7 Scientific Article The Israel Chemist and Chemical Engineer Issue 9 · January 2023 · Tevet 5783 Vinayaka Harshothama Damle is a visiting researcher at the Faculty of Information Technology and Electrical Engineering, University of Oulu. Before that, he was a doctoral researcher at the Institute for Nanotechnology & AdvancedMaterials, Bar-Ilan University, Israel. Hemoved to Israel for his PhD after completing his MSc in Physics from National Institute of Technology Karnataka, India and gaining 2 years of industrial experience in various roles parting as an electron microscopy technologist of a research facility. His doctoral research dissertation mainly focused on engineering Raman scattering phenomena to probe light-matter interactions, emphasizing development of spectroscopic techniques for material detection. His research focuses onmolecular photonics and spectroscopy, with special emphasis on device spectroscopy, nanometrology, and energy materials. challenge of developing quantitative robust and trustworthy methods of data analysis. However, many methods have been developed for enhancement of these signals over the years by many research groups. These include chemical, surface, and cavity enhancement techniques that were reported by us [2– 4]. Furthermore, the presence of highly active Raman species such as carbon particles can mask the presence of other species. Several studies have been devoted to overcoming these drawbacks. Among these different approaches, it is known that polarized Raman spectroscopy provides information on molecular orientation and bond vibrational symmetry, in addition to general chemical identification [5]. In general, in polarized RS the spectra captured are either parallel or perpendicular to the inherent polarization of the excitation laser. However, Raman optical activity deals with the polarization phenomenon differently by observing the evolution of the Raman spectrum at different polarization angles. Polarizationmeasurements provide useful information about molecular shape and the orientation of molecules in ordered materials, such as crystals, polymers, and liquid crystals. The RS modes at lower wavenumbers (< 200 cm-1) are called low-frequency Raman (LFR) modes and the technique used to analyse this region of the spectrum is called low-frequency Raman spectroscopy (LFRS); the technique is very similar to spontaneous RS. LFRS is possible due to recent development of much sharper optical filters called volume holographic filters (VHFs). These filters facilitate easy observat ion of wavenumber shifts that are as low as 5 cm-1 away from the laser line. The LFR region is rich in information relating to lattice vibrations, crystallinity, symmetry, and inter-molecular acoustic modes, as well as phonon modes [6]. LFRS for identification of crystalline phases in methylammonium lead iodide Energy conversion from light to electricity has remained a major research area since the discovery of the photo-electric effect. While many materials and technologies have been developed over the years for this purpose, semiconductorbased solar cells have been spearheading the solar cell world due to their considerably higher efficiencies in spite of being expensive. The higher cost of existing technology has led to the expansion of research beyond conventional crystalline semiconductor materials. Organo-inorganic hybrid perovskites (OHPs) have remained promising in these efforts due to their exceptional performance resulting from their intrinsic properties such as high absorption coefficient, tunable band gap, long charge carrier diffusion, low exciton binding energy etc. Methylammonium lead iodide (MAPbI3) is the most widely used perovskite solar cell material. While the performance of the perovskite solar cells (PSCs) is commendable, the stability of OHPs remain questionable due to their high sensitivity to humidity, light, and temperature. The instability affects the crystal structure of the material and leads to degradation of crystal structure [7]. Here, we Figure 1. (a) Low-Frequency Raman Spectra and (b) PL spectra of tetragonal and cubic phases of MAPbI3 confirming laser-induced phase transition. §
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