Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2020 Nov 12;5(46):30111–30122. doi: 10.1021/acsomega.0c04517

Fabrication of Thin Films from Powdered Cesium Lead Bromide (CsPbBr3) Perovskite Quantum Dots for Coherent Green Light Emission

Saif M H Qaid †,‡,*, Hamid M Ghaithan †, Bandar Ali Al-Asbahi †,§, Abdulaziz Alqasem †, Abdullah S Aldwayyan †,∥,⊥
PMCID: PMC7689956  PMID: 33251445

Abstract

graphic file with name ao0c04517_0010.jpg

High-quality thin films were obtained directly by spin-coating glass substrates with suspensions of powdered cesium lead bromide (CsPbBr3) perovskite quantum dots (PQDs). The structural properties of the films were characterized via transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) analysis, and atomic force microscopy (AFM). The crystal structure of the CsPbBr3 PQDs was unique. The optical behavior of the CsPbBr3 PQDs, including absorption and emission, was then investigated to determine the absorption coefficient and band gap of the material. The CsPbBr3 PQDs were evaluated as active lasing media and irradiated with a pulsed laser under ambient conditions. The PQDs were laser-active when subjected to optical pumping for pulse durations of 70–80 ps at 15 Hz. Amplified spontaneous emission (ASE) by the CsPbBr3 PQD thin films was observed, and a narrow ASE band (∼5 nm) was generated at a low threshold energy of 22.25 μJ cm–2. The estimated ASE threshold carrier density (nth) was ∼7.06 × 1018 cm–3. Band-gap renormalization (BGR) was indicated by an ASE red shift and a BGR constant of ∼27.10 × 10–8 eV. A large optical absorption coefficient, photoluminescence (PL), and a substantial optical gain indicated that the CsPbBr3 PQD thin films could be embedded in a wide variety of cavity resonators to fabricate unique on-chip coherent light sources.

Introduction

In the last decade, perovskite materials have become the preferred choice for many photonic applications, due to their unique crystal structures, excellent carrier mobility, high absorption coefficients, and easily tuned direct band gaps. Also, perovskite-based devices can be manufactured using simple and flexible processes with low production costs, such as solution processing.1−14 The performance of perovskites as solar light-harvesting materials in photovoltaics1,2,15 and photodetectors7 is extraordinary. Perovskites have also shown promise as active layers for light-emitting diodes (LEDs)8,9 and lasing applications.3−5,9−14

The large family of lead halide-based perovskites has ABX3 crystal structures. In these materials, A can be Cs+, CH3NH3+, or HC(NH2)2+, B represents Pb, and X can be Br–, I–, or Cl–. More recently, three-dimensional (3D) hybrid perovskites have been shown to be promising materials for light-emitting applications.6,11,16−19 These perovskites contain much smaller organic cations, such as methylammonium (MA) or formamidinium (FA), although perovskite structures that contain Cs+ are reported to have much better thermal stability and photostability.20−22 However, the perovskite band gap can be widened to ∼2.3 eV by substituting X = Br–. This will enable the limitations of current fabrication methods to be circumvented for the development of devices that emit true green light.20,23 The potential applications of CsPbBr3 are oriented mainly toward LEDs, with few reports for photodetectors and photovoltaics. These are due to their excellent carrier mobility, short radiative lifetimes, high PL quantum yields (PLQYs), narrow full widths, tunable emission wavelengths, color purity, and high absorption coefficients.

Perovskites can be fabricated in various forms, including thin films,24 single crystals,25,26 nanowires,13 and quantum dots (QDs).9 Perovskite QDs (PQDs) have more desirable optical properties than their bulk counterparts, and they are chemically robust due to quantum size effects. PQDs are also more attractive platforms than other perovskite structures in terms of enhanced optical gain and stability. These features make PQDs ideal for use in printed optoelectronic devices, such as QD LEDs, QD lasers, QD backlights for liquid crystal displays (LCDs), and lighting.27−29 By combining the advantages of perovskites with a QD structure, PQDs bring perovskite materials into the realm of quantum confinement.30,31 Compared to 3D counterparts commonly used, QDs have been intensively studied as optoelectronic materials due to their many attractive features, which include size-tunable band gaps enriching the wavelength range of absorption and emission, high PL quantum yields, increased surface–volume ratio, excellent photostability, and versatile chemical processability. Also, compared to 3D, low-dimension perovskites have high exciton binding energies due to dielectric confinement and the presence of quantum wells due to the enlarged Coulombic force between electrons and holes. Their high exciton binding energies result in high PLQYs, which makes them very promising for lighting applications.1−5,7−14,28,32

In general, the halide perovskites have been studied for quite some time, but the application of perovskites for amplified spontaneous emission (ASE) was not reported until 2014 by Xing et al.11 Since then, the use of perovskites for ASE and lasing has expanded significantly. The first report on random lasing in organo-lead halide perovskite microcrystal networks18 was published only a few months after the demonstration of ASE from MAPbX3 thin films.11 Rapid advancements in the compositions, structures, and engineered morphologies of perovskite micro–nano lasers10,11,30,33−36 have paved the way for developments in many areas due to the ultracompact physical sizes, which can confine the generated photons inside the nanostructured cavities.37 Then, the laser action will occur when the photons satisfy the resonance conditions and obtain sufficient gain.35 For example, Yakunin et al.38 used femtosecond and nanosecond lasers to stimulate ASE from CsPbX3 NCs thin films. They observed low thresholds of ∼7–15 μJ cm–2 under femtosecond excitations pulses, whereas ASE thresholds rise to ∼450 μJ cm–2 for nanosecond excitation pulses. Also, they observed that the ASE peaks were found to be red-shifted with respect to the PL maxima. They concluded that CsPbX3 NCs (10 nm) exhibit the best balance between optical performance and lowest ASE thresholds compared to CsPbX3 microcrystals and small CsPbX3 QDs (4–8 nm, chemically unstable). Another group from KAUST demonstrated ultra-air- and photostable CsPbBr3 QDs using an inorganic–organic hybrid ion pair as the capping ligand. They introduce the passivation approach to alleviate the inherent instability of the material when operating under ambient conditions or under high laser fluences. Also, they reported that the ASE thresholds of CsPbBr3 thin films under single-photon and two-photon microscopy using a femtosecond laser system as a pumping laser were 192 and 12 mJ cm–2, respectively.30 In 2019, Yan et al. studied the poor stability and aggregation problem of CsPbBr3 QDs in air, and to avoid this challenge, they introduced the 2-hexyldecanoic acid (DA) ligand into the synthesis process via a modified hot-injection method and showed that the CsPbBr3-DA QDs films exhibit property improvement and improved stability compared with the CsPbBr3–oleic acid (OA) QD films. Also, the ASE threshold of CsPbBr3-DA QDs films reduced more than 50% than that of CsPbBr3-OA QDs films; moreover, their ASE photostability was better.39 Although, a number of researchers30,38−40 have sought to reduce the ASE and lasing thresholds of CsPbBr3 QD thin films further. Also, a lot of researchers have sought to investigate the ASE/laser characterization of CsPbBr3 QD thin films through femtosecond and nanosecond laser excitation with few reports for picosecond laser excitation. In those studies, PQD solutions were used to prepare thin films. Although, for all of these efforts, there are some challenges in this field that need to solved and improved.

In this work, powdered QDs were used directly to prepare high-quality cesium lead bromide perovskite quantum dot (CsPbBr3 PQD) thin films synthesized via the modified hot-injection method using the combination of oleic acid and oleylamine as a capping agent. We analyzed the structures of the CsPbBr3 PQD thin films through several characterization techniques. Then, the optical properties of the prepared CsPbBr3 PQD films were investigated. We then explored the potential of CsPbBr3 PQD thin films as laser-active media using, for example, a picosecond laser as an optical pumping source. ASE regimes in CsPbBr3 PQD thin films were investigated in terms of PL and carrier density over a range of pumping energies. In this contribution, successful light amplification with a lower threshold of energy density and narrower FWHM has been demonstrated. This will lead to, at the threshold carrier density, the easy increase of the net gain of the material through either optical or electrical means, opening the prospects toward attempting the electrically pumped perovskite lasers. The short PL lifetime of the CsPbBr3 PQD thin films indicates that they have great potential as light-emitting materials for QD-based LEDs.

