Showing papers on "Perovskite solar cell published in 2019"

Cation and anion immobilization through chemical bonding enhancement with fluorides for stable halide perovskite solar cells

Abstract: Defects play an important role in the degradation processes of hybrid halide perovskite absorbers, impeding their application for solar cells. Among all defects, halide anion and organic cation vacancies are ubiquitous, promoting ion diffusion and leading to thin-film decomposition at surfaces and grain boundaries. Here, we employ fluoride to simultaneously passivate both anion and cation vacancies, by taking advantage of the extremely high electronegativity of fluoride. We obtain a power conversion efficiency of 21.46% (and a certified 21.3%-efficient cell) in a device based on the caesium, methylammonium (MA) and formamidinium (FA) triple-cation perovskite (Cs0.05FA0.54MA0.41)Pb(I0.98Br0.02)3 treated with sodium fluoride. The device retains 90% of its original power conversion efficiency after 1,000 h of operation at the maximum power point. With the help of first-principles density functional theory calculations, we argue that the fluoride ions suppress the formation of halide anion and organic cation vacancies, through a unique strengthening of the chemical bonds with the surrounding lead and organic cations. Defects and defect migration are detrimental for perovskite solar cell efficiency and long-term stability. Li et al. show that fluoride is able to suppress the formation of halide anion and organic cation vacancy defects by restraining the relative ions via ionic and hydrogen bonds.

From Lead Halide Perovskites to Lead-Free Metal Halide Perovskites and Perovskite Derivatives

Abstract: Despite the exciting progress on power conversion efficiencies, the commercialization of the emerging lead (Pb) halide perovskite solar cell technology still faces significant challenges, one of which is the inclusion of toxic Pb. Searching for Pb-free perovskite solar cell absorbers is currently an attractive research direction. The approaches used for and the consequences of Pb replacement are reviewed herein. Reviews on the theoretical understanding of the electronic, optical, and defect properties of Pb and Pb-free halide perovskites and perovskite derivatives are provided, as well as the experimental results available in the literature. The theoretical understanding explains well why Pb halide perovskites exhibit superior photovoltaic properties, but Pb-free perovskites and perovskite derivatives do not.

An interface stabilized perovskite solar cell with high stabilized efficiency and low voltage loss

Abstract: Stabilization of the crystal phase of inorganic/organic lead halide perovskites is critical for their high performance optoelectronic devices. However, due to the highly ionic nature of perovskite crystals, even phase stabilized polycrystalline perovskites can undergo undesirable phase transitions when exposed to a destabilizing environment. While various surface passivating agents have been developed to improve the device performance of perovskite solar cells, conventional deposition methods using a protic polar solvent, mainly isopropyl alcohol (IPA), results in a destabilization of the underlying perovskite layer and an undesirable degradation of device properties. We demonstrate the hidden role of IPA in surface treatments and develop a strategy in which the passivating agent is deposited without destabilizing the high quality perovskite underlayer. This strategy maximizes and stabilizes device performance by suppressing the formation of the perovskite δ-phase and amorphous phase during surface treatment, which is observed using conventional methods. Our strategy also effectively passivates surface and grain boundary defects, minimizing non-radiative recombination sites, and preventing carrier quenching at the perovskite interface. This results in an open-circuit-voltage loss of only ∼340 mV, a champion device with a power conversion efficiency of 23.4% from a reverse current–voltage scan, a device with a record certified stabilized PCE of 22.6%, and enhanced operational stability. In addition, our perovskite solar cell exhibits an electroluminescence external quantum efficiency up to 8.9%.

Robust Tin-Based Perovskite Solar Cells with Hybrid Organic Cations to Attain Efficiency Approaching 10.

Abstract: The stability of a tin-based perovskite solar cell is a major challenge. Here, hybrid tin-based perovskite solar cells in a new series that incorporate a nonpolar organic cation, guanidinium (GA+ ), in varied proportions into the formamidinium (FA+ ) tin triiodide perovskite (FASnI3 ) crystal structure in the presence of 1% ethylenediammonium diiodide (EDAI2 ) as an additive, are reported. The device performance is optimized at a precursor ratio (GAI:FAI) of 20:80 to attain a power conversion efficiency (PCE) of 8.5% when prepared freshly; the efficiencies continuously increase to attain a record PCE of 9.6% after storage in a glove-box environment for 2000 h. The hybrid perovskite works stably under continuous 1 sun illumination for 1 h and storage in air for 6 days without encapsulation. Such a tin-based perovskite passes all harsh standard tests, and the efficiency of a fresh device, 8.3%, is certified. The great performance and stability of the device reported herein attains a new milestone for lead-free perovskite solar cells on a path toward commercial development.

