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Mixed lead-tin halide perovskites have sufficiently low bandgaps (∼1.2 eV) to be promising absorbers for perovskite-perovskite tandem solar cells. Previous reports on lead-tin perovskites have typically shown poor optoelectronic properties compared to neat lead counterparts: short photoluminescence lifetimes (

Simple Summary The use of ibrutinib has changed the management and clinical history of patients with multiple-treated chronic lymphocytic leukemia (CLL). Nevertheless, an increasing number of patients develop resistance to treatment, with mechanisms still to be fully clarified. Since HSP70 plays a pivotal role in mediating the survival and the progression of CLL, we herein addressed the role of HSP70 and its regulator HSF1 in the development of ibrutinib-mediated resistance. We found an increase in both proteins when the treatment was failing, and thus the disease was progressing. This suggests the involvement of HSP70 in mechanisms of drug resistance. Moreover, we demonstrated that the use, at different levels, of HSP70/HSF1 axis inhibitors could represent a novel rational therapeutic approach to overcome ibrutinib resistance in those patients who relapsed after this type of treatment. Abstract The Btk inhibitor ibrutinib has significantly changed the management of chronic lymphocytic leukemia (CLL) patients. Despite its clinical efficacy, relapses occur, and outcomes after ibrutinib failure are poor. Although BTK and PLCγ2 mutations have been found to be associated with ibrutinib resistance in a fair percentage of CLL patients, no information on resistance mechanisms is available in patients lacking these mutations. The heat shock protein of 70 kDa (HSP70) and its transcription factor heat shock factor 1 (HSF1) play a role in mediating the survival and progression of CLL, as well as taking part in drug resistance in various cancers. We demonstrated that resveratrol and related phenols were able to induce apoptosis in vitro in leukemic cells from CLL untreated patients by acting on the HSP70/HSF1 axis. The same was achieved in cells recovered from 13 CLL patients failing in vivo ibrutinib treatment. HSP70 and HSF1 levels decreased following in vitro treatment, correlating to apoptosis induction. We suggest an involvement of HSP70/HSF1 axis in controlling resistance to ibrutinib in CLL cells, since their inhibition is effective in inducing in vitro apoptosis in cells from ibrutinib refractory patients. The targeting of HSP70/HSF1 axis could represent a novel rational therapeutic strategy for CLL, also for relapsing patients.

Imaging techniques, like electroluminescence and dark lock-in thermography, are valuable quality control tools as they yield quantitative and spatially resolved information about the device. In this paper, we isolated some of the conductive foil–cell interconnections of back-contact solar cells to study the appearance of these intentional failures in electroluminescence, dark lock-in thermography, and series resistance images. It has been found that isolated emitter-to-foil contacts are clearly visible in the three imaging techniques, as they show characteristic features that deviate from the features typical of functioning emitter-to-foil dots. Isolated base-to-foil contacts are instead invisible in the images obtained by electroluminescence and only hardly visible in the images obtained by the other two techniques. Only after a large amount of contacts are isolated, a local current redistribution or drastic series resistance increase is noticeable. Two graphical methods for the automatic identification of isolated emitter-to-foil contacts in electroluminescence, dark lock-in thermography, and series resistance images were also designed, showing a success rate of 97% in the investigated cells. Such techniques could represent useful tools for implementation in inline quality control processes. Moreover, the techniques and conclusions drawn in this paper can be extended to a large number of other conventional and emerging photovoltaic technologies.

International audience; Celebrating 10 years from the technological revolution brought about by the first report of halide perovskite solar cells, Symposium G of the EMRS Spring Meeting 2019 was dedicated to the memory of the late George C. Papavassiliou (Figure 1), a vibrant pioneer in the early days of the field during the 1990s. The Symposium, entitled "Halide Perovskites: low dimensions for devices", to reflect the important potential of these tunable semiconductors in technology, was designed with the intention of bringing together researchers from across all breadths and lengths of the field. From the discovery of new materials to the study of their photophysical properties-from both theory and experiment viewpoints-to more technical studies related to the implementation of perovskites into functional devices, the Symposium highlighted most aspects of the perovskite research that have been actively studied to date. In this respect, the symposium proved successful in providing key opportunities for discussions on progress in new material development as well as to introduce new potential applications beyond optoelectronics, with energy-related developments standing out. Among the 12 invited talks the 56 oral presentations and its 38 poster presentations (including a joint session with Symposium B-Emerging photovoltaics: strategies for more stable devices), the Symposium delivered lively discussion stimulated by the invited researchers who delineated the different themes of the Symposium. B. Lounis showed how the exciton-phonon coupling operates in perovskites, presenting an excellent account on the photo-physics of halide perovskite nanocrystals at the single-particle level 1. On a more applied topic, M. Bodnarchuk explained the intricacies of the synthesis and emission tuning of colloidal perovskite nanocrystals, showing how much the interface interactions between the inorganic perovskite and the organic surfactants can influence the properties, and proposed innovative methodologies on how to control the interactions 2. On the "phonon problem", R. Schaller presented a "high-throughput" study of many perovskite derivatives, experimentally pinpointing the anharmonic nature of the phonons that derive from the dynamically disordered nature of the crystal lattice 3. P. Plochocka covered the excitons present in the perovskites and highlighted very vividly how to manipulate excitons using (enormous) magnetic fields and extract useful information on their binding energy and lifetimes within the perovskite structure 4. Shifting the dimensionality to perovskite nanowires, the presentation of E. Horvath introduced many innovative methods to produce functional perovskite nanowires that can be shaped "at will" to various morphologies, by manipulating the substrate pattern and the surface conditions 5. Figure I.

