Hybrid Perovskite-Based Wireless Integrated Device Exceeding a Solar to Hydrogen Conversion Efficiency of 11.

A wireless solar water splitting device provides a means to achieve an inexpensive and highly distributed solar-to-fuel system owing to its portability, flexible scale, and simple design. Here, a highly efficient hydrogen-generating artificial leaf is introduced, which is a wireless configuration for converting solar energy into chemical energy, by integrating a hybrid perovskite (PSK) as the light absorber with catalysts for electrochemical reaction. First, a single integrated photoelectrochemical photocathode, and a spatially decoupled hydrogen evolution reaction catalyst, are fabricated. A decoupled geometry is adopted to enable the physical protection of the PSK layer from the electrolyte, thus allowing excellent stability for over 85 h. Additionally, an efficient dual photovoltaic module photocathode is fabricated to produce sufficient photovoltage to drive water splitting reactions, as well as a high photocurrent to achieve the applied-bias photoconversion efficiency (13.5%). To investigate the overall water splitting performance, a NiFe-OH catalyst is employed, and the device with a wired configuration achieves a photocurrent density of 9.35 mA cm-2 , corresponding to a solar to hydrogen (STH) efficiency of 11.5%. The device with a fully integrated wireless artificial leaf configuration exhibited a similar STH efficiency of over 11%, demonstrating the effectiveness of this cell design.

Chiral 2D Organic Inorganic Hybrid Perovskite with Circular Dichroism Tunable Over Wide Wavelength Range.

The effect of chemical-composition modification on the chiroptical property of chiral organic ammonium cation-containing organic inorganic hybrid perovskite (chiral OIHP) is investigated. Varying the mixing ratio of bromide and iodide anions in S- or R-C6H5CH2(CH3)NH3)2PbI4(1-x)Br4x modifies the band gap of chiral OIHP, leading to a shift of the circular dichroism (CD) signal from 495 to 474 nm. However, it is also found that an abrupt crystalline structure transition occurs, and the CD signal is turned off when iodide-determinant phases are transformed into the bromide-determinant phase. To obtain CD in the wavelength range where the bromide-determinant phase is supposed to exhibit chiroptical activity, that is, <474 nm, S- or R-C12H7CH2(CH3)NH3 with a larger spacer group can be adopted; thus, the CD signal can be further blue-shifted to ∼375 nm. Here, we show that chemical-composition modification of chiral OIHP affects the chiroptical properties of chiral OIHP in two ways: (1) tuning the wavelength of CD by modulating the excitonic band structure and (2) switching the CD on and off by inducing a crystalline-structure change. These properties can be utilized for structural engineering of high-performance chiroptical materials for spin-polarized light-emitting devices and polarization-based optoelectronics.

Strategies for enhancing the photocurrent, photovoltage, and stability of photoelectrodes for photoelectrochemical water splitting.

To accelerate the deployment of hydrogen produced by renewable solar energy, several technologies have been competitively developed, including photoelectrochemical (PEC), photocatalytic, and photovoltaic-electrolysis routes. In this review, we place PEC in context with these competing technologies and highlight key advantages of PEC systems. After defining the unique performance metrics of the PEC water splitting system, recently developed strategies for enhancing each performance metric, such as the photocurrent density, photovoltage, fill factor, and stability are surveyed in conjunction with the relevant theoretical aspects. In addition, various advanced characterization methods are discussed, including recently developed in situ techniques, allowing us to understand not only the basic properties of materials but also diverse photophysical phenomena underlying the PEC system. Based on the insights gained from these advanced characterization techniques, we not only provide a resource for researchers in the field as well as those who want to join the field, but also offer an outlook of how thin film-based PEC studies could lead to commercially viable water splitting systems.

Solution phase treatments of Sb2Se3 heterojunction photocathodes for improved water splitting performance.