Results and Discussion

Structural Characteristics of the CsPbBr3 PQD Thin Films

Figure 1a is a typical high-resolution transmission electron microscopy (HR-TEM) image that reveals the CsPbBr3 PQD structure. The CsPbBr3 PQDs had a cubic morphology and were quite homogeneous. The lattice fringes of a single QD with an interplanar spacing of ∼0.25 nm are visible in the inset of Figure 1b. This corresponded to the distance between adjacent (200) lattice planes, which was confirmed by performing X-ray diffraction (XRD) analysis. The PQD particles ranged from 3 to 10 nm in size with an average size of 6.5 nm. The size distribution in Figure 1c (inset) indicated that quantum confinement would occur in the PQDs. The elemental composition of the CsPbBr3 thin films was analyzed via EDS. The EDS results in Figure 1d (inset) were consistent with the elemental composition of CsPbBr3. The results also indicated that the synthesis of the PQDs via hot injection41 and a modified hot injection method42 was highly controllable and efficient.

Figure 1.

Figure 1

Open in a new tab

(a) TEM image. (b) High-resolution transmission electron microscopy images. The corresponding scale bar is 2 nm. (c) Particle size distribution of CsPbBr3 QD. (d) EDS analysis of the elements in the CsPbBr3 films.

Then, the XRD pattern of the PQDs (Figure 2a) contained strong and distinct peaks at (2θ) 15.33, 21.70, 30.87, 34.45, 37.90, and 43.93° that corresponded to diffractions from the (100), (110), (200), (210), (211), and (220) crystal planes, respectively. All of the peaks were indexed to the cubic phase in the space group Pm-3m (221) (JCPDS card no. 01-075-0412). The slight peak shifts were consistent with the formation of an alloy, and the results were in good agreement with those reported by others.33,34,36,41−53 The diffraction from the (200) plane at 30.87° was quite intense, and its appearance together with the secondary diffraction peak of the (100) plane was indicative of a highly crystalline and pure cubic phase without any defects. The pattern did not contain peaks from either of the PbBr2 and CsBr precursors.25,54 Bulk CsPbBr3 is an orthorhombic phase at room temperature and transforms into the cubic phase near 130 °C. QDs and bulk crystals with the same compositions generally have the same crystalline properties. However, CsPbBr3 in the PQDs was in the cubic phase at room temperature. CsPbBr3 crystallized in the cubic phase during the direct synthesis of the PQDs due to a combination of high temperature, QD surface effects, and surface energy contributions.34,42,47,53 The cubic crystal phase was more stable, even at room temperature.53 The average grain size of the CsPbBr3 nanocrystals (D) and lattice strain (ε) were estimated using the uniform deformation model (UDM), which was a modified Williamson–Hall (W–H) model.55D and ε were determined from the XRD data using eq 1.55−57

graphic file with name ao0c04517_m001.jpg 1

where βhkl represents the peak broadening, λ is the wavelength of the incident X-ray (0.154 nm), and k is a constant (∼0.9). The slope and intercept of the straight line in a plot of 4 sin θ vs βhkl cos θ (Figure 2b) were equal to ε and kλ/D, respectively. The values of ε and D are listed in Table S1 (Supporting Information). The grain size of the CsPbBr3 PQD film was 6.2 nm, which was consistent with the HR-TEM results (Figure 1). The large strain value was attributed to the gradual formation of the perovskite layer and hence reducing the strain. The narrow FWHMs of the diffraction peaks indicated that the dislocation density and residual stress in the crystals were both low.55 The CsPbBr3 unit cell (pm3̅m) is illustrated in Figure S1a and the super-cell in Figure S1b (Supporting Information). The image of a 2 × 2 × 2 CsPbBr3 super cell with eight formula units in Figure S1b (Supporting Information) was generated using the VESTA software.58

Figure 2.

Figure 2

Open in a new tab

(a) XRD pattern of the parent spectra of CsPbBr3 perovskite QD (red line) and CsPbBr3 (JCPDS, 01-075-0412 (blue line)) and (b) uniform deformation mode plot concluded from X-ray diffraction (XRD) spectra.

Surface Morphologies of the Thin Films

The surface roughness of a film is an important factor that affects its optical characteristics. Achieving high-performance light emission with perovskite films requires excellent surface coverage and smooth layers. Atomic force microscopy (AFM) is a powerful tool for examining the surface morphologies of films. A two-dimensional (2D) planar AFM image of a CsPbBr3 PQD film is shown in Figure 3a. The 3D topography of the film is visible in Figure 3b, for a film thickness of ∼400 nm, which is measured by a Dektak profilometer. The top-down view of the film in Figure 3a shows a generally smooth surface. Topography was examined over a 5 × 5 μm2 area, and the average roughness in the selected area (Ra) was 4.36 nm. The maximum roughness value (Rmax) was 64.3 nm, although the root-mean-square (Rq) was only 5.59 nm. This indicated that the surface of the film was smooth and uniform without pinholes and that surface coverage was good. The smooth surface of the film would reduce incident light loss at the air/PQD interface, which would promote ASE and lasing. Smoothness would also be important if the thin films were used as active layers in photonic devices. The HR-TEM, EDS, XRD, and AFM results confirmed that the CsPbBr3 PQD thin films were successfully fabricated using powdered QDs. The CsPbBr3 PQDs were small and uniformly distributed in the alloy, and the cubic phase was stable at room temperature.

Figure 3.

Figure 3

Open in a new tab

AFM images: (a) 2D plane-view and (b) 3D topography of CsPbBr3 PQD.

Optical Properties of the Thin Films

The UV–vis absorption and photoluminescence (PL) spectra of the films were recorded to characterize their optical properties. Absorption measurements provide details about the existing band states of a material, including the absorbance coefficient (α) and band gap (Eg). The recombination of photogenerated electrons and holes in a semiconductor can generate PL, so PL data provide useful information about the efficiency of electron–hole recombination and charge carrier trapping.

The absorption spectra of CsPbBr3 PQD in Figure S2a (Supporting Information) and later in Figure 5a indicated that absorption decreased as the wavelength increased. Maximum absorption was observed at 325 nm with a shoulder near 508 nm. The band-edge absorption profile showed a very small excitonic peak at the absorption edge. An extended absorption edge indicated that band-to-band electronic transitions contributed to absorption.59 Broad and strong absorption by the PQDs indicated that their light-harvesting capability was excellent. The light harvesting efficiency (LHE) spectrum is shown in Figure S2b (Supporting Information). The LHE of an optoelectronic device is a critical property that influences its power conversion efficiency (PCE).60 LHE was calculated as 1–10–A and plotted (Figure S2b). The wavelength dependence indicated that the LHE of the CsPbBr3 PQDs was 80%. The optical absorption coefficient (α) was evaluated as a function of photon energy in the region of the strongest absorption using eq 2(61) and plotted (Figure 4a) to determine what type of electron transition occurred. We then calculated the band-gap energy of the CsPbBr3 PQDs, Eg.

graphic file with name ao0c04517_m002.jpg 2

where (d) is the sample thickness. The absorption coefficient of CsPbBr3 PQD was estimated to be 1.49 × 105 cm–1 at 410 nm, which meant that light at this wavelength penetrated to a depth of 6.71 μm. It was thus possible to make CsPbBr3 PQD films that were thin and absorbed strongly. This would be crucial for a bilayered device because the PQD films had a large absorption coefficient in the visible region. The absorption coefficient of the A* is independent of the photon energy and was in the same range as those of other inorganic semiconductors, such as GaAs, CdSe, and PbSe.62−64 The optical band gap (Eg) can be determined by examining fundamental absorption at the edge, which is when a photon excites an electron to a higher-energy state.65 Tauc plots were constructed from the optical absorption data. We then determined Eg and the type of transition that occurred in the CsPbBr3 PQDs using eq 3.55,61

graphic file with name ao0c04517_m003.jpg 3

where A* is a constant that depends on the transition probability, h is Planck’s constant, and ν is the frequency of the incident radiation. A* is independent of the photon energy. The values of n for the direct and indirect band gaps were 2 and 0.5, respectively. The linearity in a plot of hν vs (αhν)2 indicates a direct band gap, while an indirect band gap is indicated by a linear plot of hν vs (αhν)1/2. Eg was estimated from the intercept of the line where no absorption occurred (α = 0). The line in Figure S3 (Supporting Information) did not cross the x-axis, so the transition was not consistent with an indirect band gap. After plotting (αhν)2 against hν (Figure 4b), we found that an n of 2 provided the best fit. The CsPbBr3 PQDs thus had a direct band gap for an allowed transition from the first valence band (VB) to the conduction band (CB). When a semiconductor has a direct band gap, the highest level in the VB and the lowest level in the CB have the same wavenumber (k). The calculated energy of the direct band gap was approximately 2.38 eV, which was in good agreement with the values in previous reports.30,34,48,66

Figure 5.

