Application of Cu3InSnSe5 Heteronanostructures as Counter

Application of Cu3InSnSe5 Heteronanostructures as Counter Electrodes for Dye-Sensitized Solar Cells. Yue Lou† ... Publication Date (Web): May 17, 20...
3 downloads 0 Views 5MB Size
Download PDF
Research Article www.acsami.org

Application of Cu3InSnSe5 Heteronanostructures as Counter Electrodes for Dye-Sensitized Solar Cells Yue Lou,† Wenjie Zhao,‡ Chunguang Li,*,† He Huang,† Tianyu Bai,⊥ Cailing Chen,† Chen Liang,† Zhan Shi,*,† Dong Zhang,§ Xiao-Bo Chen,†,¶ and Shouhua Feng† †

State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, ‡Key Laboratory of Physics and Technology for Advance Batteries (Ministry of Education), College of Physics, and §College of Physics State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, P. R. China ⊥ College of Medical Laboratory, Dalian Medical University, Dalian 116044, P. R. China ¶ School of Engineering, RMIT University, Carlton, Victoria 3053, Australia S Supporting Information *

ABSTRACT: In this research, we reported the synthesis of quaternary Cu3InSnSe5 nanoparticles with uniform size distribution and morphology for the first time through delicate controls over the chemical reaction kinetics. On the basis of the preparation strategy of Cu3InSnSe5 nanoparticles, Pt−Cu3InSnSe5 and Au− Cu3InSnSe5 heteronanostructures were designed and yielded using a simple and efficient seed growth method. These two heteronanostructures remained monodispersed without presence of any Cu3InSnSe5 nanocrystal impurities. To explore their application potentials for dye-sensitized solar cells, counter electrodes consisting of individual Cu3InSnSe5, Pt− Cu3InSnSe5, or Au−Cu3InSnSe5 constituents were fabricated. Current density−voltage (J−V) characteristics evaluation reveals that Cu3InSnSe5 nanoparticles, Pt−Cu3InSnSe5 and Au−Cu3InSnSe5 heterostructured nanoparticles display a comparative power conversion efficiency (PCE) of 5.8%, 7.6%, and 6.5% to that of a Pt-based counter electrode (7.9%), respectively. As such, we believe that the reported preparation strategy could provide new insights to the design and manufacture of counter electrode materials with controlled structure, morphology, and optimized power conversion efficiency for dye-sensitized solar cells. KEYWORDS: Cu3InSnSe5 nanoparticles, metal−semiconductor heterostructures, counter electrodes, dye-sensitized solar cells, photovoltaic performance

■

INTRODUCTION Dye-sensitized solar cells (DSSCs) are remarkable photovoltaic devices due to their cost-effectiveness, simple production processes, and high power conversion efficiency.1−5 In general, typical DSSCs exhibit sandwich structure that consists of a dyesensitized semiconductor photoanode, a liquid electrolyte, and a counter electrode. The counter electrode is essential to gather electrons produced by dye-sensitized TiO2 semiconductor photoanode and catalyze the reduction of oxidized ions in the liquid electrolyte.6 However, platinum (Pt), a prevalent counter electrode material, is too expensive to be commercialized for DSSCs. As such, it remains a challenge to develop cost-effective materials with optimal electrocatalytic activity and conductivity to those of Pt as counter electrode for DSSCs. In recent decades, it has been found that various nanomaterials can be used as counter electrode materials for DSSCs such as carbon materials,7,8 conductive polymers,9,10 nanocomposites,11−13 and inorganic materials.14−18 Of these, inorganic materials, in particular the multicomponent metal sulfides and metal selenides, showed excellent catalytic activity toward I3−/I− pairs. Such materials have been studied as counter electrodes materials for the advantage of sophisticated synthesis approaches, cost-effectiveness, and high power conversion efficiency. However, few studies focused on the long-term © XXXX American Chemical Society

