Bulk Perovskite Research Articles

Vitamin Natural Molecule Enabled Highly Efficient and Stable Planar n–p Homojunction Perovskite Solar Cells with Efficiency Exceeding 24.2%

AbstractThe defect passivation and interface energetics‐modification between perovskite and transport layers are significant for the further improvement of efficiency and stability of perovskite solar cells (PSCs). Here, a double‐layer modification engineering strategy is employed by different functionalized natural vitamins into the electron transport layer and perovskite, respectively. Considering the different role of each functional layer in PSCs, the vitamin C (VC) with high conductivity is introduced into SnO2, showing electron mobility enhancement, an interface energy‐levels offsets reduction, and enhanced interfacial charge transfer. Meanwhile, antioxidant vitamin D2 (VD2) with multiple passivating functional groups is introduced into the perovskite bulk to moderately tailor its intrinsic characteristics. The surface energetics of perovskite are changed from n‐type to p‐type, the thickness of the p‐type perovskite is 80 nm, thus the spontaneous n–p homojunction is formed in perovskite caused by VD2, which increases the built‐in electric field and the efficiency of perovskite hole extraction. The synergistic effect of VC and VD2 better heightens the charge extraction efficiency and achieves charge‐carrier transport balance in PSCs. The optimum device achieves a power conversion efficiency of 24.20% and a fill factor of 81.01% with negligible hysteresis. This efficiency is among the best PSCs employing natural molecules reported so far.

Red Perovskite Light‐Emitting Diodes: Recent Advances and Perspectives

AbstractMetal halide perovskite (MHP) materials have shown great advantages for the next‐generation optoelectronic devices, especially for light‐emitting diodes (LEDs), on account of their outstanding photoelectric properties and facile solution processability. However, the performances of red perovskite LEDs (PeLEDs) are not ready for commercialization, presumably due to the instability both of the emission spectra and operation conditions, and the toxicity of lead ions. In this review, the structures, physical properties, and preparation approaches of red emissive perovskite materials are first introduced, including 3D bulk perovskites, 2D and quasi‐2D perovskites, and colloidal perovskite nanocrystals (NCs). In addition, several strategies that contribute to the recent development and achievement of red PeLEDs are summarized in detail, mainly involving component engineering, dimension, and phase distribution modulation, ligand engineering, additive engineering, interfacial engineering, and strategies for the light out‐coupling device structure. Moreover, the challenges and corresponding solutions are discussed from three aspects of spectral stability, operational stability, and lead‐free red PeLEDs. Finally, the conclusion and outlook on the promising future of the red PeLEDs are raised.

Role of oxygen vacancy ordering on structure and reactivity of iron-doped Sr-based perovskites: A computational study

Density functional theory (DFT) methods were used to investigate the structure and reactivity of pure SrCoO3, SrFeO3, and iron-doped SrCo0.8Fe0.2O3 and SrCoxFe1-xO3 (x ​= ​0.25, 0.50, 0.75) perovskites. The electronic properties of bulk perovskites were compared to the electronic properties of iron-doped perovskites of various iron compositions within the bulk material. The effect of iron position on SrCo0.8Fe0.2O3 was investigated for various configurations, and it was found that the structure with two FeO6 polyhedra intercalated in between CoO6 polyhedra was relatively more stable than others. The presence of Fe polyhedra adjacent to each other enhances the Jahn-Teller distortion resulting in a lowered symmetry. The structure and reactivity of oxygen vacancy ordered SrCoO2.5, SrFeO2.5, and iron-doped SrCo0.8Fe0.2O2.5, SrCoxFe1-xO2.5, and SrCoxFe1-xO2.75 (x ​= ​0.25, 0.50, 0.75) corresponding to varying oxygen content was also investigated. Electron density distribution plots and Bader charges were examined to understand the bonding interactions. The work functions of perovskites with and without oxygen vacancies were calculated to predict the conductive behavior. Furthermore, hydrogen atom and hydrogen molecule was incorporated into the oxygen vacant site of perovskites to understand the structural transformation in hydrogenated perovskites and predict the plausible use of these materials in hydrogen storage. The adsorption of water on the SrFeO3 slab was also studied by molecular dynamics simulations. The water molecule is split into hydroxyl and proton, where the proton associates with the surface oxygen at a distance of 0.91 ​Å, and the hydroxyl ion occupies an oxygen vacant site on the surface coordinating with Fe at a distance of 2.73 ​Å.

