Weak Light Irradiation Research Articles

Self-sensitization-induced protonation sites for weak-light-driven hydrogen evolution in coordination polymers

The exploration on weak-light-driven catalysis is an important approach to reduce the dependence of photocatalysts on strong light and improve the efficiency of solar spectrum utilization. However, the reported photocatalysts typically necessitate high light intensity (e.g., exceeding 100 mW cm−2) for catalytic reactions, which cannot be achieved with natural solar light. Herein, a self-sensitization-induced strategy was employed to generate in-situ proton sites, enabling photocatalytic hydrogen evolution reaction (HER) even under low light intensity (10 mW cm−2). An indolocarbazole ligand (H2ICDB) was utilized to construct a paddle-wheel dicopper coordination polymer (CuICDB-DMF). By substituting the axially coordinated DMF with methanol or water, CuICDB-MeOH and CuICDB-H2O were obtained. Under weak-light irradiation (10 mW cm−2), CuICDB-H2O exhibited the highest photocatalytic HER rate of 838.4 μmol g−1 h−1 when compared to the other two counterparts. Remarkably, the substitution of axially coordinated H2O promotes charge separation and transfer efficiency through optimizing ligand-to-cluster charge transfer (LCCT) process. Moreover, density functional theory (DFT) calculations reveal that coordinated H2O substitution decreases the Gibbs free energy difference of the potential determining step (H2O* → OH* + H*) in CuICDB-H2O.

Light inducible gene expression system for Streptomyces

The LitR/CarH family comprises adenosyl B12-based photosensory transcriptional regulators that control light-inducible carotenoid production in nonphototrophic bacteria. In this study, we established a blue–green light-inducible hyperexpression system using LitR and its partner ECF-type sigma factor LitS in streptomycin-producing Streptomyces griseus NBRC 13350. The constructed multiple-copy number plasmid, pLit19, carried five genetic elements: pIJ101rep, the thiostrepton resistance gene, litR, litS, and σLitS-recognized light-inducible crtE promoter. Streptomyces griseus transformants harboring pLit19 exhibited a light-dependent hyper-production of intracellular reporter enzymes including catechol-2,3-dioxygenase and β-glucuronidase, extracellular secreted enzymes including laccase and transglutaminase, and secondary metabolites including melanin, flaviolin, and indigoidine. Cephamycin-producing Streptomyces sp. NBRC 13304, carrying an entire actinorhodin gene cluster, exhibited light-dependent actinorhodin production after the introduction of the pLit19 shuttle-type plasmid with the pathway-specific activator actII-ORF4. Insertion of sti fragment derived from Streptomyces phaeochromogenes pJV1 plasmid into pLit19 increased its light sensitivity, allowing gene expression under weak light irradiation. The two constructed Escherichia coli–Streptomyces shuttle-type pLit19 plasmids were found to have abilities similar to those of pLit19. We successfully established an optogenetically controlled hyperproduction system for S. griseus NBRC 13350 and Streptomyces sp. NBRC 13304.

Lattice Manipulation with Di-Tertiary Ammonium Spacer in Bismuth Bromide Perovskite Directs Efficient Charge Transport and Suppressed Ion Migration for Photodetector Applications.

Bismuth halide hybrid perovskites have emerged as promising alternatives to their lead halide homologs because of high chemical stability, low toxicity, and structural diversity. However, their advancements in optoelectronic field are plagued with poor charge transport, due to considerable microstrain triggered by bulky spacer. Herein, the di-tertiary ammonium spacer (N,N,N',N'-tetramethyl-1,4-butanediammonium, TMBD) is explored to direct stable 1D bismuth bromide lattice structure with relaxed microstrain. Compared to the primary pentamethylenediamine (PD)2+, the (TMBD)2+ adopting alternating alignment enables a unique H-bonds mode to distort the configuration of inorganic layers to form corner-sharing [BiBr5] near-regular chains with narrower bandgap, lower exciton binding energy, and reduced carrier-lattice interactions, thereby facilitating charge-carrier transport. Moreover, the (TMBD)2+ spacers largely suppress ion migration in perovskite lattice, as substantiated by the experimental and theoretical investigations. Consequently, (TMBD)BiBr5 single crystal photodetector delivers a 185-fold increase in current on/off ratio with respect to (PD)BiBr5 under white light irradiation, considerable responsivity (≈82.97mA W-1), detectivity (≈8.06 ×1011 Jones) under weak light (0.02mW cm-2) irradiation, in the top rank of the reported hybrid bismuth halide perovskites. This finding offers novel design criterion for high-performance lead-free perovskites.

