Solar Energy Conversion Applications Research Articles

Designing multifunctional silica coatings for enhanced broadband antireflection and microfiber contamination sensing

Multifunctional silica coatings find diverse applications in solar energy conversion and pollution monitoring sensors due to their suitability for mass manufacturing. However, the challenge lies in producing robust silica coatings on a large scale with tunable refractive index. This work presents a two-step acid/base catalyzed sol–gel process for synthesizing multifunctional silica coatings with adjustable refractive index. The coatings' porous microstructure allows them to be used as double-layer broadband antireflective coatings and enhances the sensitivity of contamination sensors. The optimized double-layer coatings, designed using computer-aided techniques, demonstrate excellent broadband antireflective performance in the visible regions and high environmental durability. They achieve a maximum transmittance of 99.87% at 591 nm, with an average transmittance of 99.40% in the visible region (400–800 nm) and 98.63% from 400 nm to 1100 nm. Additionally, the coatings exhibit robust abrasion resistance and enhanced surface hydrophobicity with a water contact angle increased from 30° to 126° through HMDS treatment. This work investigated the particle growth mechanism and the relationship between silica nanoparticle microstructure and antireflective coating properties. Furthermore, the coatings' presence of abundant micropores allows successful application onto microfiber contamination sensors, the additional loss increases from 26.40 dB to 37.69 dB over 140 min and decreases to 31.55 dB within one minute, demonstrating rapid adsorption and desorption rates. The work successfully achieves a wide range of adjustable refractive index while maintaining excellent mechanical and optical properties, addressing the traditional trade-off between high porosity and poor mechanical stability. These rationally designed multifunctional silica coatings hold great potential for high-quality broadband antireflection and high sensitivity in microfiber contamination sensing.

Effect of Annealing and Etching Times on Anatase TiO2 Hollow Sphere

The development of high-efficiency photocatalysts plays an important role in the application of solar energy conversion. Titanium dioxide (TiO2) with an anatase crystalline phase is well-known as semiconductor thin layers for solar cells. This work has constructed a novel TiO2 hollow sphere (HST) in a 2-step synthesis. The first step is coating the SiO2 template with TiO2 to build a core-shell of SiO2@TiO2 (CSST). The second step is etching via sonication to elute the SiO2 from CSST and construct the HST. The annealing of CSST for 1 to 6 hours and etching for 1 to 7 hours has resulted in the HST with different crystallite sizes and microstrains. The HST of ~90 nm has been fabricated with crystallite size of 9.53 to 20.54 nm and microstrain from 0.34 to 3.42. It was found that the optimum crystallite size and microstrain of HST obtained via annealing the CSST for 2 hours and etching for 5 hours has the best photooxidation of I- under UV irradiation. The optimum crystallite size and microstrain of HST via annealing and etching times can be recommended for the future of solar cell fabrication and applications.

Stepping toward Portable Optoelectronics with SnO2 Quantum Dot-Based Electron Transport Layers.

With a power conversion efficiency (PCE) of more than 25%, perovskite solar cells (PSCs) have shown an immense potential application for solar energy conversion. Owing to lower manufacturing costs and facile processibility via printing techniques, PSCs can easily be scaled up to an industrial scale. The device performance of printed PSCs has been improving steadily with the development and optimization of the printing process for the device functional layers. Various kinds of SnO2 nanoparticle (NP) dispersion solutions including commercial ones are used to print the electron transport layer (ETL) of printed PSCs, and high processing temperatures are often required to obtain ETLs with optimum quality. This, however, limits the application of SnO2 ETLs in printed and flexible PSCs. In this work, the use of an alternative SnO2 dispersion solution based on SnO2 quantum dots (QDs) to fabricate ETLs of printed PSCs on flexible substrates is reported. A comparative analysis of the performance and properties of the obtained devices with the devices fabricated employing ETLs made with a commercial SnO2 NP dispersion solution is carried out. The ETLs made with SnO2 QDs are shown to improve the performance of devices by ∼11% on average compared to the ETLs made with SnO2 NPs. It is found that employing SnO2 QDs can reduce trap states in the perovskite layer and improve charge extraction in devices.

