High-energy optical transitions and optical constants of CH3_3NH3_3PbI3_3 measured by spectroscopic ellipsometry and spectrophotometry

Optoelectronics based on metal halide perovskites (MHPs) have shown substantial promise, following more than a decade of research. For prime routes of commercialization such as tandem solar cells, optical modeling is essential for engineering device architectures, which requires accurate optical data for the materials utilized. Additionally, a comprehensive understanding of the fundamental material properties is vital for simulating the operation of devices for design purposes. In this article, we use variable angle spectroscopic ellipsometry (SE) to determine the optical constants of CH$_3$NH$_3$PbI$_3$ (MAPbI$_3$) thin films over a photon energy range of 0.73 to 6.45 eV. We successfully model the ellipsometric data using six Tauc-Lorentz oscillators for three different incident angles. Following this, we use critical-point analysis of the complex dielectric constant to identify the well-known transitions at 1.58, 2.49, 3.36 eV, but also additional transitions at 4.63 and 5.88 eV, which are observed in both SE and spectrophotometry measurements. This work provides important information relating to optical transitions and band structure of MAPbI$_3$, which can assist in the development of potential applications of the material.Comment: 18 pages, 4 figure

Un array lineare fra Sansepolcro e Anghiari (Alta Valtiberina): acquisizione dati e prime analisi da terremoti e microtremore

La Valtiberina è da alcuni anni una delle principali aree dell'Appennino Centro-Settentrionale sottoposta ad indagini mirate alla definizione della geometria del bacino e alla descrizione in termini di geometria e meccanismo della faglia AltoTiberina, principale responsabile dell'attività sismica dell'area. Al fine di contribuire con dati sismometrici alla ricostruzione della risposta sismica del bacino, nella seconda metà del 2005 è stato realizzato un esperimento temporaneo consistito nell'installazione di un array lineare di 8 stazioni sismiche fra Sansepolcro e Anghiari. L'array era disposto lungo una direzione NE-SW, approssimativamente ortogonale all'asse della valle per una lunghezza di circa 8 km con una spaziatura fra le stazioni di circa 1 km. Le stazioni sismiche, equipaggiate con sismometri Lennartz LE3D-5s e Guralp CMG40T accoppiati a sistemi di acquisizione Reftek 130 e Reftek 72A/07, hanno acquisito in continua per circa 5 mesi (da Maggio 2005 a Novembre 2005), registrando alcune centinaia di eventi sismici locali, regionali e telesismi

Un array lineare fra Sansepolcro e Anghiari (Alta Valtiberina): acquisizione dati e prime analisi da terremoti e microtremore

La Valtiberina è da alcuni anni una delle principali aree dell'Appennino Centro-Settentrionale sottoposta ad indagini mirate alla definizione della geometria del bacino e alla descrizione in termini di geometria e meccanismo della faglia AltoTiberina, principale responsabile dell'attività sismica dell'area. Al fine di contribuire con dati sismometrici alla ricostruzione della risposta sismica del bacino, nella seconda metà del 2005 è stato realizzato un esperimento temporaneo consistito nell'installazione di un array lineare di 8 stazioni sismiche fra Sansepolcro e Anghiari. L'array era disposto lungo una direzione NE-SW, approssimativamente ortogonale all'asse della valle per una lunghezza di circa 8 km con una spaziatura fra le stazioni di circa 1 km. Le stazioni sismiche, equipaggiate con sismometri Lennartz LE3D-5s e Guralp CMG40T accoppiati a sistemi di acquisizione Reftek 130 e Reftek 72A/07, hanno acquisito in continua per circa 5 mesi (da Maggio 2005 a Novembre 2005), registrando alcune centinaia di eventi sismici locali, regionali e telesismi.PublishedRoma, 28-30 novembreope

Phonon-assisted trapping and re-excitation of free carriers and excitons in lead halide perovskites

Despite the advances in solar cells based on lead halide perovskites, the nature of photogenerated charges and trap states within these materials remains unclear. A model describing recombination in CH3NH3PbI3−xClx has been developed that accounts for phonon-assisted free-exciton and free-carrier trapping. We utilize optical spectroscopies and observe significant co-existence of the tetragonal and orthorhombic structural phases at low temperatures. From these measurements, we evaluate the longitudinal−optical phonon energy, exciton binding energy, and temperature-dependent electronic bandgap. We use these parameters to model the temperature- and fluence-dependent time-resolved photoluminescence decays, enabling us to demonstrate how shallow traps from which carriers can be re-excited can account for the delayed recombination in lead halide perovskites. The trap-state density reaches a maximum at the tetragonal to orthorhombic phase transition at ∼140 K, suggesting the formation of disorder-induced trap states, which are shown to dominate the recombination dynamics in CH3NH3PbI3−xClx