Realizing Efficient Emission in Three-Dimensional CsCdCl3 Single Crystals by Introducing Separated Emitting Centers.

Hitherto, three-dimensional (3D) perovskite single crystals with a low exciton binding energy generally possess inferior photoluminescence (PL) performance due to the spatially unconfined nature of excitons. In this work, 3D CsCdCl3 single crystals with multiple emissions from self-trapped excitons (STEs) have been developed, which unsurprisingly exhibit a discouraging PL quantum yield (PLQY) of ∼4.8%. To improve the luminescence efficiency, Mn2+ and Sn2+ are introduced into the lattice as dopants, respectively. By embedding Mn2+ ion into CsCdCl3, the long Mn-Mn distance enables the resultant material to produce an intense orange emission (∼100% PLQY) from the d-d orbital transition (4T1-6A1) of Mn2+. Intriguingly, the embedded Sn2+ triggers the formation of Jahn-Teller-like STEs that induces a subsequent deep red emission with a PLQY of ∼28.22%, which is quite high for 3D bulk perovskites. Such a remarkable PL efficiency is attributed to the distinctive bonding mode of CsCdCl3 that encourages the expression of the Sn 5s2 lone pair. Furthermore, a white-light-emitting diode (WLED) is also fabricated with Mn2+-doped CsCdCl3 to show its potential in lighting application. This work paves a new avenue to improve the luminescence performance of bulk 3D perovskite materials.

Reduced Open‐Circuit Voltage Loss of Perovskite Solar Cells via Forming p/p+ Homojunction and Interface Electric Field on the Surfaces of Perovskite Film

AbstractThe severe nonradiative recombination losses limit the further improvement of open‐circuit voltage (Voc) and power conversion efficiency (PCE) of perovskite solar cells (PVSCs). In this work, the 4,4′‐cyclohexylidenebis [N,N‐bis(4‐methylphenyl) benzene amine] is dissolved into the antisolvent to prepare perovskite films, which reduces defects, improves the crystallinity, and induces a p/p+ homojunction on the top surface of perovskite film. Besides, the 2‐thiophenemethylammonium iodide and 2‐thiophenethylammonium iodide form interface electric field and passivate defects on the bottom surface of perovskite film. The p/p+ homojunction and interface electric field enhance the charges’ separation and transportation efficiencies in the bulk perovskite film and at the perovskite/charge transport layer interfaces, which effectively reduces nonradiative recombination losses and Voc loss of PVSCs. Consequently, low Voc loss of 0.348 V is realized, resulting in the increase in Voc from 1.082 to 1.172 V and PCE from19.15% to 23.44%. The optimized PVSCs without encapsulation maintain 88.23% of the original PCE after exposing in the air for 1500 h. This work provides a strategy to reduce the nonradiative recombination losses and Voc loss by forming p/p+ homojunction and interface electric field on the surfaces of perovskite film, which advances the development of high‐performance PVSCs.

Formate diffusion engineering of hole transport layer for highly efficient N-I-P perovskite solar cells

The dominant hole transport material in the state-of-the-art n-i-p perovskite solar cells (PSCs) mainly is Spiro-OMeTAD, which suffer from the instability issue caused by the intrinsic nature of additives and dopants. Here, a formate diffusion engineering of Spiro-OMeTAD is proposed to improve the stability and performance of PSCs. By adding a novel bis(trifluoromethyl)benzylamine formate into the Spiro-OMeTAD, both the conductivity and hole mobility of the Spiro-OMeTAD layer are enhanced. Results of ionic distribution profiling validate evidence of formate diffusion from the Spiro-OMeTAD layer into the perovskite bulk. The diffused formate could effectively reduce the interfacial non-radiative recombination of perovskite/Spiro-OMeTAD interface and adjust the interfacial energy level, thus enhancing the carrier extraction. This concurrent Spiro-OMeTAD engineering and surface passivation scheme renders higher efficiency in n-i-p PSCs. This formate diffusion strategy, which synergistically couples electrical property of hole conductor and defect passivation of perovskite layer, could open a route to develop high-performance optoelectronic devices.

