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Highly (101)-oriented p-Ag₂O thin film with high electrical resistivity was grown by rapid thermal oxidation (RTO) on clean monocrystalline p-type Si without any post-deposition annealing. From optical transmittance and absorptance data, the direct optical band gap was found to be 1.46 eV. The electrical and photovoltaic properties of Ag₂O/Si isotype heterojunction were examined in the absence of any buffer layer. Ideality factor of heterojunction was found to be 3.9. Photoresponce result revealed that there are two peaks located at 750 nm and 900 nm.

The effects of contact barrier height on performances of Si/BaSi₂ p–n heterojunction, BaSi₂ p–n homojunction and Si/BaSi₂/Si p–i–n heterojunction were numerical calculated. Band energy diagram, built-in electric field, carrier generation and carrier transportation distributed in the devices are comprehensively investigated. BaSi₂ p–n homojunction solar cells are very sensitive to front contact barrier height due to the high light absorption coefficient of front p-BaSi₂ layer. Si/BaSi₂ p–n heterojunction and BaSi₂ p–n homojunction solar cells with donor concentration $(N_D)$ less than $10^{17}{\mathrm{\text{cm}}}^{-3}$ are apparently affected by back contact barrier height. The ideal $\alpha$-Si/BaSi₂/$\alpha$-Si p–n solar cell achieves a high $V_{\mathrm{\text{oc}}}$ of 1.131 V, suggesting a promising and alternative structure to gain excellent BaSi₂-based solar cells once the Urbach tail states and defects can be effectively eliminated. The results help to fundamentally understand operation mechanism and provide intuitive guidance for achieving high-efficiency BaSi₂ solar cells.

SnSe₂/Se heterojunction films were successfully grown on fluorine-doped tin oxide (FTO) glass for the first time via a one-step solvothermal route using magnetron sputtered Sn metallic precursors, Se powders as selenium source, cyclohexanol as solvent and cyclohexanol as auxiliary solvent, respectively. The SnSe₂/Se heterojunction films consisted of Se nanoparticles or nanorods cluster and SnSe₂ network surface layers. The crystalline phase and morphology of SnSe₂/Se films were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), respectively. The photocatalysis measurements of the products for rhodamine Blue (RhB) demonstrated that SnSe₂/Se heterojunction films revealed better dye degradation properties than SnSe₂ nanosheet films due to the higher separation rates of photogenerated electron–hole pairs of SnSe₂/Se heterojunction films, which can be confirmed by surface transient photovoltage (TPV) analyzer.

Photocatalytic technology is currently the most promising technology for environmental pollution control. The preparation of photocatalysts with excellent properties is the core of the development of photocatalytic technology. TiO₂ can form a heterojunction with g-C₃N₄, which can effectively inhibit the recombination of photogenerated electron–hole pairs, improve the mobility of photogenerated carriers, and thus improve the photocatalytic performance. In this study, NaCl was used as a template, and the loose and porous g-C₃N₄/TiO₂ heterojunction composite photocatalysts were prepared by the template method. Compared to the pure g-C₃N₄ prepared by the conventional thermal polycondensation method and TiO₂, the g-C₃N₄/TiO₂ heterojunction composite photocatalysts prepared in this study exhibited a greatly increased specific surface area, an improved light absorption performance, a significantly suppressed recombination of photogenerated electrons and holes. Furthermore, the g-C₃N₄/TiO₂ heterojunction composite photocatalysts exhibited excellent photocatalytic performance.