Yielding high photovoltaic conversion efficiency by Pd-decoration on Si-based interface: A density-functional theory study

There has been showing great interest in boosting the performance of III-V/Si multi-junction solar cell, which is low-cost and offering high photovoltaic conversion efficiency. Adding noble-metal nano-array at the interface between the Si and III-V materials is one of most effective ways. This theoretical work comprehensively studied the atomic structure, electronic properties, and optical response of Pd-decoration on the Si(111) surface by using density-functional theory calculations. The structural stability calculations showed that Pd atoms could exist on Si surface in many forms. The calculated differential charge density with Bader charge showed that the charge transfer between Pd and Si atoms would increase the generation of electron-hole pairs. At the same time, Pd-decoration could reduce the work function and improve the optical conductivity of Si surface. In addition, the modification of Pd atoms would create new energy levels near the Fermi level in the band gap of Si surface. These energy levels enable Si bottom cell to undergo electron inter-band transitions under weak light irradiation, improving the utilization of weak light. This work provided a micro physical explanation for the improvement of III-V/Si solar cell by using noble-metal nano-array.

SnS2/SnS heterojunction: An all-weather-active photocatalyst for Cr(VI) removal

Photoreduction is a sustainable method for the removal of the harmful heavy metal ions. However, the low photocatalytic activity due to limited solar energy utilization and sluggish separation of photogenerated electrons/hole pairs is a major challenge. Here, we report the design and preparation of SnS2/SnS heterojunction nanosheets with full-band response for efficient photoreduction of Cr(VI). The SnS2/SnS heterojunction has a three-dimensional lamellar structure with tight interfacial links that facilitate inter-electron hole transport. Among the samples, SnS2/SnS-2 (Sn4+: Sn2+ = 1: 0.218) shows optimal photoreduction of Cr(VI) under simulated solar light. Remarkably, SnS2/SnS-2 exhibited a high removal rate of Cr(VI) under all-weather conditions, with 50% removal achieved in 2 h under sunlight and 10% removal in 2 h under cloudy condition in neutral lake water, indicating practical catalytic performance and energy-saving potential. The presence of SnS not only improves the optical absorption capacity in the near-infrared region and enhances the photo-thermal conversion efficiency, but also accelerates the separation ability of photogenerated carriers, leading to high photocatalytic efficiency. Our work provides a promising concept for continuous Cr(VI) removal under all-weather conditions, including weak light irradiation.

Dark accumulation of downstream glycolytic intermediates initiates robust photosynthesis in cyanobacteria.

Photosynthesis must maintain stability and robustness throughout fluctuating natural environments. In cyanobacteria, dark-to-light transition leads to drastic metabolic changes from dark respiratory metabolism to CO2 fixation through the Calvin-Benson-Bassham (CBB) cycle using energy and redox equivalents provided by photosynthetic electron transfer. Previous studies have shown that catabolic metabolism supports the smooth transition into CBB cycle metabolism. However, metabolic mechanisms for robust initiation of photosynthesis are poorly understood due to lack of dynamic metabolic characterizations of dark-to-light transitions. Here, we show rapid dynamic changes (on a time scale of seconds) in absolute metabolite concentrations and 13C tracer incorporation after strong or weak light irradiation in the cyanobacterium Synechocystis sp. PCC 6803. Integration of this data enabled estimation of time-resolved nonstationary metabolic flux underlying CBB cycle activation. This dynamic metabolic analysis indicated that downstream glycolytic intermediates, including phosphoglycerate and phosphoenolpyruvate, accumulate under dark conditions as major substrates for initial CO2 fixation. Compared with wild-type Synechocystis, significant decreases in the initial oxygen evolution rate were observed in 12 h dark preincubated mutants deficient in glycogen degradation or oxidative pentose phosphate pathways. Accordingly, the degree of decrease in the initial oxygen evolution rate was proportional to the accumulated pool size of glycolytic intermediates. These observations indicate that the accumulation of glycolytic intermediates is essential for efficient metabolism switching under fluctuating light environments.

