Transient Photovoltage Research Articles

Phase Reconstruction‐Directed Synthesis of Oxalate‐Functionalized Nickel Hydroxide Electrocatalyst for High‐Yield H2O2 Generation at Industrial Currents

AbstractThe electrochemical oxygen reduction reaction (2e− ORR) offers a promising approach for H2O2 production, yet developing highly active, selective, and stable electrocatalysts remains a challenge. In this work, a phase reconstruction strategy is presented to synthesize an oxalate‐adsorbed nickel hydroxide electrocatalyst (Ni(OH)2‐C2O4) through the self‐dissociation of nickel oxalate in an alkaline medium, leading to a notable enhancement in H2O2 yield at elevated current densities. Remarkably, Ni(OH)2‐C2O4 exhibits a 2e− selectivity exceeding 93% across a broad voltage range (0.0 to 0.5 V vs RHE) in 0.1 M KOH, outperforming pristine Ni(OH)2. When deployed as a gas diffusion electrode in a flow cell, the Ni(OH)2‐C2O4 catalyst demonstrates stable operation for 50 h at 200 mA cm−2, with a Faradaic efficiency surpassing 90% and a peak H2O2 yield of 6.2 mol g−1cat h−1. Comprehensive advanced characterizations, including in situ Raman spectroscopy, transient photovoltage spectra, and transient potential scanning spectra, coupled with post‐ORR analyses, reveal that surface‐adsorbed oxalate groups on Ni(OH)2 enhance the interfacial reaction kinetics between active Ni sites and reactants by inducing a charge trapping effect and forming a hydrogen‐bonded network, facilitating robust and high‐yield H2O2 production.

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.

(Invited) Parameter Prediction in Colloidal Quantum Dot Solar Cells Using Residual Neural Networks Trained on Experimental Data

Colloidal quantum dots (CQDs) are an attractive third-generation material for photovoltaics, especially as infrared materials for multi-junction solar cells. Characterization and materials parameter prediction both play a critical role in the rising efficiencies in this field. However, there are numerous materials properties that need to be measured in order to fully characterize a device, leading to high research costs and slow development times. Here, we leverage recent advancements in machine learning (ML), along with a recently-demonstrated multimodal spectral characterization method [1], to predict complex materials parameters in CQD solar cells from simple current density-voltage (JV) curves, using an algorithm trained on experimental data.[2]Past work ML prediction of materials properties has focused on using simulated data due to the difficulty in collecting enough experimental data to fully train an algorithm. While it is not feasible to fabricate thousands of devices in a typical research lab, it is possible to measure several thousand points on a single device. We used a micrometer-resolution 2D characterization method with millimeter-scale field of view to acquire enough training data using only a handful of devices, while learning the spatial relationships between materials parameters. Photoluminescence, trap state density, transient photovoltage, transient photocurrent, and carrier mobility were predicted (Figure 1) by five different residual neural networks, each using a ResNet block and containing over 300k learnable parameters. The design of the networks were based on the ResNet50 architecture [3]. We also implemented a novel neighborhood approach to reduce errors and account for spatial correlations in device behavior, leading to insights into transport mechanisms and correlation lengths in CQD thin films. This method could be used to study a wide range of material systems and devices, ultimately leading to a universal prediction model that greatly simplifies the characterization process for optoelectronic devices and accelerates development times.

Enabling Ultra‐Narrow‐Band Deep‐Blue Light‐Emitting Diode Via Trapping Injected Holes by Carbon Dots

