Photovoltaic properties of a ZnO nanorod array affected by ethanol and liquid-crystalline porphyrin

Photogenerated carrier behavior at a gas–solid interface for CO2 adsorption on Cs2AgBiBr6 nanocrystals

We used a combination of in situ TPV measurements and DFT calculations for the first time to understand the carrier transfer process at a CO2/Cs2AgBiBr6 gas–solid interface.

Controllable Epitaxial Growth of Core-Shell PbSe@CsPbBr3 Wire Heterostructures

1D semiconductor core-shell wire heterostructures are crucial for high-performance optical and optoelectronic device applications, but they are limited to the traditional semiconductor families. Here, the conformal epitaxy of CsPbBr₃ shell on PbSe wire core is realized to form the core-shell PbSe@CsPbBr₃ wire heterostructures via a chemical vapor deposition route. The Pb-particle catalysts at the tips of the PbSe wires grown by vapor-liquid-solid provide the nucleation sites for the in situ rapid growth of CsPbBr₃ cube crystals, which serve as the adatom collector for the following shell growth due to the faster adsorption of the evaporated source atoms on them than on the sidewalls of PbSe wires. This determines the directional growth of the shell along the PbSe wires from the tip to bottom. The spectral and transient photoluminescence reveals the efficient photogenerated carrier transfer from the shell to the core. Importantly, the photodetectors (PDs) based on the heterostructures show responsivity up to 4.7 × 10⁴ A W^-1 under 405 nm light illumination, and a wavelength-dependent photocurrent polarity with the excitation of the light from near- to mid-infrared (IR), which indicates potential applications in IR PDs and novel optoelectronic logical circuits.

Conductive Photo-Activated Porphyrin-ZnO Nanostructured Gas Sensor Array

Chemoresistors working at room temperature are attractive for low-consumption integrated sensors. Previous studies show that this feature can be obtained with photoconductive porphyrins-coated ZnO nanostructures. Furthermore, variations of the porphyrin molecular structure alter both the chemical sensitivity and the photoconductivity, and can be used to define the sensor characteristics. Based on these assumptions, we investigated the properties of an array of four sensors made of a layer of ZnO nanoparticles coated with porphyrins with the same molecular framework but different metal atoms. The array was tested with five volatile organic compounds (VOCs), each measured at different concentrations. Results confirm that the features of individual porphyrins influence the sensor behavior, and the differences among sensors are enough to enable the discrimination of volatile compounds disregarding their concentration.

Porphyrinoids for Chemical Sensor Applications

Porphyrins and related macrocycles have been intensively exploited as sensing materials in chemical sensors, since in these devices they mimic most of their biological functions, such as reversible binding, catalytic activation, and optical changes. Such a magnificent bouquet of properties allows applying porphyrin derivatives to different transducers, ranging from nanogravimetric to optical devices, also enabling the realization of multifunctional chemical sensors, in which multiple transduction mechanisms are applied to the same sensing layer. Potential applications are further expanded through sensor arrays, where cross-selective sensing layers can be applied for the analysis of complex chemical matrices. The possibility of finely tuning the macrocycle properties by synthetic modification of the different components of the porphyrin ring, such as peripheral substituents, molecular skeleton, coordinated metal, allows creating a vast library of porphyrinoid-based sensing layers. From among these, one can select optimal arrays for a particular application. This feature is particularly suitable for sensor array applications, where cross-selective receptors are required. This Review briefly describes chemical sensor principles. The main part of the Review is divided into two sections, describing the porphyrin-based devices devoted to the detection of gaseous or liquid samples, according to the corresponding transduction mechanism. Although most devices are based on porphyrin derivatives, seminal examples of the application of corroles or other porphyrin analogues are evidenced in dedicated sections.