Figure 5

Open in a new tab

(a) Comparison of the amplified spontaneous emission profile (green) in relation to the absorption (red) and spontaneous emission (blue) profiles of the CsPbBr3 PQD thin film on a normalized scale. (b) Transition from SE to ASE. (c) Insets show the photographs of the obtained CsPbBr3 QDs under ambient conditions and the UV lamp (365 nm) irradiation, respectively, from left to right. (d) Time-resolved PL decay dynamics of the CsPbBr3 PQDs thin film following photoexcitation.

Figure 4.

Figure 4

Open in a new tab

(a) Absorption coefficient α as a function of wavelength λ and (b) plot of (αhν)2 vs hν for CsPbBr3 QDs.

Peaks in the PL emission spectra had narrow FWHMs and indicated a high quantum yield (QY). The absorption edge and PL peak of the CsPbBr3 PQDs were located at ∼508 nm and 515 nm, respectively. The ASE peak corresponded to the end of the shallow absorption (Urbach) tail. Under UV irradiation at 365 nm, CsPbBr3 PQDs in a liquid suspension emitted bright green light (Figure 5c, inset). Green photoluminescence was observed at ∼515 nm (2.41 eV) with a line width of ∼15 nm, and the band-edge PL peak was symmetric. The FWHM of the PL peak reflected the size distribution and morphology of the PQDs. A PL peak with a narrow FWHM would indicate that the PQD film is uniform. It would also indicate good monochromaticity, which is an important parameter for lighting devices and display applications.41

The PL spectra were recorded using excitation wavelengths that ranged from 278 to 460 nm and plotted (Figure S4, Supporting Information). The most intense PL was observed with excitation wavelengths of 278 and 366 nm (Figure S5, Supporting Information). PL intensity varied depending on the excitation wavelength, but the emission maxima were consistently observed near 515 nm with a small red shift. Two types of photoexcitation are possible near the band edge of a semiconductor with a direct band gap. Photoexcitation can involve free electron–hole pairs or bound electron–hole pairs (excitons). The dominant photoexcitation process depends on the magnitude of the Coulombic attraction between the holes and electrons, which can be determined by examining the dielectric properties of the material.67 The radiative recombination of free electron–hole pairs is referred to as band-to-band recombination. The PL spectrum of the CsPbBr3 PQDs indicated that photoluminescence resulted from the direct recombination of electrons in the CB and holes in the VB.68,69

Photoluminescence quantum yield (PLQY), which is defined as the ratio of emitted photons to absorbed ones, is one of the important photonic parameters including FWHM, PLQY, ASE (or lasing energy density at the threshold), and optical gain.70 Generally, high PLQYs in films are desirable and beneficial for achieving a high optical gain. For CsPbBr3 PQDs, the relative PLQYs after overnight in the N-hexane AR solution reached up to 77% by taking rhodamine (R6G) as a reference dye (Φf = 0.95 in ethanol). We also confirmed high PLQYs by studying the differential quantum efficiency, which can be deduced from the slope of the PL vs energy density curves, as shown in Figure 7a. Thus, the highest PLQY resulted at the lowest ASE threshold.

Figure 7.

Figure 7

Open in a new tab

(a) Integrated PL intensity and FWHM behavior vs pulse energy density and (b) ASE peak position vs pulse energy density for the CsPbBr3 PQD thin film under 410 nm excitation.

The PL lifetime of the CsPbBr3 PQD films was measured to investigate the recombination dynamics. We performed single-exponential fitting, I(t) = Ae–t/τ, of the experimental curves decay on the assumption that competing PL processes would yield a clean, single-exponent line shape38 after data were fitted with a mono-, bi-, and tri-exponential function and then the best fit should be selected. The time-dependent PL decay spectrum of the CsPbBr3 PQDs is shown in Figure 5d. The PL lifetime of the CsPbBr3 PQD thin films was short, and the PL decay was fast with a lifetime of ∼14.9 ns and exhibited single-exponential distribution with the decay components with different fractional intensities of 18.2 and 14.9 nm for the fraction amplitude (A) and lifetime (τ), respectively. χ2 = 0.94, which characterized the best fitting. The method utilizing fractional intensities (A, τ) diminishes the influence of the fastest decay dynamics and increases the reliably of analysis. χ2 should be close to unity for the best fit. For the short-lived excited state, lasing with electrically pumped conditions can be realized because the long-lived excited state may accumulate and cause large optical losses via excited-state absorption and the reduction of the singlet-state population. Thus, the hot electrons might be captured before their nonradiative recombination with holes. These results indicate that CsPbBr3 PQDs have great potential as light-emitting materials for QD-based LEDs. Therefore, the PQD thin films were employed as the optical gain medium for laser fabrication.

Evaluation of PL with Optical Pumping

The ASE value of a material is a better benchmark of its intrinsic suitability for gain applications. If no modifications are made, such as sandwiching the thin film between two Bragg mirrors, the gain can be observed by pumping the thin film with a pulsed laser. If stimulated emission is achieved at a certain threshold, two features are typically observed (Figure 5b, inset). The first is that emission by the material as a function of pumping energy will change drastically at the threshold. The second feature is line narrowing in the emission spectrum, which indicates a transition from spontaneous emission to stimulated emission. Other indicators include a reduction in the carrier lifetime. ASE was evaluated at excitation wavelengths of 410, 420, 430, 440, 450, and 460 nm. ASE was clearly influenced by the excitation wavelength. The best excitation wavelength, which corresponded to a high optical density, was 410 nm based on the absorbance spectrum. The evolution of PL from SE to ASE with changes in the pumping energy was monitored. The simulated reflection spectra shown in Figure 6a,b are a 3D representation of the pump–fluence relationship. The PL results indicated two SE-to-ASE transition regimes as the pumping energy density increased. Below the pumping energy density threshold, SE was indicated by a relatively broad emission peak centered at 525 nm. ASE began when the energy density threshold was reached, and the SE peak split into two bands. At pumping energy densities above the threshold, a narrower peak characteristic of the ASE state appeared at 531 nm. There have been few studies on the origin of these two peaks in perovskite materials.9,11,71,72 A magnified image of the narrow PL peaks is shown in the inset of Figure 5a. The PL intensity and FWHM as a function of pump fluence were extracted from the spectra in Figure 6. The effect of increasing pumping energy density on PL and the FWHM is illustrated in Figure 7a. The threshold energy could be estimated from the intersection of the SE and ASE lines. The results clearly indicated that the CsPbBr3 QDs reached the ASE state at a lasing threshold energy density (Eth) of ∼2.83 μJ per pulse. This corresponded to a threshold energy density of ∼22.25 μJ cm–2 per pulse with a pumping diameter of ∼4 mm and indicated that lasing occurred at λex = 410 nm under picosecond excitation. The ASE parameters are different with different laser pulse durations from nanosecond, picosecond to femtosecond. This behavior due to the unique properties of the short and ultrashort laser pulse durations creates a more excited state. If the laser pulse ends before the excited atom becomes de-excited or, in other words, if the laser pulse duration decreases, the excited-state occupation will satisfy the ASE conditions to occur. At long pulse duration, the threshold fluence will become higher. Also, if the lifetime of the excited state is too short (short-lived state), then there will not be enough excited atoms around to undergo stimulated emission. Thus, we can use short and ultrashort laser pulse durations to avoid this since the long-lived state may accumulate and cause large optical losses via excited-state absorption and the reduction of the singlet-state population. Consequently, the hot electrons might be captured before their nonradiative recombination with holes. Therefore, our results (τ and Eth) indicate that CsPbBr3 PQDs have great potential as light-emitting materials for QD-based LEDs and can be employed as the optical gain medium for laser fabrication. It is worth mentioning that better film quality and crystallization are associated with fewer surface defects. This was consistent with the roughness value determined via AFM and would definitely contribute to stronger emission. For a high-efficiency optical output, the sufficient thickness of thin films is needed because the film thickness is an influential factor in their ASE behavior. Thus, it was found that 400 nm would be the optimal film thickness for the best ASE behavior. In our previous work,10 we warned that while decreasing the film thickness is of practical importance to reduce the ASE threshold pump current, e.g., in electrically driven LEDs, the solution processing of perovskites, newly rediscovered for their potential photonic and photovoltaic applications, can be a restraining factor. Also, the low ASE threshold of the PQDs could be attributed to high optical gain. A detailed calculation of optical gain using the variable stripe length method would be interesting for a separate paper. A low ASE threshold can also be attributed to trapping states with small cross sections, slow Auger recombination, and low rates of bimolecular recombination.73 The dimensions of quantum dots are comparable to the de Broglie wavelength of electrons, so the energy difference between two adjacent levels exceeds the product of the absolute temperature (T) and the Boltzmann constant (k). This results in quantum confinement, which limits the mobility of electrons and holes.74 The CsPbBr3 PQDs combined the advantages of perovskites and quantum confinement. Auger recombination is more likely with quantum confinement because the momentum conservation requirement is relaxed.73,75,76 Another parameter that is strongly influenced by quantum confinement is the biexciton binding energy. A biexciton consists of two neutral bound excitons that are red-shifted relative to unbound excitons due to Coulombic effects.73 When the transition from SE to ASE began, the FWHM of the spectral line suddenly decreased. When the threshold was exceeded, the PL intensity increased dramatically (Figure 7a). The FWHM decreased sharply from over 17 nm to less than 5 nm as the pumping fluence increased, and the emission band at the Eth narrowed. These were clear ASE signatures of ASE. When the sample was excited at twice the ASE threshold energy, the FWHM stabilized at ∼5 nm.

