Rashba Spin–Orbit Coupling Enhanced Carrier Lifetime in CH₃NH₃PbI₃

Abstract

Organometal halide perovskites are promising solar-cell materials for next-generation photovoltaic applications. The long carrier lifetime and diffusion length of these materials make them very attractive for use in light absorbers and carrier transporters. While these aspects of organometal halide perovskites have attracted the most attention, the consequences of the Rashba effect, driven by strong spin-orbit coupling, on the photovoltaic properties of these materials are largely unexplored. In this work, taking the electronic structure of CH3NH3PbI3 (methylammonium lead iodide) as an example, we propose an intrinsic mechanism for enhanced carrier lifetime in three-dimensional (3D) Rashba materials. On the basis of first-principles calculations and a Rashba spin-orbit model, we demonstrate that the recombination rate is reduced due to the spin-forbidden transition. These results are important for understanding the fundamental physics of organometal halide perovskites and for optimizing and designing the materials with better performance. The proposed mechanism including spin degrees of freedom offers a new paradigm of using 3D Rashba materials for photovoltaic applications.

Rashba and Dresselhaus Couplings in Halide Perovskites: Accomplishments and Opportunities for Spintronics and Spin–Orbitronics

“…[24][25][26][27][28][29] More recently, it was proposed that the centrosymmetry breaking may rather occur on a local scale through dynamical fluctuations of the structure. 30,[113][114][115][116] Hence, the Rashba-induced mechanism preventing carrier recombination is suspected to occurs also in structures with centrosymmetry, e.g. the room-temperature phase of Applications in spintronics and spin-orbitronics Systems ruled by Rashba and Dresselhaus effects have been used to design devices able to (i) generate a spin-current, (ii) detect a spin-current, and (iii) modulate a spin-current.…”

“…112 When a Rashba or Dresselhaus effect is observed on the valence and/or conduction band one can expect effect on the lifetime of the carriers. Indeed, it has been proposed that the band splitting resulting of these effects would enhance the lifetime of charge carriers because of spin-forbidden transitions 113 and the resulting A c c e p t e d m a n u s c r i p t indirect band gap. 114,115 The Rashba-Dresselhaus effect was proposed initially for hybrid perovskites on the basis of refined crystallographic structures exhibiting an interplay between lack of inversion symmetry, a strong SOC and time reversal symmetry.…”

Dynamic Stereochemical Activity of the Sn2+ Lone Pair in Perovskite CsSnBr3

“…5,92,93 Additionally, Sn 2+ displacements along certain directions split the otherwise degenerate conduction band minima in momentum due to the local symmetry-breaking. Such momentum-splitting, arising either from local distortions 94,95 or spin-orbit coupling 96,97 has been proposed to limit carrier recombination. 94,96,97 Further, the off-centering tendency of the divalent cation contributes to the lattice deformability, which would aid the formation of large polarons which may protect carriers from bimolecular recombination.…”

“…Such momentum-splitting, arising either from local distortions 94,95 or spin-orbit coupling 96,97 has been proposed to limit carrier recombination. 94,96,97 Further, the off-centering tendency of the divalent cation contributes to the lattice deformability, which would aid the formation of large polarons which may protect carriers from bimolecular recombination. 89 Emergent anharmonicity in the phonon spectrum associated with lone pair stereochemical activity also has implications for phonon lifetimes and associated properties.…”

Giant Rashba Splitting inCH3NH3PbBr3Organic-Inorganic Perovskite

“…Relativistic effects, i. e. spin-orbit coupling (SOC) and resulting spin splitting, are expected because of the constituting heavy elements [8][9][10][11][12]. Spin splitting could be strong enough to contribute to the long carrier lifetimes in OIPCs [13][14][15], and to allow for OIPCbased spintronic devices [16,17]. However, the spin splitting found in calculations [18][19][20] is extremely sensitive to the orientation of the organic cation and to distortions of the inorganic cage, with calculated Rashba parameters of energetically similar structures [19] ranging from < 0.1 eVÅ to almost 10 eVÅ.…”