Ferroelectric Alignment of Organic Cations Inhibits Nonradiative Electron–Hole Recombination in Hybrid Perovskites: Ab Initio Nonadiabatic Molecular Dynamics

Abstract

Hybrid organic-inorganic perovskites show impressive potential for photovoltaic applications and currently give rise to one of the most vibrant research areas in the field. Until recently, the electrostatic interactions between their organic and inorganic components were considered mostly for stabilization of the fragile perovskite structure. We study the effect of local interactions of polar C-N bonds in the organic layer on the nonradiative electron-hole recombination in the recently reported room-temperature ferroelectric hybrid perovskite, (benzylammonium)PbCl. Using nonadiabatic molecular dynamics and real-time time-dependent density functional theory, we show that ferroelectric alignment of the polar groups weakens the electron-phonon nonadiabatic coupling and inhibits the nonradiative charge recombination. The effect is attributed to suppression of contributions of higher frequency phonons to the electron-phonon coupling. The coupling is dominated in the ferroelectric phase by slower collective motions. We also demonstrate the importance of van der Waals interactions for the charge-phonon relaxation in the hybrid perovskite systems. Combined with the long-range charge separation achievable in the ferroelectric phase, the weakened electron-phonon coupling indicates that ferroelectric order in hybrid perovskites can lead to increased excited-state lifetimes and improved solar energy conversion performance.

Theoretical Progress on the Relationship between the Structures and Properties of Perovskite Solar Cells

“…Jankowska and Prezhdo [ 224 ] investigated the electron–hole recombination for the ferroelectric layered perovskite, (benzylammonium) 2 PbCl 4 , by combination of NAMD and time‐domain DFT (TD‐DFT). They found that the ferroelectric phase exhibited slower electron–hole recombination than the paraelectric phase due to the suppression coupling of the electronic subsystem to the high frequency phonons.…”

Recent theoretical progress in the development of perovskite photovoltaic materials

“…At the same time, it may be worth noticing, that for another system belonging to the HOIP family, characterized with more spatially extended aromatic cation, the room-temperature stable ferroelectric phase has been experimentally confirmed [152] . Recently also the effects of local ferroelectric order on photo-generated charge recombination has been investigated by means of non-adiabatic molecular dynamics simulations for this system [153] .…”

The quantum-confined Stark effect in layered hybrid perovskites mediated by orientational polarizability of confined dipoles

“…Unlike the fully inorganic semiconductors used in conventional quantum well modulators, hybrid perovskites and their layered derivatives can accommodate dipolar cations. The role of the A cations in bulk perovskites has attracted attention: numerous studies have focused on optimizing mixtures of several cations for improving device performance 19 – 21 , investigating the possibility of alignment of dipolar cations 22 – 26 , and probing the rotational dynamics of dipolar cations 27 – 32 . Although research into low-dimensional perovskites is growing, the corresponding studies have yet to be conducted in these materials; the differences with the bulk suggest that the smaller cations in low-dimensional perovskites may add intriguing properties.…”