Suppressing Hole Accumulation Through Sub-Nanometer Dipole Interfaces in Hybrid Perovskite/Organic Solar Cells for Boosting Near-Infrared Photon Harvesting.

The potential of hybrid perovskite/organic solar cells (HSCs) is increasingly recognized owing to their advantageous characteristics, including straightforward fabrication, broad-spectrum photon absorption, and minimal open-circuit voltage (VOC) loss. Nonetheless, a key bottleneck for efficiency improvement is the energy level mismatch at the perovskite/bulk-heterojunction (BHJ) interface, leading to charge accumulation. In this study, it is demonstrated that introducing a uniform sub-nanometer dipole layer formed of B3PyMPM onto the perovskite surface effectively reduces the 0.24 eV energy band offset between the perovskite and the donor of BHJ. This strategic modification suppresses the charge recombination loss, resulting in a noticeable 30 mV increase in the VOC and a balanced carrier transport, accompanied by a 5.0% increase in the fill factor. Consequently, HSCs that achieve power conversion efficiency of 24.0% is developed, a new record for Pb-based HSCs with a remarkable increase in the short-circuit current of 4.9 mA cm-2, attributed to enhanced near-infrared photon harvesting.

Fabrication of one-dimensional Zn-doped Bi2S3 nanorods for photodiode applications.

In this research, the impact of the different zinc (Zn) concentrations on the physical and optoelectronic properties of Bi2S3 nanorods as self-powered and photodiode applications was investigated. The performance of P-N junction photodiodes has been for decades since they are crucial in energy applications. The structure, degree of crystallinity, and shape of Zn-doped Bi2S3 nanorods of various doping percentages formed onto the indium tin oxide (ITO) substrates by the dip coating technique are investigated using X-ray powder diffraction (XRD) and SEM. With increasing illumination time, the current-voltage (I-V) graphs demonstrate a rise in photocurrent. The diode's idealist factor was estimated using the I-V technique under 30 min of light illumination.

Influence of SnWO4, SnW3O9, and WO3 Phases in Tin Tungstate Films on Photoelectrochemical Water Oxidation.

An essential step toward enabling the production of renewable and cost-efficient fuels is an improved understanding of the performance of energy conversion materials. In recent years, there has been growing interest in ternary metal oxides. Particularly, α-SnWO4 exhibited promising properties for application to photoelectrochemical (PEC) water splitting. However, the number of corresponding studies remains limited, and a deeper understanding of the physical and chemical processes in α-SnWO4 is necessary. To date, charge-carrier generation, separation, and transfer have not been exhaustively studied for SnWO4-based photoelectrodes. All of these processes depend on the phase composition, not only α-SnWO4 but also on the related phases SnW3O9 and WO3, as well as on their spatial distributions resulting from the coating synthesis. In the present work, these processes in different phases of tin tungstate films were investigated by transient surface photovoltage (TSPV) spectroscopy to complement the analysis of the applicability of α-SnWO4 thin films for practical PEC oxygen evolution. Pure α-SnWO4 films exhibit higher photoactivities than those of films containing secondary SnW3O9 and WO3 phases due to the higher recombination of charge carriers when these phases are present.

Dependence of Protein Immobilization and Photocurrent Generation in PSI-FTO Electrodes on the Electrodeposition Parameters.

This study investigates the immobilization of cyanobacterial photosystem I (PSI) from Synechocystis sp. PCC 6803 onto fluorine-doped tin oxide (FTO) conducting glass plates to create photoelectrodes for biohybrid solar cells. The fabrication of these PSI-FTO photoelectrodes is based on two immobilization processes: rapid electrodeposition driven by an external electric field and slower adsorption during solvent evaporation, both influenced by gravitational sedimentation. Deposition and performance of photoelectrodes was investigated by UV-Vis absorption spectroscopy and photocurrent measurements. We investigated the efficiency of PSI immobilization under varying conditions, including solution pH, applied electric field intensity and duration, and electrode polarization, with the goals to control (1) the direction of migration and (2) the orientation of the PSI particles on the substrate surface. Variation in the pH value of the PSI solution alters the surface charge distribution, affecting the net charge and the electric dipole moment of these proteins. Results showed PSI migration to the positively charged electrode at pH 6, 7, and 8, and to the negatively charged electrode at pH 4.4 and 5, suggesting an isoelectric point of PSI between 5 and 6. At acidic pH, the electrophoretic migration was largely hindered by protein aggregation. Notably, photocurrent generation was consistently cathodic and correlated with PSI layer thickness, and no conclusions can be drawn on the orientation of the immobilized proteins. Overall, these findings suggest mediated electron transfer from FTO to PSI by the used electrolyte containing 10 mM sodium ascorbate and 200 µM dichlorophenolindophenol.