AbstractNarrow‐band deep‐blue light‐emitting diodes (LEDs) (CIEy coordinate<0.08, full width at half maximum (FWHM)<20 nm) are important for the next generation of LED‐based displays. It remains a significant challenge for the design of narrow‐band deep‐blue emitters. Herein, a new strategy is proposed for constructing narrow‐band deep‐blue LEDs that are not dependent on the narrow‐band deep‐blue emitter, but only need to dope n‐type carbon dots (n‐CDs) in the active emission layer (EML) of the wide‐band blue LEDs. The n‐CDs‐LEDs show an ultra‐narrow deep‐blue emission at 430 nm with the color coordinates of (0.15, 0.04) and the FWHM of 19 nm. Wherein the EML is constructed by doping n‐CDs in Poly(9,9‐dioctylfluorene‐co‐N‐(4‐butylphenyl) diphenylamine) (TFB), which neither changes the band structure of TFB nor produces new energy levels. Transient photovoltage (TPV) and various photoelectrochemical characterizations jointly reveal that n‐CDs can trap holes to realize the carrier injection into a single energy level of TFB and achieve ultra‐narrow deep‐blue light emission. This work provides a brand‐new and simple way to realize the narrow‐band deep‐blue LEDs.

Electronic states near surfaces and interfaces of β-Ga2O3 and κ-Ga2O3 epilayers investigated by surface photovoltage spectroscopy, photoconductivity and optical absorption

Transient surface photovoltage (SPV) spectroscopy, optical absorption, and photoconductivity (PC) were applied to study electronic transitions in (-201) β-Ga2O3 and (001) κ-Ga2O3 epitaxial layers on c-plane sapphire substrates. SPV signals were distinguished for charge separation near the surface and near the layer/substrate interface. The bandgaps of β-Ga2O3 and κ-Ga2O3 epitaxial layers were found to be, respectively, about 4.75 and 4.79 eV from optical absorption measurements, about 4.8 and 4.9 eV from PC, and 4.65 and 4.9 (near the surface) from SPV measurements. Near the κ-Ga2O3 layer/substrate interface SPV instead gives a value of 4.75 eV, possibly related to the presence of an interlayer. Defect-related transitions with onset energies at about 4.5, 4.1, and 3.5 eV were observed along the whole β-Ga2O3 layer cross-section. In contrast, defects related to different transitions were differently distributed in κ-Ga2O3 epitaxial layers: transitions setting on at about 4.3 eV originate from defects uniformly distributed across the layer, while transitions starting at 2.4 eV and 1.7 eV were respectively connected with defects located near the surface or near the layer/substrate interface. The PC measurements at photo-excitation energy above the bandgap indicated that defect densities and recombination losses were much larger in κ-Ga2O3 than in β-Ga2O3.

Enhancing stability and efficiency in SnO2 based HTL-free, printable carbon-based perovskite solar cells for outdoor/indoor photovoltaics

Recent advancements in hole transport layer (HTL)-free, printable carbon-based perovskite solar cells (C-PSCs) have gained increased research interest. Notably, their scalability, cost-effectiveness, and improved stability make them particularly attractive among various perovskite solar cell configurations. In the current study, we explored the potential of un-encapsulated, HTL-free, C-PSCs in outdoor and indoor light conditions, employing different concentrations of tin oxide (SnO2) as the electron transport material. Among the investigated concentrations, 0.07 M SnO2 precursor yielded the highest power conversion efficiency (PCE), reaching 9.79% under standard 1 sun illumination and 10.40% at a lower intensity of 0.6 sun. The PSCs demonstrated a remarkable 22.37% efficiency under 1000 lx indoor CFL illumination, and attained 22.21% efficiency under LED illumination, marking the highest reported indoor photovoltaic performance for carbon-based, HTL-free PSCs. To elucidate the underlying charge-transfer process, we carried out intensity-dependent current−voltage (J-V) measurements to analyze non-radiative bulk recombination in the perovskite layer. Interfacial recombination was investigated using electrochemical impedance spectroscopy (EIS) and transient photovoltage decay measurements. Optical and electrical stimulation of C-PSCs were performed under both full sun and indoor illumination, providing insight into recombination and light absorption differences under these illuminations. Additionally, we also showcased the potential of simple, printable indoor light harvesters for self-powered applications by connecting two C-PSCs to create a self-powered temperature sensor.

