Efficient blue emission from ambient processed all-inorganic CsPbBr2Cl perovskite cubes T. Paul, B. K. Chatterjee, S. Maiti, N. Besra, S. Thakur, S. Sarkar, K. Chanda, A. Das, K. Sardar, and K. K. Chattopadhyay
Citation: AIP Conference Proceedings 1942, 120026 (2018); doi: 10.1063/1.5029066 View online: https://doi.org/10.1063/1.5029066 View Table of Contents: http://aip.scitation.org/toc/apc/1942/1 Published by the American Institute of Physics
Efficient Blue Emission From Ambient Processed AllInorganic CsPbBr2Cl Perovskite Cubes T. Paul1a, B.K. Chatterjee1, S. Maiti2, N. Besra3, S. Thakur1, S. Sarkar3, K. Chanda3, A. Das3 K. Sardar1 and K.K. Chattopadhyay1, 2b 1
School of Materials Science and Nanotechnology, Jadavpur University, Kolkata 700032, India. 2 CENIMAT/I3N, Faculdade de Ciências e Tecnologia, FCT Portugal 3 Departments of Physics, Jadavpur University, Kolkata 700032, India. Corresponding author e-mail:
[email protected],
[email protected]
Abstract. The recent resurgence of photovoltaic research has empowered all inorganic perovskite materials to take the center stage thus leading to a plethora of interesting results. Here, via a facile room-temperature synthesis protocol high quality cesium lead halide perovskite (CsPbBr2Cl) cubes has been realized. Surface morphology and crystallinity of the synthesized sample were investigated by FESEM and XRD respectively. To attain detail information of its chemical composition EDX analysis and elemental mapping were carried out. These single crystalline cubes crystallize in orthorhombic phase and exhibit strong photoluminescence emission at 482 nm with narrow FWHM value (~18nm) and photoluminescence decay time of 10.44 ns. We believe, this facile synthesis protocol will pave the way for realization other perovskite cube and thereby their usage in several optoelectronic arena like as lasing, LEDs and photo detector etc. Keywords: Perovskites, cesium lead halides, micro-cubes, photoluminescence, opto-electronics
PACS: 78.55.Qr, 42.82.Fv, 61.66.Fn
INTRODUCTION 0HWDOKDOLGHVSHURYVNLWHVERWKLQDOOLQRUJDQLFDQGRUJDQLFíLQRUJDQLFK\EULGIRUPKDYH truncated enormous research attention owing to their exceptional photo-physical features like tunable bandgap, long diffusion length, high carrier mobility and potential usage in solar cells, photo-detectors, light-emitting diodes and etc. [1-3]. Metal halide perovskites generally possess a chemical formula of ABX3 where A stands for methylammonium, Cs etc., B is Pb and Sn while X stands for halides like Cl, Br, or I. From the broad perovskite family, all-inorganic cesium lead halide (CsPbX3) is very appealing not only due their competitive optoelectronic features like tunable absorption and emission ranges and high quantum efficiency also for their more tolerant nature towards moisture, oxygen, light, heat as compared to the others. [4] First, colloidal and mono dispersed cesium lead halide nano-particles are synthesized by L. Protesescu et. al. in 2015 [5]. Since then great amount of research efforts have been devoted for the preparation of CsPbX3 with proper composition and optical tunability. CsPbX3 have already demonstrated their propitious in low-threshold lasing [6], reduced PL blinking, LEDs [7], and up-conversion perovskite nano laser [8]. To date, several documentations were made on synthesis of CsPbX3 nanoform however those are mostly confined to OD quantum dots and 1D nanowire. Furthermore, complex process controlling and low product yield associated with these synthesis protocols cast a shadow over their universal applicability. To extend the usage perspective of the halide perovskite, morphology tuned novel nanoform via facile as well budgetary synthesis approach is very alluring. In this work, we have synthesized CsPbBr2Cl micro-cube via a room temperature emulsion approach. Simplicity and large product yield are the highlight of this synthesis protocol. The as synthesized cubes are single crystalline in nature and possess good optical quality. Photo-luminescent property of CsPbBr2Cl was investigated which showed a strong and narrow emission at 482 nm with a very low FWHM value.
EXPERIMENTAL All solvents and reagents are of analytical grade and directly used without further purification. In a typical synthesis, CsCl (1.0 mmol) and PbBr2 (1.0 mmol) was dissolved in deionized water (D.I) and in DMF separately. Further an oil phase was prepared by adding hexane with oleic acid (1.0 ml) and n-octylamine (0.5 ml). CsCl solution was added drop by drop into PbBr2 solution
DAE Solid State Physics Symposium 2017 AIP Conf. Proc. 1942, 120026-1–120026-4; https://doi.org/10.1063/1.5029066 Published by AIP Publishing. 978-0-7354-1634-5/$30.00
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followed by which the final solution was mixed into the oil phase under vigorous stirring for 10 min. Tert-butanol was added afterwards with the previous solution immediately to initialize the demulsification. A pale cyan precipitate was separated by centrifugation.
CHARACTERIZATION Powder x-ray diffraction (XRD) patterns of the synthesized samples were recorded on a Bruker D8 diffractometer with Cu-KĮ UDGLDWLRQ RI ZDYHOHQJWK ǖ DW URRP WHPSHUDWXUH Product morphology was investigated with field emission scanning electron microscope (HITACHI S-4800) and energy dispersive x-ray spectroscope (EDX) was used for elemental analysis. Crystallinity of the synthesized artefact was characterized by transmission electron microscope (JEM 2100). UV-vis reflectance study of the cube was performed using Jasco V670 spectrophotometer. Photoluminescence spectra of the sample are recorded on a Horiba Jobin Yvon Fluorolog-3 spectrophotometer and Edinburgh F980 instrument.