Figure 6.

Figure 6

Open in a new tab

(a) Evolution of PL spectra with pulse energy density and (b) 3D diagram of pump–fluence relationship, for the CsPbBr3 PQD thin film under 410 nm excitation.

The abrupt change in the PL intensity coinciding with a decrease in the FWHM was also accompanied by a sudden wavelength shift from 525 to 534 nm as the pumping fluence increased. The position of the ASE peak varied with the pumping energy density, and the lasing peak at 531 nm shifted to 534 nm with respect to the PL peak (Figure 7b). Many factors could have been responsible for the ASE red shifts,29,36,68,73,75−82 such as a reabsorbance effect in single-exciton amplification,29,36,79 biexciton recombination,73,75,76,80−82 thermal effects due to heating by the pumping source, defect transitions,77 and band-gap renormalization (BGR).73,78 Band-gap renormalization (BGR) in a perovskite crystal refers to a red shift in the band gap under strong excitation.78,83,84 BGR in semiconductors is a many-body problem involving interactions between large populations of electrons and holes, which ultimately results in a red shift of the band-gap.83,84 The ASE peak underwent a red shift of ∼4 nm over the entire range of pumping energy densities, which corresponded to a BGR of approximately 12 meV. The dependence of ASE on power is illustrated in Figure 8a as a function of injected carrier density (n). The carrier density was calculated from the absorbance spectrum while taking additional absorption on the surface layer under 410 nm excitation into account.10 The clear onset of the transition from SE to ASE was observed at a threshold carrier density of approximately 7.06 × 1018 cm–3. At the threshold carrier density, the net gain of the material could be increased easily through either electrical or optical means. The BGR was estimated using eq 4.78

graphic file with name ao0c04517_m004.jpg 4

where γ is the band-gap renormalization factor. The red shift in the emission peak with increasing pumping power was used to estimate BGR. ASE was expected to appear in the region of maximum gain. ΔEBGR during excitation at 410 nm is plotted against n1/3 in Figure 8b. As expected, BGR was induced by an increase in the carrier density and reached a maximum value of ∼45 meV, which corresponded to a maximum red shift of 8 nm at a pumping energy density of ∼39 μJ cm–2. The small BGR value was attributed to unconfined photocarriers.84 BGR did not continue at pumping energy densities above ∼22.5 μJ cm–2 because the carrier density did not increase significantly with increasing fluence. Since BGR depended only on the carrier density, the energy shift was almost negligible above 22.5 μJ cm–2, given the spectral resolution of our setup (∼0.78 nm). The BGR coefficient was thus estimated at a lower carrier density. The estimated BGR was ∼27.10 × 10–8 eV cm, which was very close to the reported BGR of GaAs.78 These results indicated that the PQDs behaved like a typical semiconductor and could be evaluated using the same criteria.

Figure 8.

Figure 8

Open in a new tab

(a) Integrated PL versus injected carrier density (n) and (b) BGR versus n1/3 of CsPbBr3 PQDs.

Conclusions

CsPbBr3 PQD thin films were successfully obtained directly from powdered QDs. They possessed excellent optical properties and were strong emitters. Amplified spontaneous emission (ASE) by the CsPbBr3 PQDs and optically pumped lasing were observed with excitation under laser irradiation for picosecond pulse intervals. Low-threshold ASE and optically pumped perovskite laser emission were achieved at room temperature. The ASE threshold of the CsPbBr3 PQDs was exceptionally low, which could make them ideal candidates for photonic integration applications. Also, as far as we know, the energy density threshold of ASE reported in this work (22.25 μJ cm–2) is the lowest value reported under picosecond pulsed laser of excitation, which indicates that as-synthesized CsPbBr3 PQDs with good phase purity can be used as lasers. The purity of the cubic phase was attributed to synthesis at a high temperature. The CsPbBr3 PQDs exhibited a narrow emission line, which would be an important feature for both LEDs and lasers. Lasers should emit monochromatic light, while LEDs require narrow emission lines for color purity. The lasing features of the CsPbBr3 PQDs included a low threshold and narrow line width. These were attributed in part to quantum confinement in the CsPbBr3 PQDs, which limited PL losses. Surface coverage was good, and the surfaces of the films were smooth and contained no pinholes and few defects. This could be attributed to the combined contributions of the QD surfaces, a high reaction temperature, and surface energy as indicated by the roughness value. The photon density increased dramatically when the carrier density reached the threshold value, and stimulated recompilation became significant. The estimated ASE threshold carrier density was 7.06 × 1018 cm–3, and the estimated BGR constant of the CsPbBr3 films was 27.10 × 10–8 eV cm. The CsPbBr3 PQDs thus combined the advantages of perovskite materials with quantum confinement.

Materials and Methods

Materials

High-quality cesium lead bromide (CsPbBr3) QD powder was obtained from Quantum Solutions Company (Thuwal, Saudi Arabia, www.qdot.inc) and was prepared by a modified hot-injection process. N-Hexane AR solution (Avonchem, Cheshire, UK) was used to dissolve the CsPbBr3 PQD powder.

Fabrication of the CsPbBr3 QD Powder and QD Solution

The QDs were prepared via modified hot injection as described by Protesescu et al.42 using the combination of Oleic acid and oleylamine as a capping agent and emitted green light.

In this work, powdered QDs were used directly to prepare high-quality cesium lead bromide perovskite quantum dot (CsPbBr3 PQD) thin films. The powdered CsPbBr3 QDs and precursor materials were dissolved in a certain amount of hexane to get the required concentration. A typical film was prepared by first suspending 50 mg of the CsPbBr3 QD powder in hexane (1 mL). The suspension was left overnight to ensure complete dispersion prior to spin-coating the CsPbBr3 QD film.

Fabrication of the CsPbBr3 QD Thin Films

The CsPbBr3 thin films were fabricated by directly coating glass substrates. Therefore, glass microscope slides were used as substrates for thin-film fabrication. The substrates were sonicated by an ultrasonicator in soapy water for 15 min, followed by sonication in water alone for 15 min. The substrates were then sequentially ultrasonicated in acetone and isopropyl alcohol (IPA) for 15 min each and allowed to dry. The PQD mixture (100 μL) was dropped onto the 1 × 2 cm2 glass substrate and spin-coated at 4000 rpm for 30 s. The film thickness could be controlled by adjusting the concentration of the PQD suspension. The films were generally not annealed. To remove the solvent, the films were simply dried under vacuum for 1 h.

Structure and Morphology

High-resolution transmission electron microscopy (HR-TEM) was conducted using a 2100 HR-TEM (JEOL, Japan) at an accelerating voltage of 200 kV. The HR-TEM was equipped with an energy-dispersive X-ray spectrometer, which was used to perform elemental analysis and generate lateral distribution maps of the elements at selected locations on the samples. Elements in the samples emitted X-rays with characteristic wavelengths after excitation by the incident electron beam. A JSM-6380 scanning electron microscope (SEM, JEOL) was also used to examine the morphologies of the films. The crystal phases in the CsPbBr3 PQD films were determined via X-ray diffraction (XRD) analysis using a Miniflex 600 XRD (Rigaku, Japan) equipped with a copper Kα radiation source (λ = 1.5418 Å). Scanning from (2θ) 10–80° was performed at a scan rate of 3° min–1 with a step size of 0.02°.

Surface Characterization

Atomic force microscopy (AFM) was performed using a Multimode V AFM (Veeco, Northern Ireland) in tapping mode to examine the surface morphologies of the thin films. Film thickness was measured using a Dektak 150 stylus profiler (Bruker).

Optical Characterization

A portion of the CsPbBr3 PQD suspension was dispersed on a microscopic glass slide for optical characterization. The absorption spectra of the PQD thin films were recorded at ambient temperature using a V-670 UV–vis spectrophotometer (JASCO Corp., Japan). The photoluminescence (PL) spectra of the perovskite films were recorded using an FP-8200 fluorescence spectrophotometer (JASCO Corp., Japan) in the wavelength range from 350 to 800 nm.

