Impact of Organic Spacers on the Carrier Dynamics in 2D Hybrid Lead-Halide Perovskites

Abstract

We have carried out nonadiabatic molecular dynamics simulations combined with time-dependent density functional theory calculations to compare the properties of the two-dimensional (2D) (BA) 2 (MA)Pb 2 I 7 and three-dimensional (3D) MAPbI 3 (where MA = methylammonium and BA = butylammonium) materials. We evaluate the different impacts that the 2D-confined spacer layer of butylammonium cations and the 3D-confined methylammonium cations have on the charge carrier dynamics in the two systems. Our results indicate that, while both the MA + and BA + cations play important roles in determining the carrier dynamics, the BA + cations exhibit stronger nonadiabatic couplings with the 2D perovskite framework. The consequence is a faster hotcarrier decay rate in 2D (BA) 2 (MA)Pb 2 I 7 than in 3D MAPbI 3 . Thus, tuning of the functional groups of the organic spacer cations in order to reduce the vibronic couplings between the cations and the Pb−I framework can offer the opportunity to slow down the hot-carrier relaxations and increase the carrier lifetimes in 2D lead-halide perovskites.

Influence of the Vibrational Modes from the Organic Moieties in 2D Lead Halides on Excitonic Recombination and Phase Transition

“…In addition, our findings are experimental evidences for the predictions from the work of Zhang et al. [ 44 ] In their report they used molecular nonadiabatic simulations combined with density functional theory calculations to evaluate the impact of the organic molecules in 2D BA 2 [MAPbI 3 ]PbI 4 and 3D MAPbI 3 (MA = methylammonium) on the charge carrier dynamics. They found that coupled vibrational modes between the BA + cations and the Pb‐I framework are responsible for the fast hot‐carriers relaxation via strong electron‐phonon coupling.…”

Electronic States Modulation by Coherent Optical Phonons in 2D Halide Perovskites

“…[ 4–7 ] This is attributed to their favorable optoelectronic properties, such as large exciton binding energy, [ 8 ] sizeable oscillator strength, [ 9 ] robust chemical stability, [ 5 ] as well as facile photophysical tunability, etc. Despite the inroads in understanding various phenomena, such as spin‐selective optical Stark effect, [ 10 ] image charge effect, [ 8,11 ] and Rashba splitting [ 12 ] etc., progress remains modest for carrier–phonon coupling that significantly affects the optical and electronic properties of the 2D halide perovskites, such as absorption and photoluminescence (PL) line shape, [ 13,14 ] carrier recombination, [ 15 ] and hot carrier cooling, [ 16–18 ] etc. Although experimental observations of electron–phonon coupling are well reported, how these lattice vibrations modulate the optical properties of the halide perovskites is still an open question.…”

Tin Halide Perovskites: Progress and Challenges

“…Presently, Pb-based 2D and lower dimensional perovskites materials and devices are more prominent. [176][177][178][179][180] Therefore, the development of nontoxic Pb-free alternatives cannot be over emphasized. The geometrical, electronic and optical properties of a series of 2D Sn perovskite semiconductors (CH 3 (CH 2 ) 3 NH 3 ) 2 (CH 3 NH 3 ) n−1 Sn n I 3n+1 (n = 1, 2, and 3) theoretically investigated by Wang et al [181] revealed that the series possess strong and broad optical absorption with small electrons and holes effective masses.…”