Synthesis and Optical Properties of Lead-Free Cesium Tin Halide

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Letter

Synthesis and Optical Properties of Lead-Free Cesium Tin Halide Perovskite Quantum Rods with High Performance Solar Cells Application Lin-Jer Chen, Chi-Ron Lee, Yu-Ju Chuang, Zhao-Han Wu, and Chienyi Chen J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.6b02344 • Publication Date (Web): 21 Nov 2016 Downloaded from http://pubs.acs.org on November 22, 2016

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The Journal of Physical Chemistry Letters

Synthesis and Optical Properties of Lead-Free Cesium Tin Halide Perovskite Quantum Rods with High Performance Solar Cells Application

Lin-Jer Chen, *,† Chi-Ron Lee, † Yu-Ju Chuang, † Zhao-Han Wu,‡ and Chienyi Chen§

†Prof. Dr. Lin-Jer Chen, Dr. Chi-Ron Lee,Yu-Ju Chuang Department of Photonics, National Cheng Kung University, Tainan 70101, Taiwan E-mail: [email protected] ‡

Dr. Zhao-Han Wu

Department of Materials Science and Engineering, National Cheng Kung University, Tainan 70101, Taiwan §

Dr. Chienyi Chen

Department of Chemistry, National Cheng Kung University, Tainan 70101, Taiwan.

Keywords: Perovskite; Quantum rods; Lead-Free; Solar cells

ACS Paragon Plus Environment


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Abstract Herein, the fabrication of a lead-free cesium tin halide perovskite produced via a simple process of solvothermal is reported for the first time. The resulting CsSnX3 (X=Cl, Br and I) quantum rods show composition-tunable photoluminescence (PL) emissions over the entire visible spectral window (from 625 to 709 nm), as well as significant tunability of the optical properties. In this study, we demonstrate that through the hybrid materials (CsSnX3) with different halide, the system can be tunable in terms of photoluminescence. By replacing the halide of the CsSnX3 quantum rods, a power conversion efficiency of 12.96 % under AM 1.5 G has been achieved. This lead-free quantum rods has demonstrated to be an effective method to create absorber layer that increase light harvesting and charge collection for photovoltaic applications in its perovskite phase.

The global need for renewable and green energy alternatives continues to raise research in low-cost and high-efficiency photovoltaic devices. As one kind of the perovskite materials, all-inorganic perovskites CsPbX3 (X = I, Br, Cl) were recognized as one probable substitute of organic–inorganic perovskites.1,2 The hybrid, all-inorganic lead halide perovskites have generated enormous attention in the


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photovoltaic community due to their surprisingly rapid improvements in power conversion efficiency.3,4 While recent researches have been mostly focused on hybrid organic− inorganic compounds, the study of their inorganic analogues, like ABX3 (A = Rb, Cs; B = Ge, Sn, Pb; X = Cl, Br, I), is limited.5 However, the lead component is highly human health concern, toxicity, and subject to environment damage, particularly chemical stability.6,7 By replacing the lead component with tin at the B-site, an lead-free perovskite can be formed, obviating the problems of polluting and environmentally friendly. Towards wider application of these perovskites replacement of unsafe lead is essential. As a result, there has been a great deal of interest in replacing lead with nontoxic metals such as tin, bismuth, and germanium.8-10 Over the past several years, considerable advances have been made toward the synthesis of colloidal semiconductor nanorods or nanofibers with diameters sufficiently small to produce a quantum confinement of charge carriers. Semiconductor quantum rods (QRs) visible the transition between zero-dimensional quantum dots (QDs) and one-dimensional quantum wires.11-13 QRs volumes are larger than QDs and therefore they have significantly larger per-particle absorbance cross sections.14 This is expected to increase the optical density of electrodes covered by up to a single layer of nanoparticles and therefore improve light harvesting. QRs are of great interest for fundamental research and are highly promising novel materials for



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new technology.15,16 However, QR properties will also depend on the quality of their internal crystal structure since and may also exhibit decreased Auger recombination rates compared to those of quantum dots,17 which makes them potentially useful for advanced optoelectronic devices. Many modern methods have been developed for the synthesis of one-dimensional QRs.18,19 However, these preparation processes often need a relative high temperature, vacuum, and complexity, etc., solvothermal offers great advantages as the low cost and maneuverability.20-22 In this research we demonstrate a simple, fast, and “green” lead free of high-quality perovskite-type CsSnX3 with a uniform quantum rod shaped structure for enhancing photovoltaic efficiency. To our knowledge, this is the first example of solvothermal synthesis of high-quality CsSnX3 QRs with finely tunable PL and uniform diameters, and high performance solar cells up to 13 %.

