Showing papers on "Band gap published in 2019"

Evidence of a gate-tunable Mott insulator in a trilayer graphene moiré superlattice

Abstract: The Mott insulator is a central concept in strongly correlated physics and manifests when the repulsive Coulomb interaction between electrons dominates over their kinetic energy1,2. Doping additional carriers into a Mott insulator can give rise to other correlated phenomena such as unusual magnetism and even high-temperature superconductivity2,3. A tunable Mott insulator, where the competition between the Coulomb interaction and the kinetic energy can be varied in situ, can provide an invaluable model system for the study of Mott physics. Here we report the possible realization of such a tunable Mott insulator in a trilayer graphene heterostructure with a moire superlattice. The combination of the cubic energy dispersion in ABC-stacked trilayer graphene4–8 and the narrow electronic minibands induced by the moire potential9–15 leads to the observation of insulating states at the predicted band fillings for the Mott insulator. Moreover, the insulating states in the heterostructure can be tuned: the bandgap can be modulated by a vertical electrical field, and at the same time the electron doping can be modified by a gate to fill the band from one insulating state to another. This opens up exciting opportunities to explore strongly correlated phenomena in two-dimensional moire superlattice heterostructures. Report of the likely observation of a Mott insulator in trilayer graphene with a moire potential. The Mott state can be tuned between different filling fractions via gating, which will enable the careful study of this paradigmatic many-body state.

Robust topologically protected transport in photonic crystals at telecommunication wavelengths.

Abstract: Photonic topological insulators offer the possibility to eliminate backscattering losses and improve the efficiency of optical communication systems. Despite considerable efforts, a direct experimental demonstration of theoretically predicted robust, lossless energy transport in topological insulators operating at near-infrared frequencies is still missing. Here, we combine the properties of a planar silicon photonic crystal and the concept of topological protection to design, fabricate and characterize an optical topological insulator that exhibits the valley Hall effect. We show that the transmittances are the same for light propagation along a straight topological interface and one with four sharp turns. This result quantitatively demonstrates the suppression of backscattering due to the non-trivial topology of the structure. The photonic-crystal-based approach offers significant advantages compared with other realizations of photonic topological insulators, such as lower propagation losses, the presence of a band gap for light propagating in the crystal-slab plane, a larger operating bandwidth, a much smaller footprint, compatibility with complementary metal-oxide-semiconductor fabrication technology, and the fact that it allows for operation at telecommunications wavelengths.

Oxygen Vacancy Generation and Stabilization in CeO2–x by Cu Introduction with Improved CO2 Photocatalytic Reduction Activity

Abstract: Introducing O vacancies into the lattice of a semiconductor photocatalyst can alter its intrinsic electronic properties and band gap, thus enhancing the visible light absorption, promoting the sepa...

Absolute energy level positions in tin- and lead-based halide perovskites

Abstract: Metal halide perovskites are promising materials for future optoelectronic applications. One intriguing property, important for many applications, is the tunability of the band gap via compositional engineering. While experimental reports on changes in absorption or photoluminescence show rather good agreement for different compounds, the physical origins of these changes, namely the variations in valence and conduction band positions, are not well characterized. Here, we determine ionization energy and electron affinity values of all primary tin- and lead-based perovskites using photoelectron spectroscopy data, supported by first-principles calculations and a tight-binding analysis. We demonstrate energy level variations are primarily determined by the relative positions of the atomic energy levels of metal cations and halide anions and secondarily influenced by the cation-anion interaction strength. These results mark a significant step towards understanding the electronic structure of this material class and provides the basis for rational design rules regarding the energetics in perovskite optoelectronics.

High thermal conductivity of high-quality monolayer boron nitride and its thermal expansion.

Abstract: Heat management has become more and more critical, especially in miniaturized modern devices, so the exploration of highly thermally conductive materials with electrical insulation is of great importance. Here, we report that high-quality one-atom-thin hexagonal boron nitride (BN) has a thermal conductivity (κ) of 751 W/mK at room temperature, the second largest κ per unit weight among all semiconductors and insulators. The κ of atomically thin BN decreases with increased thickness. Our molecular dynamic simulations accurately reproduce this trend, and the density functional theory (DFT) calculations reveal the main scattering mechanism. The thermal expansion coefficients of monolayer to trilayer BN at 300 to 400 K are also experimentally measured for the first time. Owing to its wide bandgap, high thermal conductivity, outstanding strength, good flexibility, and excellent thermal and chemical stability, atomically thin BN is a strong candidate for heat dissipation applications, especially in the next generation of flexible electronic devices.

