Cs⁺ incorporation into CH₃NH₃PbI₃ perovskite:substitution limit and stability enhancement

In this study we systematically explored the mixed cation perovskite Csx(CH3NH3)1-xPbI3. We exchanged the A-site cation by dipping MAPbI3 films into a CsI solution, thereby incrementally replacing the MA+ in a time-resolved dipping process and analysed the resulting thin-films with UV-Vis, XRD, EDAX, SEM and optical depth-analysis in a high-throughput fashion. Additional in situ UV-Vis and time-resolved XRD measurements allowed us to look at the kinetics of the formation process. The results showed a discontinuity during the conversion. Firstly, small amounts of Cs+ are incorporated into the structure. After a few minutes, the Cs content approaches a limit and grains of δ-CsPbI3 occur, indicating a substitution limit. We compared this cation exchange to a one-step crystallisation approach and found the same effect of phase segregation, which shows that the substitution limit is an intrinsic feature rather than a kinetic effect. Optical and structural properties changed continuously for small Cs incorporations. Larger amounts of Cs result in phase segregation. We estimate the substitution limit of CsxMA1-xPbI3 to start at a Cs ratio x = 0.13, based on combined measurements of EDAX, UV-Vis and XRD. The photovoltaic performance of the mixed cation perovskite shows a large increase in device stability from days to weeks. The initial efficiency of mixed CsxMA1-xPbI3 devices decreases slightly, which is compensated by stability after a few days.</p

Cs⁺ incorporation into CH₃NH₃PbI₃ perovskite:substitution limit and stability enhancement

In this study we systematically explored the mixed cation perovskite Csx(CH3NH3)1−xPbI3.</p

Acquired resistance to PI3K/mTOR inhibition is associated with mitochondrial DNA mutation and glycolysis

Acquired resistance (AQR) to drug treatment occurs frequently in cancer patients and remains an impediment to successful therapy. The aim of this study was to gain insight into how AQR arises following the application of PI3K/mTOR inhibitors. H1975 lung cancer cells with EGFR T790M mutations that confer resistance to EGFR inhibitors underwent prolonged treatment with the PI3K/mTOR inhibitor, BEZ235. Monoclonal cells with stable and increased resistance to BEZ235 were obtained after 8 months treatment. These AQR clones showed class-specific resistance to PI3K/mTOR inhibitors, reduced G1 cell cycle arrest and impedance of migration following PI3K/mTOR inhibition, reduced PTEN expression and increased Akt and S6RP phosphorylation. Transcriptome analysis revealed the AQR clones had increased expression of the metabolite transporters SLC16A9 and SLC16A7, suggestive of altered cell metabolism. Subsequent experiments revealed that AQR clones possess features consistent with elevated glycolysis, including increased levels of glucose, lactate, glutamine, glucose dependence, GLUT1 expression, and rates of post-glucose extracellular acidification, and decreased levels of reactive oxygen species and rates of oxygen consumption. Combination treatment of BEZ235 with the glycolysis inhibitor 3-bromopyruvate was synergistic in AQR clones, but only additive in parental cells. DNA sequencing revealed the presence of a mitochondrial DNA (mtDNA) MT-C01 variant in AQR but not parental cells. Depletion of mitochondrial DNA in parental cells induced resistance to BEZ235 and other PI3K/mTOR inhibitors, and was accompanied by increased glycolysis. The results of this study provide the first evidence that a metabolic switch associated with mtDNA mutation can be an underlying mechanism for AQR

