Using a high-throughput approach based on density functional theory, we perform an extensive study of possible ABX₃ perovskites, where X is a non-metal and A and B span a large portion of the periodic table. We calculate the ternary phase diagram for each composition and we discuss the thermodynamic stability of perovskite phases. We find a large number of ABX₃ perovskites, which are still absent from available databases, and which are stable with respect to decomposition into known ternary, binary or elementary phases. For these structures, we then calculate electronic band gaps, hole effective masses, and the spontaneous ferroelectric and magnetic polarization, which are relevant material properties for a number of specific applications in photovoltaics, transparent contacts, piezoelectrics, and magnetoelectrics. Some of our novel perovskites exhibit promising properties for applications.

“Lead-free” piezoelectric sodium potassium niobate has been studied with respect to its defect structure when doping with CuO. The results indicate that two kinds of mutually compensating charged defect complexes are formed, $(\text{Cu}\prime \prime {\prime }_{\text{Nb}}-V_{\mathrm{O}}^{••})\prime$ and ${(V_{\mathrm{O}}^{••}-\text{Cu}\prime \prime {\prime }_{\text{Nb}}-V_{\mathrm{O}}^{••})}^{•}$ . Concerning the interplay of these defect complexes with the piezoelectric materials properties, the trimeric ${(V_{\mathrm{O}}^{••}-\text{Cu}\prime \prime {\prime }_{\text{Nb}}-V_{\mathrm{O}}^{••})}^{•}$ defect complex primarily has an elastic dipole moment and thus is proposed to impact the electromechanical properties, whereas the dimeric $(\text{Cu}\prime \prime {\prime }_{\text{Nb}}-V_{\mathrm{O}}^{••})\prime$ defect possesses an electric dipole moment in addition to an elastic distortion. Both types of defect complexes can impede domain-wall motion and may contribute to ferroelectric “hardening.”

Hybrid perovskites, such as methylammonium lead iodide, have revolutionized research on solar cells in the past few years. Well known instability and toxicity issues restrain however the large-scale application of these perovskites in commercial photovoltaic technology. It is therefore the most urgent task to find a way to chemically stabilize these and other lead-free perovskites, preserving at the same time their excellent absorption and charge-transport properties. The obvious route to follow is chemical substitution. In this work we screen the periodic table of elements for hybrid organic–inorganic halide perovskites, using high-throughput density-functional theory calculations. We consider compounds with the composition A⁺B²⁺X₃ ⁻, where A is a molecular organic cation, X is a halogen, and B is a divalent element. For the molecular cation, we vary the molecule size from sulfonium (H₃S, very small) to tert-butylammonium (C₄NH₁₂, very large). All thermodynamically stable hybrid perovskites are then further characterized by calculating their band gaps and effective masses, to identify the most promising candidates for further experimental and theoretical characterization. We find that the substitution of the organic molecule is the most promising way to enhance thermodynamic stability, while there is no optimal replacement for lead or Sn, unless one considers partial substitution or alloying.

In the lead-free perovskite potassium sodium niobate, the thermodynamically preferred lattice sites and charge states of vacancies and substitutional Cu atoms for different processing conditions are determined theoretically from first principles. For that purpose, defect-formation energies of vacancies and Cu substitutionals in different charge states are calculated with the density-functional theory in the local-density approximation using norm-conserving pseudopotentials and a mixed-basis supercell approach. The formation energy of vacancies and the relative stability of Cu substitutionals on alkali and Nb sites in potassium sodium niobate are determined for oxygen-rich and oxygen-poor processing conditions and as function of the Fermi energy, and the densities of states are analyzed in terms of free charge carriers.