Spectroscopic Evidence of Localized Small Polarons in Low-Dimensional Ionic Liquid Lead-Free Hybrid Perovskites

Abstract

Rational design is an important approach to consider in the development of low-dimensional hybrid organic−inorganic perovskites (HOIPs). In this study, 1-butyl-1-methyl pyrrolidinium (BMP), 1-(3aminopropyl)imidazole (API), and 1-butyl-3-methyl imidazolium (BMI) serve as prototypical ionic liquid components in bismuth-based HOIPs. Element-sensitive X-ray absorption spectroscopy measurements of BMPBiBr 4 and APIBiBr 5 reveal distinct resonant excitation profiles across the N Kedges, where contrasting peak shifts are observed. These 1D-HOIPs exhibit a large Stokes shift due to the small polaron contribution, as probed by photoluminescence spectroscopy at room temperature. Interestingly, the incorporation of a small fraction of tin (Sn) into the APIBiBr 5 (Sn/Bi mole ratio of 1:3) structure demonstrates a strong spectral weight transfer accompanied by a fast decay lifetime (2.6 ns). These phenomena are the direct result of Sn-substitution in APIBiBr 5 , decreasing the small polaron effect. By changing the active ionic liquid, the electronic interactions and optical responses can be moderately tuned by alteration of their intermolecular interaction between the semiconducting inorganic layers and organic moieties.

Effect of Dual-Organic Cations on the Structure and Properties of 2D Hybrid Perovskites as Scintillators

“…Table S2 displays the calculated average lifetime ( t avg ), which considers both time constants and their respective weightings to assess the overall lifetime of the crystals and the parameters derived from the fitting. By the introduction of BZA cation in a pure (PEA) 2 PbBr 4 perovskite structure, the average decay times for (PEA 1.5 BZA 0.5 )­PbBr 4 and (PEABZA)­PbBr 4 are approximately 4.9 and 3.6 times faster than that for pure (PEA) 2 PbBr 4 , respectively. Additionally, the (PEA 1.5 BZA 0.5 )­PbBr 4 crystal has a similar decay time (1.3 ns) compared to (PEABZA)­PbBr 4 crystal (1.8 ns) due to the low content of BZA being introduced into both crystal lattices.…”

“…A substantial Stokes shift of 0.06 eV was noted in the case of (BZA) 2 PbBr 4 , whereas a comparatively smaller Stokes shift of 0.01 eV was observed for (PEA 1.5 BZA 0.5 )­PbBr 4 . The significant Stokes shift in (BZA) 2 PbBr 4 can be attributed to its lower degree of self-absorption . Also due to the experimental configuration with precise excitation beam focusing, the collected emission signal comes in majority from the perovskite crystal surface.…”

“…The significant Stokes shift in (BZA) 2 PbBr 4 can be attributed to its lower degree of self-absorption. 5 Also due to the experimental configuration with precise excitation beam focusing, the collected emission signal comes in majority from the perovskite crystal surface. Thus we regard the measured PL spectra with only a minor contribution from the self-absorption effect.…”

“…Hybrid organic–inorganic perovskite (HOIP) scintillators with diverse dimensions play a pivotal role in detecting ionizing radiation due to their fast and high light yield, making them particularly well-suited for applications such as imaging, spectroscopy, and timing. − Two-dimensional (2D) HOIP crystals are promising scintillating materials for energy detection over a wide range of energies due to their exceptional luminescence efficiency, excellent photoabsorption capability, high exciton binding energy, and environmental stability. , Particularly noteworthy is the superior tunability and unique optoelectronic properties of 2D-HOIP, which make them highly desirable for scintillation applications. , Furthermore, their multiple quantum well-layered structure facilitates electron confinement effects, thereby limiting electron mobility between organic and inorganic components to a certain extent . This orderly and controlled process enhances their effectiveness as scintillators for X-ray detection …”