Materials For Solar Energy Conversion Research Articles

Unravelling the effect of oxidation/reduction sites for photocatalytic H2O2 production

Metal/semiconductor heterostructures have been widely used to drive photochemical reactions. However, understanding of the synergies between them is still limited. In this study, we discovered that under ultraviolet (UV) light, rather than visible (Vis) excitation, the redox active sites oxidize adsorbed water and reduce oxygen molecules more efficiently. In this paper, the comprehensive mechanism of Ag@TiO2 photocatalysis of H2O2 has been elucidated and confirmed their synergies in photocatalytic reactions, through in situ characterization and theoretical calculation. Our findings provide insights into the key factors that influence the difference of photoactivity in UV and Vis light, thus having important implications for the design of solar energy conversion materials as well as environmental purification materials.

II-Scheme Heterojunction Frameworks Based on Covalent Organic Frameworks and HKUST-1 for Boosting Photocatalytic Hydrogen Evolution.

Covalent organic frameworks (COFs) are one type of promising polymer semiconductors in solar-driven hydrogen production, but majority of COFs-based photocatalytic systems show low photocatalytic efficiency owing to lack of metal active sites. Herein, we reported II-Scheme heterojunction frameworks based on COF (TpPa-1) and metal-organic framework (HKUST-1) for highly efficient hydrogen production. The coordination bonding directed self-assembly of HKUST-1 on the surface of TpPa-1 endows the heterojunction frameworks (HKUST-1/TpPa-1) with strong interface interaction, optimized electronic structures and abundant redox active sites, thus remarkably boosting photocatalytic hydrogen evolution. The hydrogen evolution rate for optimal HKUST-1/TpPa-1 is as high as 10.50 mmol g-1 h-1, which is significantly enhanced when compared with that of their physical mixture (4.13 mmol g-1 h-1), TpPa-1 (0.013 mmol g-1 h-1) and Pt-based counterpart (6.70 mmol g-1 h-1). This work offers a facile approach to the construction of noble-metal-free II-Scheme heterojunctions based on framework materials for efficient solar energy conversion.

The Ferroelectric Effects of Rhombohedral and Tetragonal BiFeO3 in Photoelectrochemical Water Splitting.

The phase of BiFeO3 (BFO) as well as its domain configuration can be tuned by strain engineering. Phase change may greatly influence the properties of the polarization field and hence charge separation. However, the photoelectrochemical properties of different BFO phases have rarely been addressed. Here, the photoelectrochemical study of tetragonal (T-) and rhombohedral (R-) phase BFO films was conducted under visible light illumination. The photocurrent density of R-BFO is 5 times that of T-BFO. A ferroelectric domain study shows that T-BFO features single domain structure in contrast to the polydomain structure of R-BFO. Higher charge separation efficiency is achieved in R-BFO, dominated by the domain walls as conducting pathways for efficient charge separation and transfer. This work provides a fundamental understanding of the photoelectrochemical properties of T- and R-BFO, offering valuable insights for the development of BFO-based materials for solar energy conversion.

A Visible Light-Responsive TiO2 Photocathode Achieved by a Rh Dopant.

Developing an efficient and stable photocathode material for photoelectrochemical solar water splitting remains challenging. Herein, we demonstrate the potential of rutile TiO2 as a photocathode by Rh doping with visible light absorption up to 640 nm and an onset potential of 0.9 V versus the reversible hydrogen electrode. The dopant transforms the rutile host from an n-type semiconductor to a p-type one, as confirmed by the Mott-Schottky curve and kelvin probe force microscopy. Physical and photoelectrochemical analyses further suggest that the doping mechanism is dependent on concentration. Lower levels of dopants generate localized Rh3+, while higher levels favor Rh4+ that interacts more strongly with the O 2p orbitals. The latter is found not only to extend the visible light absorption range but also to facilitate charge transport. This work elucidates the role of the Rh dopant in adjusting the photoelectrochemical behavior of TiO2, and it provides a promising photocathode material for solar energy conversion.

