Anharmonicity-Driven Rashba Cohelical Excitons Break Quantum Efficiency Limitation.
basic_science · Level V
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- Record sourced from PubMed, PMID 33336533.
- Also identified by DOI 10.1002/adma.202005400.
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Abstract
Closed-shell light-emitting diodes (LEDs) suffer from the internal quantum efficiency (IQE) limitation imposed by optically inactive triplet excitons. Here, an unrevealed emission mechanism of lead halide perovskites (LHPs) APbX<sub>3</sub> (A = Cs/CN<sub>2</sub> H<sub>5</sub> ; X = Cl/Br/I) that circumvents the efficiency limit of closed-shell LEDs is explored. Though efficient emission is prohibited by optically inactive J = 0 in inversion symmetric LHPs, the anharmonicity arising from stereochemistry of Pb and resonant orbital-bonding network along the imaginary A<sup>+…</sup> X<sup>-</sup> (T<sub>1u</sub> ) transverse optical (TO) modes, breaks inversion symmetry, introducing disorder and Rashba-Dresselhaus spin-orbit coupling (RD-SOC). This results in bright cohelical and dark antihelical excitons. Many-body theory and first-principles calculations show that the optically active cohelical exciton is the lowest excited state in organic/inorganic LHPs. Thus, RD-SOC can drive to achieve the ideal 50% IQE by utilizing anharmonicity, much over the 25% IQE limitation for closed-shell LEDs.