Planar p–n homojunction perovskite solar cells with efficiency exceeding 21.3%

Abstract: Perovskite solar cells (PSCs) have emerged as an attractive photovoltaic technology thanks to their outstanding power conversion efficiency (PCE). Further improvement in the device efficiency is limited by the recombination of the charge carriers in the perovskite layer even when employing heterojunction-based architectures. Here, we propose and demonstrate a p-type perovskite/n-type perovskite homojunction whose built-in electric field promotes oriented transport of the photo-induced carriers, thus reducing carrier recombination losses. By controlling the stoichiometry of the perovskite precursors, we are able to induce n-type or p-type doping. We integrate the homojunction structure in a planar PSC combining a thermally evaporated p-type perovskite layer on a solution-processed n-type perovskite layer. The PSC with a MAPbI3 homojunction achieves a PCE of 20.80% (20.5% certified PCE), whereas the PSC based on a FA0.15MA0.85PbI3 homojunction delivers a PCE of 21.38%. We demonstrate that the homojunction structure is an effective approach, beyond existing planar heterojunction PSCs, to achieve highly efficient PSCs with reduced carrier recombination losses. Carrier recombination limits the power conversion efficiency of perovskite solar cells. Here the authors construct a planar p–n homojunction perovskite solar cell to promote the oriented transport of carriers and reduce recombination, thus enabling power conversion efficiency of 21.3%.

Multifunctional Chemical Linker Imidazoleacetic Acid Hydrochloride for 21% Efficient and Stable Planar Perovskite Solar Cells.

Abstract: Chemical interaction at a heterojunction interface induced by an appropriate chemical linker is of crucial importance for high efficiency, hysteresis-less, and stable perovskite solar cells (PSCs). Effective interface engineering in PSCs is reported via a multifunctional chemical linker of 4-imidazoleacetic acid hydrochloride (ImAcHCl) that can provide a chemical bridge between SnO2 and perovskite through an ester bond with SnO2 via esterification reaction and an electrostatic interaction with perovskite via imidazolium cation in ImAcHCl and iodide anion in perovskite. In addition, the chloride anion in ImAcHCl plays a role in the improvement of crystallinity of perovskite film crystallinity. The introduction of ImAcHCl onto SnO2 realigns the positions of the conduction and valence bands upwards, reduces nonradiative recombination, and improves carrier life time. As a consequence, average power conversion efficiency (PCE) is increased from 18.60% ± 0.50% to 20.22% ± 0.34% before and after surface modification, respectively, which mainly results from an enhanced voltage from 1.084 ± 0.012 V to 1.143 ± 0.009 V. The best PCE of 21% is achieved by 0.1 mg mL-1 ImAcHCl treatment, along with negligible hysteresis. Moreover, an unencapsulated device with ImAcHCl-modified SnO2 shows much better thermal and moisture stability than unmodified SnO2 .

Doping strategies for small molecule organic hole-transport materials: impacts on perovskite solar cell performance and stability

Abstract: Hybrid organic/inorganic perovskite solar cells (PSCs) have dramatically changed the landscape of the solar research community over the past decade, but >25 year stability is likely required if they are to make the same impact in commercial photovoltaics and power generation more broadly. While every layer of a PSC has been shown to impact its durability in power output, the hole-transport layer (HTL) is critical for several reasons: (1) it is in direct contact with the perovskite layer, (2) it often contains mobile ions, like Li+ – which in this case are hygroscopic, and (3) it usually has the lowest thermal stability of all layers in the stack. Therefore, HTL engineering is one method with a high return on investment for PSC stability and lifetime. Research has progressed in understanding design rules for small organic molecule hole-transport materials, yet, when implemented into devices, the same dopants, bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) and tris(2-(1H-pyrazol-1-yl)-4-tert-butylpyridine)cobalt(III) tri[bis(trifluoromethane)sulfonimide] (FK209), are nearly always required for improved charge-transport properties (e.g., increased hole mobility and conductivity). The dopants are notable because they too have been shown to negatively impact PSC stability and lifetime. In response, new research has targeted alternative dopants to bypass these negative effects and provide greater functionality. In this review, we focus on dopant fundamentals, alternative doping strategies for organic small molecule HTL in PSC, and imminent research needs with regard to dopant development for the realization of reliable, long-lasting electricity generation via PSCs.

