Fast Interfacial Carrier Dynamics Modulated by Bidirectional Charge Transport Channels in ZnIn2 S4 -based Composite Photoanodes Probed by Scanning Photoelectrochemical Microscopy.

Limited charge separation/transport efficiency remains the primary obstacle of achieving satisfying photoelectrochemical (PEC) water splitting performance. Therefore, it is essential to develop diverse interfacial engineering strategies to mitigate charge recombination. Despite obvious progress having been made, most works only considered a single-side modulation in either the electrons of conduction band or the holes of valence band in a semiconductor photoanode, leading to a limited PEC performance enhancement. Beyond this conventional thinking, we developed a novel coupling modification strategy to achieve a composite electrode with bidirectional carrier transport for a better charge separation, in which Ti2 C3 Tx MXene quantum dots (MQDs) and α-Fe2 O3 nanodots (FO) are anchored on the surface of ZnIn2 S4 (ZIS) nanoplates, resulting in markedly improved PEC water splitting of pure ZIS photoanode. Systematic studies indicated that the bidirectional charge transfer pathways were stimulated due to MQDs as "electron extractor" and S-O bonds as carriers transport channels, which synergistically favors significantly enhanced charge separation. The enhanced kinetic behavior at the FO/MQDs/ZIS interfaces was systematically and quantitatively evaluated by a series of methods, especially scanning photoelectrochemical microscopy. This work may deepen our understanding of interfacial charge separation, and provide valuable guidance for the rational design and fabrication of high-performance composite electrodes.

Unveiling the Influence of Sulfur Doping on Photoelectrochemical Performance in BiVO4/FeOOH Heterostructures.

BiVO4 is a promising photoanode for photoelectrochemical (PEC) water splitting but suffers from high charge carrier recombination and sluggish surface water oxidation kinetics that limit its efficiency. In this work, a model of sulfur-incorporated FeOOH cocatalyst-loaded BiVO4 was constructed. The composite photoanode (BiVO4/S-FeOOH) demonstrates an enhanced photocurrent density of 3.58 mA cm-2, which is 3.7 times higher than that of the pristine BiVO4 photoanode. However, the current explanations for the generation of enhanced photocurrent signals through the incorporation of elements and cocatalyst loading remain unclear and require further in-depth research. In this work, the hole transfer kinetics were investigated by using a scanning photoelectrochemical microscope (SPECM). The results suggest that the incorporation of sulfur can effectively improve the charge transfer capacity of FeOOH. Moreover, the oxygen evolution reaction model provides evidence that S-doping can induce a "fast" surface catalytic reaction at the cocatalyst/solution interface. The work not only presents a promising approach for designing a highly efficient photoanode but also offers valuable insights into the role of element doping in the PEC water-splitting system.

Self-standing boron nitride bulks enabled by liquid metals for thermal management.

Thermally conductive materials (TCMs) are highly desirable for thermal management applications to tackle the "overheating" concerns in the electronics industry. Despite recent progress, the development of high performance TCMs integrated with an in-plane thermal conductivity (TC) higher than 50.0 W (m K)-1 and a through-plane TC greater than 10.0 W (m K)-1 is still challenging. Herein, self-standing liquid metal@boron nitride (LM@BN) bulks with ultrahigh in-plane TC and through-plane TC were reported for the first time. In the LM@BN bulks, LM could serve as a bonding and thermal linker among the oriented BN platelets, thus remarkably accelerating heat transfer across the whole system. Benefiting from the formation of a unique structure, the LM@BN bulk achieved an ultrahigh in-plane TC of 82.2 W (m K)-1 and a through-plane TC of 20.6 W (m K)-1, which were among the highest values ever reported for TCMs. Furthermore, the LM@BN bulks exhibited superior compressive and leakage-free performances, with a high compressive strength (5.2 MPa) and without any LM leakage even after being crushed. It was also demonstrated that the excellent TCs of the LM@BN bulks made them effectively cool high-power light emitting diode modules. This work opens up one promising pathway for the development of high-performance TCMs for thermal management in the electronics industry.

Dual modification of BiVO4 photoanode for synergistically boosting photoelectrochemical water splitting.