Molecular engineering of organic–inorganic hybrid perovskites quantum wells

Abstract: Semiconductor quantum-well structures and superlattices are key building blocks in modern optoelectronics, but it is difficult to simultaneously realize defect-free epitaxial growth while fine tuning the chemical composition, layer thickness and band structure of each layer to achieve the desired performance. Here we demonstrate the modulation of the electronic structure—and consequently the optical properties—of organic semiconducting building blocks that are incorporated between the layers of perovskites through a facile solution processing step. Self-aggregation of the conjugated organic molecules is suppressed by functionalization with sterically demanding groups and single crystalline organic–perovskite hybrid quantum wells (down to one-unit-cell thick) are obtained. The energy and charge transfers between adjacent organic and inorganic layers are shown to be fast and efficient, owing to the atomically flat interface and ultrasmall interlayer distance of the perovskite materials. The resulting two-dimensional hybrid perovskites are very stable due to protection given by the bulky hydrophobic organic groups. A solution-processing step has been used to prepare quantum-well structures that comprise a thin layer of perovskite sandwiched between two layers of conjugated oligothiophene derivatives. The band gap of the resulting 2D hybrid perovskites can be fine-tuned by functionalizing the organic component, which also improves the stability of the system.

Two-dimensional Janus PtSSe for photocatalytic water splitting under the visible or infrared light

Abstract: Recently, two-dimensional Janus materials have attracted increasing research interest due to their particular structure and great potential in electronics, optoelectronics and piezoelectronics. Here, we propose 2D Janus PtSSe with compelling photocatalytic properties which were investigated by means of first-principles calculations. 2D Janus PtSSe exhibits high thermal, dynamic and mechanical stability. Most remarkably, single-layer PtSSe exhibits an indirect band gap of 2.19 eV, high absorption coefficients in the visible light region, appropriate band edge positions and strong ability for carrier separation and transfer, thus rendering it a promising candidate for photocatalytic water splitting. Moreover, double-layer PtSSe compounds with different stacking configurations are extraordinary photocatalysts for water splitting even under infrared light, owing to their small band gaps as well as the built-in electrical field. Our results reveal 2D PtSSe with high experimental feasibility as a new platform for the overall water splitting reaction.

Characterization of semiconductor photocatalysts

Abstract: The long-standing popularity of semiconductor photocatalysis due to its great potential in a variety of applications has resulted in the creation of numerous semiconductor photocatalysts, which stimulated the development of various characterization methods. This review aims to summarize the main characterization methods for assessing the most important properties of semiconductor photocatalysts, including their chemical composition (elemental composition, and chemical state/structure), physical properties (physical structure, crystallographic properties, optical absorption, charge dynamics, defects, and colloidal and thermal stability), and band structure (band gap, band edges/band edge offsets, and Fermi level). The discussion on each of these methods starts with a concise presentation of its fundamentals followed by carefully selected examples. At the end, a chart correlating the properties of a semiconductor with its potential characterization methods as well as outlook are provided. Overall, the aim of this review article is to help materials chemists and physicists, particularly students, in selecting suitable techniques for the characterization of semiconductor photocatalysts and potentially other relevant materials.

Heterogeneous photocatalysts: an overview of classic and modern approaches for optical, electronic, and charge dynamics evaluation

Abstract: The functionality of a photoactive semiconductor (i.e., photocatalysts, photoelectrodes, etc.) is largely dictated by three key aspects: (i) band gap; (ii) absolute potentials of the conduction band minimum and the valence band maximum; and (iii) bulk and surface charge carrier dynamics. Their relevance to governing the energetics and the photo(electro)chemical mechanisms of the semiconductor has prompted development of a multitude of characterization tools to probe the specific characteristic of the material. This review aims to summarize the current experimental techniques, including the conventional and the state-of-the-art tools, directed at examining the key aspects (i), (ii), and (iii) of semiconductors. Although not being exhaustive, this didactic review can be useful to apprise the research community of the sophisticated research tools currently available for characterization of photo(electro)catalyst semiconductors as well as to bridge the multidisciplinary knowledge.