Design of low bandgap tin-lead halide perovskite solar cells to achieve thermal, atmospheric and operational stability

Abstract: Low bandgap tin–lead iodide perovskites are key components of all-perovskite tandem solar cells, but can be unstable because tin is prone to oxidation. Here, to avoid a reaction with the most popular hole contact, we eliminated polyethylenedioxythiophene:polystyrenesulfonate as a hole transport layer and instead used an upward band offset at an indium tin oxide–perovskite heterojunction to extract holes. To suppress oxidative degradation, we improved the morphology to create a compact and large-grained film. The tin content was kept at or below 50% and the device capped with a sputtered indium zinc oxide electrode. These advances resulted in a substantially improved thermal and environmental stability in a low bandgap perovskite solar cell without compromising the efficiency. The solar cells retained 95% of their initial efficiency after 1,000 h at 85 °C in air in the dark with no encapsulation and in a damp heat test (85 °C with 85% relative humidity) with encapsulation. The full initial efficiency was maintained under operation near the maximum power point and near 1 sun illumination for over 1,000 h. Low bandgap tin–lead perovskites are crucial to making efficient all-perovskite tandem solar cells but have so far shown poor stability. By removing the hole transport layer and improving film morphology, Prasanna et al. demonstrate a low-gap perovskite solar cell that is stable for 1,000 h under heat, light and atmospheric conditions.

Performance of perovskite solar cells under simulated temperature-illumination real-world operating conditions

Abstract: Since reaching 20% efficiency, research in perovskite photovoltaics has shifted from a race for efficiency to a race for stability. For efficiency, the standard test conditions set the rules for the race. However, the term ‘stability’ is used very broadly and assessed in various ways, meaning different groups are running different races. For the application, only energy yields that can be achieved under real-world, long-term operation matter. Here, we characterize and analyse the performance of an efficient perovskite solar cell (PSC) under simulated ambient conditions based on real temperature and irradiance data from selected days over one year at a location in central Europe. We find that the PSC shows only a low decrease of efficiency with elevated temperature and low light intensity, maintaining almost optimum values for ambient conditions, under which most of the solar energy is incident on the solar cell. The overall energy yield differs from what is expected from standard test condition measurements and is influenced by reversible degradation (delivering the highest performance in the morning) and by a slight permanent degradation that is observable during the year. With reference to tandem cells, we compare the PSC with a silicon device. Real-world conditions under which solar cells operate can be different from standard testing conditions. Tress et al. investigate the effects of temperature and irradiation on the performance of a perovskite cell and a reference silicon cell, reproducing real weather conditions in the laboratory.

Two-Dimensional Halide Perovskites in Solar Cells: 2D or not 2D?

Abstract: Two-dimensional (2D) halide perovskites have recently emerged as a more stable and more versatile family of materials than three-dimensional (3D) perovskite solar cell absorbers. Although solar cells made with 2D perovskites have yet to improve their power conversion efficiencies to compete with 3D perovskite solar cells, their immense diversity offers great opportunities and avenues for research that will likely close the gap between these two. Further, 2D perovskites can have various roles within a solar cell, either as the primary light absorber, as a capping layer, passivating layer, or within a mixed 2D/3D perovskite solar cell absorber. In this Minireview, we will review the history of 2D perovskites in solar cells, the relevant properties of such materials, the different roles that they can play in a solar cell, as well as current trends and challenges.

