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Tin-based halide perovskite materials are of interest for light-emitting applications due to their broad yellow emission, but they are known to exhibit inferior stability compared to the lead- based perovskites due to tendency of Sn2+ to be readily oxidized. Here we investigated the ambient stability of a Dion-Jacobson tin bromide perovskite. We found that the optical properties of the samples were more significantly affected by the moisture rather than the ratio of Sn2+/Sn4+. The exposure to humidity resulted in changes in the ratio of 2D HDASnBr4 and hydrated 1D HDA3SnBr8 phases, with initial increase (up to ~40 h) in luminescence attributed to increasing fraction of hydrated 1D phase which contributes to self- trapped exciton emission. With further exposure to humidity, the material starts to degrade resulting in reduced luminescence after ~40 h. The use of additives for the suppression of oxidation of Sn2+, namely SnCl2 and tetraethyl orthosilicate (TEOS), results in prolonging the lifetime of the samples (>260 h for thin films with additives, compared to 180 h for thin films without additives). However, the persistence of luminescence with increased time of ambient exposure in samples prepared with additives can be attributed to the changes in the evolution of phase composition (rati-os of 2D and hydrated 1D phases) over time rather than suppressing the oxidation of Sn2+.

Photoinduced halide segregation (PHS) is a process of critical importance for the performance of perovskite solar cells with mixed halide absorber layers. However, PHS is still not well understood, especially in the case of layered mixed halide perovskites (MHPs), which are less commonly studied compared to their 3D counterparts. Here, we investigated temperature- and light-induced PHS in 2D MHPs with a phenylpropylammonium (PPA) spacer. We found that 2D PPA-based MHPs exhibited complex segregation behavior dependence on temperature and illumination intensity with the suppression of segregation observed at high temperature (attributed to the highly exothermic nature of the process) as well as moderate illumination intensities, illustrating the importance of additional processes present in this particular material, which exhibits distinctly different behavior compared to 2D MHPs with other aromatic cations.

While the constraints on the choice of organic cations are greatly relaxed for layered two- dimensional perovskites compared to three- dimensional perovskites, the shape of the spacer cation is still subject to limitations due to the size of the inorganic pocket between four adjacent corner-sharing octahedra. To investigate the effect of the spacer cation branching on the formation of Ruddlesden–Popper (RP) structures, we performed a comprehensive investigation of structures formed using tert-butyl ammonium (t- BA). We demonstrate that in contrast to pure bromides and pure iodides, the use of mixed halides enables the formation of the t-BA2PbBr2I2 RP perovskite structure with the specific ordering of the bromide and iodide anions. The t-BA spacer, despite its branched and bulky shape that prevents its deeper penetration, is able to form significant H-bonds that lead to the stabilization of the RP assembly if the inorganic pocket is designed in such a way that the bromide anions occupy terminal axial positions, while the iodides occupy equatorial positions. We obtain excellent agreement between experimentally determined and theoretically predicted structures using global optimization via a minima hopping algorithm for layered perovskites, illustrating the ability to predict the structure of RP perovskites and to manipulate the perovskite structure by the rational design of the inorganic pocket.

Various phosphonic acid based self-assembled monolayers (SAMs) have been commonly used for interface modifications in inverted perovskite solar cells. This typically results in significant enhancement of the hole extraction and consequent increase in the power conversion efficiency. However, the surface coverage and packing density of SAM molecules can vary, depending on the chosen SAM material and underlying oxide layer. In addition, different SAM molecules have diverse effects on the interfacial energy level alignment and perovskite film growth, resulting in complex relationships between surface modification, efficiency, and lifetime. Here we show that ethanolamine surface modification combined with [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) results in significant improvement in device stability compared to devices with 2PACz modification only. The significantly smaller size of ethanolamine enables it to fill any gaps in 2PACz coverage and provide improved interfacial defect passivation, while its different chemical structure enables it to provide complementary effects to 2PACz passivation. Consequently, the perovskite films are more stable under illumination (slower photoinduced segregation), and the devices exhibit significant stability enhancement. Despite similar power conversion efficiencies (PCE) between 2PACz only and combined ethanolamine-2PACz modification (PCE of champion devices ∼21.6–22.0% for rigid and ∼20.2–21.0% for flexible devices), the T80 lifetime under simulated solar illumination in ambient is improved more than 15 times for both rigid and flexible devices.

