Article pubs.acs.org/cm
Template Synthesis of CuInS2 Nanocrystals from In2S3 Nanoplates and Their Application as Counter Electrodes in Dye-Sensitized Solar Cells Bingkun Chen,†,§ Shuai Chang,‡,# Deyao Li,‡ Liangliang Chen,‡ Yongtian Wang,† Tao Chen,# Bingsuo Zou,‡ Haizheng Zhong,*,‡ and Andrey L. Rogach§ †
Beijing Engineering Research Center of Mixed Reality and Advanced Display, School of Optoelectronics, Beijing Institute of Technology, Beijing 100081, China ‡ Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems, School of Materials Science & Engineering, Beijing Institute of Technology, Beijing 100081, China # Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong S. A. R. § Department of Physics and Materials Science & Center for Functional Photonics (CFP), City University of Hong Kong, Hong Kong S. A. R. S Supporting Information *
ABSTRACT: We report the room temperature template synthesis of CuInS2 nanocrystals through incorporation of Cu+ cations into In2S3 nanoplates whose chemical composition has been controlled by varying the amount of copper ions in the reaction mixture. As a result, bandgaps of the resultant CuInS2 nanoplates can be tuned from 1.45 to 1.19 eV with [Cu]/[In] molar ratios increasing from 0.7 to 2.9, which was demonstrated by the cyclic voltammetry. We explored the use of CuInS2 nanocrystals as potential counter electrodes in dye-sensitized solar cells, and a power conversion efficiency of 6.83% was achieved without selenization and ligand exchange. The value is comparable with the performance of a control device using Pt as a counter electrode (power conversion efficiency: 7.08%) under the same device architecture.
■
single precursors,26−30 a solvothermal synthesis approach,31−33 hot-injection,4,5,34−36 and noninjection methods,7,37−41 the different reactivity of metallic cation precursors often leads to poor stoichiometric control and the formation of intermediate products, such as biphasic nanomaterials and heterostructures.42−45 For the drawbacks of such composition control to be overcome, template synthesis through cation exchange46 has been gaining popularity and allows for fabrication of ternary and quaternary NCs (such as CuInS2, CuInSe2, AgInSe2, CuInxGa1−xS, and Cu2ZnSnS4) from respective binary NCs (such as Cu2−xS, Cu2−xSe, Ag2Se).47−53 Most of these methods
INTRODUCTION
Ternary and quaternary semiconductor nanocrystals (NCs) (e.g., CuInS2, CuInSe2, CuInGaS2, CuZnSnS4) with the advantages of tunable bandgaps and more environmentally friendly constituents have been receiving significant attention for solar-harvesting and light-emitting applications, and for solution-processed devices in particular.1−17 For example, CuInS2 NCs are regarded as promising candidates as a light absorber or counter electrode (CE) in dye-sensitized solar cells (DSSCs) due to the advantages of low cost and a simple fabrication process.18−23 Because the electronic structure of these materials strongly correlate with the [Cu]/[In] ratios, there is a great need to precisely control their size, shape, surface, and composition.3,19,24,25 Although great successes have been achieved in the synthesis of ternary and quaternary NCs, providing several routes, including thermal decomposition of © 2015 American Chemical Society
Received: May 25, 2015 Revised: August 19, 2015 Published: August 19, 2015 5949
DOI: 10.1021/acs.chemmater.5b01971 Chem. Mater. 2015, 27, 5949−5956
Article
Chemistry of Materials
in a sandwiched structure. Liquid electrolyte consisting of 0.6 M 1,2dimethyl-3-propylimidazolium iodide, 0.1 M LiI, and 0.05 M I2 in a mixture of acetonitrile and 4-tert-butylpyridine (volume ratio, 1:1) was introduced into the cell through drilled holes at the back of the CE. Control devices were fabricated using Pt CE by sputtering Pt on FTO glass at 15 mA for 90 s at a power of 150 W. Characterization. The crystal structures of the samples were investigated on a Bruker/D8 FOCUS X-ray diffractometer using a Cu Kα radiation source. The samples were scanned from 20° < 2θ < 80° at an increment of 1°/min. Transmission electron microscopy (TEM) was performed on a JEM-2100F instrument operated at an acceleration voltage of 200 kV. The samples were prepared by dropping the NC dispersion into toluene on amorphous carboncoated copper grids, which were allowed to dry overnight. Energy dispersive spectroscopy (EDS) was performed on an S-4800 scanning electron microscope operating at 200 kV. X-ray photoelectron spectroscopy (XPS) was performed on a ULVAC-PHI instrument (PHIQUANTERA-II SXM) with Al Kα as the X-ray source. The sample spectra were referenced to the C 1s peak at 284.8 eV. Absorbance spectra of samples were measured on a UV-6100 UV−vis spectrophotometer and photoluminescence (PL) spectra on a F-380 luminescence spectrometer. UV−vis diffuse reflection spectra of powder samples were detected by applying a Tu-1901 UV−Vis spectrophotometer mounted with an integrating sphere accessory (IS19-1, Beijing Purkinie General Instument Co., Ltd) using BaSO4 as reference standard. Cyclic voltammetry (CV) measurements were performed on a CHI660D electrochemical workstation using glassy carbon discs (∼0.25 cm2), a Pt wire, Ag/Ag+ (Ag wires with 0.01 M AgNO3 in acetonitrile) as the working electrode, the counter electrode, and the reference electrode. A 0.1 M solution of tetrabutylammonium hexafluorophosphate in acetonitrile was used as the supporting electrolyte. All samples were purified and redissolved in toluene. The scan rate was set at 10 mV/s, and before every measurement, the electrolyte solutions were purified by purging with nitrogen to remove oxygen and water for more than 10 min. The current−voltage (J−V) characteristics of the assembled solar cells were measured on a workstation system (Keithley 236) at room temperature in air under the spectral output from a solar simulator (Newport) using an AM 1.5G filter with a light power of 100 mW/ cm2. Electrochemical impedance spectroscopy (EIS) measurements were carried out on a CHI 660D electrochemical workstation by applying a bias of 750 mV under dark conditions over a frequency range of 0.1−105 Hz and AC amplitude of 10 mV. The parameters were calculated using Z-View software (v2.1b, Scribner Associate, Incorporated).
