Study of the Hole Transport Processes in Solution-Processed Layers of the Wide Bandgap Semiconductor Copper(I) Thiocyanate (CuSCN)

Wide bandgap hole-transporting semiconductor copper(I) thiocyanate (CuSCN) has recently shown promise both as a transparent p-type channel material for thin-film transistors and as a hole-transporting layer in organic light-emitting diodes and organic photovoltaics. Herein, the hole-transport properties of solution-processed CuSCN layers are investigated. Metal-insulator-semiconductor capacitors are employed to determine key material parameters including: dielectric constant [5.1 (±1.0)], flat-band voltage [-0.7 (±0.1) V], and unintentional hole doping concentration [7.2 (±1.4) × 1017 cm-3]. The density of localized hole states in the mobility gap is analyzed using electrical field-effect measurements; the distribution can be approximated invoking an exponential function with a characteristic energy of 42.4 (±0.1) meV. Further investigation using temperature-dependent mobility measurements in the range 78-318 K reveals the existence of three transport regimes. The first two regimes observed at high (303-228 K) and intermediate (228-123 K) temperatures are described with multiple trapping and release and variable range hopping processes, respectively. The third regime observed at low temperatures (123-78 K) exhibits weak temperature dependence and is attributed to a field-assisted hopping process. The transitions between the mechanisms are discussed based on the temperature dependence of the transport energy. The wide bandgap p-type semiconductor copper(I) thiocyanate (CuSCN) has the potential to replace conventional hole-transport materials in numerous opto/electronics applications. This work provides a comprehensive analysis of the charge transport properties of solution-processed CuSCN layers. Various techniques are employed to evaluate the dielectric constant, flat-band voltage, unintentional doping concentration, density of states in the mobility gap, and hole-transport mechanisms.Department of Applied PhysicsMaterials Research Centr

Body image transformation after breast cancer diagnosis and treatment in southern Thai women

Objective: To understand the transition of changed body image after the diagnosis and surgery in women with breast cancer. Methods: Semi-structured interview and focus group with narrative approach. Thematic analysis was performed using methodological and investigator triangulation methods. Results: Participants’ body image transformation was categorized into three phases: (1) the moment of diagnosis and changed self, (2) transition and recovery, and (3) normalization. Conclusion: The truth-telling process of breast cancer diagnosis and the freedom to choose their treatment options have a profound impact on body image transformation of women with breast cancer. Family support, social construction, and social support could help women with breast cancer pass through these transitional process faster, while inappropriate truth-telling by their surgeons and not having any choice in their treatment options will delay the transitional process

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

Origin of Hole-Trapping States in Solution-Processed Copper(I) Thiocyanate (CuSCN) and Defect-Healing by I2_2 Doping

Solution-processed copper(I) thiocyanate (CuSCN) typically exhibits low crystallinity with short-range order; the defects result in a high density of trap states that limit the device performance. Despite the extensive electronic applications of CuSCN, its defect properties have not been studied in detail. Through X-ray absorption spectroscopy, pristine CuSCN prepared from the standard diethyl sulfide-based recipe is found to contain under-coordinated Cu atoms, pointing to the presence of SCN vacancies. A defect passivation strategy is introduced by adding solid I$_2$ to the processing solution. At small concentrations, the iodine is found to exist as I$^-$ which can substitute for the missing SCN$^-$ ligand, effectively healing the defective sites and restoring the coordination around Cu. Applying I$_2$-doped CuSCN as a p-channel in thin-film transistors shows that the hole mobility increases by more than five times at the optimal doping concentration of 0.5 mol%. Importantly, the on/off current ratio and the subthreshold characteristics also improve as the I$_2$ doping method leads to the defect healing effect while avoiding the creation of detrimental impurity states. An analysis of the capacitance-voltage characteristics corroborates that the trap state density is reduced upon I$_2$ addition. The contact resistance and bias-stress stability of the devices also improve. This work shows a simple and effective route to improve hole transport properties of CuSCN which is applicable to wide-ranging electronic and optoelectronic applications

Solution-processed p-type copper(I) thiocyanate (CuSCN) for low-voltage flexible thin-film transistors and integrated inverter circuits

We report on low operating voltage thin-film transistors (TFTs) and integrated inverters based on copper(I) thiocyanate (CuSCN) layers processed from solution at low temperature on freestanding plastic foils. As-fabricated coplanar bottom-gate and staggered top-gate TFTs exhibit hole-transporting characteristics with average mobility values of 0.0016 cm2 V1 s 1 and 0.013 cm2 V1 s 1 , respectively, current on/off ratio in the range 102 –104 , and maximum operating voltages between 3.5 and 10 V, depending on the gate dielectric employed. The promising TFT characteristics enable fabrication of unipolar NOT gates on flexible free-standing plastic substrates with voltage gain of 3.4 at voltages as low as 3.5 V. Importantly, discrete CuSCN transistors and integrated logic inverters remain fully functional even when mechanically bent to a tensile radius of 4 mm, demonstrating the potential of the technology for flexible electronics

Copper (I) selenocyanate (CuSeCN) as a novel hole-transport layer for transistors, organic solar cells, and light-emitting diodes

The synthesis and characterization of copper (I) selenocyanate (CuSeCN) and its application as a solution-processable hole-transport layer (HTL) material in transistors, organic light-emitting diodes, and solar cells are reported. Density-functional theory calculations combined with X-ray photoelectron spectroscopy are used to elucidate the electronic band structure, density of states, and microstructure of CuSeCN. Solution-processed layers are found to be nanocrystalline and optically transparent ( > 94%), due to the large bandgap of ≥3.1 eV, with a valence band maximum located at -5.1 eV. Hole-transport analysis performed using field-effect measurements confirms the p-type character of CuSeCN yielding a hole mobility of 0.002 cm 2 V -1 s -1 . When CuSeCN is incorporated as the HTL material in organic light-emitting diodes and organic solar cells, the resulting devices exhibit comparable or improved performance to control devices based on commercially available poly(3,4-ethylenedioxythiophene):polystyrene sulfonate as the HTL. This is the first report on the semiconducting character of CuSeCN and it highlights the tremendous potential for further developments in the area of metal pseudohalides

Copper(I) Thiocyanate (CuSCN) Hole-Transport Layers Processed from Aqueous Precursor Solutions and Their Application in Thin-Film Transistors and Highly Efficient Organic and Organometal Halide Perovskite Solar Cells

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

Electronic Properties of Copper(I) Thiocyanate (CuSCN)

With the emerging applications of copper(I) thiocyanate (CuSCN) as a transparent and solution-processable hole-transporting semiconductor in numerous opto/electronic devices, fundamental studies that cast light on the charge transport physics are essential as they provide insights critical for further materials and devices performance advancement. The aim of this article is to provide a comprehensive and up-to-date report of the electronic properties of CuSCN with key emphasis on the structure–property relationship. The article is divided into four parts. In the first section, recent works on density functional theory calculations of the electronic band structure of hexagonal β-CuSCN are reviewed. Following this, various defects that may contribute to the conductivity of CuSCN are discussed, and newly predicted phases characterized by layered 2-dimensional-like structures are highlighted. Finally, a summary of recent studies on the band-tail states and hole transport mechanisms in solution-deposited, polycrystalline CuSCN layers is presented