(Invited) From Bulk to Nanostructured Perovskites

The dimensionality of semiconductors has a crucial role in determining their properties. Recently, metal halide perovskites have been demonstrated with many exciting applications, attracting wide attention to further their development for advanced optoelectronics, such as photovoltaics, photodetectors, light-emitting diodes, and lasers. At length scales down to nanoscale regimes, surface features as well as quantum confinement effects become dominant in regulating the material properties of perovskite materials. In past years, our group focus on the synthesis and characterization of metal halide perovskites with different configurations, ranging from bulk films, microplates, nanosheets, to nanowires. The corresponding physical properties and device applications were also systematically studied based on their widely tunable dimensionality, morphologies, and compositions.Specifically, for perovskite bulk films, surface defects and bulk structural order significantly affect their device performance. Through optimizing processing techniques, self-assembled quasi-2D perovskite films with graded phase distribution were successfully prepared. Gradient type-II band alignments along the out-of-plane direction of perovskites with spontaneous separation of photo-generated electrons and holes are obtained, which is later employed to construct self-powered vertical-structure photodetectors for the first time. Without any driving voltage, the device exhibited impressive performance with the responsivity up to 444 mA/W and ultrashort response time down to 52 µs. In addition, to assess the intrinsic material properties of crystalline perovskites, freestanding MAPbI3 nanosheets and lead-free Cs3Sb2I9 microplates were fabricated by two-step chemical vapor deposition method, in which excellent optoelectronic performance (e.g., responsively of MAPbI3 nanosheet is measured to be 40 A/W) together with ultra-fast response speed (down to 58 µs) and superior thermal stability were obtained.For nanostructured perovskites, understanding the dimensional features and their impact on the materials and devices is becoming increasingly important. Lately, we reported the direct vapor-liquid-solid growth of single-crystalline all-inorganic lead halide perovskite (i.e., CsPbX3; X = Cl, Br, or I) NWs. These NWs exhibited high-performance photodetection with the responsivity exceeding 4489 A/W and detectivity over 7.9 × 1012 Jones toward the visible light regime. Field-effect transistors based on individual CsPbX3 NWs were also fabricated to show the impressive carrier mobility of 3.05 cm2/Vs, being higher than other all-inorganic perovskite devices. Besides, the realization of high-mobility CsPbBr3 NW devices is reported via a simple surface charge transfer doping strategy. After MoO3 decoration and device fabrication, the hole mobility of CsPbBr3/MoO3 core-shell NW device is significantly enhanced to 23.3 cm2/Vs. All these results provide important guidelines for the further improvement of these perovskite nanostructures for practical utilization.

Ab initio computations of BaZrO3, CaTiO3, SrTiO3 perovskite as well as WO3 and ReO3 (001) surfaces

We computed, at the ab initio level, BaZrO3, CaTiO3, SrTiO3 as well as WO3 and ReO3 (001) surfaces and analyzed systematic tendencies therein. As obtained by our ab initio hybrid DFT-HF computations, at BO2-terminated (001) surfaces of investigated ABO3 perovskites as well as WO3 and ReO3 oxides, all top-layer ions shift in the direction of the crystal bulk. The single-deviation from this tendency is upward shift of the WO2-terminated WO3 (001) surface top layer O ion by the magnitude of +0.42% of the bulk lattice constant a0. In contrary, all second layer ions, with the single exception of ReO2-terminated ReO3 (001) surface O ion, shifts upwards. Our computed BO2-terminated SrTiO3, CaTiO3, BaZrO3, WO3 and ReO3 (001) surface Γ–Γ band gaps always are smaller than their respective bulk Γ–Γ band gaps. The B–O ion chemical bond populations in the SrTiO3, CaTiO3 and BaZrO3 perovskite bulk are always smaller than at their nearby BO2-terminated (001) surfaces. On the contrary, the W–O and Re–O ion chemical bond populations in the WO3 (0.142e) and ReO3 (0.212e) bulk are slightly larger than at nearby the WO2- and ReO2-terminated WO3 and ReO3 (001) surfaces (0.108e and 0.170e). Nonetheless, the W–O and Re–O chemical bond populations between the W and Re ions located in the upper layer and the O ions located in the second layer of the WO2- and ReO2-terminated (001) surfaces (0.278e and 0.262e) are the absolutely largest bond populations in the WO3 and ReO3 crystals.

