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High mobility thin‐film transistor technologies that can be implemented using simple and inexpensive fabrication methods are in great demand because of their applicability in a wide range of emerging optoelectronics. Here, a novel concept of thin‐film transistors is reported that exploits the enhanced electron transport properties of low‐dimensional polycrystalline heterojunctions and quasi‐superlattices (QSLs) consisting of alternating layers of In2O3, Ga2O3, and ZnO grown by sequential spin casting of different precursors in air at low temperatures (180–200 °C). Optimized prototype QSL transistors exhibit band‐like transport with electron mobilities approximately a tenfold greater (25–45 cm2 V−1 s−1) than single oxide devices (typically 2–5 cm2 V−1 s−1). Based on temperature‐dependent electron transport and capacitance‐voltage measurements, it is argued that the enhanced performance arises from the presence of quasi 2D electron gas‐like systems formed at the carefully engineered oxide heterointerfaces. The QSL transistor concept proposed here can in principle extend to a range of other oxide material systems and deposition methods (sputtering, atomic layer deposition, spray pyrolysis, roll‐to‐roll, etc.) and can be seen as an extremely promising technology for application in next‐generation large area optoelectronics such as ultrahigh definition optical displays and large‐area microelectronics where high performance is a key requirement.

This study reports the development of copper(I) thiocyanate (CuSCN) hole-transport layers (HTLs) processed from aqueous ammonia as a novel alternative to conventional n-alkyl sulfide solvents. Wide bandgap (3.4–3.9 eV) and ultrathin (3–5 nm) layers of CuSCN are formed when the aqueous CuSCN–ammine complex solution is spin-cast in air and annealed at 100 °C. X-ray photoelectron spectroscopy confirms the high compositional purity of the formed CuSCN layers, while the high-resolution valence band spectra agree with first-principles calculations. Study of the hole-transport properties using field-effect transistor measurements reveals that the aqueous-processed CuSCN layers exhibit a fivefold higher hole mobility than films processed from diethyl sulfide solutions with the maximum values approaching 0.1 cm2 V−1 s−1. A further interesting characteristic is the low surface roughness of the resulting CuSCN layers, which in the case of solar cells helps to planarize the indium tin oxide anode. Organic bulk heterojunction and planar organometal halide perovskite solar cells based on aqueous-processed CuSCN HTLs yield power conversion efficiency of 10.7% and 17.5%, respectively. Importantly, aqueous-processed CuSCN-based cells consistently outperform devices based on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate HTLs. This is the first report on CuSCN films and devices processed via an aqueous-based synthetic route that is compatible with high-throughput manufacturing and paves the way for further developments

An aqueous and carbon-free metal-oxide precursor route is used in combination with a UV irradiation-assisted low-temperature conversion method to fabricate low-voltage ZnO transistors with electron mobilities exceeding 10 cm(2) /Vs at temperatures <180 °C. Because of its low temperature requirements the method allows processing of high-performance transistors onto temperature sensitive substrates such as plastic.

Oxide semiconductor based thin-fi lm transistors (TFTs) are a promising technology for application in large-area electronics. [ 1 ] Despite their relatively short history, oxide TFTs with chargecarrier mobilities exceeding 100 cm 2 V − 1 s − 1 [ 2,3 ] have already been demonstrated, a performance that is superior to that of amorphous silicon (a-Si) and comparable to polycrystalline Si (poly-Si). Unfortunately, these high-mobility oxide TFTs are usually manufactured using costly vacuum-based processing methodologies. [ 1 , 4-8 ] In an effort to address this problem, recent research has been focussing on the development of TFTs using alternative deposition methods based on solution-processable oxide semiconductors. [ 9 -14 ] Whilst progress on solution-processed oxide semiconductors has been rapidly advancing, research efforts towards the development of new dielectrics has been relatively slow, with most of the reported work performed using conventional dielectrics (e.g., SiO 2 ) with few exceptions. [ 9 , 15,16 ] As a result, the majority of oxide transistors reported to date operate at relatively high voltages and hence consume signifi cantly more power. In order to circumvent this bottleneck, recent work has been focusing on the development of low-voltage oxide transistors, including the use of ultra-thin dielectrics, [ 17 ] high -k dielectrics, [ 15 ] and electrolyte gate dielectrics. [ 18 ] Oxide transistors based on high -k dielectrics have received the most attention and a number of high mobility, low-voltage devices have been demonstrated. [ 15 , 17 ] The high -k materials studied to date include transition metal oxides such as Ta 2 O 5 , TiO 2 , [19][20][21][22] ZrO 2 , [23][24][25][26] Al 2 O 3 , [ 27 ] HfO 2 , [ 28 ] and silicates, [ 29 ] as well as ferroelectric materials such as Pb(Zr,Ti) O 3 and (Ba,Sr)TiO 3 . [ 30 , 31 ] Among these, ZrO 2 and HfO 2 are the most extensively studied dielectrics and are widely considered to be excellent candidates because of their relatively high dielectric constants, good thermal stability, and large band gaps. [32][33][34] Despite their attractive properties, however, ZrO 2 and HfO 2 based TFTs are usually realised using stringent and potentially costly manufacturing techniques. [35][36][37][38][39] Here we demonstrate how spray pyrolysis (SP), a simple and large-area-compatible deposition technique, can be used for the processing of high-quality ZrO 2 layers onto glass substrates containing prepatterned indium tin oxide (ITO) electrodes. We demonstrate their use in high-mobility, low-voltage TFTs based on either ZnO or Li-doped ZnO fi lms deposited by SP [10][11][12][13][14] directly onto ITO/ZrO 2 . Optimised TFTs based on ITO/ZrO 2 / Li-ZnO multilayer structures deposited sequentially at substrate temperatures of 400-450 ° C exhibit excellent electrontransport characteristics with operating voltages below 6 V and a maximum electron mobility on the order of 85 cm 2 V − 1 s − 1 . To our knowledge, this is the highest reported mobility value for transistors bas...

24.04.15 KB. OK to add published OA paper to spira

The present work details a facile and low-temperature (125C) solution-processed Al-doped ZnO (AZO) buffer layer functioning very effectively as electron accepting/hole blocking layer for a wide range of polymer:fullerene bulk heterojunction systems, and yielding power conversion efficiency in excess of 10% (8%) on glass (plastic) substrates. We show that ammonia addition to the aqueous AZO nanoparticle solution is a critically important step toward producing compact and smooth thin films which partially retain the aluminum doping and crystalline order of the starting AZO nanocrystals. The ammonia treatment appears to reduce the native defects via nitrogen incorporation, making the AZO film a very good electron transporter and energetically matched with the fullerene acceptor. Importantly, highly efficient solar cells are achieved without the need for additional surface chemical passivation or modification, which has become an increasingly common route to improving the performance of evaporated or solution-processed ZnO ETLs in solar cells.

Coplanar electrodes formed from asymmetric metals separated on the nanometre length scale are essential elements of nanoscale photonic and electronic devices. Existing fabrication methods typically involve electron-beam lithography—a technique that enables high fidelity patterning but suffers from significant limitations in terms of low throughput, poor scalability to large areas and restrictive choice of substrate and electrode materials. Here, we describe a versatile method for the rapid fabrication of asymmetric nanogap electrodes that exploits the ability of selected self-assembled monolayers to attach conformally to a prepatterned metal layer and thereby weaken adhesion to a subsequently deposited metal film. The method may be carried out under ambient conditions using simple equipment and a minimum of processing steps, enabling the rapid fabrication of nanogap electrodes and optoelectronic devices with aspect ratios in excess of 100,000.