start from binary copper(I) sulfide/selenide, and the cation exchange takes place at high temperatures. In2S3 is a III−VI group semiconductor with a bandgap of 2.0−2.3 eV, which may exist in three different crystal phases: αIn2S3 (defective cubic structure), β-In2S3 (defective spinel structure), and γ-In2S3 (layered hexagonal structure).54 As compared to the use of the Cu2−xS precursor template, the formation of CuInS2 from In2S3 is energetically favorable.55 For example, Lei and co-workers56 fabricated CuInS2 NCs using a solvothermal method on the basis of micrometer-sized spinel In3−xS4 templates. Recent advances in colloidal synthesis has provided layered In2S3 NCs, including nanoplates, nanosheets, and nanobelts.57−60 The large surface to volume ratio as well as the abundant vacancies present in In2S3 nanoplates make them ideal templates to accommodate substituting ions. This motivated us to explore the template synthesis of CuInS2based NCs from In2S3 nanoplates at room temperature. In2S3 nanoplates were first synthesized by a heating method from InCl3, S powder, and oleylamine.59,60 Then, CuInS2 NCs were obtained by adding copper precursor (CuI dissolved in 1dodecanethiol = CuI/DDT) into the solution of as-synthesized In2S3 nanoplates at room temperature. We demonstrate how the composition of the resulting CuInS2 nanoplates can be controlled by adjusting the molar ratios of the precursors, which results in the composition-tunable bandgaps. Subsequently, we explored the use of these CuInS2 NCs as counter electrodes in DSSCs. A power conversion efficiency (PCE) of 6.83%, which compares favorably to conventional Pt (PCE = 7.08%) counter electrodes under the same device architecture, is achieved with thermal annealed CuInS2 NCs films on fluorine-doped tin oxide-coated (FTO) glass. To the best of our knowledge, this is the highest efficiency seen for DSSCs with CuInS2 as the counter electrode without selenization and ligand exchange.
■
EXPERIMENTAL SECTION
Materials. Copper(I) iodide (CuI, Alfa Aesar, 98%), indium(III) chloride (InCl3, Alfa Aesar, ⩾ 99.8%), sulfur (S, Alfa Aesar, 99%), oleylamine (OLA, Acros Organics, 80%−90%), zinc acetate dihydrate (Zn(OAc)2, Alfa Aesar, ⩾ 97%), 1-dodecanethiol (DDT, Alfa Aesar, 98%), and 1-octadecene (ODE, Alfa Aesar, 90%) were used as received without further purification. Synthesis of In2S3 Nanoplates. The synthesis of indium sulfide nanoplates was performed according to a previously reported method.59,60 Briefly, 1 mmol anhydrous InCl3 and 1.5 mmol sulfur powder were added to 20 mL of OLA; the mixture was stirred under vacuum for 30 min and heated at 110 °C for 1 h and at 215 °C for 1 h. After cooling to room temperature, methanol was added to precipitate the products. The precipitate was washed with methanol and toluene twice, dried under vacuum at 60 °C, and used for the preparation of CuInS2 nanoplates. Synthesis of CuInS2 Nanoplates. 0.326 g In2S3 nanoplates was dissolved into 30 mL toluene under vigorous stirring for 12 h. Different volumes of clear 0.05 M solution of CuI in DDT have been injected into the solution of In2S3 nanoplates (0.5 mL per minute), leading to an immediate color change from yellow to brown. The resulting CuInS2 nanoplates were precipitated by acetone and redissolved in toluene. Preparation of CuInS 2 Counter Electrodes and the Fabrication of DSSC Devices. The as-prepared CuInS2 NCs were dispersed in toluene (100 mg/mL), and the resulting solution was spin-coated onto FTO substrates at 600 rpm for 40 s. The films were annealed under the protection of argon at 200 °C for 40 min or at 480 °C for 15 min, respectively, to finalize the crystallization. The CuInS2 CEs were assembled with anode electrodes composed of N719 sensitized mesoporous TiO2 (12 μm) with a device area of 0.126 cm2
■
RESULTS AND DISCUSSION The template synthesis of CuInS2 NCs was accomplished through two steps. In the first step, In2S3 nanoplates were synthesized by heating a mixture of InCl3, sulfur powder, and OLA at 215 °C. In the second step, incorporation of Cu+ into the In2S3 nanoplates was accomplished through injection of Cu precursor (CuI/DDT) at room temperature. It can be seen from Figure 1a and b that the color of powdered samples changed from yellow to black, corresponding to the red shift of the absorption band edge as the transformation proceeded from binary In2S3 to ternary CuInS2. As illustrated in Figure 1c, this is accompanied by an absorption edge shift from 610 nm (Eg = 2.03 eV) to 910 nm (Eg = 1.36 eV). The CuInS2 nanoplates synthesized by this method did not exhibit any PL in contrast to red-emitting quaternary CuInZnS 2 NCs that were synthesized using In2S3 nanoplates as templates at higher temperature (220 °C). As shown in Figure S1 in the Supporting Information, CuInZnS2 NCs with PL emission at 654 nm show an average size of 5 nm. Figure 2a shows a TEM image of indium sulfide nanoplates with their corresponding side view presented in Figure 2b. The 5950
DOI: 10.1021/acs.chemmater.5b01971 Chem. Mater. 2015, 27, 5949−5956
Article
Chemistry of Materials
Powder X-ray diffraction (XRD) measurements (Figure 3a) reveal different degrees of the lattice evolution upon trans-
Figure 1. Photographs of (a) In2S3 and (b) CuInS2 powdered samples. (c) UV−vis diffuse reflection spectra of In2S3 and CuInS2 nanoplates with a [Cu]/[In] molar ratio of 1.1.