Emerging contaminants such as nanoplastics and nanoparticles likely experience similar environmental behaviours, fate and effects but our knowledge of their combined toxicity is scanty. This study, therefore, investigated the joint toxicity of polystyrene nanoplastics (PNPs) and zinc oxide nanoparticles (ZnO-NPs) to an ecologically important rotifer Brachionus koreanus, and compared with the joint toxicity of PNPs and Zn ions (Zn-IONs from ZnSO

Coated zinc oxide nanoparticles (ZnO-NPs) are more commonly applied in commercial products but current risk assessments mostly focus on bare ZnO-NPs. To investigate the impacts of surface coatings, this study examined acute and chronic toxicities of six chemicals, including bare ZnO-NPs, ZnO-NPs with three silane coatings of different hydrophobicity, zinc oxide bulk particles (ZnO-BKs), and zinc ions (Zn-IONs), toward a marine copepod, Tigriopus japonicus. In acute tests, bare ZnO-NPs and hydrophobic ZnO-NPs were less toxic than hydrophilic ZnO-NPs. Analyses of the copepod's antioxidant gene expression suggested that such differences were governed by hydrodynamic size and ion dissolution of the particles, which affected zinc bioaccumulation in copepods. Conversely, all test particles, except the least toxic hydrophobic ZnO-NPs, shared similar chronic toxicity as Zn-IONs because they mostly dissolved into zinc ions at low test concentrations. The metadata analysis, together with our test results, further suggested that the toxicity of coated metal-associated nanoparticles could be predicted by the hydrophobicity and density of their surface coatings. This study evidenced the influence of surface coatings on the physicochemical properties, toxicity, and toxic mechanisms of ZnO-NPs and provided insights into the toxicity prediction of coated nanoparticles from their coating properties to improve their future risk assessment and management.

Developing dopant-free hole-transporting materials (HTMs) for high-performance perovskite solar cells (PVSCs) has been a very active research topic in recent years since HTMs play a critical role in optimizing interfacial charge carrier kinetics and in turn determining device performance. Here, a novel dendritic engineering strategy is first utilized to design HTMs with a D-A type molecular framework, and diphenylamine and/or carbazole is selected as the building block for constructing dendrons. All HTMs show good thermal stability and excellent film morphology, and the key optoelectronic properties could be fine-tuned by varying the dendron structure. Among them, MPA-Cz-BTI and MCz-Cz-BTI exhibit an improved interfacial contact with the perovskite active layer, and non-radiative recombination loss and charge transport loss can be effectively suppressed. Consequently, high power conversion efficiencies (PCEs) of 20.8% and 21.35% are achieved for MPA-Cz-BTI and MCz-Cz-BTI based devices, respectively, accompanied by excellent long-term storage stability. More encouragingly, ultrahigh fill factors of 85.2% and 83.5% are recorded for both devices, which are among the highest values reported to date. This work demonstrates the great potential of dendritic materials as a new type of dopant-free HTMs for high-performance PVSCs with excellent FF.

Summary Simultaneously improving device efficiency and stability is the most important issue in perovskite solar cell (PSC) research. Here, we strategically introduce a multi-functional interface layer (MFIL) with integrated roles of: (1) electron transport, (2) moisture barrier, (3) near-infrared photocurrent enhancement, (4) trap passivation, and (5) ion migration suppression to enhance the device performance. The narrow-band-gap non-fullerene acceptor, Y6, was screened out to replace the most commonly used PCBM in the inverted PSCs. A significantly improved power conversion efficiency of 21.0% was achieved, along with a remarkable stability (up to 1,700 h) without encapsulation under various external stimuli (light, heat, and moisture). Furthermore, systematic studies of the molecular orientation or passivation and the charge carrier dynamics at the interface between perovskite and MFIL were presented. These results offer deep insights for designing advanced interlayers and establish the correlations between molecular orientation, interface molecular bonding, trap state density, non-radiation recombination, and the device performance.

