Degradation mechanism of hybrid tin-based perovskite solar cells and the critical role of tin (IV) iodide

Tin perovskites have emerged as promising alternatives to toxic lead perovskites in next-generation photovoltaics, but their poor environmental stability remains an obstacle towards more competitive performances. Therefore, a full understanding of their decomposition processes is needed to address these stability issues. Herein, we elucidate the degradation mechanism of 2D/3D tin perovskite films based on (PEA)0.2(FA)0.8SnI3 (where PEA is phenylethylammonium and FA is formamidinium). We show that SnI4, a product of the oxygen-induced degradation of tin perovskite, quickly evolves into iodine via the combined action of moisture and oxygen. We identify iodine as a highly aggressive species that can further oxidise the perovskite to more SnI4, establishing a cyclic degradation mechanism. Perovskite stability is then observed to strongly depend on the hole transport layer chosen as the substrate, which is exploited to tackle film degradation. These key insights will enable the future design and optimisation of stable tin-based perovskite optoelectronics

One-Year Water-Stable and Porous Bi(III) Halide Semiconductor with Broad-Spectrum Antibacterial Performance

Hybrid metal halide semiconductors are a unique family of materials with immense potential for numerous applications. For this to materialize, environmental stability and toxicity deficiencies must be simultaneously addressed. We report here a porous, visible light semiconductor, namely, (DHS)Bi2I8 (DHS = [2.2.2] cryptand), which consists of nontoxic, earth-abundant elements, and is water-stable for more than a year. Gas- and vapor-sorption studies revealed that it can selectively and reversibly adsorb H2O and D2O at room temperature (RT) while remaining impervious to N2 and CO2. Solid-state NMR measurements and density functional theory (DFT) calculations verified the incorporation of H2O and D2O in the molecular cages, validating the porous nature. In addition to porosity, the material exhibits broad band-edge light emission centered at 600 nm with a full width at half-maximum (fwhm) of 99 nm, which is maintained after 6 months of immersion in H2O. Moreover, (DHS)Bi2I8 exhibits bacteriocidal action against three Gram-positive and three Gram-negative bacteria, including antibiotic-resistant strains. This performance, coupled with the recorded water stability and porous nature, renders it suitable for a plethora of applications, from solid-state batteries to water purification and disinfection

Distinct Behaviour of the Homeodomain Derived Cell Penetrating Peptide Penetratin in Interaction with Different Phospholipids

Penetratin is a protein transduction domain derived from the homeoprotein Antennapedia. Thereby it is currently used as a cell penetrating peptide to introduce diverse molecules into eukaryotic cells, and it could also be involved in the cellular export of transcription factors. Moreover, it has been shown that it is able to act as an antimicrobial agent. The mechanisms involved in all these processes are quite controversial.In this article, we report spectroscopic, calorimetric and biochemical data on the penetratin interaction with three different phospholipids: phosphatidylcholine (PC) and phosphatidylethanolamine (PE) to mimic respectively the outer and the inner leaflets of the eukaryotic plasma membrane and phosphatidylglycerol (PG) to mimic the bacterial membrane. We demonstrate that with PC, penetratin is able to form vesicle aggregates with no major change in membrane fluidity and presents no well defined secondary structure organization. With PE, penetratin aggregates vesicles, increases membrane rigidity and acquires an α-helical structure. With PG membranes, penetratin does not aggregate vesicles but decreases membrane fluidity and acquires a structure with both α-helical and β–sheet contributions.These data from membrane models suggest that the different penetratin actions in eukaryotic cells (membrane translocation during export and import) and on prokaryotes may result from different peptide and lipid structural arrangements. The data suggest that, for eukaryotic cell penetration, penetratin does not acquire classical secondary structure but requires a different conformation compared to that in solution