Artificial light harvesting system of CM6@Zn-MOF nanosheets with highly enhanced photoelectric performance.

As donors for effective energy transfer, metal-organic frameworks (MOFs) have attracted the attention of many experts in the field of artificial light-harvesting materials. This study introduces a novel two-dimensional Zn-MOF, synthesized using flexible 1,3-phenyldiacetic acid (H2mpda) and rigid 1,3,5-tris(1-imidazolyl)benzene (tib) as organic ligands. Through atomic force microscopy (AFM), we have determined the monolayer thickness of this novel material to be 5 nm. Achieving two-dimensional Zn-MOF nanosheets with large BET surface area was made possible by employing ultrasonic stripping techniques. The fluorescence emission spectrum of Zn-MOF nanosheets overlaps with the UV-vis absorption spectrum of coumarin 6 (CM6), so they can be used as a donor and acceptor for fluorescence resonance energy transfer (FRET) to construct an artificial light-harvesting system (ALHS). Compared with single crystal Zn-MOF, CM6@Zn-MOF(2) has a larger BET surface area (41 m2/g), higher quantum yield (Φfl, 30.56 %), narrower energy gap (Eg, 2.87 eV), and the light-harvesting range extends to the visible green light area. Notably, CM6@Zn-MOF(2) demonstrates a robust photocurrent response, characterized by a photocurrent on/off ratio (Ilight/Idark) of 21, and a maximum photocurrent density that surpasses that of pure Zn-MOF (2.25:1). This study successfully designed a high-performance photoelectric conversion material CM6@Zn-MOF(2), which laid a certain theoretical foundation for new artificial optical acquisition systems and electrochemical material selection.

The Light Wavelength, Intensity, and Biasing Voltage Dependency of the Dark and Photocurrent Densities of a Solution-Processed P3HT:PC61BM Photodetector for Sensing Applications.

The promising possibility of an organic photodetector (OPD) is emerging in the field of sensing applications for its tunable absorption range, flexibility, and large-scale fabrication abilities. In this work, we fabricated a bulk heterojunction OPD with a device structure of glass/ITO/PEDOT:PSS/P3HT:PC61BM/Al using the spin-coating process and characterized the dark and photocurrent densities at different applied bias conditions for red, green, and blue incident LEDs. The OPD photocurrent density exhibited a magnitude up to 2.5-3 orders higher compared to the dark current density at a -1 V bias while it increased by up to 3-4 orders at zero bias conditions for red, green, and blue lights, showing an increasing trend when a higher voltage is applied in the negative direction. Different OPD inner periphery shapes, the OPD to LED distance, and OPD area were also considered to bring the variation in the OPD dark and photocurrent densities, which can affect the on/off ratio of the OPD-LED hybrid system and is a critical phenomenon for any sensing application.

Enhanced Electrochemical Performance of Tin Oxide Quantum Dots on Reduced Graphene Oxide under Light.

The study utilized a simple and cost-effective approach to improve the photoelectrochemical (PEC) water-splitting performance of various materials, including reduced graphene oxide (rGO), tin oxide nanostructures (SnO2), and rGO/SnO2 composites. The composites examined were rS15, containing 15 mg of rGO and 45 mg of SnO2, and rS5, with 5 mg of rGO and 50 mg of SnO2, tested in a sodium hydroxide (NaOH) electrolyte. Notably, the rS5 electrode showed a significant increase in PEC efficiency in 0.1 M NaOH, achieving a peak photocurrent density of 13.24 mA cm-2 under illumination, which was seven times higher than that of pristine rGO nanostructures. This enhancement was attributed to the synergistic effects of the heterostructure, which reduced resistance and minimized charge recombination, thereby maximizing the catalytic activity across the various electrochemical applications. Furthermore, the rS5 anode demonstrated improved Tafel parameters, indicating faster reaction kinetics and lower overpotential for efficient current generation. These results highlight the potential for optimizing nanostructures to significantly enhance PEC performance, paving the way for advancements in sustainable water-splitting technologies.