Electron transport layers (ETLs) are critical for improving device performance and stability of perovskite solar cells (PVSCs). Herein, a distannylated electron-deficient bithiophene imide (BTI-Tin) is synthesized, which enables us to access structurally novel acceptor–acceptor (A–A) type polymers. Polymerizing BTI-Tin with dibrominated naphthalene diimide (NDI-Br) and perylene diimide (PDI-Br) affords two A–A copolymers P(BTI-NDI) and P(BTI-PDI). The all-acceptor backbone yields both low-lying highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels for the polymers, which combined with their high electron mobility render P(BTI-NDI) and P(BTI-PDI) as promising ETLs for perovskite solar cells (PVSCs). When applied as ETLs to replace the conventional [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) in planar p–i–n PVSCs, the PC61BM-free devices based on P(BTI-NDI) and P(BTI-PDI) achieve remarkable power conversion efficiencies (PCEs) of 19.5% and 20.8%, respectively, with negligible hysteresis. Such performance is attributed to efficient electron extraction and reduced charge recombination. Moreover, the devices based on P(BTI-NDI) and P(BTI-PDI) ETLs show improved stability compared to the PC61BM based ones due to the higher hydrophobicity of the new ETLs. This work provides important guidelines for designing n-type polymers to replace PC61BM as efficient ETLs for high-performance PVSCs with improved stability.

The current hazard assessment of the emerging chemical contaminant, zinc oxide nanoparticles (ZnO-NPs), seldom considers the influence of environmental factors. However, under seasonal variation and global climate change, marine organisms are exposed to a changing environment with different regimes of temperature and salinity. This study, therefore, investigated the toxicity of ZnO-NPs, zinc oxide bulk-particles and zinc ions, to the marine copepod Tigriopus japonicus under the combined influence of temperature and salinity. The toxicity of ZnO-NPs generally increased with increasing temperature. At 15 °C, ZnO-NPs were less toxic because they generated fewer reactive oxygen species (ROS) and the copepods entered dormancy. At 35 °C, ZnO-NPs became more toxic because of their increased ROS production and potential physical impairments associated with the agglomerated particles, in addition to the thermal stress faced by the copepods. Their toxicity generally increased with decreasing salinity, due to their enhanced ion dissolution and osmotic pressure faced by the copepods at low salinity. Hence, ZnO-NPs were most toxic to the copepods at high temperature and low salinity, though temperature was a more influential factor than salinity. Based on the effect thresholds generated from the response surface model with consideration of the joint effect of temperature and salinity, the current marine water quality criteria may not provide adequate protection to marine organisms against ZnO-NPs. Our results provide new insights into the toxicity and modes of action of ZnO-NPs, and highlight the current deficiency of regulations under different regimes of temperature and salinity.

The performance and stability of inverted perovskite solar cells (PSC), in particular, those with stable metal oxide hole transport layers, are limited by the instability of perovskite/electron transport layer heterojunctions. In this work, we demonstrate a successful strategy for passivating and stabilizing the perovskite/electronic transport layer n-type heterojunction in a nickel oxide based inverted planar PSC by using chemically stable inorganic CdxZn1−xSeyS1−y quantum dots (QDs). Experimental and theoretical results demonstrate that the defects/traps (unsaturated Pb2+ and mobile iodine ions) on perovskite surfaces can be substantially suppressed by the QDs, leading to a significant reduction of interfacial recombination and more stable n-type heterojunction. Consequently, a significant enhancement of the open-circuit voltage from 1.075 V to 1.162 V and power conversion efficiency from 19.47% to 21.63% is achieved for the QD passivated perovskite-based devices. We also demonstrate that the stabilized n-type hetero-junction results in a dramatic improvement of long-term and operational device stability. Our work demonstrates an effective and simple way to stabilize the perovskite/electron transport layer interface to develop high efficiency stable inverted planar PSCs, which will bring these devices closer to future commercial applications.