Figure 3. (a) XRD patterns of the In2S3 NC template and CuInS2 nanoplates with different [Cu]/[In] molar ratios. Bulk reflexes for In2S3 (JCPDS #25−0390) and CuInS2 (JCPDS #65−2732) are presented by line spectra. (b) EDS spectrum of CuInS2 nanoplates with a [Cu]/[In] molar ratio equal to 2.7. Crystal structures of In2S3 (c) and CuInS2 nanoplates (d) with tetragonal phase and CuInS2 nanoplates with chalcopyrite phase (e) are represented by schemes. (c−e) Copper atoms in green, indium atoms in gray, and sulfur atoms in yellow and larger size. Blue circles represent In atom vacancy of In2S3.
formation from In2S3 NC templates to CuInS2 nanoplates with gradually increasing [Cu]/[In] molar ratios in the reaction mixture. For the CuInS2 sample with [Cu]/[In] equal to 1.0, both peak positions (2θ of 27.1°, 30.4°, 47.8°) and the relative peak intensities matched well with the bulk tetragonal β-In2S3 (defective spinel structure) (JCPDS #25-0390). EDS spectra were collected to quantitatively analyze the composition and to estimate the [Cu]/[In] molar ratios of the samples. A typical EDS spectrum is shown in Figure 3b and indicates the existence of three elements, Cu, In, and S, in CuInS2 nanoplates. Schematic diagrams of the possible structure transformation from In2S3 to CuInS2 with the [Cu]/[In] ratio equal to 1.0 are shown in Figure 3c and d, respectively, and indicate that the Cu+ ions are only incorporated into the host In2S3 lattice in this case. For the other three CuInS2 samples with [Cu]/[In] ratios equal to 1.1, 2.7, and 2.9, the three main peaks locate at 2θ of 27.9°, 46.3°, and 54.9°, and their relative intensities match well with the bulk chalcopyrite CuInS2 (JCPDS #65-2732), indicating that phase transformation occurred, as shown in Figure 3e. XPS (Figure 4a) demonstrates the presence of only two elements (In and S) in In2S3 nanoplates and three elements, Cu, In, and S, in the resulting CuInS2 nanoplates. Their copper high-resolution XPS spectra (Figure 4b) show two symmetric peaks at 932.6 and 952.2 eV. The peak splitting of 19.6 eV is consistent with the literature reported values for Cu(I).61−63 The indium high-resolution-XPS spectra shown in Figure 4c are
Figure 2. TEM images of (a,b) In2S3 and corresponding (c,d) CuInS2 nanoplates with a [Cu]/[In] ratio equal to 1.1.
crystalline plates have a lateral dimension of 35 ± 5 nm and a thickness of 0.6 ± 0.1 nm. Panels c and d in Figure 2 show TEM images of CuInS2 NCs, which maintained their platelike 2D shape, which was very similar to that of the In2S3 nanoplates. Their lateral dimension was 29 ± 6 nm, and the thickness was 1.5 ± 0.5 nm, representing a 2-fold increase as compared to In2S3 nanoplates, which can be related to incorporation of Cu+ ions into the host structure. Cu+ ions have a larger radius (96 pm) in comparison to In3+ ions (81 pm); hence, the incorporation of Cu+ cations into the crystal lattice of the pristine In2S3 nanoplates led to a thickness increase due to the enlarged volume with the change from In2S3 to CuInS2 nanoplates. We further studied the shape evolution of CuInS2 NCs with the increasing [Cu]/[In] molar ratios. As illustrated in Figure S2, the platelike shape changed to a foamlike layered structure for the sample with a [Cu]/[In] molar ratio of 2.9. 5951
DOI: 10.1021/acs.chemmater.5b01971 Chem. Mater. 2015, 27, 5949−5956
Article
Chemistry of Materials
Figure 4. XPS survey spectrum (a), high-resolution Cu 2p doublet (b), In 3d doublet (c), and S 2P doublet (d) for In2S3 nanoplates and CuInS2 NCs with varying [Cu]/[In] ratios.
indicative of In(III) in both the In2S3 and CuInS2 samples due to the presence of In 3d peaks located at 444.7 and 452.2 eV. Conversely, the S 2p XPS data (Figure 4d) show differences between the In2S3 and CuInS2 nanoplates, indicating a different chemical environment in terms of the formation of Cu−S bonds. CuInS2 NCs are widely explored as a promising semiconductor material for solar harvesting applications. Varying chemical composition of these ternary semiconductor NCs provides an efficient way to control their energy bandgaps.3 We have performed cyclic voltammetry measurements to determine the absolute energy level positions (conduction and valence band minima/maxima) and the bandgaps of CuInS2 nanoplates. This method has been successfully applied to study CdS, CdSe, CdTe, CdSxSe1−x, as well as Cu2−xSeyS1−y and CZTSeS NCs in this respect.64−72 The CV method is based on the transient analysis of gaining and losing electrons on the electrode’s surface. The injection of electrons to the conduction band minimum (CBM) generates the reduction current, and the extraction of electrons from the valence band maximum (VBM) results in an oxidation current. The samples for CV measurements were deposited onto the glassy carbon electrodes from their respective toluene solutions. The onset of oxidation and reduction peaks were identified and labeled by dotted lines in Figure 5a with the corresponding CBM/VBM and the related bandgaps for both In2S3 and CuInS2 nanoplates with different [Cu]/[In] ratios presented in Figure 5b. As can be seen in Figure 5a, well-pronounced oxidation and reduction peaks of In2S3 nanoplates are apparent at 1.74 V and −0.59 V, respectively, whereas for the CuInS2 samples, multiple peaks occurred outside the gap (where there was no appreciable current) in the range of approximately 0.92−1.04 V (vs Ag/Ag+) for oxidation and approximately −0.27 to −0.41 V for reduction. The oxidation potential moved to the negative
Figure 5. (a) Cyclic voltammograms of In2S3 and CuInS2 nanoplates with different [Cu]/[In] ratios as indicated. (b) Estimated absolute positions of the CBM and VBM and the respective bandgaps. The horizontal dotted lines represent band positions of the redox potentials of water splitting at pH 7 in aqueous solution.