Nowadays, using solar energy to convert CO₂ into hydrocarbon fuels such as CO and methanol is considered as an attractive approach to alleviate environmental pollution and the energy crisis. However, the easy recombination of photo-generated carriers and holes of photocatalyst is still the main factor that inhibits photocatalytic performance for CO₂ conversion. In this study, the BiO${}_{2-x}$/Bi₂O${}_{2.75}$ heterojunction complex was successfully synthesized via a facile hydrothermal method. The BiO${}_{2-x}$/Bi₂O${}_{2.75}$ heterogeneous catalyst shows greatly improved photocatalytic performance for CO₂ reduction, and the CO and CH₄ yields obtained on BiO${}_{2-x}$/Bi₂O${}_{2.75}$ are 6.8 and 16 times compared with pure BiO${}_{2-x}$. The improved photocatalytic performance can be ascribed to the rapid charge separation on BiO${}_{2-x}$/Bi₂O${}_{2.75}$ interface, thereby providing a favorable surface with suitable electronic structure for CO₂ reduction. Subsequently, a possible photocatalytic mechanism was proposed to explain the improved performance of photocatalytic CO₂ reduction.

The transparent semiconducting copper iodide (CuI) films were deposited by pulsed laser deposition (PLD) and their structural and optoelectrical properties in the power output of TiO₂|Dye|CuI cells are reported. These CuI films exhibited optical transmittance of over 80% in the wavelength range from 400 to 900 nm and a minimum resistivity of about 2 KΩ-cm. An efficient charge generation is observed through the illumination of the TiO₂ layer of the fabricated p-CuI|Dye|n-TiO₂ cells. The cells performances have been given in the current–voltage (I–V) working curve under illumination when exposed to AM 1.5 illumination condition (100 mW/cm², 25°C). The maximum short circuit photo current density (J_sc) of about 12.2 mA/cm² and open circuit photo voltage (V_oc) of about 480 mV were obtained for the TiO₂|Dye|CuI cells with good reproducibility. The fill factor (FF) and power conversion efficiency (η) were about 47.8% and 2.8%, respectively.

The presence of the antibiotics in the wastewater has posed a huge risk to aquatic life and human health. It is a great significance to develop an effective technology to treat the antibiotics-containing wastewater. In this study, a series of g-C₃N₄/NH₂-MIL-88B(Fe) composite photocatalysts are synthesized through a simple one-step method. The structure and optical properties of prepared photocatalysts are detected by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–Vis absorption spectra (UV–Vis DRS), photoluminescence (PL) spectroscopy and transient photocurrent techniques, respectively. FESEM and TEM show that MOF is uniformly dispersed in petaloid g-C₃N₄. The uniform dispersion of Fe-MOFs in the heterojunction composites increases the specific surface area ($S_{\mathrm{\text{BET}}})$ of g-C₃N₄, which results in a great adsorption property for the nanocomposite. The capture experiment shows that $•$${\text{O}}_2^{-}$ and ${\text{h}}^{+}$ are the main active substances in ciprofloxacin (CIP) degradation. These prepared composite photocatalysts exhibit excellent CIP photodegradation activity under visibly light irradiation with an apparent rate constant of 0.0127${\text{min}}^{-1}$ (3.74 times as the rate of single component). The remarkable catalytic performance can be ascribed to the fact that the g-C₃N₄/NH₂-MIL-88B(Fe) heterojunction inhibits the recombination of photoinduced electron–hole pairs and improved the visible light absorption.

In this work, highly active graphitic carbon nitride composite photocatalysts with an isotype heterojunction semiconductor structure have been prepared through the molecular composite precursors consisting of urea and melamine. These photocatalysts were characterized by XRD, SEM, TEM, UV-Vis, BET and transient photocurrent responses. The photodegradation of dyes in aqueous solution under visible-light irradiation has been investigated over carbon nitride photocatalysts consisting of different urea/melamine mass ratios. Further studies by photocurrent indicate that the photosynergistic effect of isotype heterojunction can remarkably enhance the photoinduced interfacial charge transfer, thereby increasing the charge separation during the photocatalytic reaction.

