Defect-Dependent Nonlinear Absorption in the Lead-Free Double-Perovskite Cs₂AgBiBr₆

Abstract

Lead-free perovskites have attracted increasing attention because they can address the toxicity and instability problems inherent to lead-halide perovskites. Furthermore, the nonlinear optical (NLO) properties of lead-free perovskites are rarely explored. Herein, we report significant NLO responses and defect-dependent NLO behavior of Cs2AgBiBr6. Specifically, a thin film of pristine Cs2AgBiBr6 exhibits strong reverse saturable absorption (RSA), while a film of Cs2AgBiBr6 with defects (denoted as Cs2AgBiBr6(D)) shows saturable absorption (SA). The nonlinear absorption coefficients are ca. 4.0 × 104 cm GW–1 (515 nm laser excitation) and 2.6 × 104 cm GW–1 (800 nm laser excitation) for Cs2AgBiBr6 and −2.0 × 104 cm GW–1 (515 nm laser excitation) and −7.1 × 103 cm GW–1 (800 nm laser excitation) for Cs2AgBiBr6(D). The optical limiting threshold of Cs2AgBiBr6 is 8.1 × 10–4 J cm–2 (515 nm laser excitation). The samples show excellent long-term performance stability in air. The RSA of pristine Cs2AgBiBr6 correlates with excited-state absorption (515 nm laser excitation) and excited-state absorption following two-photon absorption (800 nm laser excitation), while the defects in Cs2AgBiBr6(D) strengthen the ground-state depletion and Pauli blocking, resulting in SA.

Donor–π–Acceptor Porphyrin-Assisted Bifunctional Defect Passivation for Enhanced Temporal Domain-/Wavelength-Dependent Nonlinear Absorption Properties in Perovskite Films

“…Porphyrin passivation repairs defect states between the perovskite band gap; thus, there is a need to delve into the NLO mechanism that underlies the photoexcitation process of these perovskite materials. The estimation of the band-gap energy (E g ) for all samples was conducted using Tauc's equation, which relies on the analysis of UV−vis spectra, 52 and the Tauc plots are displayed in Figure S18. The pristine and porphyrin-passivated MAPbI 3 films have E g values of 1.60− 1.62 eV, large than the energy (hν) of a single photon process (1.55 eV) but less than that of a two-photon process (3.1 eV) at 800 nm.…”

Understanding the polaron behavior in Cs2CuSbCl6 halide double perovskite

“…; M = Ag + , K + , Li + ; M' = Sb 3+ , In 3+ or Bi 3+ and X = I À , Br À or Cl À ) double perovskites have become an object of significant interest due to their environmental and structural stability, low toxicity, defect tolerance, and exceptional optoelectronic properties. [1][2][3][4][5][6] These qualities have made them increasingly popular in applications such as solar cells, X-ray detectors, photodetectors, and photocatalysts. [7][8][9][10] Achieving high-performance for these applications often requires the use of high-quality perovskite single crystals (SCs).…”

0D MXene quantum dots/2D MXene derived metal–organic frameworks for enhanced nonlinear optical absorption across spectral and temporal regimes

“…Nonlinear optical (NLO) materials play a pivotal role in various optical applications, such as optical limiting, optical switching, optical communications, and so on. [1][2][3] A wide range of materials has captured significant attention, including graphene, [4][5][6] transition metal sulfides, [7][8][9][10][11][12][13] black phosphorus, 14,15 perovskite, [16][17][18] polymers, 19,20 and MXene, [21][22][23][24][25][26] among others. Within these NLO materials, metal-organic frameworks (MOFs), [27][28][29] boasting tunable structures and diverse compositions, have emerged as ideal materials for NLO applications.…”