Carbon Nitride Materials for Water Splitting Photoelectrochemical Cells.

Abstract: Graphitic carbon nitride materials (CNs) have emerged as suitable photocatalysts and heterogeneous catalysts for various reactions thanks to their tunable band gap, suitable energy-band position, high stability under harsh chemical conditions, and low cost However, the utilization of CN in photoelectrochemical (PEC) and photoelectronic devices is still at an early stage owing to the difficulties in depositing high-quality and homogenous CN layer on substrates, its wide band gap, poor charge-separation efficiency, and low electronic conductivity In this Minireview, we discuss the synthetic pathways for the preparation of various structures of CN on substrates and their underlying photophysical properties and current photoelectrochemical performance The main challenges for CN incorporation into PEC cell are described, together with possible routes to overcome the standing limitations toward the integration of CN materials in PEC and other photoelectronic devices

Fully Conjugated Two-Dimensional sp2 -Carbon Covalent Organic Frameworks as Artificial Photosystem I with High Efficiency.

Abstract: The synthesis of fully conjugated sp2 -carbon covalent organic frameworks (COF) is extremely challenging given the difficulty of the formation of very stable carbon-carbon double bonds (-C=C-). Here, we report the successful preparation of a 2D COF (TP-COF) based on triazine as central planar units bridged by sp2 -carbon linkers through the -C=C- condensation reaction. High-resolution-transmission electron microscopy (HRTEM) clearly confirmed the tessellated hexagonal pore structure with a pore center-to-center distance of 2 nm. Powder X-ray diffraction (PXRD) together with structural simulations revealed an AA stacking mode of the obtained layered structure. TP-COF turned out to be an excellent semiconductor material with a LUMO energy of -3.23 eV and a band gap of 2.36 eV. Excitingly, this novel sp2 -carbon conjugated TP-COF exhibited unprecedented coenzyme regeneration efficiency and can significantly boost the coenzyme-assisted synthesis of l-glutamate to a record-breaking 97 % yield within 12 minutes.

Identifying substitutional oxygen as a prolific point defect in monolayer transition metal dichalcogenides.

Abstract: Chalcogen vacancies are generally considered to be the most common point defects in transition metal dichalcogenide (TMD) semiconductors because of their low formation energy in vacuum and their frequent observation in transmission electron microscopy studies. Consequently, unexpected optical, transport, and catalytic properties in 2D-TMDs have been attributed to in-gap states associated with chalcogen vacancies, even in the absence of direct experimental evidence. Here, we combine low-temperature non-contact atomic force microscopy, scanning tunneling microscopy and spectroscopy, and state-of-the-art ab initio density functional theory and GW calculations to determine both the atomic structure and electronic properties of an abundant chalcogen-site point defect common to MoSe2 and WS2 monolayers grown by molecular beam epitaxy and chemical vapor deposition, respectively. Surprisingly, we observe no in-gap states. Our results strongly suggest that the common chalcogen defects in the described 2D-TMD semiconductors, measured in vacuum environment after gentle annealing, are oxygen substitutional defects, rather than vacancies.

Band gap engineered zinc oxide nanostructures via a sol–gel synthesis of solvent driven shape-controlled crystal growth

Abstract: A reliable sol–gel approach, which combines the formation of ZnO nanocrystals and a solvent driven, shape-controlled, crystal-growth process to form well-organized ZnO nanostructures at low temperature is presented. The sol of ZnO nanocrystals showed shape-controlled crystal growth with respect to the solvent type, resulting in either nanorods, nanoparticles, or nanoslates. The solvothermal process, along with the solvent polarity facilitate the shape-controlled crystal growth process, augmenting the concept of a selective adhesion of solvents onto crystal facets and controlling the final shape of the nanostructures. The XRD traces and XPS spectra support the concept of selective adhesion of solvents onto crystal facets that leads to yield different ZnO morphologies. The shift in optical absorption maxima from 332 nm in initial precursor solution, to 347 nm for ZnO nanocrystals sol, and finally to 375 nm for ZnO nanorods, evidenced the gradual growth and ripening of nanocrystals to dimensional nanostructures. The engineered optical band gaps of ZnO nanostructures are found to be ranged from 3.10 eV to 3.37 eV with respect to the ZnO nanostructures formed in different solvent systems. The theoretical band gaps computed from the experimental XRD spectral traces lie within the range of the optical band gaps obtained from UV-visible spectra of ZnO nanostructures. The spin-casted thin film of ZnO nanorods prepared in DMF exhibits the electrical conductivity of 1.14 × 10−3 S cm−1, which is nearly one order of magnitude higher than the electrical conductivity of ZnO nanoparticles formed in hydroquinone and ZnO sols. The possibility of engineering the band gap and electrical properties of ZnO at nanoscale utilizing an aqueous-based wet chemical synthesis process presented here is simple, versatile, and environmentally friendly, and thus may applicable for making other types of band-gap engineered metal oxide nanostructures with shape-controlled morphologies and optoelectrical properties.