Dion–Jacobson (DJ) perovskites have been demonstrated to be highly promising for improved lifetime and stability of solar cells, but their applications in light emitting diodes (LEDs) have been scarce. A large number of potential spacer ligands have not been explored, offering potential to achieve significant improvements in spectral regions where DJ perovskite-based LEDs lag behind other perovskite counterparts. Therefore, we investigated the effect of the choice of spacer cation on the properties and green light emitting diode applications of DJ perovskites. We found that optimized mixing of the spacer cations results in perovskite films with improved morphology and a change in phase distribution, leading to enhanced funneling and more efficient light emission. Devices containing mixed spacer cations 1,6-hexanediammonium (HDA) and 1,10-decanediammonium (DDA) exhibited significant enhancement of the external quantum efficiency (EQE), with a maximum value for DDA0.75HDA0.25 of 9.41% significantly higher than that obtained for pure HDA (1.23%) and DDA (7.28%), as well as increased lifetime with T50 of 70 min for the optimized composition, compared to 4 min for pure HDA and 60 min for pure DDA. The maximum EQE can be further increased by triphenylphosphine oxide passivation to 12.85%.

Two-dimensional lead halide perovskites are promising materials for optoelectronics due to the tunability of their properties with the number of lead halide layers and the choice of an organic spacer. Physical understanding for the rational design of materials primarily requires knowledge of crystal structure. Two-dimensional lead halide perovskites are usually prepared in the form of films, complicating the experimental determination of structure. To enable theoretical studies of experimentally unresolvable structures as well as high-throughput virtual screening, we present an algorithm for crystal structure prediction of lead halide perovskites. Using an automatically prepared classical potential we show that our algorithm enables fast access to a structure that can be used for further first-principles studies.

Hybrid organic–inorganic perovskites have attracted great attention as the next generation materials for photovoltaic and light-emitting devices. However, their environment instability issue remains as the largest challenge for practical applications. Recently emerging two- dimensional (2D) perovskites with Ruddlesden– Popper structures are found to greatly improve the stability and aging problems. Furthermore, strong confinement of excitons in these natural quantum-well structures results in the distinct and narrow light emission in the visible spectral range, enabling the development of spectrally tunable light sources. Besides the strong quasi- monochromatic emission, some 2D perovskites composed of the specific organic cations and inorganic layer structures emit a pronounced broadband emission. Herein, we report the light- emitting properties and the degradation of low- dimensional perovskites consisting of the three shortest alkylammonium spacers, mono- ethylammonium (EA), n-propylammonium (PA), and n- butylammonium (BA). While (BA)2PbI4 is known to form well-oriented 2D thin films consisting of layers of corner-sharing PbI6 octahedra separated by a bilayer of BA cations, EA with shorter alkyl chains tends to form other types of lower- dimensional structures. Nevertheless, optical absorption edges of as-prepared fresh EAPbI3, (PA)2PbI4, and (BA)2PbI4 are obviously blue- shifted to 2.4–2.5 eV compared to their 3D counterpart, methylammonium lead iodide (MAPbI3) perovskite, and they all emit narrow excitonic photoluminescence. Furthermore, by carefully optimizing deposition conditions, we have achieved a predominantly 2D structure for (PA)2PbI4. However, unlike (BA)2PbI4, upon exposure to ambient environment, (PA)2PbI4 readily transforms to a different crystal structure, exhibiting a prominently broadband light from ∼500 to 800 nm and a gradual increase in intensity as structural transformation proceeds.

Simultaneously improving efficiency and stability, which are particularly crucial factors for the commercialization of perovskite solar cells (PSCs), remains a major challenge. For high-efficiency normal PSCs, the development of stable dopant-free hole-transport materials (HTMs) seems imperative. Here, we developed potential donor-acceptor small molecules (BTTI) as HTMs for normal planar PSCs. Through tailoring its alkyl side-chain length as BTTI-C6, BTTI-C8, and BTTI-C12, our results show that upon shortening the side chain of BTTI, the hole mobility, film-forming capability, and resultant device performance were remarkably improved, with the device conversion efficiencies of 19.69% for BTTI-C6, 18.89% for BTTI-C8, and 17.49% for BTTI-C12. Meanwhile, compared to those made with the routine doped Spiro-OMeTAD, devices based on our dopant-free HTMs exhibited significantly improved stability. This work paves the way to the development of effective dopant-free HTMs for high-performance PSCs.