Antimony selenide (Sb2Se3) is an auspicious material for solar energy conversion that has seen rapid improvement over the past ten years, but the photovoltage deficit remains a challenge. Here, simple and low-temperature treatments of the p-n heterojunction interface of Sb2Se3/TiO2-based photocathodes for photoelectrochemical water splitting were explored to address this challenge. The FTO/Ti/Au/Sb2Se3 (substrate configuration) stack was treated with (NH4)2S as an etching solution, followed by CuCl2 treatment prior to deposition of the TiO2 by atomic layer deposition. The different treatments show different mechanisms of action compared to similar reported treatments of the back Au/Sb2Se3 interface in superstrate configuration solar cells. These treatments collectively increased the onset potential from 0.14 V to 0.28 V vs. reversible hydrogen electrode (RHE) and the photocurrent from 13 mA cm-2 to 18 mA cm-2 at 0 V vs. RHE as compared to the untreated Sb2Se3 films. From SEM and XPS studies, it is clear that the etching treatment induces a morphological change and removes the surface Sb2O3 layer, which eliminates the Fermi-level pinning that the oxide layer generates. CuCl2 further enhances the performance due to the passivation of the surface defects, as supported by density functional theory molecular dynamics (DFT-MD) calculations, improving charge separation at the interface. The simple and low-cost semiconductor synthesis method combined with these facile, low-temperature treatments further increases the practical potential of Sb2Se3 for large-scale water splitting.

Impedance spectroscopy of Sb2Se3 photovoltaics consisting of (Sb4Se6)n nanoribbons under light illumination.

Sb2Se3, consisting of one-dimensional (Sb4Se6)n nanoribbons has drawn attention as an intriguing light absorber from the photovoltaics (PVs) research community. However, further research is required on the performance-limiting factors in Sb2Se3 PVs. In this study, we investigated the charge carrier behavior in Sb2Se3 PVs by impedance spectroscopy (IS) under light illumination. (Sb4Se6)n nanoribbons with two different orientations were used to investigate the effect of crystal orientation on the device performance. Regardless of the (Sb4Se6)n orientation, negative capacitance was observed at forward bias, representing a recombination pathway at the TiO2/Sb2Se3 interface. A comparison of the recombination resistances and lifetimes of two different Sb2Se3 PVs showed that a better interface could be formed by placing the (Sb4Se6)n ribbons parallel to the TiO2 layer. Based on these observations, an ideal structure of the Sb2Se3/TiO2 interface is proposed, which will enhance the performance of Sb2Se3 PVs toward its theoretical limit.

Bi2 S3 -Cu3 BiS3 Mixed Phase Interlayer for High-Performance Cu3 BiS3 -Photocathode for 2.33% Unassisted Solar Water Splitting Efficiency.

To realize practical solar hydrogen production, a low-cost photocathode with high photocurrent density and onset potential should be developed. Herein, an efficient and stable overall photoelectrochemical tandem cell is developed with a Cu3 BiS3 -based photocathode. By exploiting the crystallographic similarities between Bi2 S3 and Cu3 BiS3 , a one-step solution process with two sulfur sources is used to prepare the Bi2 S3 -Cu3 BiS3 blended interlayer. The elongated Bi2 S3 -Cu3 BiS3 mixed-phase 1D nanorods atop a planar Cu3 BiS3 film enable a high photocurrent density of 7.8 mA cm-2 at 0 V versus the reversible hydrogen electrode, with an onset potential of 0.9 VRHE . The increased performance over the single-phase Cu3 BiS3 thin-film photocathode is attributed to the enhanced light scattering and charge collection through the unique 1D nanostructure, improved electrical conductivity, and better band alignment with the n-type CdS layer. A solar-to-hydrogen efficiency of 2.33% is achieved under unassisted conditions with a state-of-the-art Mo:BiVO4 photoanode, with excellent stability exceeding 21 h.

Solution-Processed Cu2S Nanostructures for Solar Hydrogen Production.