side and the reduction potential to the positive side for CuInS2 samples with increasing [Cu]/[In] ratios. As a result, their bandgaps can be tuned from 1.45 to 1.19 eV for the samples with [Cu]/[In] molar ratios increasing from 0.7 to 2.9. The bandgap of the CuInS2 with [Cu]/[In] ratio of 2.9 is 1.19 eV, which is close to the decomposition energy levels of water (indicated in Figure 5 by horizontal dotted lines), indicating its potential applicability for water splitting. To explore the potential use of CuInS2 NCs in solutionprocessed photovoltaic devices, we deposited them on FTO substrates and used them as CEs for DSSCs. The device structure is shown in Figure 6a. The as-prepared CuInS2 films were annealed at elevated temperature to remove the organic molecules from the NCs surface as well as to initiate crystallization of the nanoparticles. Significant indium loss was observed during the annealing of CuInS2 films at high temperature (480 °C), which was attributed to the evaporation of the In2S binary phase, as confirmed by the detected change in the [Cu]/[In] ratios of the CuInS2 nanoplates before and after annealing at this temperature (change from 1.9 to 2.9). The J−V characteristics of three DSSCs employing either CuInS2 CEs annealed at two different temperatures (200 or 480 °C) or a conventional Pt CE are displayed in Figure 6b, and their detailed device parameters are listed in Table 1. The PCE of the cell was significantly enhanced to 6.83% (JSC = 12.81 mA/cm2, VOC = 0.743 V, FF = 71.8%) when using 5952
DOI: 10.1021/acs.chemmater.5b01971 Chem. Mater. 2015, 27, 5949−5956
Article
Chemistry of Materials
Figure 6. (a) Device structure of a DSSC with sintered CuInS2 NCs as a CE. (b) J−V characteristics of DSSC devices using CuInS2 with an initial [Cu]/[In] ratio equal to 1.9 annealed at 200 or 480 °C or Pt as the CE.
Figure 7. (a) Nyquist plots of DSSC devices using CuInS2 with an initial [Cu]/[In] ratio equal to 1.9 annealed at 200 or 480 °C or Pt as the counter electrode. The inset in (a) shows the equivalent circuit at the high frequency region. (b) Enlarged Nyquist plot at high frequency region for the three DSSC devices studied.
Table 1. Photovoltaic and EIS Parameters of DSSCs with CEs made of Pt or CuInS2 with an Initial [Cu]/[In] Ratio Equal to 1.9 Annealed at Two Different Temperatures As Indicated CE Pt CuInS2 (200 °C) CuInS2 (480 °C)
Jsc (mA/cm2)
Voc (V)
FF (%)
PCE (%)
Rs (Ω)
Rct (Ω)
13.40 10.74
0.736 0.642
71.8 41.2
7.08 2.84
17.2 19.4
6.6 476.5
12.81
0.743
71.8
6.83
18.2
8.2
become very close to those of the Pt CE. This confirms the assumption that the sintering process enhances the conductivity and catalytic activity of CuInS2 CE. Further investigations showed that the efficiencies of DSSCs based on CuInS2 CEs with [Cu]/[In] molar ratios of 0.8 and 0.4 (after annealing) are slightly lower than that of the devices discussed above. As shown in Figure S4 and Table S1, PCEs of DSSCs fabricated with CuInS2 CEs sintered at 480 °C having [Cu]/[In] ratios of 0.8 and 0.4 were 6.65% and 6.31%, respectively. This reduction may be attributed to lower conductivity due to the lower copper concentration.
■
CuInS2 NCs annealed at 480 °C as the CE, which becomes comparable to the performance of the control device (7.08%) with a Pt CE (Figure 6b). In DSSCs, FF determines the overall performance of the cell and is mainly affected by the charge transfer processes at each interface in the device. As the cells studied here were fabricated in an identical way except for the different CE materials, the greatly improved FF of the device based on the CuInS2 CE annealed at 480 °C should be related to the improved charge transfer at the CE/electrolyte interface. The removal of organic capping molecules of NCs, as well as the better crystallization of CuInS2 annealed at 480 °C as compared to 200 °C (see XRD patterns presented in Figure S3), both contribute to the improvement of the CE conductivity as well as their electrocatalytic activity. In addition, the adhesion of the CE materials with the substrates was improved after sintering at 480 °C, making them more robust in the electrolyte environment. To study the electron transport for various CEs employed in this work, we performed electrochemical impedance spectroscopy under dark conditions. After fitting the EIS spectra to a Nyquist plot, the intercept on the real axis at the highest frequency represents the series resistance (Rs) of the cells, and the diameter of the first semicircle in the high frequency regime determines the charge-transfer resistance at the CE/electrolyte interface (Rct). Figure 7 shows the Nyquist plots of three DSSC devices studied here. The values of Rs and Rct obtained from EIS data are listed in Table 1. The cell with 200 °C annealed CuInS2 CE has a distinctively large Rct, 2 orders of magnitude higher than that of the cells using Pt CE or 480 °C sintered CuInS2 CE. Such a large Rct suggests inefficient reduction of triiodide at the CE surface and poor charge transport ability of the CE material, which in turn causes severe electron loss at the CE/electrolyte interface. Furthermore, the Rs of this cell is higher when compared to the other two devices, which is related to its poor FF. For the device with 480 °C sintered CuInS2 CE, the Rs and Rct values are remarkably reduced and
CONCLUSIONS In summary, we introduced a template-based method for the synthesis of ternary CuInS2 NCs from binary In2S3 nanoplates. The synthesis includes two simple steps (i.e., fabrication of the template In2S3 nanoplates and incorporation of Cu+ ions at room temperature). The chemical composition of CuInS2 nanoplates in terms of the [Cu]/[In] molar ratios has been tuned from 0.7 to 2.9 by changing the content of the copper precursor. As a result, the bandgaps of the CuInS2 nanoplates could be tuned from 1.45 to 1.19 eV as evidenced from the CV measurements. We further explored the use of CuInS2 NC films as counter electrodes in dye-sensitized solar cells, achieving a conversion efficiency of 6.83% without selenization and ligand exchange. Our CV results also suggest that CuInS2 nanoplates may be potentially suitable materials for water splitting, owing to their bandgaps and absolute CBM/VBM positions. Related experiments are currently underway. The template synthesis of the 2D-layered materials introduced in this work provides an alternative route for the shape and composition control of ternary and quaternary semiconductor nanocrystals with enhanced performance in solution-processed photovoltaic devices.