Enable strong electrical coupling between the InZnP@PbS collodial quantum dots in films via the two-step ligand exchange method

Colloidal quantum dots (CQDs) are promising materials for building next-generation solution-processed, high-performance, and low-cost optoelectronic devices. The photoelectric properties of the resulting films are not only determined by the intrinsic characteristics of the CQDs but are also significantly affected by the electrical coupling between them. However, enhancing the electrical coupling in CQD-based films is still a big challenge. In this work, a two-step ligand exchange strategy has been conducted to solve the above issue, where the InZnP@PbS CQDs have been used as the case. First, the Meerwein salt (Et3OBF4) solution in N, N-dimethylformamide (DMF) has been employed to peel off the native ligands that are strongly capped on the surface of oil-soluble CQDs, resulting in a neat surface. Second, iodide ions are linked to the neat surface of the CQDs to narrow the distance between them and passivate their defects, establishing strong electrical coupling. Transient surface photovoltage (TSPV) and photo-conductance tests confirm that the resulting InZnP@PbS–I CQDs films possess good photoelectric properties and stability. In the fabricated solid-state solar cells, 3.1 % of the photoelectric conversion efficiency (PCE) has been achieved under 1 sun. The current results are outstanding for III-V group CQD-based all solid-state solar cells.

Influence of photoanode pre-heating treatment temperatures prior to dye immersion process on dye-sensitized solar cells photovoltaic performances

Several efforts of photoanode treatment, such as surface modification, doping introduction, defect engineering, and heating treatment, have been developed to improve the photovoltaic performances of dye-sensitized solar cells (DSSC). Amid these options, alternative routes that require less demanding conditions are highly sought. Here we introduce an effective and convenient, non-vacuum low-temperature procedure to enhance the DSSC’s photovoltaic performances by photoanode pre-heating treatment prior to the dye immersion process. The experimental result showed that pre-heating treatment at 120 °C improves the efficiency and short-circuit current by about 28.4% and 19.1%, respectively. The conducted transient photovoltage measurements revealed that the increase of pre-heating temperatures leads to a longer electron lifetime and higher charge collection efficiency.

An ultrahigh hydrogen production rate of photocatalyst Fe2S2(CO)6/MoS2/CdS integrated mimic hydrogenase and capacitor for H2 evolution with longer lifetime of photoexcited electrons

The hydrogenase mimics provide an innovative strategy for photocatalytic hydrogen production; however, the efficiency mismatch between electron production and utilization results in low hydrogen production rate. Herein, we report the integration of non-noble metal cocatalyst MoS2 decorated with hydrogenase model complex Fe2S2(CO)6 and CdS QDs to assemble Fe2S2(CO)6/MoS2/CdS QDs, which exhibited an excellent hydrogen production rate of 10,836 μmol/g/h. This rate is 127.4, 9.1, and 1.6 times higher than that of CdS QDs, Fe2S2(CO)6/CdS QDs, and MoS2/CdS QDs, respectively. In comparison to CdS or MoS2/CdS, transient photovoltage (TPV) measurements revealed that the photovoltage response of Fe2S2(CO)6/MoS2/CdS increased numerically by 3.3 times; meanwhile, Fe2S2(CO)6/MoS2/CdS significantly extended the lifetime of photo-generated electrons. The excellent performance was attributed to the distinct capacitance effect and functional active site of Fe2S2(CO)6/MoS2/CdS, which boosted electron storage and redistribution at the interface to alleviate recombination losses and facilitate hydrogen production.

Comprehensive Study of Carrier Recombination in High‐Efficiency CdTe Solar Cells Using Transient Photovoltage