Time-Resolved PL Measurements

The time-resolved PL measurements were performed using a Shamrock SR-500i spectrometer (Andor) equipped with an MS257 ICCD detector (Oriel Instruments). The samples were optically pumped with an Nd: YAG laser, Solara, LPS 1500 (3rd harmonic, wavelength: 355 nm, pulse width: 11 ns, repetition rate: 100 Hz, energy density: 1.5 μJ cm–2). An optical fiber attached to the ICCD camera and a lens system collected part of the emitted light from the samples.

Laser Experiments

To investigate the ASE and lasing properties of the films, power-dependent ASE spectra were recorded at the sample edges near the ends of the excitation strips using an LT-2215-OPG optical parametric generator (OPG, 3photon, Lithuania). The OPG was constructed with barium borate (β-BaB2O4) and had a tunable range of 425–2,300 nm. A LOTUS II Q-switched Nd:YAG picosecond laser (LOTIS, Belarus) was used for excitation with a pulse duration of 70–80 ps at a repetition rate of 15 Hz. The signals emitted by the samples were directed through an optical fiber and a collimating lens. A QE65 Pro spectrograph (Ocean Optics) with a spectral resolution of 0.78 nm was used as the detector for all lasing and ASE measurements. All measurements were performed in air at room temperature (293 K). A schematic diagram of the laser setup used in the experiment investigate the presence of stimulated emission is shown in Figure S6 (Supporting Information).

ASE Measurements

The pumping laser beam was passed through a plate with an aperture ∼2 mm in diameter. The laser beam was focused to have a radius of ∼2 mm using a reflective microscope objective lens with a focal length of 10 cm, and the signals emitted by the samples were directed through an optical fiber. The pumping laser energy density was adjusted using a variable neutral density (ND) filter wheel. The energy of the laser was measured using an LM-P-209 coherent thermal sensor head. The laser energy density was attenuated, which enabled us to study the threshold dependence on energy density.

Data Analysis

A custom Python-based program developed in our research group was used to analyze the large amount of data collected in the study. The program enabled us to rapidly obtain Gaussian fits of dual PL emission peaks in multiple data files.

Acknowledgments

The authors extend their appreciation to the Deputyship for Research & Innovation, “Ministry of Education“ in Saudi Arabia for funding this research work through the project no. (IFKSURG-1440-038).

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.0c04517.

  • Schematic diagram of the laser setup. More details about the structural and optical properties of CsPbBr3 QD perovskite thin films (PDF)

Author Contributions

All authors have given approval to the final version of the manuscript.

The authors declare no competing financial interest.

Supplementary Material

ao0c04517_si_001.pdf (1.2MB, pdf)