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.chemmater.5b01971. Material characterizations (TEM images, HRTEM images, XRD patterns, UV−vis, and PL spectra) of CuZnInS2 alloy NCs; additional TEM and HRTEM images of In2S3 and CuInS2 NCs with different [Cu]/ [In] ratios; the XRD patterns of CuInS2 NCs before and after annealing; J−V curves and photovoltaic perform5953
DOI: 10.1021/acs.chemmater.5b01971 Chem. Mater. 2015, 27, 5949−5956
Article
Chemistry of Materials
■
(13) Kolny-Olesiak, J.; Weller, H. Synthesis and Application of Colloidal CuInS2 Semiconductor Nanocrystals. ACS Appl. Mater. Interfaces 2013, 5, 12221−12237. (14) Coughlan, C.; Singh, A.; Ryan, K. M. Systematic Study into the Synthesis and Shape Development in Colloidal CuInxGa1‑xS2 Nanocrystals. Chem. Mater. 2013, 25, 653−661. (15) Singh, A.; Coughlan, C.; Laffir, F.; Ryan, K. M. Systematic Study into the Synthesis and Shape Development in Colloidal CuInxGa1‑xS2 Nanocrystals. ACS Nano 2012, 6, 6977−6983. (16) Yu, X.; An, X.; Shavel, A.; Ibanez, M.; Cabot, A. The Effect of The Ga Content on The Photocatalytic Hydrogen Evolution of CuIn1‑xGaxS2 Nanocrystals. J. Mater. Chem. A 2014, 2, 12317−12322. (17) Sun, X. Y.; Ding, K.; Hou, Y.; Gao, Z. Y.; Yang, W. S.; Jing, L. H.; Gao, M. Y. Bifunctional Superparticles Achieved by Assembling Fluorescent CuInS2@ZnS Quantum Dots and Amphibious Fe3O4 Nanocrystals. J. Phys. Chem. C 2013, 117, 21014−21020. (18) Yin, Z.; Hu, Z. L.; Ye, H. H.; Teng, F.; Yang, C. H.; Tang, A. W. One-pot Controllable Synthesis of Wurtzite CuInS2 Nanoplates. Appl. Surf. Sci. 2014, 307, 489−494. (19) Pan, Z. X.; Mora-Sero, I.; Shen, Q.; Zhang, H.; Li, Y.; Zhao, K.; Wang, J.; Zhong, X. H.; Bisquert, J. High-Efficiency ″Green″ Quantum Dot Solar Cells. J. Am. Chem. Soc. 2014, 136, 9203−9210. (20) McDaniel, H.; Fuke, N.; Pietryga, J. M.; Klimov, V. I. Engineered CuInSexS2−x Quantum Dots for Sensitized Solar Cells. J. Phys. Chem. Lett. 2013, 4, 355−361. (21) Yi, L. X.; Liu, Y. Y.; Yang, N. L.; Tang, Z. Y.; Zhao, H. J.; Ma, G. H.; Su, Z. G.; Wang, D. One Dimensional CuInS2-ZnS Heterostructured Nanomaterials as Low-Cost and High-Performance Counter Electrodes of Dye-Sensitized Solar Cells. Energy Environ. Sci. 2013, 6, 835−840. (22) Zhang, Z. Y.; Zhang, X. Y.; Xu, H. X.; Liu, Z. H.; Pang, S. P.; Zhou, X. H.; Dong, S. M.; Chen, X.; Cui, G. L. CuInS2 Nanocrystals/ PEDOT:PSS Composite Counter Electrode for Dye-Sensitized Solar Cells. ACS Appl. Mater. Interfaces 2012, 4, 6242−6246. (23) Yao, R. Y.; Zhou, Z. J.; Hou, Z. L.; Wang, X.; Zhou, W. H.; Wu, S. X. An Alternative Counter-Electrode Material for Dye-Sensitized Solar Cells. ACS Appl. Mater. Interfaces 2013, 5, 3143−3148. (24) Jaffe, J. E.; Zunger, A. Theory of the Band-Gap Anomaly in ABC2 Chalcopyrite Semiconductors. Phys. Rev. B: Condens. Matter Mater. Phys. 1984, 29, 1882−1906. (25) Draguta, S.; McDaniel, H.; Klimov, V. I. Tuning Carrier Mobilities and Polarity of Charge Transport in Films of CuInSexS2−x Quantum Dots. Adv. Mater. 2015, 27, 1701. (26) Castro, S. L.; Bailey, S. G.; Raffaelle, R. P.; Banger, K. K.; Hepp, A. F. Nanocrystalline Chalcopyrite Materials (CuInS2 and CuInSe2) via Low-Temperature Pyrolysis of Molecular Single-Source Precursors. Chem. Mater. 2003, 15, 3142−3147. (27) Ng, M. T.; Boothroyd, C. B.; Vittal, J. J. One-Pot Synthesis of New-Phase AgInSe2 Nanorods. J. Am. Chem. Soc. 2006, 128, 7118− 7119. (28) Nairn, J. J.; Shapiro, P. J.; Twamley, B.; Pounds, T.; von Wandruszka, R.; Fletcher, T. R.; Williams, M.; Wang, C. M.; Norton, M. G. Preparation of Ultrafine Chalcopyrite Nanoparticles via the Photochemical Decomposition of Molecular Single-Source Precursors. Nano Lett. 2006, 6, 1218−1223. (29) Torimoto, T.; Adachi, T.; Okazaki, K.-i.; Sakuraoka, M.; Shibayama, T.; Ohtani, B.; Kudo, A.; Kuwabata, S. Facile Synthesis of ZnS−AgInS2 Solid Solution Nanoparticles for a Color-Adjustable Luminophore. J. Am. Chem. Soc. 2007, 129, 12388−12389. (30) Ogawa, T.; Kuzuya, T.; Hamanaka, Y.; Sumiyama, K. Synthesis of Ag-In Binary Sulfide Nanoparticles-Structural Tuning and Their Photoluminescence Properties. J. Mater. Chem. 2010, 20, 2226−2231. (31) Du, W. M.; Qian, X. F.; Yin, J.; Gong, Q. Shape- and PhaseControlled Synthesis of Monodisperse, Single-Crystalline Ternary Chalcogenide Colloids Through a Convenient Solution Synthesis Strategy. Chem. - Eur. J. 2007, 13, 8840−8846. (32) Wang, D. S.; Zheng, W.; Hao, C.; Peng, Q.; Li, Y. D. General Synthesis of I-III-VI2 Ternary Semiconductor Nanocrystals. Chem. Commun. 2008, 2556−2558.