Fig. 1 (a) and (b) shows that the optical absorbance and photoluminescence of all the inorganic perovskite QRs are continuous red-shifted to longer wavelengths because of the confinement of the halide. 23 The quantum rods exhibit typically sharp absorption onsets, similar to the bulk dispersion. The slight shift of the first transition to longer wavelengths, when comparing CsSnCl3 to CsSnI3, might be caused by a slight change in the lattice constant of the surrounding atoms. Although a red shift in


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the absorption band was found for CsSnX3 (starting from Cl to Br to I), a 80 nm shift in the absorption onset (from 588 to 668 nm) was observed when halide (Chloride or bromide or Iodide) was used in the formation of CsSnX3 under similar conditions, which confirms the formation of mixed halide perovskite. Moreover, the overall intensity of the absorption band was altered. As such, the addition of different amounts of Br and I seems to affect the optical properties of the perovskite composites. With the increased ratios of Br and I, the light absorption of the perovskite QRs in the visible light range was gradually enhanced. This good agreement indicates that the halide improvement is primarily attributed to the enhanced absorption due to the lattice constant with larger atoms. The photoluminescence (excited by light with λ = 532 nm) emission wavelength to be tuned from 625 to 709 nm with a full width at half-maximum (FWHM) around 32 nm.

The purity and crystallinity of the CsSnX3 quantum rods with different weight addition ratios of Cl, Br and I were confirmed by XRD, as shown in Fig. 2. QRs of CsSnI3 were identified to be orthorhombic (JCPDS file no. 43-1162), CsSnBr3 cubic (JCPDS file no. 70-1645) and CsSnCl3 monoclinic (JCPDS file no. 71-2023) at room temperature.

24,25

This reversible anion exchange (CsSnCl3 to CsSnBr3 to CsSnI3)

experiment confirms that the size and size distribution of the QRs remained intact throughout all anion-exchange process. Therefore, the CsSnX3 QRs obtained after



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anion exchange, despite having a quantumscale distribution, did not exhibit any excitonic features. The atom ratio of Cs: Sn: X (X= Cl, Br, and I) is around 1:1:3, which further verifies that the resulting products are CsSnCl3, CsSnBr3, and CsSnI3. Accordingly, since larger I atoms replace Br and Cl, the size of CsSnX3 QRs slightly increases. Similar to other semiconductors, the PL peak shifts toward longer wavelengths as the CsSnX3 QRs size increases.

26

Both the absorption and PL

emission peak of the CsSnX3 QRs continuously red-shift along with the increase of Br or I content, reflecting the concomitant change of the band gap. These results are in good agreement with recent investigations on perovskite hybrids, where the single crystalline structures possess a narrower band gap and a subsequent red-shifted PL emission, suggesting lower trap densities due to coherent structural units that are tighter in the single crystal. 27 As shown in Fig. 3 a-c, the typical XPS survey spectra for both sets in the entire binding energy region indicate that Cs, Sn, and I exist, which demonstrates the high purity of the as-synthesized CsSnI3 QRs. Two distinct Cs 3d peaks appear at 726.6 (2p3/2) and 740.4 eV (2p1/2) with a binding energy splitting of 13.8 eV, thereby verifying the presence of Cs. 28 The peaks of Sn 3d located at 485.3 (3d5/2) and 493.7 (3d3/2) eV confirm the Sn state. 29 The peaks of I 3d5/2 located at 619.9 and 630.9 eV, 30

are in good agreement with values reported for the oxidation state of halides. As


