Stuart Thomas

High‐Mobility Low‐Voltage ZnO and Li‐Doped ZnO Transistors Based on ZrO2 High‐k Dielectric Grown by Spray Pyrolysis in Ambient Air

Sequential layers of the high-k dielectric ZrO2 and the electron transporting semiconductors ZnO and Li-doped ZnO are deposited onto conductive indium tin oxide electrodes using spray pyrolysis. With these structures, thin-film transistors are fabricated with operating voltages below 6 V and maximum electron mobilities on the order of 85 cm(2) V-1 s(-1).

Solution-processable metal oxide semiconductors for thin-film transistor applications

In this review, we discuss the merits of solution-processed metal oxide semiconductors and consider their application in thin-film transistors for large-area electronics.

The Influence of Polymer Purification on Photovoltaic Device Performance of a Series of Indacenodithiophene Donor Polymers

A series of low bandgap indacenodithiophene polymers is purified by recycling SEC in order to isolate narrow polydispersity fractions. This additional purification step is found to have a significant beneficial influence on the solar cell performance and the reasons for this performance increase are investigated.

Spray-Deposited Li-Doped ZnO Transistors with Electron Mobility Exceeding 50 cm(2)/Vs

Ambient spray pyrolysis is used for the deposition of high quality polycrystalline ZnO films utilizing blends of precursor solutions based on Zinc and Lithium acetates and the demonstration of n-channel thin-film transistors with electron mobility exceeding 50 cm(2)/Vs (see figure).

Low-voltage ZnO thin-film transistors based on Y2O3 and Al2O3 high-k dielectrics deposited by spray pyrolysis in air

We report the application of ambient spray pyrolysis for the deposition of high-k polycrystalline Y2O3 and amorphous Al2O3 dielectrics and their use in low-voltage ZnO thin-film transistors. The films are studied by means of atomic force microscopy, UV-visible absorption spectroscopy, impedance spectroscopy, and field-effect measurements. ZnO transistors based on spray pyrolysed Y2O3 and Al2O3 dielectrics show low leakage currents, and hysteresis-free operation with a maximum electron mobility of 34 cm2/V s and current on/off ratio on the order of 105. This work is a significant step toward high-performance oxide electronics manufactured using simple and scalable processing methods.

Synthesis of novel thieno[3,2-b]thienobis(silolothiophene) based low bandgap polymers for organic photovoltaics

Thieno[3,2-b]thienobis(silolothiophene), a new electron rich hexacyclic monomer has been synthesized and incorporated into three novel donor-acceptor low-bandgap polymers. By carefully choosing the acceptor co-monomer, the energy levels of the polymers could be modulated and high power conversion efficiencies of 5.52% were reached in OPV devices.

p-channel thin-film transistors based on spray-coated Cu2O films

Thin films of cuprous oxide (Cu2O) were grown using solution-based spray pyrolysis in ambient air and incorporated into hole-transporting thin-film transistors. The phase of the oxide was confirmed by X-ray diffraction measurements while the optical band gap of the films was determined to be ∼2.57 eV from optical transmission measurements. Electrical characterization of Cu2O films was performed using bottom-gate, bottom-contact transistors based on SiO2 gate dielectric and gold source-drain electrodes. As-prepared devices show clear p-channel operation with field-effect hole mobilities in the range of 10−4–10−3 cm2 V−1 s−1 with some devices exhibiting values close to 1 × 10−2 cm2 V−1 s−1.

Indium oxide thin-film transistors processed at low temperature via ultrasonic spray pyrolysis.

The use of ultrasonic spray pyrolysis is demonstrated for the growth of polycrystalline, highly uniform indium oxide films at temperatures in the range of 200-300 °C in air using an aqueous In(NO3)3 precursor solution. Electrical characterization of as-deposited films by field-effect measurements reveals a strong dependence of the electron mobility on deposition temperature. Transistors fabricated at ∼250 °C exhibit optimum performance with maximum electron mobility values in the range of 15-20 cm(2) V (-1) s(-1) and current on/off ratio in excess of 10(6). Structural and compositional analysis of as-grown films by means of X-ray diffraction, diffuse scattering, and X-ray photoelectron spectroscopy reveal that layers deposited at 250 °C are denser and contain a reduced amount of hydroxyl groups as compared to films grown at either lower or higher temperatures. Microstructural analysis of semiconducting films deposited at 250 °C by high resolution cross-sectional transmission electron microscopy reveals that as-grown layers are extremely thin (∼7 nm) and composed of laterally large (30-60 nm) highly crystalline In2O3 domains. These unique characteristics of the In2O3 films are believed to be responsible for the high electron mobilities obtained from transistors fabricated at 250 °C. Our work demonstrates the ability to grow high quality low-dimensional In2O3 films and devices via ultrasonic spray pyrolysis over large area substrates while at the same time it provides guidelines for further material and device improvements.

High electron mobility thin-film transistors based on Ga2O3 grown by atmospheric ultrasonic spray pyrolysis at low temperatures

We report on thin-film transistors based on Ga2O3 films grown by ultrasonic spray pyrolysis in ambient atmosphere at 400–450 °C. The elemental, electronic, optical, morphological, structural, and electrical properties of the films and devices were investigated using a range of complementary characterisation techniques, whilst the effects of post deposition annealing at higher temperature (700 °C) were also investigated. Both as-grown and post-deposition annealed Ga2O3 films are found to be slightly oxygen deficient, exceptionally smooth and exhibit a wide energy bandgap of ∼4.9 eV. Transistors based on as-deposited Ga2O3 films show n-type conductivity with the maximum electron mobility of ∼2 cm2/V s.

Solution-processed dye-sensitized ZnO phototransistors with extremely high photoresponsivity

We report the fabrication of light-sensing thin-film transistors based on solution processed films of ZnO, as the channel material, functionalized with an organic dye as the light sensitizer. Due to the presence of the dye, the hybrid devices show exceptionally high photosensitivity to green light of 106 and a maximum photoresponsivity on the order of 104 A/W. The high performance is argued to be the result of the grain barrier limited nature of electron transport across the polycrystalline ZnO film and its dependence on charge carrier density upon illumination with green light. In addition to the excellent photoresponsivity and signal gain, the hybrid ZnO-dye photoactive layer exhibits high optical transparency. The unique combination of simple device fabrication and distinctive physical characteristics, such as optical transparency, renders the technology attractive for application in large-area transparent photodetectors.