Mixed Halide Perovskite Films by Vapor Anion Exchange for Spectrally Stable Blue Stimulated Emission

Abstract

All-inorganic perovskites such as CsPbX 3 have attracted huge attention because of its superior stability. [6] So far, perovskite nanowires, microplates, and films have been used to realize lasing or amplified spontaneous emission (ASE). Both lasing and ASE are a kind of light amplification through stimulated emission when there is an inverted population between two energy states. [7] Stimulated emission is that an incident single photon stimulates other recombination and creates an additional photon which is exactly the same as oneself. [8] When the excitation fluence exceeds a certain threshold and population inversion is achieved, the probability of generating stimulated emission is greater than that of absorption for an incident photon, thus realizing light amplification and optical gain. ASE or lasing will occur only if optical gain is larger than optical loss. [7a] Unlike lasers, ASE does not require a resonant cavity. [7b,9] That is, it is necessary to construct the resonant cavity for the transformation from ASE to lasing. Remarkably, perovskite nanowires [10] and microplates [11] can use their own nanostructures as resonant cavities to amplify light and achieve lasing. However, the difficulties in precise position control largely limit their integration with other optical and electrical devices. [12] By contrast, perovskite films are simple to prepare and easy to integrate with other optical and electronic devices. [12,13] Lasing or ASE based on CsPbX 3 films have been demonstrated in red and green spectral regions. [6b,13,14] However, there are few report about blue lasing or ASE based on CsPbX 3 film. The factors restricting the realization of blue lasing or ASE are the preparation of high-quality films and the improvement of spectral stability. On the one hand, the low solubility of chlorine sources such as CsCl in the precursor aggravates the fabrication of the films, [15] which lead to poor quality of films and more scattering losses. On the other hand, the mixed halides perovskites generally undergo ion migration under the stimuli of light or electric filed, resulting in phase separation and spectral instability. [16] Especially, ion migration will be more obvious under high flux excitation needed for reaching population inversion. [17] Therefore, it's of great significance to prepare high-quality thin films with good spectral stability for blue ASE or laser.In this work, we demonstrate blue ASE from mixed-Br/Cl quasi-2D Cs-based perovskite films prepared by a facile vapor anion exchange (VAE) method. Unlike the method of directly Solution-processed all-inorganic CsPbX 3 perovskites exhibit outstanding optoelectronic properties and are being considered as a promising optical gain medium, with impressive performance in the green and red region. However, the development of CsPbX 3 for blue emission is still lagging far behind, owing to difficulties in thin films synthesis and spectral instability subject to light irradiation. Here, a facile vapor anion exchange (VAE) method that enables pr...

Colloidal CdSe/CdS Core/Crown Nanoplatelets for Efficient Blue Light Emission and Optical Amplification

“…This number is consistent with the reported amplified spontaneous emission thresholds for blue-emitting CdSe (50 μJ/cm 2 ), or CdS and CdS/ZnS NPLs (50–250 μJ/cm 2 ), and is significantly lower than typical thresholds for blue quantum dots (∼1 mJ/cm 2 ) ,, unless the latter are carefully engineered to introduce a smooth confinement potential, which reduces the threshold to 60 μJ/cm 2 . Moreover, our values are comparable to typical thresholds (63–190 μJ/cm 2 ) reported for blue-emitting perovskite nanostructures. − …”

“…33 Moreover, Lu et al reported a value of g net = 129 cm −1 using quasi-2D mixed-Br/Cl Cs-based perovskite films fabricated via a vapor anion exchange method. 47 Since these modal gain values are well below our material gain coefficients, we can conclude that our g i present state-of-the-art values for solution-processed blue-emitting nanomaterials.…”

Compositional gradient engineering and applications in halide perovskites

“…It is usually necessary to ensure that the source is volatile or volatile under certain conditions, ions volatilized into the vapor phase do not introduce other impurities, and the volatilized vapor does not cause corrosion and damage to the film surface. In view of this, common vapor-phase sources include precursor vapors, volatile HX (X = Cl, Br, I), diphenylphosphinyl chloride (DPPOCl), 60 TiCl 4 , 61 and so on. Sun et al 62 proposed an ingeniously designed temperature bridge to construct the compositional gradient.…”

Vapor Phase Growth of Centimeter‐Sized Band Gap Engineered Cesium Lead Halide Perovskite Single‐Crystal Thin Films with Color‐tunable Stimulated Emission

“…They achieved tunable emission and ASE from green region to blue region at room temperature based on those polycrystalline films. [17] However, compared with CsPbX 3 single-crystal thin films, CsPbX 3 polycrystalline film exhibit higher threshold and lower optical gain due to their structural inhomogeneities, rough surface, unavoidable grain boundaries, and higher trap densities. In contrast, perovskite single-crystal thin films (SCTFs) have a flat surface, lower trap densities and fewer defects, which is beneficial to enhance laser device performance and stabilities.…”