Effect of uniaxial strains on electronic and optical properties of SnSe from first-principles calculations

In this work, we systematically investigate the uniaxial strain dependence of the electronic and optical properties of SnSe using first-principles calculations and the Bethe−Salpeter equation (BSE) approach. The calculated results show that uniaxial strains significantly affect the main peaks of density of states (DOS) in the valence band and conduction band through the influence on the densities of Sn s/p-states and Se p-state. The main peaks of the real ε1(ω) and imaginary ε2(ω) parts of the dielectric function can be enhanced by suitable uniaxial strains. In particular, the peaks of ε1(ω) and ε2(ω) along the a-axis increase by 34.8 % and 54.8 % with a red shift under the strain εa = −6 %, respectively. The high absorption coefficient in a wide energy range induced by uniaxial strains suggests a bright prospect for its applications in solar energy conversion. Our work indicates that strain engineering can be an efficient method to modulate the optical properties of SnSe and opens up a new avenue to its practical application.

Ultrafast Deposition of NiFe Metal-organic Framework Catalysts Boosts BiVO4 Photoanode for Efficient Solar Water Splitting.

The severe photocorrosion of BiVO4 limits its application in solar energy conversion in the long-term photoelectrochemical stability test. Herein, we synthesized a Fe@Ni-MOFs/BiVO4 photoanode by a simple ultrasonic method and ultrafast deposition, which avoids the problems of damaging the surface structure of photoelectrode. The Fe@Ni-MOFs/BiVO4 shows a photocurrent density of 4.89 mA cm-2 at 1.23 VRHE with an onset potential of 0.25 VRHE under one sun illumination. Importantly, a stability over 30 h at 0.7 VRHE can be obtained, which is so far the best stability character for MOFs-based cocatalysts decorated on BiVO4. During operation, Fe@Ni-MOFs transforms into a homogeneous and active hydroxide layer covering the surface, which exposes more active sites for OER reactions. This work demonstrates a simple strategy for MOFs co-catalysts to obtain fast hole transfer capability and reduce carrier recombination, thereby improving PEC performance.

Microwave-assisted synthesis of edge-grafted carbon nitride by triazole rings for efficient photocatalytic hydrogen evolution

Copolymerization of conjugated nitrogen heterocycles within carbon nitride nowadays is proven to be a successful strategy to promote charge separation. Here, a novel edge-grafted carbon nitride nanosheets by triazole rings were synthesized from the copolymerization of dicyandiamide and 3-amino-1, 2, 4-triazole via microwave-assisted heating with improved yield. Based on the building of a feasible donor-acceptor (D-A) system by such edge grafting, the rapid charge transfer pathways were formed. Benefiting from the thin-layer structure of carbon nitride via microwave-assisted heating and abundant π electrons by intramolecular doping, the system showed enhanced visible light absorption from n-π∗ electrons transition, facile charge separation and transfer, and then an increased H2 evolution rate (637.58 μmol h−1 g−1), which is 17.43 times than the triazole modified sample from conventional thermal condensation method. This work enlightens an innovative pathway for the regulation of carbon nitride photocatalysts by conjugated nitrogen heterocycles for efficient solar energy conversion applications.

Fluorinated Antimony(V) Tetraarylporphyrins as High-Valent Electron Acceptors with Unparalleled Reduction Potentials