Bismuth vanadate (BiVO4) is a promising nanomaterial for photoelectrochemical (PEC) water oxidation. However, the serious charge recombination and sluggish water oxidation kinetics limit its performance. Herein, an integrated photoanode was successfully constructed by modifying BiVO4 (BV) with In2O3 (In) layer and further decorating amorphous FeNi hydroxides (FeNi). The BV/In/FeNi photoanode exhibited a remarkable photocurrent density of 4.0 mA cm-2 at 1.23 VRHE, which is approximately 3.6 times larger than that of pure BV. And the water oxidation reaction kinetics has an over 200% increased. This improvement was mainly because the formation of BV/In heterojunction inhibited charge recombination, and the decoration of cocatalyst FeNi facilitated the water oxidation reaction kinetics and accelerated hole transfer to electrolyte. Our work provides another possible route to develop high-efficiency photoanodes for practical applications in solar conversion.

Analysis of the clinical outcomes of microbial contamination caused by environmental contamination of the embryology laboratory during IVF-ET treatment cycles.

BACKGROUND: Bacterial contamination may cause loss of or damage to cultured oocytes or embryos, resulting in the lack of transplantable embryos during IVF embryo culture. However, there are few reports about IVF embryo contamination caused by embryology laboratories. In this work, we evaluated clinical pregnancy outcomes and the risk of maternal and infant complications after embryo contamination caused by environmental pollution during IVF. METHODS: The authors retrospectively analyzed 2490 IVF-ET ovulation induction therapy cycles in the Reproductive Center of Yichang Central People's Hospital from January 2015 to May 2022. According to the presence or absence of embryo culture medium contamination, the two groups were divided into an embryo contamination cycle and a nonembryo contamination cycle. The primary outcome parameters were the characteristics and progress of embryo culture medium contamination. Embryo laboratory outcomes, pregnancy outcomes, and maternal and infant complications were secondary outcome parameters. RESULTS: One case of embryo contamination originated from semen contamination. The remaining 15 cases involved environmental contamination outbreaks in embryo culture chambers, caused by Staphylococcus pasteuri. Compared with conventional uncontaminated IVF cycles, the 15 cases of contaminated embryo cycles showed no significant difference in embryo laboratory outcomes, pregnancy outcomes, or maternal and infant complications except for a slightly higher rate of fetal growth retardation. Ultimately, 11 live-born infants were successfully delivered, of which 2 were premature. The remaining 4 patients did not become pregnant after 1-2 transfers due to a lack of transferable embryos. CONCLUSION: When the embryo culture medium is contaminated due to the environmental contamination of the IVF culture room, it is feasible to perform daily rapid rinsing of the culture medium and avoid blastocyst culture as remedial treatment. However, the long-term impact on offspring needs further prospective research.

Highly Facile Strategy for Detecting D2O in H2O by Porphyrin-Based Luminescent Probes.

Owing to their almost similarities in size, shape, and chemical reactivity, effectively distinguishing deuteroxide (D2O) in water (H2O) remains an ongoing challenge, and the examples of a D2O probe are still quite scarce. Herein, since H2O can decrease the lifetime of a singlet oxygen as a vital intermediate and an H/D exchange in the luminescence process of porphyrins, we systematically investigated the enhanced ultraviolet-visible (UV-vis), photoluminescence (PL), and electrochemiluminescence (ECL) of water-soluble tetrakis(carboxphenyl)porphyrin (TCPP) in D2O. The findings showed that these luminescent properties had been greatly enhanced with the increase of the D2O fraction in water. Consequently, we first developed the highly facile methods of detecting D2O in H2O by the UV-vis, PL, and ECL of TCPP, respectively. Impressively, the ECL analysis exhibited a great superiority with a lower detection limit of 0.29 nM. The work not only achieves the challenging task of distinguishing between H2O and D2O but also provides a unique strategy to enhance the luminescent performance of porphyrin.

Insights into the Enhanced Photoelectrochemical Performance through Construction of the Z-Scheme and Type II Heterojunctions.