As one of the basic bismuth nitrates, Bi₂O₂(OH)(NO₃) (denoted as BION) has been reported to exhibit powerful photodegradation activity for various contaminants. However, pure BION could only be irradiated by UV light due to broad bandgap ($\sim$3.14eV). Herein, Bi₂S₃/Bi₂O₂(OH)(NO₃) (denoted as BS-BION) heterojunction was prepared by an in situ ion exchange reaction between BION and aqueous thiourea solution ($\mathrm{\text{pH}}\approx 3$). The resulting heterojunction possessed good visible light absorption and closely contacted interfaces, which benefited effective separation and transfer of photogenerated charges, thus leading to excellent photocatalytic activity for the degradation of rhodamine B (RhB) under visible light irradiation. Furthermore, the as-prepared heterojunction photocatalyst also presented high photochemical stability, which may be of great significance for practical application.

Novel n-SrTiO₃/p-BiOI heterojunction composites were successfully fabricated by loading SrTiO₃ particles onto the surface of BiOI nanoflakes via a two-step method. The as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), energy-disperse X-ray spectroscopy (EDS), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), diffuse reflectance spectroscopy (DRS) and electrochemical measurements. The results show that the n-SrTiO₃/p-BiOI heterojunction composites are composed of perovskite structure SrTiO₃ and tetragonal phase BiOI. The composites exhibit excellent photocatalytic performance for the degradation of crystal violet (CV) solution under simulated solar light irradiation, which is superior to that of pristine BiOI and SrTiO₃. The 30wt.%SrTiO₃/BiOI composite is found to be the optimal composite, over which the dye degradation reaches 92.5% for 30min of photocatalysis. The photocatalytic activity of the 30wt.%SrTiO₃/BiOI composite is found to be 3.94 times and 28.2 times higher than that of bare BiOI and SrTiO₃, respectively. The reactive species trapping experiments suggest that $•{\mathrm{\text{O}}}_2^{-}$ and holes are the main active species responsible for the CV degradation. In addition, the electrochemical measurements elucidate the effective separation of photoinduced electron–hole pairs. Moreover, on the basis of experimental and theoretical results, a possible mechanism for the enhanced photocatalytic performance of the SrTiO₃/BiOI heterojunction composites is also proposed.

In this work, a highly efficient p-type Cu₃P/$n$-type g-C₃N₄ heterojunction photocatalyst was synthesized in situ. XRD, UV–Vis, N₂ adsorption, TEM, XPS, PL, and EIS are used to characterize the as-prepared catalysts. The results show that Cu₃P nanoparticles are highly dispersed onto the g-C₃N₄ surface, which obviously promotes the separation rate of electrons and holes. The charge transfer between Cu₃P and g-C₃N₄ follows the “Z-scheme” mechanism. The as-prepared Cu₃P/g-C₃N₄ heterojunction photocatalyst displays the ammonium ion production rate of 7.5mgL${}^{-1}$h${}^{-1}$g${}_{\mathrm{\text{cat}}}^{-1}$, which is 28.8 times higher than that of neat g-C₃N₄, as well as good catalytic stability. The possible reaction mechanism is proposed.

This paper reports the design of a photoelectrochemical (PEC) sensing method for detecting levofloxacin (LEVX) in tablets. In this paper, a three-dimensional plasma Bi/BiPO₄/BiOI heterojunction was fabricated by a two-step method, in which Bi-metal and BiPO₄ were fixed on the surface of BiOI with beads. The composites were characterized by a variety of analytical methods. Bi/BiPO₄/BiOI-5% showed better photocatalytic activity than BiPO₄/BiOI. Indium tin oxide (ITO) modified with the Bi/BiPO₄/BiOI-5% composites was used to determine LEVX and achieved linear detection ranges of 0.2–2 $\mu$M and 2–7 $\mu$M. These composites present alternative materials for the analysis of antibiotics.

