Executive Summary : | "As most of the fossil fuel energy sources are declining towards an end, the quest for natural, renewable energy sources is becoming an area of utmost importance. At this moment, solar energy plays an integral role promoting the research in the field of photovoltaic, photocatalysis and magneto-optics to be an important avenue to hunt for alternative source of energy. Finding novel materials for solar cell applications is at the heart of these fields.
Hybrid lead-halide perovskites (CH3NH3PbX3; X=I,Br,Cl) have drawn tremendous attention in the field of photovoltaics due to their outstanding optoelectronic properties making them suitable for light emitting diodes (LED) and photodetecting applications. The major drawbacks of MAPbX3 are the toxicity due to Pb and poor stabilty due to migrating ions. Replacement of organic cation by ingorganic Cs+1 helps in stabilizing the system but presence of Pb is still a concern. In recent times, B-site ordered double perovskite halides(DPH) A2BB’X6 have grabbed significant attention as an alternative material. Cation ordering at B-site opens up scope of doping/alloying by accommodating different transition metal(TM) ions. The presence of Cs+1 at A site and absence of Pb makes these DPHs stable and environment friendly as well as offers the possibility of +1 and +3 oxidation state of B and B’ ions (e.g. Ag, Cu for B and Bi, Cr, Mn for B’). Double perovskites (DP) with Bi at B’ site are in limelight due to their interesting properties associated with lone-pair. Previous study on nonmagnetic Cs2AgInCl6 shows enhancement of photoluminescence quantum yield(PLQY) by doping Bi at B’-site with different concentrations[1]. Study on Cs2AgBiX6 shows indirect large bandgap ~ 2.1 eV with mixing of 4d orbitals and halogen 3p/4p orbitals[2]. A promising material for photovoltaic application should acquire few properties e.g. narrow (1.1-1.8 eV) and direct bandgap, high carrier mobility and absorption coefficient, high defect tolerance. Introducing magnetism into nonmagnetic DPHs can reduce the bandgap significantly and Fe+3 doping is reported to be a clever strategy in achieving the same in Cs2AgInCl6[3]. A detailed magnetic properties of Fe based double-perovskite halides is still unexplored. Here we propose to study the effect of magnetic element(3+) alloying in lead-free DPH Cs2AgBiX6, with chemical formula Cs2AgBi1-xMxX6 (M=Transition metal). We plan to engineer the band structure and hence optimize the optoelectronic properties for photovoltaic/photocatalysis applications. We shall also explore the interplay of induced magnetization with spin-orbit coupling combining 5d-3d elements and hence investigate the magneto-optic Kerr/Faraday effects. We shall also explore all the above properties for pure magnetic double perovskites Cs2AgMX6 (M=Transition metal). [1] D. Manna et al., Phys. Chem Lett. 2020, 11, 2113-2120
[2] E. T. McClure et al., Chem. Mater. 2016, 28, 1348-1354
[3] F. Ji et al., Chem. Sci. 2021, 12, 1730-1735" |