Direct Imaging of the Recombination/Reduction Sites in Porous TiO₂ Electrodes

In photoelectrochemical cells, one major recombination pathway involves a reaction between the photogenerated electrons that diffuse inside the semiconductor electrode and holes, in the form of oxidized ions, which travel in the electrolyte to the counter electrode. Here we present direct imaging of the recombination/reduction sites in two types of porous TiO₂ electrodes, P25 and submicrometer particles, chosen for studying the influence of the TiO₂ particles’ sizes and shapes on the recombination sites. The sites were labeled with 2–5 nm silver particles, electrodeposited on the TiO₂ surface using chronoamperometry. The model assumes that reduction and recombination are similar with respect to the electron transfer from the TiO₂ surface to an ionic electron acceptor in the electrolyte redox mediator/Ag⁺ ion. Consequently the metal deposit marks the reaction locations. This first high-resolution view clearly identifies the connecting points between TiO₂ particles and then the {101} facets as the sites of recombination

Photovoltage Behavior in Perovskite Solar Cells under Light-Soaking Showing Photoinduced Interfacial Changes

The photovoltage of perovskite solar cells (PSCs) was studied over a wide range of light intensities, showing changes from pristine to light-soaking (LS) conditions, explained using a specific model of spatial charge distribution. Migration of ions and vacancies under photovoltage conditions results in localized charge redistribution manifested as positive charge accumulation at the TiO2 or TiO2–MgO interlayer–perovskite interface, signifying photoinduced interfacial upward band bending. Consequentially, generation of an electrostatic potential (Velec) and an increase in interfacial recombination rate are confirmed. The magnitude and effect of Velec and interfacial recombination on the photovoltage depend on the illumination intensity and on the LS duration. PSCs with mesoporous Al2O3 showed similar changes, validating the role of the compact TiO2. Faster generation and a gradual increase of Velec are apparent under LS, which expresses the constant migration of ions and vacancies toward the interface. The nonrigid TiO2–perovskite interface calls for a vital perspective change of PSCs

Rituximab identified as an independent risk factor for severe PJP: A case-control study.

ObjectivePneumocystis jirovecii pneumonia (PJP) was reported among immunosuppressed patients with deficits in cell-mediated immunity and in patients treated with immunomodulatory drugs. The aim of this study was to identify risk-factors for PJP in noninfected HIV patients.MethodsThis retrospective, test negative, case-control study was conducted in six hospitals in Israel, 2006-2016. Cases were hospitalized HIV-negative patients with pneumonia diagnosed as PJP by bronchoalveolar lavage. Controls were similar patients negative for PJP.ResultsSeventy-six cases and 159 controls were identified. Median age was 63.7 years, 65% males, 34% had hematological malignancies, 11% inflammatory diseases, 47% used steroids and 9% received antilymphocyte monoclonal antibodies. PJP was independently associated with antilymphocyte monoclonal antibodies (OR 11.47, CI 1.50-87.74), high-dose steroid treatment (OR 4.39, CI 1.52-12.63), lymphopenia (OR 8.13, CI 2.48-26.60), low albumin (OR 0.15, CI 0.40-0.54) and low BMI (OR 0.80, CI 0.68-0.93).ConclusionIn conclusion, rituximab, which is prescribed for a wide variety of malignant and inflammatory disorders, was found to be significant risk-factor for PJP. Increased awareness of possible PJP infection in this patient population is warranted

Extremely Slow Photoconductivity Response of CH₃NH₃PbI₃ Perovskites Suggesting Structural Changes under Working Conditions

Photoconductivity measurements of CH₃NH₃PbI₃ deposited between two dielectric-protected Au electrodes show extremely slow response. The CH₃NH₃PbI₃, bridging a gap of ∼2000 nm, was subjected to a DC bias and cycles of 5 min illumination and varying dark duration. The approach to steady -state photocurrent lasted tens of seconds with a strong dependence on the dark duration preceding the illumination. On the basis of DFT calculations, we propose that under light + bias the methylammonium ions are freed to rotate and align along the electric field, thus modifying the structure of the inorganic scaffold. While ions alignment is expected to be fast, the adjustment of the inorganic scaffold seems to last seconds as reflected in the extremely slow photoconductivity response. We propose that under working conditions a modified, photostable, perovskite structure is formed, depending on the bias and illumination parameters. Our findings seem to clarify the origin of the well-known hysteresis in perovskite solar cells