In this work, (n)InSe/(p)ZnSe and (n)InSe/(p)ZnSe/(n)InSe heterojunction thin film transistor (TFT) devices are produced by the thermal evaporation technique. They are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy and optical spectroscopy techniques. While the InSe films are found to be amorphous, the ZnSe and InSe/ZnSe films exhibited polycrystalline nature of crystallization. The optical analysis has shown that these devices exhibit a conduction band offsets of 0.47 and valence band offsets of 0.67 and 0.74eV, respectively. In addition, while the dielectric spectra of the InSe and ZnSe displayed resonance peaks at 416 and 528THz, the dielectric spectra of InSe/ZnSe and InSe/ZnSe/InSe layers indicated two additional peaks at 305 and 350THz, respectively. On the other hand, the optical conductivity analysis and modeling in the light of free carrier absorption theory reflected low values of drift mobilities associated with incident alternating electric fields at terahertz frequencies. The drift mobility of the charge carrier particles at femtoseconds scattering times increased as a result of the ZnSe sandwiching between two InSe layers. The valence band offsets, the dielectric resonance at 305 and 350THz and the optical conductivity values nominate TFT devices for use in optoelectronics.

Epitaxial layers of ZnTe have been grown on a (111) oriented CdTe single crystal substrate by thermal evaporation technique at 180°C and a pressure of 10^-6 Torr. X-ray diffraction pattern indicated a highly oriented crystallographic growth of ZnTe (111) layer on CdTe (111) substrate. C–V measurements are carried out at frequencies of 10 kHz and 100 kHz. 1/C² versus the forward bias voltage gave a straight line in the voltage range from 1 to 3 V. Extrapolation of 1/C² → 0 led to an estimated value of the built-in potential of about 0.58 V. The calculated charge carrier concentration in the lightly doped over-grown layer, ZnTe, has been found to be p = 1.7 × 10¹⁶cm^-3. It was found that energy band diagram constructed according to the electron affinity model is not the adequate one to explain the capacitance–voltage behavior. Therefore, one should take into account the effect of interface states on the energy band diagram. The interface states density has been estimated to be ~10¹³cm^-2 for (111) ZnTe/(111)CdTe heterojunction system. The interface states were identified as hole traps for the ZnTe/CdTe heterojunction. Accordingly, a band bending downward both materials, and a depletion zone in both of them are expected.

Hierarchical heterostructure of rutile TiO₂ nanoflower array on anatase TiO₂ sheet was fabricated by a two-step method. Anatase TiO₂ sheet was synthesized by a modified dip coating method, followed by the formation of rutile TiO₂ nanoflower array via a wet chemical route. Studies by X-ray diffraction and scanning electron microscopy indicated the formation of hierarchical heterostructure. Tests on degradation of methylene blue under UV light illumination showed that the hierarchical TiO₂ film exhibited superior photocatalytic performance to those with monophased anatase and rutile TiO₂ films and commercial P25 film. It was attributed to efficient separation of photogenerated charge carriers and prevention of the unfavorable multiple electron transfer on biphase interface. Investigation on the influence of addition of scavengers on photocatalysis suggested that hydroxy radicals and superoxide anion radicals dominated the photocatalytic degradation of MB. The hierarchical TiO₂ film exhibited excellent photocatalytic stability in cycling tests.

Thiourea (Th)-doped CdO thin films were deposited on glass and crystalline p-type Si (100) substrates for various Th doping concentrations (0.3, 0.5 and 0.7 at.%) using spin coating method. Some structural parameters, such as the crystallite size, lattice constant, dislocation density (δ) and strain in the films were obtained from XRD analysis in which the polycrystalline structure with cubic nature and (111) preferential orientation was confirmed. CdO thin film has not shown any change in crystal phase after Th doping. The optical study emerged that the Th doping caused important changes in the transmittance, absorbance and reflectance spectra. The optical transmittance above 80% range from 720 nm to 800 nm is obtained for 0.3% Th-doped CdO thin films. The rectifying behavior increases with increasing Th content in CdO while Th-doped CdO/p-Si heterojunction exhibits low rectifying character.

