Hybrid halide perovskites represent one of the most promising solutions toward the fabrication of all solid nanostructured solar cells, with improved efficiency and long-term stability. This article aims at investigating the structural properties of iodide/chloride mixed-halide perovskites and correlating them with their photovoltaic performances. We found out that, independent of the components ratio in the precursor solution, Cl incorporation in an iodide-based structure, is possible only at relatively low concentration levels (below 3–4%). However, even if the material band gap remains substantially unchanged, the Cl doping dramatically improves the charge transport within the perovskite layer, explaining the outstanding performances of meso-superstructured solar cells based on this material.

Hybrid halide perovskites represent one of the most promising solutions toward the fabrication of all solid nanostructured solar cells with improved efficiency and long-term stability. This article aims at investigating the structural properties of the iodide/chloride mixed-halide perovskites and correlating them with the photovoltaic performances of the related sensitized solar cells. We found out that, independently on the components ratio in the precursor solution, Cl incorporation, in a I-based structure, is possible only at relatively low concentration levels (below 3-4%). However, even if the material band-gap remains substantially unchanged, incorporation of Cl as a dopant dramatically improves the charge transport within the perovskite layer, explaining the outstanding performances of meso-superstructured solar cells based on this material.

The influence of thermal treatments on the properties of mixed bromide-iodide organolead perovskites (MAPbI3−xBrx, MA=CH3NH3) is investigated in films prepared in air by single-step solution processes based on different precursor solutions. Initially, the bandgap energy (EG) dependence on composition is reconsidered on films obtained by mixtures of tri-halide solutions.An EG(x) relation is obtained that is expected to be independent of the film properties and can be used to assess perovskite composition. In these samples recombination centres are observed whose energy depth increases with x, likely involving the simultaneous presence of iodide and bromide, while the Urbach energy increases with the grain surface-to-volume ratio, which points out that the defects giving sub-bandgap absorption originate from grain boundaries. Tri-halide mixtures allow perovskite synthetic processes suitable for solar cell production, being fast and reproducible. A slight MABr excess in the solution made of MABr and PbI2 gives MAPbI2Br films free of PbI2 phases and with a high compositional stability, but non-radiative recombination channels can make the material not appropriate for high efficiency solar cells.Finally, the solution made of MAI and PbBr2 (3:1 molar ratio) is the less promising for solar cell production because its non-stoichiometric nature synthesis reproducibility an issue.

Wurtzite ZnS and ZnO porous nanostructures have been obtained by annealing ZnS(en)0.5 nanosheets in air at different times and temperatures. The evolution of the morphological and structural transformation has been investigated at the nanoscale by transmission and scanning electron microscopy (TEM and SEM) analysis. At the annealing temperature of 400 °C, the ZnS(en)0.5 hybrid decomposes by a topotactic transformation, giving ZnS nanosheets. By increasing the annealing time, the gradual transformation ZnS→ZnO is observed to take place at the nanoscale. The transformation completes with the formation of highly porous ZnO crystals when the annealing temperature is increased to 600 °C. Remarkably, all the structural and morphological transformation steps during the annealing preserve the nanosheet crystalline character. These processes have been related to the materials photocatalytic activity in methylene blue degradation under UV–visible irradiation. The ZnS(en)0.5 precursor is the weakest photocatalyst, whereas porous ZnO is the strongest. Samples treated at 400 °C show degradation efficiencies that are intermediate between ZnS(en)0.5 and ZnO platelets and decrease with increasing annealing time due to the formation of ZnS/ZnO heterojunctions.

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