Tracking crustal assimilation processes in kimberlites from the Alto Paranaíba Igneous Province, Brazil: Petrographic and geochemical controls and the role of perovskites

Anomalous kimberlite varieties from the Cretaceous Alto Paranaíba Igneous Province (APIP, Brazil) do not follow simple classification charts, showing abundant evidence of interaction with crustal xenoliths. In this paper, we track the potential effects of crustal assimilation processes on textural, mineralogical, geochemical and isotopic signatures. Formation of reaction diopside and poikilitic phlogopite, as well as Fe/Nb variations in perovskites, records progressive increases of not only alumina and K2O contents, but also of silica activity and fO2, compatible with the assimilation of and/or interaction with the Si-rich crust. High bulk rock “contamination indexes”, decreasing Ce/Pb and Gd/Lu and slightly increasing Rb/Sr ratios are observed in the APIP kimberlite varieties and/or facies showing progressively more remarkable petrographic evidence of crustal contamination. Significant variability of 87Sr/86Sri ratios detected in whole rock, bulk perovskite concentrates (TIMS, MC-ICP-MS) and in-situ perovskite (multi-grain approach, LA-MC-ICP-MS) of the Indaiá-I/Limeira-I intrusions (0.70507–0.70539) and their satellites Indaiá-II/Limeira-II/III (0.70508–0.70592), of the different Pântano facies (0.70513–0.70551), and of the Catalão 1b (0.70495–0.706546) indicates a tendency to more radiogenic Sr isotope compositions during kimberlite open-system crystallization. Geochemical modeling indicates the important crustal contribution to the genesis of these anomalous occurrences, with an extensive crust input for the Indaiá-II and Limeira-II/III occurrences, consistent with their petrographic evidence. The potassic to ultrapotassic geochemical affinity and the similarities between contaminated APIP kimberlite and bulk kamafugite compositions can be related to the incorporation/digestion of crustal components to the parental kimberlite magma.

Trap passivation and suppressed electrochemical dynamics in perovskite solar cells with C60 interlayers

In this study, we quantify the impact of C60-passivation layers in Cs0.15FA0.85PbI2.75Br0.25 double-cation perovskite solar cells. We apply a combination of impedance spectroscopy, photoluminescence (PL) spectroscopy, and X-ray diffraction (XRD) to identify the origin for the increase in power conversion efficiencies and operational stability for solar cells fabricated with C60/ZnO electron transport layer (ETL) versus reference cells with a ZnO ETL. XRD reveals an increase in PbI2 while PL spectroscopy reveals an increase in Br-rich regions in the perovskite bulk in devices containing C60 interlayers. We apply impedance spectroscopy to quantify the electrochemical dynamics in both solar cell architectures. Solar cells with C60/ZnO ETL demonstrate less pronounced and slower electrochemical dynamics in the impedance spectra than solar cells with ZnO ETL. We conclude that C60 leads to the formation of PbI2-rich and Br-rich domains in the perovskite absorber layer, resulting in reduced recombination losses and improved operational stability.

Effect of surface treatment of sputtered nickel oxide in inverted perovskite solar cells

Nickel oxide (NiOx) is promising hole transport material for efficient and stable lead halide perovskite solar cell (PSC) due to its promising optoelectronic properties and superior moisture resistivity. Herein, we investigate the effect of surface treatment of sputtered NiOx film using ethanol (NiOx-EtOH) in device parameters of PSC. Ethanol treatment of NiOx facilitates the growth of high-quality perovskite film (larger grain size, better crystallinity, and faster carrier injection). The device with NiOx-EtOH demonstrated the champion power conversion efficiency of ∼13.52% (with open circuit voltage (VOC) ∼1.075 V) of 1 cm2 large-area device. While the device with pristine NiOx has a device efficiency of 11.78% (with VOC ∼0.99 V). This report corroborates that the PSC with NiOx-EtOH improves device performance owing to hydrophilicity, defect passivation of sputtered NiOx surface, and attenuation of recombination in the perovskite bulk.

