http://repo.lib.jfn.ac.lk/ujrr/handle/123456789/125 2026-09-19T12:35:29Z http://repo.lib.jfn.ac.lk/ujrr/handle/123456789/13103 Title: Deep insight into structural and optoelectronic properties of mixed anion perovskites Authors: Chapa Pamodani Wanniarachchi, W.A.; Eidsvåg, H.; Arunasalam, T.; Ravirajan, P.; Velauthapillai, D.; Vajeeston, P. Abstract: Here we present the optoelectronic properties of pure inorganic lead-free halide perovskites in the form of Cs2AgBiX6 (X=Br, Cl, F, I) using the density functional theory calculations on cubic phase (Fm 3̅m) and tetragonal phase (I4/m). First, all the structures of the two phases were optimized at the PBE level. Structural, electronic, optical properties, phonon, and thermal properties of Cs2AgBiX6 in cubic (Fm 3̅m) and tetragonal phases (I4/m) were obtained using the VASP code. Tetragonal phases of all compounds of the form Cs2AgBiX6, except Cs2AgBiBr6, are reported here for the very first time. Among all the Cs2AgBiX6 (X=F, Cl, Br, I) structures, the cubic phase of Cs2AgBiBr6 was seen to have the highest absorption coefficient along with prominent electronic features that are favorable for optoelectronic applications. Thus, the cubic phase of Cs2AgBiBr6 was selected as the host lattice and bromine atoms were partly replaced with chlorine and iodine atoms. Electronic and optical properties of these mixed halide compounds of Cs2AgBiBr6−xFx, Cs2AgBiBr6−xClx, and Cs2AgBiBr6−xIx where x=1, 2, 3, 4, 5 are investigated with hybrid functional HSE06 level. The electronic structure revealed that these mixed compounds exhibited indirect band gap nature regardless of the halide substitution (different x concentration) and the band gap of Cs2AgBiBr6 could be varied with the substitutions of fluorine, chlorine, and iodine atoms. Our in-depth analysis shows that Cs2AgBiBr6 and their mixed halides have the potential to become active double perovskite materials for photovoltaic applications and as photocatalysts for water splitting. 2024-01-01T00:00:00Z http://repo.lib.jfn.ac.lk/ujrr/handle/123456789/13102 Title: Natural sensitizer extracted from Mussaenda erythrophylla for dye‑sensitized solar cell Authors: Rajaramanan, T.; Gourji, F.H.; Elilan, Y.; Yohi, S.; Senthilnanthanan, M.; Ravirajan, P.; Velauthapillai, D. Abstract: In this study, a natural dye from the flowers of Mussaenda erythrophylla extracted separately in ethanol and de-ionized water was employed as a photosensitizer in DSSCs. The quantitative phytochemical analyses were performed on both extracts. The existence of flavonoids (anthocyanin) and chlorophyll a pigments in the ethanol extract of the dye was confirmed by the UV–Visible spectroscopy. The stability study performed on the said ethanol extract confirmed that the dye extracted in ethanol was stable in the dark and did not degrade for nearly 50 days. The presence of the dye molecules and uniform adsorption of them on the P25-TiO2 surface were confirmed by fourier transform infrared spectroscopy and atomic force microscopy, respectively. Moreover, the influence of dye concentration and pH on the optical properties of the dye was also studied. The natural dye extracted in ethanol was employed in DSSCs, fabricated by utilizing the said dye sensitized P25-TiO2 photoanodes, I −/I − 3 electrolyte, and Pt counter electrode. Photovoltaic performances of the fabricated devices were determined under simulated irradiation with the intensity of 100 mWcm– 2 using AM 1.5 filter. The device fabricated with the P25-TiO2 photoanode sensitized by the dye extracted in ethanol at pH = 5 exhibited the best power conversion efficiency (PCE) of 0.41% with the JSC of 0.98 mAcm– 2 which could be attributed to the optimum light absorption in the visible region of solar spectrum by the chlorophyll a and anthocyanin molecules in the extracted natural dye. 2023-01-01T00:00:00Z http://repo.lib.jfn.ac.lk/ujrr/handle/123456789/13101 Title: Resistance to the larvicide temephos and altered egg and larval surfaces characterize salinity‑tolerant Aedes aegypti Authors: Sivabalakrishnan, K.; Thanihaichelvan, M.; Tharsan, A.; Eswaramohan, T.; Ravirajan, P.; Hemphill, A.; Ramasamy, R.; Surendran, S.N. Abstract: Aedes aegypti, the principal global vector of arboviral diseases and previously considered to oviposit and undergo preimaginal development only in fresh water, has recently been shown to be capable of developing in coastal brackish water containing up to 15 g/L salt. We investigated surface changes in eggs and larval cuticles by atomic force and scanning electron microscopy, and larval susceptibility to two widely-used larvicides, temephos and Bacillus thuringiensis, in brackish water-adapted Ae. aegypti. Compared to freshwater forms, salinity-tolerant Ae. aegypti had rougher and less elastic egg surfaces, eggs that hatched better in brackish water, rougher larval cuticle surfaces, and larvae more resistant to the organophosphate insecticide temephos. Larval cuticle and egg surface changes in salinity-tolerant Ae. aegypti are proposed to respectively contribute to the increased temephos resistance and egg hatchability in brackish water. The findings highlight the importance of extending Aedes vector larval source reduction efforts to brackish water habitats and monitoring the efficacy of larvicides in coastal areas worldwide. 2023-01-01T00:00:00Z http://repo.lib.jfn.ac.lk/ujrr/handle/123456789/13100 Title: Iodine-free acetonitrile-modified BmimI ionic liquid electrolyte with in-situ triiodide formation for efficient dye-sensitized solar cells Authors: Rajaramanan, T.; Gourji, F.H.; Zhao, Y.; Senthilnanthanan, M.; Ravirajan, P.; Velauthapillai, D. Abstract: In this study, an iodine-free 1-butyl-3-methylimidazolium iodide (BmimI) ionic liquid, modified with acetonitrile (AN), was employed as a redox mediator using a facile approach to enhance DSSC performance. The optical properties of BmimI-AN(1:2) electrolyte (BmimI: AN = 1:2 w/w) indicate low absorption and high transmittance in the visible region. In addition to the UV-Vis spectra, Raman spectra also confirm the presence of the in-situ generated I−3 ions, which are sufficient to complete the reaction mechanism in DSSCs. Conductivity measurements revealed that the BmimI-AN(1:2) electrolyte possesses excellent ionic conductivity compared to BmimI and standard commercial I−/I−3 electrolytes. The photovoltaic performances of the fabricated devices were analysed under simulated irradiation at an intensity of 100 mWcm–2 using a Xe lamp with an AM 1.5 filter. The BmimI-AN(1:2) electrolyte led to a higher power conversion efficiency (PCE) in DSSC, reaching up to 6.26 ± 0.21%, primarily due to improvements in VOC and JSC. Apart from the transparent nature of the BmimI-AN(1:2) electrolyte, it suppresses charge recombination, resulting in a higher electron lifetime in DSSCs. Moreover, DSSCs with the BmimI-AN(1:2) electrolyte exhibited short-term stability comparable to that of standard commercial electrolytes under ambient conditions, with the potential for further improvement through future optimization. 2026-01-01T00:00:00Z