Differential Response of the Photoluminescence and Photocurrent of Polycrystalline CH(3)NH(3)PbI(3 )and CH3NH3PbBr3 to the Exposure to Oxygen and Nitrogen

Because of their excellent photoelectric properties, organic-inorganic metal halide perovskites (MHPs), such as methylammonium lead triiodide, CH3NH3PbI3 (MAPbI(3)), and methylammonium lead tribromide, CH3NH3PbBr3 (MAPbBr(3)), are of great interest for the emerging MHPs-based photovoltaic technology. Despite extensive research efforts focused on physicochemical aspects of both MAPbI(3) and MAPbBr(3), the impact of environmental extremes, including various gaseous media, on their photo-electric properties remains poorly understood. In this context, here, the MHPs-based gas-sensing elements were grown by one-step solution process on the outer surface of cylindrical in shape quartz substrates with diameters varying in the range of 80-1100 mu m. The elongated cylinder-shaped geometry and high surface-to-volume ratios of the thus-prepared deposits revealed advantageous for designing miniature, light-transparent gas-flow chambers and made it possible to investigate the photoluminescence (PL) and photocurrent (PC) responses of both MHPs exposed to the precisely controlled recurrent flow of either O-2 or N-2. In addition, we could also collect the PL responses for the deposits of MAPbI(3 )and MAPbBr(3), positioned side-by-side close to each other and therefore simultaneously exposed to identical environmental conditions. Specifically, we found that under exposure to O-2 the PL responses of MAPbI(3) and MAPbBr(3 )were markedly opposite; i.e., the PL decreased for MAPbI(3), whereas it increased for MAPbBr(3). In contrast, under the exposure to N-2, the PL of MAPbI(3 )increased, while it decreased for MAPbBr(3). A considerably differential behavior was also found for the PC responses. In particular, under recurrent exposures to both gaseous media, the PL and PC responses of MAPbBr(3) correlated, whereas for MAPbI(3) they anticorrelated. In conclusion, the distinctly opposite PL and PC responses of polycrystalline deposits of MAPbI(3) and MAPbBr(3 )to O-2 and N-2 reported herein point to markedly contrasting properties of the surface carrier traps and defects for these two MHPs. This study also evidences that a side-by-side arrangement of elongated cylindrically shaped substrates coated with two different MHPs, due to their differential responses to exposure to O-2 or N-2, can function as a simple differential gas detector

Fighting Health Hazards in Lead Halide Perovskite Optoelectronic Devices with Transparent Phosphate Salts

Organic-inorganic lead halide perovskite (CH3NH3PbI3) solar cells have surpassed 25% power conversion efficiency, being ready for industrial-scale production of cheap photovoltaic (PV) panels. In this action, the major hurdle is its lead content, which in case of device failure, could be washed into the soil, entering the food chain. Since there is a zero tolerance on lead in the human organism, this health hazard is a critical obstacle for commercialization. Here, we propose a solution to this problem by incorporating phosphate salts (e.g., (NH4)(2)HPO4) in PV and other perovskite-based optoelectronic devices in various architectures. Phosphate salts do not react with CH3NH3PbI3 and do not alter its advantageous optoelectronic properties, but in a wet environment, they react immediately with lead, forming a highly insoluble compound, precluding this way the spread of lead into the environment. It is expected that this study will stimulate research, enabling lead halide perovskite solar cells to reach a similar environmental risk category as the commercially available, nonwater-soluble heavy metal-containing CdTe and gallium diselenide technologies

Characterization of Fe2+ ions in Fe,H/SSZ-13 zeolites: FTIR spectroscopy of CO and NO probe molecules