Interfacial Engineering Based on Polyethylene Glycol and Cuprous Thiocyanate Layers for Efficient and Stable Perovskite Solar Cells

AbstractCuprous thiocyanate (CuSCN) is an ideal inorganic hole transport material for perovskite solar cells (PSCs). However, polar solvents for film deposition of CuSCN run a risk of destroying the perovskite light‐absorbing layer. There is also a poor contact between perovskites and CuSCN, restricting photovoltaic performance and operational stability of PSCs. In this work, a polyethylene glycol (PEG‐10000) is employed as an interlayer to effectively overcome the obstacles mentioned above. By introducing this ultra‐thin layer at the interface between (MAFA)Pb(IBr)3 and CuSCN, the power conversion efficiency (PCE) and operational stability of the related PSCs are both greatly improved. The results confirm that the insertion of PEG cannot only prevent the destruction of bulk perovskites but also reduce the traps/defects at the interface through its strong chemical bonding with undercoordinated ions, which significantly lowers the potential barrier between the perovskite and the hole transport layer. An improved PCE of 19.2% can be achieved in the CuSCN‐based PSCs by interface engineering with PEG. The introduction of PEG can also protect the perovskite film from moisture attack, and greatly enhance device stability. The PEG‐treated PSCs without encapsulation maintain more than 90% of the initial efficiency after 1860 h in the ambient air.

Impact of Co2+ on the magneto-optical response of MAPbBr3: An inspective study of doping and quantum confinement effect

The current work establishes the excitonic magneto-optic (M − O) effects of magnetic circular dichroism (MCD) in Cobalt (Co2+) doped diamagnetic organic−inorganic hybrid CH3NH3PbBr3 perovskites at low magnetic field and room temperature. The solution-processed perovskites are prepared in the form of single crystal thin films and quantum dots. The structural studies confirm the successful doping of the Co2+ in the perovskite lattice. Further, the perovskites are investigated as diluted magnetic semiconductors (DMSs) related to the dopant concentration effect and the size effect on their M − O properties. Magnetic dopant Cobalt leads to the strong sp-d exchange coupling that generates higher values of Zeeman splitting (ΔEZ) than the pristine MAPbBr3 due to the excitonic 1s Pb–Br absorption quantified by analysis of MCD. The ΔEZ value increases with the Co concentration up to 10 mol % and then starts decreasing. This concentration dependency can be linked with the luminescence of the perovskites with the Co2+ doping. The rise and fall of the MO and PL properties can be defined by the formation of Co–Co pairs in heavily doped perovskites which can influence the spin conditions of the paramagnetic Co ions. Using the Kramers–Kronig relations with MCD, the calculated Verdet constant exhibits a massive increase in value with the doping of cobalt, much higher than the industry standard Faraday rotator indicating their probable usability in this industry. Further in the quantum dots, the quantum confinement effect is pronounced that increases the MCD and hence the ΔEZ multiple times higher than the bulk perovskite films. These results provide a promising pathway for the study of solution-processed hybrid perovskites as DMSs for spintronics.

Interface-Driven Multiferroicity in Cubic BaTiO3-SrTiO3 Nanocomposites.

Perovskite multiferroics have drawn significant attention in the development of next-generation multifunctional electronic devices. However, the majority of existing multiferroics exhibit ferroelectric and ferromagnetic orderings only at low temperatures. Although interface engineering in complex oxide thin films has triggered many exotic room-temperature functionalities, the desired coupling of charge, spin, orbital and lattice degrees of freedom often imposes stringent requirements on deposition conditions, layer thickness and crystal orientation, greatly hindering their cost-effective large-scale applications. Herein, we report an interface-driven multiferroicity in low-cost and environmentally friendly bulk polycrystalline material, namely cubic BaTiO3-SrTiO3 nanocomposites which were fabricated through a simple, high-throughput solid-state reaction route. Interface reconstruction in the nanocomposites can be readily controlled by the processing conditions. Coexistence of room-temperature ferromagnetism and ferroelectricity, accompanying a robust magnetoelectric coupling in the nanocomposites, was confirmed both experimentally and theoretically. Our study explores the 'hidden treasure at the interface' by creating a playground in bulk perovskite oxides, enabling a broad range of applications that are challenging with thin films, such as low-power-consumption large-volume memory and magneto-optic spatial light modulator.