We demonstrate a simple and inexpensive method of surface polarity control of ZnO grown by pulsed laser deposition (PLD). The polarity control is achieved in a straightforward way by changing the thickness of MgO buffer layer. The Zn- and O-polar ZnO films possess very distinct growth rate, electron concentration and mobility as well as different defect structures. These different structural and electronic properties result in significant differences in surface reactivity and device performance. For example, Pd Schottky diodes fabricated onto the O-polar ZnO film exhibit lower barrier height and ideality factor compared with the equivalent Zn-polar devices, while methylammonium lead iodide perovskite films are readily formed on O-terminated and rapidly decompose on Zn-terminated surfaces. This can be attributed to higher photocatalytic activity of Zn-terminated surface, as well as higher surface coverage of adsorbed hydroxyl groups. Consequently, our results indicate that polarity engineering to obtain favorable O-terminated surface can result in improved performance of ZnO-containing optoelectronic devices, while Zn-terminated surfaces could be of interest for photocatalytic and sensing applications.

Doping in organic–inorganic perovskite semiconductors is an effective method to tailor their optoelectronic properties. In this work, manganese-doped perovskite films with different Mn/Pb ratios ranging from 0% to 2% were systematically studied. The device performance of 0.2% Mn-doped devices was improved compared to that of a device without Mn. However, a further increase of the doping concentration induced a decrease in performance. Several characteristics (especially different scanning probe microscopy characteristics) reveal that an increased dopant concentration results in reduced crystallinity and a change in the film morphology and causes a deterioration in photovoltaic performance for higher dopant concentrations. In the best-performing samples (0.2%), a shift in the valence band level and band gap are found which are responsible for the increased open circuit voltage, while increased grain boundaries and lower surface charge density are responsible for a small reduction in the short circuit current. Thus, multifunctional scanning probe microscopy approaches, combined with different film characterization techniques, offer us effective tools to investigate the impact of doping in the perovskite materials and the corresponding device performance.

Coated zinc oxide nanoparticles (ZnO-NPs) are more commonly applied in commercial products but current risk assessments mostly focus on bare ZnO-NPs. To investigate the impacts of surface coatings, this study examined acute and chronic toxicities of six chemicals, including bare ZnO-NPs, ZnO-NPs with three silane coatings of different hydrophobicity, zinc oxide bulk particles (ZnO-BKs), and zinc ions (Zn-IONs), toward a marine copepod

Perovskite solar cells (PSCs) are known to be sensitive to the exposure to ambient humidity, which typically results in the degradation and deterioration of performance, although positive effects of exposure to moisture have also been reported, due to recrystallization of the perovskite. Common approach to improve stability is to use 3D/2D perovskite active layer, where 2D capping layer is prepared by spin coating the bulky organic cation halide. Herein, it is shown that optimizing the exposure of the capping layer prepared by spin coating phenylethylammonium iodide (PEAI) to ambient atmosphere results in substantial improvement of the PSC performance. Furthermore, the initial effects of PEAI treatment are dependent on the NiO x /perovskite interface, but in all cases except at very high humidity (80– 85% RH) optimized exposure to ambient results in improved performance. The variations in device performance with PEAI treatment and ambient exposure can be attributed to defect passivation and changes in the charge extraction due to energy-level alignment at the interfaces. The best performing devices have passivation of NiO x /perovskite interface and PEAI treatment of top surface followed by exposure to ambient atmosphere at RH of 40–45%, which results in the power conversion efficiency increase from 20.3% to 22.4%.

The nonlinear optical properties of low-dimensional polycrystalline halide perovskite films consisting of ethylammonium (EA) and butylammonium (BA) cations are investigated using Z-scan technique. Across the band-edge, two-dimensional (BA)2PbI4 exhibits a transition from saturable absorption (SA) to reverse-SA and its nonlinear absorption and nonlinear refractive index are much smaller than those of bulk counterparts. Meanwhile, EAPbI3 with one-dimensionality of the inorganic structure shows the SA behavior both above and below band-edge and the estimated nonlinear optical parameters of polycrystalline EAPbI3 are comparable to those of single-crystalline ones, attributed to high dielectric contrast between the inorganic and organic elements in one-dimensional structures.

This work reports the impact of electron transport layers (ETLs) on the performance of perovskite solar cells (PSCs). The ETLs are based on tin (IV) oxide (SnO 2 ) prepared in different nanostructures. The carrier transport properties of PSCs are systematically characterized and the underlying mechanism for the enhancement in performance of PSCs is found. The strategies for optimizing the interface between the ETL and perovskite are demonstrated, yielding a champion device with a power conversion efficiency (PCE) of 20.8 %.

