Deciphering the Ultrafast Nonlinear Optical Properties and Dynamics of Pristine and Ni-Doped CsPbBr₃ Colloidal Two-Dimensional Nanocrystals

Abstract

While the unabated race persists in achieving record efficiencies in solar cells and other photonic/optoelectronic devices using lead halide perovskite absorbers, a comprehensive picture of the correlated third-order nonlinear optical (NLO) properties is yet to be established. The present study is aimed at deciphering the role of dopants in multiphoton absorption properties of intentionally engineered CsPbBr 3 colloidal nanocrystals (NCs). The charge separation of the plasmonsemiconductor conduction band owing to the hot electron transfer at the interface was demystified using the dynamics of the bleached spectral data from femtosecond (fs) transient absorption spectroscopy with broadband capabilities. The NLO properties studied through the fs Z-scan technique revealed that Ni-doped CsPbBr 3 NCs exhibited strong third-order NLO susceptibility of ∼10 −10 esu. The exotic photophysical phenomena in these pristine and Ni-doped CsPbBr 3 colloidal twodimensional (2D) NCs reported herein are believed to provide the avenues to address the critical variables involved in the structural differences and their correlated optoelectronic properties.

Nonlinear Photonics Using Low‐Dimensional Metal‐Halide Perovskites: Recent Advances and Future Challenges

“…Excellent 2PA capability of CsPbBr 3 was quantified utilizing the OA Z‐scan method with fs pulsed laser excitation at 800 nm, and giant σ 2 value of ≈1.2 × 10 5 GM and ≈4.2 × 10 5 GM before and after the local field effect correction was revealed. Following this intriguing report, so far more than 34 other research works [ 92–96,99,101–111,138,189,234–248 ] on the 2PA response of NCs of 3D metal‐halide perovskites have been carried out and published. 2PA performance from NCs of 3D organic–inorganic MAPbX 3 and all‐inorganic CsPbX 3 (X = Cl, Br, I, or mixed halide) was the research focus in most of the published articles.…”

“…The inherent σ 2 values of MAPbX 3 and CsPbX 3 NCs were determined to be in the range of ≈(10 5 to 10 7 ) GM across the visible–NIR excitation wavelength range of ≈(600–1250) nm. [ 92–96,99,101–111,138,189,234–237,239–248 ] The variation of σ 2 values can be attributed to one or some of the following factors: different sample compositions (e.g., different A + or X − in AMX 3 ), assorted sample sizes, various sample shapes, diverse sample quality, different excitation wavelengths, discrepant excitation pulsed lasers. On the other hand, Jiang et al.…”

“…In addition to tuning and optimizing 2PA properties of 3D metal‐halide perovskite NCs via manipulating their intrinsic attributes (e.g., composition, size, shape, sample quality) or taking advantage of their inherent spectral dependence, assorted external modulation strategies have been developed to promote the 2PA performance of 3D metal‐halide perovskites NCs. The strategies include: developing core–shell structure, [ 92 ] doping with transition metal ions (e.g., Mn 2+ ), [ 109,110,246 ] encapsulation in the voids of MOFs, [ 111 ] etc.…”

“…More than nine research reports [ 102,105,106,108,110,138,245,246,248 ] have investigated the shape‐dependent 2PA properties in 3D metal‐halide perovskite NCs, where most of them focused on characterizing the diverse 2PA capability in CsPbX 3 nanocubes and nanoplates. In comparison with CsPbX 3 nanocubes, CsPbX 3 nanoplates with thinner thickness (several nm) and resulting stronger quantum confinement in the vertical direction exhibited enhanced 2PA capability with larger volume‐normalized σ 2, [ 105,106,108,110,138,245,246 ] as demonstrated in Figure 6d,j,k. Specifically, Lin et al.…”

“…Various external modulating strategies have been developed for optimizing their 2PA performance. More than 10 research articles [ 92,109–111,239,242–244,246,258 ] have reported about seven external strategies for tuning the 2PA response of 3D metal‐halide perovskite NCs, including: developing core–shell structure, [ 92 ] transition metal ion doping (Mn 2+ , Ni 2+ ), [ 109,110,246 ] incorporating with Si photonic structure, [ 239 ] confinement within a MOF core, [ 111 ] growing 3D/0D metal‐halide perovskite nanocomposites, [ 242 ] hybridizing with metal NCs, [ 243,244 ] hybridizing with hydrophobic zeolites, [ 258 ] as illustrated in Figure 6e,l–n. Our group developed multidimensional core–shell MAPbBr 3 /(OA) 2 PbBr 4 (CH 3 NH 3 PbBr 3 /(C 8 H 17 NH 3 ) 2 PbBr 4 ) nanospheres to enhance the σ 2 and 2PPL intensity for about one order of magnitude compared to that of the core‐only MAPbBr 3 nanospheres with similar size across the wide wavelength range of (675–1100) nm, [ 92 ] as manifested in Figure 6e.…”