Understanding the effect of multiple configurations in polymeric carbon nitride for efficient solar-driven hydrogen peroxide photosynthesis

A oxygen and potassium co-doped polymeric carbon nitride (O/K-PCNs) was simply constructed by an acid gas cutting strategy for photocatalytic H2O2 generation. The effect of each accompanied configurations on photosynthesis of H2O2 was systematically analyzed. The C–O–C structure formed by O doping is capable of decreasing K ions incorporated energy barrier, thus remarkably improving the content of crucial K active sites. Dual heteroatom sites synergistically enhance O2 adsorption and surface ORR by a bridge K–O–O–C model. Moreover, the accompanied cyano defect and poly(heptazine imide) is responsible for improving in-plane and interlayer carriers separation, respectively. The optimal O/K-PCNs exhibits 60-fold higher photocatalytic H2O2 production rate than pure PCN. A positive correlation between the H2O2 production rate and the K heteratoms content was established. This work clarifies role of multiple configurations in PCN, especially O-containing groups, providing a new insight for design heteroatoms-doped materials for solar energy conversion.

Control over Charge Separation by Imine Structural Isomerization in Covalent Organic Frameworks with Implications on CO2 Photoreduction.

Two-dimensional covalent organic frameworks (COFs) are an emerging class of photocatalytic materials for solar energy conversion. In this work, we report a pair of structurally isomeric COFs with reversed imine bond directions, which leads to drastic differences in their physical properties, photophysical behaviors, and photocatalytic CO2 reduction performance after incorporating a Re(bpy)(CO)3Cl molecular catalyst through bipyridyl units on the COF backbone (Re-COF). Using the combination of ultrafast spectroscopy and theory, we attributed these differences to the polarized nature of the imine bond that imparts a preferential direction to intramolecular charge transfer (ICT) upon photoexcitation, where the bipyridyl unit acts as an electron acceptor in the forward imine case (f-COF) and as an electron donor in the reverse imine case (r-COF). These interactions ultimately lead the Re-f-COF isomer to function as an efficient CO2 reduction photocatalyst, while the Re-r-COF isomer shows minimal photocatalytic activity. These findings not only reveal the essential role linker chemistry plays in COF photophysical and photocatalytic properties but also offer a unique opportunity to design photosensitizers that can selectively direct charges.

Nanostructured metal-oxide materials for solar energy absorption and conversion for industrial heater applications

As the most plentiful energy source on Earth, solar energy possesses the potential to fulfill all of humanity's energy requirements if harnessed to its full extent. Unlike finite fossil fuels, solar energy is a renewable resource that can be utilized indefinitely and does not contribute to climate change. The applicability of metal-oxides (TiO2) multi-ring resonator broad solar absorber (MOMRAB) for solar energy applications was examined in this work. A metal oxide layer and a multi-ring resonator structure combine to absorb sunlight at a variety of wavelengths (200 nm–900 nm) in the MOMRAB. While the metal oxide layer absorbs sunlight in the visible and infrared portions of the spectrum, the multi-ring resonator structure traps sunlight and lengthens its route within the MOMRAB. The MOMRAB is a promising material for a variety of applications due to its good absorptance (95.07 %) and polarization insensitivity across a wide wavelength range from 200 nm to 900 nm (700 nm). Along with examining the resonator's electric field, the research also included the polarization independence and incidence angle independence of the structure. Radiation barriers, solar induction systems, water and air warmers, and industrial heaters are a few possible uses for the MOMRAB. It is appropriate for space and satellite missions due to its zero transmittance and capacity to absorb a sizable amount of space radiation.

Application of graphdiyne for promote efficient photocatalytic hydrogen evolution

The photocatalytic hydrogen evolution technology converts solar energy into clean and environmentally friendly hydrogen energy, which is considered an effective means to solve environmental pollution and energy crisis. The unique sp and sp2 hybrid carbon network structure of graphdiyne endows it with excellent carrier mobility, and high porosity, making it a promising photocatalytic material for solar energy conversion. This article provides a detailed description of the unique structural properties and adjustable bandgap of graphdiyne. In addition, a detailed review was provided on the modification strategies of graphdiyne based catalysts for photocatalytic hydrogen evolution, including titanium based photocatalysts, metal oxide photocatalysts, double hydroxide catalysts, metal organic framework photocatalysts and other typical semiconductors. Finally, the challenges and opportunities for developing graphdiyne semiconductors for photocatalytic water splitting were proposed. Timely review is expected to contribute to the rapid development of graphdiyne in the field of photocatalytic hydrogen evolution.