Bimodal functionality of highly conductive nanostructured silver film towards improved performance of photosystem I-based graphene photocathode.

We present the novel design of photosystem I (PSI)-based biosolar cell, whereby conductive transparent electrode materials, such as ITO or FTO, are replaced with glass covered with silver island film. This nanostructured metallic layer combines high electric conductance with enhancing the absorption efficiency of the PSI biocatalyst via the plasmonic effect. We demonstrate strong enhancement of the photocurrent generated in the biohybrid electrode composed of oriented layers of PSI reaction centers due to plasmonic interactions of the PSI fluorophores and redox centres with the conductive silver island film.

Green Preparation of S, N Co-Doped Low-Dimensional C Nanoribbon/C Dot Composites and Their Optoelectronic Response Properties in the Visible and NIR Regions.

The green production of nanocomposites holds great potential for the development of new materials. Graphene is an important class of carbon-based materials. Despite its high carrier mobility, it has low light absorption and is a zero-bandgap material. In order to tune the bandgap and improve the light absorption, S, N co-doped low-dimensional C/C nanocomposites with polymer and graphene oxide nanoribbons (the graphene oxide nanoribbons were prepared by open zipping of carbon nanotubes in a previous study) were synthesized by one-pot carbonization through dimensional-interface and phase-interface tailoring of nanocomposites in this paper. The resulting C/C nanocomposites were coated on untreated A4 printing paper and the optoelectronic properties were investigated. The results showed that the S, N co-doped C/C nanoribbon/carbon dot hybrid exhibited enhanced photocurrent signals of the typical 650, 808, 980, and 1064 nm light sources and rapid interfacial charge transfer compared to the N-doped counterpart. These results can be attributed to the introduction of lone electron pairs of S, N elements, resulting in more transition energy and the defect passivation of carbon materials. In addition, the nanocomposite also exhibited some electrical switching response to the applied strain. The photophysical and doping mechanisms are discussed. This study provides a facile and green chemical approach to prepare hybrid materials with external stimuli response and multifunctionality. It provides some valuable information for the design of C/C functional nanocomposites through dimensional-interface and phase-interface tailoring and the interdisciplinary applications.

Smartphone-based point-of-care photoelectrochemical immunoassay coupling with ascorbic acid-triggered photocurrent-polarity conversion switching.

Photocurrent-polarity conversion strategies are typically realized by constructing complex photovoltaic electrodes or changing the relevant conditions, but most involve poor photogenerated carrier transfer efficiency and cumbersome experimental steps. To this end, a photoelectrochemical (PEC) biosensor by utilizing ascorbic acid (AA)-induced photocurrent-polarity-switching was proposed for the detection of carcinoembryonic antigen (CEA). Under light excitation, the electron donor AA was oxidized by the photogenerated holes of photoactive material Co-NC/CdS, resulting in the conversion of cathodic photocurrent to the anodic direction. In the presence of the target CEA, alkaline phosphatase (ALP) was introduced into the microplates by the sandwiched immunoreaction, which then catalyzed the production of AA from ascorbic acid-2-phosphate (AAP). Finally, the catalytic product AA was transferred onto Co-NC/CdS-modified screen-printed carbon electrode, thus activating photocurrent-polarity-switching platform. The anodic photocurrent values gradually increased with increasing CEA concentration in the range of 0.02-80 ng mL-1 and reached a limit of detection (LOD) of 8.47 pg mL-1 (S/N = 3). In addition, the results of actual sample detection prove the reliability of the constructed PEC biosensor. Importantly, this work relies on a mobile smartphone wireless Bluetooth device coupled with the PEC biosensor for immediate detection, providing another idea for detecting CEA in clinical diagnosis.

