Materials For Solar Energy Conversion Research Articles

Ligand-assisted synthesis of novel π-SnS tetrahedrons for enhanced photocatalytic H2 evolution from water

Tin sulfide (SnS) is a potentially promising chalcogenide material for efficient solar energy conversion. In this study, pure π-SnS particles with a novel cubic phase were successfully synthesized by a simple one-pot solvothermal reaction method. The effects of solvothermal reaction time and amount of the ligand, hexamethyldisilazane (HMDS), on physical and photocatalytic properties were investigated. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction revealed that the obtained π-SnS consisted of tetrahedral particles with a high degree of crystallinity and exhibited a cubic phase. UV-Vis transmission spectra and photoluminescence (PL) revealed that the bandgap of π-SnS particles was about 1.62 eV. Importantly, the H2 evolution capacity of π-SnS particles prepared with Tin-HMDS complexes was dramatically improved. About 12-fold and 23-fold larger amounts of H2 were produced than the amounts produced by π-SnS particles prepared without HMDS and α-SnS particles with similar size, respectively. Post-annealing treatment further confirmed the existence of surface ligands and their importance for the photocatalytic activity of particles. X-ray photoelectron spectroscopy (XPS) revealed HMDS ligands instead of oleylamine molecules interacted with π-SnS particles.

Molecular ladder polymer network enables scalable and robust solar water oxidation

Organic polymers with tunable band structures and light absorption properties offer a versatile alternative to inorganic materials for solar energy conversion. However, advancing organic polymers for efficient solar water oxidation has been hindered by challenges in charge separation and transport. Here we develop a molecular strategy to achieve an apparent quantum yield of 22 % for solar water oxidation by using a ladder polymer network coupled with a FeNi catalyst. Solar irradiation of the photocatalytic network produces high-flux excited states capable for catalyst activation, generating persistent charge-separated states available for water oxidation. The network exhibits high robustness during 125-hour solar water oxidation, showing negligible decrease in the photocatalytic activity. Owing to improved charge transport, the photocatalytic network is scaled up from 1.0 cm2 to 25 cm2 without sacrificing the quantum efficiency. Our findings herald the potential of ladder polymer networks toward scalable manufacturing of high-efficiency and cost-effective organic photocatalysts.

Mechanically Exfoliated InP Thin Films for Solar Energy Conversion Devices

III‐V semiconductors are favoured photo absorber materials for solar energy conversion due to their ideal bandgap, yet their high‐cost hinders widespread adoption. Utilizing thin films of these semiconductors presents a viable way to address the cost‐related challenges. Here, a novel mechanical exfoliation technique is demonstrated, also known as controlled spalling, as a cost‐effective and facile way to obtain thin films of III‐V semiconductors. As a proof of concept, 15 μm thick InP films are successfully exfoliated from their original wafers. Thorough characterization using cathodoluminescence and photoluminescence spectroscopy confirms that the opto‐electronic properties of the exfoliated InP films remain unaffected. Utilizing these InP thin films, InP thin‐film heterojunction solar cells with efficiencies exceeding 13% are demonstrated. Additionally, InP photoanodes are fabricated by integrating NiFeOOH catalyst onto these InP thin‐film solar cells, achieving an impressive photocurrent density of 19.3 mA cm−2 at 1.23 V versus reversible hydrogen electrode, along with an applied bias photon‐to‐current efficiency of ≈4%. Overall, this study showcases the efficacy of controlled spalling in advancing economically viable and efficient III‐V semiconductor‐based solar energy conversion devices.

