Inhomogeneous Defect Distribution in Mixed-Polytype Metal Halide Perovskites

Abstract

The competition between corner-, edge-, and face-sharing octahedral networks is a cause of phase inhomogeneity in metal halide perovskite thin-films. Here we probe the charged iodine vacancy distribution and transport at the junction between cubic and hexagonal polytypes of CsPbI3 from first-principles materials modeling. We predict a lower defect formation energy in the face-sharing regions, which correlates with a longer Pb–I bond length and causes a million-fold increase in local defect concentration. These defects are predicted to be more mobile in the face-sharing regions with a reduced activation energy for vacancy-mediated diffusion. We conclude that hexagonal phase inclusions or interfaces will act as defect sinks that could influence carrier dynamics in perovskite-based solar cells and electrical devices.

Halide Anion-Exchange-Driven Structural Phase Transition in CsPbX3 Perovskites: Alloys versus Heterostructures

“…20,21 Vacancy-mediated anion diffusion via the conventional hopping mechanism is widely regarded as the most probable way of inducing anion exchange in MHPs. 22 Owing to the flexible lattice and abundant halide vacancies in CsPbX 3 , anion exchange can be driven by a large halide concentration gradient between the exterior and interior of the perovskite structures. 23 Evidence of vacancy-mediated anion exchange has been determined by time-resolved photoluminescence (PL) spectra, 24 nanoprobe X-ray fluorescence, 25 and molecular dynamics (MD) simulations.…”

“…Accompanied by a growing number of experimental findings on anion exchange in CsPbX 3 perovskites, mechanistic insights into the anion-exchange-driven structural transformation are of great interest and fundamental importance for both the regulation of properties and device applications. Hence, great efforts have been devoted to the understanding of the anion-exchange mechanism in CsPbX 3 (X = Cl, Br, I) perovskites. , Vacancy-mediated anion diffusion via the conventional hopping mechanism is widely regarded as the most probable way of inducing anion exchange in MHPs . Owing to the flexible lattice and abundant halide vacancies in CsPbX 3 , anion exchange can be driven by a large halide concentration gradient between the exterior and interior of the perovskite structures .…”

Bromine Incorporation Affects Phase Transformations and Thermal Stability of Lead Halide Perovskites

“…These point spectra have emission peaks at the same wavelengths but overall lower intensity due to variations in height of the film caused by secondary phases growing on the surface. 65 As the annealing temperature increases from 150 to 250 °C, CsFAPbI (Figure 2k) loses the sharp characteristic perovskite peak around 780 nm 47,59 and instead broadens into a wide peak spanning 600−800 nm. This broad peak is indicative of the formation of hexagonal-FAPbI 3 phases (also known as 2H, 4H, and 6H).…”

Eliminating Halogen Vacancies Enables Efficient MACL‐Assisted Formamidine Perovskite Solar Cells

“…As reported, the Pb 6p and I 5s orbitals dominate the band edges of perovskite. [21] The shallow defects on the surface can affect the electron arrangement around the atom. [22,23] Compared with defect-free and V I − perovskite film in Figure 1c, the presence of V I − will cause the defect state on the surface of perovskite, resulting in the corresponding reduction of Pb 6p electronic states, leading to significant defect energy levels (at 1.85 eV).…”