Polarons in Metal Halide Perovskites

Abstract

The peculiar optoelectronic properties of metal‐halide perovskites, partly underlying their success in solar cells and light emitting devices, are likely related to the complex interplay of electronic and structural features mediated by formation of polarons. In this paper the current status of polaron physics in metal‐halide perovskites is reviewed based on a first‐principles computational perspective, which has delivered hitherto noaccessible insights into the electronic and structural features associated with polaron formation in this materials class. The role of organic (dipolar) versus inorganic (spherical) A‐site cations is extensively analyzed, these cations are related to modulation of the energetics and structural extension of polarons in lead‐halide perovskites. Further tuning of polaron energetics is achieved by individual variations in metal (e.g., Pb → Sn) and halide (e.g., I → Br), showing a transition from a semilocalized to a localized polaron regime in which charge holes can be trapped at isolated Sn centers. The vastly varying and tunable nature of charge lattice interactions represents a peculiarity of metal‐halide perovskites that should be taken into account when designing novel materials or targeting specific compositional engineering of existing perovskites.

Mixed Conductivity of Hybrid Halide Perovskites: Emerging Opportunities and Challenges

“…In this regard, in-depth analysis is required to elucidate the mechanisms and establish structureproperty relationships that define guidelines for suitable molecular design toward addressing the challenges of controlling ion migration in various hybrid perovskite compositions. This further involves understanding the underlying polaronic effects on the properties of various compositions (Zhou et al, 2019;Meggiolaro et al, 2020) and dimensionalities (Srimath Kandada and Silva, 2020). Moreover, since the reported lifetimes of hybrid perovskite devices vary due to different assessment procedures, rigorous stability testing protocols are being established (Khenkin et al, 2020) that allow for a critical assessment of the operating conditions.…”

“…), encased by divalent-metal-halide-based (B mostly Pb 2+ or Sn 2+ ; X I − , Br − or Cl − ) octahedral framework (Grätzel, 2017). Such versatile ionic systems feature remarkable light-absorption coefficients as well as a high defect tolerance due to an interplay of electronic and structural features (Meggiolaro et al, 2020) that can account for exceptional charge-carrier lifetimes (Kim and Petrozza, 2020) of interest to a number of optoelectronic devices, from solar cells and photodetectors to light-emitting diodes (Rong et al, 2018;Snaith, 2018). As a result, they have been proven effective light-absorbers in photovoltaic devices leading to extraordinary performances that have in just a decade surpassed 25% , along with exceptional light-emission (Abdi-Jalebi et al, 2018;Lin et al, 2018;Smith et al, 2019) and photodetection capacities (Lei et al, 2020).…”

Halide Perovskite Materials for Energy Storage Applications

“…The polaronic characters (either positive or negative) have been found ubiquitous in lead halide perovskites; [ 262 ] the formation of large polarons, as a result of the coupling between photogenerated charges and optical lattice phonons, is proposed as one of the most fascinating mechanism to explain the peculiar optoelectronic properties of the halide perovskites. [ 263 ] The energy level alignment involving the conduction band, valence band, Fermi level, and work function between the electrode materials and additives are important for efficient charge generation, transports, and collection in halide perovskite‐based devices under the illumination condition. The interplay among phonons, photons, and lithium ion movement should be comprehensively described.…”

Dynamic polaronic screening for anomalous exciton spin relaxation in two-dimensional lead halide perovskites

“…On the other hand, in contrast to conventional inorganic semiconductors, the crystal lattice of lead halide perovskites is soft and polar and exhibits large anharmonicity and dynamic disorder, leading to strong electron-phonon coupling (5). As a result, both experimental and theoretical studies have implied that charge carriers in 3D perovskites are dressed by surrounding lattice deformation, forming large polarons (6)(7)(8)(9)(10). The polaronic effect has been considered as one key factor to the exceptional photophysical properties of 3D perovskites, including slow electron-hole bimolecular recombination (6)(7)(8)(9)(10) and hot carrier thermalization (11).…”