical conductivity by Joule heating like electrical safety fuses. The heating power is supplied electrically. The critical power required to “blow up” the fuse is strongly reduced by notches. The influence of the notch design can be predicted reasonably well using a simple thermal model. The critical power becomes less than 1 mW for fuses with notches narrower than 2 μm. This power can be delivered by organic transistors already at modest voltages, opening the way of integration of these memory elements in all-polymer circuits.

We studied the self-organization process of F16CuPc films (20–30 ML) on stepped Al2O3 (1120) substrates. X-ray diffraction measurements revealed a highly ordered layered structure with the molecules in a nearly upright configuration. The morphology, investigated by atomic force microscopy, consisted of long (several microns) and narrow (20–100 nm) needlelike terraces unidirectionally aligned along one of the main crystallographic directions of the Al2O3 (1120) surface. High resolution atomic force microscopy images revealed in-plane molecular order with the molecular stacking direction parallel to the needlelike terraces. Such anisotropic morphology is the result of a self-organization process of F16CuPc in elongated crystallites driven to a preferential orientation by the interaction with the substrate. Spectroscopic ellipsometry showed that these films exhibit anisotropic optical properties correlated with the molecular arrangement.

Room temperature data of impedance and phase angle in pellets of electrochemically synthesized ClO4− doped poly(3-methylthiophene) (P3MT) were analyzed assuming the sample being represented by a parallel resistor-capacitor (RC) circuit or by a series RC circuit. The last assumption proved to be the correct one, and to confirm it we use the sample as the RC component of a resistor-capacitor-inductor series resonator. We discuss the possibility of this RC series behavior to be due to a charge-density wave characteristic also evidenced from the huge values of the low-frequency dielectric constant of the system.

A large contrast ratio (>ΔΤ = 60%) and rapid switching (0.3–1 s) electrochromic (EC) polymer device that consists of a laminated two-layer structure between two electrodes was prepared. The new design consists of an indium tin oxide (ITO) glass electrode, a cathodic EC polymer film, a solid electrolyte, and a counterelectrode that replaces the anodic EC polymer and ITO electrode. Four EC polymers including two new EC polymers, Poly[3-methyl-3′-propyl-3,4-dihydro-2H-thieno(3,4-b)(1,4)dioxepine] (PProDOT-MePro) and Poly[3,3-diethyl-3,4-dihydro-2H,7H-(1,4)dioxepino(2,3-c)pyrrole] (PProDOP-Et2), were synthesized as cathodic EC polymers. A carbon-based counterelectrode was prepared for comparison with an Au-based counterelectrode. Several kinds of polymer gel electrolytes were prepared for comparison. The devices (windows) were increased in area from 0.028 × 0.04 in.2, 1 × 1 in.2 to 3 × 3 in.2 Three main components, the EC polymer film, the gel electrolyte, and the counterelectrode, were studied and their optical properties, conductivities, and repeatabilities were compared. The effects of window size on the contrast ratio, switching speed, power usage, and repeatability were studied.