Carrier localization on the nanometer-scale limits transport in metal oxide photoabsorbers

Metal oxides are considered as stable and low-cost photoelectrode candidates for hydrogen production by photoelectrochemical solar water splitting. However, their power conversion efficiencies usually suffer from poor transport of photogenerated charge carriers, which has been attributed previously to a variety of effects occurring on different time and length scales. In search for common understanding and for a better photo-conducting metal oxide photoabsorber, CuFeO2, α-SnWO4, BaSnO3, FeVO4, CuBi2O4, α-Fe2O3, and BiVO4 are compared. Their kinetics of thermalization, trapping, localization, and recombination are monitored continuously 100 fs–100 µs and mobilities are determined for different probing lengths by combined time-resolved terahertz and microwave spectroscopy. As common issue, we find small mobilities < 3 cm2V-1s-1. Partial carrier localization further slows carrier diffusion beyond localization lengths of 1–6 nm and explains the extraordinarily long conductivity tails, which should not be taken as a sign of long diffusion lengths. For CuFeO2, the localization is attributed to electrostatic barriers that enclose the crystallographic domains. The most promising novel material is BaSnO3, which exhibits the highest mobility after reducing carrier localization by annealing in H2. Such overcoming of carrier localization should be an objective of future efforts to enhance charge transport in metal oxides.Published versionThe authors acknowledge the financial support for this work from the Helmholtz International Research School "Hybrid Integrated Systems for Conversion of Solar Energy" (HI-SCORE), an initiative co-funded by the Initiative and Networking Fund of the Helmholtz Association (HIRS-0008). M.K. acknowledges funding from the German Bundesministerium fuer Bildung and Forschung (BMBF), project "H2Demo" (no. 03SF0619K). We acknowledge Avner Rothschild for providing lab facilities at the Technion. Open access funding enabled and organized by Projekt DEAL

Open Circuit Potential Build-Up in Perovskite Solar Cells from Dark Conditions to 1 Sun

The high open-circuit potential (<i>V</i>_oc) achieved by perovskite solar cells (PSCs) is one of the keys to their success. The <i>V</i>_oc analysis is essential to understand their working mechanisms. A large number of CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> PSCs were fabricated on single large-area substrates and their <i>V</i>_oc dependencies on illumination intensity, <i>I</i>₀, were measured showing three distinctive regions. Similar results obtained in Al₂O₃ based PSCs relate the effect to the compact TiO₂ rather than the mesoporous oxide. We propose that two working mechanisms control the <i>V</i>_oc in PSCs. The rise of <i>V</i>_oc at low <i>I</i>₀ is determined by the employed semiconductor n-type contact (TiO₂ or MgO coated TiO₂). In contrast, at <i>I</i>₀ close to AM1.5G, the employed oxide does not affect the achieved voltage. Thus, a change of regime from an oxide-dominated <i>E</i>_Fn (as in the dye sensitized solar cells) to an <i>E</i>_Fn, directly determined by the CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> absorber is suggested

High-Resolution Study of TiO₂ Contact Layer Thickness on the Performance of Over 800 Perovskite Solar Cells

In this Letter, we systematically explore the influence of TiO₂ thickness with nanometric variations over a range of 20–600 nm on the photovoltaic parameters (open-circuit voltage, short circuit current, fill-factor, and power conversion efficiency) of CH₃NH₃PbI₃-based solar cells. We fabricate several sample libraries of 13 × 13 solar cells on large substrates with spatial variations in the thickness of the TiO₂ layers while maintaining similar properties for the other layers. We show that the optimal thickness is ∼50 nm for maximum performance; thinner layers typically resulted in short-circuited cells, whereas increasing the thickness led to a monotonic decrease in performance. Furthermore, by assuming a fixed bulk resistivity of TiO₂, we were able to correlate the TiO₂ thickness to the series and shunt resistances of the devices and model the variation in the photovoltaic parameters with thickness using the diode equation to gain quantitative insights