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such, these results demonstrate that CsSnI3 QRs have been successfully synthesized. Fig. 3d shows the time-resolved PL decay curve of the CsSnX3 QRs. PL decay dynamics were recorded with 50 µW of 3.0 eV photons produced by a 35 fs, 2 kHz Ti: sapphire laser. The mean maximum-intensity lifetimes for samples CsSnCl3, CsSnBr3, and CsSnI3 were 16.3, 21.4, and 25.8 ns respectively, and corresponds to the previously reported radiative relaxation time of the exciton associated with the hybrid perovskite nanocrystals.31 For QRs with CsSnI3, the longest components are over 25.8 ns, which are significantly longer than the lifetimes typically observed for the other perovskite hybrid QRs. We suggest that this results from halide atom inhomogeneity (i.e., atomic weight.) and exciton radiative recombination in the small nanocrystals.32 Fig. 4a and Fig. S1 display the transmission electron microscopy (TEM) images of the perovskite CsSnX3 QRs, and show the microscopic morphology and structural information of the composite. It can be seen form Fig. 4a that the perovskite sample has the rod-like structure of CsSnI3. As seen in Fig. 4a inset, the HRTEM image of an individual CsSnI3 QRs confirms the crystalline structure with an observed lattice spacing of 0.62 and 0.64 nm, corresponding to the (220) and (202) planes of perovskite CsSnI3, respectively. In the PL spectra of all perovskite QRs, the PL emission bands are significantly enhanced compared to that of the CsSnX3 QRs, which demonstrates that increasing the atomic weight has effectively passivated the



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defects on the surface of the CsSnX3. 33 Moreover, the PL intensity increases and red shifts with increasing atomic weight. As atomic weight increases from Cl to I, the intensity of the PL emission enhancement with the various halide ratio QRs. Further, the position of the PL emission band was slightly red shift, indicating that the size distribution of the CsSnX3 QRs increased during the solvothermal process. On the other hand, the CsSnI3 QRs have very good crystallinity, which is preferred for improving the PL performance. However, compositional analysis by XPS showed that the average composition of the QRs in the sample had a molar Cs/Sn/X (X=Cl, Br, and I) ratio of 1:1:3 and the composition of individual particles measured by EDS were 1:1:3, with a variation from particle to particle of less than the experimental error of approximately ±2 atom % (see Table 1). Accordingly, the continuity of the fiber suggests that our CsSnX3 QRs are of high quality. The samples have diameters of about 5 nm ( 150 quantum rods ), with a diameter deviation of about 15−18%, which indicates the high quality of our samples. Additionally, the typical samples had lengths of several tens of nanometers. Fig. 4b-e shows elemental mapping of Cs, Sn, and I in CsSnI3 QRs obtained via TEM energy-dispersive X-ray spectroscopy (EDS). These images suggest the formation of ternary perovskite CsSnI3 QRs consisting of a Cs (blue), Sn (green), and I (red) distributed throughout the QR. The quantitative EDS analysis shows a Cs: Sn: I atomic ratio around 1: 1.1: 3.2 in the CsSnI3 QR, which is


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quite close to the nominal 1:1:3 ratios given by stoichiometry of the precursor solutions. This result makes it clear that the QR is mainly composed of CsSnI3. Similar quantitative results were also obtained from the EDS measurements (SEM) and X-ray photoelectron spectroscopy (XPS) analysis (Table 1). The exemplary morphological and cross sectional images of the after the spin-coating and annealing samples are shown in Fig. S2. According to these SEM images, it should be noted that the grain size increased with annealing process. Fig. 5 a shows typical current density–voltage ( J–V ) curves for lead-free all-inorganic perovskite solar cells with these different halides, which was obtained in the presence of different concentrations of halide under Air mass (AM) 1.5G solar irradiation and the photovoltaic parameters were summarized in Table 2. The best solar cell performance was measured when using the CsSnI3 QRs perovskite and the photovoltaic parameters are determined as short-circuit current density (Jsc) = 23.21 mA cm−2, open-circuit voltage (Voc) = 0.86 V, fill factor (FF) = 0.65, and the power conversion efficiency (PCE) of 12.96 %, respectively. The best solar cell using CsSnBr3 QRs perovskite shows Jsc = 21.12 mA cm−2, Voc = 0.85 V, FF = 0.58, and PCE = 10.46 %. The best solar cell using CsSnCl3 QRs shows Jsc = 19.82 mA cm−2, Voc = 0.87 V, FF = 0.52, and PCE= 9.66 %. The PCE decreases to 9.66 % for the perovskite solar cells with a decrease in the atomic volume by Cl. This decrease is