Regulating the Crystallization Kinetics and Lattice Strain of Lead-Free Perovskites with Perovskite Quantum Dots

The growth of high-quality tin-based perovskite films remains a grand challenge due to uncontrollable crystallization kinetics. Here, we report a facile strategy to realize an epitaxial-like growth of highly oriented tin-based perovskite films with the assistance of perovskite quantum dots (PQDs). Synchrotron-based in situ X-ray scattering results reveal that PQDs can act as nucleation centers to promote the growth of highly oriented perovskite crystals for both FASnI3 and MASnI3 systems. Remarkably, the degree of lattice strain can be readily modulated by tuning the lattice mismatch between various PQDs and bulk perovskites, thus reducing defect density and improving efficiencies. The efficiency of MASnI3 PSCs with PQDs has been pushed to 12.49%, which is the highest of this type reported so far. Furthermore, the film and device stability are enhanced owing to the improved film quality and the protection of hydrophobic ligands from PQDs.

Suppressing Nonradiative Recombination in Lead–Tin Perovskite Solar Cells through Bulk and Surface Passivation to Reduce Open Circuit Voltage Losses

Lead–Tin perovskite solar cells (Pb/Sn PSCs) are limited by the intrinsic instability of Sn(II), which tends to oxidize forming Sn vacancies in perovskite films. Herein, a Lewis base β-guanidinopropionic acid (GUA) and hydrazinium iodide (HAI) are introduced to effectively passivate the perovskite bulk and surface, respectively. The synergistic approach leads to Pb/Sn PSCs with a promising power conversion efficiency of 20.5% owing to the significantly reduced nonradiative recombination and voltage losses. As a result, the VOC × FF product of PSCs is significantly improved, which is among the highest values documented in the literature, being favorable for perovskite-based tandem applications. Additionally, the strategy demonstrated in this work could also improve the stability of PSCs by enhancing the chemical robustness of the perovskite layer. These results emphasize the significance of bulk and surface passivation in the development of efficient and stable PSCs based on Pb/Sn perovskites.

Recent Progress on Defect Passivation of All‐Inorganic Halide Perovskite Solar Cells

AbstractAll‐inorganic halide perovskite materials have attracted increasing attentions in recent years due to their superior stability and adjustable band gap which make them very suitable for the top cells of multi‐junction solar cells. Nonetheless, the power conversion efficiency of all‐inorganic halide perovskite solar cells is still far from satisfaction. The widespread use of the conventional solution method in the preparation process causes many different defects and carrier transport barriers at the grain boundaries and interfaces of the perovskite films, which can cause severe hysteresis behavior and non‐radiative recombination, resulting in low efficiency and hindering their rapid commercialization. While, the selection of suitable passivation materials and techniques can have the most significant potential in reducing the defect recombination centers between the bulk perovskite, the film surface and grain boundaries, and the interface between the various communities (perovskite/electron transport layer [ETL], perovskite/hole transport layer [HTL]). Herein, this study reviews the current research process on various passivation strategies developed for all‐inorganic halide perovskite solar cells, especially for the defects in the perovskite surface, and grain boundaries, perovskite/HTL interface and perovskite/ETL interface. Finally, the authors look ahead to the prospects and challenges of exploring defect passivation in all‐inorganic halide perovskite solar cells.

Surface reaction for efficient and stable inverted perovskite solar cells.