1D Lead Bromide Hybrids Directed by Complex Cations: Syntheses, Structures, Optical and Photocatalytic Properties.

This study presents the synthesis, structural characterization, and evaluation of the photocatalytic performance of two novel one-dimensional (1D) lead(II) bromide hybrids, [Co(2,2'-bpy)3][Pb2Br6CH3OH] (1) and [Fe(2,2'-bpy)3][Pb2Br6] (2), synthesized via solvothermal reactions. These compounds incorporate transition metal complex cations as structural directors, contributing to the unique photophysical and photocatalytic properties of the resulting materials. Single-crystal X-ray diffraction analysis reveals that both compounds crystallize in monoclinic space groups with distinct 1D lead bromide chain configurations influenced by the nature of the complex cations. Optical property assessments show band gaps of 3.04 eV and 2.02 eV for compounds 1 and 2, respectively, indicating their potential for visible light absorption. Photocurrent measurements indicate a significantly higher electron-hole separation efficiency in compound 2, correlated with its narrower band gap. Additionally, photocatalytic evaluations demonstrate that while both compounds degrade organic dyes effectively, compound 2 also exhibits notable hydrogen evolution activity under visible light, a property not observed in 1. These findings highlight the role of metal complex cations in tuning the electronic and structural properties of lead(II) bromide hybrids, enhancing their applicability in photocatalytic and optoelectronic devices.

Pressure-Tuning Localized Excitons Toward Enhanced Emission, Photocurrent Enhancement and Piezochromism in Unconventional ACI-Type 2D Hybrid Perovskites.

Simultaneous enhancement of free excitons (FEs) emission and self-trapped excitons (STEs) emission remains greatly challenging because of the radiative pathway competition. Here, a significant fluorescence improvement, associated with the radiative recombination of both FEs and STEs is firstly achieved in an unconventional ACI-type hybrid perovskite, (ACA)(MA)PbI4 (ACA=acetamidinium) crystals with {PbI6} octahedron units, through hydrostatic pressure processing. Note that (ACA)(MA)PbI4 exhibits a 91.5-fold emission enhancement and considerable piezochromism from green to red in a mild pressure interval of 1 atm to 2.5 GPa. The substantial distortion of both individual halide octahedron and the Pb-I-Pb angles between two halide octahedra under high pressure indeed determines the pressure-tuning localized excitons behavior. Upon higher pressure, photocurrent enhancement is also observed, which is attributed to the promoted electronic connectivity in (ACA)(MA)PbI4. The anisotropic compaction reduces the distance between neighboring organic molecules and {PbI6} octahedra, leading to the enhancement of hydrogen bonding interactions. This work not only offers a deep understanding of the structure-optical relationships of ACI-type perovskites, but also presents insights into breaking the limits of luminescent efficiency by pressure-suppressed nonradiative recombination.

3D-Mapping and Manipulation of Photocurrent in an Optoelectronic Diamond Device.

Establishing connections between material impurities and charge transport properties in emerging electronic and quantum materials, such as wide-bandgap semiconductors, demands new diagnostic methods tailored to these unique systems. Many such materials host optically-active defect centers which offer a powerful in situ characterization system, but one that typically relies on the weak spin-electric field coupling to measure electronic phenomena. In this work, charge-state sensitive optical microscopy is combined with photoelectric detection of an array of nitrogen-vacancy (NV) centers to directly image the flow of charge carriers inside a diamond optoelectronic device, in 3D and with temporal resolution. Optical control is used to change the charge state of background impurities inside the diamond on-demand, resulting in drastically different current flow such as filamentary channels nucleating from specific, defective regions of the device. Conducting channels that control carrier flow, key steps toward optically reconfigurable, wide-bandgap optoelectronics are then engineered using light. This work might be extended to probe other wide-bandgap semiconductors (SiC, GaN) relevant to present and emerging electronic and quantum technologies.

Acousto-Drag Photovoltaic Effect by Piezoelectric Integration of Two-Dimensional Semiconductors.