Cu2S is a promising solar energy conversion material due to its suitable optical properties, high elemental earth abundance, and nontoxicity. In addition to the challenge of multiple stable secondary phases, the short minority carrier diffusion length poses an obstacle to its practical application. This work addresses the issue by synthesizing nanostructured Cu2S thin films, which enables increased charge carrier collection. A simple solution-processing method involving the preparation of CuCl and CuCl2 molecular inks in a thiol-amine solvent mixture followed by spin coating and low-temperature annealing was used to obtain phase-pure nanostructured (nanoplate and nanoparticle) Cu2S thin films. The photocathode based on the nanoplate Cu2S (FTO/Au/Cu2S/CdS/TiO2/RuO x ) reveals enhanced charge carrier collection and improved photoelectrochemical water-splitting performance compared to the photocathode based on the non-nanostructured Cu2S thin film reported previously. A photocurrent density of 3.0 mA cm-2 at -0.2 versus a reversible hydrogen electrode (V RHE) with only 100 nm thickness of a nanoplate Cu2S layer and an onset potential of 0.43 V RHE were obtained. This work provides a simple, cost-effective, and high-throughput method to prepare phase-pure nanostructured Cu2S thin films for scalable solar hydrogen production.

Crystal orientation-dependent etching and trapping in thermally-oxidised Cu2O photocathodes for water splitting.

Ammonia solution etching was carried out on thermally-oxidised cuprous oxide (TO-Cu2O) in photocathode devices for water splitting. The etched devices showed increased photoelectrochemical (PEC) performance compared to the unetched ones as well as improved reproducibility. -8.6 mA cm-2 and -7 mA cm-2 photocurrent density were achieved at 0 V and 0.5 V versus the reversible hydrogen electrode (VRHE), respectively, in the champion sample with an onset potential of 0.92 VRHE and a fill factor of 44%. An applied bias photon-to-current efficiency of 3.6% at 0.56 VRHE was obtained, which represents a new record for Cu2O-based photocathode systems. Capacitance-based profiling studies showed a strong pinning effect from interfacial traps in the as-grown device, and these traps were removed by ammonia solution etching. Moreover, the etching procedure gave rise to a diverse morphology of Cu2O crystals based on the different crystallographic orientations. The distribution of crystallographic orientations and the relationship between the crystal orientation and the morphology after etching were examined by electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM). The high-index crystal group showed a statistically higher PEC performance than the low-index group. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) revealed metallic copper at the Cu2O/Ga2O3 interface, which we attribute as the dominant trap that limits the PEC performance. It is concluded that the metallic copper originates from the reduction of the CuO impurity layer on the as-grown Cu2O sample during the ALD process, while the reduction from Cu2O to Cu is not favourable.

Evaluation of a blockchain-based dynamic consent platform (METORY) in a decentralized and multicenter clinical trial using virtual drugs.

Blockchain is a novel data architecture characterized by a chronological sequence of blocks in a decentralized manner. We aimed to evaluate the real-world feasibility of a blockchain-based dynamic consent platform (METORY) in a decentralized and multicenter trial. The study consisted of three visits (i.e., screening and 2 follow-up visits) with a 2-week interval. Each subject was required to report the self-measured body temperatures and take a virtual investigational drug by entering the unique drug code on the application. To simulate real-world study settings, two major (i.e., changes in the schedule of body temperature measurement) and three minor protocol amendments (i.e., nonsignificant changes without any changes in the procedures) were set. Overall study completion rates, proportion of consent, and response time to each protocol amendment and adherence were evaluated. A total of 60 subjects (30 in each center) were enrolled in two study centers. All subjects completed the study, and the overall proportion of consent to each protocol amendment was 95.7 ± 13.7% (mean ± SD), with a median response time of 0.2 h. Overall, subjects took 90.8% ± 19.2% of the total drug, whereas compliance with the schedule was 69.1% ± 27.0%. Subjects reported 96.7% ± 4.2% of the total body temperature measurements whereas the adherence to the schedule was 59.0% ± 25.0%, which remarkably decreased after major protocol amendments. In conclusion, we evaluated a blockchain-based dynamic consent platform in real clinical trial settings. The results suggested that major changes should be avoided unless subjects' proper understanding is warranted.

METORY: Development of a Demand-Driven Blockchain-Based Dynamic Consent Platform Tailored for Clinical Trials.

