Università degli studi di Modena e Reggio Emilia

Nanocluster aggregation sources based on magnetron-sputtering represent precise and versatile means to deposit a controlled quantity of metal nanoparticles at selected interfaces. In this work, we exploit this methodology to produce Ag/MgO nanoparticles (NPs) and deposit them on a glass/FTO/TiO2 substrate, which constitutes the mesoscopic front electrode of a monolithic perovskite-based solar cell (PSC). Herein, the Ag NP growth through magnetron sputtering and gas aggregation, subsequently covered with MgO ultrathin layers, is fully characterized in terms of structural and morphological properties while thermal stability and endurance against air-induced oxidation are demonstrated in accordance with PSC manufacturing processes. Finally, once the NP coverage is optimized, the Ag/MgO engineered PSCs demonstrate an overall increase of 5% in terms of device power conversion efficiencies (up to 17.8%).

Iron-based extended metal atom chains (EMACs) are potentially high-spin molecules with axial magnetic anisotropy and thus candidate single-molecule magnets (SMMs). We herein compare the tetrairon(II), halide-capped complexes [Fe4(tpda)3Cl2] (1Cl) and [Fe4(tpda)3Br2] (1Br), obtained by reacting iron(II) dihalides with [Fe2(Mes)4] and N2,N6-di(pyridin-2-yl)pyridine-2,6-diamine (H2tpda) in toluene, under strictly anhydrous and anaerobic conditions (HMes = mesitylene). Detailed structural, electrochemical and Mossbauer data are presented along with direct-current (DC) and alternating-current (AC) magnetic characterizations. DC measurements revealed similar static magnetic properties for the two derivatives, with chiMT at room temperature above that for independent spin carriers, but much lower at low temperature. The electronic structure of the iron(II) ions in each derivative was explored by ab initio (CASSCF-NEVPT2-SO) calculations, which showed that the main magnetic axis of all metals is directed close to the axis of the chain. The outer metals, Fe1 and Fe4, have an easy-axis magnetic anisotropy (D = -11 to -19 cm-1, |E/D| = 0.05-0.18), while the internal metals, Fe2 and Fe3, possess weaker hard-axis anisotropy (D = 8-10 cm-1, |E/D| = 0.06-0.21). These single-ion parameters were held constant in the fitting of DC magnetic data, which revealed ferromagnetic Fe1-Fe2 and Fe3-Fe4 interactions and antiferromagnetic Fe2-Fe3 coupling. The competition between super-exchange interactions and the large, noncollinear anisotropies at metal sites results in a weakly magnetic non-Kramers doublet ground state. This explains the SMM behavior displayed by both derivatives in the AC susceptibility data, with slow magnetic relaxation in 1Br being observable even in zero static field.

The stringlike complex [Fe4(tpda)3Cl2] (2; H2tpda = N2,N6-bis(pyridin-2-yl)pyridine-2,6-diamine) was obtained as the first homometallic extended metal atom chain based on iron(II) and oligo-α-pyridylamido ligands. The synthesis was performed under strictly anaerobic and anhydrous conditions using dimesityliron, [Fe2(Mes)4] (1; HMes = mesitylene), as both an iron source and a deprotonating agent for H2tpda. The four lined-up iron(II) ions in the structure of 2 (Fe⋯Fe = 2.94-2.99 Å, Fe⋯Fe⋯Fe = 171.7-168.8°) are wrapped by three doubly deprotonated twisted ligands, and the chain is capped at its termini by two chloride ions. The spectroscopic and electronic properties of 2 were investigated in dichloromethane by UV-vis-NIR absorption spectroscopy, 1H NMR spectroscopy, and cyclic voltammetry. The electrochemical measurements showed four fully resolved, quasi-reversible one-electron-redox processes, implying that 2 can adopt five oxidation states in a potential window of only 0.8 V. Direct current (dc) magnetic measurements indicate dominant ferromagnetic coupling at room temperature, although the ground state is only weakly magnetic. On the basis of density functional theory and angular overlap model calculations, this magnetic behavior was explained as being due to two pairs of ferromagnetically coupled iron(II) ions (J = -21 cm-1 using JŜi·Ŝj convention) weakly antiferromagnetically coupled with each other. Alternating-current susceptibility data in the presence of a 2 kOe dc field and at frequencies up to 1.5 kHz revealed the onset of slow magnetic relaxation below 2.8 K, with the estimated energy barrier Ueff/kB = 10.1(1.3) K.