Photoelectrochemical (PEC) water splitting technology is a promising strategy toward producing sustainable hydrogen fuel. However, it is an essential bottleneck to reduce severe charge recombination for the improvement of PEC performance. Construction of heterojunction systems, such as Z-scheme and type II heterojunctions, could efficiently boost charge separation, whereas the mechanism of charge separation is still ambiguous. We describe herein a charge transfer system designed with Bi2WO6/Bi2S3 (BWO/BS) as a prototype. In this system, Au nanoparticles act as charge relays to engineer a charge transfer pathway, and the obtained BWO/Au/BS photoanode achieves a remarkable photocurrent density of 0.094 mA cm-2 at 1.23 V versus reversible hydrogen electrode (vs RHE), over approximately 1.2 and 2.3 times larger than those of BWO/BS/Au and BWO, exhibiting long-term photostability. More importantly, scanning photoelectrochemical microscopy (SPECM) and intensity-modulated photocurrent spectroscopy (IMPS) studies are performed to in situ-capture the photogenerated hole during the PEC process. Operando analysis reveals that the Z-scheme BWO/Au/BS system (1.33 × 10-2 cm s-1) exhibits higher charge transfer kinetics compared to the type II BWO/BS/Au heterostructure (0.85 × 10-2 cm s-1) while efficiently suppressing charge recombination for optimized PEC activity. Note that this smart strategy can also be extended to other semiconductor-based photoanodes such as BiVO4. Our study offers an effective pathway for the rational design of highly efficient charge separation for solar conversion based on water splitting.

Significantly Promoting the Photogenerated Charge Separation by Introducing an Oxygen Vacancy Regulation Strategy on the FeNiOOH Co-Catalyst.

Semiconductor/co-catalyst coupling is considered as a promising strategy to enhance the photoelectrochemical (PEC) conversion efficiency. Unfortunately, this model system is faced with a serious interface recombination problem, which limits the further improvement of PEC performances. Here, a FeNiOOH co-catalyst with abundant oxygen vacancies on BiVO4 is fabricated through simple and economical NaBH4 reduction to accelerate hole transfer and achieve efficient electron-hole pair separation. The photocurrent of the BV (BiVO4 )/Vo-FeNiOOH system is more than four times that of pure BV. Importantly, the charge transfer kinetics and charge carrier recombination process are studied by scanning photoelectrochemical microscopy and intensity modulated photocurrent spectroscopy in detail. In addition, the oxygen vacancy regulation proposed is also applied successfully to other semiconductors (Fe2 O3 ), demonstrating the applicability of this strategy.

Interfacial repairing of semiconductor-electrocatalyst interfaces for efficient photoelectrochemical water oxidation.

Photoelectrochemical (PEC) water splitting is an attractive strategy to convert and store of intermittent solar power into fuel energy. However, the detrimental charge recombination of photogenerated electrons and holes severely limits its efficiency. Despite electrocatalyst loading can obviously improve the PEC conversion efficiency, current systems still suffer from high recombination owing to the surface states. Herein, an interface "repairing" strategy is proposed to suppress the recombination at the semiconductor/electrocatalyst interface. NiOx layer acts as an interfacial repairing layer to efficiently extract photogenerated charge carriers and eliminate the surface states via high hole-transfer kinetics rather than as a traditional electrocatalyst. As expected, the resulting repaired system yields an impressive photocurrent density of 4.58 mA cm-2 at 1.23 V (vs. RHE), corresponding to a more than three-fold increase compared to BiVO4 (1.40 mA cm-2). Our work offers an appealing maneuver to improve the water oxidation performance for the semiconductor/electrocatalyst coupling system.

MnO2 Nanospheres Assisted by Cysteine Combined with MnO2 Nanosheets as a Fluorescence Resonance Energy Transfer System for "Switch-on" Detection of Glutathione.

Manganese dioxide nanosheets combined with cysteine-assisted emitting manganese dioxide nanospheres (Cys-MnO2 nanospheres) is fabricated for the first time as an "off-on" fluorescence detection platform for glutathione (GSH). In this sensing system, Cys-MnO2 nanospheres served as energy donors, while MnO2 nanosheets were used as both energy acceptors and recognition units. MnO2 nanosheets can effectively quench the fluorescence of Cys-MnO2 nanospheres through the fluorescence resonance energy transfer (FRET). The addition of GSH could reduce MnO2 nanosheets into Mn2+, disrupting the FRET process and restoring the fluorescence of Cys-MnO2 nanospheres. Under the optimum conditions, the "switch-on" platform we established has a wide response to GSH with a range of 5-50 µM and 150-800 µM, as well as a superior specificity. Importantly, all components of the sensor are nontoxic, biocompatible, easily prepared, and have a high utilization of raw materials. Moreover, the sensing system achieved satisfactory results in human serum, showing a tremendous potential in the field of biomedicine.