Nanoscale engineering of semiconductor photocatalysts boosting charge separation for solar-driven H2 production: Recent advances and future perspective

Abstract Photocatalytic hydrogen (H₂) production is regarded as an efficient method for generating renewable energy. Despite recent advancements in photocatalytic water splitting, the solar-to-hydrogen conversion efficiency of photocatalysts remains well below the 10% target needed for commercial viability due to ongoing scientific challenges. This review comprehensively analyzes recent advancements in nanoscale engineering of photocatalytic materials, emphasizing techniques to enhance photogenerated charge separation for efficient solar hydrogen production. Here we highlight the nanoscale engineering strategies for effective charge separation including crystal engineering, junction engineering, doping-induced charge separation, tailoring optoelectronic properties, hierarchical architecture, defects engineering, various types of heterojunctions, and polarity-induced charge separation, and discuss their unique properties including ferroelectric on spatial charge separation along with the fundamental principles of light-induced charge separation/transfer mechanisms, and the techniques for investigation. This study, critically assesses strategies for effective photogenerated charge separation to enhance photocatalytic hydrogen production and offers guidance for future research to design efficient energy materials for solar energy conversion.

SPR Effect Enables Flexible Electronic Environment and Activity of Cd0.7In2.2S4-30 for High-Performance Pyro-PEC Catalytic Capability.

Plasma-semiconductor systems hold significant promise in the field of photoelectrocatalysis. In this study, the pyroelectric material cadmium indium sulfide (Cd0.7In2.2S4-30) and Pt were used as catalysts, and a temperature gradient was introduced to investigate the influence of surface plasmon resonance (SPR) effect on the pyroelectric and photocatalytic performance. Interestingly, under the influence of the SPR effect, Cd0.7In2.2S4-30 demonstrates a 1.6-fold and 1.4-fold increase in current density under photocatalytic and pyro-photoelectrocatalytic conditions at 1.23 V vs RHE, respectively. Furthermore, under the protection of surface metal Pt, a notable enhancement in the charge separation efficiency and stability of the photoelectrode material is observed. The combination of outstanding performance reveals that Pt noble metal ions, influenced by the SPR effect, generate a localized electric field at the adjacent semiconductor interface, enhancing the charge transfer capability between metal nanoparticles and the semiconductor, thereby promoting electron-hole separation and improving semiconductor photocatalytic activity. Additionally, the SPR effect increases the yield of high-energy pyro-electrons on plasma metal and facilitates their effective transfer to the semiconductor, thereby promoting the generation of thermally induced electrons. This study reveals the multifaceted of SPR effects on the behaviors of semiconductors and provides an opportunity to rationally design metal-semiconductor photocatalytic materials for efficient solar energy conversion.

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.

Dual back interface engineering optimized charge carrier dynamics in Sb2(S,Se)3 photocathodes for efficient solar hydrogen production.

Antimony sulfoselenide (Sb2(S,Se)3) is a promising sunlight absorber material for solar energy conversion in photovoltaic (PV) cells and photoelectrochemical (PEC) photoelectrodes due to its excellent photoelectric properties. However, the obtained thin-film and back contact properties significantly influence the PEC performance of photocathodes, causing severe bulk recombination, carrier transport loss, and deteriorating half-cell solar-to-hydrogen (HC-STH) efficiency. This study introduces an intriguing dual back interface engineering strategy for Sb2(S,Se)3 photocathodes by incorporating an intermediate MoO2 layer and a secondary carrier transport channel of Au to strengthen charge carrier dynamics. The synergistic assembly of these dual back interface layers improves the growth kinetics and achieves the optimal orientation of Sb2(S,Se)3 thin films by increasing substrate wettability. Moreover, by shortening the back contact barrier height and passivating defect-assisted recombinations, these dual back underlayers simultaneously enhance carrier transport and separation efficiencies. As a result, the photocurrent density of the champion Sb2(S,Se)3 photocathode increases from 5.89 to 32.60 mA cm-2, and the HC-STH conversion efficiency improves significantly from 0.30% to 3.58%, representing the highest value for Sb2(S,Se)3-based photocathodes. This work highlights the effectiveness of dual back interface engineering in promoting the PEC performance of chalcogenide photocathodes for solar hydrogen evolution applications.

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.