Light-to-electricity conversion is crucial for energy harvesting and photodetection, requiring efficient electron-hole pair separation to prevent recombination. Traditional junction-based mechanisms using built-in electric fields fail in nonbarrier regions. Homogeneous material harvesting under a photovoltaic effect is appealing but is only realized in noncentrosymmetric systems via a bulk photovoltaic effect. Here we report the realization of a photovoltaic effect by employing surface acoustic waves (SAWs) to generate zero-bias photocurrent in the conventional layered semiconductor MoSe2. SAWs induce periodic modulation to electronic bands and drag the photoexcited pairs toward the traveling direction. The photocurrent is extracted from a local barrier. The separation of generation and extraction processes suppresses recombination and yields a large nonlocal photoresponse. We distinguish the acousto-electric drag and electron-hole pair separation effect by fabricating devices of different configurations. The acousto-drag photovoltaic effect, enabled by piezoelectric integration, offers an efficient light-to-electricity conversion method, independent of semiconductor crystal symmetry.

Heterojunction photoelectric device with fast response speed and low power consumption composed of WSSe and AlN.

Through the accurate calculation of density functional theory, reveal the excellent photoelectric properties of the AlN/WSSe and WSSe/AlN heterojunction. Especially, the hole mobility of the AlN/WSSe heterojunction is as high as 3919 cm2Vs-1in armchair direction, and the hole mobility of the WSSe/AlN heterojunction is as high as 4422 cm2Vs-1in the zigzag direction. Interestingly, when two H atoms are adsorbed in the WSSe surface, the Gibbs free energy change are -0.093 eV and -0.984 eV, which tends to zero, which can promote the spontaneous reaction of electrocatalytic water decomposition to produce H2. In addition, the AlN/WSSe heterojunction exhibits significant photoelectric effect photocurrent (1.15 a02/photon) in the armchair direction and the heterojunctions have lower threshold voltage (1.5 V), that indicate the AlN/WSSe and WSSe/AlN heterojunction have great application prospect in manufacturing high-performance optoelectronic devices with fast response and low power consumption.

Semiconducting Properties of Delaminated Titanium Nitride Ti4N3Tx MXene with Gate-Tunable Electrical Conductivity.

MXenes have garnered significant attention due to their atomically thin two-dimensional structure with metallic electronic properties. However, it has not yet been fully achieved to discover semiconducting MXenes to implement them into gate-tunable electronics such as field-effect transistors and phototransistors. Here, a semiconducting Ti4N3Tx MXene synthesized by using a modified oxygen-assisted molten salt etching method under ambient conditions, is reported. The oxygen-rich synthesis environment significantly enhances the etching reaction rate and selectivity of Al from a Ti4AlN3 MAX phase, resulting in well-delaminated and highly crystalline Ti4N3Tx MXene with minimal defects and high content of F and O, which led to its improved hydrophobicity and thermal stability. Notably, the synthesized Ti4N3Tx MXene exhibited p-type semiconducting characteristics, including gate-tunable electrical conductivity, with a current on-off ratio of 5 × 103 and a hole mobility of ∼0.008 cm2 V-1 s-1 at 243 K. The semiconducting property crucial for thin-film transistor applications is evidently associated with the surface terminations and the partial substitution of oxygen in the nitrogen lattice, as corroborated by density functional theory (DFT) calculations. Furthermore, the synthesized Ti4N3Tx exhibits strong light absorption characteristics and photocurrent generation. These findings highlight the delaminated Ti4N3Tx as an emerging two-dimensional semiconducting material for potential electronic and optoelectronic applications.

Photocurrent Spectroscopy of Dark Magnetic Excitons in 2D Multiferroic NiI2.

Two-dimensional (2D) antiferromagnetic (AFM) semiconductors are promising components of opto-spintronic devices due to terahertz operation frequencies and minimal interactions with stray fields. However, the lack of net magnetization significantly limits the number of experimental techniques available to study the relationship between magnetic order and semiconducting properties. Here, they demonstrate conditions under which photocurrent spectroscopy can be employed to study many-body magnetic excitons in the 2D AFM semiconductor NiI2. The use of photocurrent spectroscopy enables the detection of optically dark magnetic excitons down to bilayer thickness, revealing a high degree of linear polarization that is coupled to the underlying helical AFM order of NiI2. In addition to probing the coupling between magnetic order and dark excitons, this work provides strong evidence for the multiferroicity of NiI2 down to bilayer thickness, thus demonstrating the utility of photocurrent spectroscopy for revealing subtle opto-spintronic phenomena in the atomically thin limit.