Cadmium telluride (CdTe) solar cells represent a commercially successful photovoltaic technology, with an annual production capacity approaching 20 GW. However, improving the open‐circuit voltage (VOC) remains challenging. This study aims to deepen the understanding of charge carrier recombination in CdTe solar cells and to explore alternative dynamical characterization methods that address the limitations found in conventionally used time‐resolved photoluminescence for CdTe solar cells. Transient photovoltage and transient photocurrent techniques are utilized to investigate charge carrier dynamics under conditions resembling real‐world solar cell operation. The results reveal that an effective nonradiative recombination lifetime of 580 ns dominates the charge dynamics at VOC values below 850 mV. Above this threshold, radiative recombination becomes significant, with a radiative recombination coefficient of 1.1 × 10−9 cm3 s−1. Additionally, the stationary charge carrier density at 1 sun is determined to be around 1 × 1014 cm−3. By accurately determining both radiative and nonradiative recombination, this work provides a comprehensive understanding of carrier dynamics in high‐performing CdTe devices and paves the way for improving the VOC and performance of CdTe solar cells.

Stable MOF-In2S3/ZnFe layered dioxide heterostructures for improving photocatalytic degradation: Degradation pathways, kinetics, and charge migration

In this paper, MOF-In2S3 were modified by ZnFe-layered dioxides (LDO) with strong stability to obtain high catalytic performance composite. The successful preparation of ZnFe-LDO/MOF-In2S3 not only retains the advantages of large specific surface area of MOF-In2S3 and the stability of ZnFe-LDO, but also improves its charge separation efficiency and the light absorption region through the construction of heterojunctions. As expected, the experimental results show that ZnFe-LDO/MOF-In2S3 has superior photo-electrocatalytic properties. The photocatalytic degradation efficiency of ZnFe-LDO/MOF-In2S3 for TCH and OTC reach 92.92% and 80%, respectively, within 25 min. And the corresponding degradation rate constants are up to 1.41332 and 0.45451 L·mg−1·min−1, respectively, which are accord with the pseudo-second-order kinetic constants. The intermediate of 0.6LDO/M-I degradation of TCH was proposed by liquid mass spectrometry (LC-MS). Notably, a special transient surface photovoltage (TPV) technique was used for discussing the charge transfer kinetics and the lifetime of photogenerated carriers. Based on Mott-Schottky (M-S), Ultraviolet-visible absorption spectrum (UV), X-ray Photoelectron Spectroscopy (XPS) results, electron paramagnetic resonance (EPR) results, and active substance capture experiment results, a Z-scheme heterojunction system was proposed. The above research work proposed a new approach to enhance the stability of catalytic materials by using the aid of layered dioxides. In addition, the characterization of surface photovoltage provides a new way to study charge transfer.

Improvement in stability and exploring the photovoltaic properties of CsPbI2Br thin films for perovskite solar cells

The phase stability and quality of CsPbI2Br perovskite film directly determines the performance of perovskite solar cells (PSCs). However, there is a lack of research on phase stability of perovskite films of PSCs. Here, by simply controlling precursors with specified ratios and solvents, the phase stability, charge transfer resistance and electron lifetime improve significantly which is useful for high performance in perovskite solar cells. Besides this, the information about trap centres by a novel technique Charge Deep Level Transient Spectroscopy (Q-DLTS) also helps to improve efficiency of perovskite solar cells. In this work, CsPbI2Br perovskite thin films have been synthesized using simple solution processing method, by varying CsBr and PbI2 precursors with specified ratios of 1.05 M:1 M and 1.10 M:1 M in Dimethysulfoxide (DMSO) and Dimethyl formamide (DMF). The CsPbI2Br film with ratio of 1.05:1 has more phase stability in ambient air at room temperature than that of 1.10:1. Drop casting method was adopted for thin films preparation and structurally cubic phase of perovskite films obtained by X-ray diffraction (XRD). Scanning electron microscope (SEM) showed more homogeneity on the surface of the sample with ratio 1.05:1 and energy dispersive x-ray spectroscopy (EDX) confirmed the presence of same amounts in chemical composition. Fourier transform infrared spectroscopy (FTIR) transmittance spectra showed that main peak is generally observed because of stretching vibrations of lead-iodide ions. In UV–visible (UV-Vis) little effect was observed on the energy band gaps i.e. 1.93 eV for 1.05 M:1 M and 1.96 eV for 1.10 M:1 M. The electrochemical impedance spectroscopy (EIS) measurements were performed for electronic charges accumulation on the surface of the films which showed semi-circles Nyquist plots and frequency dependent Bode plots were used to find electron lifetime. The charge transfer resistance (Rct) decreased from 52Ω to 45Ω and electron life time were approximately equal to 0.10 s and 0.09 s for the ratio of 1.10:1 and 1.05:1. I-V measurements showed an Ohmic contact formation providing insights into defect concentrations with a linear response to applied bias. Recombination lifetimes were investigated using transient photovoltage (TPV) at various biases, no correlation between the applied bias and recombination lifetime was found. Q-DLTS indicated presence of 3 trap centers for the charge carriers which were actively responsible for degradation of the perovskite material, these traps serve as recombination centres that reduce the overall power conversion efficiency (PCE) of solar cells. Photoluminescence spectroscopy (PL) analysis was done to verify the energy bandgap value which was found similar in comparison to UV–VIS.

