The phase transitions between the various polymorphs of FAPbI 3 (FAPI, FA = formamidinium [CH(NH 2 ) 2 ] + ) are studied by anelastic, dielectric, and X-ray diffraction measurements on samples pressed from δ-FAPI (2H phase) yellow powder. The samples become orange after application of as little as 0.2 GPa, which has been explained in terms of partial transformations to the other hexagonal polymorphs 4H and 6H. The phenomenon is discussed in the light of what is known about the stability of the various polymorphs of hybrid and inorganic perovskites ABX 3 with large A cations and hence a large tolerance factor t.Remarkably, FAPI at room and higher temperatures behaves like a perovskite with a large t, while just below room temperature it behaves like a perovskite with a small t. The kinetics of the transformations between the polymorphs is enhanced by small amounts of intercalated water. It seems therefore worthy to try improving the atomic diffusion and crystallization during synthesis, and hence the final photovoltaic performance, through controlled small amounts of water that should be thoroughly removed after a sufficiently homogeneous and smooth microstructure is achieved.

Nonplanar titanyl phthalocyanine (TiOPc) molecules, characterized by a central, highly dipolar Ti−O group, can offer further degrees of freedom in tailoring the properties of hybrid organic−inorganic structures. Here, we combine scanning tunneling microscopy and low-energy electron diffraction measurements with ab initio density functional theory calculations to investigate the interaction of TiOPc molecules with the Ag(100) surface. Isolated molecules are adsorbed with the macrocycle parallel to the surface in two different configurations: with the O atom pointing outward (UP configuration) or with the O atom pointing toward the surface (DOWN configuration). A different interaction of UP and DOWN molecules with the surface can account for their different orientation on the surface as well as for the observation of marked chiral effects only for UP molecules. Self-assembled domains of randomly mixed UP and DOWN molecules form at the monolayer coverage, driven by a subtle interplay between the molecule−surface interaction, the intermolecular dipolar attraction, and the side interaction between adjacent molecules. Chiral patterns of isolated molecules, observed by STM, are transferred to these domains. Remarkably, theoretical calculations disclose an interfacial nature of such chiral properties. Finally, a metallic behavior observed for the monolayer disappears for TiOPc molecules in a second layer, which are electronically decoupled from the substrate.

Thin nanoporous TiO 2 layers, deposited by dc reactive sputtering, have been functionalized with a novel unsymmetrical Zn(II) phthalocyanine (ZnPc-II) bearing a push−pull system, properly designed for application in dye sensitized solar cells. The anchoring process has been studied by combining visible absorption (vis), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) in order to investigate the molecular assembly during the early stage of the sensitizing process. The vis and XPS measurements indicate that the ZnPc-II surface density (d surf , molecules/cm 2 ) and its binding geometry are strongly affected by the concentration of the grafting solutions. It has been observed that the ZnPc-II surface density monotonically increases by increasing the solution concentration up to a saturation of d surf ∼ 1.0 × 10 13 molecules/cm 2 . Angle resolved XPS analyses indicate that at low molecular surface density a strong interaction between the ZnPc-II aromatic macrocycle and the TiO 2 surface occurs, suggesting a planar binding geometry. The increase of the molecular surface density is accompanied by a mitigation of the surface−molecule interaction that leads to a different ZnPc-II binding geometry. Conductive atomic force microscopy has demonstrated that the charge transport through the dye−TiO 2 interface strongly depends on the binding arrangements which exhibit different threshold values in the local I−V characteristics.

We have investigated the formation and the properties of ultrathin films of ruthenium phthalocyanine (RuPc) vacuum deposited on graphite by scanning tunneling microscopy and synchrotron photoemission spectroscopy measurements, interpreted in close conjunction with ab initio simulations. Thanks to its unique dimeric structure connected by a direct Ru-Ru bond, (RuPc) can be found in two stable rotameric forms separated by a low-energy barrier. Such isomerism leads to a peculiar organization of the molecules in flat, horizontal layers on the graphite surface, characterized by a chessboard-like alternation of the two rotamers. Moreover, the molecules are vertically connected to form π-stacked columnar pillars of akin rotamers, compatible with the high conductivity measured in (RuPc) powders. Such features yield an unprecedented supramolecular assembly of phthalocyanine films, which could open interesting perspectives toward the realization of new architectures of organic electronic devices.

A new unsymmetrical zinc phthalocyanine sensitizer has been synthesised. The anchoring of the molecule to nanocrystalline TiO(2) films is realised by a carboxylic group connected to a phenyl ethynyl moiety. Density Functional Theory (DFT) calculations show significant and positive effects of such a functionalization. Electron injection into the semiconductor and photocurrent generation in DSSC are also presented.