Tailoring Optical Properties of Luminescent Semiconducting Nanocrystals through Hydrostatic, Anisotropic Static, and Dynamic Pressures

Abstract

Studies on the hydrostatic-pressure-dependent optical properties of av ariety of metal-halide perovskites will be discussed below.M etal-halide perovskites (MHPs), which have the general formula ABX 3 [A = Cs + ,C H 3 NH 3 + (methylammonium, MA), HC(NH 3 ) 2 2+ (formamidinium, FA), etc.; B = Pb 2+ ,S n 2+ ,e tc.; and X = Cl, Br, or I],h ave been widely studied because of their tremendous potential for use in many optoelectronic applications,i ncluding solar cells, [18][19][20][21] LEDs, [22][23][24][25][26] photodetectors, [27,28] and scintillators. [29] Thee xceptional optical performance of MHPs can be attributed to their strong optical absorption, [30,31] low exciton binding energy, [32] long exciton diffusion lengths, [33] high carrier mobility, [34,35] defect tolerance, [36][37][38] and facile synthesis. [35,39] Lead-halide perovskites (LHPs) are ac lass of MHPs that have shown great promise as aresult of the abovementioned unique properties and their relatively high stability. [40] LHP NCs are of particular interest because of their extremely bright and narrow photoluminescence (PL) band and the ease of tuning their emission wavelengths by tuning both the halide composition and the size of the NCs. [41][42][43][44][45][46][47] Thef ollowing subsections will outline how the application of hydrostatic pressure alters the optical properties of avariety of LHP NCs. All-Inorganic CsPbX 3 PerovskitesCs + is acommonly used A-site cation in all-inorganic LHP NCs because its large ionic radius (R A = 1.88 )a llows the formation of astable perovskite phase,asdetermined by the Goldschmidt tolerance factor. [48] CsPbBr 3 NCs have been shown to possess an ear-unity photoluminescence quantum yield (PLQY), narrow (i.e.8 6meV) full width at half max (FWHM), and superior stability to both CsPbI 3 and CsPbCl 3 . [49,50] When subjected to hydrostatic pressures up to about 1.4 GPa, the PL spectra of CsPbBr 3 NCs was redshifted, widened, and decreased in intensity until ca. 1.3 GPa, at which pressure the PL was sharply quenched (Figure 1). [51] Thea uthors attributed the discontinuity to an isostructural phase transformation of the Pbnm space group. [51] Firstprinciple calculations suggested that the shift in the emission and the phase change were due to pressure-induced variations of the BrÀPb bond lengths and shrinkage of the Pb-Br-Pb bond angles within the lead bromide octahedra. [51] Interest-Angewandte Chemie Minireviews 9774 www.angewandte.org

Pressure-Induced Structural and Optical Transitions in Luminescent Bulk Cs4PbBr6

“…The PL redshift, followed by a blueshift and the emission quenching have been observed in the hybrid and all-inorganic metal halide perovskite; however, there is no agreement about its origin. This process was ascribed to pressure-induced distortions of the band structure, underlying structural phase transitions, orbital interactions due to the octahedral tilting, amorphization, among other effects, as described in the review from Biesold et al 42 PL studies have been carried out on luminescent and nonluminescent Cs 4 PbBr 6 nanocrystals. Both compounds are structurally equivalent under ambient conditions, according to De Bastiani et al 54 The phase I to II transition was also confirmed in those samples.…”

“…The PL redshift, followed by a blueshift and the emission quenching have been observed in the hybrid and all-inorganic metal halide perovskite; however, there is no agreement about its origin. This process was ascribed to pressure-induced distortions of the band structure, underlying structural phase transitions, orbital interactions due to the octahedral tilting, amorphization, among other effects, as described in the review from Biesold et al…”

“…As a thermodynamical variable, high pressure is a straightforward and robust tool to tune the structural and electronic properties of materials and explore the arising of new phenomena not existent under ambient conditions. Thus, hydrostatic pressure can modify bond lengths and bond angles in metal halide materials without changing the chemical composition. − Under hydrostatic pressure, the inorganic framework is modified by B–X bond contraction and B–X–B bridge bending, coupled with the BX 6 octahedral tilting . The pressure effect on lead halide 3D perovskites has drawn extensive attention and demonstrated an unavoidable impact on their optical properties. ,,, Low-dimensional metal halides were also investigated using high-pressure experiments .…”

Strain Relaxation for Perovskite Lattice Reconfiguration

“…However, the laboratory interest in volumetric strain is mainly focused on compressive strain (hydrostatic strain) rather than tensile strain, perhaps because uniform volume stretching is difficult to achieve, or related research value remains to be further explored. [29,30] In terms of theoretical calculations, both Berdiyorov's and Jing's teams explored the properties of perovskite materials by hydrostatic strain. The former focused on electronic transport properties, while the latter comprehensively investigated the effects of structural, electronic, and optical properties.…”

Performance Improvement of Perovskite Solar Cells by Interactions between Nano‐Sized Quantum Dots and Perovskite

“…[6,7] Quantum dot (QD) materials are endowed with quantum confinement effect, conducive to both the energy and charge transfer from/to the contacted perovskite absorber and therefore favorable for the performance improvement of PSCs. [8][9][10][11] With the incorporation of quantum dots (QDs), new path for energy transfer is constructed, and overlap between the excitation spectrum of perovskite and the emission spectrum of QDs is obtained, raising light absorption. [12] In addition, QDs assist in charge transfer as the mediators that form better energy-level alignment between perovskite layer and charge transporting layers (CTLs), contributing to the performance improvement of PSC devices.…”