Regensburg 2016 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 21: Hybrid and Perovskite Photovoltaics II (joint session CPP/DF/DS/HL, organized by CPP)
CPP 21.6: Talk
Tuesday, March 8, 2016, 12:15–12:30, H37
Mixed Pb:Sn methyl-ammonium halide perovskites: Thermodynamic stability and optoelectronic properties — •Lars Winterfeld, Ksenia Korshunova, Wichard J.D. Beenken, and Erich Runge — Institut für Physik, Technische Universität Ilmenau, 98693 Ilmenau, Germany
Using density functional theory, we investigate systematically mixed MA(Pb:Sn)X3 perovskites, where MA is CH3NH3+, and X is Cl, Br or I. Our results cover optoelectronic properties, structural and thermodynamic stability. Ab initio calculations of the orthorhombic, tetragonal and cubic perovskite phases show that the substitution of lead by tin has a much weaker influence on both structure and cohesive energies than the substitution of the halogen. The thermodynamic stability of the MA(Pb:Sn)X3 mixtures at finite, non-zero temperatures is studied within the Regular Solution Model. We predict that it will be possible to create iodide mixtures at any temperature. Mixing is unlikely for the low-temperature phase of bromide and chloride compounds, where instead local clusters are more likely to form. We further predict that in the high-temperature cubic phase, Pb and Sn compounds will mix for both MA(Pb:Sn)Br3 and MA(Pb:Sn)Cl3 due to the entropy contribution to the Helmholtz free energy. We calculated optoelectronic properties using both DFT and post-DFT methods (including self-consistent GW) with and without spin orbit coupling. Interestingly, the optoelectronic properties are not just a linear combination of the non-mixed parent structures and are not limited by the non-mixed values, which allows band gap engineering.