RESULTS & DISCUSSIONS XRD pattern of the synthesized sample depicted in Figure 1a confirms that CsPbBr2Cl crystalizes in orthorhombic phase. The XRD profile H[KLELW%UDJJ¶VSHDNVDWș= 15.39°, 21.73°, 30.87°, 34.58° and 37.98° which corresponds to the diffractions from (100), (110), (200), (210) and (211) planes. Zoom in view of the peak at 30.87° related to 200 planes exhibits intense doublet feature which further authorizes that CsPbBr2Cl crystals are grown in orthorhombic phase [8]. FESEM images of all-inorganic perovskite CsPbBr2Cl samples are depicted in Fig. 1b. Large scale morphological uniformity of the sample is obvious from this
FIGURE 1. (a) XRD) pattern, (b) FESEM, (c) HRTEM images CsPbBr2Cl microcube, (d) EDX spectra and (e), (f) corresponding elemental mapping of a single cube. figure which shows large numbers of cube like structures over the entire region. High magnification view of in the inset (Fig. 1b) of a single CsPbBr2Cl micro-cube depicts size of ~ 1μm. Fig. 1c displays a typical high resolution transmission electron microscopy (HRTEM) image of the as-synthesized CsPbBr2Cl micro-cube. The graph demonstrate parallel lattice fringes with inter-planer spacing (d) ~ 0.28 nm corresponding to the (200) crystal plane of orthorhombic CsPbBr2Cl. Such well-defined lattice fringes further confirms the single crystal nature of the synthesized sample. EDX spectrum and corresponding elemental mapping of a single shown in Fig. 1(d-f) respectively reveal the only presence of Cs, Pb, Br and Cl in CsPbBr2Cl sample. Absence of any
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impurity element related peaks in the spectrum corroborate the XRD results of pure phase formation. It is observed that the atomic ratio of elements are in well accordance with their actual stoichiometry i.e. Cs:Pb:Br:Cl = 20:18:44:18. Homogenous distribution of the elements in mapping further confirms the successful preparation of the mixed perovskite.
Optical properties UV-Vis spectroscopic measurement of the as prepared perovskite sample is carried out to estimate the band-gap. Fig. 2a shows the diffuse reflectance spectra, i.e. 5 DV D IXQFWLRQ RI SKRWRQ ZDYHOHQJWK Ȝ QP 7KH VKDUS GLPLQXWLRQ LQ 5 at a particular wavelength indicates highly crystalline and direct band gap nature of the perovskite. Accessed value of the energy band-gap of the micro cube is found to be~ 2.57 eV. Fig. 2b shows the photoluminescence (PL) emission spectra of CsPbBr2Cl sample at room temperature. CsPbBr2Cl is found to exhibit a strong and narrow emission at 482 nm. Such positioning the emission peak is attributed to the near band edge emission of the CsPbBr2Cl and corroborates with the literature. Furthermore absence of any defect related emission in the emission spectra confirms the high optical quality of the sample. A CIE chromaticity diagram shown in Fig. 2c confirms that as-synthesized microcubes of CsPbBr2Cl sample is luminescent in blue region with luminescence co-ordinate x=0.25, y=0.22. Time-resolved PL decay curve of the micro-cube CsPbBr2Cl sample is shown in Fig. 2d. The time-resolved PL decay data of microcube CsPbBr2Cl sample is fitted to triexponential decay function given in equation (1) and PL decay lifetimes was calculated using equation (2) respectively.
FIGURE 2. (a) UV-vis reflectance (nm) (b) PL emission spectra (c) CIE 1931 chromaticity coordinates (d) PL decay and fitting curves of the light emission at 482 nm of the CsPbBr2Cl micro-cube
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ܣ+ ܤଵ ݁ ି௧/ఛభ + ܤଶ ݁ ି௧/ఛమ + ܤଷ ݁ ି௧/ఛయ
(1)
߬௩ = (ܤଵ ߬ଵଶ + ܤଶ ߬ଶଶ + ܤଷ ߬ଷଶ )/(ܤଵ ߬ଵ + ܤଶ ߬ଶ + ܤଷ ߬ଷ )
(2)
In the above equation, A depicts an instrumental constant, B1, B2 and B3 DUHGHFD\FRQVWDQWVUHODWHGWRWKHGHFD\WLPHVIJ1IJ2 and IJ3 respectively. From the graph, goodness of fitting (Ȥ2) is found to be ~1.094 which suggests excellent quality of fitting. The average life time (IJav) for NC CsPbBr2Cl is estimated to be 10.44 ns.
CONCLUSIONS In conclusion, all-inorganic cesium lead halide perovskite CsPbBr2Cl microcube were synthesized by a room temperature solution process. Zero thermal budget and large scale preparation are the highlights of the synthesis protocol. As synthesized CsPbBr2Cl micro-cubes are single crystalline structure and they exhibit intense photoluminescence at blue region (482 nm) and Pl decay time of 10.44 ns. Our work suggests that all-inorganic cesium lead halide perovskite CsPbBr2Cl microcube is a promising candidate for their usage in integrated photonic and optoelectronic devices.
ACKNOWLEDGEMENTS One of the authors TP would like to acknowledge the Department of Science Technology (DST), Govt. of India for INSPIRE fellowship (IF160045). The authors also wish to thank the UGC, Government of India, for the ‘University with potential for excellence’ scheme.
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