A series of fluorinated antimony(V) porphyrins, SbTPP(OMe)2·PF6, SbTPP(OTFE)2·PF6, SbT(4F)PP(OMe)2·PF6, SbT(35F)PP(OMe)2·PF6, SbT(345F)PP(OMe)2·PF6, SbT(4CF3)PP(OMe)2·PF6, SbT(35CF3)PP(OMe)2·PF6, and SbT(35CF3)PP(OTFE)2·PF6, have been synthesized with phenyl [P], 4-fluorophenyl [(4F)P], 3,5-difluorophenyl [(35F)P], 3,4,5-difluorophenyl [(345F)P], 4-trifluoromethylphenyl [(4CF3)P], and 3,5-bis(trifluoromethyl)phenyl [(35CF3)P], in the meso-positions. Additionally, the SbTPP(OTFE)2·PF6 and SbT(35CF3)PP(OTFE)2·PF6 carry trifluoroethoxy units in their axial-positions. The fluorination on the porphyrin peripherals ranges from zero fluorine atoms in SbTPP(OMe)2·PF6 to 30 fluorine atoms in SbT(35CF3)PP(OTFE)2·PF6. X-ray crystallography confirmed the structures of the investigated antimony(V) porphyrins. The absorption spectra depend on the number of fluorine atoms as it is blue-shifted with increasing fluorination. The series also exhibited rich redox chemistry with two reduction processes and one oxidation process. Remarkably, these porphyrins manifested the lowest reduction potentials reported among the main-group porphyrins, which are as low as -0.08 V vs SCE for SbT(35CF3)PP(OTFE)2·PF6. On the contrary, the oxidation potentials were found to be very large, that is equal to 2.20 V vs SCE or even higher for SbT(4CF3)PP(OMe)2·PF6 or SbT(35CF3)PP(OMe)2·PF6 and SbT(35CF3)PP(OTFE)2·PF6, respectively. These unprecedented potentials are due to a combination of two factors: (i) the +5-oxidation state of antimony in the porphyrin cavity and (ii) the presence of the strong electron-withdrawing fluorine atoms on the porphyrin peripherals. Density functional theory (DFT) calculations were used to support the experimental results. The systematic study of antimony(V) porphyrins, especially their high potentials, make them ideal for the construction of photoelectrodes and excellent electron acceptors for photoelectrochemical cells and artificial photosynthetic systems, respectively, for solar energy conversion and storage applications.

Regulation on the electrical and optical properties of two-dimensional stacked graphene quantum dots/gold quantum dots/tungsten sulfide heterostructures

Two-dimensional (2D) transition metal dichalcogenides (TMDCs), like WS2, have been particularly promising in the application of solar energy conversion. Nevertheless, how to enhance the absorption capacity and photogenerated dcharge transfer is yet challenging. Herein, 2D stacked heterostructures were firstly constructed by 2D Au quantum dots (QDs), graphene quantum dots (GQDs) and WS2 monolayer. Compared with WS2 monolayer, the absorption abilities of the Au QDs/WS2 heterostructures in visible-near infrared light region of 450–2300 nm increase evidently. Simultaneously, charge redistribution occurs at the WS2–Au interfaces and generates the built-in electric field with the direction from Au QDs to the WS2 monolayer. This built-in electric field is conducive to boosting photo-induced charge separation and transfer. Notably, more obvious charge transfer and stronger built-in electric field can be achieved in WS2–Au6 interface after introducing the GQDs. Therefore, this work provides unique insights for designing new WS2-based heterostructures to improve the solar energy conversion.

Single-atom cobalt-incorporating carbon nitride for photocatalytic solar hydrogen conversion: An X-ray spectromicroscopy study

The use of carbon nitride-based materials and light to drive catalytic water splitting has enormous potential for the production of hydrogen. Revealing the processes of molecular conjugation, nucleation, and crystallization in crystalline carbon nitride is expected to enhance the photocatalytic activity through the creation of isotype heterojunctions and active sites. In this work, the addition of cobalt salts in ionothermal synthesis was found to promote the phase transition of heptazine-based crystalline carbon nitride (CCN) to triazine-based poly (triazine imide) (PTI), resulting in the formation of a single-atom cobalt-doped coordinated isotype CCN/PTI heterojunction. The new hybrid orbital modulates the atomic/electronic structure and the band gap of the CCN/PTI heterojunction, and synergistically increases the absorption of visible light, accelerating the separation and transfer of photoexcited electrons and holes. Synchrotron-based X-ray spectroscopy and microscopy are used to identify the origin of the improved performance of the single-atom cobalt-doped CCN/PTI heterojunction in the photocatalytic hydrogen evolution reaction. This work demonstrates that synchrotron X-ray spectroscopy is a promising tool for designing materials aimed at enhancing photocatalytic activity in solar energy conversion applications.

A review on energy conversion applications of graphene-based nanomaterials and environmental remediation

Graphene is popular for its striking physicochemical properties. Conversely, the application of pure graphene is greatly limited inert owing to its inert nature. Therefore, one of the greatest approaches to investigate graphene's intrinsic features is by functionalization. The highly conductive rGO (reduced graphene oxide) sheet is generally used as a suitable solid support for catalysts that not only inhibit carrier recombination but also improve carrier mobility to power a variety of solar energy conversion applications. According to various studies, the photocatalytic H2 production rate was found to be significantly increased by the potential electron storing and transferring characteristics of the rGO sheet, going from 16656 mol/h for Cu2O-TiO2 to 110968 mol/h for Cu2O-TiO2/rGO, or an increase of at least 7 times. The Cu2O-rGO-C3N4 photocatalyst 139 considerably enhanced the photocatalytic 4-nitrophenol reduction in comparison to the Cu2O-C3N4 photocatalyst alone. The oxygen reduction reaction, photocatalytic water splitting, photocatalytic degradation of organic contaminants, and polymer solar cells were only a few of the applications that rGO-based nanocomposites were used for in the current study.

Atomic Nickel on Graphitic Carbon Nitride as a Visible Light-Driven Hydrogen Production Photocatalyst Studied by X-ray Spectromicroscopy

The photocatalytic production of solar hydrogen through water splitting by graphitic carbon nitride (g-C3N4) has gained substantial interest due to its advantageous characteristics, such as eco-friendliness, wealth on the earth, favorable bandgap, and easy preparation. Nevertheless, the performance for photocatalytic overall water splitting has been significantly restricted owing to the rapid recombination of charge carriers and slow catalytic kinetics. This investigation demonstrates the utilization of a single-atom Ni-terminating agent to coordinate with the heptazine moieties of g-C3N4, resulting in the formation of a new electronic orbital. g-C3N4 with single-atom Ni-termination can achieve highly efficient photocatalytic overall water splitting into H2 and H2O2 upon visible light irradiation, without requiring the use of any additional cocatalysts. The underlying cause of the enhanced photocatalytic performance of single-atom Ni-incorporated g-C3N4 in hydrogen evolution reaction is identified using synchrotron X-ray spectroscopy and microscopy. The X-ray spectro-microscopic results discover that the new hybrid orbital that is critical for optimizing photocatalysis is associated with carbon defects. The atomic and electronic structures and the band gap of g-C3N4 are adjusted by the new hybrid orbital. Moreover, it synergistically enhances visible light absorption, thereby promoting the separation and transfer of photogenerated charge carriers. The single-atom Ni and the adjacent C atom are recognized as the active sites for water oxidation and reduction, respectively, supporting the efficient photocatalytic splitting of water via a two-electron transfer pathway. This study demonstrated a promising material design for promoting photocatalytic activity in solar energy conversion applications.

2D hexagonal boron nitride for solar energy conversions

The optoelectronic properties of free standing monolayer (ML) hexagonal boron nitride (h-BN) is investigated for potential solar energy conversion applications using the density functional theory (DFT) full potential linearized augmented plane wave (FP-LAPW) method. In addition, the bulk optical properties have also been calculated for the sake of comparison. The dielectric functions, optical conductivities and the optical constants are evaluated using the relaxed structures from electronic total energy pseudopotential calculations. The results reinforce previous research on h-BN DUV optoelectronics and demonstrate the suitability of its use as a component in deep ultraviolet (DUV) and energy conversion devices.

Impact of the RF Power on the Copper Nitride Films Deposited in a Pure Nitrogen Environment for Applications as Eco-Friendly Solar Absorber

This material can be considered to be an interesting eco-friendly choice to be used in the photovoltaic field. In this work, we present the fabrication of Cu3N thin films by reactive radio-frequency (RF) magnetron sputtering at room temperature, using nitrogen as the process gas. Different RF power values ranged from 25 to 200 W and gas pressures of 3.5 and 5 Pa were tested to determine their impact on the film properties. The morphology and structure were exhaustively examined by Atomic Force Microscopy (AFM), Fourier Transform Infrared (FTIR) and Raman Spectroscopies and X-ray Diffraction (XRD), respectively. The AFM micrographs revealed different morphologies depending on the total pressure used, and rougher surfaces when the films were deposited at the lowest pressure; whereas FTIR and Raman spectra exhibited the characteristics bands related to the Cu-N bonds of Cu3N. Such bands became narrower as the RF power increased. XRD patterns showed the (100) plane as the preferred orientation, that changed to (111) with the RF power, revealing a worsening in structural quality. Finally, the band gap energy was estimated from transmission spectra carried out with a Perkin Elmer 1050 spectrophotometer to evaluate the suitability of Cu3N as a light absorber. The values obtained demonstrated the capability of Cu3N for solar energy conversion applications, indicating a better film performance under the sputtering conditions 5.0 Pa and RF power values ranged from 50 to 100 W.

Fluorophore-induced plasmonic current for solar energy collection.

Biological chromophores and certain model organisms present a unique opportunity in solar energy harvesting. Currently, solar energy conversion efficiency ranges from mid to upper teens, necessitating multiple panels to generate electricity. This is a problem since many agricultural farms in the sunbelt are transitioning into solar farms, supporting the growing demand for electricity, and further deepening existing food crisis. Therefore, the system's efficiency, stability, and longevity are crucial. Advances in plasmonic materials offer promising results due to their compatibility with fluorescent biosensors and various fluorophores, suggesting potential applications in solar energy conversion. In this presentation, we discuss a technique called fluorophore-induced plasmonic current (FIPC), where plasmonic thin films and a fluorophore solution are used to generate current as a function of fluorophore concentration. In addition, we consider a few fabrication methods to increase the current response and extend the lifetime of the system. Key takeaway suggests a working range of concentration where the magnitude of current change is proportional to the increase in concentration. Our preliminary data on thin film fabrication demonstrates an increase in current response within the working range as well as lower signal to noise, leading to a stable baseline current. Future work in this project will combine our present system with molecules such as chlorophyll a and b, along with photoautotrophs like algae.

A tube heat transfer prediction model considering static friction coefficient of dense particle flow

Particulate material is an important heat transfer medium in industry. The heat transfer process of dense particle flow around tubes has important applications in industrial waste heat and solar energy conversion. However, rapid prediction of particle heat transfer processes is still worth investigating, especially when the particle flow is affected by the coefficient of friction. A heat transfer model of dense particle flow around a tube was established, the effects of particle size, density and static friction coefficient on the heat transfer characteristics were explored, and a heat transfer prediction equation considering the static friction coefficient was constructed originally. The results show that the particle size has the most significant effect on the heat transfer. As the particle size increases from 2 mm to 4 mm, the average effective heat transfer coefficient of the tube decreases from 262.35 W/(m2·K) to 217.31 W/(m2·K). The effect of particle density on the heat transfer is reflected in the difference in the heat capacity of the particles, and has little effect on the flow of the particles. The particle static friction coefficient mainly affects heat transfer by affecting the flow state of the particle flow. The average contact number decreases from 63.9 to 38.9. The relative error of the modified model is reduced from 8.9% to 3.78%.

One step fabrication of nanostructured nickel thin films on porous nickel foam for drastic electrocatalytic oxygen evolution

The oxygen evolution reaction (OER) is crucial for sustainable hydrogen production through competitive water electrocatalysis. In this work, nanostructured nickel (Ni) thin films deposited on porous nickel foam (NF) substrate are investigated for improved OER catalysis in alkaline medium. The time-dependent fabrication of Ni thin films is achieved via aerosol-assisted chemical vapor deposition (AACVD), which has shown promising impact on the OER performance. Particularly, the nanoscale Ni@NF electrocatalyst after 60-min of deposition showed outstanding OER properties including minimum overpotential of 285 and 423 mV to reach the current decade (10 mAcm−2) and even higher than 1000 mA/cm2, respectively. The electrode exhibits a small Tafel slope with a value of 70 mV dec−1, a higher TOF, a large electrochemically active surface area, better charge transport performance, and long-term stability over 20 h of continuous operation without significant loss. This OER catalytic activity for pristine Ni electrocatalysts is a significant milestone and is found much better than the benchmark noble metal OER catalysts as well as many other well-known 3D transition metal catalysts. The impressive OER performance is attributed to the synergic effect generated between nanostructured-Ni and porous NF substrate, which enhances the electrical conductivity of the designed catalysts. The low manufacturing cost, robustness, and durability make this catalyst viable in solar energy conversion and storage applications.

Carbon Quantum Dots Accelerating Surface Charge Transfer of 3D PbBiO2I Microspheres with Enhanced Broad Spectrum Photocatalytic Activity-Development and Mechanism Insight.

The development of a highly efficient, visible-light responsive catalyst for environment purification has been a long-standing exploit, with obstacles to overcome, including inefficient capture of near-infrared photons, undesirable recombination of photo-generated carriers, and insufficient accessible reaction sites. Hence, novel carbon quantum dots (CQDs) modified PbBiO2I photocatalyst were synthesized for the first time through an in-situ ionic liquid-induced method. The bridging function of 1-butyl-3-methylimidazolium iodide ([Bmim]I) guarantees the even dispersion of CQDs around PbBiO2I surface, for synchronically overcoming the above drawbacks and markedly promoting the degradation efficiency of organic contaminants: (i) CQDs decoration harness solar photons in the near-infrared region; (ii) particular delocalized conjugated construction of CQDs strength via the utilization of photo-induced carriers; (iii) π-π interactions increase the contact between catalyst and organic molecules. Benefiting from these distinguished features, the optimized CQDs/PbBiO2I nanocomposite displays significantly enhanced photocatalytic performance towards the elimination of rhodamine B and ciprofloxacin under visible/near-infrared light irradiation. The spin-trapping ESR analysis demonstrates that CQDs modification can boost the concentration of reactive oxygen species (O2•-). Combined with radicals trapping tests, valence-band spectra, and Mott-Schottky results, a possible photocatalytic mechanism is proposed. This work establishes a significant milestone in constructing CQDs-modified, bismuth-based catalysts for solar energy conversion applications.

Synergistic effect of gold NPs modified graphitic carbon nitride nanotubes (g-CNT) with the role of hot electrons and hole scavengers for boosting solar hydrogen production

The efficient and selective photocatalysts for the evolution of hydrogen are highly demanding, however, many semiconductors are complex in nature and have lower photocatalytic efficiency. This is because of their small exposed surface area, poor light penetration, and unregulated charge recombination rate. Herein, well-designed graphitic carbon nitride with hierarchical nanotextures loaded with plasmonic gold (Au) nanoparticles has been investigated for stimulating photocatalytic H2 evolution. Hole scavengers, diffusion effects, duration, and mass transfer were used to evaluate the photoactivity activity in a slurry type continuous flow photoreactor system. Due to better charge carrier separation and enhanced light permeability, H2 evolution was boosted by two times when bulk g-C3N4 structure was alternated with graphitic carbon nitride nanotubes (g-CNT). The maximum H2 generation rate was 455 μmol g−1 h−1 with 0.3% Au/g-CNT nanotexture, which was 17.8 and 8.9 times greater than utilizing g-C3N4 and g-CNT samples, respectively. The key factors influencing this improvement in photoactivity were the unique interlayer opening, higher light penetration, more light utilization due to plasmonic effect, enhanced surface reactive active sites, and decreased charge carrier recombination. The hot electrons due to plasmonic gold was another important feature to promote H2 evolution rate under solar energy. It is possible to employ these freshly developed nanotextures, which have a gold plasmonic effect, for solar energy conversion and other energy-related applications.

Numerical Simulation and Structure Optimization of Multilayer Metamaterial Plus-Shaped Solar Absorber Design Based on Graphene and SiO2 Substrate for Renewable Energy Generation

Renewable energy is the energy for future generations as it is clean and widely available. The solar absorber is a sustainable energy source that converts solar energy into heat energy. The structural optimization is analyzed to enhance the absorption of the multilayer design. The proposed efficient solar absorber is made of a multilayer plus-shaped resonator supported by a SiO2 substrate with a graphene spacer. The multilayer approach is utilized to enhance the absorption of the overall structure. The absorption of the multilayer solar absorber design is presented with AM 1.5 response observing the amount of energy absorbed from solar radiation. The different structural parameters are optimized to obtain the efficiency plus-shaped absorber design. The results of a different angle of incidence clearly show that the absorber is giving high absorption over a wide-angle range. The design results are also being analyzed with other similar works to show the improvement. The proposed absorber with high efficiency will be a good choice for solar thermal energy conversion applications.

Recent advances of cobalt-based nitride catalysts in solar energy conversion

This review predominantly focuses on the progress of a variety of cobalt-based nitride materials, especially pertaining to their photo(electro)catalytic applications in solar energy conversion.