Large lattice distortions and size-dependent bandgap modulation in epitaxial halide perovskite nanowires

Abstract

Metal-halide perovskites have been shown to be remarkable and promising optoelectronic materials. However, despite ongoing research from multiple perspectives, some fundamental questions regarding their optoelectronic properties remain controversial. One reason is the high-variance of data collected from, often unstable, polycrystalline thin films. Here we use ordered arrays of stable, single-crystal cesium lead bromide (CsPbBr 3) nanowires grown by surface-guided chemical vapor deposition to study fundamental properties of these semiconductors in a one-dimensional model system. Specifically, we uncover the origin of an unusually large size-dependent luminescence emission spectral blue-shift. Using multiple spatially resolved spectroscopy techniques, we establish that bandgap modulation causes the emission shift, and by correlation with state-of-the-art electron microscopy methods, we reveal its origin in substantial and uniform lattice rotations due to heteroepitaxial strain and lattice relaxation. Understanding strain and its effect on the optoelectronic properties of these dynamic materials, from the atomic scale up, is essential to evaluate their performance limits and fundamentals of charge carrier dynamics.

Vertically Aligned CsPbBr3 Nanowire Arrays with Template-Induced Crystal Phase Transition and Stability

“… 48 One possible reason for the blue-shift is, with decreasing diameter, the larger surface-to-volume ratio will create more surface of CsPbBr 3 NWs. Since CsPbBr 3 is a relatively soft material, 49 , 50 more surface between AAO and NWs means more lattice distortion, which affects the energy band structure of CsPbBr 3 and possibly causes the emission wavelength blue-shift. 39 , 51 A second possible reason is strain between the NWs and the AAO pores, like the explanations of PL blue-shift in CsPbBr 3 NWs in previous reports.…”

“… 39 , 51 A second possible reason is strain between the NWs and the AAO pores, like the explanations of PL blue-shift in CsPbBr 3 NWs in previous reports. 20 , 21 , 26 , 48 , 50 …”

Deconvoluting Energy Transport Mechanisms in Metal Halide Perovskites Using CsPbBr3 Nanowires as a Model System

“…The transport of photons or charge carriers in such structures is considered to be mainly confined to the long axis of the nanowire, which simplifies the interpretation of the data. Meanwhile, due to the highly homogenous nature of single-crystalline nanowires, such a structure is almost free from structural and compositional perturbations that could cause local fluctuations in the bandgap, [29] introduce additional non-radiative recombination pathways, [30] and reduced mobility. [31] To deconvolute the spectroscopic signatures, we employ wide-field photoluminescence (PL) emission and excitation microscopy with both temporal and spectral resolution, and the ability to control the localization of both excitation and detection, thus being able to separate the two regions.…”

“…The transport of photons or charge carriers in such structures is considered to be mainly confined to the long axis of the nanowire, which simplifies the interpretation of the data. Meanwhile, due to the highly homogenous nature of single‐crystalline nanowires, such a structure is almost free from structural and compositional perturbations that could cause local fluctuations in the bandgap, [ 29 ] introduce additional non‐radiative recombination pathways, [ 30 ] and reduced mobility. [ 31 ]…”

Graphoepitaxy of Large Scale, Highly Ordered CsPbBr3 Nanowire Array on Muscovite Mica (001) Driven by Surface Reconstructed Grooves

“…Furthermore, the thermal expansion coefficient in 110 nm wide NW is 288.41 μeV K −1 (Figure 4c, red) and quite larger than that in 500 nm wide NW (48 μeV K −1 , Figure 4c, violet), which may be due to enhanced lattice distortion in thinner NWs. [ 49 ] It should be noted that the lattice distortion does not significantly reduce the crystal quality (Figure S13, Supporting Information). Generally, the temperature dependence behaviors are similar to that of the NWs with similar sizes growing along the [110] and [101] directions, suggesting the comparable optical and crystal quality of these NWs (Figure S14, Table S1, Supporting Information).…”