Exciton physics and device application of two-dimensional transition metal dichalcogenide semiconductors

Abstract: Two-dimensional group-VI transition metal dichalcogenide semiconductors, such as MoS2, WSe2 and others, exhibit strong light-matter coupling and possess direct band gaps in the infrared and visible spectral regimes, making them potentially interesting candidates for various applications in optics and optoelectronics. Here, we review their optical and optoelectronic properties with emphasis on exciton physics and devices. As excitons are tightly bound in these materials and dominate the optical response even at room-temperature, their properties are examined in depth in the first part of this article. We discuss the remarkably versatile excitonic landscape, including bright, dark, localized and interlayer excitons. In the second part, we provide an overview on the progress in optoelectronic device applications, such as electrically driven light emitters, photovoltaic solar cells, photodetectors and opto-valleytronic devices, again bearing in mind the prominent role of excitonic effects. We conclude with a brief discussion on challenges that remain to be addressed to exploit the full potential of transition metal dichalcogenide semiconductors in possible exciton-based applications.

Large-Scale Benchmark of Exchange-Correlation Functionals for the Determination of Electronic Band Gaps of Solids.

Abstract: We compile a large data set designed for the efficient benchmarking of exchange–correlation functionals for the calculation of electronic band gaps. The data set comprises information on the experimental structure and band gap of 472 nonmagnetic materials and includes a diverse group of covalent-, ionic-, and van der Waals-bonded solids. We used it to benchmark 12 functionals, ranging from standard local and semilocal functionals, passing through meta-generalized-gradient approximations, and several hybrids. We included both general purpose functionals, like the Perdew–Burke–Ernzerhof approximation, and functionals specifically crafted for the determination of band gaps. The comparison of experimental and theoretical band gaps shows that the modified Becke–Johnson is at the moment the best available density functional, closely followed by the Heyd–Scuseria–Ernzerhof screened hybrid from 2006 and the high-local-exchange generalized-gradient approximation.

Band structure and topological properties of twisted double bilayer graphene

Abstract: We study the electronic band structure and the topological properties of the twisted double bilayer graphene, or a pair of AB-stacked bilayer graphenes rotationally stacked on top of each other. We consider two different arrangements, AB-AB and AB-BA, which differ in the relative orientation. For each system, we calculate the energy band and the valley Chern number using the continuum Hamiltonian. We show that the AB-AB and the AB-BA have similar band structures, while the Chern numbers associated with the corresponding bands are completely different. In the absence of the perpendicular electric field, in particular, the AB-AB system is a trivial insulator when the Fermi energy is in a gap, while the AB-BA is a valley Hall insulator. Also, the lowest electron and hole bands of the AB-AB are entangled by the symmetry protected band touching points, while they are separated in the AB-BA. In both cases, the perpendicular electric field immediately opens an energy gap at the charge neutral point, where the electron branch becomes much narrower than the hole branch, due to the significant electron-hole asymmetry.

Absolute energy level positions in tin and lead based halide perovskites

Abstract: Metal-halide perovskites are promising materials for future optoelectronic applications. One intriguing property, important for many applications, is the tunability of the band gap via compositional engineering. While experimental reports on changes in absorption or photoluminescence show rather good agreement for wide variety of compounds, the physical origins of these changes, namely the variations in valence band and conduction band positions, are not well characterized. Knowledge of these band positions is of importance for optimizing the energy level alignment with charge extraction layers in optoelectronic devices. Here, we determine ionization energy and electron affinity values of all primary tin and lead based perovskites using photoelectron spectroscopy data, supported by first-principles calculations. Through analysis of the chemical bonding, we characterize the key energy levels and elucidate their trends via a tight-binding analysis. We demonstrate that energy level variations in perovskites are primarily determined by the relative positions of the atomic energy levels of metal cations and halide anions. Secondary changes in the perovskite energy levels result from the cation-anion interaction strength, which depends on the volume and structural distortions of the perovskite lattices. These results mark a significant step towards understanding the electronic structure of this material class and provides the basis for rational design rules regarding the energetics in perovskite optoelectronics.

