Lead-Free Perovskites for Lighting and Lasing Applications: A Minireview

Abstract

Research on materials with perovskite crystal symmetry for photonics applications represent a rapidly growing area of the photonics development due to their unique optical and electrical properties. Among them are high charge carrier mobility, high photoluminescence quantum yield, and high extinction coefficients, which can be tuned through all visible range by a controllable change in chemical composition. To date, most of such materials contain lead atoms, which is one of the obstacles for their large-scale implementation. This disadvantage can be overcome via the substitution of lead with less toxic chemical elements, such as Sn, Bi, Yb, etc., and their mixtures. Herein, we summarized the scientific works from 2016 related to the lead-free perovskite materials with stress on the lasing and lighting applications. The synthetic approaches, chemical composition, and morphology of materials, together with the optimal device configurations depending on the material parameters are summarized with a focus on future challenges.

Keywords: LED; lasing; lead-free; nanocrystals; perovskite; photonics; superluminescence.

Figure 1

(a) Plot of publications number in the last decade: on perovskite materials (blue columns), on lead-free perovskite materials (orange squares), and on perovskite NCs (orange triangles). (b) Plot of publications number in the last decade: On lasing (orange columns), on lasing in perovskite materials (black circles).

Figure 2

Synthesis of lead-free perovskites. (a) SEM images of Cs₂SnI₆; (b) calculated phase diagram of Cs–Sn–I. Reproduced with permission [31]. Copyright WILEY-VCH Verlag, GmbH & Co. KGaA, Weinheim, Germany, 2019. (c) Visualized dual emission between the hydrated and dehydrated species, fabricated by embedding the perovskite material, Cs₂InBr₅⋅H₂O into an etched butterfly pattern. Reproduced with permission [34]. Copyright WILEY-VCH Verlag, GmbH & Co. KGaA, Weinheim, Germany, 2018. (d) Schematic representation on the phase formation of Cs₂AgInCl₆:Bi NCs at different synthesis temperatures (180–280 °C) in three steps: (I) Complexing of optimized precursors including OA, OlAm, and HCl; (II) AgNO₃ and InCl₃ reacting with OA to form Ag−oleate and In−oleate and oleylammonium chlorine. Ag⁰ NPs are formed by the reduction of Ag+ in the presence of amine ligands; (III) formation of Cs₂AgInCl₆ NCs at different synthesis temperatures followed by the injection of CsOA; (e) UV−Vis absorption (dashed line), photoluminescence (PL) (excitation at 368 nm), and PL excitation (emission at 580 nm) spectra of Bi-doped Cs₂AgInCl₆ NCs dispersion in hexane obtained at different synthesis temperatures (180–280 °C); the insets show the samples irradiated under a 365 nm UV lamp. Reproduced with permission [45]. Copyright American Chemical Society, 2019. (f) Photograph of an as-synthesized large-area CsSn_0.5Ge_0.5I₃ perovskite thin film on a glass substrate showing dark reddish color. (g) Photograph of as-synthesized CsSn_0.5Ge_0.5I₃ perovskite solid using the melt-crystallization method. (h) Schematic illustration of the single-source evaporation method for the deposition of ultrasmooth CsSn_0.5Ge_0.5I₃ perovskite thin film. Reproduced with permission [56] Copyright Springer Nature Limited, 2019. (i) Image of (C₈NH₁₂)₄Bi_0.57Sb_0.43Br₇·H₂O single crystal. (j) Powder X-ray diffraction (PXRD) patterns of (C₈NH₁₂)₄Bi_0.57Sb_0.43Br₇·H₂O (black line) and (C₈NH₁₂)₄BiBr₇·H₂O (red line). Reproduced with permission [52]. Copyright WILEY-VCH Verlag, GmbH & Co. KGaA, Weinheim, Germany, 2019.

Figure 3

Lead-free film perovskite-based LEDs. (a) Cross-sectional SEM image of device; (b) normalized electroluminescence (EL) spectrum of the Cs₃Sb₂I₉ film. Reproduced with permission [73]. Copyright American Chemical Society, 2019. (c) Activation energy and photoluminescence quantum yields (PLQY) of Cs₂Ag_xNa_1−xInCl₆ powder vs. Na content. The dashed lines are guides for the eye. (d) Cs₂Ag_1−xNa^xInCl₆ Luminosity function (dashed line) and photoluminescence spectra (solid lines) of Cs₂Ag_0.60Na_0.40InCl₆ measured at different temperatures from 233 K to 343 K. Reproduced with permission [74]. Copyright Springer Nature Limited, 2018.

Figure 4

Lead-free perovskite nanomaterials based down-conversion LEDs. (a) Schematic representation of the synthesis of the 2D (OCTAm)₂SnBr₄ by a facile aqueous acid-based synthetic method in ambient air. (b) Images of yellow phosphors, blue/green phosphors, and their blends with different ratios embedded in PS films under sunlight (top panel) and 365 nm UV light (bottom panel). The first row in each panel are a yellow–blue phosphor mixture, and the second is a yellow–blue–green mixture. (c) Chromaticity coordinates of different ratios of the phosphor mixture plotted on the CIE1931 chromaticity chart: Blue phosphor (square), yellow phosphor (round), yellow–blue phosphor 4:1 (triangle), and yellow–blue–green phosphor 4:1:1.5 (star). Reproduced with permission [76]. Copyright Royal Society of Chemistry, 2019. (d) Photograph of the colloidal suspension and film of (OAm)₂SnBr₄ perovskites under UV light. (e) Normalized absorption (Abs), PL excitation (PLE, monitored at 620 nm), and PL (excited by 365 nm) spectra of the (OAm)₂SnBr₄ perovskite film. Reproduced with permission [75]. Copyright American Chemical Society, 2019. (f) Absorption and photoluminescence spectra of CsBr:Eu²⁺ NCs. The inset depicts the optical images of the NCs dispersed in hexane with and without illumination by a 365 nm UV lamp. (g) EL spectra and of the white LED operated under different forward bias currents. Reproduced with permission [77]. Copyright WILEY-VCH Verlag, GmbH & Co. KGaA, Weinheim, Germany, 2019.

