Electroactive Nanoporous Metal Oxides and Chalcogenides by Chemical Design

The archetypal silica- and aluminosilicate-based zeolite-type materials are renowned for wide-ranging applications in heterogeneous catalysis, gas-separation and ion-exchange. Their compositional space can be expanded to include nanoporous metal chalcogenides, exemplified by germanium and tin sulfides and selenides. By comparison with the properties of bulk metal dichalcogenides and their 2D derivatives, these open-framework analogues may be viewed as three-dimensional semiconductors filled with nanometer voids. Applications exist in a range of molecule size and shape discriminating devices. However, what is the electronic structure of nanoporous metal chalcogenides? Herein, materials modeling is used to describe the properties of a homologous series of nanoporous metal chalcogenides denoted np-MX2, where M = Si, Ge, Sn, Pb, and X = O, S, Se, Te, with Sodalite, LTA and aluminum chromium phosphate-1 structure types. Depending on the choice of metal and anion their properties can be tuned from insulators to semiconductors to metals with additional modification achieved through doping, solid solutions, and inclusion (with fullerene, quantum dots, and hole transport materials). These systems form the basis of a new branch of semiconductor nanochemistry in three dimensions.

S2 functional (HSE06) 3 with 25% of the short-range semi-local exchange replaced by the exact non-local Hartree−Fock exchange.
In order to provide the eigenvalue spectrum on an absolute energy scale, we employ a recently reported approach for porous solids 4 . For the reference electrostatic potential we use a spherical average of the Hartree potential in a sphere of r = 2 Å with an origin at the center of the pore. The variance within the sphere is checked to ensure a plateau in the potential is present with no internal electric fields. The analysis code for this calculation, which can also calculate planar and macroscopic averages of electrostatic potentials and charge densities, is freely available. The electrostatic potential was sampled on a grid of mesh density >14 points/Å. Structural stability was determined relative to the common condensed phases of metal chalcogenides. Experimentally determined unit cells were used as starting point, with the exception of GeTe 2 , PbS 2 , PbTe 2 , and SnTe 2 , where there have been no experimental reports of these binary materials. Using the Materials Project, 5 structures for the aforementioned compositions were obtained using the structure generator function, and numerous MX 2 structures were computed. The lowest energy structures were used as the standard states. The minimum energy space groups were found to be P-3m1 (SiTe 2 -type), P-3m1 (CdI 2 -type), I4/mcm (PbSe 2 -type), and P-3m1 (SnSe 2 -type) for GeTe 2 , PbS 2 , PbTe 2 , and SnTe 2 , respectively.  Table S1: Electron energies for zeolitic materials examined herein. VBM = valence band maximum; CBM = conduction band minimum; E g = band gap; P = potential; Φ = workfunction; EA = electron affinity; a = lattice constant; V = volume; dH = Enthalpic cost of formation of the porous solids with respect to the dense phase.  Figure S2: Band alignment and band structures of SiO 2 polymorphs. Figure S3: An example of a photo-assisted formation of a Sn III center from charge transfer from guest SPIRO-OMeTAD 6 .

Dopant concentration examination
The concentration of dopants as discussed in the isovalent substitutions in the manuscript concern only one substitution per crystallographic unit cell. Depending on the structure this corresponds to 1-5%. It is, at least computationally, possible to include higher dopant concentrations through the inclusion of two S atom substitutions in place of the native framework O. In the case where these S atoms are placed vicinally (not depicted in Figure   S4), the framework is unstable due to the increase in torsion around the central metal. The framework was able to support two S atoms, however, if they were spatially separated.
Electronically, there is a minor shift in VBM energy that can be attributed to the structural distortion associated with the decreased Si-S-Si bond angle. Indeed, the S atoms in the Si 12 O 22 S 2 material are not equivalent (two valence bands are observed in the electronic band structure, and at low S loadings the SOD network exhibits significant structural distortion.
Energetically, we can use the doubly doped sulfide to gain insight into the stability of these solid solutions. Using the SiO 2 and SiS 2 standard states, we compute the relative stability of the Si 12 O 22 S 2 material to be 0.05 eV per ion less stable than porous oxide. Figure S4: Alignment of the HSE06 electronic band structures of S-substituted SOD-SiO 2 .

Parent binary electronic structure
The electronic band structures of the binary compounds display a similar trend to the nanoporous materials. Band structures presented in Figure S5 are taken from the Materials Project database. 7 Figure S5: Electronic band structures of minimum energy SiX 2 phases, as presented on the Materials Project website (https://materialsproject.org) calculated using the PBE exchangecorrelation functional. 7