Experimental and DFT insights of the Zn-doping effects on the visible-light photocatalytic water splitting and dye decomposition over Zn-doped BiOBr photocatalysts

Abstract: Synergetic experimental and DFT insights of energy band structures and photogenerated rate-limiting reactive species are indispensable to design impurity-doped photocatalysts for photocatalytic environment remediation and solar fuels. Herein, despite the larger bandgap (Eg) of the Zn-doped BiOBr samples, they exhibited superior activity to BiOBr in the photocatalytic water splitting but impaired the photodegradation of Rhodamine B under visible-light illumination. Based on the spectral and electrochemical impedance characterisations and DFT simulations, the wider bandgaps of Zn-doped BiOBr samples were explicitly assigned to the more positive valence band maxima (VBM) and more negative conduction band minima (CBM). The enhanced photocatalytic water splitting on the Zn-doped BiOBr was arisen from the higher redox chemical potentials of charge carriers on respective CBM and VBM, suppressed back reactions and depressed recombination of photogenerated charge carriers. However, the reduced e−-h+ recombination on the Zn-doped BiOBr cannot cancel the detrimental influences from the weaker light absorption and dye-sensitisation effects, leading to slower RhB photodegradation.

Borocarbonitrides, BxCyNz, 2D Nanocomposites with Novel Properties

Abstract: Chemical doping of graphene is necessary to generate a band gap that is valuable for a range of applications. Chemical doping of graphene with elements like nitrogen and boron gives rise to useful ...

Machine-Learning-Assisted Accurate Band Gap Predictions of Functionalized MXene

Abstract: MXenes are two-dimensional (2D) transition metal carbides and nitrides, and are invariably metallic in pristine form. While spontaneous passivation of their reactive bare surfaces lends unprecedented functionalities, consequently a many-folds increase in number of possible functionalized MXene makes their characterization difficult. Here, we study the electronic properties of this vast class of materials by accurately estimating the band gaps using statistical learning. Using easily available properties of the MXene, namely, boiling and melting points, atomic radii, phases, bond lengths, etc., as input features, models were developed using kernel ridge (KRR), support vector (SVR), Gaussian process (GPR), and bootstrap aggregating regression algorithms. Among these, the GPR model predicts the band gap with lowest root-mean-squared error (rmse) of 0.14 eV, within seconds. Most importantly, these models do not involve the Perdew–Burke–Ernzerhof (PBE) band gap as a feature. Our results demonstrate that machin...

VI3—a New Layered Ferromagnetic Semiconductor

Abstract: 2D materials are promising candidates for next-generation electronic devices. In this regime, insulating 2D ferromagnets, which remain rare, are of special importance due to their potential for enabling new device architectures. Here the discovery of ferromagnetism is reported in a layered van der Waals semiconductor, VI3 , which is based on honeycomb vanadium layers separated by an iodine-iodine van der Waals gap. It has a BiI3 -type structure ( R 3 ¯ , No.148) at room temperature, and the experimental evidence suggests that it may undergo a subtle structural phase transition at 78 K. VI3 becomes ferromagnetic at 49 K, below which magneto-optical Kerr effect imaging clearly shows ferromagnetic domains, which can be manipulated by the applied external magnetic field. The optical bandgap determined by reflectance measurements is 0.6 eV, and the material is highly resistive.

Origin of band gaps in 3d perovskite oxides.

