Study of Inorganic Halide (Cs2CuCl4) Perovskite Quantum dots for Energy Harvesting Devices

Study of Inorganic Halide (Cs2CuCl4) Perovskite Quantum dots for Energy Harvesting Devices

Thatheyus Peter. X¹ , Geetha. D^2* , Kamalarasan.V³

^1,2Department of Physics, Annamalai University, Chidambaram, Tamil Nadu-India

³Department of Nuclear Physics, University of Madras, Chennai, Tamil Nadu-India

Corresponding Author Email: geeramphyau@gmail.com

DOI : http://dx.doi.org/10.53709/CHE.2021.v02i02.002

Abstract

Keywords

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1. Introduction

Metal halides with the perovskite crystal structure, recently used as energy converting materials because of their power conversion efficiencies up to 22% [1-3]. Owing to the higher stability of inorganic material, it becomes frequently used, and it can be tunable up to 700nm and for high quantum yields. Hence the incorporation of QDs into bulk inorganic perovskite enabled decoying of charge transport and light emission/sensitization heading to more efficient optoelectronic devices [4-6].

In these quantum dots, electrons and holes are confined three-dimensionally within the Bohr excitation radius. The specimen of Quantum dots is on the nanometer scale. As of this small-scale size of Quantum Dots, they contain distinct electronic energy, which results in individual optical properties [7]. High quantum yield, narrow and uniform emission spectra, and excitation due to we had these QDs have to use full over traditional inorganic quantum dots [8]. These quantum dots have narrow excitation and uniform emission spectra in a wide range of wavelengths, along with narrow full width at half maximum value (FWHM) [9-12]. By altering the basic structure of the quantum dots, they can emit from the UV to the NIR region in an absolutely facile mode; based on these aspects, quantum dots offer new opportunities in various fields. This combined property of nanomaterials results in developing new research areas of energy storage [13, 14].

Generally, Lot of approaches have been used to prepare QDs. But the precipitation approach is uncomplicated, cost-less, and eco-friendly. Also, it has some limitations viz., underprivileged properties and minimum luminescence intensity. To overcome with

strategies like dopped with inorganic halides. In the present work, novel perovskite quantum dots (Cs₂CuCl₄) were synthesized. A combination of inorganic halide group compounds having good absorption and emission. In this halide perovskite Quantum dots having high quantum yield and we can observe morphology, Bandgap in future, we construct a goods solar cells, LED, Supercapacitor, Magnetic properties.

2. Experimental details

2.1. Materials

Copper Chloride (CuCl₂), Cesium Chloride (CsCl₂), dimethylformamide (DMF), oleic acid (OA), and oleyl amine (OLA) were purchased from Sd. fine chemicals and were used without further purification.

2.1.1 Preparation

The Cs₂CuCl₄ quantum dots were prepared by an improved ligand-assisted re-precipitation (LARP) technique at room temperature. Copper chloride (CuCl₂) 1 mM, cesium chloride (CsCl) 2mM, DMF, and oleic acid–OLA were purchased without further purification. (0.168g) of CsCl and (0.067g) of CuCl2 were loaded into a mixture of 2ML DMF and then stirred. Octylamine and oleic acid as ligands added perovskite precursors then formed Quantum dots.  The resultant QDs were quasi-spherical with a means size of 5 nm. The reaction mechanism of as-prepared samples is given below.

The mechanism of Cs2CuCl4 QDs formation reaction can be express

3. Results and Discussion

3.1. Structural analysis (XRD)

To know about structural parameters, we recorded the x-ray diffraction pattern of quantum dots Cs₂CuCl₄. Obtained x-ray diffraction spectra for Quantum dots are presented in Fig. (1), which shows a thin film pattern of the inorganic perovskite Cs₂CuCl₄ quantum dots [QDs]. The QDs diffraction peaks observed at 2θ= 11.0, 16.4, 18.6, 20.5, 23.3, 29.0, 31.0, 34.2, and 37.4^oC corresponds to the planes of (101), (111) (200), (112), (103), (122), (302), (204) and (024) respectively. All diffraction peaks are well indexed to the orthorhombic crystal structure of Cs₂CuCl₄ QDs and space group Pnma with a lattice constant of a=9.769 b=7.607 and c=12.381 [JCPDS card no 79-1321]. No impurity is found in the pattern. Thin-film XRD pattern of mixed halide [Cl] Cs₂CuCl₄ QDs was inferred with the powder XRD pattern of [Cs₂CuBr₄/I₄] QDs and exhibiting orthorhombic crystal structure [15-16]. These characterizations are accurately proved that the Cs₂CuCl₄ quantum dots formed when the precursor ratio is 2:1. Here, using Scherer’s equation were calculated the particle size of QD.

D=0.9λ/βcosθ  (1)

Wherein the crystallite size, k -shape factor, λ -wavelength of the x-ray (λ=1.5406 Å), b-full width at half maximum (FWHM) of the peak and q-angle of the diffraction. hese samples could be assessed the lattice parameters. The lattice parameters for tetragonal structure Cs₂CuCl₄ QDs are calculated from the following equation.

