| Description: | [DPS Seminar] Dr. Arpan Krishna Deb (Shiv Nadar University) -- Ab initio design of tin based perovskites and chalcogenides for energy applications. |
| Date: | Wednesday, Sep 21, 2016 |
| Time: | 2 p.m. - 3 p.m. |
| Venue: | 113, DPS Meeting Room, RC |
| Details: | Great efforts are being made to develop materials that can convert abundant solar energy in to electrical energy efficiently and economically to save environment from burning of fossil fuels. Moreover, reserves of fossil fuels are getting depleted and therefore alternate energy sources are required. Recently high efficiency of ∼ 15-20% has been achieved with Methyl Lead Halide perovskite as light absorber. But there is also a simultaneous thrust in research to design lead free materials. This talk comprises two kinds of materials which are designed to have electronic properties suitable for opto- electronic devices. There are several factors that make Methyl Lead Halide perovskite family so interesting 1) There is a direct band gap of about 1-1.5 eV and this is very good for high optical absorption of solar radiation. 2) It is reported that there are p-p optical transitions that are favourable because the Pb atoms behave as divalent and their 5s states do not lose their s electrons though they hybridize significantly with the halogen p states. Hence the lower parts of the conduction band of organo-lead halides are mainly made up of the unoccupied Pb 5p orbitals while the top of the VB mainly comprises the halogen p orbitals mixed with significant component of Pb 5s orbital. 3) These halides exhibit ambipolar charge transport and very long electron hole diffusion lengths. The effective masses of the electrons and holes are small and also the electron-hole binding energy is small. Further improvements have been obtained by manipulating the chemical composition by substitution of e.g. Cl in place of iodine to form a mixed organo-metallic halide that has been found to improve the efficiency and the stability of the solar cells. We here report Ab initio calculations on lead-free materials like the mixed halides CsSn(X x Y 1−x ) 3 , X and Y = I, Cl, and Br and one and few layers of SnX and GeX (X=S, Se) semiconductors using GGA and HSE06 formalisms as implemented within the framework of Density Functional Theory. We find that the electronic properties of these materilas are similar to the recently discovered promising perovskite materials for photovoltaics and suggest that the layered materials can also be exploited for photovoltaics and opto-electronic applications with the possibility of band gap engineering. |
| Calendar: | Seminar Calendar (entered by ghossain) |