The effect of alkylammonium tail length in phenyl-alkyl spacer cations in quasi-2D Ruddlesden–Popper perovskites on the phase distribution in low n films (n = 2 stoichiometry) is investigated. An increase in alkyl chain length suppresses the formation of the n = 1 phase (and consequently higher n phases), which is attributed to the change in the packing arrangement of spacer cations from parallel (one and two carbon atom alkyl chains) to non-parallel (3 carbon atom alkyl chains). A single blue emission peak corresponding to the n = 3 phase (466 nm) and n = 2 phase (436 nm) is obtained in the PL spectra of phenylpropylammonium quasi-2D perovskites with methylammonium (MA) and formamidinium (FA) cations, respectively. The same trends in phase distribution, namely a reduction in the proportion of the n = 1 phase with increasing alkyl chain length, are observed for both MA- and FA-based perovskites. However, FA-based samples exhibited higher crystallinity but worsened morphology (more pinholes) and less efficient funneling compared to MA-based samples. Consequently, efficient sky-blue LEDs with the highest EQE of 3.35% are obtained for PPA2MAPb2Br7 perovskite.

In lead halide perovskite solar cells (PSCs), the valence band maximum of NiOx matches well with that of MAPbI3 or FAPbI3, while its conduction band minimum is much higher than that of the perovskite materials. Consequently, it can serve the function of hole transport layers (HTL), as well as light-in window of p-i-n inverted planar PSCs owing to its large band gap of 3.7 eV. In this work, MAPbI3 and mixed cation FA0.85MA0.15Pb(Br0.15I0.85)3 devices with room temperature solution processed NiOx as HTL were fabricated in a typical device structure of “ITO ⧹ NiOx ⧹ Perovskites ⧹ PC61BM ⧹ Zirconium (IV) Acetylacetonate ⧹ Ag”. Both kinds of devices exhibit excellent performance with a champion cells conversion efficiency of 19.45% and 17.77% for the FAMA and the pure MA, respectively. The hole extraction ability of NiOx as HTLs was extensively characterized by different techniques, and it was confirmed that room temperature solution processed NiOx serves as an excellent HTL in the inverted planar PSCs.

Various kinds of semiconductor materials, organic and inorganic, served effectively as electrons or holes transport materials for perovskite solar cells (PSCs). However, their direct function has rarely been reported other than examining their effect in the final photovoltaic devices. In this work, a general and facile method was employed to determine to a point the type of carriers transferred by both SnO2 and NiO popular charge transport materials in PSCs via scanning Kelvin probes microscopy. The sign of the increment of the surface potential voltage measured tells directly whether electrons or holes were extracted by these carrier transport materials while its mapping can also provide the extraction difference between grain interiors and grain boundaries. Both MAPbI3 and CsFAMA triple cation perovskites were involved in the test with the same conclusion. Along with time-resolved photoluminescence, the extraction rate of each kind of material can be distinguished. This work definitely offers us a gener...

In this work, we report systematic studies on improving the optical and electrical properties of four-terminal perovskite/c-Si tandem solar cells. Light harvesting power of the device is significantly enhanced due to the complementary absorption spectra of the perovskite and c-Si absorber materials. To obtain high power conversion efficiency (PCE) for the device, careful engineering of optoelectronic properties of the devices are accomplished through: 1. Oxygen annealing treatment for reducing defect density of perovskite materials; 2. Optical engineering of the transparent electrode (MoO3/Au/MoO3) to obtain high transmission at long wavelengths for the tandem solar cell applications; and 3. Enhancement of light harvesting power achieved by using the novel biomimicking elastomeric petals as the light trapping layer. The individual perovskite solar cell (PSC) with MoO3/Au/MoO3 electrode with or without light trapping layer yields an average PCE of 16.6% and 16.0% respectively. By combining c-Si bottom cell with perovskite top cell mechanically, an overall PCE of 22.4% is achieved for the averaged value, which is a promising result for future development of perovskite based tandem solar cells.