       δ=1/D²                                                                        (2)

The above formulae calculate crystallite size, dislocation density, and lattice parameters, then its tabulate in table 1.

Table 1: Structural parameters of Cs₂CuCl₄ Quantum Dots

Fig. 1. XRD pattern of Cs₂CuCl₄ QDs

3.2 Optical studies

Fig 2(a) shows the UV-Visible spectra of perovskite QDs of Cs₂CuCl₄. The absorption spectrum was recorded for these perovskite Quantum Dots has been detecting by the UV-Visible spectrum. The corresponding band gap obtained is 2.82 eV. The onset of the blue absorption shift is obtained due to bandgap edge shift 2.82 eV. In General, the blue-shifted optical spectra can be caused to the concentration of the perovskite, and it is best leading to the more vital interaction between Cu and Cl orbital [17]. The lesser conduction band of the copper halide perovskite is composed of the Cu 3d orbitals and Cl 3p orbitals. The respective absorption band edge shifts from 200 to 400 nm. The absorption band edge shifts to the higher wavelength increases when the size of the Nps.

The PL-emission spectrum of the QDs was measured for the Cs₂CuCl₄ solution as shown in Fig 2 (b), remaining details of the optical behavior of PL as shown in Fig 2 (c). The observed 274nm wavelength of excitation reflects the bright, broad emission peak between 400 to 520, which was confirmed by 300nm wavelength of excitation energy, and It was observed the sharp peak of broad bright blues green emission was monitored at 488nm. The sharp peak of the emission of FWHM is 19.2, for Cs₂CuCl₄ quantum dots.

Fig. 2. (a) Optical absorption spectra (b) Band gap energy of the Cs₂CuCl₄ QDs (c). Photoluminescence Spectra of Cs₂CuCl₄ QDs

3.3 Morphological studies (HR-TEM)

The surface morphological studies of the as-synthesized perovskite quantum dots [QDs] have been investigated by HR-TEM, representative HR-TEM image of the QDs is portrayed in Fig 3 (a & b). In this TEM, images clear that the prepared samples are single particles [dots] having the size of 5 to 10 nm. Cs₂CuCl₄ QDs were quasi-spherical in shape and distributed homogeneously. The presented typical HR-TEM Image and the size distribution of synthesized Cs₂CuCl₄ QDs. The images confirm that the synthesized sample was a halogen component inorganic perovskite quantum dot. Fig 3 (b) shows 9.10 is the average particle size of Cs₂CuCl₄ QDs It is gained from HR-TEM analysis, which is slightly higher than the crystallite size calculated from XRD analysis. Further Fig 3 (d), represents the size distribution of the histograms graph. From the HR-TEM images of the Cs₂CuCl₄ QDs can be calculated the lattice spacing and found to be 0.20 nm, which corresponds to (112) lattice plane. The crystal nature of the samples can be determined from the selected area (electron) diffraction pattern [Fig3 (c)], and the selected area electron diffraction (SAED) pattern indicates the single-crystalline nature of the Cs₂CuCl₄ nanoparticles.

Fig. 3. HR TEM images of Cs₂CuCl₄ QDs (a) 20nm (b) 50nm(c) SAED pattern (d) Histogram of particle size distribution of Cs₂CuCl₄QDs

3.4. Morphological analysis (SEM/EDS)

The SEM micrographs of perovskite QDs of Cs₂CuCl₄ particle prepared by the re-precipitation method as shown in fig 4. (a). From that characterization, Fig 4(a, b) shows a morphology image at different magnification which reveals flower-like structures with precursor dependent petal shapes. When the petal is a tapered QDs self-assembled from lots of nanorods. The EDX spectrum is composed the Cu, Cs, Cl elements. The perovskite Quantum dots cannot be visualized in SEM images, discarding the dots are agglomerate in low magnification.  HR-TEM study will help to confirm the quantum dot. Fig.4 (c) Shows the typical EDX spectrum of various elements in the Cs₂CuCl₄ sample. EDX spectrum is composed of CS, Cu, Cl elements. The element Cl, Cu present in K shell and Cs element present in L shell, the EDX shows fitting ratio 0.495.

Fig.4. (a, b) SEM image of of Cs₂CuCl₄QDs (c) EDX spectra (d) Mass and atomic value of Cs₂CuCl₄ QDs

5. Conclusion

In summary, a novel inorganic halide perovskite (Cs₂CuCl₄) quantum dots are prepared successfully by the reprecipitation method is proposed, wherein each molecule is capable of coordinating the cations and anions. As synthesized samples were characterized the optical and structural properties were examined XRD UV-Vis, and PL techniques showed that the sample has unique optical properties. By optimizing the halide composition and the ratio of the precursors (2:1), uniform quantum dots were harvested (visualized in HR-TEM). These Quantum Dots showed broad bluish-green emission upon excitation with 274 nm. These advantages will promote this new material in the field of energy harvesting devices viz., LED, solar cell. The simple synthesis for preparing perovskite Quantum Dots is the innovative research with few more transition metals-based perovskite nano crystals in the next level.

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