Inkjet‐Printed Nanocrystal Photodetectors Operating up to 3 μm Wavelengths

Abstract

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 ...

Short-wave infrared colloidal quantum dot photodetectors on silicon

“…By tuning the size of the QDs, the electrical and optical properties (such as the absorption cut-off wavelength) can be tuned due to the quantum size effect 8 . Furthermore, the fact that these QDs are available in solution makes it easy to do large-area heterogeneous integration on substrates, using dip coating or printing, which can offer a considerable cost reduction as compared to thermal evaporation or epitaxially grown layer stacks 9 . Therefore, in this paper we investigate the use of two kinds of colloidal quantum dot materials, PbS and HgTe, for shortwave infrared photodetector application.…”

Infrared Emitting HgTe Quantum Dots and Their Waveguide and Optoelectronic Devices

“…In subsequent work they extended this idea by decorating a ZnO nanowire with HgTe QDs directly on the surface so that when illuminated at energies above the HgTe QD bandgap but below the ZnO bandgap the resulting QD photocharge on the outside of the nanowire reduced the width of the conduction channel along its axis giving rise to a photogating effect in the nanowire's photoconductive response [98]. From about 2006 onwards the Heiss group also turned their attention to HgTe photodetectors and in 2007 [99] reported the fabrication of HgTe QD pho- toconductive thin film detectors fabricated by inkjet printing from organic solvent (see Figure 11c). The QDs had been synthesized by the aqueous route and then transferred into organic solvent by ligand exchange of the short chain water soluble thiols for dodecanethiol.…”

Micropattern Deposition of Colloidal Semiconductor Nanocrystals by Aerodynamic Focusing

“…Because these properties can also be easily tailored through choice of growth conditions, they are potentially useful for various optoelectronic devices, including light-emitting diodes (Colvin et al 1994;Steckel et al 2003), photodetectors (Böberl et al 2007; Konstantatos et al 2006;Oertel et al 2005), and solar cells (Gur et al 2005;Huynh et al 2002;Leschkies et al 2007;Liu and Kamat 1993;Robel et al 2006). For some of these devices, the deposition of NC assemblies with controlled patterns is an essential step in the fabrication process.…”

“…Common methods include drop casting (Murray et al 2001), spin coating (Finlayson et al 2000;Snee et al 2005), electrophoretic deposition (Islam and Herman 2002), and mist deposition (Zhu et al 2008). Direct-write methods such as ink-jet printing (Böberl et al 2007;Tekin et al 2007) are also attractive because they avoid mask screening, lithography, and pre-patterning of the substrate and can therefore simplify micropatterning and allow inexpensive and rapid prototyping (Chrisey 2000).…”