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The structural instability of organometal halide perovskites (OHP) is one of the major issues concerning commercialization of perovskite solar cells. Probing this intrinsic instability is one of the major milestones and challenging tasks toward enhancing the lifespan of the material. Here we have incorporated Cs ions into methylammonium lead iodide (MAPbI3) films and studied the thin film structural and optical properties. Incorporation of Cs into MAPbI3 leads to formation of both α-CsPbI3 and ∂-CsPbI3 phases, black and yellow, respectively, as indicated by the evolution of the optical band edge and X-ray diffraction (XRD) spectrum. At a concentration of 20% Cs ions, we observe the existence of a stable α-CsPbI3 phase. Incorporating 59% or more Cs ions yields the yellow phase of CsPbI3, due to alloying of Cs with the MAPbI3 matrix. The structural transformations observed in absorption spectra and XRD are confirmed by low-frequency Raman spectroscopy. The thermally induced structural fluctuations in pure M...

Sb2Se3 has emerged as an important photoelectrochemical (PEC) and photovoltaic (PV) material due to its rapid rise in photoconversion efficiencies. However, despite its binary nature, Sb2Se3 has a complex defect chemistry, which reduces the maximum photovoltage that can be obtained. Thus, it is important to understand these defects and to develop passivation strategies in order to further improve this material. In this work, a comprehensive investigation of the charge carrier dynamics of Sb2Se3 and the influence of sulfur treatment on its optoelectronic properties was performed using time resolved microwave conductivity (TRMC), photoluminescence (PL) spectroscopy and low frequency Raman spectroscopy (LFRS). The key finding in this work is that upon sulfur treatment of Sb2Se3, the carrier lifetime is increased by the passivation of deep defects in Sb2Se3 in both the surface region and the bulk, which is evidenced by increased charge carrier lifetime of TRMC decay dynamics, increased radiative recombination efficiency and decreased deep defect level emission (PL), and improved long-range order in the material (LFRS). These findings provide crucial insights into the defect passivation mechanisms in Sb2Se3 paving the way for developing highly efficient PEC and PV devices.

Sb2Se3 has emerged as an important photoelectrochemical PEC and photovoltaic PV material due to its rapid rise in photoconversion efficiencies. However, Sb2Se3 has a complex defect chemistry, which reduces the maximum photovoltage. Thus, it is important to understand these defects and develop defect passivation strategies in Sb2Se3. A comprehensive investigation of the charge carrier dynamics of Sb2Se3 and the influence of sulfur treatment on its optoelectronic properties is performed using time resolved microwave conductivity TRMC , photoluminescence PL spectroscopy, and low frequency Raman spectroscopy LFR . The key finding in this work is that upon sulfur treatment of Sb2Se3, the carrier lifetime is increased by the passivation of deep defects in Sb2Se3 in both the surface region and the bulk, which is evidenced by increased charge carrier lifetime of TRMC decay dynamics, increased radiative recombination efficiency, decreased deep defect level emission PL , and the emergence of new vibration modes by LFR

Raman spectroscopy is a widely used characterization technique in material science. It is a non-destructive tool with relatively simple instrumentation, and provides intrinsic qualitative information of analytes by probing their vibrational modes. In many cases, Raman enhancement is essential for detecting low-intensity signals in high-noise environments, spectrally unresolved features, and hidden modes. Here we present optical and Raman spectroscopic characterization of fullerene C 60 in a gold microcavity. The fabrication of single-layered gold mirrors is facile, low cost and direct but was proven to give considerably significant enhancement. The findings of this work demonstrate the cavity resonance as a powerful tool in obtaining tunability over individual peak for selective enhancement in the tuned spectral range. The PL of the material within the cavity has demonstrated a red shift assumed to be caused by the low-energy transitions. These transitions are induced by virtual low-energy states generated by the cavity. We further observe that adopting this principle enables resolution of active Raman modes that until now were unobserved. Finally, we assigned the new experimentally observed modes to the corresponding motions calculated by DFT.

Raman spectroscopy has been shown to be a powerful spectroscopic approach for detecting gases. It is capable of detecting gases that possess no infrared absorption feature, such as diatomics, and it also does not suffer from signal saturation as can be the case for transmission measurements. However, the Achilles heel of Raman based gas detection is the low scattering cross section. Here we show that introducing gas into an optical open micro-cavity (OMC) can greatly enhance the Raman signal. The enhancement comes from 2 factors: namely confining the light longer in the gas containing volume, hence strengthening the light-matter interaction, and also directing the Raman scattering in a more collimated fashion towards the detector. The OMC has been designed such that the separation between the mirrors is piezo controlled, hence it is possible to scan the micro-cavity resonances and tune the OMC to a particular Raman transition. Using the OMC, with laser excitation at 532 nm, we show detection of several gases simultaneously such as nitrogen and oxygen, and discuss prospects for boosting the limit of detection. The presentation will cover the design consideration of the Tip, Tilt, Z microcavity having a range of 40 micron and a positioning resolution of 10 nm. The design comprises an intrinsic position to allow close loop operation. Response time is in the msec range to facilitate fast scanning. The spectrometer set up will be presented as well as representative experimental results.

Finding renewable energy sources is of paramount importance to meet the increasing global energy demand whilst minimizing the impact on the environment. The research community has focused on solar energy as it is endlessly available, and have ranked the methylammonium lead iodide (MAPbI3) as one of the most promising candidate amongst perovskite solar cells. Despite its high efficiency, the MAPbI3 is sensitive to humidity, light, and temperature, its instability affects primarily on the crystalline structure and eventually leads to degradation. Three crystalline structures are known for this material, orthorhombic, tetragonal, and cubic which exist in different temperatures. Here we report on several processes detected from laser excitation of MAPbI3 single crystal at ambient conditions. A phase transition from tetragonal to cubic phase was induced by excitation of over 15 mW laser power. The phases were characterized by LF-Raman and photoluminescence, taken simultaneously with the increase of exciting laser power and the spectral changes were assigned to the structural differences. In addition, Raman stimulation of iodine vapors signal was observed, those vapors were generated from the core of the focus wherein the highest temperature led to degradation. The stimulated Raman phenomenon was enabled due to the unique properties of the MAPbI3 single crystal and revealed viability to use this material for additional applications in other research fields.

Ni-P alloy thin films was developed as a robust electrode material for alkaline water splitting for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), through electrodeposition technique. The influence of alloy composition, achieved through induced codeposition of the reluctant non-metal, i.e. phosphorous (P) on its electrocatalytic activity was studied, and arrived at the best composition of alloy for HER and OER. The water splitting efficacy of the alloy films was tested in 1.0 M KOH using electrochemical methods such as cyclic voltammetry and chronopotentiometry. The experimental observation shows that the alloy thin film with 9.0 wt.% of P and 4.2 wt.% of P are the best electrode materials for HER and OER, respectively. The electrocatalytic performance of alloy films towards HER and OER were related to its surface topography, composition and crystal structure through field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses, respectively.