Hierarchical Natural Pollen Cell-Derived Composite Sorbents for Efficient Atmospheric Water Harvesting.

Freshwater scarcity is a critical challenge threatening human survival especially due to poverty and arid and off-grid regions. Sorption-based atmospheric water harvesting (AWH) has emerged as a promising strategy for clean water production. However, most of the high-capacity sorbents are limited by the poor sorption/desorption kinetics and uncontrollable liquid leakage problem. Inspired by the plant transpiration process, we develop an environmentally friendly LiCl@pollen cell-polypyrrole (LiCl@PC-PPy) composite sorbent by confining the LiCl hygroscopic agent in the cages of the PC-PPy. The composite sorbent exhibits much improved sorption/desorption kinetics owing to the hydrophilicity of the hierarchical porous structure of the pollen cells, which provides abundant water sorption active sites and diffusion pathways and forms a concave meniscus on cell skeletons to maximize the thermal utilization efficiency. Moreover, the big cavities of the PC-PPy cages can serve as a water reservoir to reduce liquid leakage. As a result, the sorbent can capture atmospheric water to 85% of its own weight under 60% relative humidity (RH) within 2 h and rapidly release the water within 1 h under weak light irradiation of 0.8 sun. As a proof-of-concept demonstration, the fabricated AWH device can absorb 1.55 gwater/gsorbent at night and collect 1.53 gwater/gsorbent of water in 1-day outdoor operation, and the collected water can meet the drinking water standards defined by the World Health Organization (WHO) and Environmental Protection Agency (EPA).

High-performance self-powered ultraviolet photodetector based on BiOCl/TiO2 heterojunctions: Carrier engineering of TiO2

For low-energy photoelectric devices, it is essential to develop self-powered photodetectors (PDs), because it can work independently, wirelessly and sustainably. The heterojunction PDs based on BiOCl nanoflakes (NFs) and anatase TiO2 film fabricated by the hydrothermal method demonstrate the excellent ultraviolet (UV) photoresponse properties without external power supply. The strong built-in electric field formed at the heterojunction interface and the efficient carrier transmission characteristic of TiO2 film can improve the self-powered performance of PDs. The optimized heterojunction device with TiO2 film grown for 1.75 h exhibits a high photocurrent-to-dark current ratio of 103, responsivity of 0.17 A/W, remarkable detectivity of 1.3 × 1012 Jones, linear dynamic range of 70 dB and fast response speed of 23 ms under 0 V bias and weak UV light irradiation (340 nm, 0.18 mW/cm2). These results demonstrate that the BiOCl/TiO2 heterojunction devices have great application potential in the future UV communications systems.

High-performance floating-gate organic phototransistors based on n-type core-expanded naphthalene diimides

In the field of organic phototransistor, achieving both broad-spectral and high photosensitivity has always been a big challenge. The innovation of device structure has previously proven to be a possible solution to this problem. Here in this study, a novel organic phototransistor based on a high mobility n-type small molecule as the conducting layer and an isolated bulk heterojunction light-absorbing layer as the floating gate has been demonstrated in this study. With the special designed device structure, the phototransistor shows extremely high sensitivity to broad spectral and weak light irradiation, and the photoresponsivity and photocurrent/dark-current ratio of the device can reach up to 4840 mA/W and 1.8 × 105 respectively. For conclusion, this study suggests a potential way to obtain high-performance phototransistors at room temperature, which will further promote the commercial application of organic phototransistors.

Weak-light-driven Ag–TiO2 photocatalyst and bactericide prepared by coprecipitation with effective Ag doping and deposition

TiO2 can mainly absorb ultraviolet light (UV) and thus the strong light irradiation of photocatalyst is highly needed to obtain efficient charge carrier (electrons and holes) production for subsequent reactions. In this paper, Ag–TiO2 nanoparticles with high Ag dispersibility were prepared by different Ag contents (0–6 at. %) and calcination temperatures (200–600 °C) using a coprecipitation method. Results showed that Ag inhibited the transformation of anatase to rutile TiO2, resulting in the decreased Eg and increased amounts of chemisorbed hydroxyl oxygen as well as oxygen vacancy. 2% Ag–TiO2 possessed the best and high photocatalytic efficiency under weak UV and visible light irradiation (15W). The bactericidal activity of Ag–TiO2 nanoparticles was also enhanced compared with pure TiO2, and further enhanced with Ag content. The superior performance was mainly ascribed to the synergistic effect of Ag and TiO2.