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primarily the result of reduced Jsc, Voc, and FF. The IV and PCE values of the CsSnI3 are better than the values measured for the CsSnBr3 and CsSnCl3 demonstrating the benefits of CsSnI3 as absorber materials. Note that the Cs: Sn: I = 1:1.1:3.2 molar ratio in the device was found to be optimum for device performance (see Table 2). A group of devices, with 10–15 devices for each composition cases, were fabricated in order to further explain the relationship between device performance and halide ratio. From these studies, we conclude that a definite amount of I precursor enhances all the photovoltaic parameters. In addition, it is well known that the crystalline of perovskite decide ultimate performance of the constructed devices since defects in the crystals will form shorting and trapping sites for charge recombination. Crystalline will also very influence the ability of transport, charge separation, and diffusion length.34 The high FF further demonstrates the active charge transfer and extraction of such a planar p-i-n heterojunction.35 This resulted in the greater efficiency of the device formed on quantum rods which motivated us to explore our solvothermal influence on this facile system. The external quantum efficiency (EQE) plotted in Fig. 5b confirms the increased Jsc of these devices, in which the merged Jsc for the devices derived from lead-free perovskite CsSnI3, CsSnBr3 and CsSnCl3 is 12.96, 10.46, and 9.66 %, respectively. As can be seen, the maximum EQE peaks of the top-performing devices can reach over 63 % (CsSnCl3), 65 % (CsSnBr3) and 70 % (CsSnI3) EQE. We study


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the use of the lead-free all inorganic QRs as absorber materials in the perovskite solar cells considering that they may improve the cell characteristics due to several reasons: low cost, nontoxic compounds, inorganic hybrid possess better chemical, photo-stabilities and thermal effect than organic composites.36 This is expected to increase the optical density of active layer and therefore improve light harvesting. Furthermore, the surface area of QRs are larger compared to bulk, which may allow larger contact area and hence improve the conversion efficiency. This can further improve charge separation efficiency leading to higher performance of the perovskite solar cells. To further investigate charge transport and recombination in perovskite solar cells, impedance spectroscopy and transient photocurrent decay were undertaken. The devices were measured at forward bias between 0.5 and 1.0 V in the dark, and Fig. S3 gives the Nyquist curves at 1.0 V bias as an example and the recombination resistance results fitted with equivalent circuit model. The recombination between electrons in perovskite layer and hole-transporting material (HTM) has been suggested to play a key role in determining the open-circuit voltage. Transient photocurrent decay is another powerful tool and has also been used to investigate the electron-transport process. The fitted processes are provided in the Supporting Information and the fitted results are shown in Fig. S4. The pore character and the large specific surface area are believed to benefit the deposition of perovskite QRs



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and therefore highly efficient perovskite solar cells. In order to rule out performance decay process, we have studied the PL intensity, thermal stability and photovoltaic parameters of the perovskite CsSnI3 as a function of the hybrid composition. MAPbI3 (for details see the Supporting Information) and CsSnI3 QR devices were submitted to a long term degradation process in air, and the decay of their fluorescence signal was recorded both under dark storage and during illumination (three pairs of samples for each case). The collected fluorescence spectra are presented in Fig. 6a and b compares the normalized fluorescence intensity calculated using the peak values of such spectra at 709 nm, following laser excitation at 532 nm, as a function of the dark storage and illumination times. As a result, the fluorescence signal of the MAPbI3 device degrades rapidly upon illumination following a first order exponential decay. Upon 30 mins of illumination, MAPbI3 based only emitted very weakly, and the photoluminescence almost disappeared upon 120 mins of exposure in air. After 2 month storage in the dark in air, no shift in photoluminescence position was observed for the CsSnI3 quantum rods, as shown in Fig. 6c. This approach led to a colloidal stability of the quantum rods in air for more than 2 months. To compare the thermal stability of CsSnI3 and MAPbI3 quantitatively, we carried out thermogra-vimetric analysis (TGA) under a nitrogen and oxygen atmosphere (Fig. 6d), which shows the onset of decomposition temperature of CsSnI3


