ZIF-L-derived porous C-doped ZnO/CdS graded nanorods with Z-scheme heterojunctions for enhanced photocatalytic hydrogen evolution

This study presents a novel approach for synthesizing C–ZnO/CdS graded nanorods derived from metal–organic frameworks (MOFs) that can be applied as a catalyst for photocatalytic hydrogen evolution from pure water. Porous C-doped ZnO was prepared by a self-template method using imidazole-like metal–organic backbone (ZIF-L) as a precursor through a two-step calcination method. CdS nanoparticles were deposited on ZIF-L surface by chemical deposition. The two-step calcination method introduced elemental C, and the unique architecture of ZIF-L played an essential role in forming the hierarchical structure of the porous ZnO nanorods. Compared with other ZnO/CdS catalysts, the C-doped ZnO/CdS graded nanorods exhibited remarkable photocatalytic activity for hydrogen production. The highest hydrogen production rate of 20.25 mmol g^?1 h^?1 with an apparent quantum yield (AQY) of 24.7% at 365 nm obtained over C–ZnO/CdS with Pt as co-catalyst, which was 24.4 and 65.3 times higher than that over CdS (0.83 mmol g^?1 h^?1) and ZnO (0.31 mmol g^?1 h^?1), respectively. This outcome was attributed to (i) the formation of Z-scheme heterojunction that significantly promoted the separation and migration of photogenerated electron–hole pairs; (ii) C doping that reduced the bandgap of ZnO and broadened its spectral response range; and (iii) the ordered arrangement of porous nanorods that effectively reduced the recombination rate of the electron–hole pairs.     

Boron-doped zinc oxide layers grown by metal-organic CVD for silicon heterojunction solar cells applications

In this work, we focus on ZnO:B layers as an alternative TCO for application on a-Si:H/c-Si heterojunction solar cells. First, the optimization of the material has been done in terms of optical and electrical properties. We have also studied the behaviour of ZnO:B against ageing. Finally, complete heterojunction solar cells have been fabricated with different back-side TCO configurations to understand the ageing mechanisms and to deeply study the influence of degradation on the solar cells parameters. Stable efficiencies up to 16.6% on polished n-type c-Si were obtained on 25 cm² heterojunction solar cells fabricated at low temperatures.     

Fast fabrication of Co3O4 and CuO/BiVO4 composite photocatalysts with high crystallinity and enhanced photocatalytic activity via ultrasound irradiation

A facile and efficient approach for the fabrication of Co₃O₄ and CuO/BiVO₄ composite photocatalysts was developed by intense ultrasound irradiation at room temperature. The as-synthesized samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy, UV-vis diffuse reflectance spectra (UV-vis DRS), and Brunauer-Emmett-Teller (BET) surface areas. The photocatalytic activity of the composite catalysts was evaluated by photocatalytic degradation of acid orange II under visible light (λ > 420 nm) irradiation. Results showed that under intense ultrasonic irradiation, the precursors of copper acetate and cobaltous acetate could transform into CuO and Co₃O₄, respectively and the amorphous BiVO₄ can easily crystallize to highly crystalline BiVO₄. The composite photocatalysts exhibited much higher photocatalytic activity than that of pure BiVO₄. The enhanced photocatalytic performance could be attributed to the high crystallinity of BiVO₄ and the formed p-n heterojunction of Co₃O₄/BiVO₄ or CuO/BiVO₄. These two factors can effectively suppress the recombination of photogenerated hole-electron pairs.     

Junction model and transport mechanism in hybrid PEDOT:PSS/n-GaAs solar cells

This study investigates the junction formation and interface properties of PEDOT:PSS/n-GaAs hybrid solar cells on planar GaAs substrates. Barrier height, photocurrent, dark saturation current and build-in potential at this hybrid interface are measured by varying n-GaAs doping concentrations. The work function and valence band edge of the polymer are extracted from ultraviolet photoelectron spectroscopy to construct the band diagram of the hybrid n-GaAs/PEDOT:PSS junction. The current-voltage characteristics were analyzed by using abrupt (p⁺n) junction and Schottky junction models. Contrary to the earlier results from the PEDOT:PSS/n-Si solar cells, the experimental evidence clearly suggested that the interface between n-GaAs and PEDOT:PSS more likely exhibited a Schottky type instead of a p⁺n junction. The current transport is governed by the thermionic emission of majority carriers over a barrier and not by diffusion. The dark saturation current density increases markedly owing to the increasing surface recombination rate in heavier n-doped GaAs substrates, leading to significant deterioration in solar cells performance.     