We synthesized mesoporous silica nanospheres (MSNs) with small particle size (under 100 nm) and large surface areas (>800 m2/g) by modified Stober method. We investigated coating of oxygen adsorber materials (iron-based and titania-based) by atomic layer deposition on the prepared MSNs. We found that MSNs without any coating are capable of adsorbing oxygen by physisorption, and that due to their high surface areas they can outperform commercial oxygen scavengers for atmospheres with moderate and low humidity levels. Their performance is further enhanced for optimized thickness of FeOx or TiOx coating, where chemisorption contributes to oxygen scavenging process. To further investigate the oxygen adsorption on MSNs, samples with different annealing times were prepared and characterized, and the oxygen adsorption could be attributed to incomplete removal of silicon precursor residue. While the samples with prolonged annealing time do not exhibit oxygen adsorption, the high oxygen adsorption capacity can be restored by glucose treatment which results in carbon-based surface coating of MSNs. Due to their fast response and high oxygen adsorption capacity, the prepared materials are highly promising as oxygen scavengers, in particular for applications in dry environments where humidity activation is undesirable.

The performance of quasi-2D perovskite light emitting diodes (LEDs) with mixed small cations, cesium and formamidinium (FA), is significantly affected by their ratio. The best devices obtained for Cs:FA ratio of 1:1 exhibit a maximum external quantum efficiency (EQE) of 12.1%, maximum luminance of 15 070 cd m−2 and maximum current efficiency of 46.1 cd A−1, which is significantly higher (about 3 times) compared to devices with FA only (maximum EQE of 4.1%, maximum luminance of 4521 cd m−2) and Cs-only (maximum EQE of 4.0%, maximum luminance of 4886 cd m−2). The photoluminescence quantum yield of the Cs:FA 1:1 sample is similarly enhanced, 21.3% compared 5.4% and 6%, for FA-only and Cs-only samples, respectively. It can be observed that the Cs:FA ratio significantly affects the crystallization of the perovskite, with the optimal 1:1 ratio resulting in the formation of tetragonal Cs0.5FA0.5PbBr3 phase (different from cubic FAPbBr3 and orthorhombic CsPbBr3) with pronounced preferential orientation as well as a significant reduction in the trap density, which leads to a substantial improvement in the light- emitting performance.

In this study, detailed investigations of low-frequency noise (LFN) characteristics of hybrid chemical vapor deposition (HCVD)- and solution-grown CH3NH3PbI3 (MAPI) solar cells are reported. It has been shown that LFN is a ubiquitous phenomenon observed in all semiconductor devices. It is the smallest signal that can be measured from the device; hence, systematic characterization of the LFN properties can be utilized as a highly sensitive nondestructive tool for the characterization of material defects in the device. It has been demonstrated that the noise power spectral densities of the devices are critically dependent on the parameters of the fabrication process, including the growth ambient of the perovskite layer and the incorporation of the mesoscopic structures in the devices. Our experimental results indicated that the LFN arises from a thermally activated trapping and detrapping process, resulting in the corresponding fluctuations in the conductance of the device. The results show that the presenc...

We demonstrate an evaporation-based combinatorial approach for fast screening of precursor combinations for the synthesis of novel perovskite materials. Nine material combinations can be explored simultaneously, which enabled us to synthesize nine different lead-free perovskite compounds. The structural properties (morphology, crystal structure) and optical properties (UV–vis absorption spectra, photoluminescence) of the prepared materials were investigated. Among these materials, several Sn-based and Pd-based perovskites exhibit strong absorption in the visible spectral range and thus may be of interest for photovoltaic applications. In addition, butyl ammonium tin iodide exhibits bright red emission, and it is of interest for potential light emitting applications.

We demonstrate that annealing at 850 °C in the presence of Cu universally results in robust antibacterial activity under ambient illumination for TiO2 nanoparticles, different from those annealed in a quartz crucible without metal or in the presence of Ti. Resulting robust antibacterial activity occurred after annealing regardless of the initial properties and crystal structure of the starting samples (two anatase, one rutile, and P25). A clear difference in the powder color from white to gray and a pure rutile crystal structure is observed after annealing in all of the samples. ESR measurements, however, reveal obvious differences in the defects present in the samples annealed under different conditions. Strong antibacterial activity is observed under ambient illumination for samples annealed in the presence of Cu, despite the lower activity for photocatalytic degradation of common dyes such as methylene blue after annealing. Antibacterial activity could not be attributed to the presence of Cu (no activi...