Near-Infrared Small Molecule as a Specific Fluorescent Probe for Ultrasensitive Recognition of Antiparallel Human Telomere G-Quadruplexes.

In the past 10 years, many fluorescent probes have been developed to recognize G-quadruplexes (G4s) since G4s play an important role in biological systems. However, the selectivity and sensitivity of existing probes for G4s limit their further applications. Herein, we design and synthesize a new probe (TOVJ) by introducing 9-vinyljulolidine into TO. The new probe exhibits almost no fluorescence in an aqueous solution. Upon interacting with G4s, especially the antiparallel G4s, the fluorescence intensity was greatly enhanced (maximum 2742-fold) with a large Stokes shift of 198 nm and the maximum emission peak at 694 nm (near-infrared region). TOVJ showed high sensitivity and selectivity to G4s over other DNA topologies (ssDNA/dsDNA), especially to antiparallel G4s. For antiparallel human telomere G4 detection, the limits of detection of Hum24 and 22AG Na+ were as low as 164 and 231 pM, respectively. This indicates that TOVJ is a highly sensitive fluorescence sensor that can be effectively used for antiparallel human telomere G4 detection. The result of live-cell imaging showed that TOVJ could enter live cells and locate in the mitochondria.

Signal Amplification Strategy Using Atomically Gold-Supported VO2 Nanobelts as a Co-reaction Accelerator for Ultrasensitive Electrochemiluminescent Sensor Construction Based on the Resonance Energy Transfer Platform.

Luminol, as a classical luminophore, plays a crucial role in electrochemiluminescence (ECL). However, the traditional luminol-H2O2 ECL system suffers from the self-decomposition of H2O2 at ambient temperature, which hinders its further application in quantitative analysis. In this work, for the first time, we developed atomically gold-supported two-dimensional VO2 nanobelts (Au/VO2) as an advanced co-reaction promoter to speed up the reduction of dissolved oxygen to superoxide radicals (O2•-), which react with the luminol anion radical and greatly promote the ECL emission. The ECL resonance energy transfer (ECL-RET) between the hollow manganese dioxide nanospheres and luminol results in a conspicuously decreased ECL signal response, and in the presence of glutathione (GSH), effective redox reaction between manganese dioxide and GSH restores the ECL signal. As a consequence, the designed sensor based on ECL-RET-assisted Au/VO2 signal amplification showed outstanding performance for "signal-on" detection of GSH in the concentration range of 10-3 to 10-10 M, and the detection limit was as low as 0.03 nM. The ECL sensor displayed excellent specificity and was successfully utilized to target GSH in real human serum samples. Importantly, this work not only highlights a powerful avenue for constructing an ultrasensitive ECL sensor for GSH but also provides some inspiration for the further design of high-performance co-reaction accelerators using the ECL technique.

Hypoxia and pH co-triggered oxidative stress amplifier for tumor therapy.

To keep fast proliferation, tumor cells are exposed to higher oxidative stress than normal cells and they upregulate the amount of some antioxidants such as glutathione (GSH) against reactive oxygen species to maintain the balance. This phenomenon is severe in hypoxic tumor cells. Although researchers have proposed a series of treatment strategies based on regulating the intracellular reactive oxygen species level, few of them are related to the hypoxic tumor. Herein, a novel organic compound (PLC) was designed by using lysine as a bridge to connect two functional small molecules, a hypoxia-responsive nitroimidazole derivative (pimonidazole) and a pH-responsive cinnamaldehyde (CA) derivative. Then, the oxidative stress amplifying ability of PLC in hypoxic tumor cells was evaluated. The acidic microenvironment of tumor can trigger the release of CA to produce reactive oxygen species. Meanwhile, large amount of nicotinamide adenine dinucleotide phosphate (NADPH) can be consumed to decrease the synthesis of GSH during the bio-reduction process of the nitro group in PLC under hypoxic conditions. Therefore, the lethal effect of CA can be amplified for the decrease of GSH. Our results prove that this strategy can significantly enhance the therapeutic effect of CA in the hypoxic tumor cells.

Rational design of copper encapsulated within nitrogen-doped carbon core-shell nanosphere for efficiently photocatalytic peroxymonosulfate activation.