Graphene oxide/perovskite interfaces for photovoltaics

Graphene-based materials hold a promising prospect for their utilization in perovskite solar cell devices as electron-extraction or hole-transport layers. Here, we investigate the role of oxidized graphene when interfaced with the perovskite MAPbI. Using first-principles calculations based on density functional theory, we study the change in the structural and electronic properties of the heterostructures with the oxidation level. We show that, depending on the concentration of the epoxy functional groups, only reduced graphene oxide would be advantageous for the extraction of photogenerated charge carriers. For oxygen concentration up to 33%, both hole and electron carriers could be extracted, whereas for concentrations between 33 and 66%, electron transfer is favored. For concentrations above 66%, it should not be possible to extract carriers. Moreover, the analysis of the charge density rearrangement at the interface due to the oxidization of graphene shows that the interfacial dipole decreases with the increase in the oxygen content. Finally, we report the modification of the band gap and the work-function in the oxidized graphene for different rearrangements of the epoxy groups on the graphene sheet. This study shows that the reduced graphene oxide with specific oxidation levels could effectively be incorporated as a selective contact in heterojunction devices for applications in perovskite solar cells

Graphene oxide/perovskite interfaces for photovoltaics

Graphene-based materials hold a promising prospect for their utilization in perovskite solar cell devices as electron-extraction or hole-transport layers. Here, we investigate the role of oxidized graphene when interfaced with the perovskite MAPbI. Using first-principles calculations based on density functional theory, we study the change in the structural and electronic properties of the heterostructures with the oxidation level. We show that, depending on the concentration of the epoxy functional groups, only reduced graphene oxide would be advantageous for the extraction of photogenerated charge carriers. For oxygen concentration up to 33%, both hole and electron carriers could be extracted, whereas for concentrations between 33 and 66%, electron transfer is favored. For concentrations above 66%, it should not be possible to extract carriers. Moreover, the analysis of the charge density rearrangement at the interface due to the oxidization of graphene shows that the interfacial dipole decreases with the increase in the oxygen content. Finally, we report the modification of the band gap and the work-function in the oxidized graphene for different rearrangements of the epoxy groups on the graphene sheet. This study shows that the reduced graphene oxide with specific oxidation levels could effectively be incorporated as a selective contact in heterojunction devices for applications in perovskite solar cells

Adsorption of yellow bemacid CM-3R dye from aqueous solutions onto raw and sodium bentonite

Discharges from the textile industries are heavily loaded with various dyes which requires their treatment. The most common method is to adsorb on solids high surface area, for example, clay material highly available and whose leaves are good natural adsorbents. In present study we used a local bentonite available in its natural form and sodium form for the adsorption of a dye CM-3R yellow bemacid provided by BEZEMA. The evaluation of the effect of various variables is driven by a series of experiments as the contact time, initial concentration of the dye, the initial pH. The different parameters show that the adsorption of the dye is favoured to 240 min, pH 2 and a temperature of 19 ºC. The sodium bentonite yielded good performance results due to the improvement of its adsorption properties. The best correlation of experimental results are obtained with the Langmuir model for sodium bentonite (R % = 0.998) and Freundlich for the raw bentonite (0997

Entropy stabilization effects and ion migration in 3D “hollow” halide perovskites

A recently discovered new family of 3D halide perovskites with the general formula (A)1–x(en)x(Pb)1–0.7x(X)3–0.4x (A = MA, FA; X = Br, I; MA = methylammonium, FA = formamidinium, en = ethylenediammonium) is referred to as “hollow” perovskites owing to extensive Pb and X vacancies created on incorporation of en cations in the 3D network. The “hollow” motif allows fine tuning of optical, electronic, and transport properties and bestowing good environmental stability proportional to en loading. To shed light on the origin of the apparent stability of these materials, we performed detailed thermochemical studies, using room temperature solution calorimetry combined with density functional theory simulations on three different families of “hollow” perovskites namely en/FAPbI3, en/MAPbI3, and en/FAPbBr3. We found that the bromide perovskites are more energetically stable compared to iodide perovskites in the FA-based hollow compounds, as shown by the measured enthalpies of formation and the calculated formation energies. The least stable FAPbI3 gains stability on incorporation of the en cation, whereas FAPbBr3 becomes less stable with en loading. This behavior is attributed to the difference in the 3D cage size in the bromide and iodide perovskites. Configurational entropy, which arises from randomly distributed cation and anion vacancies, plays a significant role in stabilizing these “hollow” perovskite structures despite small differences in their formation enthalpies. With the increased vacancy defect population, we have also examined halide ion migration in the FA-based “hollow” perovskites and found that the migration energy barriers become smaller with the increasing en content