Circularly Polarized Photoluminescence of Chiral 2D Halide Perovskites at Room Temperature

Abstract

Chiral halide perovskites have attracted considerable attention because of their chiroptical, second-harmonic generation, and ferroelectricity properties and their potential application in chiroptoelectronics and chiral spintronics. However, the fundamental research of these properties is insufficient. In this work, chiral perovskites were synthesized using precursor solutions with various stoichiometric ratios ⟨n⟩. The chiral perovskite film prepared from the solution with ⟨n⟩ = 1 is composed of (R-/S-/rac-MBA) 2 PbBr 4 , whereas the films prepared from the solutions with ⟨n⟩ larger than 1 are a mixture of (R-/S-/rac-MBA) 2 (CsMA) n−1 Pb n Br 3n+1 with n = 1 and large n values. A photoluminescence quantum yield of approximately 90 was obtained. Symmetric circular dichroism (CD) spectra were observed without an external magnetic field. Under various magnetic fields, magnetic field-induced CD features are superimposed with the intrinsic chirality-induced CD features. For the ⟨n⟩ = 1 chiral perovskite film, the energy level splitting induced by chiral molecules are a few 10 μeV, whereas the energy level splitting induced by magnetic fields are at the range of ∼−250 to ∼250 μeV. Circularly polarized photoluminescence spectra were observed at room temperature and associated with the spin-preserved energy funneling from highly energetic phases to the lower energetic phases.

Defect-Induced Circularly Polarized Luminescence of Chiral Perovskite Films

“…The g CD values of GECP films show peaks similar to that of the CD spectrum, which eliminates the dependence of CD signal on film thickness, simultaneously. 27 This result clearly demonstrates that GECP films and NECP films have similar chiral optical properties, and the amount of MABr plays an important role in the crystal structure and CD response of chiral MBAPbBr 3 films.…”

“…The UV−vis spectra of GECP films are similar to that of the NECP films with a peak at 320 nm, as shown in Figure2c, which can be ascribed to the exciton absorption from dielectric and quantum confinement in the semiconducting PbBr 6 4− -layered structure according to previous reports. 26,27 The PL spectra show that the GECP films exhibit a strong green emission at 530 nm with an excitation wavelength at 365 nm. No detectable PL signal of the NECP films can be obtained, which can be attributed to the indirect band gap energy with a fast nonradiative transition.…”

“…To investigate the optical chirality of GECP films, we calculated circular dichroism (CD) and absorption dissymmetry factor g CD , respectively, as shown in Figure a,c. g CD is defined as the difference in absorbance of left- and right-circularly polarized light, , which can be calculated by the following equation: g CD = CDmdeg 32 , 980 × absorbance …”

“…These results are consistent with previous reports. 11,27 The GE-rac-film cannot exhibit a chiroptical response due to the nature of racemic modification. Furthermore, it can be observed that the CD peaks of films significantly change with the increase of MABr (Figure S10).…”

“…It indicates that the GECP films can absorb an unequal amount of LCP and RCP light and generate an unequal amount of spin-up and spin-down excitons after being excited by unpolarized light. 27,29 No CPL signal can be observed for the GE-rac-film even though it can emit green luminescence (Figure S12). Meanwhile, the CPL response is silent for NECP films due to their indirect gap property, as shown in Figure S13.…”