Fabrication of Si heterojunction solar cells using P-doped Si nanocrystals embedded in SiNx films as emitters

Si heterojunction solar cells were fabricated on p-type single-crystal Si (sc-Si) substrates using phosphorus-doped Si nanocrystals (Si-NCs) embedded in SiN_x (Si-NCs/SiN_x) films as emitters. The Si-NCs were formed by post-annealing of silicon-rich silicon nitride films deposited by electron cyclotron resonance chemical vapor deposition. We investigate the influence of the N/Si ratio in the Si-NCs/SiN_x films on their electrical and optical properties, as well as the photovoltaic properties of the fabricated heterojunction devices. Increasing the nitrogen content enhances the optical gap E₀₄ while deteriorating the electrical conductivity of the Si-NCs/SiN_x film, leading to an increased short-circuit current density and a decreased fill factor of the heterojunction device. These trends could be interpreted by a bi-phase model which describes the Si-NCs/SiN_x film as a mixture of a high-transparency SiN_x phase and a low-resistivity Si-NC phase. A preliminary efficiency of 8.6% is achieved for the Si-NCs/sc-Si heterojunction solar cell.     

Ultrasound assisted synthesis of polythiophene/SnO2 hybrid nanolatex particles for LPG sensing

Polythiophene (PTP) coated SnO₂ nano-hybrid particles have been synthesized using an ultrasound assisted in situ oxidative polymerization of thiophene monomers. Reference experiments have also been performed in the absence of ultrasound to clearly illustrate the effect of ultrasonic irradiations. FTIR results show broadening and shifting of peaks toward lower wave numbers, suggesting better conjugation and chemical interactions between PTP and SnO₂ particles. Due to strong synergetic interaction between the SnO₂ nanoparticles and polythiophene, this hybrid nanocomposite has the potential application as chemical sensors. It has been observed that PTP/SnO₂ hybrid sensors could detect liquefied petroleum gas (LPG) with high sensitivity at room temperature. PTP/SnO₂ hybrid composite containing 20 wt% SnO₂ showed the maximum sensitivity at room temperature. The sensing mechanism of PTP/SnO₂ hybrid nanocomposites to LPG was mainly attributed to the effects of p–n heterojunction between PTP and SnO₂.     

Measure the barrier height of manganite p–n heterojunction by activation energy measurement

The barrier height of the manganite based p–n heterojunction is identified from the activation energy. The La_0.35Pr_0.32Ca_0.33MnO₃/Nb-doped SrTiO₃ p–n heterojunction is fabricated by the pulse laser deposition technology. The junction shows good rectifying behavior which can be well described by the Shockley equation. A satisfactorily logarithmic linear dependence of resistance on temperature is observed, and also the relation between bias and activation energy (E_A) deduced from the R−1/T curves is linear. As a result, the interfacial barrier of the heterojunction is obtained by extrapolating the Bias –E_A plot to Y axis, which is 0.95 eV.     

Investigation of WO3/ZnO thin-film heterojunction-based Schottky diodes for H2 gas sensing

A comparative study of Schottky diode hydrogen gas sensors based on Pd/WO₃/Si and Pd/WO₃/ZnO/Si structure is presented in this work. Atomic force microscopy and X-ray photoelectron spectroscopy reveal that the WO₃ sensing layer grown on ZnO has a rougher surface and better stoichiometric composition than the one grown on the Si substrate. Analysis of the I–V characteristics and dynamic response of the two sensors when exposed to different hydrogen concentrations and various temperatures indicate that with the addition of the ZnO layer, the diode can exhibit a larger voltage shift of 4.0 V, 10 times higher sensitivity, and shorter response and recovery times (105 s and 25 s, respectively) towards 10,000-ppm H₂/air at 423 K. Study on the energy band diagram of the diode suggests that the barrier height is modulated by the WO₃/ZnO heterojunction, which could be verified by the symmetrical sensing properties of the Pd/WO₃/ZnO/Si gas sensor with respect to applied voltage.     

Application of a polymer heterojunction in dye-sensitized solar cells

Using a blend heterojunction consisting of a C₆₀ derivative, [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM), and poly(3-hexylthiophene) (P3HT) as a charge carrier transfer medium to replace the I₃⁻/I⁻ redox electrolyte, a novel TiO₂/dye/PCBM/P3HT dye-sensitized solar cell was fabricated and characterized. It was found that the P3HT/PCBM heterojunction widened the incident light harvest range from ultraviolet to visible light, and improved the photoelectrical response of the dye-sensitized solar cell. We investigated the influence of the PCBM/P3HT ratio and barrier layer on the photoelectric performance of the solar cell and proposed optimized preparation conditions. The optimized solar cell with a barrier layer and PCBM/P3HT ratio of 1:2 had a short circuit current density of 5.52 mA cm⁻², an open circuit voltage of 0.87 V, a fill factor of 0.640 and a light-to-electric energy conversion efficiency of 3.09% under a simulated solar light irradiation of 100 mW cm⁻².