Research on solution processible semiconducting materials is rapidly making progress towards the goal of providing viable alternatives to silicon-based technologies for applications where lower-cost manufacturing and new product features such as mechanical flexibility and optical transparency are desired. One family of materials that has been the subject of intense research over the past twenty years is organic semiconductors.[1] Use of organic materials offers the prospect of low manufacturing cost combined with some desirable physical characteristics such as ease of processing and mechanical flexibility. Despite the impressive progress achieved in recent years a number of obstacles, especially poor air-stability, device performance that is insufficient for a variety of applications and device to device variability, have to be overcome before the advantageous manufacturability, and hence the economic benefits associated with organic semiconductors, can be fully exploited.While research in the area of organic materials and devices has been intensifying, a different class of semiconducting materials, namely metal oxide semiconductors (MOxS), has emerged as possible alternative technology.[2] Metal oxides incorporate important qualities that are currently absent from organic-based semiconductors. For instance, they generally exhibit higher carrier mobilities which are already sufficient for use in optical displays, such as current-driven organic light-emitting diode (OLED) based displays. An additional advantage of MOxS relevant to many electronic applications is the superb optical transparency resulting -2 -from their wide bandgap. The latter makes oxide semiconductors particularly interesting for use in transparent electronics [3] as well as in backplanes for the next generation of currentdriven displays. [4,5] For application in see-through electronics, in particular, transparent thin-film transistors (TFTs) with high switching speeds and low power consumption are required.[6] So far the opacity of amorphous silicon and the insufficient performance of organic semiconductors have impeded the development of such devices. In this respect, MOxS materials simultaneously fulfil the requirements for optical transparency and high charge carrier mobility. In addition, they provide excellent chemical stability combined with mechanical robustness. [7] A further advantage associated with MOxS is the diverse range of techniques that can be employed for thin-film deposition.[7] These include, sputtering, [8][9][10] pulsed-laser deposition (PLD), [11] metalorganic chemical vapour deposition (MOCVD), [12,13] as well as solution processing methods such as dip coating, [14] spin coating [15][16][17][18] and spray pyrolysis (SP). [19][20][21] Solution processing, in particular, offers a number of advantages, which are well known from the area of organic electronics, with the most important being the prospect of easy patterning on large area substrates. In most cases, however, control over the morphology of solution processed film...

The ever increasing demand for high performance electronic devices that can be fabricated onto large-area substrates employing low manufacturing cost techniques has given a boost to the development of alternative types of semiconductor materials, such as organics and metal oxides, with desirable physical characteristics that are absent in their traditional inorganic counterparts. Metal oxide semiconductors, in particular, are very attractive for implementation into thin-film transistors (TFTs) [1][2] mainly because of their high charge 2 carrier mobility, high optical transparency, excellent chemical stability, mechanical stress tolerance and processing versatility [3][4][5] . Oxide semiconductors are usually grown using vacuum-based techniques such as sputtering [6][7][8] , pulsed laser deposition [9] , chemical vapour deposition [10] , and ion-assisted deposition [11][12] . Based on these methods, the synthesis of a wide range of metal oxide semiconductors with high charge carrier mobilities and low carrier concentration has been demonstrated [7] . Many of these materials have been investigated for applications in thin-film electronics where transistors with electron mobilities up to 140 cm 2 /Vs have been demonstrated [7,[11][12][13][14][15][16] . Despite the great promise however, the application of vacuum-based technologies for the deposition of complex oxide semiconductors suffers from incompatibility with large-area substrates and hence high manufacturing cost. To this end, the development of alternative deposition methods based on solution processing paradigms could provide a breakthrough in both cost and performance by marrying fabrication simplicity with high-throughput manufacturing.In recent years a wide variety of soluble precursors compounds have been examined as potential alternatives for the fabrication of oxide-based TFTs using large area deposition methods including spin casting, dip coating and spray pyrolysis. For example, metal oxides such as zinc oxide (ZnO) [17][18][19][20][21][22] , indium oxide (In 2 O 3 ) [23][24] , indium gallium oxide (InGaO) [25] , indium zinc oxide (InZnO) [18][19][20][21][22][23][24][25][26] and zinc tin oxide (ZnSnO) [27] have been synthesised using soluble precursors and implemented into TFT structures. Despite the process simplicity, excellent charge carrier mobilities have been achieved, clearly demonstrating the significant potential of this alternative processing methodology. Here we show how spray pyrolysis (SP) can be used for the deposition of doped ZnO films and the fabrication of high electron mobility TFTs onto large area substrates under ambient atmosphere. Doping is achieved by simple physical blending of the soluble precursor compounds in water or alcohol based solutions. Among the various dopants studied, transistors fabricated using Li doped ZnO were 3 found to yield the best performance with maximum electron mobility > 50 cm 2 /Vs and on/off current modulation ratio exceeding 10 6 .Preparation of the Li doped precursor solutions is described in th...

The role of the substrate temperature on the structural, optical, and electronic properties of ZnO thin films deposited by spray pyrolysis using a zinc acetate precursor solution is reported. Analysis of the precursor compound using thermogravimentry and differential scanning calorimetry indicates complete decomposition of the precursor at around 350 °C. Film characterization using Fourier Transform Infrared Spectroscopy (FTIR), photoluminescence spectroscopy (PL), and ultraviolet–visible (UV–Vis) optical transmission spectroscopy suggests the onset of ZnO growth at temperatures as low as 100 °C as well as the transformation to a polycrystalline phase at deposition temperatures >200 °C. Atomic force microscopy (AFM) and X‐ray diffraction (XRD) reveal that as‐deposited films exhibit low surface roughness (rms ≈ 2.9 nm at 500 °C) and a crystal size that is monotonously increasing from 8 to 32 nm for deposition temperatures in the range of 200–500 °C. The latter appears to have a direct impact on the field‐effect electron mobility, which is found to increase with increasing ZnO crystal size. The maximum mobility and current on/off ratio is obtained from thin‐film transistors fabricated using ZnO films deposited at >400 °C yielding values on the order of 25 cm2 V−1s−1 and 106, respectively.

An alternative approach for the development of high‐performance unipolar and ambipolar thin‐film transistors and integrated circuits based on hybrid heterostructures comprising a phase‐separated solution processed p‐type organic small‐molecule:polymer semicondcutor blend and a spray‐coated n‐type ZnO semiconductor layer is demonstrated.

We report the application of spray pyrolysis (SP) for the deposition of high quality zinc oxide (ZnO) films and the fabrication of thin-film transistors. The chemical, structural, optical, and electronic properties of as-deposited ZnO films are studied using infrared spectroscopy, atomic force microscopy, UV-visible spectroscopic ellipsometry, and field-effect measurements. SP ZnO films are found to be uniform and polycrystalline with a band gap of 3.32 eV. ZnO transistors exhibit n-channel characteristics with electron mobility in the range 10–22 cm2/Vs. Device performance is found to depend on the work function of source/drain metal electrodes and on the device architecture employed.