ance of DSSCs using CuInS2 CEs with various [Cu]/[In] molar ratios (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work is supported under National Basic Research Program of China (No. 2013CB328804), Natural Science Foundation of China (No. 21573018), Guandong Province Technology Council of China (Project R-IND4601), SRG project of City University of Hong Kong (11306415), China Postdoctoral Science Foundation (2014M550621), and The Hong Kong Scholar Program (XJ2014046).
■
REFERENCES
(1) Kershaw, S. V.; Susha, A. S.; Rogach, A. L. Narrow Bandgap Colloidal Metal Chalcogenide Quantum Dots: Synthetic Methods, Heterostructures, Assemblies, Electronic and Infrared Optical Properties. Chem. Soc. Rev. 2013, 42, 3033−3087. (2) Kovalenko, M. V.; Manna, L.; Cabot, A.; Hens, Z.; Talapin, D. V.; Kagan, C. R.; Klimov, V. I.; Rogach, A. L.; Reiss, P.; Milliron, D. J.; Guyot-Sionnnest, P.; Konstantatos, G.; Parak, W. J.; Hyeon, T.; Korgel, B. A.; Murray, C. B.; Heiss, W. Prospects of Nanoscience with Nanocrystals. ACS Nano 2015, 9, 1012−1057. (3) Zhong, H. Z.; Bai, Z. L.; Zou, B. S. Tuning the Luminescence Properties of Colloidal I−III−VI Semiconductor Nanocrystals for Optoelectronics and Biotechnology Applications. J. Phys. Chem. Lett. 2012, 3, 3167−3175. (4) Panthani, M. G.; Akhavan, V.; Goodfellow, B.; Schmidtke, J. P.; Dunn, L.; Dodabalapur, A.; Barbara, P. F.; Korgel, B. A. Synthesis of CuInS2, CuInSe2, and Cu(InxGa1‑x)Se2 (CIGS) Nanocrystal ″Inks″ for Printable Photovoltaics. J. Am. Chem. Soc. 2008, 130, 16770−16777. (5) Koo, B.; Patel, R. N.; Korgel, B. A. Synthesis of CuInSe2 Nanocrystals with Trigonal Pyramidal Shape. J. Am. Chem. Soc. 2009, 131, 3134−3135. (6) Panthani, M. G.; Stolle, C. J.; Reid, D. K.; Rhee, D. J.; Harvey, T. B.; Akhavan, V. A.; Yu, Y.; Korgel, B. A. CuInSe2 Quantum Dot Solar Cells with High Open-Circuit Voltage. J. Phys. Chem. Lett. 2013, 4, 2030−2034. (7) Li, L.; Daou, T. J.; Texier, I.; Tran Thi Kim, C.; Nguyen Quang, L.; Reiss, P. Highly Luminescent CuInS2/ZnS Core/Shell Nanocrystals: Cadmium-Free Quantum Dots for In Vivo Imaging. Chem. Mater. 2009, 21, 2422−2429. (8) Aldakov, D.; Lefrancois, A.; Reiss, P. Ternary and Quaternary Metal Chalcogenide Nanocrystals: Synthesis, Properties and Applications. J. Mater. Chem. C 2013, 1, 3756−3776. (9) Lefrancois, A.; Luszczynska, B.; Pepin-Donat, B.; Lombard, C.; Bouthinon, B.; Verilhac, J.-M.; Gromova, M.; Faure-Vincent, J.; Pouget, S.; Chandezon, F.; Sadki, S.; Reiss, P. Enhanced Charge Separation in Ternary P3HT/PCBM/CuInS2 Nanocrystals Hybrid Solar Cells. Sci. Rep. 2015, 5, 7768 (1−8). (10) Guo, Q. J.; Kim, S. J.; Kar, M.; Shafarman, W. N.; Birkmire, R. W.; Stach, E. A.; Agrawal, R.; Hillhouse, H. W. Development of CuInSe2 Nanocrystal and Nanoring Inks for Low-Cost Solar Cells. Nano Lett. 2008, 8, 2982−2987. (11) Witt, E.; Kolny-Olesiak, J. Recent Developments in Colloidal Synthesis of CuInSe2 Nanoparticles. Chem. - Eur. J. 2013, 19, 9746− 9753. (12) Kruszynska, M.; Borchert, H.; Parisi, J.; Kolny-Olesiak, J. Synthesis and Shape Control of CuInS2 Nanoparticles. J. Am. Chem. Soc. 2010, 132, 15976−15986. 5954
DOI: 10.1021/acs.chemmater.5b01971 Chem. Mater. 2015, 27, 5949−5956
Article
Chemistry of Materials (33) Yang, Y. H.; Chen, Y. T. Solvothermal Preparation and Spectroscopic Characterization of Copper Indium Diselenide Nanorods. J. Phys. Chem. B 2006, 110, 17370−17374. (34) Allen, P. M.; Bawendi, M. G. Ternary I-III-VI Quantum Dots Luminescent in the Red to Near-Infrared. J. Am. Chem. Soc. 2008, 130, 9240−9241. (35) Tang, J.; Konstantatos, G.; Hinds, S.; Myrskog, S.; PattantyusAbraham, A. G.; Clifford, J.; Sargent, E. H. Heavy-Metal-Free SolutionProcessed Nanoparticle-Based Photodetectors: Doping of Intrinsic Vacancies Enables Engineering of Sensitivity and Speed. ACS Nano 2009, 3, 331−338. (36) Xie, R. G.; Rutherford, M.; Peng, X. G. Formation of HighQuality I-III-VI Semiconductor Nanocrystals by Tuning Relative Reactivity of Cationic Precursors. J. Am. Chem. Soc. 2009, 131, 5691− 5697. (37) Zhong, H. Z.; Zhou, Y.; Ye, M. F.; He, Y. J.; Ye, J. P.; He, C.; Yang, C. H.; Li, Y. F. Controlled Synthesis and Optical Properties of Colloidal Ternary Chalcogenide CuInS2 Nanocrystals. Chem. Mater. 