How transport layer properties affect perovskite solar cell performance: insights from a coupled charge transport/ion migration model

Abstract: The effects of transport layers on perovskite solar cell performance, in particular anomalous hysteresis, are investigated. A model for coupled ion vacancy motion and charge transport is formulated and solved in a three-layer planar perovskite solar cell. Its results are used to demonstrate that the replacement of standard transport layer materials (spiro-OMeTAD and TiO2) by materials with lower permittivity and/or doping leads to a shift in the scan rates at which hysteresis is most pronounced to rates higher than those commonly used in experiment. These results provide a cogent explanation for why organic electron transport layers can yield seemingly “hysteresis-free” devices but which nevertheless exhibit hysteresis at low temperature. In these devices the decrease in ion vacancy mobility with temperature compensates for the increase in hysteresis rate with use of low permittivity/doping organic transport layers. Simulations are used to classify features of the current–voltage curves that distinguish between cells in which charge carrier recombination occurs predominantly at the transport layer interfaces and those where it occurs predominantly within the perovskite. These characteristics are supplemented by videos showing how the electric potential, electronic and ionic charge profiles evolve across a planar perovskite solar cell during a current–voltage scan. Design protocols to mitigate the possible effects of high ion vacancy distributions on cell degradation are discussed. Finally, features of the steady-state potential profile for a device held near the maximum power point are used to suggest ways in which interfacial recombination can be reduced, and performance enhanced, via tuning transport layer properties.

Impacts of alkaline on the defects property and crystallization kinetics in perovskite solar cells

Abstract: Further minimizing the defect state density in the semiconducting absorber is vital to boost the power conversion efficiency of solar cells approaching Shockley-Queisser limit. However, it lacks a general strategy to control the precursor chemistry for defects density reduction in the family of iodine based perovskite. Here the alkaline environment in precursor solution is carefully investigated as an effective parameter to suppress the incident iodine and affects the crystallization kinetics during film fabrication, via rationale adjustment of the alkalinity of additives. Especially, a ‘residual free’ weak alkaline is proposed not only to shrink the bandgap of the absorber by modulating the stoichiometry of organic cation, but also to improve the open circuit voltage in the resultant device. Consequently, the certified efficiency of 20.87% (Newport) is achieved with one of the smallest voltage deficits of 413 mV in the planar heterojunction perovskite solar cell.

Carbon-based materials for stable, cheaper and large-scale processable perovskite solar cells

Abstract: Almost ten years after their first use in the photovoltaic (PV) field, perovskite solar cells (PSCs) are now hybrid devices that, in addition to having reached silicon performance, can accelerate the energy transition and boost the use of abundant elements for their manufacturing process. However, noble metals (in particular gold) represent the most typically used sources for back electrode fabrication, and this issue has been intensively considered by the research community in the last five years. This review shows how the most promising solution, considering also the need to develop a large-scale production process, is based on the use of carbon-based materials for the preparation of back electrodes. Graphite, carbon black, graphene and carbon nanotubes (CNTs) have been proposed, functionalized and characterized, leading to laboratory-scale solar cells and modules capable of providing excellent efficiencies and ensuring stability greater than those of gold-based devices. Strengthened by these results and its hydrophobizing properties, carbon has also started to be used as an electron transporting material (ETM), with excellent results on both rigid and flexible substrates. This review discusses the major advances and the updated state-of-the-art in the carbon-based PSC scenario, keeping a solid trajectory where the accessibility, low cost, high electrical conductivity, chemical stability and controllable porosity of carbon are highlighted and exploited in the design of upscalable hybrid solar cells.

Interfacial Engineering at the 2D/3D Heterojunction for High-Performance Perovskite Solar Cells.

Abstract: Perovskite solar cells based on two-dimensional/three-dimensional (2D/3D) hierarchical structure have attracted significant attention in recent years due to their promising photovoltaic performance and stability. However, obtaining a detailed understanding of interfacial mechanism at the 2D/3D heterojunction, for example, the ligand-chemistry-dependent nature of the 2D/3D heterojunction and its influence on charge collection and the final photovoltaic outcome, is not yet fully developed. Here we demonstrate the underlying 3D phase templates growth of quantum wells (QWs) within a 2D capping layer, which is further influenced by the fluorination of spacers and compositional engineering in terms of thickness distribution and orientation. Better QW alignment and faster dynamics of charge transfer at the 2D/3D heterojunction result in higher charge mobility and lower charge recombination loss, largely explaining the significant improvements in charge collection and open-circuit voltage (VOC) in complete solar cells. As a result, 2D/3D solar cells with a power-conversion efficiency of 21.15% were achieved, significantly higher than the 3D counterpart (19.02%). This work provides key missing information on how interfacial engineering influences the desirable electronic properties of the 2D/3D hierarchical films and device performance via ligand chemistry and compositional engineering in the QW layer.

