Solid-State Nuclear Magnetic Resonance of Triple-Cation Mixed-Halide Perovskites

Mixed-cation lead mixed-halide perovskites are the best candidates for perovskite-based photovoltaics, thanks to their higher efficiency and stability compared to the single-cation single-halide parent compounds. TripleMix (Cs0.05MA0.14FA0.81PbI2.55Br0.45 with FA = formamidinium and MA = methylammonium) is one of the most efficient and stable mixed perovskites for single-junction solar cells. The microscopic reasons why triplecation perovskites perform so well are still under debate. In this work, we investigated the structure and dynamics of TripleMix by exploiting multinuclear solid-state nuclear magnetic resonance (SSNMR), which can provide this information at a level of detail not accessible by other techniques. 133Cs, 13C, 1 H, and 207Pb SSNMR spectra confirmed the inclusion of all ions in the perovskite, without phase segregation. Complementary measurements showed a peculiar longitudinal relaxation behavior for the 1 H and 207Pb nuclei in TripleMix with respect to single-cation single-halide perovskites, suggesting slower dynamics of both organic cations and halide anions, possibly related to the high photovoltaic performances

Singling Out the Role of Molecular Weight in the Crystallization Kinetics of Polyester/Clay Bionanocomposites Obtained by In Situ Step Growth Polycondensation

The isothermal crystallization kinetics of a set of bio-nanocomposites produced by in situ catalytic step growth polycondensation of adipic acid and 1,4-butanediol in the presence of Moroccan clay beidellite (BDT) organo-modified with hexadecyltrimethylammonium bromide (cetyltrimethylammonium bromide, CTA) was investigated and compared with that of the parent poly(butylene adipate) (PBA) matrices from which the clay had been extracted. In situ bio-nanocomposites had different contents (0−5 wt %) of CTA/BDT nanofillers characterized by different extents of organo-modification (CTA/BDT equivalent ratios from 0 to 5). Theb isothermal crystallization rates of the ionanocomposites and of the parent PBA matrices were investigated by differential scanning calorimetry (DSC) at 45, 40, and 37 °C and analyzed according to the Avrami model. The bionanocomposites with an intermediate (2 wt %) concentration of organoclays with a higher CTA/BDT ratio (3 and 5) showed the highest exfoliation degree, along with an increase in the crystallization rates, compared to those of the parent PBA matrices, which was larger than that in the other nanocomposites. The lack of a simple correlation between the nanoclay content/composition and crystallization kinetics was ascribed to the molecular mass, an additional variable for in situ bio-nanocomposites as compared to nanocomposites prepared by simple physical blending of nanoclays with a single polymer matrix. The specific contribution of the molecular mass to the crystallization kinetics was untangled from those of the organoclay content and CTA/BDT ratio by comparing each bio-nanocomposite with its parent polymer matrix. The crystallization rate of the nanocomposites was always found to reach a maximum within an intermediate range of molecular weights of the polymer matrix, a behavior previously reported only for pure polymers. Such differences in the crystallization rate of in situ bio-nanocomposites may affect the crystalline phase morphology and, in polymorphs such as in PBA, phase composition, with consequent effects on properties that may be of interest for specific applications

Studi cinetici di cristallizzazione isoterma del polibutilene adipato e di suoi nanocompositi tramite analisi DSC e spettroscopia FTIR

Abbiamo studiato la cinetica di cristallizzazione isoterma del polibutilene adipato e di suoi nanocompositi con argilla beidellite, tramite le tecniche DSC e spettroscopia FTIR. L'analisi dei dati è stata condotta utilizzando il modello cinetico di Avrami. Sono stati confrontati i parametri ottenuti dalle due tecniche per i vari campioni con diversi pesi molecolari medi e diversa percentuale di argilla. Per l'interpretazione dei risultati ci siamo avvalsi di immagini al microscopio ottico e TEM dei nanocompositi

Solid State NMR techniques for the study of 2D and mixed lead halide perovskites

In questo lavoro di tesi sono state studiate perovskiti piombo alogeno tramite NMR allo stato solido. Tali materiali sono molto studiati grazie alle loro ottime prestazioni in applicazioni optoelettroniche quali celle solari, LEDs e lasers. Tra le perovskiti piombo alogeno, noi ci focalizzati su perovskiti 2D Ruddlesden-Popper con formula chimica BA2MA(n-1)PbnI(3n+1) per n=1, 2 e 3 e una perovskite 3D con mix di ioni Cs0.05FA0.81MA0.14PbBr0.45I2.55. Sfruttando un approccio multinucleare, l’NMR allo stato solido ha permesso di caratterizzare il network inorganico costituito da ottaedri PbX6 uniti ai vertici tamite spettri 207Pb, mentre esperimenti sui nuclei 1H e 13C hanno permesso di ottenere informazioni sui cationi organici presenti. The thesis work focuses on the application of Solid-State Nuclear Magnetic Resonance (SSNMR) to study lead halide perovskites. This type of materials are intensively investigated semiconductors thanks to their good performance in optoelectronic devices, such as solar cells, LEDs and lasers. Here we applied SSNMR on the last two scopes, investigating a perovskite with a mix of ions Cs0.05FA0.81MA0.14PbBr0.45I2.55 and 2D Ruddlesden-Popper with chemical formula BA2MA(n-1)PbnI(3n+1) for n=1, 2 e 3. By a multinuclear NMR approach, we could obtain information about the inorganic network of corner sharing PbX6 octahedra by acquiring 207Pb spectra, whereas 1H and 13C experiments were employed to characterize the organic cations