The recent advent of the dynamic consent concept intensified the data integrity issue in clinical trials. Incorporating blockchain technology into a dynamic consent platform can be a feasible solution. Due to various clinical trial settings, a demand-driven development strategy is required. We developed a blockchain-based dynamic consent platform named METORY tailored for clinical trials. The platform consisted of three parts: web and mobile application user interface, study management platform, and blockchain platform. Hyperledger Fabric, an enterprise-grade private blockchain framework, was used to integrate blockchain into the study consent platform. We conducted user acceptance tests and applied feedback to the improvement of the platform. Identity and role-based access control was constructed by combining mobile-application-based certificate system and access control functionalities in Hyperledger fabric. Data were encrypted using SHA-256 prior to transmission to blockchain server and TLS protocol was used for in-transit encryption. File-system level encryption was separated implemented within the security measures from Amazon RDS. Users' experience in the clinical trial was acceptable in the ease and usefulness of the platform.

Thiol-Amine-Based Solution Processing of Cu2 S Thin Films for Photoelectrochemical Water Splitting.

Cu2 S is a promising solar energy conversion material owing to its good optical properties, elemental earth abundance, and low cost. However, simple and cheap methods to prepare phase-pure and photo-active Cu2 S thin films are lacking. This study concerns the development of a cost-effective and high-throughput method that consists of dissolving high-purity commercial Cu2 S powder in a thiol-amine solvent mixture followed by spin coating and low-temperature annealing to obtain phase-pure crystalline low chalcocite Cu2 S thin films. After coupling with a CdS buffer layer, a TiO2 protective layer and a RuOx hydrogen evolution catalyst, the champion Cu2 S photocathode gives a photocurrent density of 2.5 mA cm-2 at -0.3 V vs. reversible hydrogen electrode (VRHE ), an onset potential of 0.42 VRHE , and high stability over 12 h in pH 7 buffer solution under AM1.5 G simulated sunlight illumination (100 mW cm-2 ). This is the first thiol-amine-based ink deposition strategy to prepare phase-pure Cu2 S thin films achieving decent photoelectrochemical performance, which will facilitate its future scalable application for solar-driven hydrogen fuel production.

Benchmark performance of low-cost Sb2Se3 photocathodes for unassisted solar overall water splitting.

Determining cost-effective semiconductors exhibiting desirable properties for commercial photoelectrochemical water splitting remains a challenge. Herein, we report a Sb2Se3 semiconductor that satisfies most requirements for an ideal high-performance photoelectrode, including a small band gap and favourable cost, optoelectronic properties, processability, and photocorrosion stability. Strong anisotropy, a major issue for Sb2Se3, is resolved by suppressing growth kinetics via close space sublimation to obtain high-quality compact thin films with favourable crystallographic orientation. The Sb2Se3 photocathode exhibits a high photocurrent density of almost 30 mA cm-2 at 0 V against the reversible hydrogen electrode, the highest value so far. We demonstrate unassisted solar overall water splitting by combining the optimised Sb2Se3 photocathode with a BiVO4 photoanode, achieving a solar-to-hydrogen efficiency of 1.5% with stability over 10 h under simulated 1 sun conditions employing a broad range of solar fluxes. Low-cost Sb2Se3 can thus be an attractive breakthrough material for commercial solar fuel production.

High-Performance Phase-Pure SnS Photocathodes for Photoelectrochemical Water Splitting Obtained via Molecular Ink-Derived Seed-Assisted Growth of Nanoplates.

Although tin monosulfide (SnS) is one of the promising earth-abundant semiconducting materials for photoelectrochemical water splitting, the performance of SnS photocathodes remains poor. Herein, we report a stepwise approach for the fabrication of highly efficient photocathodes based on SnS nanoplates via elaborate modulation of molecular solutions. It is demonstrated that phase-pure SnS nanoplates without detrimental secondary phases (such as SnS2 and Sn2S3) can be readily obtained by adjusting the amounts of Sn and S in the precursor solution. Additionally, the orientation of SnS nanoplates is controlled by implementing different types of SnS seed layers. The orientations of the SnS seed layers are changed according to the molecular shapes of the Sn-S bonds in the molecular solutions, depending on the relative nucleophilicity of the molecular moieties formed by specific thiol-amine reactions. The molecular Sn-S sheets in the seed ink was obtained by the reaction in a solvent mixture of thiogylcolic acid and ethanolamine. By contrast, the short Sn-S molecular rods result from the reaction in a solvent mixture of 2-mercaptoethanol and ethylenediamine. Interestingly, the relatively short rodlike morphology of the SnS seed induces the growth of SnS nanostructures faceted by preferred (111) and (101) planes, leading to fast charge transport. With the formation of a proper band alignment with n-type CdS and TiO2, the preferred (111)- and (101)-oriented SnS nanoplate-based photocathode exhibited a photocurrent density of -19 mA cm-2 at 0 V versus a reversible hydrogen electrode, establishing a new benchmark for SnS photocathodes.