Stable Efficiency Exceeding 20.6% for Inverted Perovskite Solar Cells through Polymer-Optimized PCBM Electron-Transport Layers.

Abstract: Fullerene derivative, such as [6,6]-phenyl C61 butyric acid methyl ester (PCBM), is widely used as an electron-transport layer (ETL) in inverted perovskite solar cell (PSC). However, its low electron mobility, complexity in achieving quality film formation, and severe nonradiative recombination at perovskite/PCBM interface due to the large electron capture region, lead to lower efficiency for inverted PSCs compared to the normal structures. Herein, we demonstrate an effective and practical strategy to overcome these challenges. Conjugated n-type polymeric materials are mixed together with PCBM to form a homogeneous bulk-mixed (HBM) continuous film with high electron mobility and suitable energy level. HBM film is found to completely cap the perovskite surface to enhance the electron extraction. The critical electron capture radius of the HBM decreases to 12.52 nm from 14.89 nm of PCBM due to the large relative permittivity, resulting in reduced nonradiative recombination at perovskite/HBM interface. The e...

Enhancing the Performance of Inverted Perovskite Solar Cells via Grain Boundary Passivation with Carbon Quantum Dots.

Abstract: Nonradiative recombination, the main energy loss channel for open circuit voltage (Voc), is one of the crucial problems for achieving high power conversion efficiency (PCE) in inverted perovskite solar cells (PSCs). Usually, grain boundary passivation is considered as an effective way to reduce nonradiative recombination because the defects (uncoordinated ions) on grain boundaries are passivated. We added the hydroxyl and carbonyl functional groups containing carbon quantum dots (CQDs) into a perovskite precursor solution to passivate the uncoordinated lead ions on grain boundaries. Higher photoluminescence intensity and longer carrier lifetime were demonstrated in the perovskite film with the CQD additive. This confirmed that the addition of CQDs can reduce nonradiative recombination by grain boundary passivation. Additionally, the introduction of CQDs could increase the thickness of the perovskite film. Consequently, we achieved a champion device with a PCE of 18.24%. The device with CQDs retained 73.4%...

Conjugated Molecules “Bridge”: Functional Ligand toward Highly Efficient and Long‐Term Stable Perovskite Solar Cell

Abstract: Interfacial ligand passivation engineering has recently been recognized as a promising avenue, contributing simultaneously to the optoelectronic characteristics and moisture/operation tolerance of perovskite solar cells. To further achieve a win-win situation of both performance and stability, an innovative conjugated aniline modifier (3-phenyl-2-propen-1-amine; PPEA) is explored to moderately tailor organolead halide perovskites films. Here, the conjugated PPEA presents both “quasi-coplanar” rigid geometrical configuration and distinct electron delocalization characteristics. After a moderate treatment, a stronger dipole capping layer can be formed at the perovskite/transporting interface to achieve favorable banding alignment, thus enlarging the built-in potential and promoting charge extraction. Meanwhile, a conjugated cation coordinated to the surface of the perovskite grains/units can form preferably ordered overlapping, not only passivating the surface defects but also providing a fast path for charge exchange. Benefiting from this, a ≈21% efficiency of the PPEA-modified solar cell can be obtained, accompanied by long-term stability (maintaining 90.2% of initial power conversion efficiency after 1000 h testing, 25°C, and 40 ± 10 humidity). This innovative conjugated molecule “bridge” can also perform on a larger scale, with a performance of 18.43% at an area of 1.96 cm​. Keywords​: conjugation, delocalization, interfacial dipole, perovskite, solar cells

Thermal degradation of formamidinium based lead halide perovskites into sym-triazine and hydrogen cyanide observed by coupled thermogravimetry-mass spectrometry analysis

Abstract: The thermal stability and decomposition products of formamidinium, a widely used organic cation in perovskite solar cell formulation, were investigated. The thermal degradation experiments of formamidinium-based perovskites and their halide precursors were carried out under helium atmosphere and vacuum at a constant heating rate of 20 °C min−1. In addition, pulsed heating steps were employed under illumination/dark conditions to simulate a more realistic working temperature condition for photovoltaic devices. The identification of gas decomposition products was based on the quadrupole mass spectrometry technique. The released amounts of sym-triazine, formamidine, and hydrogen cyanide (HCN) were observed to highly depend on the temperature. For the experimental conditions used in this study, sym-triazine was obtained as the thermal product of degradation at temperatures above 95 °C. Below this temperature, only formamidine and HCN generation routes were observed. The energy pathways of formamidinium thermal degradation under photovoltaic working temperature conditions were further assessed by density functional theory calculations. The results indicated that formamidinium was more resilient to thermal degradation and the release of irreversible decomposition products compared to methylammonium because of a larger enthalpy and activation energy obtained for the decomposition reactions. The HCN instantaneous concentration observed during the low temperature heating tests and the estimations of the maximum release of HCN achievable per meter-square of an FA based perovskite based solar cell were compared to acute exposure guideline levels of airborne HCN concentration.