Abstract: With their broad range of properties, ABO3 transition metal perovskite oxides have long served as a platform for device applications and as a testing bed for different condensed matter theories. Their insulating character and structural distortions are often ascribed to dynamical electronic correlations within a universal, symmetry-conserving paradigm. This view restricts predictive theory to complex computational schemes, going beyond density functional theory (DFT). Here, we show that, if one allows symmetry-breaking energy-lowering crystal symmetry reductions and electronic instabilities within DFT, one successfully and systematically recovers the trends in the observed band gaps, magnetic moments, type of magnetic and crystallographic ground state, bond disproportionation and ligand hole effects, Mott vs. charge transfer insulator behaviors, and the amplitude of structural deformation modes including Jahn-Teller in low temperature spin-ordered and high temperature disordered paramagnetic phases. We then provide a classification of the four mechanisms of gap formation and establish DFT as a reliable base platform to study the ground state properties in complex oxides. It is often stated that first principles studies of transition metal oxides require dynamically correlated methods to correctly produce gap formation, magnetism and structural distortions. Varignon et al. show instead that static correlations are sufficient to capture these features in the ABO3 oxide series.

Two-Dimensional PC6 with Direct Band Gap and Anisotropic Carrier Mobility.

Abstract: Graphene and phosphorene are two major types of atomically thin two-dimensional materials under extensive investigation. However, the zero band gap of graphene and the instability of phosphorene greatly restrict their applications. Here, we make first-principle unbiased structure search calculations to identify a new buckled graphene-like PC6 monolayer with a number of desirable functional properties. The PC6 monolayer is a direct-gap semiconductor with a band gap of 0.84 eV, and it has an extremely high intrinsic conductivity with anisotropic character (i.e., its electron mobility is 2.94 × 105 cm2 V–1 s–1 along the armchair direction, whereas the hole mobility reaches 1.64 × 105 cm2 V–1 s–1 along the zigzag direction), which is comparable to that of graphene. On the other hand, PC6 shows a high absorption coefficient (105 cm–1) in a broad band, from 300 to 2000 nm. Additionally, its direct band gap character can remain within a biaxial strain of 5%. All these appealing properties make the predicted PC6 ...

Bi2WO6-x nanosheets with tunable Bi quantum dots and oxygen vacancies for photocatalytic selective oxidation of alcohols

Abstract: Herein, Bi2WO6-x nanosheets with tunable Bi quantum dots and oxygen vacancies have been synthesized by a facile hydrothermal treatment combining in-situ redox reaction route, which exhibited the highly enhanced activity for selective oxidation of aromatic alcohols to carbonyl compounds in aqueous medium under visible-light irradiation for the first time. Results revealed that the highly enhanced activity of this photocatalyst was mainly attributed to the synergetic effect of Bi quantum dots and oxygen vacancies, which resulted in the narrowed energy band gap by inducing the formation of defect state level below the conduction band, the enhanced light-harvesting ability and the improved separation efficiency of photocharges. Meanwhile, this photocatalyst also displayed excellent durability owing to the strong interaction between Bi quantum dots and robust Bi2WO6-x nanosheets against significant deactivation caused by either the leaching of Bi quantum dots or the structural collapse of Bi2WO6-x nanosheets, showing its good potential in practical applications.

Perovskite Quantum Dot Solar Cells with 15.6% Efficiency and Improved Stability Enabled by an α-CsPbI3/FAPbI3 Bilayer Structure

Abstract: We developed lead halide perovskite quantum dot (QD) solar cells with a combinational absorbing layer based on stacked α-CsPbI3 and FAPbI3. α-CsPbI3 QDs, with a relatively wide bandgap of 1.75 eV, ...

Cesium Lead Inorganic Solar Cell with Efficiency beyond 18% via Reduced Charge Recombination.

Abstract: Cesium-based inorganic perovskite solar cells (PSCs) are promising due to their potential for improving device stability. However, the power conversion efficiency of the inorganic PSCs is still low compared with the hybrid PSCs due to the large open-circuit voltage (VOC ) loss possibly caused by charge recombination. The use of an insulated shunt-blocking layer lithium fluoride on electron transport layer SnO2 for better energy level alignment with the conduction band minimum of the CsPbI3-x Brx and also for interface defect passivation is reported. In addition, by incorporating lead chloride in CsPbI3-x Brx precursor, the perovskite film crystallinity is significantly enhanced and the charge recombination in perovksite is suppressed. As a result, optimized CsPbI3-x Brx PSCs with a band gap of 1.77 eV exhibit excellent performance with the best VOC as high as 1.25 V and an efficiency of 18.64%. Meanwhile, a high photostability with a less than 6% efficiency drop is achieved for CsPbI3-x Brx PSCs under continuous 1 sun equivalent illumination over 1000 h.