A Review of Low‐Temperature Solution‐Processed Metal Oxide Thin‐Film Transistors for Flexible Electronics

Following the ever-expanding technological demands, printed electronics has shown palpable potential to create new and commercially viable technologies that will benefit from its unique characteristics, such as, large-area and wide range of substrate compatibility, conformability and low-cost. Through the last few decades, printed/solution-processed field-effect transistors (FETs) and circuits have witnessed immense research efforts, technological growth and increased commercial interests. Although printing of functional inks comprising organic semiconductors has already been initiated in early 1990s, gradually the attention, at least partially, has been shifted to various forms of inorganic semiconductors, starting from metal chalcogenides, oxides, carbon nanotubes and very recently to graphene and other 2D semiconductors. In this review, the entire domain of printable inorganic semiconductors is considered. In fact, thanks to the continuous development of materials/functional inks and novel design/printing strategies, the inorganic printed semiconductor-based circuits today have reached an operation frequency up to several hundreds of kilohertz with only a few nanosecond time delays at the individual FET/inverter levels; in this regard, often circuits based on hybrid material systems have been found to be advantageous. At the end, a comparison of relative successes of various printable inorganic semiconductor materials, the remaining challenges and the available future opportunities are summarized.

Printed Electronics Based on Inorganic Semiconductors: From Processes and Materials to Devices.

A hysteresis-free and high-efficiency planar perovskite solar cell was developed using a solution-processed SnO2 electron-transporting layer (ETL). Tin(IV) isopropoxide dissolved in isopropanol (IPA) was spin-coated on a fluorine-doped tin oxide (FTO) substrate in a nitrogen atmosphere. The effects of annealing temperature and precursor concentration on the photovoltaic performance were systematically investigated. The annealing temperature was scanned from 100 °C to 500 °C, whereby the 250 °C-annealed SnO2 film demonstrated the best performance along with negligible current–voltage hysteresis. The SnO2 film annealed at 250 °C was X-ray amorphous, while it was observed to be nanocrystallite from SnO2 annealed at 500 °C. The faster stabilization of the photocurrent and lower interfacial capacitance for the 250 °C-annealed SnO2 than for the 500 °C-annealed one were responsible for the markedly reduced hysteresis. The photovoltaic performance and hysteresis were influenced by the precursor concentration, where a concentration of 0.1 M showed hysteresis-free higher performance among the concentrations investigated ranging from 0.05 M to 0.2 M owing to a larger and faster photoluminescence quenching. The planar (HC(NH2)2PbI3)0.875(CsPbBr3)0.125 perovskite that was formed on the 40 nm-thick, 0.1 M-based and 250 °C-annealed SnO2 thin film delivered a power conversion efficiency (PCE) of 19.17% averaged out from the forward scan PCE of 19.40% and the reverse scan PCE of 18.93%.

Solution-processed SnO2 thin film for a hysteresis-free planar perovskite solar cell with a power conversion efficiency of 19.2%

To achieve enhanced photocatalytic activity for the degradation of lindane, we prepared metal–semiconductor composite nanoparticles (NPs). Zn@ZnO core–shell (CS) nanocomposites, calcined ZnO, and Ag-doped ZnO (ZnO/Ag) nanostructures were prepared using pulsed laser ablation in liquid, calcination, and photodeposition methods, respectively, without using surfactants or catalysts. The as-prepared catalysts were characterized by using X-ray diffraction (XRD), field-emission scanning electron microscopy, high-resolution transmission electron microscopy, ultraviolet–visible (UV–vis) spectroscopy, and photoluminescence spectroscopy. In addition, elemental analysis was performed by energy dispersive X-ray spectroscopy. The obtained XRD and morphology results indicated good dispersion of Zn and Ag NPs on the surface of the ZnO nanostructures. Investigation of the photocatalytic degradation of lindane under UV–vis irradiation showed that Zn@ZnO CS nanocomposites exhibit higher photocatalytic activity than the other prepared samples. The maximum degradation rate of lindane was 99.5% in 40 min using Zn@ZnO CS nanocomposites. The radical trapping experiments verified that the hydroxyl radical (·OH) was the main reactive species for the degradation of lindane.

Enhanced photocatalytic degradation of lindane using metal-semiconductor Zn@ZnO and ZnO/Ag nanostructures.

A combined experimental and computational study is presented to identify the salient features of the adsorption of water molecules from a humid gas on the surface of a film of cadmium sulfide nanoparticles (CdSNPs). It is well known that, apart from showing exquisite optical and electrical properties, CdSNPs are also capable of adsorbing humidity from the gas or vapors. In the present study, we explore the variation in the electrical conductivity of a film of CdSNPs with the variation in the flowrate of a humid gas, which can lead to the development of a humidity or a flowrate sensor. The computational study shows that the increase in the concentration of adsorbed molecules with the enhancement in the flowrate of the humid gas can lead to a variation in the electrical conductance of the CdSNP film. The adsorption of water molecules on the sensor is correlated with the band bending of the CdSNP film owing to the ionization of the adsorbed molecules on the sensor surface. The electrical conductance of the sensor is found to vary in the range of 55–95% when the flowrate of the humid gas is varied from ∼200 to 600 L/min, at a relative humidity of ∼97%. A logarithmic dependence of the flowrate of the humid gas with the concentration of the water molecules adsorbed on the film surface is found to explain the experimental observations.

D.M. Priyadarshini

Papers

Effect of annealing ambient on SnO 2 thin film transistors

Enhanced photoluminescence and heterojunction characteristics of pulsed laser deposited ZnO nanostructures