IrOx @In2 O3 Heterojunction from Individually Crystallized Oxides for Weak-Light-Promoted Electrocatalytic Water Oxidation.

Multi-field coupling, especially photo-assisted electrocatalysis, has recently been studied to further improve the oxygen evolution reaction (OER). In this study, an n-type cubic In2 O3 semiconductor is employed for the first time to load IrOx species (Ir-In2 O3 mass ratio: 17.6 %). Consequently, the IrOx @In2 O3 heterojunction, which exhibits outstanding OER performance promoted by weak-light irradiation, is formed. Notably, IrOx (approximately 1.7 nm in size) and In2 O3 are observed to crystallize independently during heterogeneous nucleation with no Ir atoms doped in the In2 O3 lattice. This avoids Ir loss and ensures the full exposure of all Ir-based sites. The IrOx @In2 O3 heterojunction exhibits enhanced electrocatalytic water oxidation with overpotential values of 190 and 231 mV at current densities of 10 and 50 mA cm-2 , surpassing all IrOx -based catalyst results reported to date. Nano-sized IrOx on the surface, irradiated by the weak-light beam of LED-365 (1.8 mW cm-2 ), can be fully activated as an OER site. Moreover, the overpotential is further reduced to 176 and 210 mV to deliver the corresponding current. This work is anticipated to aid in the design of more efficient multi-field coupling OER systems.

Nicotinamide‐Modified PEDOT:PSS for High Performance Indoor and Outdoor Tin Perovskite Photovoltaics

Tin perovskites are generally considered as promising candidates to solve the issue of toxicity for lead perovskites. However, the open‐circuit voltage (VOC) of tin perovskite solar cells is usually lower than expected. Herein, the hole‐transporting layer of PEDOT:PSS is treated with nicotinamide, and the tin perovskite active layer is deposited on the treated film to prepare a perovskite photovoltaic device. The fabricated device presented an increased VOC from 0.63 to 0.82 V, yielding an improved power conversion efficiency (PCE) increased from 4.77% to 8.28%. More importantly, under the weak light (1000 lux) irradiation of a simulated indoor light source, the device presented a PCE as high as 14.40%, which is the highest indoor efficiency for tin‐based perovskite photovoltaics reported so far. The promising indoor performance of tin perovskite photovoltaics paves a new way to fabricate eco‐friendly indoor photovoltaics by using lead‐free tin perovskites.

Contribution of dark current density to the photodetecting properties of thieno[3,4-b]pyrazine-based low bandgap polymers

Recently, near infrared (NIR) organic photodetectors (OPDs) have been extensively studied. Bulk heterojunction NIR OPDs composed of a high-bandgap polymer donor (PD) and a low-bandgap non-fullerene acceptor (NFA) showed the best performance, whereas the low-bandgap PD-based OPDs were relatively unsuccessful due to the high level of dark current density (Jd) under a negative bias. In this study, we synthesized three low-bandgap PDs based on a thieno[3,4-b]pyrazine (TP) moiety and developed red-NIR OPDs by blending them with a low-bandgap NFA. We found that the PD having a shallow HOMO energy level generated the largest ground-state electron transfer at negative bias, which overestimated the responsivity (R) and detectivity (D*) in OPDs. Notably, under weak light irradiation of 0.1 mW/cm2 at -2V, the contribution of Jd on Jph reached 99.6%. Thus, we modified the existing R and D* equations to better understand photodetecting properties at low light intensity, and these modified equations gave more realistic R and D* values in OPDs. On the other hand, a low-bandgap PD showing low Jd in OPDs was highly beneficial to detect a low light signal because the Jd negligibly contributed to Jph in OPDs. The low Jd values of OPDs at negative bias resulted in a high on/off signal ratio and constant R and D* values at different light intensities.

Recent Advances on Pt-Free Electro-Catalysts for Dye-Sensitized Solar Cells.

