The field of organic electronics has seen tremendous progress over the last years and all‐solution‐based processes are believed to be one of the key routes to ultra low‐cost roll‐to‐roll device and circuit fabrication. In this regard a variety of functional materials has been successfully designed for inkjet printing. While orthogonal‐solvent approaches have frequently been used to tackle the solubility issue in multilayer solution processing, the focus of this work lies on printed metal electrodes for organic field‐effect transistors (OFET) and their curing concepts. Two metallic inkjet‐printable materials are studied: i) a silver‐copper nanoparticle based dispersion and ii) a soluble organic silver‐precursor. Photoelectron spectroscopy reveals largely metallic properties of the cured materials, which are compared with respect to OFET performance and process‐related issues. Contact resistance of the prepared metal electrodes is significantly larger than that of evaporated top‐contact gold electrodes. As direct patterning via inkjet printing limits the reliably achievable channel length to values well above 10 μm, the influence of contact resistance is rather small, however, and overall device performance is comparable.

Solution-processable semiconductors, allowing cost effective mass production by printing or spraying techniques, are applicable to the fabrication of a wide range of electronic devices such as solar cells, [1] light-emitting diodes, [2,3] thin film transistors [4,5] and photodetectors. [6] The class of solution-processable semiconductors comprises soluble conjugated polymers or precursor molecules as well as colloidal, organic or inorganic nanoparticles. The latter usually have the advantage of a higher stability in ambient conditions. Inkjet-printing represents a powerful, economic tool for accurate deposition of liquids which is not only useful for graphics applications, but has also enormous potential for the direct writing of electronic devices. [4,7,8] Here, we show for the first time the highly reproducible ink-jet printing of semiconducting nanocrystals for the fabrication of optoelectronic devices. In particular, we printed photoconducting detectors operating in the infrared. Detectors operating in this spectral region are of particular importance for biological applications, remote sensing and night-vision imaging. We demonstrate (a) room temperature detectivities up to D* = 3.2 × 10 10 cm Hz 1/2 W -1 close to the important telecommunication wavelength region and (b) operation up to a wavelength of 3 lm, so far not achieved with any other solution processable material.Initially the high potential of inorganic nanocrystals for optoelectronic devices was demonstrated in light emitting diodes operating in the visible, based on blends of conjugated polymers and CdSe nanocrystals.[9] Reversing this concept led to the development of first photovoltaic devices, first harvesting only the visible part of the sun spectrum. [1,[10][11][12] Nowadays, attempts are reported to push the maximum wavelength of the solar cells further to the infrared, [13,14] however, with the degradation of their performance. For light detection in the infrared, besides photovoltaic devices [15] also photoconductive devices [6,16,17] have been studied. These are not necessarily based on polymer/nanocrystal blends, [15,17] but also densely packed inorganic nanocrystal films [6,16] have been applied. The inorganic films have the advantage of a higher stability in ambient conditions and offer the possibility to expand the spectral region of operation to even longer wavelength. E. g. devices operating up to 1.6 lm wavelength have been demonstrated with PbS nanocrystals [6] and operation up to 1.8 lm was obtained with hydrophilic HgTe nanocrystals.[16]The photosensitive material used in the presented study are hydrophobic HgTe nanocrystals (NC), initially synthesized in aqueous solution [18] at room temperature via a reaction between Hg(ClO 4 ) 2 and H 2 Te gas in the presence of short-chain hydrophilic thiols such as thioglycerol or mercaptoethanolamine as stabilizer. The sizes of the nanocrystals are controlled via Ostwald ripening by a post synthetic heat treatment at around 80°C. After synthesis the initial thiol shell is partly replaced ...

The fabrication of organic light‐emitting devices (OLEDs) from semiconducting polymer nanospheres (SPNs) deposited from aqueous dispersions is described. It is found that the active device layer consists of a homogeneous single layer of light‐emitting SPNs. The OLEDs exhibit an electroluminescence onset at the SPN energy gap, which can be attributed to field‐enhanced charge‐carrier injection at the nanostructured Al cathode.

We present a detailed and comprehensive picture of the photophysics including device applications within the polyfluorene family of conjugated polymers. First, the photophysics of pristine polyfluorenes in solution and film is outlined, including a discussion of the so-called β-phase, which is characterised by a more planar ground state configuration. Particular attention is also dedicated to the occurence of low energy emission bands, which often deteriorate the initially blue emission of polyfluorenes, especially in electroluminescent devices. Although the origin of these emission features has been the object of a controversial discussion, strong evidence for our current ascription to emissive on-chain fluorenone defects is given also in contrast to previous assignments to aggregates, excimers, or exciplexes. According to the current attribution fluorenone-containing polyfluorenes can be described as a guest host system. Following this picture the photoexcitation dynamics from the fs to the ms regime is outlined. Finally, polymer light emitting diodes (PLEDs) based on polyfluorene-type emitters are discussed, especially related to their degradation mechanisms and possible remedies provided by chemistry to reduce the oxidative degradation of polyfluorene-based PLEDs.

We report on a distinct defect related emission band between 2.45 and 2.6 eV in blue light emitting polyfluorene type polymer light emitting devices. The origin of this novel feature at 2.45–2.6 eV which becomes apparent in addition to the well investigated emission band from bulk keto defects at 2.3 eV is spatially located close to the cathode of the device. It is identified as being related to chemical defects in the polymer, formed by a chemical reaction of the polymer in the presence of the deposited cathode metals Al or Ca.

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We study the feasibility of semiconducting polymer nanospheres deposited from miniemulsions as an approach to form organic multilayer structures and devices from an all solution based process. A detailed study of the wetting and film forming properties of the dispersed semiconducting polymer nanospheres on different polar and non-polar organic surfaces is given. The transmission and fluorescence properties of the polymer multilayer structures are studied. Organic light emitting devices based on such multilayer structures are presented and their properties are discussed.