Abstract
Hybrid perovskites are among the most promising materials for optoelectronic applications. Their 2D crystalline form is even more interesting since the alternating inorganic and organic layers naturally forge a multiple quantum-well structure, leading to the formation of stable excitonic resonances. Nevertheless, a controlled modulation of the quantum well width, which is defined by the number of inorganic layers (n) between two organic ones, is not trivial and represents the main synthetic challenge in the field. Here, a conceptually innovative approach to easily tune n in lead iodide perovskite single-crystalline flakes is presented. The judicious use of potassium iodide is found to modulate the supersaturation levels of the precursors solution without being part of the final products. This allows to obtain a fine tuning of the n value. The excellent optical quality of the as synthesized flakes guarantees an in-depth analysis by Fourier-space microscopy, revealing that the excitons orientation can be manipulated by modifying the number of inorganic layers. Excitonic out-of-plane component, indeed, is enhanced when "n" is increased. The combined advances in the synthesis and optical characterization fill in the picture of the exciton behavior in low-dimensional perovskite, paving the way to the design of materials with improved optoelectronic characteristics.
Highlights
The quantum well thickness in Ruddlesden– Popper halide perovskites (RPPs) can be adjusted by varying the inorganic layers number “n” (i.e., n = 1,2,3, etc.) resulting in changes of the bandgap energies, electronic confinement, exciton binding energy,[18] and providing an unprecedented opportunity to fully determine the magnitude of in-plane (IP) and out-of-plane (OP) excitonic components and their modulation moving from 2D to 3D
We exploit as-prepared RPPs as platform to investigate by Fourier-resolved polarized photoluminescence (PL) the dipole orientation of the excitons in low dimensional systems, finding that the out-of-plane excitonic component is increased with the thickness of the quantum well. These results expand the knowledge on the chemistry involved in the complex synthesis of these hybrid semiconductors and on the fundamental physical properties of RPPs, allowing to correlate their structure with their variable exciton anisotropy that could be widely exploited in polarizationresolved optical devices
Synthesis of 2D perovskites (2D-PVKs) Single-Crystalline Flakes (C12)2(MA)Pb2I7, (C12)2(MA)2Pb3I10, (C12)2(MA)3Pb4I13, and (C12)2(MA)4Pb5I16 having n = 2, 3, 4, and 5 named C12n2, C12n3, C12n4, and C12n5, respectively, are prepared using a new one-step synthetic approach in which lead iodide (PbI2), n-dodecylammonium iodide (C12H25NH3I), methy lammonium iodide (CH3NH3I or MAI), and KI are dissolved in water/acetonitrile mixture
Summary
Hybrid organic–inorganic perovskites (PVKs) are in the research spotlight thanks to their outstanding photophysical properties combined with mild synthetic condition, straightforward processability, and tunable optical and electrical properties in function of their structure.[1,2] Such unique combination of factors is underpinning their diffusion as key active materials in solar cells,[3] light-emitting diodes,[4] photodetectors,[5,6] and photonic devices,[7,8,9,10,11,12] enabling significant breakthrough that are hard-to-reach with other classes of materials. The quantum well thickness in RPPs can be adjusted by varying the inorganic layers number “n” (i.e., n = 1,2,3, etc.) resulting in changes of the bandgap energies, electronic confinement, exciton binding energy,[18] and providing an unprecedented opportunity to fully determine the magnitude of in-plane (IP) and out-of-plane (OP) excitonic components and their modulation moving from 2D to 3D systems. The customization of these systems has interesting implications for the functionality of various optoelectronic devices. These results expand the knowledge on the chemistry involved in the complex synthesis of these hybrid semiconductors and on the fundamental physical properties of RPPs, allowing to correlate their structure with their variable exciton anisotropy that could be widely exploited in polarizationresolved optical devices
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