Perovskite solar cells (PSCs) with an inverted structure (often referred to as the p-i-n architecture) are attractive for future commercialization owing to their easily scalable fabrication, reliable operation and compatibility with a wide range of perovskite-based tandem device architectures1,2. However, the power conversion efficiency (PCE) of p-i-n PSCs falls behind that of n-i-p (or normal) structure counterparts3-6. This large performance gap could undermine efforts to adopt p-i-n architectures, despite their other advantages. Given the remarkable advances in perovskite bulk materials optimization over the past decade, interface engineering has become the most important strategy to push PSC performance to its limit7,8. Here we report a reactive surface engineering approach based on a simple post-growth treatment of 3-(aminomethyl)pyridine (3-APy) on top of a perovskite thin film. First, the 3-APy molecule selectively reacts with surface formamidinium ions, reducing perovskite surface roughness and surface potential fluctuations associated with surface steps and terraces. Second, the reaction product on the perovskite surface decreases the formation energy of charged iodine vacancies, leading to effective n-type doping with a reduced work function in the surface region. With this reactive surface engineering, the resulting p-i-n PSCs obtained a PCE of over 25 per cent, along with retaining 87 per cent of the initial PCE after over 2,400 hours of 1-sun operation at about 55 degrees Celsius in air.

Influence of the Thermal Processing and Doping on LaMnO3 and La0.8A0.2MnO3 (A = Ca, Sr, Ba) Perovskites Prepared by Auto-Combustion for Removal of VOCs

Single-phase oxygen stoichiometric LaMnO3 and doped La0.8A0.2MnO3 (A = Ca, Sr, Ba) perovskites have been prepared by a simple one-step auto-combustion method. Cation-deficient LaMnO3+δ and La0.8A0.2MnO3+δ were obtained by calcination of the former samples in air at 750 °C. The samples were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction, temperature-programmed oxygen desorption, and N2 physisorption in order to apply them as catalysts in the complete catalytic oxidation of acetone as a model volatile organic compound. The studied phases show the expected orthorhombic and rhombohedral perovskite crystal structures. Catalytic experiments performed with all the samples show measurable activity already at 100 °C. At 200 °C, doped La0.8A0.2MnO3 samples show higher activity than undoped LaMnO3, with increasing conversion with larger A-cation size. Calcined samples also show higher activity than as-prepared ones making La0.8Ba0.2MnO3+δ the best catalyst at this temperature. All doped samples show >95% acetone conversion at T ≥ 250 °C with a weak dependence on the sample processing or A cation doping. The collected evidence confirms that the most important factors for the catalytic activity of these oxides are the Mn4+/Mn3+ molar ratio on the surface of the samples and the cation-deficiency of the bulk perovskite structure. In addition, increasing the symmetry of the bulk crystal structure appears to have an additional favourable effect. Despite the observation of the presence of surface carbonates, we show that it is possible to use the as-prepared samples without further thermal treatment with good results in the oxidation of acetone.

Air Induced Formation of Cs3Bi2Br9/Cs3BiBr6 Bulk Heterojunction and Its Dual‐band Photodetection Abilities for Light Communication

AbstractMetal‐halide perovskites have long carrier diffusion lengths, low trap densities, and high carrier mobilities, and are therefore of value in the development of photodetectors (PDs). However, the research on dual‐band lead‐free perovskite bulk heterojunction has not been well developed. Here, a novel air induced formation of Cs3Bi2Br9/Cs3BiBr6 bulk heterojunction, reaching a high‐performance dual‐band photodetecting performance with an ultra‐violet main band (360 nm) peak responsivity of 5.6 mA W−1 and a blue sub‐band (450 nm) peak responsivity of 0.6 mA W−1 at 2 V, is reported. The bulk heterojunction exhibits superior photodetecting performance than that of lateral heterojunction. Furthermore, the PD exhibits a fast response speed (rise time 1.4 µs and decay time 2.0 µs) and good cyclic stability. Theoretical and experimental characterizations suggest Cs3Bi2Br9 exhibits a more stable structure in air than that of Cs3BiBr6. The dual‐band photodetection abilities of Cs3Bi2Br9/Cs3BiBr6 bulk‐heterojunction demonstrate great application prospects in light communication. These state‐of‐the‐art findings shed light on the fabrication of novel dual‐band high‐performance PDs based on lead‐free perovskite bulk‐heterojunction.