References

  1. Kojima A.; Teshima K.; Shirai Y.; Miyasaka T. Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc. 2009, 131, 6050–6051. 10.1021/ja809598r. [DOI] [PubMed] [Google Scholar]
  2. Akkerman Q. A.; Motti S. G.; Srimath Kandada A. R.; Mosconi E.; D’Innocenzo V.; Bertoni G.; Marras S.; Kamino B. A.; Miranda L.; De Angelis F.; Petrozza A.; Prato M.; Manna L. Solution Synthesis Approach to Colloidal Cesium Lead Halide Perovskite Nanoplatelets with Monolayer-Level Thickness Control. J. Am. Chem. Soc. 2016, 138, 1010–1016. 10.1021/jacs.5b12124. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Mitzi D. B.; Feild C. A.; Schlesinger Z.; Laibowitz R. B. Transport, Optical, and Magnetic Properties of the Conducting Halide Perovskite CH3NH3SnI3. J. Solid State Chem. 1995, 114, 159–163. 10.1006/jssc.1995.1023. [DOI] [Google Scholar]
  4. Chondroudis Konstantinos.; M D. B. Electroluminescence from an Organic–Inorganic Perovskite Incorporating a Quaterthiophene Dye within Lead Halide Perovskite Layers. Chem. Mater. 1999, 11, 3028–3030. 10.1021/cm990561t. [DOI] [Google Scholar]
  5. Baikie T.; Fang Y.; Kadro J. M.; Schreyer M.; Wei F.; Mhaisalkar S. G.; Gratzel M.; White T. J. Synthesis and Crystal Chemistry of the Hybrid Perovskite (CH3NH3)PbI3 for Solid-State Sensitised Solar Cell Applications. J. Mater. Chem. A 2013, 1, 5628. 10.1039/c3ta10518k. [DOI] [Google Scholar]
  6. Tan Z.-K.; Moghaddam R. S.; Lai M. L.; Docampo P.; Higler R.; Deschler F.; Price M.; Sadhanala A.; Pazos L. M.; Credgington D.; Hanusch F.; Bein T.; Snaith H. J.; Friend R. H. Bright Light-Emitting Diodes Based on Organometal Halide Perovskite. Nat. Nanotechnol. 2014, 9, 687–692. 10.1038/nnano.2014.149. [DOI] [PubMed] [Google Scholar]
  7. Dou L.; Yang Y.; Micheal; You J.; Hong Z.; Chang W.-H.; Li G.; Yang Y. Solution-Processed Hybrid Perovskite Photodetectors with High Detectivity. Nat. Commun. 2014, 5, 5404 10.1038/ncomms6404. [DOI] [PubMed] [Google Scholar]
  8. Kumawat N. K.; Gupta D.; Kabra D. Recent Advances in Metal Halide-Based Perovskite Light-Emitting Diodes. Energy Technol. 2017, 5, 1734–1749. 10.1002/ente.201700356. [DOI] [Google Scholar]
  9. Kondo T.; Azuma T.; Yuasa T.; Ito R. Biexciton Lasing in the Layered Perovskite-Type Material (C6H13NH3)2PbI4. Solid State Commun. 1998, 105, 253–255. 10.1016/S0038-1098(97)10085-0. [DOI] [Google Scholar]
  10. Qaid S. M. H.; Khan M. N.; Alqasem A.; Hezam M.; Aldwayyan A. Restraining Effect of Film Thickness on the Behaviour of Amplified Spontaneous Emission from Methylammonium Lead Iodide Perovskite. IET Optoelectron. 2019, 13, 2–6. 10.1049/iet-opt.2018.5035. [DOI] [Google Scholar]
  11. Xing G.; Mathews N.; Lim S. S.; Yantara N.; Liu X.; Sabba D.; Grätzel M.; Mhaisalkar S.; Sum T. C. Low-Temperature Solution-Processed Wavelength-Tunable Perovskites for Lasing. Nat. Mater. 2014, 13, 476–480. 10.1038/nmat3911. [DOI] [PubMed] [Google Scholar]
  12. Deschler F.; Price M.; Pathak S.; Klintberg L. E.; Jarausch D.-D.; Higler R.; Hüttner S.; Leijtens T.; Stranks S. D.; Snaith H. J.; Atatüre M.; Phillips R. T.; Friend R. H. High Photoluminescence Efficiency and Optically Pumped Lasing in Solution-Processed Mixed Halide Perovskite Semiconductors. J. Phys. Chem. Lett. 2014, 5, 1421–1426. 10.1021/jz5005285. [DOI] [PubMed] [Google Scholar]
  13. Zhu H.; Fu Y.; Meng F.; Wu X.; Gong Z.; Ding Q.; Gustafsson M. V.; Trinh M. T.; Jin S.; Zhu X.-Y. Lead Halide Perovskite Nanowire Lasers with Low Lasing Thresholds and High Quality Factors. Nat. Mater. 2015, 14, 636–642. 10.1038/nmat4271. [DOI] [PubMed] [Google Scholar]
  14. Mitzi D. B.; Chondroudis K.; Kagan C. R. Organic-Inorganic Electronics. IBM J. Res. Dev. 2001, 45, 29–45. 10.1147/rd.451.0029. [DOI] [Google Scholar]
  15. Xu W.; Lei G.; Tao C.; Zhang J.; Liu X.; Xu X.; Lai W. Y.; Gao F.; Huang W. Precisely Controlling the Grain Sizes with an Ammonium Hypophosphite Additive for High-Performance Perovskite Solar Cells. Adv. Funct. Mater. 2018, 28, 1802320 10.1002/adfm.201802320. [DOI] [Google Scholar]
  16. Deschler F.; Price M.; Pathak S.; Klintberg L. E.; Jarausch D.-D.; Higler R.; Hüttner S.; Leijtens T.; Stranks S. D.; Snaith H. J.; Atatüre M.; Phillips R. T.; Friend R. H. High Photoluminescence Efficiency and Optically Pumped Lasing in Solution-Processed Mixed Halide Perovskite Semiconductors. J. Phys. Chem. Lett. 2014, 5, 1421–1426. 10.1021/jz5005285. [DOI] [PubMed] [Google Scholar]
  17. Zhang Q.; Ha S. T.; Liu X.; Sum T. C.; Xiong Q. Room-Temperature near-Infrared High-Q Perovskite Whispering-Gallery Planar Nanolasers. Nano Lett. 2014, 14, 5995–6001. 10.1021/nl503057g. [DOI] [PubMed] [Google Scholar]
  18. Dhanker R.; Brigeman A. N.; Larsen A. V.; Stewart R. J.; Asbury J. B.; Giebink N. C. Random Lasing in Organo-Lead Halide Perovskite Microcrystal Networks. Appl. Phys. Lett. 2014, 105, 151112 10.1063/1.4898703. [DOI] [Google Scholar]
  19. Sutherland B. R.; Hoogland S.; Adachi M. M.; Wong C. T. O.; Sargent E. H. Conformal Organohalide Perovskites Enable Lasing on Spherical Resonators. ACS Nano 2014, 8, 10947–10952. 10.1021/nn504856g. [DOI] [PubMed] [Google Scholar]
  20. Amat A.; Mosconi E.; Ronca E.; Quarti C.; Umari P.; Nazeeruddin M. K.; Grätzel M.; De Angelis F. Cation-Induced Band-Gap Tuning in Organohalide Perovskites: Interplay of Spin-Orbit Coupling and Octahedra Tilting. Nano Lett. 2014, 14, 3608–3616. 10.1021/nl5012992. [DOI] [PubMed] [Google Scholar]
  21. Kulbak M.; Gupta S.; Kedem N.; Levine I.; Bendikov T.; Hodes G.; Cahen D. Cesium Enhances Long-Term Stability of Lead Bromide Perovskite-Based Solar Cells. J. Phys. Chem. Lett. 2016, 7, 167–172. 10.1021/acs.jpclett.5b02597. [DOI] [PubMed] [Google Scholar]
  22. Yantara N.; Bhaumik S.; Yan F.; Sabba D.; Dewi H. A.; Mathews N.; Boix P. P.; Demir H. V.; Mhaisalkar S. Inorganic Halide Perovskites for Efficient Light-Emitting Diodes. J. Phys. Chem. Lett. 2015, 6, 4360–4364. 10.1021/acs.jpclett.5b02011. [DOI] [PubMed] [Google Scholar]
  23. Auf Der Maur M.; Pecchia A.; Penazzi G.; Rodrigues W.; Di Carlo A. Efficiency Drop in Green InGaN/GaN Light Emitting Diodes: The Role of Random Alloy Fluctuations. Phys. Rev. Lett. 2016, 116, 027401 10.1103/PhysRevLett.116.027401. [DOI] [PubMed] [Google Scholar]
  24. Löper P.; Stuckelberger M.; Niesen B.; Werner J.; Filipič M.; Moon S. J.; Yum J. H.; Topič M.; De Wolf S.; Ballif C. Complex Refractive Index Spectra of CH3NHPbI3 Perovskite Thin Films Determined by Spectroscopic Ellipsometry and Spectrophotometry. J. Phys. Chem. Lett. 2015, 6, 66–71. 10.1021/jz502471h. [DOI] [PubMed] [Google Scholar]
  25. Zhang M.; Zheng Z.; Fu Q.; Chen Z.; He J.; Zhang S.; Chen C.; Luo W. Synthesis and Single Crystal Growth of Perovskite Semiconductor CsPbBr3. J. Cryst. Growth 2018, 484, 37–42. 10.1016/j.jcrysgro.2017.12.020. [DOI] [Google Scholar]
  26. Kunugita H.; Hashimoto T.; Kiyota Y.; Udagawa Y.; Takeoka Y.; Nakamura Y.; Sano J.; Matsushita T.; Kondo T.; Miyasaka T.; Ema K. Excitonic Feature in Hybrid Perovskite CH3NH3PbBr3 Single Crystals. Chem. Lett. 2015, 44, 852–854. 10.1246/cl.150204. [DOI] [Google Scholar]
  27. Song J.; Li J.; Li X.; Xu L.; Dong Y.; Zeng H. Quantum Dot Light-Emitting Diodes Based on Inorganic Perovskite Cesium Lead Halides (CsPbX3). Adv. Mater. 2015, 27, 7162–7167. 10.1002/adma.201502567. [DOI] [PubMed] [Google Scholar]
  28. Sutherland B. R.; Sargent E. H. Perovskite Photonic Sources. Nat. Photonics 2016, 10, 295–302. 10.1038/nphoton.2016.62. [DOI] [Google Scholar]
  29. Dang C.; Nurmikko A. Beyond Quantum Dot LEDs: Optical Gain and Laser Action in Red, Green, and Blue Colors. MRS Bull. 2013, 38, 737–742. 10.1557/mrs.2013.183. [DOI] [Google Scholar]
