Investigation of the Chemical Effect of Solvent during Ligand Exchange on Nanocrystal Thin Films for Wearable Sensor Applications

Abstract

Ligand exchange processes have been attracting tremendous interest and are necessary when fabricating nanocrystal (NC) thin films for various applications. As ligand exchange processes are based on solution treatment processes, understanding solvents’ effects on the ligand exchange process is necessary. Herein, we investigated the effects of exchanging solvents and rinsing solvents on silver (Ag) NC thin films during the ligand exchanging and rinsing steps. We studied the relationships between solvent properties, such as polarity and steric hindrance, and the structural, electronic, and electromechanical properties of NC thin films. A model system was proposed to explain the obtained relationships. We found that exchanging solvents and rinsing solvents during the ligand exchange process should be separated to regulate the ligand exchange process so that films with desired properties can be obtained. Films optimized for different purposes (highly conductive/highly electromechanically sensitive) were fabricated with the same materials and ligands using different solvents for each process. On the basis of these films, we fabricated a flexible strain sensor using an all-solution process at room temperature. This device exhibits excellent performance, including a high gauge factor up to 400, and high reliability, and stability; furthermore, it can detect minute human motion and sound.

Transient Lattice Response upon Photoexcitation in CuInSe2 Nanocrystals with Organic or Inorganic Surface Passivation

“…Ligand selection is critical to implementation of a given nanocrystal composition in applications owing to significant effects on solution processing and electrical conductivity. − Ligand identity impacts the rate of thermalization as observed in this pulsed excitation mode with isolated NCs dispersed in solvent. The temperature–time profile of a film of nanocrystals, whether in a light-emitting application or additive manufacturing process, is influenced not only by the rate of thermalization, but also on thermal properties (heat capacity, thermal transport) of surrounding or proximal media.…”

Chemical Effect of Halide Ligands on the Electromechanical Properties of Ag Nanocrystal Thin Films for Wearable Sensors

“…(ii) With time, some small Ag NCs are absorbed by the neighboring large NCs. The integration of small Ag NCs with large Ag NCs leads to the growth of the large NCs, as in the case of Ostwald ripening. − Simultaneously, as the small-size NCs are absorbed, the region where these were originally located becomes an empty space or pore. (iii) As the Ostwald ripening process continues, the sizes of pores and NCs increase.…”

“…For application in the healthcare system, tiny and light wearable sensors are preferred. High-performance sensors with high sensitivity are also required to properly detect the subtle movements of target objects, including human motion, − ,, heartbeat, voice, and pulse.…”

All‐Solution Processed Multicolor Patterning Technique of Perovskite Nanocrystal for Color Pixel Array and Flexible Optoelectronic Devices

“…For example, researchers have attempted to change the surface of numerous materials, including lead halide perovskite. [17][18][19][20][21][22] Recently, strategies have been developed to change the original ligand to a ligand with a specific functional group, i.e., a bromide or amide functional group, which can bind to the surface of lead halide perovskite in a stronger manner. [23][24][25][26] Furthermore, introducing a high dipole moment cation on the perovskite surface or additional surface layers, such as polymeric or inorganic shells, has also been extensively investigated.…”