Photocatalysis utilizing solar energy is a promising strategy for mitigating energy crisis and environmental pollution. Exploring a cost-effective, stable, eco-friendly, and efficient photocatalytic system is extremely urgent. Herein, copper encapsulated within nitrogen-doped carbon nanosphere (Cu@NC) possessing a unique core-shell structure with high catalytic activity was prepared by ion-exchange and pyrolysis using resin as support. The protective carbon shell can prevent the leaching of metal ions and deactivation of the catalyst. Benefiting from the special structure, Cu@NC exhibited excellent activity and durability toward the degradation of tetracycline by the activation of peroxymonosulfate (PMS). The radical trapping experiments and electron spin resonance analyses were applied to elucidate the main reactive species. This work highlights the great potential of Cu@NC core-shell nanosphere as photocatalyst, which provides a new opportunity for the remediation of environmental pollution.

Insight into interface charge regulation through the change of the electrolyte temperature toward enhancing photoelectrochemical water oxidation.

The desired photoelectrochemical performance can be achieved by temperature regulation, but the nature for this improvement remains a controversial topic. Herein, we employed BiVO4/CoOx as a typical model system, and explored the fate of photogenerated holes at the different interfaces among BiVO4/CoOx/electrolyte by means of intensity modulated photocurrent spectroscopy (IMPS), scanning photoelectrochemical microscopy (SPECM) and traditional electrocatalysis characterization methods. Systematic quantitative analysis of the kinetics of photogenerated holes transfer at the BiVO4/CoOx interface under illumination and surface water oxidation at the CoOx/electrolyte interface in the dark indicates that increasing temperature could not only enhance the surface catalytic reaction kinetics but also facilitate the interfacial charge transfer. As expected, the integrated system exhibited a remarkable photocurrent density of 3.6 mA cm-2 (1.23 VRHE, AM 1.5G, 45 °C), which is approximately 2.1 times higher than that of BiVO4/CoOx (15 °C). This work provides a promising strategy for achieving efficient photoelectrochemical water splitting.

Enhanced Photoelectrochemical Water Splitting on Nickel-Doped Cobalt Phosphate by Modulating both Charge Transfer and Oxygen Evolution Efficiencies.

Detrimental charge recombination at photoanode/electrolyte junctions severely impedes photoelectrochemical (PEC) performance. The deposition of cobalt phosphate (CoPi) onto photoanodes is an efficient approach to achieve high PEC efficiency. However, achieving performances at the required remains a huge challenge, owing to the passivation effect of CoPi. In this study, function-tunable strategy, whereby the passivation role is switched with the activation role, is exploited to modulate PEC performance through simultaneous activation of interface charge transfer and surface catalysis. By depositing nickel-doped CoPi onto a BiVO4 (BV) substrate, the integrated system (BV/Ni1 Co7 Pi) exhibits a remarkable photocurrent density (4.15 mA cm-2 ), which is a 4.6-fold increase relative to BV (0.90 mA cm-2 ). Moreover, the satisfactory performance can be also achieved on α-Fe2 O3 photoanode. These findings provide guidance for improving the efficiency of CoPi on photoanodes for PEC water oxidation.

Insight into the Transition-Metal Hydroxide Cover Layer for Enhancing Photoelectrochemical Water Oxidation.

Depositing a transition-metal hydroxide (TMH) layer on a photoanode has been demonstrated to enhance photoelectrochemical (PEC) water oxidation. However, the controversial understanding for the improvement origin remains a key challenge to unlock the PEC performance. Herein, by taking BiVO4 /iron-nickel hydroxide (BVO/Fx N4-x -H) as a prototype, we decoupled the PEC process into two processes including charge transfer and surface catalytic reaction. The kinetic information at the BVO/Fx N4-x -H and Fx N4-x -H/electrolyte interfaces was systematically evaluated by employing scanning photoelectrochemical microscopy (SPECM), intensity modulated photocurrent spectroscopy (IMPS) and oxygen evolution reaction (OER) model. It was found that Fx N4-x -H acts as a charge transporter rather than a sole electrocatalyst. PEC performance improvement is mainly ascribed to the efficient suppression of charge recombination by fast hole transfer kinetics at BVO/Fx N4-x -H interface.

