A-site composition-property relations in halide perovskites: which descriptors do what?

Abstract The vastness of halide perovskite (HP) properties and applications is greatly a consequence of their compositional versatility. A large part of this versatility stems from A-site compositional engineering in the ABX 3 stoichiometry, enabling fine-tuning of the desired properties. The current literature provides in-depth knowledge of how A-site cations affect these properties. However, there is a certain sense of mystery surrounding understanding exactly why the different cations cause different effects. To provide more insight into finding answers to that, we here propose describing diverse A-site HP compositions using a combination of their effective descriptors, namely the radii, dipole moments, number of N-H bonds, and entropy of mixing. For this purpose, a total of 65 three-dimensional ABX 3 compositions were synthesized and their structures, optoelectronic, and electrical behavior were characterized. The extracted properties of the obtained single-phase solid solutions, namely, tetragonal-to-cubic transition temperature, band gap, Urbach energies, electrical conductivity, and I-V hysteresis, were correlated with the four descriptors using statistical tools. Examples of relevant effects were found for the entropy in reducing and number of N-H bonds in increasing the phase transition temperature, the dipole moment in increasing the band gap, the radius in reducing the Urbach energy and the dipole moment and N-H bonds in mitigating the charge transport characteristics. The results provide suitable rules of thumb for qualitative prediction of property changes upon varying the A-site in 3D ABX 3 halide perovskites.