Formation of a built-in field at the porphyrin/ITO interface directly proven by the time-resolved photovoltage technique

Two assemblies, porphyrin powder/ITO and porphyrin film/ITO, were built by a facile method. The time-resolved photovoltage technique was utilized to prove the behaviour of photo-induced charges in the two assemblies. The photovoltage results show that the porphyrin film/ITO assembly displays a reversal polarity response, which is different from the response of porphyrin powder/ITO. This phenomenon is due to the effect of a built-in field on photo-induced charge behaviour at the porphyrin film/ITO interface. This result is beneficial for the development of a measuring method for detecting heterojunction interface formation and understanding the photoelectric process in photoelectric materials and devices.

A composition-tunable ZnxCd1−xSe/ZnO core–shell nanowire array: mechanisms for the enhanced charge separation and its photovoltaic applications

The mechanism for enhanced charge separation was discussed and the charge transport model was established.

Improved sensitivity of polychlorinated-biphenyl-orientated porous-ZnO surface photovoltage sensors from chemisorption-formed ZnO-CuPc composites

We report a new mechanism for the enhancement of porous-ZnO surface photovoltage (SPV) response to polychlorinated biphenyls (PCBs, a notorious class of persistent organic pollutants as global environmental hazard) based on copper phthalocyanine (CuPc) chemisorptive bonding on porous-ZnO. A new ZnO-CuPc composite is formed on the porous-ZnO surface due to the interaction between the surface ZnO and CuPc, with its valence band (VB) energy level being higher than that of the pristine porous-ZnO. So that the efficiency of the photogenerated-electron transfer from the composite VB to the adjacent ZnO's surface states is drastically increased due to the reduced energy gap between the transition states. As a result, the sensitivity of the PCB-orientated SPV sensor is much improved by showing amplified variation of the SPV-signals perturbed by PCBs adsorbed on the ZnO-CuPc@porous-ZnO sensitive material.

BiFeO3/TiO2 nanotube arrays composite electrode: construction, characterization, and enhanced photoelectrochemical properties

This work aims at the exploration of nanostructured ferroelectric-material-modified semiconductor electrodes for enhanced photo-induced activity. A well-aligned BiFeO3/TiO2-nanotubes (NTs) array with visible-light activity was successfully synthesized on a titanium sheet by combining anodization and an ultrasonic-immersion method followed by annealing. The structural and optical properties of the TiO2-NTs and the composite BiFeO3/TiO2-NTs were comparatively characterized. The composite BiFeO3/TiO2-NTs grown on a Ti sheet and used as an electrode exhibited a stronger absorption in the visible region and a much higher photoconversion efficiency than the pure TiO2-NTs/Ti electrode. Electrochemical impedance investigation attested to a significant improvement of the interfacial electron-transfer kinetics with enhanced separation of electron-hole pairs. The as-prepared composite electrode showed a high efficiency for photoelectrocatalytic degradation towards rhodamine B under visible-light irradiation (λ > 400 nm). The enhanced photoelectrocatalytic activity of the composite electrode could be attributed to the synergistic effect between the lowered electron-hole recombination rate by the applied bias and the wider spectral response promoted by the BiFeO3 component.

Surface photovoltage phase spectra for analysing the photogenerated charge transfer and photocatalytic activity of ZnFe2O4-TiO2 nanotube arrays

The transfer properties of the photogenerated charge carriers in TiO2 nanotube arrays (TNAs) and ZnFe2O4 modified TiO2 nanotube arrays (ZFO-TNAs) were investigated by surface photovoltage phase spectra. The modification of ZnFe2O4 on TNAs will lead to a new process of photogeneration of charge carriers. When irradiated with UV or visible light, before ZnFe2O4 modification photogenerated holes can transfer to the surface of TNAs; while after ZnFe2O4 modification, a process of photogenerated electrons transferring to the surface occurred. The different detected photogenerated charge transfer processes agree well with the photocatalytic reduction of Cr(VI) and the degradation of methyl orange experiments, which confirmed that the photogenerated holes transferring to the surface of the TNAs or ZFO-TNAs were beneficial for the reactions of photocatalytic reduction and electrons transferring to the surface were beneficial for photocatalytic degradation.