2008, 20, 6434−6443. (38) Zhong, H. Z.; Lo, S. S.; Mirkovic, T.; Li, Y. C.; Ding, Y. Q.; Li, Y. F.; Scholes, G. D. Noninjection Gram-Scale Synthesis of Monodisperse Pyramidal CuInS2 Nanocrystals and Their SizeDependent Properties. ACS Nano 2010, 4, 5253−5362. (39) Zhong, H. Z.; Wang, Z. B.; Bovero, E.; Lu, Z. H.; van Veggel, F. C. J. M.; Scholes, G. D. Colloidal CuInSe2 Nanocrystals in the Quantum Confinement Regime: Synthesis, Optical Properties, and Electroluminescence. J. Phys. Chem. C 2011, 115, 12396−12402. (40) Chen, B. K.; Zhong, H. Z.; Zhang, W. Q.; Tan, Z. A.; Li, Y. F.; Yu, C. R.; Zhai, T. Y.; Bando, Y.; Yang, S. Y.; Zou, B. S. Highly Emissive and Color-Tunable CuInS2-Based Colloidal Semiconductor Nanocrystals: Off-Stoichiometry Effects and Improved Electroluminescence Performance. Adv. Funct. Mater. 2012, 22, 2081−2088. (41) Li, L.; Pandey, A.; Werder, D. J.; Khanal, B. P.; Pietryga, J. M.; Klimov, V. I. Efficient Synthesis of Highly Luminescent Copper Indium Sulfide-Based Core/Shell Nanocrystals with Surprisingly Long-Lived Emission. J. Am. Chem. Soc. 2011, 133, 1176−1179. (42) Choi, S. H.; Kim, E. G.; Hyeon, T. One-Pot Synthesis of Copper-Indium Sulfide Nanocrystal Heterostructures with Acorn, Bottle, and Larva Shapes. J. Am. Chem. Soc. 2006, 128, 2520−2521. (43) Han, W.; Yi, L. X.; Zhao, N.; Tang, A. W.; Gao, M. Y.; Tang, Z. Y. Synthesis and Shape-Tailoring of Copper Sulfide/Indium SulfideBased Nanocrystals. J. Am. Chem. Soc. 2008, 130, 13152−13161. (44) Connor, S. T.; Hsu, C. M.; Weil, B. D.; Aloni, S.; Cui, Y. Phase Transformation of Biphasic Cu2S-CuInS2 to Monophasic CuInS2 Nanorods. J. Am. Chem. Soc. 2009, 131, 4962−4966. (45) Wang, Y. H. A.; Zhang, X. Y.; Bao, N. Z.; Lin, B. P.; Gupta, A. Synthesis of Shape-Controlled Monodisperse Wurtzite CulnxGa1‑xS2 Semiconductor Nanocrystals with Tunable Band Gap. J. Am. Chem. Soc. 2011, 133, 11072−11075. (46) Gupta, S.; Kershaw, S. V.; Rogach, A. L. 25th Anniversary Article: Ion Exchange in Colloidal Nanocrystals. Adv. Mater. 2013, 25, 6923−6944. (47) Langevin, M. A.; Ritcey, A. M.; Ni Allen, C. Air-Stable NearInfrared AgInSe2 Nanocrystals. ACS Nano 2014, 8, 3476−3482. (48) Kuzuya, T.; Hamanaka, Y.; Itoh, K.; Kino, T.; Sumiyama, K.; Fukunaka, Y.; Hirai, S. Phase Control and Its Mechanism of CuInS2 Nanoparticles. J. Colloid Interface Sci. 2012, 388, 137−143. (49) De Trizio, L.; Prato, M.; Genovese, A.; Casu, A.; Povia, M.; Simonutti, R.; Alcocer, M. J. P.; D’Andrea, C.; Tassone, F.; Manna, L. Strongly Fluorescent Quaternary Cu-In-Zn-S Nanocrystals Prepared from Cu1‑xInS2 Nanocrystals by Partial Cation Exchange. Chem. Mater. 2012, 24, 2400−2406. (50) Lesnyak, V.; George, C.; Genovese, A.; Prato, M.; Casu, A.; Ayyappan, S.; Scarpellini, A.; Manna, L. Alloyed Copper Chalcogenide Nanoplatelets via Partial Cation Exchange Reactions. ACS Nano 2014, 8, 8407−8418. (51) Wu, X. J.; Huang, X.; Qi, X. Y.; Li, H.; Li, B.; Zhang, H. CopperBased Ternary and Quaternary Semiconductor Nanoplates: Tem-
plated Synthesis, Characterization, and Photoelectrochemical Properties. Angew. Chem., Int. Ed. 2014, 53, 8929−8933. (52) Akkerman, Q. A.; Genovese, A.; George, C.; Prato, M.; Moreels, I.; Casu, A.; Marras, S.; Curcio, A.; Scarpellini, A.; Pellegrino, T.; Manna, L.; Lesnyak, V. From Binary Cu2S to Ternary Cu-In-S and Quaternary Cu-In-Zn-S Nanocrystals with Tunable Composition via Partial Cation Exchange. ACS Nano 2015, 9, 521−531. (53) Van der Stam, W.; Berends, A. C.; Rabouw, F. T.; Willhammar, T.; Ke, X.; Meeldijk, J. D.; Bals, S.; Donega, C. d. M. Luminescent CuInS2 Quantum Dots by Partial Cation Exchange in Cu2−xS Nanocrystals. Chem. Mater. 