Tailoring the Band Gap in 3D Hybrid Perovskites by Substitution of the Organic Cations: (CH₃NH₃)_1−2y(NH₃(CH₂)₂NH₃)_2yPb_1−yI₃ (0≤y≤0.25)

Abstract

Tuning the optical properties of MAPbI (MA=methylammonium) is a key requirement to increase the efficiency of perovskite solar cells (PSCs). Simple precipitation from solution allows the partial substitution of MA in MAPbI by H NCH CH NH (H en). Surprisingly, there is 1:1 exchange of the monovalent cation MA by the dication H en. The charge compensation results from a deficit of Pb , leading to a series MA (H en) Pb I with 0≤y≤0.25. This model has been supported by single-crystal measurements and NMR investigations. The substitution results in a continuous shift of the band gap from 1.51 to 2.1 eV and a color change from black to orange-red. The H en content stabilizes the cubic high-temperature (HT) form of MAPbI . There is a linear correlation between band gap and unit cell volume. The substitution enables controlled band gap tuning because the extent of substitution is closely related to the applied MA:H en ratio in solution.

Hollow metal halide perovskite nanocrystals with efficient blue emissions

“…In contrast, the diffraction peaks for the samples EDA5 and EDA5-Na displayed small shifts to lower 2 as a result of unit cell expansion. This shift of diffraction peaks could be well explained to result from the incorporation of large EDA 2+ cations [ionic radius, 333 pm (32)] within the 3D perovskite structure, which has previously been shown in other halide perovskites (32)(33)(34)(35)(36). Previous reports had proposed lattice strain caused by Pb-X (X = Cl, Br, I) bond elongation (35) and the formation of a hollow 3D structure (32) as mechanisms to explain lattice expansion upon the incorporation of large organic cations.…”

A combined molecular dynamics and experimental study of two-step process enabling low-temperature formation of phase-pure α-FAPbI 3

“…The remaining iodide (I − ) from MAI is placed on the Pb-I octahedra to have a final charge-neutral layered MAPbI 3 structure. This model is based on experimentally reported intercalated PbI 2 structures (29,30). We verify the stability of this structure by carrying out a variable cell enthalpic optimization with both classical MD simulations and density functional theory (DFT) calculation.…”

It's a trap! On the nature of localised states and charge trapping in lead halide perovskites

“…The intentional incorporation of small molecules in 3D perovskites (ethylenediammonium 141 ) can promote lead and halide vacancy formation in the 3D structure, creating a less connected perovskite structure and a blue-shift in the direct bandgap. 141,142 The less dense 3D perovskite is commonly called a hollow perovskite, and provides a fundamentally new way to manipulate perovskite intrinsic properties through defect engineering, without changing dimensionality or halide composition. Most importantly, hollow perovskites exhibit improved air stability 141 compared to their unmodified counterparts and allow for efficient solar cells (B17%; Pb/Snbased).…”