Minimizing voltage loss in wide-bandgap perovskites for tandem solar cells

Abstract: Perovskites with bandgaps between 1.7 and 1.8 eV are optimal for tandem configurations with crystalline silicon (c-Si) because they facilitate efficient harvest of solar energy. In that respect, achieving a high open-circuit voltage (VOC) in such wide-bandgap perovskite solar cells is crucial for a high overall power conversion efficiency (PCE). Here, we provide key insights into the factors affecting the VOC in wide-bandgap perovskite solar cells. We show that the influence of the hole transport layer (HTL) on VOC is not simply through its ionization potential but mainly through the quality of the perovskite–HTL interface. With effective interface passivation, we demonstrate perovskite solar cells with a bandgap of 1.72 eV that exhibit a VOC of 1.22 V. Furthermore, by combining the high-VOC perovskite solar cell with a c-Si solar cell, we demonstrate a perovskite–Si four-terminal tandem solar cell with a PCE of 27.1%, exceeding the record PCE of single-junction Si solar cells.

Overcoming Zinc Oxide Interface Instability with a Methylammonium‐Free Perovskite for High‐Performance Solar Cells

Abstract: Perovskite solar cells have achieved the highest power conversion efficiencies on metal oxide n‐type layers, including SnO2 and TiO2. Despite ZnO having superior optoelectronic properties to these metal oxides, such as improved transmittance, higher conductivity, and closer conduction band alignment to methylammonium (MA)PbI3, ZnO is largely overlooked due to a chemical instability when in contact with metal halide perovskites, which leads to rapid decomposition of the perovskite. While surface passivation techniques have somewhat mitigated this instability, investigations as to whether all metal halide perovskites exhibit this instability with ZnO are yet to be undertaken. Experimental methods to elucidate the degradation mechanisms at ZnO–MAPbI3 interfaces are developed. By substituting MA with formamidinium (FA) and cesium (Cs), the stability of the perovskite–ZnO interface is greatly enhanced and it is found that stability compares favorably with SnO2‐based devices after high‐intensity UV irradiation and 85 °C thermal stressing. For devices comprising FA‐ and Cs‐based metal halide perovskite absorber layers on ZnO, a 21.1% scanned power conversion efficiency and 18% steady‐state power output are achieved. This work demonstrates that ZnO appears to be as feasible an n‐type charge extraction layer as SnO2, with many foreseeable advantages, provided that MA cations are avoided.

Oxygen‐Vacancy‐Introduced BaSnO3−δ Photoanodes with Tunable Band Structures for Efficient Solar‐Driven Water Splitting

Abstract: To achieve excellent photoelectrochemical water-splitting activity, photoanode materials with high light absorption and good charge-separation efficiency are essential. One effective strategy for the production of materials satisfying these requirements is to adjust their band structure and corresponding bandgap energy by introducing oxygen vacancies. A simple chemical reduction method that can systematically generate oxygen vacancies in barium stannate (BaSnO3 (BSO)) crystal is introduced, which thus allows for precise control of the bandgap energy. A BSO photoanode with optimum oxygen-vacancy concentration (8.7%) exhibits high light-absorption and good charge-separation capabilities. After deposition of FeOOH/NiOOH oxygen evolution cocatalysts on its surface, this photoanode shows a remarkable photocurrent density of 7.32 mA cm-2 at a potential of 1.23 V versus a reversible hydrogen electrode under AM1.5G simulated sunlight. Moreover, a tandem device constructed with a perovskite solar cell exhibits an operating photocurrent density of 6.84 mA cm-2 and stable gas production with an average solar-to-hydrogen conversion efficiency of 7.92% for 100 h, thus functioning as an outstanding unbiased water-splitting system.