Quantum Dot/TiO2 Nanocomposite-Based Photoelectrochemical Sensor for Enhanced H2O2 Detection Applied for Cell Monitoring and Visualization.

This work exploits the possibility of using CdSe/ZnS quantum dot (QD)-electrodes to monitor the metabolism of living cells based on photoelectrochemical (PEC) measurements. To realize that, the PEC setup is improved with respect to an enhanced photocurrent signal, better stability, and an increased signal-to-noise ratio, but also for a better biocompatibility of the sensor surface on which cells have been grown. To achieve this, a QD-TiO2 heterojunction is introduced with the help of atomic layer deposition (ALD). The heterojunction reduces the charge carrier recombination inside the semiconductor nanoparticles and improves the drift behavior. The PEC performance is carefully analyzed by adjusting the TiO2 thickness and combining this strategy with multilayer immobilizations of QDs. The optimal thickness of this coating is ≈5 nm; here, photocurrent generation can be enhanced significantly (e.g., for a single QD layer electrode by more than one order of magnitude at 0 V vs Ag/AgCl). The resulting optimized electrode is used for hydrogen peroxide (H2O2) sensing with a good sensitivity down to µmolar concentrations, reusability, stability, response rate, and repeatability. Finally, the sensing system is applied to monitor the activity of cells directly grown on top of the electrode surface.

Harnessing Persistent Photocurrent in a 2D Semiconductor-Polymer Hybrid Structure: Electron Trapping and Fermi Level Modulation for Optoelectronic Memory.

Recently, 2D semiconductor-based optoelectronic memory has been explored to overcome the limitations of conventional von Neumann architectures by integrating optical sensing and data storage into one device. Persistent photocurrent (PPC), essential for optoelectronic memory, originates from charge carrier trapping according to the Shockley-Read-Hall (SRH) model in 2D semiconductors. The quasi-Fermi level position influences the activation of charge-trapping sites. However, the correlation between quasi-Fermi level modulations and PPC in 2D semiconductors has not been extensively studied. In this study, we demonstrate optoelectronic memory based on a 2D semiconductor-polymer hybrid structure and confirm that the underlying mechanism is charge trapping, as the SRH model explains. Under light illumination, electrons transfer from polyvinylpyrrolidone to p-type tungsten diselenide, resulting in high-level injection and majority carrier-type transitions. The quasi-Fermi level shifts upward with increasing temperature, improving PPC and enabling optoelectronic memory at 433 K. Our findings offer valuable insights into optimizing 2D semiconductor-based optoelectronic memory.

THz Generation by Two-Color Plasma: Time Shaping and Ultra-Broadband Polarimetry.

The generation of terahertz radiation via laser-induced plasma from two-color femtosecond pulses in air has been extensively studied due to its broad emission spectrum and significant pulse energy. However, precise control over the temporal properties of these ultra-broadband terahertz pulses, as well as the measurement of their polarization state, remain challenging. In this study, we review our latest findings on these topics and present additional results not previously reported in our earlier works. First, we investigate the impact of chirping on the fundamental wave and the effect of manipulating the phase difference between the fundamental wave and the second-harmonic wave on the properties of generated terahertz pulses. We demonstrate that we can tune the time shape of terahertz pulses, causing them to reverse polarity or become bipolar by carefully selecting the correct combination of chirp and phase. Additionally, we introduce a novel technique for polarization characterization, termed terahertz unipolar polarimetry, which utilizes a weak probe beam and avoids the systematic errors associated with traditional methods. This technique is effective for detecting polarization-structured terahertz beams and the longitudinal component of focused terahertz beams. Our findings contribute to the improved control and characterization of terahertz radiation, enhancing its application in fields such as nonlinear optics, spectroscopy, and microscopy.