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is significantly higher than that of MAPbI3. In the case of CsSnI3 (onset ~450 °C), CsSnI3 is more stable (with respect to evaporation or decomposition) than MAPbI3, and in this case, the latter is lost first. In fact, CsSnI3 is somewhat more thermally stable than MAPbI3. The stability of the sealed cells is remarkably improved, as can be seen in Fig. 6e-h, which shows temporal evolution of J-V curves and the extracted photovoltaic parameters (Voc, Jsc, FF, and PCEs included) values from long-term stability tests for more than 240 h. It may also be that the polar organic MA cation makes MAPbI3 more hydrophilic in character than CsSnI3, and thus allows water molecules to permeate faster through the edges of the devices, increasing the decomposition rate. Here we report such comparison between the Cs based and MA based lead halide perovskites in terms of thermal and optical properties, and the corresponding photovoltaic device performance and stability. CsSnX3 (X=Cl, Br, and I) with tunable emission wavelength ranging from 625 to 709 nm have been prepared through a versatile and relatively inexpensive technique of the composite quantum rods under different halide salt conditions. This work finds that the characteristic of the optical properties in lead-free all inorganic perovskites can be altered through solvothermal without annealing process, which grants them attractive for novel optoelectronic devices. High quality lead-free perovskite QRs with composition- tunable emission have been synthesized using a simple



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solvothermal synthetic approach. Emission wavelengths covering the visible spectrum window can be facilely tuned by the variation of the composition of halide salts. Finally, a remarkable enhancement in the photovoltaic performance of the CsSnX3 devices to power conversion efficiency close to 13 % was realized. We strongly believe that this work would contribute toward the fundamental understanding of structural, morphological and optical properties of the lead-free halide perovskite quantum rods and would be useful for inexpensive nontoxic optical materials, light absorbers for solar cells, or other electric devices, LED, and biosensor materials.

Experimental

Tin (II) chloride (SnCl2, 99.999%), Tin (II) bromide (SnBr2, 99.999%), Tin (II) iodide (SnI2, 99.999%), cesium carbonate (Cs2CO3, reagent Plus, 99%). Octadecylamine (ODA, 97%), octadecene (ODE, technical grade, 90%), oleylamine (OLAM, 90%), oleic acid (OA, 90%), diethylenetriamine (DETA, 99%), trioctylphosphine oxide (TOPO, 99%) and the spiro-OMeTAD were purchased from Sigma-Aldrich. Absolute ethanol (Alfa Aesar, 99.8%), toluene (Sigma-Aldrich, 99.8%), and hydrochloric acid (Alfa Aesar, 36.5%). Titanium diisopropoxide bis (acetylacetonate) were purchased from Alfa Aesar.


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In a typical synthesis, 0.7 g of SnBr2 (2.3 mmol) (or 0.45/0.86 g of SnCl2/SnI2, respectively), 60 mL of ODE, 6 mL of OA and 6 mL of OLAM were loaded in a 100 mL four-neck flask and dried under a vacuum for 1 h at 120 °C. Then, a mixture of 10 mL of ODE with 5 mL of previously synthesized Csoleate (2 g of Cs2CO3 degassed in 60 mL of ODE and 5 mL of OA at 120 °C for 1 h), hydrochloric acid (1 mg), TOPO and DETA were heated with stirring at 80 °C, while purging continuously with nitrogen for 1 h. The reagents were loaded into a 50 mL Teflon lined autoclave, which was then filled with anhydrous DETA up to 80% of the total volume. The autoclave was sealed and was maintained at 180 0C for 6 h, and then quantum rods solution was quickly cooled down to room temperature with an ice bath, and the products were transferred to a glovebox. After this step, the solution was filtrated, washed by excess acetone, distilled water, and toluene by centrifugation, respectively. Finally, dried in a vacuum at 80 °C for 3 h and prepared products were redispersed in toluene for further use.

