Electronic band structure trends of perovskite halides: Beyond Pb and Sn to Ge and Si

Abstract

The trends in electronic band structure are studied in the cubic ABX3 halide perovskites for A= Cs, B=Pb, Sn, Ge, Si and X=I, Br, Cl. The gaps are found to decrease from Pb to Sn and from Ge to Si, but increase from Sn to Ge. The trend is explained in terms of the atom s-levels of the group-IV element and the atomic sizes which changes the amount of hybridisation with X-p and hence the valence band width. Along the same series spin-orbit coupling also decreases and this tends to increase the gap because of the smaller splitting of the conduction band minimum. Both effects compensate each other to a certain degree. The trend with halogens is to reduce the gap from Cl to I, i.e. with decreasing electro-negativity. The role of the tolerance factor in avoiding octahedron rotations and octahedron edge-sharing is discussed. The Ge containing compounds have tolerance factor t > 1 and hence do not show the series of octahedral rotation distortions and the existence of edge-sharing octahedral phases known for Pb and Sn based compounds, but rather a rhombohedral distortion. CsGeI3 is found to have a suitable gap for photovoltaics both in its cubic (high-temperature) and rhombohedral (low-temperature) phases. The structural stability of the materials in the different phases is also discussed. We find the rhombohedral phase to have lower total energy and slightly larger gaps but to present a less significant distortion of the band structure than the edge-sharing octahedral phases, such as the yellow phase in CsSnI3. The corresponding silicon based compounds have not yet been synthesized and therefore our estimates are less certain but indicate a small gap for cubic CsSiI3 and CsSiBr3 of about 0.2±0.2 eV and 0.8±0.6 eV for CsSiCl3. The intrinsic stability of the Si compounds is discussed.

Defining the topological influencers and predictive principles to engineer the band structure of halide perovskites

“…We find that with this cutoff, the number of plane waves lies in the range 10 3 -10 4 . The Brillouin zone integration is car- There exist a few articles in the literature discussing the electronic structure of CsSnI 3 obtained from DFT calculations [9,20,[26][27][28][29]. The focus of these articles is mainly confined to examine the bandgap of the compound and its suitability for photovoltaic applications.…”

“…(a) Bar chart representing the various crystal phases of inorganic and organic halide perovskites. The data is collected from different literature works[17,27,28,[37][38][39][40][41][42][43][44][45]. (b) Surface states of centrosymmetric and non-centrosymmetric systems.…”

Organic–inorganic metal halide hybrids beyond perovskites

“…Germanium in the same Group IV was also reported to form 3D perovskite structures with MA + , FA + and Cs + [41,42]. With higher tolerance factor t, Ge based metal halide perovskites have higher structural stability but still suffer from its high reactivity with oxidants [43,44]. There are a number of review articles available for 3D metal halide perovskites, their properties, and applications in optoelectronic devices [45,46].…”

Computational high throughput screening of inorganic cation based halide perovskites for perovskite only tandem solar cells

“…The structural and thermodynamic stability of the perovskites is an important aspect to look at, in order to use them for suitable practical applications. Inorganic halide perovskites, in general, are more stable than their hybrid counterparts, the instability of which are owed to the weakly bonded soft organic cation [32][33][34][35][36][37][38][39][40][41][42][43][44]. However, the degree of stability varies with the variation of the 3 inorganic cations using in this study.…”

“…Inorganic materials are known to have higher stability than the organic materials, especially at higher temperatures [29][30][31]. This aspect has been exploited quite well experimentally, in which the organic cation has been replaced by the inorganic Cs + cation that resulted in a rapid decrease in instability problems, thereby promising a relatively higher intrinsic or thermodynamic stability against decomposition to binary halide products [32][33][34][35][36][37][38][39][40][41][42][43][44]. However, theoretical investigation towards this pressing issue is still limited [11][12][13][14][15][16][17][18][19].…”