Tuning the Optical Properties of Perovskite Nanoplatelets through Composition and Thickness by Ligand‐Assisted Exfoliation

Abstract

High-quality hybrid halide perovskite nanocrystals are fabricated through a simple, versatile, and efficient two-step process involving a dry step followed by a ligand-assisted liquid-phase exfoliation step. The emission wavelength of the resulting nanocrystals can be tuned either through composition by varying the halide content or by reducing their thickness.

Advances in Quantum‐Confined Perovskite Nanocrystals for Optoelectronics

“…[21] The thickness of nanoplatelets obtained in the reprecipitation method can also be controlled by varying the ratio of oleylamine and oleic acid ligands used, reported by Levchuk et al [29] In addition to the bottom-up reprecipitation method, perovskite nanocrystals can also be fabricated in a top-down fashion, as we recently demonstrated in the ligand-assisted transformation of bulk perovskites into nanoplatelets of various compositions and thicknesses by means of ultrasonication. [9] Figure 1c shows the photograph of solutions of colloidal MAPbI 3 nanoplatelets (n = 1,2,3, ≥3 and ∞) illuminated Figure 1. a) Schematic illustration of the quantum confinement effect on the energy levels of semiconductor nanocrystals.…”

“…[5] Although most of the initial studies were mainly focused on thin films of perovskite for solar cells, [6,7] recently there has been growing interest in highly luminescent nanocrystalline perovskites for many optoelectronic applications. [2,[8][9][10][11][12] Perovskites generally possess an ABX 3 type crystal structure, where B is a…”

“…Similarly, perovskite nanocrystals of reduced dimensionality exhibit quantum confinement effects, as shown for the case of nanoplatelets in 2015. [8][9][10]21,22] Despite recent advances, an accurate understanding of thickness-and dimensionality-dependent optical properties of perovskite nanocrystals still proves elusive due to difficulties in the controlled syntheses and characterization of their dimensions. Additionally, while many recent publications present perovskite nanocrystals, most of these show negligible or no quantum confinement.…”

“…[17] Recent studies have shown that nanocrystalline perovskites exhibit enhanced PLQYs and offer tunable optical properties not only through their constituent ions but also through their size. [3,[8][9][10][11]15,18,19] Quantum size effects, as illustrated in Figure 1a, have been extensively investigated in conventional semiconductor nanocrystals such as metal chalcogenides and utilized for a wide range of applications during the last two decades. [20] As the size of the nanocrystals approaches the exciton Bohr radius of the material, quantum confinement effects start to influence the excitonic wave function and the energetic states of the exciton, leading to blueshifted photoluminescence (Figure 1a).…”

Hybrid Photovoltaics – from Fundamentals towards Application

“…Moreover, if the nanoparticles maintain their quantum confinement character, they exhibit high exciton binding energies in the range of several hundred meV, which is not favorable for charge separation. [102][103][104] If the exciton binding energy is considerably larger than the thermal energy, the spontaneous formation of free electrons and holes becomes difficult. Therefore, it is evident that just blending the two components may not lead to highly efficient photovoltaic systems with morphological control and stability.…”