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Decreasing the electronic confinement in layered perovskites through intercalation † † Electronic supplementary information (ESI) available. CCDC 1487885 . For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6sc02848a Click here for additional data file. Click here for additional data file.

View Article: PubMed Central - PubMed

ABSTRACT

We show that post-synthetic small-molecule intercalation can significantly reduce the electronic confinement of 2D hybrid perovskites. Using a combined experimental and theoretical approach, we explain structural, optical, and electronic effects of intercalating highly polarizable molecules in layered perovskites designed to stabilize the intercalants. Polarizable molecules in the organic layers substantially alter the optical and electronic properties of the inorganic layers. By calculating the spatially resolved dielectric profiles of the organic and inorganic layers within the hybrid structure, we show that the intercalants afford organic layers that are more polarizable than the inorganic layers. This strategy reduces the confinement of excitons generated in the inorganic layers and affords the lowest exciton binding energy for an n = 1 perovskite of which we are aware. We also demonstrate a method for computationally evaluating the exciton's binding energy by solving the Bethe–Salpeter equation for the exciton, which includes an ab initio determination of the material's dielectric profile across organic and inorganic layers. This new semi-empirical method goes beyond the imprecise phenomenological approximation of abrupt dielectric-constant changes at the organic–inorganic interfaces. This work shows that incorporation of polarizable molecules in the organic layers, through intercalation or covalent attachment, is a viable strategy for tuning 2D perovskites towards mimicking the reduced electronic confinement and isotropic light absorption of 3D perovskites while maintaining the greater synthetic tunability of the layered architecture.

No MeSH data available.


Slabs of (IC6)2[PbI4] (A) and (IC6)2[PbI4]·2I2 (B) and their corresponding calculated high-frequency dielectric profiles ε∞,⊥. Here, ε∞,⊥ is the high-frequency dielectric constant perpendicular to the direction of layer propagation. Dark green, purple, blue, and grey spheres represent Pb, I, N, and C atoms, respectively. Hydrogen atoms omitted for clarity.
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fig5: Slabs of (IC6)2[PbI4] (A) and (IC6)2[PbI4]·2I2 (B) and their corresponding calculated high-frequency dielectric profiles ε∞,⊥. Here, ε∞,⊥ is the high-frequency dielectric constant perpendicular to the direction of layer propagation. Dark green, purple, blue, and grey spheres represent Pb, I, N, and C atoms, respectively. Hydrogen atoms omitted for clarity.

Mentions: The bulk high-frequency dielectric response (ε∞) corresponds to an average response over all layers of the perovskite and is not suited to describe the difference in dielectric constant between the organic and the inorganic layers. We therefore used a method designed to compute ε∞ profiles for nanoscale slabs and composite systems10,51 to estimate the respective contributions from the organic and inorganic layers to the bulk ε∞ value. Profiles of the high-frequency dielectric constant perpendicular to the layers (ε∞,⊥) in (IC6)2[PbI4] and (IC6)2[PbI4]·2I2 are shown in Fig. 5. The behavior of ε∞,⊥ changes substantially when I2 molecules intercalate. The average ε∞,⊥ dielectric profile stemming from the inorganic layers increases from 5.4 to 7.0 when including I2. For the ε∞,⊥ dielectric profile associated with the organic layers, we see a dramatic three-fold increase from 3.7 to 11.1 upon I2 intercalation. Therefore, I2 intercalation significantly decreases the dielectric confinement of excitons in the inorganic layers by better screening electric field lines in the organic layer.


Decreasing the electronic confinement in layered perovskites through intercalation † † Electronic supplementary information (ESI) available. CCDC 1487885 . For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6sc02848a Click here for additional data file. Click here for additional data file.
Slabs of (IC6)2[PbI4] (A) and (IC6)2[PbI4]·2I2 (B) and their corresponding calculated high-frequency dielectric profiles ε∞,⊥. Here, ε∞,⊥ is the high-frequency dielectric constant perpendicular to the direction of layer propagation. Dark green, purple, blue, and grey spheres represent Pb, I, N, and C atoms, respectively. Hydrogen atoms omitted for clarity.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384564&req=5

fig5: Slabs of (IC6)2[PbI4] (A) and (IC6)2[PbI4]·2I2 (B) and their corresponding calculated high-frequency dielectric profiles ε∞,⊥. Here, ε∞,⊥ is the high-frequency dielectric constant perpendicular to the direction of layer propagation. Dark green, purple, blue, and grey spheres represent Pb, I, N, and C atoms, respectively. Hydrogen atoms omitted for clarity.
Mentions: The bulk high-frequency dielectric response (ε∞) corresponds to an average response over all layers of the perovskite and is not suited to describe the difference in dielectric constant between the organic and the inorganic layers. We therefore used a method designed to compute ε∞ profiles for nanoscale slabs and composite systems10,51 to estimate the respective contributions from the organic and inorganic layers to the bulk ε∞ value. Profiles of the high-frequency dielectric constant perpendicular to the layers (ε∞,⊥) in (IC6)2[PbI4] and (IC6)2[PbI4]·2I2 are shown in Fig. 5. The behavior of ε∞,⊥ changes substantially when I2 molecules intercalate. The average ε∞,⊥ dielectric profile stemming from the inorganic layers increases from 5.4 to 7.0 when including I2. For the ε∞,⊥ dielectric profile associated with the organic layers, we see a dramatic three-fold increase from 3.7 to 11.1 upon I2 intercalation. Therefore, I2 intercalation significantly decreases the dielectric confinement of excitons in the inorganic layers by better screening electric field lines in the organic layer.

View Article: PubMed Central - PubMed

ABSTRACT

We show that post-synthetic small-molecule intercalation can significantly reduce the electronic confinement of 2D hybrid perovskites. Using a combined experimental and theoretical approach, we explain structural, optical, and electronic effects of intercalating highly polarizable molecules in layered perovskites designed to stabilize the intercalants. Polarizable molecules in the organic layers substantially alter the optical and electronic properties of the inorganic layers. By calculating the spatially resolved dielectric profiles of the organic and inorganic layers within the hybrid structure, we show that the intercalants afford organic layers that are more polarizable than the inorganic layers. This strategy reduces the confinement of excitons generated in the inorganic layers and affords the lowest exciton binding energy for an n = 1 perovskite of which we are aware. We also demonstrate a method for computationally evaluating the exciton's binding energy by solving the Bethe–Salpeter equation for the exciton, which includes an ab initio determination of the material's dielectric profile across organic and inorganic layers. This new semi-empirical method goes beyond the imprecise phenomenological approximation of abrupt dielectric-constant changes at the organic–inorganic interfaces. This work shows that incorporation of polarizable molecules in the organic layers, through intercalation or covalent attachment, is a viable strategy for tuning 2D perovskites towards mimicking the reduced electronic confinement and isotropic light absorption of 3D perovskites while maintaining the greater synthetic tunability of the layered architecture.

No MeSH data available.