Since Prof. Grätzel and co-workers achieved breakthrough progress on dye-sensitized solar cells (DSSCs) in 1991, DSSCs have been extensively investigated and wildly developed as a potential renewable power source in the last two decades due to their low cost, low energy-intensive processing, and high roll-to-roll compatibility. During this period, the highest efficiency recorded for DSSC under ideal solar light (AM 1.5G, 100 mW cm−2) has increased from ~7% to ~14.3%. For the practical use of solar cells, the performance of photovoltaic devices in several conditions with weak light irradiation (e.g., indoor) or various light incident angles are also an important item. Accordingly, DSSCs exhibit high competitiveness in solar cell markets because their performances are less affected by the light intensity and are less sensitive to the light incident angle. However, the most used catalyst in the counter electrode (CE) of a typical DSSC is platinum (Pt), which is an expensive noble metal and is rare on earth. To further reduce the cost of the fabrication of DSSCs on the industrial scale, it is better to develop Pt-free electro-catalysts for the CEs of DSSCs, such as transition metallic compounds, conducting polymers, carbonaceous materials, and their composites. In this article, we will provide a short review on the Pt-free electro-catalyst CEs of DSSCs with superior cell compared to Pt CEs; additionally, those selected reports were published within the past 5 years.

Bioinspired construction of light-harvesting antenna via hierarchically co-assembling approach

Biomimetic construction of artificial photosystem capable of converting light energy to chemical energy is a promising strategy in solving the increasing serious energy and environmental problems. Herein, we present a new strategy to construct light-harvesting antenna via hierarchical co-assembly of short-peptide and porphyrin and subsequent self-metallization process. The hierarchically organized antenna exhibits both excellent photocatalytic performance and remarkable sustainability under strong light irradiation (35000 lx) and extraordinary sensitivity to weak light (700 lx). In such cases, light energy can be converted into chemical energy and stored in the energy-storage molecules (nicotinamide adenine dinucleotide, NADH) even under weak light irradiation. This provides a promising step towards an artificial photosystem that can utilize weak light. Moreover, the structures and properties of the antenna are dependent on the competition of short-peptide self-assembling and co-assembling with porphyrin molecules and can be regulated by their molar ratio. This provides new insights into the design and construction of light-harvesting antennas with integrated functionality via precise control of pigments aggregation and coupling of different functional units.

Huge upconversion luminescence enhancement by a cascade optical field modulation strategy facilitating selective multispectral narrow-band near-infrared photodetection

Since selective detection of multiple narrow spectral bands in the near-infrared (NIR) region still poses a fundamental challenge, we have, in this work, developed NIR photodetectors (PDs) using photon upconversion nanocrystals (UCNCs) combined with perovskite films. To conquer the relatively high pumping threshold of UCNCs, we designed a novel cascade optical field modulation strategy to boost upconversion luminescence (UCL) by cascading the superlensing effect of dielectric microlens arrays and the plasmonic effect of gold nanorods, which readily leads to a UCL enhancement by more than four orders of magnitude under weak light irradiation. By accommodating multiple optically active lanthanide ions in a core-shell-shell hierarchical architecture, developed PDs on top of this structure can detect three well-separated narrow bands in the NIR region, i.e., those centered at 808, 980, and 1540 nm. Due to the large UCL enhancement, the obtained PDs demonstrate extremely high responsivities of 30.73, 23.15, and 12.20 A W−1 and detectivities of 5.36, 3.45, and 1.91 × 1011 Jones for 808, 980, and 1540 nm light detection, respectively, together with short response times in the range of 80–120 ms. Moreover, we demonstrate for the first time that the response to the excitation modulation frequency of a PD can be employed to discriminate the incident light wavelength. We believe that our work provides novel insight for developing NIR PDs and that it can spur the development of other applications using upconversion nanotechnology.