Comparative Analysis of PRAME Expression in 127 Acral and Nail Melanocytic Lesions

: PRAME (PReferentially expressed Antigen in MElanoma), a cancer testis antigen expressed in low levels in gonadal, endometrial, and adrenal gland tissues, has been recently considered a valuable tool in the differential diagnosis between benign and malignant melanocytic lesions. The aim of the current study is to perform PRAME immunostaining on a large series of benign and malignant acral lesions to evaluate the reproducibility of data reported in the literature and to validate PRAME as an affordable tool in the differential diagnosis between benign and malignant acral melanocytic tumors. Immunohistochemical analysis for PRAME was performed in 127 benign and malignant acral and nail melanocytic lesions. To better correlate PRAME expression with the nature (benign vs. malignant) of the lesions, we categorized PRAME tumor cells percentage positivity and intensity in a cumulative score obtained by adding the quartile of positive tumor cells (0, 1+, 2+, 3+, 4+) to PRAME expression intensity in tumor cells (0, 1+, 2+, 3+). Adopting an arbitrary PRAME expression score of < 5 versus ≥5 resulted in a correct identification of 82.5% of benign and 87.1% of malignant lesions. PRAME immunohistochemistry demonstrated good sensitivity and specificity in the diagnosis of acral melanocytic lesions, however, in line with the previous literature, we identified a subset of challenging cases such as acral Spitz nevi, in situ melanomas, and small, thin, invasive melanomas in which PRAME did not correlate with morphologic features. This suggests that PRAME can be a valid tool to be incorporated in a diagnostic clinicopathologic algorithm, subject to morphologic characteristics

Resonant energy transfer properties of perovskite nanocrystals

Perovskite nanocrystals of the form FAPbBr3 display significant promise in the field of optoelectronics. In particular, these nanocrystals could bridge the 'green gap' of LED technology, and also serve to down-convert ultraviolet light for harvesting using silicon-based photovoltaic cells. To remain competitive with traditional devices, optimising the energy transfer between the nanocrystal and the device is crucial, however very little investigation has been performed into this subject. Here, we characterise the energy transfer dynamics of FAPbBr3 nanocrystals on a silicon substrate using time resolved photoluminescence. We also use deposited 'spacer layers' to vary the displacement of the nanocrystals from the silicon in order to observe the effect on the energy-transfer dynamics. We find that the overall photo luminescent lifetime increases when reducing the distance between between the nanocrystals and the silicon layer, which runs counter to the expected behaviour. This suggests that the presence of an optically-active substrate suppresses photo luminescent lifetime and, further, suggests that nanocrystal-to-nanocrystal transfer is highly efficient.</p

Single-junction solar cells based on p-i-n GaAsSbN heterostructures grown by liquid phase epitaxy

In this paper we present single heterojunction p-i-n GaAsSbN/GaAs solar cells grown by lowtemperature liquid-phase epitaxy (LPE) – this is of interest as a component of multi-junction solar cell devices. The quaternary absorber layer was characterized by low excitation power photoluminescence to give the temperature dependence of the band gap. This conformed to the Varshni function at low temperatures to within 10 meV, indicating relatively small alloy potential fluctuations. The absorption properties and the transport of the photogenerated carriers in the heterostructures was investigated using surface photovoltage method. A power conversion efficiency of 4.15 % (AM1.5, 1000 W.m-2) was measured for p-i-n GaAsSbN/GaAs solar cells, which is comparable to the efficiency of MOCVD grown devices of this type. This is promising for the first report of LPE grown GaAsSbN/GaAs solar cells since the current record efficiency for the cells based on these compounds grown by MBE stands just at 6 %. The long-wavelength photosensitivity of the cells determined from external quantum efficiency and surface photovoltage measurements was shown to be extended to 1040 nm.<br/

Lateral growth of MoS₂ 2D material semiconductors over an insulator via electrodeposition

Developing novel techniques for depositing transition metal dichalcogenides is crucial for the industrial adoption of 2D materials in optoelectronics. In this work, the lateral growth of molybdenum disulfide (MoS2) over an insulating surface is demonstrated using electrochemical deposition. By fabricating a new type of microelectrodes, MoS2 2D films grown from TiN electrodes across opposite sides are connected over an insulating substrate, hence, forming a lateral device structure through only one lithography and deposition step. Using a variety of characterization techniques, the growth rate of MoS2 is shown to be highly anisotropic with lateral to vertical growth ratios exceeding 20-fold. Electronic and photo-response measurements on the device structures demonstrate that the electrodeposited MoS2 layers behave like semiconductors, confirming their potential for photodetection applications. This lateral growth technique paves the way toward room temperature, scalable, and site-selective production of various transition metal dichalcogenides and their lateral heterostructures for 2D materials-based fabricated devices. </p