To fabricate the all-inorganic CsSnX3 (X=Cl, Br and I) perovskite hybrid solar cell (indium tin oxide (ITO) /TiO2/ CsSnX3 / HTM /Au). ITO glass (15 Ω sq-1) was cleaned using a three step ultrasonic process of ethanol, distilled water and acetone for 10 min, respectively. After drying under a nitrogen stream, substrates were further cleaned by UV ozone for 6 min. Subsequently, TiO2 precursor (titanium



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diisopropoxide bis(acetylacetonate)) was spin coated onto the ITO substrate at 3500 rpm for 70s to produce as thickness between 250–300 nm and annealed at 350 oC for 1h in air. To avoid oxygen and moisture, the substrates were transferred into a nitrogen filled glove box. Sequentially, precursor solutions of CsSnX3 perovskites (160mg/ml) in toluene were spin coated at 6000 rpm for 80s and dried on hot-plate at 110 oC for 10 min. The spiro-OMeTAD hole transporting materials (HTM) solution (10 mg/ml) in toluene was spin-coated at 2500 rpm for 40s on top of perovskite layer. Finally, gold electrodes were deposited under vacuum (＜10-6 Torr) on top of the HTM by thermal evaporation. The device area was fixed to 1 cm2. All device fabrications were conducted below 50% of relative humidity. The as-prepared samples were characterized by X-ray powder diffraction (XRD), and transmission electron microscopy (TEM). XRD was carried out on a D/MAX-500 X-ray powder diffraction system with Cu Ka radiation ( ë= 1.5418 Å). A scanning rate of 0.02o was applied to record the patterns in the 2 Theta range of 10-80o. TEM characterization was conducted on a JEM-2000EX system using an acceleration voltage of 160 kV. The average rod diameter and the aspect ratio of the beads were calculated from the TEM images. PL was performed on PerkinElmer LS55 luminescence spectrometer made by PerkinElmer Company in United States, excited by a wavelength of 532 nm line of a pulse xenon lamp at room temperature. XPS


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measurements were carried out using PHI 5000 VersaProbe X-ray Photoelectron Spectroscopy (ULVAC-PHI, Inc., Japan). Current–voltage measurements were performed using a Keithley 2400 source meter. Solar cells were masked using a nonreflective metal aperture of 1 cm2 which defined the active area. The EQE spectra were measured by combining a monochromated 450 W xenon lamp (Oriel) with a sourcemeter (Keithley 2400) and calculated using a calibrated Si photodiode (OSI-Optoelectronics).

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS The authors would like to thank the Ministry of Science and Technology, Taiwan (MOST) (contract 103-2112-M-006-016-MY3) and Department of Photonics, National Cheng Kung University for supporting this research.

REFERENCES (1) Hossain, M. I.; Alharbi, F. H.; Tabet, N. Copper oxide as inorganic hole transport material for lead halide perovskite based solar cells. Solar Energy 2015, 120, 370.



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(2) Seth, S.; Mondal, N.; Patra, S.; Samanta, A. Fluorescence Blinking and Photoactivation of All-Inorganic Perovskite Nanocrystals CsPbBr3 and CsPbBr2I. J. Phys. Chem. Lett. 2016, 7, 266−271. (3) Green, M. A.; Ho-Baillie, A.; Snaith, H. J. The emergence of perovskite solar cells. Nat. Photonics 2014, 8, 506. (4) Yang, W. S.; Noh, J. H.; Jeon, N. J.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I. High-performance photovoltaic perovskite layers fabricated through intramolecular exchange. Science 2015, 348, 1234. (5) Huang, C.; Fu, N.; Liu, F.; Jiang, L.; Hao X.; Huang, H. Highly efficient perovskite solar cells with precursor composition-dependent morphology. Sol. Energy Mater. Sol. Cells 2016, 145, 231. (6) Senthilarasu, S.; Fernández, E. F.; Almonacid, F.; Mallick, T. K. Effects of spectral coupling on perovskite solar cells under diverse climatic conditions. Sol. Energy Mater. Sol. Cells 2015, 133, 92. (7) 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. (8) Akkerman, Q. A.; D’Innocenzo, V.; Accornero, S.; Scarpellini, A.; Petrozza, A.;