Effective nitrogen doping of TiO2 polymorphs at mild temperatures for visible-light-responsive hydrogen evolution

Herein, a mild-temperature nitrogen doping route with the urea-derived gaseous species as the active doping agent is proposed to realize visible-light-responsive photocatalytic hydrogen evolution both for the anatase and rutile TiO2. DFT simulations reveal that the cyanic acid (HOCN), derived from the decomposition of urea, plays a curial role in the effective doping of nitrogen in TiO2 at mild temperatures. Photocatalytic performance demonstrates that both the anatase and rutile TiO2 doped at mild temperatures exhibit the highest hydrogen evolution rates, although the ones prepared at high temperatures possess higher absorbance in the visible range. Steady-state and transient surface photovoltage characterizations of these doped TiO2 polymorphs prepared at different temperatures reveal that harsh conditions (high temperature reaction) typically result in the formation of intrinsic defects that are detrimental to the transport of the low-energy visible-light-induced electrons, while the mild-temperature nitrogen-doping could flatten the pristine upward band bending without triggering the formation of Ti3+, thus achieving enhanced visible-light-responsive hydrogen evolution rates. We anticipate that our findings will provide inspiring information for shrinking the gap between the visible-light-absorbance and the visible-light-responsiveness in the band engineering of wide-bandgap metal-oxide photocatalysts.

Post-annealing-free BaOxFy/LiF-based stack electron-selective contacts for high efficiency crystalline silicon solar cells featuring ultra-low contact resistivity

In silicon heterojunction and tunnel oxide passivating contact crystalline silicon (c-Si) solar cells based on successful passivating contacts technologies, an annealing activation step is indispensable to achieve a suitably low contact resistivity (ρc), which is a costly and non-ideal process. Here, combined with a calcium aluminium (Ca:Al) alloy electrode, a low work function barium oxide and lithium fluoride (BaOxFy/LiF) stack electron-selective contact (ESC) without an annealing activation step on c-Si solar cells clinches an ultra-low ρc of 1.4 mΩ·cm2 delivering a power conversion efficiency (PCE) of 20.5 %. The BaOxFy/LiF/Ca:Al stack structure is built by BaOx/LiF/Ca/Al hybrid structure via a facile continuous thermal evaporation process. As a proof of concept, the stacked BaOxFy/LiF/Ca:Al/Al contact is applied to the rear side of c-Si solar cells, achieving a PCE of 20.5 % with an open-circuit voltage of 625.7 mV, an impressive fill factor of 83.5 % and a short-circuit current density of 39.2 mA/cm2. With the aid of a transient photovoltage setup, the carrier recombination mechanism of the stacked BaOxFy/LiF/Ca:Al structure is explored. This work demonstrates an alternative idea for undoped ESCs, showing potential for next-generation cost-effective ultrathin-slice c-Si solar cells (∼80 μm) with high efficiency, and low-parasitic light absorption losses.