Preparation of photoactive graphene oxide-Cu2O/Cu nanostructures by the electrochemical treatment of Cu[sbnd]Ni leaching solutions using graphite electrodes

Sustainable and economic separation of Cu and Ni from their leaching solutions is a long-standing challenge. Here, the electrolysis of synthetic CuNi leaching solutions is examined using graphite electrodes in order to continuous separation of these metals, and also the preparation of photoactive graphene oxide (GO)-Cu2O/Cu hybrid structures. The carbon materials produced were characterized by various techniques including X-ray diffraction, Raman, Fourier-transform infrared and ultraviolet–visible spectroscopy, as well as electron microscopy. The proposed electrochemical approach is based on the surface exfoliation of the graphite anode to form GO, and the copper deposition on the cathode, followed by the chemical formation of Cu2O anchored on the surface of GO flakes. The concentration of Cu2+ in the solution is found to gradually reduce from an initial value of 2.79 to 0.37 g/l during 5 h of electrolysis, while the Ni2+ concentration remains almost unchanged. Moreover, the hybrid structure produced is found to be effective for the degradation of methyl orange under natural indoor weak light irradiation, with high cycling stability. The mechanism involved in the process is discussed.

Cancer Photothermal Therapy with ICG-Conjugated Gold Nanoclusters.

The coming era of precision nanomedicine demands engineered nanoparticles that can be readily translated into the clinic, like that of molecular agents, without being hindered by intrinsic size heterogeneity and long-term body retention. Herein we report that conjugation of indocyanine green (ICG), an FDA-approved near-infrared (NIR) dye, onto an atomically precise glutathione-coated Au25 (GS-Au25) nanocluster led to a molecular-like photothermal nanoparticle (ICG4-GS-Au25) with significantly enhanced ICG photostability and tumor targeting. Under weak NIR light irradiation conditions, free ICG failed to suppress tumor growth but the original tumors were completely eradicated with ICG4-GS-Au25. In the meantime, "off-target" ICG4-GS-Au25 was effectively cleared out from the body like small-molecule drugs after glutathione-mediated biotransformation in the liver. These findings highlight the merits of molecular-like nanomedicines, offering a new pathway to meet FDA's criteria for the clinical translation of nanomedicines.

Multicolor Broadband and Fast Photodetector Based on InGaAs–Insulator–Graphene Hybrid Heterostructure

AbstractBroadband light detection is crucial for a variety of optoelectronic applications in modern society. As an important‐near infrared (NIR) photodetector, InGaAs PIN photodiodes demonstrate high detection performance. However, they have a limited response range because of optical absorption by the window layer or substrate. To exploit the broadband absorption capability of narrow‐bandgap InGaAs, a phototransistor based on a hybrid InGaAs‐SiO2‐graphene heterostructure is presented. In this system, graphene serves as a transparent conducting channel to sense optical absorption in the InGaAs. In contrast to InGaAs PIN photodiodes, the hybrid InGaAs phototransistor demonstrates multicolor photodetection over a broadband wavelength range from the ultraviolet to NIR. Furthermore, it manifests a high photoresponsivity of above 103 A W−1 under weak light irradiation, a large external quantum efficiency, and a fast response speed of 200 kHz. The results pave the way for the development of high‐performance broadband photodetectors based on mixed‐dimensional heterostructures.

Microwave Characteristics Analysis of Typical Photosensitive Material InP Under Weak Light Irradiation Based on Quasi-Optical Resonator

In this paper, the microwave characteristics of typical photosensitive material InP under different light irradiation are studied. The measurement sensor is a reflection-type hemispherical quasi-optical resonator with an operating frequency range from 20 to 40 GHz, an operating mode of TEM00q, and a quality factor of 18,000 or more. For the short-time irradiation experiment, the variation of InP microwave characteristics with the irradiation power of 20 mW, 60 mW, 100 mW, and 200 mW, is studied by frequency-domain and time-domain scanning methods, respectively. The measurement results indicate that the microwave characteristics of InP change significantly even under weak light irradiation. Taking 100 mW and 200 mW irradiation power as examples, the long-time irradiation experiment performed on InP lasting 1.5 min is carried out. The measurement result curves clearly show the influence of the thermal and non-thermal effects on the InP microwave characteristics at the instant of the monochrome light source opening and closing and during irradiation. Furthermore, the temperature distribution of InP during 200 mW irradiation is real-time imaged by a thermal infrared imager to verify the existence of thermal effect during irradiation. The measurement results are in good agreement with the theoretical analysis. The microwave properties of InP under short-time and long-time irradiation are analyzed by frequency-domain and time-domain scanning methods, especially the effects of thermal and non-thermal on microwave properties during long-term irradiation.