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Prato, M.; Manna, L. Tuning the Optical Properties of Cesium Lead Halide Perovskite Nanocrystals by Anion Exchange Reactions. J. Am. Chem. Soc. 2015, 137, 10276. (9) Nolas, G. S.; Weakley, T. J. R.; Cohn, J. L. Structural, Chemical, and Transport Properties of a New Clathrate Compound: Cs8Zn4Sn42. Chem. Mater. 1999, 11, 2470-2473. (10) Betancur, R.; Ramirez, D.; Montoya, J. F.; Jaramillo, F. A calorimetric approach to reach high performance perovskite solar cells. Sol. Energy Mater. Sol. Cells 2016, 146, 44. (11) Chen, X.; Nazzal, A. Y.; Xiao, M.; Peng, Z. A.; Peng, X. Photoluminescence from single CdSe quantum rods. J. Lumin. 2002, 97, 205-11. (12) Jia, G.; Xu, S.; Wang, A. Emerging strategies for the synthesis of monodisperse colloidal semiconductor quantum rods. J. Mater. Chem. C 2015, 3, 8284-93. (13) Mukhina, M. V.; Maslov, V. G.; Baranov, A. V.; Fedorov, A. V.; Berwick, K. Photoinduced anisotropy in an ensemble of CdSe/ZnS quantum rods. RSC Adv. 2013, 3, 20746-9. (14) Shaviv, E.; Salant, A.; Banin, U. Size Dependence of Molar Absorption Coefficients of CdSe Semiconductor Quantum Rods. ChemPhysChem 2009, 10, 1028-31.



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(15) Golobostanfard, M. R.; Abdizadeh, H. Tandem structured quantum dot/rod sensitized solar cell based on solvothermal synthesized CdSe quantum dots and rods. J. Power Sources 2014, 256, 102-10. (16) Comas, F.; Studart, N.; Marques, G. E. Optical phonons in semiconductor quantum rods. Solid State Commun. 2004, 130, 477-80. (17) Kazes, M.; Lewis, D. Y.; Ebenstein, Y.; Mokari, T.; Banin, U. Lasing from Semiconductor Quantum Rods in a Cylindrical Microcavity. Adv. Mater. 2002, 14, 317-21. (18) Jia, G.; Banin, U. A General Strategy for Synthesizing Colloidal Semiconductor Zinc Chalcogenide Quantum Rods. J. Am. Chem. Soc. 2014, 136, 11121-7. (19) Kazes, M.; Oron, D.; Shweky, I.; Banin, U. Temperature Dependence of Optical Gain in CdSe/ZnS Quantum Rods. J. Phys. Chem. C 2007, 111, 7898-905. (20) Lu, C. H.; Lee, C. H.; Wu, C. H. Microemulsion-mediated solvothermal synthesis of copper indium diselenide powders. Sol. Energy Mater. Sol. Cells 2010, 94, 1622-6. (21) Oki, A.; Adams, L.; Luo, Z. Solvothermal synthesis of carbon nanotube-B2O3 nanocomposite using tributyl borate as boron oxide source. Inorg. Chem. Commun. 2008, 11, 275-8. (22) Kageyama, H.; Oaki, Y.; Imai, H. Basicity-controlled synthesis of Li4Ti5O12


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CsSnCl3

450

CsSnCl3 CsSnBr3

Intensity (a.u.)

CsSnBr3

Absorbance (a.u.)

CsSnI3

500

550

600

650

700

CsSnI3

550

750

600

650

700

750

800

Wavelength (nm)

Wavelength (nm)

Figure 1. (a) Optical absorption and (b) photoluminescence spectra for different compositions of CsSnX3 (X= Cl, Br and I).

20

30

(220)

40

50

(202)

60

CsSnI3 (242)

(101)

Relative Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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(121)

CsSnBr3

(202)

(242)

(101)

CsSnCl3

(110)

(220) (200)

20

30

40

50

60

2 theta (degree)

Figure 2. XRD patterns for varying halide composition of perovskites (CsSnI3 , CsSnBr3, and CsSnCl3).


Sn 3d at 485.3 eV

Intensity (arb. units)

Cs 3d at 726.6 eV

Cs 3d at 740.4 eV

745

740

735

730

725

Sn 3d at 493.7 eV

484

720

486

488

Binding energy (eV)

Binding energy (eV)

I 3d at 619.9 eV

635

630

625

620

615

Normalized PL intensity (a.u.)