Figure 5

Architecture of perovskite-based lasers. (a) Simplified laser configuration. (b) Principle of stimulated emission occurred in active media: SE—spontaneous emission, ASE—amplified spontaneous emission. (c) Types of resonator’s geometries: DBR—distributed Bragg reflector, F-P—Fabry–Perot, RL—random lasing, WGM—whispery gallery mode. Insets in (c) are the examples of the morphology of perovskite materials used for DBR [82], F-P [83], RL [84], and WGM [85] resonators. Adopted with permission [82]. Copyright Royal Society of Chemistry, 2018; Adopted with permission [83]. Copyright American Chemical Society, 2018; Adopted with permission [84]. Copyright American Chemical Society, 2018; Adopted with permission [85]. Copyright Royal Society of Chemistry, 2019.

Figure 6

Resonators vs. perovskite material’s morphology. DBR: (a) Scheme of vertical-cavity surface-emitting lasers (VCSEL) device; (b) output power vs. pump energy density; (c) PL spectrum and (d) far-field beam distribution at pump energy density above threshold; (e) energy density of laser threshold energy vs. the PL peak position. Reproduced with permission [120]. Copyright WILEY-VCH Verlag, GmbH & Co. KGaA, Weinheim, Germany, 2019. F-P: (f) Microimages (bright field, green channel, yellow channel); (g) pump fluence dependent PL spectra of central region of CsPbBr_xI_3−x nanowires. Reproduced with permission [125]. Copyright WILEY-VCH Verlag, GmbH & Co. KGaA, Weinheim, Germany, 2018. F-P combined with WGM disk: (h) Scheme of the switchable single-mode lasing from a perovskite microwire coupled with an organic microdisk; (i) transition from multimode to single-mode lasing of the typical MAPbBr₃ nanowire coupled with a microdisk. Reproduced with permission [103]. Copyright American Chemical Society, 2018.

Figure 7

Resonators vs. perovskite material’s morphology. WGM: (a,c,d) lasing spectra of the CsPbBr₃ microcuboids of different size, the insets are corresponding SEM images of the samples; (b) numerical simulations on the standing wave field distributions, which are confined in the square cross-section of cube with size of 1.7 µm. Reproduced with permission [96]. Copyright American Chemical Society, 2019. Array of WGM resonators: (e) Scheme of microlasers array fabrication, false-color SEM image, and a photo of a 1 × 1 cm² array; (f) lasing spectra from perovskite microlasers from MAPbI₃ (brown curve), MAPbBrI₂ (red curve), and MAPbBr₃ (green curve), the insets are PL images of the samples. Reproduced with permission [108]. Copyright American Chemical Society, 2019. RL: (g) Optical images of the (BA)₂PbI₄ (n = 1) single crystal bottom and top surface; (h) lasing spectra from high-quality homologous 2D perovskite single crystals with n = 1, 2, 3. Reproduced with permission [111]. Copyright American Chemical Society, 2018. (i) Scheme of a fabrication CsPbBr₃ QD-embedded glass (QDs@glass) via in-situ crystallization; (k) up-conversion PL spectra of QDs@glass vs. the pump power of 800 nm laser, the inset is a photo of sample excited with energy density above threshold; (l) PL intensity vs. pump energy density. Reproduced with permission [118]. Copyright American Chemical Society, 2018.

Figure 8

Lasing in lead-free perovskite materials. (a) Optical image of a butterfly scale from the white part of the wing. Inset is a photograph of the butterfly. (b) SEM image showing lamellae (vertical structures) in the scale. (c) Variable fluence measurements reveal the amplified spontaneous emission (ASE) thresholds of the SnF₂-treated samples. (d) Wide PL and ASE wavelength tunability from CsSnBr_xI_3−x films fabricated by facile mixing the precursor solutions under 500 nm pump pulses (50 fs, 1 kHz). (e) A comparison of the PL, ASE, and single-mode lasing of CsSnI₃ (20% SnF₂) under 650 nm pump pulses (50 fs, 1 kHz). Reproduced with permission [126]. Copyright WILEY-VCH Verlag, GmbH & Co. KGaA, Weinheim, Germany, 2016. (f) Variation in PL intensity and FWHM with pumped energy. (g) Thermal tunability of the AIPQD−CLC laser at E = 5.0 μJ/pulse at 20, 25, 30, 40, and 45 °C. (h) Tuning of the lasing emission of AIPQD−CLC laser by changing the chiral dopant content in the CLC. (i) Electrical tunability of the AIPQD−CLC laser at E = 4.0 μJ/pulse under AC voltages of 0−20 V (1 kHz). Reproduced with permission [127]. Copyright American Chemical Society, 2018.