Integrated optical modulator for signal up-conversion over radio-on-fiber link.

An integrated optical modulator, which consists of a dual-sideband suppressed carrier (DSB-SC) modulator cascaded with a single-sideband (SSB) modulator, is proposed for signal up-conversion over Radio-on-Fiber. Utilizing a single-drive domain inverted structure in both modulators, balanced modulations were obtained without complicated radio frequency (RF) driving circuits and delicate RF phase adjustments. Intermediate frequency (IF) band signal was up-conversed to 60GHz band by using the fabricated device and was transmitted over optical fiber. Experiment results show that the proposed device enables millimeter wave generation and signal transmission without any power penalty caused by chromatic dispersion.

Recent Advances in Earth-Abundant Photocathodes for Photoelectrochemical Water Splitting.

The conversion of solar energy into hydrogen through photoelectrochemical (PEC) water splitting is an attractive way to store renewable energy. Despite the intriguing concept of solar hydrogen production, efficient PEC devices based on earth-abundant semiconductors should be realized to compete economically with conventional steam reforming processes. Herein, recent milestones in photocathode development for PEC water splitting, particularly in earth-abundant semiconductors, in terms of new techniques for enhancing performance, as well as theoretical aspects, are highlighted. In addition, recent research into newly emerging low-cost p-type semiconductors in the PEC field, such as Cu2 BaSn(S,Se)4 and Sb2 Se3 , are scrutinized and the advantages and disadvantages of each material assessed.

Controlled Electrodeposition of Photoelectrochemically Active Amorphous MoS x Cocatalyst on Sb2Se3 Photocathode.

Amorphous molybdenum sulfide (a-MoS x) is a promising hydrogen evolution catalyst owing to its low cost and high activity. A simple electrodeposition method (cyclic voltammetry) allows uniform formation of a-MoS x films on conductive surfaces. However, the morphology of a-MoS x deposited on a TiO2/Sb2Se3 photocathode could be modulated by varying the starting potential. The cathodically initiated a-MoS x showed conformal filmlike morphology, whereas anodic initiation induced inhomogeneous particulate deposition. The filmlike morphology of a-MoS x was subjected to catalyst activation, which improved the photocurrent density and reduced the charge-transfer resistance at the semiconductor/electrolyte interface, as compared to that of its particulate counterpart. X-ray photoelectron spectroscopy confirmed that different chemical states of a-MoS x (photoelectrochemically active sites) were developed on the basis of the electrodeposited a-MoS x morphology. The research provides an effective approach for uniformly depositing cost-effective a-MoS x on nanostructured photoelectrodes, for photoelectrochemical water splitting.

Photoelectrodes based on 2D opals assembled from Cu-delafossite double-shelled microspheres for an enhanced photoelectrochemical response.

Although a unique light-harvesting property was recently demonstrated in a photocathode based on 2-dimensional (2D) opals of CuFeO2-shelled SiO2 microspheres, the performance of a monolayer of ultra-thin CuFeO2-shelled microspheres is limited by ineffective charge separation. Herein, we propose an innovative design rule, in which an inner CuFeO2/outer CuAlO2 double-shelled heterojunction is formed on each partially etched microsphere to obtain a hexagonally assembled 2D opal photoelectrode. Our Cu-delafossite double-shelled photocathode shows a dramatically improved charge separation capability, with a 9-fold increase in the photocurrent compared to that of the single-shelled counterpart. Electrochemical impedance spectroscopy clearly confirms the reduced charge transport/transfer resistance associated with the Cu-delafossite double-shelled photocathode, while surface photovoltage spectra reveal enhanced polarization of the photogenerated carrier, indicating improved charge separation capability with the aid of the heterojunction. Our finding sheds light on the importance of heterojunction interfaces in achieving optimal charge separation in opal architectures as well as the inner-shell/electrolyte interface to expedite charge separation/transport.

