Bismuth-Based Perovskite Derivates with Thermal Voltage Exceeding 40 mV/K.

Heat is an inexhaustible source of energy, and it can be exploited by thermoelectronics to produce electrical power or electrical responses. The search for a low-cost thermoelectric material that could achieve high efficiencies and can also be straightforwardly scalable has turned significant attention to the halide perovskite family. Here, we report the thermal voltage response of bismuth-based perovskite derivates and suggest a path to increase the electrical conductivity by applying chalcogenide doping. The films were produced by drop-casting or spin coating, and sulfur was introduced in the precursor solution using bismuth triethylxanthate. The physical-chemical analysis confirms the substitution. The sulfur introduction caused resistivity reduction by 2 orders of magnitude, and the thermal voltage exceeded 40 mV K-1 near 300 K in doped and undoped bismuth-based perovskite derivates. X-ray diffraction, Raman spectroscopy, and grazing-incidence wide-angle X-ray scattering were employed to confirm the structure. X-ray photoelectron spectroscopy, elemental analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were employed to study the composition and morphology of the produced thin films. UV-visible absorbance, photoluminescence, inverse photoemission, and ultraviolet photoelectron spectroscopies have been used to investigate the energy band gap.

Two-Step Synthesis of Bismuth-Based Hybrid Halide Perovskite Thin-Films.

Lead halide perovskites have been revolutionary in the last decade in many optoelectronic sectors. Their bismuth-based counterparts have been considered a good alternative thanks to their composition of earth-abundant elements, good chemical stability, and low toxicity. Moreover, their electronic structure is in a quasi-zero-dimensional (0D) configuration, and they have recently been explored for use beyond optoelectronics. A significant limitation in applying thin-film technology is represented by the difficulty of synthesizing compact layers with easily scalable methods. Here, the engineering of a two-step synthesis in an air of methylammonium bismuth iodide compact thin films is reported. The critical steps of the process have been highlighted so that the procedure can be adapted to different substrates and application areas.

Dye-catalyst dyads for photoelectrochemical water oxidation based on metal-free sensitizers.

Dye-Sensitized Photoelectrochemical Cells (DS-PECs) have been emerging as promising devices for efficient solar-induced water splitting. In DS-PECs, dyes and catalysts for water oxidation and/or reduction are typically two separate components, thus limiting charge transfer efficiency. A small number of organometallic dyes have been integrated with a catalyst to form an integrated dye-catalyst dyad for photoanodes, but until now no dyads based on metal-free organic dyes have been reported for photoanodes. We herein report the first example of dyad-sensitized photoanodes in DS-PEC water splitting based on metal-free organic dyes and a Ru catalyst. The di-branched donor-π-acceptor dyes carry a donor carbazole moiety which has been functionalized with two different terminal pyridyl ligands in order to coordinate a benchmark Ru complex as a water oxidation catalyst, affording water oxidation dyads. The two dyads have been fully characterized in their optical and electrochemical properties, and XPS has been used to confirm the presence of the catalyst bonded to the dye anchored to the semiconductor anode. The two dyads have been investigated in DS-PEC, showing an excellent faradaic efficiency (88% average across all cells, with a best cell efficiency of 95%), thus triggering new perspectives for the design of efficient molecular dyads based on metal-free dyes for DS-PEC water splitting.

High charge carrier mobility in solution processed one-dimensional lead halide perovskite single crystals and their application as photodetectors.

Organic inorganic hybrid metal halide perovskites have emerged as promising candidates for photovoltaics and light-emitting diodes. Recently, interest has been growing in the properties of low-dimensional metal halide perovskites, and one-dimensional versions with strong quantum confinement have demonstrated highly efficient broadband luminescence. Nevertheless, the charge transport mechanism in these low dimensional perovskites remains unclear. In this work, we characterised the charge mobility in one-dimensional perovskite single crystals using a space charge limited current method. Temperature dependent charge mobility measurements indicated that localized polarons at high temperature are replaced by delocalized polarons at low temperature with extended states in the polaronic band. A minimum mobility of 4.51 cm2 V-1 s-1 was measured at room temperature. UV photodetectors based on these crystals show an ultrahigh photoresponsivity of 132.3 A W-1. These findings show the promise of high mobility low dimensional perovskite materials for optoelectronic applications.

Growth and Characterization of Cu2Zn1-xFexSnS4 Thin Films for Photovoltaic Applications.

Photovoltaics is a promising technology to produce sustainable energy, thanks to the high amount of energy emitted by the sun. One way of having solar cells with low production costs is to apply thin-film technology and with earth-abundant raw materials. A keen interest is arising in kesterite compounds, which are chalcogenides composed of abundant and non-toxic elements. They have already achieved excellent performance at the laboratory level. Here, we report the synthesis and characterization of mixed chalcogenides based on copper, zinc, iron, and tin. Solutions have been studied with different zinc and iron ratios. The distortion of the elementary cell of kesterite increases with the addition of iron until a phase transition to stannite occurs. The process of synthesis and deposition proposed herein is cheap and straightforward, based on the sol-gel technique. These thin films are particularly attractive for use in cheap and easily processable solar cells. The synthesized layers have been characterized by X-ray diffraction, UV-Vis absorption, and Raman, X-ray photoelectron, and energy-dispersive X-ray spectroscopy measurements.