  30. Pan J.; Sarmah S. P.; Murali B.; Dursun I.; Peng W.; Parida M. R.; Liu J.; Sinatra L.; Alyami N.; Zhao C.; Alarousu E.; Ng T. K.; Ooi B. S.; Bakr O. M.; Mohammed O. F. Air-Stable Surface-Passivated Perovskite Quantum Dots for Ultra-Robust, Single- and Two-Photon-Induced Amplified Spontaneous Emission. J. Phys. Chem. Lett. 2015, 6, 5027–5033. 10.1021/acs.jpclett.5b02460. [DOI] [PubMed] [Google Scholar]
  31. Aharon S.; Cohen B. El.; Etgar L. Hybrid Lead Halide Iodide and Lead Halide Bromide in Efficient Hole Conductor Free Perovskite Solar Cell. J. Phys. Chem. C 2014, 118, 17160–17165. 10.1021/jp5023407. [DOI] [Google Scholar]
  32. Zhu P.; Zhu J. Low-dimensional Metal Halide Perovskites and Related Optoelectronic Applications. InfoMat 2020, 2, 341–378. 10.1002/inf2.12086. [DOI] [Google Scholar]
  33. Eaton S. W.; Lai M.; Gibson N. A.; Wong A. B.; Dou L.; Ma J.; Wang L. W.; Leone S. R.; Yang P. Lasing in Robust Cesium Lead Halide Perovskite Nanowires. Proc. Natl. Acad. Sci. U. S. A. 2016, 113, 1993–1998. 10.1073/pnas.1600789113. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Zhang Q.; Su R.; Liu X.; Xing J.; Sum T. C.; Xiong Q. High-Quality Whispering-Gallery-Mode Lasing from Cesium Lead Halide Perovskite Nanoplatelets. Adv. Funct. Mater. 2016, 26, 6238–6245. 10.1002/adfm.201601690. [DOI] [Google Scholar]
  35. Liu Zhengzheng.; et al. Advances in Inorganic and Hybrid Perovskites for Miniaturized Lasers in: Nanophotonics - Ahead of Print. Nanophotonics 2020, 2251–2272. 10.1515/nanoph-2019-0572. [DOI] [Google Scholar]
  36. Huang C. Y.; Zou C.; Mao C.; Corp K. L.; Yao Y. C.; Lee Y. J.; Schlenker C. W.; Jen A. K. Y.; Lin L. Y. CsPbBr3 Perovskite Quantum Dot Vertical Cavity Lasers with Low Threshold and High Stability. ACS Photonics 2017, 4, 2281–2289. 10.1021/acsphotonics.7b00520. [DOI] [Google Scholar]
  37. Wei G. Q.; Wang X. D.; Liao L. S. Recent Advances in 1D Organic Solid-State Lasers. Adv. Funct. Mater. 2019, 29, 1902981 10.1002/adfm.201902981. [DOI] [Google Scholar]
  38. Yakunin S.; Protesescu L.; Krieg F.; Bodnarchuk M. I.; Nedelcu G.; Humer M.; De Luca G.; Fiebig M.; Heiss W.; Kovalenko M. V. Low-Threshold Amplified Spontaneous Emission and Lasing from Colloidal Nanocrystals of Caesium Lead Halide Perovskites. Nat. Commun. 2015, 6, 8056 10.1038/ncomms9056. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Yan D.; Shi T.; Zang Z.; Zhou T.; Liu Z.; Zhang Z.; Du J.; Leng Y.; Tang X. Ultrastable CsPbBr 3 Perovskite Quantum Dot and Their Enhanced Amplified Spontaneous Emission by Surface Ligand Modification. Small 2019, 15, 1901173 10.1002/smll.201901173. [DOI] [PubMed] [Google Scholar]
  40. Wang Y.; Zhi M.; Chang Y. Q.; Zhang J. P.; Chan Y. Stable, Ultralow Threshold Amplified Spontaneous Emission from CsPbBr3 Nanoparticles Exhibiting Trion Gain. Nano Lett. 2018, 18, 4976–4984. 10.1021/acs.nanolett.8b01817. [DOI] [PubMed] [Google Scholar]
  41. Su Y.; Chen X.; Ji W.; Zeng Q.; Ren Z.; Su Z.; Liu L. Highly Controllable and Efficient Synthesis of Mixed-Halide CsPbX3 (X = Cl, Br, I) Perovskite QDs toward the Tunability of Entire Visible Light. ACS Appl. Mater. Interfaces 2017, 9, 33020–33028. 10.1021/acsami.7b10612. [DOI] [PubMed] [Google Scholar]
  42. Protesescu L.; Yakunin S.; Bodnarchuk M. I.; Krieg F.; Caputo R.; Hendon C. H.; Yang R. X.; Walsh A.; Kovalenko M. V. Nanocrystals of Cesium Lead Halide Perovskites (CsPbX 3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut. Nano Lett. 2015, 15, 3692–3696. 10.1021/nl5048779. [DOI] [PMC free article] [PubMed] [Google Scholar]
  43. Beal R. E.; Slotcavage D. J.; Leijtens T.; Bowring A. R.; Belisle R. A.; Nguyen W. H.; Burkhard G. F.; Hoke E. T.; McGehee M. D. Cesium Lead Halide Perovskites with Improved Stability for Tandem Solar Cells. J. Phys. Chem. Lett. 2016, 7, 746–751. 10.1021/acs.jpclett.6b00002. [DOI] [PubMed] [Google Scholar]
  44. Li C.; Zang Z.; Han C.; Hu Z.; Tang X.; Du J.; Leng Y.; Sun K. Enhanced Random Lasing Emission from Highly Compact CsPbBr3 Perovskite Thin Films Decorated by ZnO Nanoparticles. Nano Energy 2017, 40, 195–202. 10.1016/j.nanoen.2017.08.013. [DOI] [Google Scholar]
  45. He X.; Qiu Y.; Yang S. Fully-Inorganic Trihalide Perovskite Nanocrystals: A New Research Frontier of Optoelectronic Materials. Adv. Mater. 2017, 29, 1700775 10.1002/adma.201700775. [DOI] [PubMed] [Google Scholar]
  46. MØller CHR. KN. Crystal Structure and Photoconductivity of Cæsium Plumbohalides. Nature 1958, 182, 1436. 10.1038/1821436a0. [DOI] [Google Scholar]
  47. Nedelcu G.; Protesescu L.; Yakunin S.; Bodnarchuk M. I.; Grotevent M. J.; Kovalenko M. V. Fast Anion-Exchange in Highly Luminescent Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, I). Nano Lett. 2015, 15, 5635–5640. 10.1021/acs.nanolett.5b02404. [DOI] [PMC free article] [PubMed] [Google Scholar]
  48. Yoon H. C.; Lee S.; Song J. K.; Yang H.; Do Y. R. Efficient and Stable CsPbBr 3 Quantum-Dot Powders Passivated and Encapsulated with a Mixed Silicon Nitride and Silicon Oxide Inorganic Polymer Matrix. ACS Appl. Mater. Interfaces 2018, 10, 11756–11767. 10.1021/acsami.8b01014. [DOI] [PubMed] [Google Scholar]
  49. Cottingham P.; Brutchey R. L. On the Crystal Structure of Colloidally Prepared CsPbBr 3 Quantum Dots. Chem. Commun. 2016, 52, 5246–5249. 10.1039/C6CC01088A. [DOI] [PubMed] [Google Scholar]
  50. Yassitepe E.; Yang Z.; Voznyy O.; Kim Y.; Walters G.; Castañeda J. A.; Kanjanaboos P.; Yuan M.; Gong X.; Fan F.; Pan J.; Hoogland S.; Comin R.; Bakr O. M.; Padilha L. A.; Nogueira A. F.; Sargent E. H. Amine-Free Synthesis of Cesium Lead Halide Perovskite Quantum Dots for Efficient Light-Emitting Diodes. Adv. Funct. Mater. 2016, 26, 8757–8763. 10.1002/adfm.201604580. [DOI] [Google Scholar]
  51. Pan J.; Quan L. N.; Zhao Y.; Peng W.; Murali B.; Sarmah S. P.; Yuan M.; Sinatra L.; Alyami N. M.; Liu J.; Yassitepe E.; Yang Z.; Voznyy O.; Comin R.; Hedhili M. N.; Mohammed O. F.; Lu Z. H.; Kim D. H.; Sargent E. H.; Bakr O. M. Highly Efficient Perovskite-Quantum-Dot Light-Emitting Diodes by Surface Engineering. Adv. Mater. 2016, 28, 8718–8725. 10.1002/adma.201600784. [DOI] [PubMed] [Google Scholar]
  52. Stoumpos C. C.; Malliakas C. D.; Peters J. A.; Liu Z.; Sebastian M.; Im J.; Chasapis T. C.; Wibowo A. C.; Chung D. Y.; Freeman A. J.; Wessels B. W.; Kanatzidis M. G. Crystal Growth of the Perovskite Semiconductor CsPbBr3: A New Material for High-Energy Radiation Detection. Cryst. Growth Des. 2013, 13, 2722–2727. 10.1021/cg400645t. [DOI] [Google Scholar]
  53. Bekenstein Y.; Koscher B. A.; Eaton S. W.; Yang P.; Alivisatos A. P. Highly Luminescent Colloidal Nanoplates of Perovskite Cesium Lead Halide and Their Oriented Assemblies. J. Am. Chem. Soc. 2015, 137, 16008–16011. 10.1021/jacs.5b11199. [DOI] [PubMed] [Google Scholar]
  54. Wang W.; Wu Y.; Wang D.; Zhang T. Effective Control of the Growth and Photoluminescence Properties of CsPbBr3/Cs4PbBr6 Nanocomposites by Solvent Engineering. ACS Omega 2019, 4, 19641–19646. 10.1021/acsomega.9b02248. [DOI] [PMC free article] [PubMed] [Google Scholar]
  55. Al-Asbahi B. A.; Qaid S. M. H.; Hezam M.; Bedja I.; Ghaithan H. M.; Aldwayyan A. S. Effect of Deposition Method on the Structural and Optical Properties of CH3NH3PbI3 Perovskite Thin Films. Opt. Mater. 2020, 103, 109836 10.1016/j.optmat.2020.109836. [DOI] [Google Scholar]
  56. Hall W. H. X-Ray Line Broadening in Metals. Proc. Phys. Soc. A 1949, 62, 741–743. 10.1088/0370-1298/62/11/110. [DOI] [Google Scholar]