Structure-based screening of sp2 hybridized small donor bridges as donor: acceptor switches for optical and photovoltaic applications: DFT way.

This research aims to investigate the potential of pyrazine-based small donor moieties as donor-acceptor switches for optical and photovoltaic applications. The designed organic dyes have a high light harvesting efficiency (LHE) and can potentially generate significant electrical energy. The study focuses on understanding the structural and electronic properties of these dyes through the analysis of dihedral angles, bond lengths, and energies of frontier molecular orbitals The UV-Vis spectroscopy parameters of the designed organic dyes revealed their absorption characteristics, including transition energies, wavelengths (λmax), and oscillator strengths (f). The photovoltaic properties of the developed organic dyes show a range of values: a range of 0.95-0.99 for LHE and a range of 1.77-33.02 W for maximum power output (Pmax) with the highest value for dye DDP5. For their stabilization energies, their natural bond orbitals had values ranging from 0.56 to 128.48kcal/mol, their E(j)E(i) values from 0.22 to 1.29 a.u, and their Fi,j values from 0.024 to 0.213kcal/mol. Out of all dyes, the DDP5 produced highest push-pull effect and can be good choice for further studies. The design of these novel organic materials for effective and economical solar energy conversion will be aided by evaluating the potential of 5,10-diphenyl-5,10-dihydrophenazine as a donor moiety and determining the structure-property correlations controlling the photovoltaic performance of the compounds.

Novel composite phase change materials supported by oriented carbon fibers for solar thermal energy conversion and storage

Phase change materials (PCMs) have aroused significant interest as promising materials for solar thermal energy conversion and storage. However, the long-standing shortcomings of liquid leakage, low thermal conductivity, and weak solar absorptance limit their practical applications. Herein, novel composite phase change materials (CPCMs) with anisotropic heat conduction are manufactured by mixing continuous carbon fibers (CFs) and palmitic acid (PA)/olefin block copolymer (OBC) mixtures using pressure induction and vacuum treatment. Because the oriented CFs in the vertical direction can offer heat transfer channels inside the composites, the vertical and horizontal thermal conductivities of the CPCMs are 5.84 W·K−1·m−1 and 1.34 W·K−1·m−1, respectively, resulting in a relatively high anisotropic degree of 4.36. Furthermore, to improve the absorption of solar radiation for the composite, carbon black is applied to the upper surface of the CPCMs, achieving a high total solar absorptance of 0.966. Due to the combination of the high solar absorptance of the carbon black and the high vertical thermal conductivity within the composites, the CPCMs exhibit outstanding solar-to-thermal efficiencies of 87.54% ∼ 95.08% at 1– 3 kW·m−2. In addition, stability testing also confirms that the CPCMs have excellent leakage-proof properties, thermal stability, and cyclic stability for long-term utilization. This work can provide an efficient route to synthesize high-performance CPCMs for solar thermal applications.

Post‐Synthetic Silver Ion and Sulfurization Treatment for Enhanced Performance in Sb2Se3 Water Splitting Photocathodes

AbstractIn the past decade, antimony selenide (Sb2Se3) has made significant progress as a solar energy conversion material. However, the photovoltage deficit continues to pose a challenge and is a major hurdle that must be overcome to reach its maximum solar conversion efficiency. In this study, various post‐synthetic treatments are employed, of which the combination of a solution phase silver nitrate treatment and sulfurization has shown to be the most effective approach to mitigate the photovoltage deficit in this Sb2Se3‐based device. A significant enhancement in the photovoltage is observed after the treatments, as evident by the increase in the onset potential from 0.18 to 0.40 V versus reversible hydrogen electrode. Multiwavelength Raman shows that combining these two treatments removes amorphous Se and metallic Sb from the surface and yields a high‐quality surface layer of Sb2(S1−x, Sex)3 on the bulk Sb2Se3 photoabsorber layer. X‐ray photoelectron spectroscopy with depth profiling reveals extensive incorporation of silver into the film. Density functional theory calculations suggest that silver ions can intercalate between the [Sb4Se6]n ribbons and remain in the Ag+ state. This effective treatment combination brings the practicality of the Sb2Se3 photocathode for water splitting one step closer to large‐scale applications.

Directional spatial charge separation in well-designed S-scheme In2S3–ZnIn2S4/Au heterojunction toward highly efficient photocatalytic hydrogen evolution

Constructing efficient and stable photocatalysts are quite crucial for solar-to-hydrogen energy conversion, which remains a great challenge. Nowadays, many photocatalysts still suffer from low solar energy conversion efficiency due to the rapid recombination of photoirradiated carriers mainly caused by their random flow. Regulating charge separation and transport is essential to improve the catalytic activity of photocatalysts toward highly efficient photocatalytic hydrogen production. Herein, a S-scheme In2S3–ZnIn2S4/Au heterojunction with coherent interfaces were constructed. Particularly, as a reduction cocatalyst, the plasmonic metallic Au nanoparticles were loading on the outer surface of S-scheme In2S3–ZnIn2S4 heterojunction. The coordination of S-scheme heterojunction and reductive cocatalyst can produce a directional spatial charge separation and transfer in In2S3–ZnIn2S4/Au heterojunction, leading to a highly efficient photocatalytic hydrogen production. As expected, the well-designed S-scheme In2S3–ZnIn2S4/Au heterojunction presents a remarkable H2 production rate of 12,369 μmol h−1 g−1. This charge transfer modulation mechanism may be applied to design other remarkable photocatalytic materials for efficient solar energy conversion.

Live Cell and Hybrid Material Based Bio-Photoelectrochemical Cells for Clean Solar Energy Conversion

Photosynthetic organisms and complexes are attractive starting materials for solar energy conversion (SEC). I will describe here how the remarkable photocatalytic activity of the photosynthetic apparatus can provide overall water splitting with oxygen and hydrogen production in Bio-Photo-Electro-Chemical (BPEC) cells (Fig. 1). Use of isolated photosynthetic systems tightly associated with different electrodes has the benefit of potentially high reaction center density. However, the cross-section for light absorption is poor, leading to sub-optimal activity. Disconnection from biological repair mechanisms leads to limited lifetime. On the other hand, use of intact, live systems have the benefit of evolutionarily optimized light harvesting antennas for improved energy absorption and transfer, and all of these organisms have excellent repair systems leading to essentially endless activity. However, how these intact systems can be functionally connected to the BPEC depends on the morphology, permeability and flux of electron carriers. We will show here that we can obtain significant electrical current using a variety of live photosynthetic organisms, each with benefits and drawbacks. Cyanobacteria1,2 and microalgae3 are applied directly to the BPEC anode, providing continuous current densities in the 10’s of μA/cm2. Use of photosynthetic tissues from macroalgae (seaweeds)4 or higher plants5 require tight association with metallic anodes (stainless steel, aluminum, etc.) leading to current densities of >50mA/cm2, with high ionic strength electrolyte solutions supporting these increased current densities. Succulents can serve as their own BPEC6. In all cases, the major electron carrier is NADPH which is released by the cells and tissues into the electrolyte. A different strategy is to use isolated photosynthetic complexes and chemically connect them to the electrochemical cell. To overcome the problem of lower number of light absorbing chromophores connected to each reaction center we can use either isolated biological light harvesting (LH) complexes or nanoparticles (NPs). As Photosystem II (PSII) is the only enzyme that catalyzes light-induced water oxidation, we focus on its use in these systems. PSII can be isolated from a wide variety of organisms, each with relative benefits or disadvantages: isolation ease and cost, quantity per cell, stability to heat or other external stress, etc. PSII contains chlorophyll a which absorbs well in the 400-500nm and 600-700nm region, limiting the quantum efficiency in the gap in the green absorption region (500 - 600 nm). To overcome this limitation, we have used two strategies: stabilizing the interaction between PSII and isolated thermophilic cyanobacterial Phycobilisomes LH complex within an Os-complex-modified hydrogel on macro-porous indium tin oxide electrodes (MP-ITO). This results in notably improved, wavelength dependent, incident photon-to-electron conversion efficiencies7. Another strategy was to isolate market-purchased spinach PSII (cheap and abundant) and associate them via a unique binding shell to gold-nanoparticles (Au-NPs)8. These Au-NP were shown to serve as both light harvesting modules in the green gap, as well as conduits of electrons from the bound PSII to the BPEC, leading to record current densities were obtained. Figure 1