2015, 27, 621−628. (54) Diehl, R.; Nitsche, R. Vapour Growth of Three In2S 3 Modifications by Iodine Transport. J. Cryst. Growth 1975, 28, 306− 310. (55) Migge, H.; Grzanna, J. Thermochemistry in the System Cu-In-S At 723 K. J. Mater. Res. 1994, 9, 125−131. (56) Lei, S. J.; Wang, C. Y.; Liu, L.; Guo, D. H.; Wang, C. N.; Tang, Q. L.; Cheng, B. C.; Xiao, Y. H.; Zhou, L. Spinel Indium Sulfide Precursor for the Phase-Selective Synthesis of Cu-In-S Nanocrystals with Zinc-Blende, Wurtzite, and Spinel Structures. Chem. Mater. 2013, 25, 2991−2997. (57) Acharya, S.; Sarkar, S.; Pradhan, N. Subnanometer Thin betaIndium Sulfide Nanosheets. J. Phys. Chem. Lett. 2012, 3, 3812−3817. (58) Acharya, S.; Dutta, M.; Sarkar, S.; Basak, D.; Chakraborty, S.; Pradhan, N. Synthesis of Micrometer Length Indium Sulfide Nanosheets and Study of Their Dopant Induced Photoresponse Properties. Chem. Mater. 2012, 24, 1779−1785. (59) Park, K. H.; Jang, K.; Son, S. U. Synthesis, Optical Properties, and Self-Assembly of Ultrathin Hexagonal In2S3 Nanoplates. Angew. Chem., Int. Ed. 2006, 45, 4608−4612. (60) Zhong, H. Z.; Ye, M. F.; Zhou, Y.; Yang, C. H.; Li, Y. F. Synthesis of ln2S3 Nanoplates and Their Self-Assembly into Superlattices. J. Nanosci. Nanotechnol. 2007, 7, 4346−4352. (61) Liu, L. G.; Zhong, H. Z.; Bai, Z. L.; Zhang, T.; Fu, W. P.; Shi, L. J.; Xie, H.; Deng, L. G.; Zou, B. S. Controllable Transformation from Rhombohedral Cu1.8S Nanocrystals to Hexagonal CuS Clusters: Phase- and Composition-Dependent Plasmonic Properties. Chem. Mater. 2013, 25, 4828−4834. (62) Xie, Y.; Riedinger, A.; Prato, M.; Casu, A.; Genovese, A.; Guardia, P.; Sottini, S.; Sangregorio, C.; Miszta, K.; Ghosh, S.; Pellegrino, T.; Manna, L. Copper Sulfide Nanocrystals with Tunable Composition by Reduction of Covellite Nanocrystals with Cu+ Ions. J. Am. Chem. Soc. 2013, 135, 17630−17637. (63) Kundu, M.; Hasegawa, T.; Terabe, K.; Yamamoto, K.; Aono, M. Structural Studies of Copper Sulfide Films: Effect of Ambient Atmosphere. Sci. Technol. Adv. Mater. 2008, 9, 035011. (64) Poznyak, S. K.; Osipovich, N. P.; Shavel, A.; Talapin, D. V.; Gao, M. Y.; Eychmuller, A.; Gaponik, N. Size-Dependent Electrochemical Behavior of Thiol-Capped CdTe Nanocrystals in Aqueous Solution. J. Phys. Chem. B 2005, 109, 1094−1100. (65) Haram, S. K.; Quinn, B. M.; Bard, A. J. Electrochemistry of CdS Nanoparticles: A Correlation Between Optical and Electrochemical Band Gaps. J. Am. Chem. Soc. 2001, 123, 8860. (66) Inamdar, S. N.; Ingole, P. P.; Haram, S. K. Determination of Band Structure Parameters and the Quasi-Particle Gap of CdSe Quantum Dots by Cyclic Voltammetry. ChemPhysChem 2008, 9, 2574−2579. (67) Markad, G. B.; Battu, S.; Kapoor, S.; Haram, S. K. Interaction between Quantum Dots of CdTe and Reduced Graphene Oxide: Investigation through Cyclic Voltammetry and Spectroscopy. J. Phys. Chem. C 2013, 117, 20944−20950. (68) Ingole, P. P.; Markad, G. B.; Saraf, D.; Tatikondewar, L.; Nene, O.; Kshirsagar, A.; Haram, S. K. Band Gap Bowing at Nanoscale: Investigation of CdSxSe1‑x Alloy Quantum Dots through Cyclic Voltammetry and Density Functional Theory. J. Phys. Chem. C 2013, 117, 7376−7383. (69) Haram, S. K.; Kshirsagar, A.; Gujarathi, Y. D.; Ingole, P. P.; Nene, O. A.; Markad, G. B.; Nanavati, S. P. Quantum Confinement in CdTe Quantum Dots: Investigation through Cyclic Voltarnmetry 5955
DOI: 10.1021/acs.chemmater.5b01971 Chem. Mater. 2015, 27, 5949−5956
Article
Chemistry of Materials Supported by Density Functional Theory (DFT). J. Phys. Chem. C 2011, 115, 6243−6349. (70) Osipovich, N. P.; Shavel, A.; Poznyak, S. K.; Gaponik, N.; Eychmueller, A. Electrochemical Observation of the Photoinduced Formation of Alloyed ZnSe(S) Nanocrystals. J. Phys. Chem. B 2006, 110, 19233−19237. (71) Romanov, S. G.; Chigrin, D. N.; Torres, C. M. S.; Gaponik, N.; Eychmuller, A.; Rogach, A. L. Emission Stimulation in a Directional Band Gap of a CdTe-Loaded Opal Photonic Crystal. Phys. Rev. E 2004, 69, 046606. (72) Li, Y. C.; Zhong, H. Z.; Li, R.; Zhou, Y.; Yang, C. H.; Li, Y. F. High-Yield Fabrication and Electrochemical Characterization of Tetrapodal CdSe, CdTe, and CdSexTe1−x Nanocrystals. Adv. Funct. Mater. 2006, 16, 1705−1716.
5956
DOI: 10.1021/acs.chemmater.5b01971 Chem. Mater. 2015, 27, 5949−5956
