Polymer Thin-Film Dewetting-Mediated Growth of Wettability-Controlled Titania Nanorod Arrays for Highly Responsive, Water-Stable Self-powered UV Photodetectors

Abstract

Holey layer of the TiO2 nanorod-covered surface obtained by the self-organization of polysterene (PS) templates is shown to achieve programmable wettability by creating nano- to micrometer-scale porosity, which is useful to demonstrate stable and self-powered Schottky junction-based UV photodetectors. The wettability characterized by static water contact angle (WCA) is found to be ∼40° (weak hydrophilic) with the nanorod film of micrometer-scale pores with a diameter of 9.91 μm and periodicity of 2.8 μm. In contrast, the holey layer of the TiO2 nanorod-covered surface with pores with a diameter of 90 nm and periodicity of pores of 1.4 μm shows a WCA ≈ 166°, which do not require any low surface energy coating and physical deposition techniques. A pure phase solution-processed superhydrophobic holey 1D TiO2 nanorod film in sandwiched configuration with platinized fluorine-doped tin oxide (FTO) electrodes shows self-powered and fast UV detection (rise time, ∼44 ms; decay time, ∼25 ms) with very high responsivity (25 A/W). The superhydrophobic sample hinders the water molecules from infiltrating into the sandwich junction, making the device performance extremely stable even in humid conditions.

Feature Size Modulation in Dewetting of Nanoparticle-Containing Ultrathin Polymer Films

“…It is well known that the size (diameter, d D ), number density ( N D ), and periodicity (λ D ) of the dewetted droplets strongly depend on the initial film thickness ( h F ), which allow creation of nano and mesoscale features with feature size on demand by simply altering the initial film thickness. Meso patterns obtained by dewetting have been used in various applications such as enhancing photoluminescence, water harvesting, − fabrication of water stable UV detectors, and so on . On the other hand, the inherent randomness of the dewetted features can be circumvented by dewetting the film on either topographically or chemically patterned substrates to obtain large area ordered structures with programmable wetting, optical, and transport properties. − Recently, Verma and Sharma fabricated an array of microlenses by submerged dewetting, where the dewetted droplets have a very high contact angle due to reduced surface tension and act as microlenses. , Apart from homopolymer thin films, dewetting has also been observed in various other types of films such as liquid crystals, − sol–gel derived inorganic thin films, and so on.…”

“…Meso patterns obtained by dewetting have been used in various applications such as enhancing photoluminescence, 24 water harvesting, 25−27 fabrication of water stable UV detectors, and so on. 28 On the other hand, the inherent randomness of the dewetted features can be circumvented by dewetting the film on either topographically or chemically patterned substrates to obtain large area ordered structures with programmable wetting, optical, and transport properties. 29−41 array of microlenses by submerged dewetting, where the dewetted droplets have a very high contact angle due to reduced surface tension and act as microlenses.…”

Ordering in Dewetting of a Thin Polymer Bilayer with a Topographically Patterned Interface

“…While such instabilities are undesirable in coatings, 11 the morphological evolution and selforganization during dewetting involve rich physics and have emerged as a novel, rapid mesofabrication technique with the ability to program feature size and periodicity by controlling initial conditions such as h and the surface/interfacial tension of the surrounding medium. 8 Dewetting-mediated patterned surfaces have been utilized in enhancing photoluminescence, 12 fabrication of microlenses, 10 enhanced water harvesting, 13 fabrication of stable photodetectors, 14 and so on.…”

High-Performance Chlorophyll-b/Si Nanowire Heterostructure for Self-Biasing Bioinorganic Hybrid Photodetectors

“…Currently, organic PDs are considered as the alternatives to their inorganic counterparts regarding processing ease, adaptability with flexible substrates, tunable absorption characteristics, inexpensive production, for large-area integration . In recent days, significant advancements in organic PDs are made in terms of their performances efficiency, which have reached to or even exceed the performances of a few inorganic PDs. − However, most of the organic materials suffer from instability, low mobility, high operating voltage, and enhance environmental pollution during processing or use of the materials. Therefore, it is utmost important to find out suitable device materials that overcome the entire drawback.…”