International audience; Grain size in polycrystalline halide perovskite films is known to have an impact on the optoelectronic properties of the films, but its influence on their soft structural properties and phase transitions is unclear. Here, temperature-dependent X-ray diffraction, absorption, and macro- and micro-photoluminescence measurements are used to investigate the tetragonal to orthorhombic phase transition in thin methylammonium lead iodide films with grain sizes ranging from the micrometer scale down to the tens of nanometer scale. It is shown that the phase transition nominally at approximate to 150 K is increasingly suppressed with decreasing grain size and, in the smallest grains, the first evidence of a phase transition is only seen at temperatures as low as approximate to 80 K. With decreasing grain size, an increasing magnitude of the hysteresis is also seen in the structural and optoelectronic properties when cooling to, and then upon heating from, 100 K. This work reveals the remarkable sensitivity of the optoelectronic, physical, and phase properties to the local environment of the perovskite structure, which will have large ramifications for phase and defect engineering in operating devices.

Halide perovskites are emerging as valid alternatives to conventional photovoltaic active materials owing to their low cost and high device performances. This material family also shows exceptional tunability of properties by varying chemical components, crystal structure, and dimensionality, providing a unique set of building blocks for new structures. Here, highly stable self-assembled lead–tin perovskite heterostructures formed between low bandgap 3D and higher bandgap 2D components are demonstrated. A combination of surface-sensitive X-ray diffraction, spatially resolved photoluminescence, and electron microscopy measurements is used to reveal that microstructural heterojunctions form between high bandgap 2D surface crystallites and lower bandgap 3D domains. Furthermore, in situ X-ray diffraction measurements are used during film formation to show that an ammonium thiocyanate additive delays formation of the 3D component and thus provides a tunable lever to substantially increase the fraction of 2D surface crystallites. These novel heterostructures will find use in bottom cells for stable tandem photovoltaics with a surface 2D layer passivating the 3D material, or in energy transfer devices requiring controlled energy flow from localized surface crystallites to the bulk.

Mixed-halide lead perovskites have attracted significant attention in the field of photovoltaics and other optoelectronic applications due to their promising bandgap tunability and device performance. Here, the changes in photoluminescence and photoconductance of solution-processed triple-cation mixed-halide (Cs0.06MA0.15FA0.79)Pb(Br0.4I0.6)3 perovskite films (MA: methylammonium, FA: formamidinium) are studied under solar-equivalent illumination. It is found that the illumination leads to localized surface sites of iodide-rich perovskite intermixed with passivating PbI2 material. Time- and spectrally resolved photoluminescence measurements reveal that photoexcited charges efficiently transfer to the passivated iodide-rich perovskite surface layer, leading to high local carrier densities on these sites. The carriers on this surface layer therefore recombine with a high radiative efficiency, with the photoluminescence quantum efficiency of the film under solar excitation densities increasing from 3% to over 45%. At higher excitation densities, nonradiative Auger recombination starts to dominate due to the extremely high concentration of charges on the surface layer. This work reveals new insight into phase segregation of mixed-halide mixed-cation perovskites, as well as routes to highly luminescent films by controlling charge density and transfer in novel device structures.

Light-emitting diodes based on halide perovskites have recently reached external quantum efficiencies of over 20%. However, the performance of visible perovskite light-emitting diodes has been hindered by non-radiative recombination losses and limited options for charge-transport materials that are compatible with perovskite deposition. Here, we report efficient, green electroluminescence from mixed-dimensional perovskites deposited on a thin (~1 nm) lithium fluoride layer on an organic semiconductor hole-transport layer. The highly polar dielectric interface acts as an effective template for forming high-quality bromide perovskites on otherwise incompatible hydrophobic charge-transport layers. The control of crystallinity and dimensionality of the perovskite layer is achieved by using tetraphenylphosphonium chloride as an additive, leading to external photoluminescence quantum efficiencies of around 65%. With this approach, we obtain light-emitting diodes with external quantum efficiencies of up to 19.1% at high brightness (>1,500 cd m−2). Green perovskite light-emitting diodes with external quantum efficiencies of up to 19.1% at high brightness can be created by depositing an ultrathin layer of strongly polar lithium fluoride between the perovskite and hole-transport layers.