Encapsulation of Porphyrin-Fe/Cu Complexes into Coordination Space for Enhanced Selective Oxidative Dehydrogenation of Aromatic Hydrazides.

The encapsulation of specific nanoentities into hollow nanomaterials derived from metal organic frameworks has attracted continuous and growing research attentions owing to their unique structural properties and unusual synergistic functions. Herein, using the phase transformation of uniform rhombi dodecahedron ZIF-67, hollow nano-shell with a well-defined morphology is successfully prepared. Particularly, the iron-oxygen complex, that is formed by the interaction between TCPP-Fe/Cu (TCPP = tetrakis(4-carboxyphenyl)-porphyrin) and oxygen, can be acted as an ideal proton acceptor for practical organic reactions. Considering the unique adaptability of hollow ZIFs (named HZ) to the transformation of encapsulated TCPP-Fe/Cu bimetallic catalytic active sites, a heterogeneous catalyst (defined as HZ@TCPP-Fe/Cu) through morphology-controlled thermal transformation and rear assemble processes is designed and constructed. Under heterogeneous conditions, HZ@TCPP-Fe/Cu serves as a multifunctional molecular selector to promote the oxidative dehydrogenation of different aromatic hydrazide derivatives with high selectivity toward primary carbon among primary, secondary, and tertiary carbons that are unachievable by other traditional homogeneous catalysts. The high catalytic activity, selectivity, and recyclability of the catalyst proposed here are attractive advantages for an alternative route to the environmentally benign transformation of aromatic hydrazides to aromatic azobenzene.

Aggregation-Induced Electrochemiluminescence of Tetraphenylbenzosilole Derivatives in an Aqueous Phase System for Ultrasensitive Detection of Hexavalent Chromium.

Herein, aggregation-induced electrochemiluminescence (AIECL) of tetraphenylbenzosilole derivatives in an aqueous phase system with the participation of a co-reactant was systematically investigated for the first time. All organics that we studied exhibit excellent stability and dramatically enhanced electrochemiluminescence (ECL) and photoluminescence (PL) emission when the water fraction increases. The influence of substituents in the structure of tetraphenylbenzosilole derivatives on AIECL performance was proved by fluorescence, cyclic voltammetry, and related theoretical calculation. Among them, 2,3-bis(4-cyanophenyl)-1,1-diphenyl-benzosilole (TPBS-C) with strong electron-withdrawing cyano groups exhibits the best ECL behavior with the highest ECL efficiency (184.36%). The strongest ECL emission of TPBS-C not only stems from the aggregated molecules that restrict the intramolecular motion of peripheral phenyl groups, which inhibits the nonradiative transition, but also comes from the fact that TPBS-C has the lowest reduction potential, and twice the reduction process of TPBS-C occurs to produce more anion radicals (TPBS-C·-). Significantly, the ECL sensor based on TPBS-C nanoaggregates exhibits excellent detection performance for toxic Cr(VI) with a wide linear range from 10-12 to 10-4 M and an extremely low detection limit of 0.83 pM. This work developed an efficient luminophore with unique AIECL properties and realized the ultrasensitive detection of Cr(VI) in the aqueous phase system.

Enhancing Charge Separation through Oxygen Vacancy-Mediated Reverse Regulation Strategy Using Porphyrins as Model Molecules.

Highly efficient charge separation has been demonstrated as one of the most significant steps playing decisive roles in enhancing the overall efficiency of photoelectrochemical (PEC) processes. In this study, by employing 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin-Ni (NiTCPP) as a prototype, an oxygen vacancy (Vo)-mediated reverse regulation strategy is proposed for tuning hole transfer, which in turn can accelerate the transport of electrons and thus enhancing charge separation. The optimal NiO/NiTCPP system exhibits much higher (≈40 times) photocurrent and longer (≈13 times) lifetime of charge carriers compared with those of pure NiTCPP. Furthermore, the electron transfer kinetic rate constant (Keff ) is quantitatively determined by an efficient scanning photoelectrochemical microscopy (SPECM). The Keff of the optimal system has a 5.7-fold improvement. In addition, the similar enhancement in charge separation from other semiconductors (CoTCPP and FeTCPP) are also observed, indicating that the Vo-mediated reverse regulation strategy is a promising pathway for tuning the properties of light harvesters in solar energy conversion.