Recently, as applications based on triboelectricity have expanded, understanding the triboelectric charging behavior of various materials has become essential. This study investigates the triboelectric charging behaviors of various 2D layered materials, including MoS , MoSe , WS , WSe , graphene, and graphene oxide in a triboelectric series using the concept of a triboelectric nanogenerator, and confirms the position of 2D materials in the triboelectric series. It is also demonstrated that the results are obviously related to the effective work functions. The charging polarity indicates the similar behavior regardless of the synthetic method and film thickness ranging from a few hundred nanometers (for chemically exfoliated and restacked films) to a few nanometers (for chemical vapor deposited films). Further, the triboelectric charging characteristics could be successfully modified via chemical doping. This study provides new insights to utilize 2D materials in triboelectric devices, allowing thin and flexible device fabrication.

In this communication, a novel CdSe/CdS/ZnO nanowire array fabricated by a 3-step solution-based method was used as a photoanode of a quantum dot sensitized solar cell, which generated a maximum power conversion efficiency of 4.15%.

We report the presence of defects in CH3NH3PbI3, which is one of the main factors that deteriorates the performance of perovskite solar cells.

2D semiconductors, especially transition metal dichalcogenide (TMD) monolayers, are extensively studied for electronic and optoelectronic applications. Beyond intensive studies on single transistors and photodetectors, the recent advent of large‐area synthesis of these atomically thin layers has paved the way for 2D integrated circuits, such as digital logic circuits and image sensors, achieving an integration level of ≈100 devices thus far. Here, a decisive advance in 2D integrated circuits is reported, where the device integration scale is increased by tenfold and the functional complexity of 2D electronics is propelled to an unprecedented level. Concretely, an analog optoelectronic processor inspired by biological vision is developed, where 32 × 32 = 1024 MoS2 photosensitive field‐effect transistors manifesting persistent photoconductivity (PPC) effects are arranged in a crossbar array. This optoelectronic processor with PPC memory mimics two core functions of human vision: it captures and stores an optical image into electrical data, like the eye and optic nerve chain, and then recognizes this electrical form of the captured image, like the brain, by executing analog in‐memory neural net computing. In the highlight demonstration, the MoS2 FET crossbar array optically images 1000 handwritten digits and electrically recognizes these imaged data with 94% accuracy.

Although cadmium chalcogenide quantum dot-sensitized photoanode can utilize the whole visible region of the solar spectrum, its poor photochemical stability owing to hole-induced anodic corrosion remains a major problem for the application in photoelectrochemical hydrogen generation systems. Here, modification with IrO x •nH 2 O, a well-known water-oxidation catalyst substantially improves the photochemical stability of the quantum dot-sensitized photoanode. Moreover, it induces an increased photocurrent and a cathodic shift of the onset potential. This is the first example that an oxygen-evolution catalyst is employed on a quantum dot-sensitized electrode system, and it shows 13.9 mA cm −2 (at 0.6 V) and −0.277 V vs the reversible hydrogen electrode (RHE), which are the highest photocurrent density and the lowest onset potential attained with a ZnO-based electrode, respectively. An average hydrogen evolution rate of 240 μmol h −1 cm −2 at 0.6 V vs RHE has been achieved on a IrO x •nH 2 O modified electrode, with almost 100% of faradaic efficiency.

We report a facile wet-chemical route for the fabrication of a superhydrophobic ZnO nanowire surface modified with fatty acids. A systematic study was performed on the relationship between carbon chain length of fatty acid and wetting states of well-aligned ZnO nanowire arrays. The wettability of the ZnO nanowire array was monotonically converted from hydrophilicity to hydrophobicity by increasing the carbon chain length of the chemisorbed fatty acid. The superhydrophobic surface obtained with stearic acid (SA, C18) showed a maximum water contact angle (CA) of 167°, which decreased gradually under UV illumination, due to UV-enhanced decomposition of SA monolayer. XPS analysis confirmed the photodecomposition of SA molecules through UV irradiation. Also, a selective area UV photopatterning was demonstrated using a photomask on the modified ZnO nanowire array.

A photoelectrochemical device with a novel hierarchical heterostructure coupled with narrow bandgap semiconductors is demonstrated for efficient hydrogen generation via water splitting. The heterostructures consist of ZnO nanowire branches grown on WO x nanowhisker stems, which offer a large surface area and efficient charge transport path. The assembly of CdSe/CdS narrow bandgap cosensitizers on hierarchical ZnO/WO x nanostructures is shown to enhance light harvesting in the visible light region. The cosensitized ZnO/WO x heterostructures demonstrate efficient light absorption up to a wavelength of 800 nm as well as enhanced photoelectrochemical properties when used as photoanodes. Furthermore, CdSe/CdS cosensitized ZnO/WO x has a type II cascade band structure, resulting in efficient charge transport, which was confirmed by open circuit voltage decay measurements. Our photoelectrochemical system produced a high photocurrent density of 11 mA/cm2 at −0.5 V (vs SCE) under 1.5 AM irradiation for hydrogen generation.

Although triboelectrification is a well-known phenomenon, fundamental understanding of its principle on a material surface has not been studied systematically. Here, we demonstrated that the surface potential, especially the surface dipoles and surface electronic states, governed the triboelectrification by controlling the surface with various electron-donating and -withdrawing functional groups. The functional groups critically affected the surface dipoles and surface electronic states followed by controlling the amount of and even the polarity of triboelectric charges. As a result, only one monolayer with a thickness of less than 1 nm significantly changed the conventional triboelectric series. First-principles simulations confirmed the atomistic origins of triboelectric charges and helped elucidate the triboelectrification mechanism. The simulation also revealed for the first time where charges are retained after triboelectrification. This study provides new insights to understand triboelectrification.