The atomic composition ratio of solution-processed oxide semiconductors is crucial in controlling the electrical performance of thin-film transistors (TFTs) because the crystallinity and defects of the random network structure of oxide semiconductors change critically with respect to the atomic composition ratio. Herein, the relationship between the film properties of nitrate precursor-based indium-zinc-oxide (IZO) semiconductors and electrical performance of solution-processed IZO TFTs with respect to the In molar ratio was investigated. The thickness, morphological characteristics, crystallinity, and depth profile of the IZO semiconductor film were measured to analyze the correlation between the structural properties of IZO film and electrical performances of the IZO TFT. In addition, the stoichiometric and electrical properties of the IZO semiconductor films were analyzed using film density, atomic composition profile, and Hall effect measurements. Based on the structural and stoichiometric results for the IZO semiconductor, the doping effect of the IZO film with respect to the In molar ratio was theoretically explained. The atomic bonding structure by the In doping in solution-processed IZO semiconductor and resulting increase in free carriers are discussed through a simple bonding model and band gap formation energy.

Understanding the chemical reaction pathway of the metal–salt precursor is essential for modifying the properties of solution-processed metal-oxide thin films and further improving their electrical performance. In this study, we focused on the structural growth of solution-processed amorphous indium-zinc-oxide (a-IZO) films and the electrical behavior of a-IZO thin-film transistors (TFT). To this end, solution-processed a-IZO films were prepared with respect to the Zn molar ratio, and their structural characteristics were analyzed. For the structural characteristic analysis of the a-IZO film, the cross-section, morphology, crystallinity, and atomic composition characteristics were used as the measurement results. Furthermore, the chemical reaction pathway of the nitrate precursor-based IZO solution was evaluated for the growth process of the a-IZO film structure. These interpretations of the growth process and chemical reaction pathway of the a-IZO film were assumed to be due to the thermal decomposition of the IZO solution and the structural rearrangement after annealing. Finally, based on the structural/chemical results, the electrical performance of the fabricated a-IZO TFT depending on the Zn concentration was evaluated, and the electrical behavior was discussed in relation to the structural characteristics.

Understanding the density of state (DOS) distribution in solution-processed indium-zinc-oxide (IZO) thin-film transistors (TFTs) is crucial for addressing electrical instability. This paper presents quantitative calculations of the acceptor-like state distribution of solution-processed IZO TFTs using thermal energy analysis. To extract the acceptor-like state distribution, the electrical characteristics of IZO TFTs with various In molarity ratios were analyzed with respect to temperature. An Arrhenius plot was used to determine electrical parameters such as the activation energy, flat band energy, and flat band voltage. Two calculation methods, the simplified charge approximation and the Meyer–Neldel (MN) rule-based carrier–surface potential field-effect analysis, were proposed to estimate the acceptor-like state distribution. The simplified charge approximation established the modeling of acceptor-like states using the charge–voltage relationship. The MN rule-based field-effect analysis validated the DOS distribution through the carrier–surface potential relationship. In addition, this study introduces practical and effective approaches for determining the DOS distribution of solution-processed IZO semiconductors based on the In molarity ratio. The profiles of the acceptor-like state distribution provide insights into the electrical behavior depending on the doping concentration of the solution-processed IZO semiconductors.

The density of donor-like state distributions in solution-processed indium–zinc-oxide (IZO) thin-film transistors (TFTs) is thoroughly analyzed using photon energy irradiation. This study focuses on quantitatively calculating the distribution of density of states (DOS) in IZO semiconductors, with a specific emphasis on their variation with indium concentration. Two calculation methods, namely photoexcited charge collection spectroscopy (PECCS) and photocurrent-induced DOS spectroscopy (PIDS), are employed to estimate the density of the donor-like states. This dual approach not only ensures the accuracy of the findings but also provides a comprehensive perspective on the properties of semiconductors. The results reveal a consistent characteristic: the Recombination–Generation (R-G) center energy E_T, a key aspect of the donor-like state, is acquired at approximately 3.26 eV, irrespective of the In concentration. This finding suggests that weak bonds and oxygen vacancies within the Zn-O bonding structure of IZO semiconductors act as the primary source of R-G centers, contributing to the donor-like state distribution. By highlighting this fundamental aspect of IZO semiconductors, this study enhances our understanding of their charge-transport mechanisms. Moreover, it offers valuable insight for addressing stability issues such as negative bias illumination stress, potentially leading to the improved performance and reliability of solution-processed IZO TFTs. The study contributes to the advancement of displays and technologies by presenting further innovations and applications for evaluating the fundamentals of semiconductors.

Organic photodetectors (OPDs) offer considerable promise for low-power, solution-processable biosensing and imaging applications; however, their performance remains limited by spectral mismatch and interfacial trap states. In this study, a highly sensitive polymer photodiode was developed via trace incorporation (0.8 wt%) of InP/ZnSe/ZnS quantum dots (QDs) into a PTB7-Th:PC₇₁BM bulk heterojunction (BHJ) matrix. This QD doping approach enhanced the external quantum efficiency (EQE) across the 540–660 nm range and suppressed the dark current density at −2 V by passivating interface trap states. Despite a slight decrease in optical absorption at the optimized composition, the internal quantum efficiency (IQE) increased significantly from ~80% to nearly 95% resulting in a net EQE improvement. This suggests that QD incorporation improved charge transport without compromising charge separation efficiency. As a result, the device achieved a specific detectivity (D*) of 1.8 × 10¹³ Jones, representing a 93% improvement over binary BHJs, along with an ultra-low dark current density of 7.76 × 10⁻¹⁰ A/cm². Excessive QD loading, however, led to optical losses and increased dark current, underscoring the need for precise compositional control. Furthermore, the enhanced detectivity led to a 4 dB improvement in the signal-to-noise ratio (SNR) of photoplethysmography (PPG) signals in the target wavelength range, enabling more reliable biophotonic sensing without increased power consumption. This work demonstrates that QD-based spectral and interfacial engineering offers an effective and scalable route for advancing the performance of OPDs, with broad applicability to low-power biosensors and high-resolution polymer–QD imaging systems.

This study investigates the influence of post-deposition thermal annealing temperature on the crystal structure, chemical composition, and electrical performance of solution-processed indium oxide (In₂O₃) thin films. Based on thermogravimetric analysis (TGA) of the precursor solution, annealing temperatures of 350, 450, and 550 °C were adopted. The resulting In₂O₃ films were characterized using ultraviolet–visible (UV–Vis) spectroscopy, atomic force microscopy (AFM), Raman spectroscopy, and Hall-effect measurements to evaluate their optical, morphological, crystalline polymorphism, and electrical properties. The results revealed that the film annealed at 450 °C exhibited a field-effect mobility of 4.28 cm²/V·s and an on/off current ratio of 2.15 × 10⁷. The measured hysteresis voltages were 3.11, 1.80, and 0.92 V for annealing temperatures of 350, 450, and 550 °C, respectively. Altogether, these findings indicate that an annealing temperature of 450 °C provides an optimal balance between the electrical performance and device stability for In₂O₃-based thin-film transistors (TFTs), making this condition favourable for high-performance oxide electronics.