Charge Carrier Dynamics at Carbon/Perovskite Interface: Implications on Carbon‐Based HTM‐Free Solar Cell Stability

Carbon‐based hole transport material (HTM)‐free perovskite solar cells (CPSCs) are an innovative device architecture that mitigates inherent challenges associated with record‐breaking perovskite solar cells (PSCs), which rely on metal/HTMs, including instability, manufacturing intricacy, and elevated costs. The photovoltaic efficiency and stability of CPSCs are profoundly influenced by the charge carrier dynamics at the interfaces. Herein, the charge carrier dynamics at the carbon(C)–perovskite interface in CPSCs and its implications on photovoltaic performances and stability, an aspect that has received limited exploration thus far are probed, are investigated using transient surface photovoltage (Tr‐SPV) and transient photoluminescence measurements. The study reveals that the C‐electrode effectively acts as a selective barrier, impeding electrons while facilitating the extraction of holes at the C–perovskite interface. This selective blocking mechanism holds significant implications for improving the performance and stability of CPSCs over HTM‐free PSCs with gold(Au) electrodes. The stability of CPSCs is evaluated by measuring shelf life, maximum power point tracking, Tr‐SPV, and X‐Ray diffraction measurements. By delving into these pivotal aspects, this work aims to contribute to the advancement and understanding of CPSCs for sustainable and efficient energy conversion.

Construction of fast charge-transferred 0D/2D BiOBr/Bi2WO6 S-scheme heterojunction with enhanced photocatalytic performance

Novel Bi-based photocatalysts play an increasing role in dealing with environmental pollution and resource shortages. Among these Bi-based materials, BiOBr and Bi2WO6 have gained intensive attraction due to the appropriate energy band alignments and their anisotropic crystal structure. 0D/2D BiOBr/Bi2WO6 heterojunction was constructed by depositing BiOBr nanoparticles on few-layer Bi2WO6 nanosheets. The structure, optical property, and micromorphology of samples were characterized by XRD, XPS, UV–vis DRS, SEM, TEM, and AFM. The photoluminescence, photocurrent density, and electrochemical impedance spectroscopy (EIS) as well as the transient surface photovoltage (TSPV) were performed to explore the transfer of photoinduced charge carriers. The photocatalytic efficiency of the heterojunction is much improved, about 2.67 folds higher than that of pristine Bi2WO6. The fast separation and migration and the prolonged lifetime of photogenerated carriers in the BiOBr/Bi2WO6 heterojunction are validated by photoelectrochemical tests. The influence factors, versatility, and reusability of the heterojunction are also evaluated. Radical trapping test reveals that h+ and ·O2− are predominant active species and make a major contribution to the photoactivity of the BiOBr/Bi2WO6 heterojunction. The formed energy-band bending, the built-in electric field, and the S-scheme charge transfer strategy are thermodynamically and kinetically favorable for the photoactivity and stability of the heterojunction.

Enhancing the Efficiency and Stability of Perovskite Solar Cells through Defect Passivation and Controlled Crystal Growth Using Allantoin.

In this study, we present a robust approach that concurrently manages crystal growth and defect passivation within the perovskite layer through the introduction of a small molecule additive─allantoin. The precise regulation of crystal growth in the presence of allantoin yields perovskite films characterized by enhanced morphology, larger grain size, and improved grain orientation. Notably, the carbonyl and amino groups present in allantoin passivate under-coordinated Pb2+ and I- defects, respectively, through molecular interactions. Trap density in the perovskite layer is measured, and it is 0.39 × 1016 cm-3 for the allantoin-incorporated device and 0.83 × 1016 cm-3 for the pristine device. This reduction in defects leads to reduced trap-assisted nonradiative recombination, as confirmed by the photoluminescence, transient photo voltage, and impedance measurements. As a result, when these allantoin-incorporated perovskite films are implemented as the active layer in solar cells, a noteworthy efficiency enhancement to 20.63% is attained, surpassing the 18.04% of their pristine counterparts. Furthermore, devices with allantoin exhibit remarkable operational stability, maintaining 80% of their efficiency even after 500 h of continuous illumination, whereas the pristine device degraded to 65% of its initial efficiency in 400 h. Also, allantoin-incorporated devices exhibited exceptional stability against high humidity and elevated temperatures.

