University of Perugia, Italy
By Dr. Giacomo-Giorgi, University of Perugia, Italy.
Organic-Inorganic Halide Perovskites (OIHPs) are undoubtedly playing the key role in the realm of modern photovoltaics (PV): [1] bulk OIHPs, characterized by the general ABX3 stoichiometry, have been shown indeed to possess unique features in solar-to-energy applications. [2] Nevertheless, the presence of few intrinsic detrimental issues still prevents their usage for device mass production. Critical in this sense is the presence of both a hydrophilic organic moiety (i.e. methylammonium, CH3NH3+, MA, A-site cation) which enhances the air/moisture mediated degradability, thus limiting the lifetime of 3D OIHPs based devices, and of a pollutant, Pb (B-site cation), which raises the con-cerns towards environmental issues. While for this latter drawback the immediate solu-tion is the replacement of lead with other, more ecofriendly, cations,[3] the possible solu-tion of the former involves the total/partial replacement of MA with longer chain, hy-drophobic, aromatic or aliphatic, cations whose presence induces a change in the dimen-sionality of the final systems. These so-called mixed 2D/3D Ruddlesden-Popper Perov-skites (RPPs) have emerged as an alternative to 3D bulk for their superior photo- and chemical-stability coupled with high-performance optoelectronic properties. Several experimental papers have been recently published revealing the interest of the community towards this class of materials. [4] At the same time ab-initio studies focusing on the role of many-body effects are very limited and their results are not yet conclusive.
In my seminar, after a quick voyage over the general properties of the 3D bulk OIHPs, I will discuss my work based on Density Functional Theory (DFT), Green Function (GW), and Bethe Salpeter Equation (BSE) simulations, which has shown the appealing optoelectronic properties of novel and overlooked Pb-free fully inorganic perovskites. [5] Focusing then on the A-site cation replacement, I will introduce RPPs discussing their electronic and optical properties ‒obtained with the same theoretical setup‒ both as iso-lated nanosheets (NS) and as periodic quantum wells (QW). [6] I will finally rationalize the relationship existing between structures (number of layers) and optoelectronic features.
References
[1] Kojima, A. et al., J. Am. Chem. Soc., 2009, 131, 6050-6051.
[2] See among the others: (a) G.G. et al., J. Phys. Chem. Lett. 2013, 4, 4213−4216; (b) Xing, G. et al., Science, 2013, 342, 344−347; (c) Stranks, S. D. et al., Science, 2013, 342, 341−344; (d) G.G. and Yamashita, K., J. Mater. Chem. A, 2015, 3, 8981-8991.
[3] Ogomi, Y. et al., J. Phys. Chem. Lett., 2014, 5, 1004–1011.
[4] Mitzi, D., Chem. Mater. 1996, 8, 791-800.
[5] G.G., et al., J. Mater. Chem. C, 2018, 6, 10197-10201.
Biography
Giacomo Giorgi (GG) is Associate Professor at the Department of Civil & Environmental Engineering (DICA) at the University of Perugia. He is nowadays focusing his research on the ab-initio study of electronic and optical properties of materials for solar-to-energy conversion. He is author of approximately 70 publications including articles in international peer-reviewed journals, several book chapters, and review articles. He has given a total ~20 invited talks, lectures, and seminars.
After obtaining his PhD (2003) under the supervision of Prof. A. Sgamellotti, he has spent his first postdoctoral experience at the University of Tokyo in 2006 in the group led by Prof. Koichi Yamashita, group where he spent a period of research from 2009 to 2012. In 2012 he has got a Project Assistant Professorship at the Research Center for Advanced Science and Technology (RCAST) at The University of Tokyo in the group of led by Prof. Hiroshi Segawa. From 2013 to 2015 he has been Senior Researcher at the Department of Chemical Syste Engineering, The University of Tokyo, Japan, still in the group led by Koichi Yamashita.