Time-Resolved Observations of Photo-Generated Charge-Carrier Dynamics in Sb2Se3 Photocathodes for Photoelectrochemical Water Splitting.

Solar-energy conversion by photoelectrochemical (PEC) devices is driven by the separation and transfer of photogenerated charge carriers. Thus, understanding carrier dynamics in a PEC device is essential to realizing efficient solar-energy conversion. Here, we investigate time-resolved carrier dynamics in emerging low-cost Sb2Se3 nanostructure photocathodes for PEC water splitting. Using terahertz spectroscopy, we observed an initial mobility loss within tens of picoseconds due to carrier localization and attributed the origin of carrier localization to the rich surface of Sb2Se3 nanostructures. In addition, a possible recombination at the interface between Sb2Se3 and the back contact is elucidated by time-resolved photoluminescence analysis. We also demonstrated the dual role of the RuO x co-catalyst in reducing surface recombination and enhancing charge transfer in full devices using intensity-modulated spectroscopy. The relatively low onset potential of the Sb2Se3 photocathode is attributed to the sluggish charge transfer at a low applied bias rather than to fast surface recombination. We believe that our insights on carrier dynamics would be an important step toward achieving highly efficient Sb2Se3 photocathodes.

Investigating Recombination and Charge Carrier Dynamics in a One-Dimensional Nanopillared Perovskite Absorber.

Organometal halide perovskite materials have become an exciting research topic as manifested by intense development of thin film solar cells. Although high-performance solar-cell-based planar and mesoscopic configurations have been reported, one-dimensional (1-D) nanostructured perovskite solar cells are rarely investigated despite their expected promising optoelectrical properties, such as enhanced charge transport/extraction. Herein, we have analyzed the 1-D nanostructure effects of organometal halide perovskite (CH3NH3PbI3- xCl x) on recombination and charge carrier dynamics by utilizing a nanoporous anodized alumina oxide scaffold to fabricate a vertically aligned 1-D nanopillared array with controllable diameters. It was observed that the 1-D perovskite exhibits faster charge transport/extraction characteristics, lower defect density, and lower bulk resistance than the planar counterpart. As the aspect ratio increases in the 1-D structures, in addition, the charge transport/extraction rate is enhanced and the resistance further decreases. However, when the aspect ratio reaches 6.67 (diameter ∼30 nm), the recombination rate is aggravated due to high interface-to-volume ratio-induced defect generation. To obtain the full benefits of 1-D perovskite nanostructuring, our study provides a design rule to choose the appropriate aspect ratio of 1-D perovskite structures for improved photovoltaic and other optoelectrical applications.

Enhanced Photocurrent of Transparent CuFeO2 Photocathodes by Self-Light-Harvesting Architecture.

Efficient sunlight-driven water-splitting devices can be achieved by using an optically and energetically well-matched pair of photoelectrodes in a tandem configuration. The key for maximizing the photoelectrochemical efficiency is the use of a highly transparent front photoelectrode with a band gap below 2.0 eV. Herein, we propose two-dimensional (2D) photonic crystal (PC) structures consisting of a CuFeO2-decorated microsphere monolayer, which serve as self-light-harvesting architectures allowing for amplified light absorption and high transparency. The photocurrent densities are evaluated for three CuFeO2 2D PC-based photoelectrodes with microspheres of different sizes. The optical analysis confirmed the presence of a photonic stop band that generates slow light and at the same time amplifies the absorption of light. The 410 nm sized CuFeO2-decorated microsphere 2D PC photocathode shows an exceptionally high visible light transmittance of 76.4% and a relatively high photocurrent of 0.2 mA cm-2 at 0.6 V vs a reversible hydrogen electrode. The effect of the microsphere size on the carrier collection efficiency was analyzed by in situ conductive atomic force microscopy observation under illumination. Our novel synthetic method to produce self-light-harvesting nanostructures provides a promising approach for the effective use of solar energy by highly transparent photocathodes.