  57. Nath D.; Singh F.; Das R. X-Ray Diffraction Analysis by Williamson-Hall, Halder-Wagner and Size-Strain Plot Methods of CdSe Nanoparticles- a Comparative Study. Mater. Chem. Phys. 2020, 239, 122021 10.1016/j.matchemphys.2019.122021. [DOI] [Google Scholar]
  58. Maqbool M.; Rehman G.; Ali L.; Shafiq M.; Iqbal R.; Ahmad R.; Khan T.; Jalali-Asadabadi S.; Maqbool M.; Ahmad I. Structural, Electronic and Optical Properties of CsPbX 3 (X = Cl, Br, I) for Energy Storage and Hybrid Solar Cell Applications. J. Alloys Compd. 2017, 705, 828–839. 10.1016/j.jallcom.2017.02.147. [DOI] [Google Scholar]
  59. Comin R.; Walters G.; Thibau E. S.; Voznyy O.; Lu Z. H.; Sargent E. H. Structural, Optical, and Electronic Studies of Wide-Bandgap Lead Halide Perovskites. J. Mater. Chem. C 2015, 3, 8839–8843. 10.1039/C5TC01718A. [DOI] [Google Scholar]
  60. He W.; Wang R.; Zhou C.; Yang J.; Li F.; Xiang X. Controlling the Structure and Photoelectrochemical Performance of BiVO 4 Photoanodes Prepared from Electrodeposited Bismuth Precursors: Effect of Zinc Ions as Directing Agent. Ind. Eng. Chem. Res. 2015, 54, 10723–10730. 10.1021/acs.iecr.5b02460. [DOI] [Google Scholar]
  61. Yakuphanoglu F.; Sekerci M.; Ozturk O. F. The Determination of the Optical Constants of Cu(Ii) Compound Having 1-Chloro-2,3-o-Cyclohexylidinepropane Thin Film. Opt. Commun. 2004, 239, 275–280. 10.1016/j.optcom.2004.05.038. [DOI] [Google Scholar]
  62. Yin W.-J.; Shi T.; Yan Y. Unique Properties of Halide Perovskites as Possible Origins of the Superior Solar Cell Performance. Adv. Mater. 2014, 26, 4653–4658. 10.1002/adma.201306281. [DOI] [PubMed] [Google Scholar]
  63. Li R.; Wei Z.; Zhao H.; Yu H.; Fang X.; Fang D.; Li J.; He T.; Chen R.; Wang X. Linear and Nonlinear Optical Characteristics of All-Inorganic Perovskite CsPbBr3 Quantum Dots Modified by Hydrophobic Zeolites. Nanoscale 2018, 10, 22766–22774. 10.1039/C8NR07256F. [DOI] [PubMed] [Google Scholar]
  64. Makarov N. S.; Guo S.; Isaienko O.; Liu W.; Robel I.; Klimov V. I. Spectral and Dynamical Properties of Single Excitons, Biexcitons, and Trions in Cesium-Lead-Halide Perovskite Quantum Dots. Nano Lett. 2016, 16, 2349–2362. 10.1021/acs.nanolett.5b05077. [DOI] [PubMed] [Google Scholar]
  65. Yakuphanoglu F.; Cukurovali A.; Yilmaz I. Refractive Index and Optical Absorption Properties of the Complexes of a Cyclobutane Containing Thiazolyl Hydrazone Ligand. Opt. Mater. 2005, 27, 1363–1368. 10.1016/j.optmat.2004.09.021. [DOI] [Google Scholar]
  66. Rainò G.; Nedelcu G.; Protesescu L.; Bodnarchuk M. I.; Kovalenko M. V.; Mahrt R. F.; Stöferle T. Single Cesium Lead Halide Perovskite Nanocrystals at Low Temperature: Fast Single-Photon Emission, Reduced Blinking, and Exciton Fine Structure. ACS Nano 2016, 10, 2485–2490. 10.1021/acsnano.5b07328. [DOI] [PMC free article] [PubMed] [Google Scholar]
  67. Saba M.; Quochi F.; Mura A.; Bongiovanni G. Excited State Properties of Hybrid Perovskites. Acc. Chem. Res. 2016, 49, 166–173. 10.1021/acs.accounts.5b00445. [DOI] [PubMed] [Google Scholar]
  68. Olbright G. R.; Klem J.; Owyoung A.; Brennan T. M.; Binder R.; Koch S. W. Many-Body Effects in the Luminescence of Highly Excited Indirect Superlattices. J. Opt. Soc. Am. B 1990, 7, 1473–1480. 10.1364/JOSAB.7.001473. [DOI] [Google Scholar]
  69. Wang X.; Zhou H.; Yuan S.; Zheng W.; Jiang Y.; Zhuang X.; Liu H.; Zhang Q.; Zhu X.; Wang X.; Pan A. Cesium Lead Halide Perovskite Triangular Nanorods as High-Gain Medium and Effective Cavities for Multiphoton-Pumped Lasing. Nano Res. 2017, 10, 3385–3395. 10.1007/s12274-017-1551-1. [DOI] [Google Scholar]
  70. Jiang Y.; Liu Y.-Y.; Liu X.; Lin H.; Gao K.; Lai W.-Y.; Huang W. Organic Solid-State Lasers: A Materials View and Future Development. Chem. Soc. Rev. 2020, 49, 5885–5944. 10.1039/D0CS00037J. [DOI] [PubMed] [Google Scholar]
  71. Priante D.; Dursun I.; Alias M. S.; Shi D.; Melnikov V. A.; Ng T. K.; Mohammed O. F.; Bakr O. M.; Ooi B. S. The Recombination Mechanisms Leading to Amplified Spontaneous Emission at the True-Green Wavelength in CH3NH3PbBr3 Perovskites. Appl. Phys. Lett. 2015, 106, 081902 10.1063/1.4913463. [DOI] [Google Scholar]
  72. Chen K.; Barker A. J.; Morgan F. L. C.; Halpert J. E.; Hodgkiss J. M. Effect of Carrier Thermalization Dynamics on Light Emission and Amplification in Organometal Halide Perovskites. J. Phys. Chem. Lett. 2015, 6, 153–158. 10.1021/jz502528c. [DOI] [PubMed] [Google Scholar]
  73. Vale B. R. C.; Socie E.; Burgos-Caminal A.; Bettini J.; Schiavon M. A.; Moser J. E. Exciton, Biexciton, and Hot Exciton Dynamics in CsPbBr3 Colloidal Nanoplatelets. J. Phys. Chem. Lett. 2020, 11, 387–394. 10.1021/acs.jpclett.9b03282. [DOI] [PubMed] [Google Scholar]
  74. Parak W. J.; Manna L.; Nann T. Fundamental Principles of Quantum Dots. Nanotechnology 2010, 73–96. 10.1002/9783527628155.nanotech004. [DOI] [Google Scholar]
  75. Mondal A.; Aneesh J.; Kumar Ravi V.; Sharma R.; Mir W. J.; Beard M. C.; Nag A.; Adarsh K. V. Ultrafast Exciton Many-Body Interactions and Hot-Phonon Bottleneck in Colloidal Cesium Lead Halide Perovskite Nanocrystals. Phys. Rev. B 2018, 98, 115418 10.1103/PhysRevB.98.115418. [DOI] [Google Scholar]
  76. Robel I.; Gresback R.; Kortshagen U.; Schaller R. D.; Klimov V. I. Universal Size-Dependent Trend in Auger Recombination in Direct-Gap and Indirect-Gap Semiconductor Nanocrystals. Phys. Rev. Lett. 2009, 102, 1–4. 10.1103/PhysRevLett.102.177404. [DOI] [PubMed] [Google Scholar]
  77. Veldhuis S. A.; Boix P. P.; Yantara N.; Li M.; Sum T. C.; Mathews N.; Mhaisalkar S. G. Perovskite Materials for Light-Emitting Diodes and Lasers. Adv. Mater. 2016, 28, 6804–6834. 10.1002/adma.201600669. [DOI] [PubMed] [Google Scholar]
  78. Yang Y.; Ostrowski D. P.; France R. M.; Zhu K.; van de Lagemaat J.; Luther J. M.; Beard M. C. Observation of a Hot-Phonon Bottleneck in Lead-Iodide Perovskites. Nat. Photonics 2015, 10, 1–7. 10.1038/nphoton.2015.213. [DOI] [Google Scholar]
  79. Dang C.; Lee J.; Breen C.; Steckel J. S.; Coe-Sullivan S.; Nurmikko A. Red, Green and Blue Lasing Enabled by Single-Exciton Gain in Colloidal Quantum Dot Films. Nat. Nanotechnol. 2012, 7, 335–339. 10.1038/nnano.2012.61. [DOI] [PubMed] [Google Scholar]
  80. Yakunin S.; Protesescu L.; Krieg F.; Bodnarchuk M. I.; Nedelcu G.; Humer M.; De Luca G.; Fiebig M.; Heiss W.; Kovalenko M. V. Low-Threshold Amplified Spontaneous Emission and Lasing from Colloidal Nanocrystals of Caesium Lead Halide Perovskites. Nat. Commun. 2015, 6, 8056 10.1038/ncomms9056. [DOI] [PMC free article] [PubMed] [Google Scholar]
  81. Grim J. Q.; Christodoulou S.; Di Stasio F.; Krahne R.; Cingolani R.; Manna L.; Moreels I. Continuous-Wave Biexciton Lasing at Room Temperature Using Solution-Processed Quantum Wells. Nat. Nanotechnol. 2014, 9, 891–895. 10.1038/nnano.2014.213. [DOI] [PubMed] [Google Scholar]
  82. Klimov V. I.; Mikhailovsky A. A.; Xu S.; Malko A.; Hollingsworth J. A.; Leatherdale C. A.; Eisler H. J.; Bawendi M. G. Optical Gain and Stimulated Emission in Nanocrystal Quantum Dots. Science 2000, 290, 314–317. 10.1126/science.290.5490.314. [DOI] [PubMed] [Google Scholar]
  83. Brinkman W. F.; Rice T. M. Electron-Hole Liquids in Semiconductors. Phys. Rev. B 1973, 7, 1508–1523. 10.1103/PhysRevB.7.1508. [DOI] [Google Scholar]
  84. Tränkle G.; Leier H.; Forchel A.; Haug H.; Ell C.; Weimann G. Dimensionality Dependence of the Band-Gap Renormalization in Two- and Three-Dimensional Electron-Hole Plasmas in GaAs. Phys. Rev. Lett. 1987, 58, 419–422. 10.1103/PhysRevLett.58.419. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ao0c04517_si_001.pdf (1.2MB, pdf)

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES