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C2.10 - Computational Design of Novel Hybrid Perovskites 
April 7, 2015   4:45pm - 5:00pm

Solar cells based on hybrid metal-organic halide perovskites have been polarizing the attention of the photovoltaics community in the past 3 years due to their ever increasing efficiencies, currently over 19%. This success is largely due to methylammonium lead iodide and mixed halide having band gaps approaching the Shockley-Queisser limit (1.55 eV) and electron and hole diffusion lenghts exceeding 1 micron. Additionally, these electronic properties can be tuned by mixing different halides, metal atoms or cations. In this context computational design can assist the search for novel and even more efficient perovskites by exploring a vast materials library in silico. In this work we elucidate the interplay between the electronic properties and the structure of the lead-iodide perovskite network. We model the perovskite unit cell by four ideal corner sharing octahedra, which can rigidly rotate within the constraints of an orthorhombic unit cell. We show that the structure can be uniquely identified two geometrical parameters, the apical and equatorial Pb-I-Pb bond angles. Furthermore we show a strong correlation between the calculated band gap and these angles. In addition, we show that the magnitude of the Pb-I-Pb angles can be directly controlled by changing the size of the cation component at the center of the cuboctahedral cavity. Based on this finding we propose 17 lead-iodide perovskite absorbers containing different cations at the center of the lead-iodide network, 14 of which have not been reported thus far. The band gaps for these potential novel absorbers are theoretically tunable over 1 eV. Moreover, the band gap trends exhibited are consistent accross different computational approaches (density functional theory and GW - with and without spin-orbit coupling) [1,2] Experiments motivated by this study not only confirmed our predicted trends, but also lead to the synthesis of the novel mixed Rb{1-x}Cs{x}PbI3 perovskite. [1] Filip, M. R., Eperon, G., Snaith, H. J. & Giustino, F., (2014) [2] Filip, M. R. & Giustino, F., (2014) This work was supported by the European Research Council (EU FP7 / ERC grant no. 239578), the UK Engineering and Physical Sciences Research Council (Grant NO. EP/J009857/1) and the Leverhulme Trust (Grant RL-2012-001). G.E.E. is supported by the UK EPSRC and Oxford Photovoltaics Ltd. through a Nanotechnology KTN CASE award. Calculations were performed at the Oxford Supercomputing Centre and the Oxford Materials Modelling Laboratory.

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