The IR spectra of adsorbed CO and NO probe molecules were used to characterize the coordination chemistry of Fe2+ ions in solution ion exchanged Fe,H/SSZ-13 zeolites. The effects of Fe ion exchange levels, as well as the sample pre-treatment conditions, on the adsorption of these probe molecules were investigated. The ion exchange levels (in the range of the study) did not affect significantly the IR spectra of either probe molecule, and the IR features and their intensity ratios were very similar. Experiments with both probe molecules substantiated the presence of two distinct types of Fe2+ ions in cationic positions. We assign these two Fe2+ ions to two distinct cationic positions: Fe2+ in 6R and 8R positions. NO initially adsorbs preferentially onto Fe2+ sites in the 6R position, and then populates sites in the 8R. Fe2+ ions in the 8R positions require the interaction of more than one NO molecule to move them out from their adsorbate-free cationic positions. As soon as they move from their stable positions, they are able to bind to multiple NO molecules, and form mostly tri-nitrosyls. These tri-nitrosyls, however, are only stable in the presence of gas phase NO; under dynamic vacuum they lose one of the NO molecules from their coordination sphere and form stable di-nitrosyls. The adsorption of CO is much weaker on Fe2+ sites than that of NO, and requires cryogenic sample temperatures to initiate CO adsorption. Under the conditions applied in this study, only mono-carbonyl formation was observed. Reduction in H2 at 773 K increased the number of Fe2+ adsorption sites, primarily in the 8R locations. Oxidation by N2O, on the other hand, selectively reduced the adsorption of both CO and NO on the Fe2+ sites in 8R positions. Adsorbed oxygen left behind from the decomposition of N2O at 573 K readily reacted with CO to produce CO2 even at 150 K.clos

Competitive ion-exchange of manganese and gadolinium in titanate nanotubes

Homogeneous Mn2+ and Gd3+ intercalation of scroll-type trititanate nanotubes using a post-synthesis ion exchange method is reported. Compared to Mn2+, Gd3+ ion-exchange shows larger saturation intercalation levels. Upon co-doping, weak interactions between the dopant ions were found to modify the incorporated concentrations. Electron spin resonance (ESR) measurements, performed at several frequencies, confirmed the homogeneous distribution of Mn2+ and Gd3+. Detailed simulation of ESR spectra identified a large spread of the local structural distortions of the occupied sites as a result of a wide range of curvature radii of the titanate nanotubes. (C) 2016 Elsevier B.V. All rights reserved

Radiation detection and energy conversion in nuclear reactor environments by hybrid photovoltaic perovskites

Detection and direct power conversion of high energy and high intensity ionizing radiation could be a key element in next generation nuclear reactor safety systems and space-born devices. For example, the Fukushima catastrophe in 2011 could have been largely prevented if 1% of the reactor's remnant radiation (gamma-rays of the nuclear fission) were directly converted within the reactor to electricity to power the water cooling circuit. It is reported here that the hybrid halide perovskite methylammonium lead triiodide could perfectly play the role of a converter. Single crystals were irradiated by a typical shut-down gamma-spectrum of a nuclear reactor with 7.61 x 10(14) Bq activity exhibit a high-efficiency of gamma-ray to free charge carrier conversion with radiation hardening. The power density of 0.3 mW/kg of methylammonium lead triiodide at 50 Sv/h means a four times higher efficiency than that for silicon-based cells. The material was stable to the limits of the experiment without changing its performance up to 100 Sv/h dose rate and 57 Sv H*(10) ambient total gamma-dose. Moreover, the gamma-shielding performance of methylammonium lead triiodide was found to be superior to both ordinary and barite concrete

Three-Dimensionally Enlarged Photoelectrodes by a Protogenetic Inclusion of Vertically Aligned Carbon Nanotubes into CH3NH3PbBr3 Single Crystals

We demonstrate that single crystals of methylammonium lead bromide (MAPbBr(3)) could be grown directly on vertically aligned carbon nanotube (VACNT) forests. The fast-growing MAPbBr3 single crystals engulfed the protogenetic inclusions in the form of individual CNTs, thus resulting in a three-dimensionally enlarged photosensitive interface. Photodetector devices were obtained, detecting low light intensities (similar to 2.0 nW) from the UV range to 550 nm. Moreover, a photocurrent tivaS recorded at zero external bias voltage which points to the plausible formation of a p-n junction resulting from interpenetration of MAPbBr(3) single crystals into the VACNT forest. This reveals that vertically aligned CNTs can be used as electrodes in operationally stable perovskite-based optoelectronic devices and can serve as a versatile platform for future selective electrode development

Light-Emitting Electrochemical Cells of Single Crystal Hybrid Halide Perovskite with Vertically Aligned Carbon Nanotubes Contacts

Based on the reported ion migration under an electric field in hybrid lead halide perovskites we have developed a bright, light-emitting electrochemical cell with CH3NH3PbBr3 single crystals directly grown on vertically aligned carbon nanotube forests as contact electrodes. Under the applied electric field, charged ions in the crystal drift and accumulate in the vicinity of the electrodes, resulting in an in operando formed p-i-n heterojunction. The decreased interface energy barrier and the strong charge injection due to the CNT tip enhanced electric field result in a bright green light emission up to 1800 cd/m(2) at room temperature (average approximate to 60 cd/m(2)). Beyond the light emission, this original device architecture points to the possibility of implementing vertically aligned CNTs as electrodes in operationally stable perovskite-based optoelectronic devices