Copper oxide was prepared by simple chemical method and deposited on quartz glass and single crystal PSi for solar cell and Photodetector applications by drop casting method. XRD measurements reveal that the film was polycrystalline in nature. The average crystalline size of film was (17.46) nm. In order to investigate the optical characteristics of CuO, researchers took a recording of the transmittance against wavelength. It was determined that the optical energy gap of CuO is equal to 3.5 electron volts. The efficiency of solar cell was (0.27)% and the maximum value of spectral detectivity was 5*10${}^{10}$ (cm Hz${}^{0.5}$ W${}^{-1})$.

The novel Cu₂O/$e$-HTi₂NbO₇ heterojunction nanocomposite was assembled through a facile exfoliation-restacking route. The as-prepared nanocomposite and its precursors, Cu₂O and $e$-HTi₂NbO₇, were characterized by means of X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), N₂ adsorption–desorption measurements, laser Raman spectroscopy (LRS) and UV–Vis diffuse reflection spectroscopy (UV–Vis DRS). The photocatalytic performance was evaluated by photocatalytic oxidation of ethyl mercaptan (EM) and photocatalytic degradation of methylene blue (MB) dyes under sunlight irradiation. The results showed that Cu₂O nanoparticles were successfully distributed on the surface of $e$-HTi₂NbO₇ nanosheets, and the intensity of spectral absorption of the as-prepared nanocomposite in the visible-light region was significantly enhanced. The as-prepared nanocomposite displayed the enhanced photocatalytic activity than the Cu₂O nanoparticles and HTi₂NbO₇ nanosheets due to the formation of a heterojunction structure between Cu₂O nanoparticles and HTi₂NbO₇ nanosheet and a possible photocatalytic mechanism was suggested.

A novel strontium titanate/binary metal sulfide (SrTiO₃/SnCoS₄) heterostructure was synthesized by a simple two-step hydrothermal method. The visible-light-driven photocatalytic performance of SrTiO₃/SnCoS₄ composites was evaluated in the degradation of methyl orange (MO) under visible light irradiation. The photocatalytic performance of SrTiO₃/SnCoS₄-5% is much higher than that of pure SrTiO₃, SnCoS₄, SrTiO₃/SnS₂ and SrTiO₃/CoS₂. The SrTiO₃/SnCoS₄ composite material with 5wt.% of SnCoS₄ showed the highest photocatalytic efficiency for MO degradation, and the degradation rate could reach 95% after 140min irradiation time. The enhanced photocatalytic activity was ascribed to not only the improvement of visible light absorption efficiency, but also the construction of a heterostructure which make it possible to effectively separate photoexcited electrons and holes in the two-phase interface.

To develop an efficient and recyclable photocatalyst, ternary magnetic Fe₃O₄@ZnO/g-C₃N₄ nanocomposites were synthesized for the photodegradation of methylene blue (MB). The microstructures, magnetic response and photocatalytic activity of the as-prepared nanocomposites were characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), N₂ adsorption–desorption isotherms and spectrophotometer. All results indicate that ZnO nanoparticles anchor on the surface of Fe₃O₄ nanoparticles and Fe₃O₄@ZnO exists on the surface of g-C₃N₄ to form Fe₃O₄@ZnO/g-C₃N₄ nanocomposites. The photocatalytic activity to MB of Fe₃O₄@ZnO/g-C₃N₄ nanocomposites is significantly higher than those of pristine g-C₃N₄ and Fe₃O₄@ZnO. Owing to the heterojunctions between the interface of g-C₃N₄ and ZnO, the high separation efficiency of the photogenerated electrons and holes increases the radicals $•$OH and $•$O${}_2^{-}$ to photodegrade MB. Fe₃O₄@ZnO/g-C₃N₄ (20%) presents the highest MB removal of 93.74% and could be easily separated from solution with magnetic separation method.