100 I 3d at 630.9 eV


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



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CsSnCl3 CsSnBr3

80

CsSnI3

60 40 20 0 0

20

Binding energy (eV)

40

60

80

100

Delay time (ns)

Figure 3. (a) XPS Cs 3d spectra for CsSnI3; (b) XPS Sn 3d spectra for CsSnI3; (c) XPS I 3d spectra for CsSnI3 and, (d) Time-dependent PL decays of various CsSnX3 quantum rods prepared with different halide (CsSnCl3, CsSnBr3, and CsSnI3 ) in toluene, averaged across measurements from 5 samples.



Figure 4. (a) Typical High-resolution TEM image of the perovskite CsSnI3 quantum rods. Inset is selected zoom-in TEM images of the several QRs (b) TEM image of the obtained perovskite quantum rods and corresponding energy dispersive spectroscopy (EDS) elemental mapping images, which confirms that the (c) Cs, (d) Sn, and (e) I are sequentially and uniformly deposited onto the entire surface of the CsSnI3 quantum rods on a copper grid. The scale bar is 5 nm.

80

CsSnI3

80

CsSnCl3 CsSnBr3

CsSnBr3 60

CsSnI3

60

CsSnCl3

IPCE (%)

Current Density (mA cm 2 )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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40 20

40

20

0 -20

0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Voltage (V)

500

600

700

800

Wavelength (nm)

Figure 5. (a) J–V characteristics of CsSnI3 (blue), CsSnBr3 and CsSnCl3 ( red, and black) solar cells. (b) EQE of CsSnX3 perovskite devices with different halide ratio. The photovoltaic results are summarized in Table 2.



1.05 1.00 0.95 0.90 0.85 0.80 0.75

MAPbI3 CsSnI3

0.70 0.65 0

5

10

15

20

25

0.9 0.8 0.7 0.6 0.5

MAPbI3 CsSnI3

0.4 0

30

5

Cs SnI Cs SnI

3 3

15

20

25

100

1d ay

80

60 da ys 1 d ay

TG %

40000

3

10

Illumination time (min)

MAPb I 3 60 da ys MAP bI

50000

Intensity (a.u.)

1.0

Time in dark (hrs)

60000

30000

60

20000

40

10000

20

MAPbI3 in O2 MAPbI3 in N2 CsSnI3 in O2 CsSnI3 in N2

0

0

550

600

650

700

750

800

100

850

200

300

24

0.9

22

Jsc(mA/cm 2 )

Vo c (V)

1.0

0.8 0.7 0.6

400

500

600

700

Temp Cel

Wavelength (nm)

MAPbI3 CsSnI3

20 18 16

MAPbI3

14

CsSnI3

0.5 0

2

4

6

8

10

12

14

16

0

18

2

4

6

8

10

12

14

16

14

16

18

Time (Days)

Time (Days) 16 0.65

14 12

0.60

PEC (%)

Fill Factor (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



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0.55

10 8 6

0.50 MAPbI3

MAPbI3 CsSnI3

4

CsSnI3

0.45

2 0

2

4

6

8

10

12

14

16

18

0

2

4

Time (Days)

6

8

10

12

18

Time (Days)

Figure 6. (a) Normalized fluorescence decay of reference (MAPbI3) and CsSnI3 quantum rod devices stored in the dark. (b) Normalized fluorescence decay of reference and CsSnI3 quantum rod devices illuminated at certain time intervals. Excitation wavelength at 532 nm using an Nd:YAG ns laser. (c) PL spectra of the CsSnI3 quantum rods and CH3NH3PbI3 with storage times (1 day and 60 days). (d) TGA curves of CsSnI3 and MAPbI3 under a nitrogen and oxygen atmosphere. Temporal evolution of photovoltaic parameter values, (e) VOC, (f) JSC, (g) fill factor (FF), and (h) efficiency, for the reference and CsSnI3 quantum rod-based devices.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 1 Measured CsSnX3 quantum rods Composition

Table 2 Summarized photovoltaic parameters derived from current– voltage curves recorded within 24 h (after device fabrication) for the different perovskite devices with different halide ratio.


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Synthesis and Optical Properties of Lead-Free Cesium Tin Halide

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