Bis‐ and Tris‐norbornadienes with High Energy Densities for Efficient Molecular Solar Thermal Energy Storage

AbstractMolecular solar thermal energy storage (MOST) systems can convert, store and release solar energy in chemical bonds, i.e., as chemical energy. In this work, phenyl‐ and naphthyl‐linked bis‐ and tris‐norbornadienes are presented as promising MOST systems with very high energy densities. The substrates were synthesized by Suzuki–Miyaura coupling reactions and their absorption properties and characteristic parameters for MOST applications were investigated. The norbornadiene derivatives showed absorption onsets of up to 386 nm and photoisomerization quantum yields of 56 % per photoisomerization event. The resulting quadricyclane products have half‐lifes up to 14 d and very high energy densities of up to 734 kJ/kg. Overall, these norbornadienes fulfill necessary criteria for an optimal MOST system and are, therefore, a highly promising basis for the development of materials for efficient solar energy conversion and storage.

Bis- and Tris-norbornadienes with High Energy Densities for Efficient Molecular Solar Thermal Energy Storage.

Molecular solar thermal energy storage (MOST) systems can convert, store and release solar energy in chemical bonds, i.e., as chemical energy. In this work, phenyl- and naphthyl-linked bis- and tris-norbornadienes are presented as promising MOST systems with very high energy densities. The substrates were synthesized by Suzuki-Miyaura coupling reactions and their absorption properties and characteristic parameters for MOST applications were investigated. The norbornadiene derivatives showed absorption onsets of up to 386 nm and photoisomerization quantum yields of 56% per photoisomerization event. The resulting quadricyclane products have half-lifes up to 14 d and very high energy densities of up to 734 KJ/Kg. Overall, these norbornadienes fulfill necessary criteria for an optimal MOST system and are, therefore, a highly promising basis for the development of materials for efficient solar energy conversion and storage.

Non-Covalent Assembly of Multiple Fluorophores in Edible Protein/Lipid Hydrogels for Applications in Multi-Step Light Harvesting and White-Light Emission.

The design and production of biodegradable and sustainable non-toxic materials for solar-energy harvesting and conversion is a significant challenge. Here, our goal was to report the preparation of novel protein/lipid hydrogels and demonstrate their utility in two orthogonal fundamental studies-light harvesting and white-light emission. Our hydrogels contained up to 90% water, while also being self-standing and injectable with a syringe. In one application, we loaded these hydrogels with suitable organic donor-acceptor dyes and demonstrated the energy-transfer cascade among four different dyes, with the most red-emitting dye as the energy destination. We hypothesized that the dyes were embedded in the protein/lipid phase away from the water pools as monomeric entities and that the excitation of any of the four dyes resulted in intense emission from the lowest-energy acceptor. In contrast to the energy-transfer cascade, we demonstrate the use of these gels to form a white-light-emitting hydrogel dye assembly, in which excitation migration is severely constrained. By restricting the dye-to-dye energy transfer, the blue, green, and red dyes emit at their respective wavelengths, thereby producing the composite white-light emission. The CIE color coordinates of the emission were 0.336 and 0.339-nearly pure white-light emission. Thus, two related studies with opposite requirements could be accommodated in the same hydrogel, which was made from edible ingredients by a simple method. These gels are biodegradable when released into the environment, sustainable, and may be of interest for energy applications.

A Data-Driven Platform for Two-Dimensional Hybrid Lead-Halide Perovskites.

The exceptional properties of two-dimensional hybrid organic-inorganic lead-halide perovskites (2D HOIPs) have led to a rapid increase in the number of low-dimensional materials for optoelectronic engineering and solar energy conversion. The flexibility and controllability of 2D HOIPs create a vast structural space, which presents an urgent issue to effectively explore 2D HOIPs with better performance for practical applications. However, the traditional RP-DJ classification method falls short in describing the influence of structure on the electronic properties of 2D HOIPs. To overcome this limitation, we employed inorganic structure factors (SF) as a classification descriptor, which considers the influence of inorganic layer distortion of 2D HOIPs. And we investigated the relationship between SF, other physicochemical features, and band gaps of 2D HOIPs. By using this structural descriptor as a feature for a machine learning model, a database of 304920 2D HOIPs and their structural and electronic properties was generated. A large number of previously neglected 2D HOIPs were discovered. With the establishment of this database, experimental data and machine learning methods were combined to develop a 2D HOIPs exploration platform. This platform integrates searching, download, analysis, and online prediction, providing a useful tool for the further discovery of 2D HOIPs.

