Intrinsic doping limitations in inorganic lead halide perovskites

Combining Trivalent Ion-Doping with Halide Alloying to Increase the Efficiency of Tin Perovskites

Tin-halide perovskites (THP) are emerging materials for photovoltaics with optoelectronic properties potentially rivaling lead-based analoges. Their efficiencies in solar cells are, however, severely limited by the high sensitivity of tin to oxygen and the heavy p-doping natively present in the material. While the effects of oxygen can be mitigated by using reducing agents upon the synthesis and by encapsulating the device, the native p-doping caused by the high density of acceptor defects remains a challenge to be further addressed for prolonging carrier lifetimes and, consequently, device efficiency. In this work, potential compositional engineering strategies aimed at reducing the p-doping of this class of materials and increasing their efficiency in solar cells are investigated. Based on density functional theory simulations it is demonstrated that THP doping with d1s2 trivalent ions effectively decreases the hole background density and the density of the deep defects responsible for the non-radiative recombination in these materials. This effect is enhanced by alloying iodide with small fractions of bromide, up to 33%. Higher bromide fractions, instead, are detrimental due to the increased non-radiative recombination. These results may provide useful guidelines to experimentalists for improving the optoelectronic quality of THPs and consequently of the ensuing devices.

All-inorganic lead halide perovskite nanocrystals applied in advanced display devices

Advanced display devices are in greater demand due to their large color gamut, high color purity, ultrahigh visual resolution, and small size pixels. All-inorganic lead halide perovskite (AILHP) nanocrystals (NCs) possess inherent advantages such as narrow emission width, saturated color, and flexible integration, and have been developed as functional films, light sources, backlight components, and display panels. However, some drawbacks still restrict the practical application of advanced display devices based on AILHP NCs, including working stability, large-scale synthesis, and cost. In this review, we focus on AILHP NCs, review the recent progress in materials synthesis, stability improvement, patterning techniques, and device application. We also highlight the important role of materials systems in creating advanced display devices, followed by the challenges and opportunities in industrial processes. This review provides beneficial inspiration for the future development of AILHP NCs in colorful and white backlight, as well as high resolution full-color displays.

Comparing the Cubic and Tetragonal Phases of MAPbI3 at Room Temperature

Stability and maintenance of the crystal structure are the main drawbacks of the application of organic-inorganic perovskites in photovoltaic devices. The ΔT = 62 K robust shift of the structural phase transition observed here allows us to conduct a comprehensive study at room temperature of the tetragonal versus cubic phase on MAPbI₃. The absence of the shift in the cubic transition for all-inorganic CsPbI₃ samples confirms the importance of both orientation and dynamics of the organic cations. Our results provide a unique opportunity to evaluate the physical properties of both cubic and tetragonal phases of MAPbI₃ at the same temperature, eliminating different phonon effects as possible causes for different properties. Besides higher electrical resistivity, the perovskite cubic phase presents a faster charge carrier lifetime than the tetragonal phase and partial PL quenching, pointing toward increased trap-assisted nonradiative recombination. The light absorption coefficient in the cubic phase is larger than the absorption in the tetragonal phase in the green region.

How cation nature controls the bandgap and bulk Rashba splitting of halide perovskites

Because of instability issues presented by metal halide perovskites based on methylammonium (MA), its replacement to Cs $$ \mathrm{Cs} $$ has emerged as an alternative to improve the materials' durability. However, the impact of this replacement on electronic properties, especially gap energy and bulk Rashba splitting remains unclear since electrostatic interactions from organic cations can play a crucial role. Through first-principles calculations, we investigated how organic/inorganic cations impact the electronic properties of MAPbI 3 $$ {\mathrm{MAPbI}}_3 $$ and CsPbI 3 $$ {\mathrm{CsPbI}}_3 $$ perovskites. Although at high temperatures the organic cation can assume spherical-like configurations due to its rotation into the cages, our results provide a complete electronic mechanism to show, from a chemical perspective based on ab initio calculations at 0 K $$ 0\ \mathrm{K} $$ , how the MA $$ \mathrm{MA} $$ dipoles suppression can reduce the MAPbI 3 $$ {\mathrm{MAPbI}}_3 $$ gap energy by promoting a degeneracy breaking in the electronic states from the PbI 3 $$ {\mathrm{PbI}}_3 $$ framework, while the dipole moment reinforcement is crucial to align theory ↔ $$ \leftrightarrow $$ experiment, increasing the bulk Rashba splitting through higher Pb $$ \mathrm{Pb} $$ off-centering motifs. The lack of permanent dipole moment in Cs $$ \mathrm{Cs} $$ results in CsPbI 3 $$ {\mathrm{CsPbI}}_3 $$ polymorphs with a pronounced Pb $$ \mathrm{Pb} $$ on-centering-like feature, which causes suppression in their respective bulk Rashba effect.