Electrical transport through self-assembled colloidal nanomaterials and their perspectives

Colloidal nanoparticles developed as interesting objects to establish twoor threedimensional super-structures with properties not known from conventional bulk materials. Beyond, the properties can be tuned and quantum effects can be exploited. This allows understanding electronic and optoelectronic transport phenomena and developing corresponding devices. The state-of-the-art in this field will be reviewed and possible challenges and prospects will be identified. focus article Copyright c © EPLA, 2017 Introduction. – In the recent years, 2D and 3D material printing developed to a serious alternative in product development and even in customized serial production. Beyond pure massive objects it is a vision to be able to process semiconductor channels and metal circuits by easy and cheap assembly techniques, like roll-to-roll processing, microcontact printing, offset printing, dip-coating, and mainly inkjet printing. This could lead to transistors, photo-sensors, light-emitting diodes (LEDs), display devices, solar cells, or even whole integrated circuits, such as radio-frequency identification devices (RFID). By 3D printing layered layouts become possible, with insulating but interconnecting layers between the circuits or even 3D device architectures are conceivable. Such a device could include energy harvesting (printed solar cells), energy storage (in batteries or super-capacitors), information processing in a layer in between, and a display technology (LEDs), all processed on flexible substrates. In order to have available corresponding inks, inorganic solutionsuspended high-quality materials are necessary. The colloidal synthesis of nanostructures offers the possibility to tune the properties of the materials over a wide range, e.g., the optical bandgap of semiconductor nanoparticles is a matter of size. In solution they can be produced at low material and energy costs, with (a)Contribution to the Focus Issue Self-assemblies of Inorganic and Organic Nanomaterials edited by Marie-Paule Pileni. (b)E-mail: [email protected] high flexibility and efficiency in synthesis, and with high tunability in their properties. Conceivable are faster and less expensive processors, more efficient solar cells and fuel cells, batteries and super-capacitors with faster charging periods, more charging cycles, and higher capacities. This is mostly due to the materials’ low-dimensional nature which results in quantum effects and/or high surface-tovolume ratios. Their properties might depend not only on their atomic composition but also on their dimensions. Scientifically, low-dimensional objects represent exceptionally interesting model systems which allow the extension of classical and the development of new concepts with ground-breaking insights [1]. Also for future technologies this opens new perspectives: Examples are single-electron transistors [2,3], well-defined tunable optical emitters [4,5], and efficient charge storage [6,7]. Further they can be used as fluorescence markers in medicine and biology [8,9] in tumor staining [10,11] in hyperthermia [12,13] and as NMR contrast agents [14,15]. In flat panel displays they are used in modern background illumination systems (e.g., in SonyTM displays with TriluminosTM technology) [16]. Thin films of semiconductor nanoparticles can be used as active layers for inexpensive transistors [17,18], photo-detectors [19,20], solar cells [21–23], and as chemical sensors [24,25]. Syntheses, materials and properties. – Inorganic colloidal nanoparticles are usually defined by organic ligands. In most cases, such ligands are long-chained