Light-induced charge transfer at the CH3NH3PbI3/TiO2 interface-a low-temperature photo-electron paramagnetic resonance assay

The performance of organic-inorganic metal halide perovskites-based (MHPs) photovoltaic devices critically depends on the design and material properties of the interface between the light-harvesting MHP layer and the electron transport layer (ETL). Therefore, the detailed insight into the transfer mechanisms of photogenerated carriers at the ETL/MHP interface is of utmost importance. Owing to its high charge mobilities and well-matched band structure with MHPs, titanium dioxide (TiO2) has emerged as the most widely used ETL material in MHPs-based photovoltaic devices. Here, we report a contactless method to directly track the photo-carriers at the ETL/MHP interface using the technique of low-temperature electron paramagnetic resonance (EPR) in combination with in situ illuminations (Photo-EPR). Specifically, we focus on a model nanohybrid material consisting of TiO2-based nanowires (TiO(2)NWs) dispersed in the polycrystalline methylammonium lead triiodide (MAPbI(3)) matrix. Our approach is based on observation of the light-induced decrease in intensity of the EPR signal of paramagnetic Ti3+ (S=1/2) in non-stoichiometric TiO(2)NWs. We associate the diminishment of the EPR signal with the photo-excited electrons that cross the ETL/MHP interface and contribute to the conversion of Ti3+ states to EPR-silent Ti2+ states. Overall, we infer that the technique of low-temperature Photo-EPR is an effective strategy to study the transfer mechanisms of photogenerated carriers at the ETL/MHP interface in MAPbI(3)-based photovoltaic and photoelectronic systems

Pressure-induced transformation of CH3NH3PbI3: the role of the noble-gas pressure transmitting media

The photovoltaic perovskite, methylammonium lead triiodide [CH3NH3PbI3 (MAPbI(3))], is one of the most efficient materials for solar energy conversion. Various kinds of chemical and physical modifications have been applied to MAPbI(3) towards better understanding of the relation between composition, structure, electronic properties and energy conversion efficiency of this material. Pressure is a particularly useful tool, as it can substantially reduce the interatomic spacing in this relatively soft material and cause significant modifications to the electronic structure. Application of high pressure induces changes in the crystal symmetry up to a threshold level above which it leads to amorphization. Here, a detailed structural study of MAPbI(3) at high hydrostatic pressures using Ne and Ar as pressure transmitting media is reported. Single crystal X-ray diffraction experiments with synchrotron radiation at room temperature in the 0-20 GPa pressure range show that atoms of both gaseous media, Ne and Ar, are gradually incorporated into MAPbI(3), thus leading to marked structural changes of the material. Specifically, Ne stabilizes the high-pressure phase of Ne(x)MAPbI(3) and prevents amorphization up to 20 GPa. After releasing the pressure, the crystal has the composition of Ne(0.97)MAPbI(3), which remains stable under ambient conditions. In contrast, above 2.4 GPa, Ar accelerates an irreversible amorphization. The distinct impacts of Ne and Ar are attributed to differences in their chemical reactivity under pressure inside the restricted space between the PbI6 octahedra

Dry-pressed anodized titania nanotube/CH3NH3PbI3 single crystal heterojunctions: The beneficial role of N doping

Highly ordered, anodically grown TiO2 nanotubes on titanium supports were annealed in ammonia atmosphere in order to incorporate nitrogen doping (≤2 at.%) in the titanium oxide lattice. FESEM micrographs revealed nanotubes with an average outer diameter of 101.5 ± 1.5 nm and an average wall thickness of about 13 nm. Anatase crystals were formed inside the tubes after annealing in ammonia atmosphere for 30 min. With further annealing, rutile peaks appeared due to the thermal oxidation of the foil and rise as the duration of heat treatment was increased. The concentration and chemical nature of nitrogen in the nanotube arrays can be correlated to the optical response of dry-pressed heterojunctions of doped TiO2/CH3 NH3PbI3 single crystals. The N-TiO2/perovskite heterojunction with the highest amount of interstitial nitrogen exhibited an improved photocurrent, indicating the importance of the semiconductor doping-based heterojunction optimization strategies to deliver competitive levels of halide perovskite-based optoelectronic devices to be envisioned for urban infrastructures.Peer reviewed version of the paper: [https://machinery.mas.bg.ac.rs/handle/123456789/4043