Copper Nitride: A Versatile Semiconductor with Great Potential for Next-Generation Photovoltaics

Copper nitride (Cu3N) has gained significant attention recently due to its potential in several scientific and technological applications. This study focuses on using Cu3N as a solar absorber in photovoltaic technology. Cu3N thin films were deposited on glass substrates and silicon wafers via radio-frequency magnetron sputtering at different nitrogen flow ratios with total pressures ranging from 1.0 to 5.0 Pa. The thin films’ structural, morphology, and chemical properties were determined using XRD, Raman, AFM, and SEM/EDS techniques. The results revealed that the Cu3N films exhibited a polycrystalline structure, with the preferred orientation varying from 100 to 111 depending on the working pressure employed. Raman spectroscopy confirmed the presence of Cu-N bonds in characteristic peaks observed in the 618–627 cm−1 range, while SEM and AFM images confirmed the presence of uniform and smooth surface morphologies. The optical properties of the films were investigated using UV-VIS-NIR spectroscopy and photothermal deflection spectroscopy (PDS). The obtained band gap, refractive index, and Urbach energy values demonstrated promising optical properties for Cu3N films, indicating their potential as solar absorbers in photovoltaic technology. This study highlights the favourable properties of Cu3N films deposited using the RF sputtering method, paving the way for their implementation in thin-film photovoltaic technologies. These findings contribute to the progress and optimisation of Cu3N-based materials for efficient solar energy conversion.

Alternative lead-free mixed-valence double perovskites for high-efficiency photovoltaic applications

Lead-based organic-inorganic hybrid perovskites have exhibited great potential in photovoltaics, achieving power conversion efficiencies (PCEs) exceeding 25%. However, the toxicity of lead and the instability of these materials under moist conditions pose significant barriers to large-scale production. To overcome these limitations, researchers have proposed mixed-valence double perovskites, where Cs2AuIAuIIII6 is a particularly effective absorber due to its suitable band gap and high absorptance efficiency. To further extend the scope of these lead-free materials, we varied the trivalent gold ion and halogen anion in Cs2AuIAuIIII6, resulting in 18 new structures with unique properties. Further, using first-principles calculations and elimination criteria, we identified four materials with ideal band gaps, small effective carrier mass, and strong anisotropic optical properties. According to theoretical modeling, Cs2AuSbCl6, Cs2AuInCl6, and Cs2AuBiCl6 are potential candidates for solar cell absorbers, with a spectroscopic limited maximum efficiency (SLME) of approximately 30% in a 0.25 μm-thick film. These three compounds have not been previously reported, and therefore, our work provides new insights into potential materials for solar energy conversion. We aim for this theoretical exploration of novel perovskites to guide future experiments and accelerate the development of high-performance photovoltaic devices.

Multi-layered Ti–Si solar absorber design based on tungsten material for solar thermal energy conversion

We present a solar absorber with a higher absorptance with Multi-layers Titanium (Ti)- Silicon (Si) based on Tungsten material. Tungsten is used as a ground layer, and Si and Ti are stacked in multilayered positions above that. The absorptance can be calculated in six peak wavelengths between the overall wavelength spectrum for 0.2–3 μm. The overall solar absorptance is 93.87% with a bandwidth of 2300 nm, above 95% with a bandwidth of 1000 nm, and above 97% at 800 nm. The situation of solar absorptance is improved by adding multi-layered structure and this is also exhibited with the respective absorptance (A), reflectance (R), and transmittance (T) step by step. Moreover, all absorptance are distributed in one figure, and AM 1.5 figure is also included. The solar absorption variation can also be checked by changing the parameters of ground layer width and thickness, and Ti and Si resonator thickness. The solar absorption situation can be expressed in TE and TM modes by changing the degree from 0 to 50. The electric field intensity and comparison between other published works are also presented. Thus, the proposed solar absorber can be possible to use in many ways with a higher absorptance. It can be provided from individual home facilities to production in large industries.