We investigated transmission electron microscopy artifacts obtained using standard sample preparation protocols applied to the investigation of Escherichia coli cells exposed to common nanomaterials, such as TiO2, Ag, ZnO, and MgO. While the common protocols for some nanomaterials result only in known issues of nanomaterial-independent generation of anomalous deposits due to fixation and staining, for others, there are reactions between the nanomaterial and chemicals used for post-fixation or staining. Only in the case of TiO2 do we observe only the known issues of nanomaterial-independent generation of anomalous deposits due to exceptional chemical stability of this material. For the other three nanomaterials, different artifacts are observed. For each of those, we identify causes of the observed problems and suggest alternative sample preparation protocols to avoid artifacts arising from the sample preparation, which is essential for correct interpretation of the obtained images and drawing correct conclusions on cell-nanomaterial interactions. Finally, we propose modified sample preparation and characterization protocols for comprehensive and conclusive investigations of nanomaterial-cell interactions using electron microscopy and for obtaining clear and unambiguous revelation whether the nanomaterials studied penetrate the cells or accumulate at the cell membranes. In only the case of MgO and ZnO, the unambiguous presence of Zn and Mg could be observed inside the cells.

Perovskite solar cell research has been attracting increasing attention in recent years. In this review paper, we will provide an overview of the recent developments in terms of material composition, deposition techniques, and the device architecture (the choice of charge transport layers and electrodes). Then, we will critically discuss some of the major problems, namely device stability, hysteresis, environmental implications due to the presence of a toxic metal (lead), and difficulties in fabrication of large area and/or flexible devices. In addition, we will also discuss tandem cells and modules, as well as the application of perovskites in other devices and the integration of perovskite solar cells with other devices. Finally, we discuss future outlook and important issues which need to be addressed for the wide scale applications of these devices. Lifetime and stability are identified as the key issue to be addressed for wide scale applications, and the majority of environmental impact is due to the use of organic solvents or other components in the device, not the lead-containing perovskite absorber. The standardisation of the testing conditions and more studies involving outdoor testing are needed for convincing demonstrations of good stability as opposed to dark storage testing. Another key issue is upscaling and reproducibility of the film preparation, which can be problematic due to high sensitivity of the perovskite film to the processing conditions. To overcome these obstacles multilaboratory collaborative efforts would be highly desirable.

In this paper, systematic investigations on the fabrication and characterization of high performance TiO2 nanorod array perovskite solar cells (NAPSCs) are reported. The TiO2 nanorods, of length around 350–400 nm, were grown by solvothermal technique directly on glass/FTO substrates. From the scanning transmission electron microscopy (STEM) we demonstrate that excellent crystallinity for the TiO2 nanorods can be produced using the solvothermal technique. Precursor consisting of a mixture of PbI2, CH3NH3I (MAI) and CH3NH3Cl (MACl) was used for the growth of perovskite thin films on the glass/FTO/TiO2 nanorod array (TiO2-NA) substrates. It is found that the morphology and quality of the perovskite layer depend strongly on the concentration of MACl in the precursor. Experimental studies on femtosecond transient absorption (fs-TA) indicate that the incorporation of TiO2-NA greatly enhances the collection efficiency of the photo-generated carriers due to substantial increase of interfacial area between the perovskite and TiO2-NA, leading to a reduction in carrier diffusion distance. It is shown to be the key factor that the proposed technique facilitates the use of a thicker perovskite absorber layer (∼500 nm) without compromising on the series resistance. Detailed J–V characterization shows that the NAPSCs exhibit negligible hysteresis with a power conversion efficiency (PCE) >19% for the champion device.

Hollow V2O5 microspheres were successfully synthesized by a solvothermal method and subsequent calcination. The rigid hollow V2O5 cathode prepared in isopropanol solvent exhibited excellent cycling performance and rate capability. Within a voltage window of 2.5 to 4 V, a maximum specific discharge capacity of 128 mA h g−1 was delivered at 1 A g−1. Even after 500 cycles, the capacity retention was 92.2%.