Interaction of metal ions in high efficiency seawater hydrogen peroxide production by a carbon-based photocatalyst

Photocatalytic seawater splitting is a promising method for producing hydrogen peroxide (H2O2). However, the presence of metal ions usually deactivates catalysts and causes undesirable reactions, highlighting the need for deeply understanding these interactions. Herein, a carbon-based composite photocatalyst (CQM) is fabricated for photocatalytic production of H2O2. The metal ions strongly affect the photocatalytic activity of the CQM catalyst with order of Mg2+ > Al3+ > Ca2+ > K+, consistent with the surface effective electron concentration calculated from transient photovoltage (TPV) technology. Notably, with the presence of Mg2+ at 0.36 mol L−1, the H2O2 yield is 12,812 μmol g−1 h−1. Under the guidance of machine learning, the H2O2 yield is further improved to 19,560 μmol g−1 h−1 by adjusting the concentration of multiple ions. Significantly, in a real seawater system, the photoproduction of H2O2 on CQM reaches up to a recorded value of 11306 μmol g−1 h−1 under visible light illumination.

Highly efficient dye-sensitized solar cells achieved by matching energy levels between pseudohalogen redox couples and organic donor−π−acceptor cyanoacrylic acid dyes

A good match of energy levels between dyes and redox couples is an important factor to reduce energy loss and further improve the power conversion efficiency of dye-sensitized solar cells (DSSCs). Pseudohalogens were introduced as an improved alternative to iodide/triiodide (I−/I3−) couples to achieve this goal. Herein, we used SCN−/(SCN)2 and SeCN−/(SeCN)2 as redox couples combined with organic donor-π-acceptor cyanoacrylic acid dyes, 3-{5-[N,N-Bis(9,9-dimethylfluoren-2 -yl)phenyl]thieno[3,2-b]thiophene-2-yl}-2-cyano-acrylic acid (C201) and 3-{5-[N,N-bis(4-diphenylamino)pheny]thieno[3,2-b]thiophen-2-yl}-2-cyano-acrylic acid (C207), respectively. Appropriate combination of SeCN−/(SeCN)2 couple (0.54 V vs. NHE) and C207 dye (0.75 V vs. NHE) yield an overall efficiency of 6.96 ± 0.54 %, which is comparable to the widely used I−/I3− couples. Moreover, at the optimized SCN−/(SCN)2 concentration ratio (25mM/100 mM), the C201-based DSSCs achieved an efficiency up to 8.62 ± 0.44 %, and the performance was 16 % higher than that of I−/I3− couples. The origin of this improvement was found to be the efficient regeneration of C201 dye with a reduced energy loss at a driving force of 0.19 eV using the SCN−/(SCN)2 couple. The electrochemical transient photovoltage decay spectroscopy studies further reveal that the pseudohalogen redox couples increases the redox potential to benefit the photovoltage of the cell and increase the electron lifetime. These results show the potential of exploiting redox couples with suitable heterogeneous electron-transfer rates and energy levels matched to selected dyes.

Exciton formation dynamics at the SiO2/Si interface

Excitons can operate as carriers for energy transduction in optoelectronics, and engineering their dynamics is of great interest. Here, we employ time-resolved terahertz spectroscopy to analyze exciton formation dynamics as a function of temperature for a (100) N-type silicon substrate passivated by native SiO2. By analyzing the frequency-resolved complex conductivity as a function of temperature we resolve the photophysics for the formation of free carriers into excitons. Notably, we observe a relatively long-lived ~300 ps transient population of free carriers at temperatures well below the Mott transition (4 K). We rationalize this by transient photophysics at the SiO2/N-type-Si surface, where holes localize and release under high injection conditions due to a transient surface photovoltage effect. We believe our results have implications for the design of excitonic-based electronic applications operating at cryogenic temperatures and accessed optically.