stability, one of the key specifications for commercial DSCCs. Meanwhile, though ternary or quaternary selenide semiconductors with a wide range of particle size and morphology have been synthesized by a variety of techniques, little attention has been drawn to the investigation of counter electrode materials for DSSCs. Recent advances on the counter electrodes materials remain on the use of traditional multicomponent copper-based semiconductor compounds such as Cu2ZnSnS4, Cu2ZnSnSe4, and CuInS2.6,18−24 As such, we aim to design and develop new counter electrode materials with controllable structure and composition to build DSSC devices with reasonable price, high power conversion efficiency, and promising long-term battery performance. On the basis of this, we can further incorporate multiple catalytic segments in one individual nanostructure through the way of construction of metal−semiconductor heterostructures to explore their synergistic effect on the performance of DSSC devices. In this work, we report a simple strategy for the synthesis of quaternary wurtzite Cu3InSnSe5 nanoparticles with uniform morphology and narrow size distribution for the first time. The Received: March 3, 2017 Accepted: May 11, 2017

A

DOI: 10.1021/acsami.7b03117 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

(0.025 mmol), InCl3 (0.025 mmol), OLA (4 mL), and DDT (0.25 mL) at 200 °C. Then temperature was quickly raised to 230 °C, and the diphenyl diselenide/OLA solution (0.625 mL) was swiftly injected followed by holding at 240 °C for 12 min. Preparation of Au−Cu3InSnSe5 Nanocrystals. As the preparation of Au−Cu3InSnSe5, spherical Au nanocrystals were first prepared as seeds. HAuCl4 (80 mg) was dissolved into OLA (20 mL) with magnetic stirring under nitrogen gas protection, and then the solution was held at 120 °C for 5 min. The solution finally turned to purple and had metallic luster, which indicated the formation of Au nanocrystals. Subsequently, Au/OLA solution (10 mL) was mixed with CuCl (0.075 mmol), SnCl2 (0.025 mmol), InCl3 (0.025 mmol), and OLA (8 mL) at 120 °C. Then temperature was quickly raised to 230 °C, and the diphenyl diselenide/ OLA solution (0.625 mL) was swiftly injected followed by holding at 240 °C for 12 min. Fabrication of DSSCs. Mo-coated glass substrates were ultrasonically cleaned with ethanol, acetone, and isopropanol respectively for 30 min. Spin-coating technique was employed to deposit a thin film consisting of nanocrystals on the clean Mo-coated glass substrate to yield nanocrystals/Mo counter electrodes. In brief, the as-prepared Cu3InSnSe5, Pt−Cu3InSnSe5, and Au−Cu3InSnSe5 nanocrystals were individually dispersed in terpineol slurry and toluene mixed solution (1:1 10 mg/mL) and sonicated for several minutes to form a uniform solution. Then the solutions were spin-coated onto the clean Mo-coated glass substrates (24 mm × 14 mm) at 600 rpm for 40 s followed by vacuum drying at 60 °C. Subsequently, the films were annealed at 400 °C for 1 h in nitrogen atmosphere to remove the organic ligands that could hinder interparticle electron transport. Neat Mo-coated glass and Pt-coated glass were used as counter electrodes for the following photovoltaic performance tests as controls. In addition, commercial P25 TiO2 nanoparticles were used to prepare TiO2 films (thickness 12 μm, effective area 0.196 cm2) by screenprinting method. Then they were immersed in an N-719 dye ethanolic solution (3 × 10−4 mol/L Dyesol) overnight followed by drying in nitrogen atmosphere to get dye-sensitized TiO2 photoanodes. Sandwich-structured solar cells were constructed by clipping the NCs/Mo counter electrodes (or Pt-FTO counter electrodes) and dye-sensitized TiO2 photoanodes. Surlyn 1760−200 was used as spacer between the electrodes and followed by filling the interspace with liquid electrolyte consisting of LiI (0.5 mol/L), I2 (0.05 mol/L), tertbutylpyridine (0.5 mol/L), and 1-ethyl-3-methylimidazolium iodide (0.1 mol/L) in propylene carbonate. Material Characterization. Crystallographic characteristics of the nanomaterials were determined by X-ray diffraction (XRD) on a Rigaku D/max-2500 diffractometer with Cu−Kα radiation operated at 200 mA and 40 kV. Morphology information on quaternary Cu3InSnSe5 nanoparticles and Pt/Au−Cu3InSnSe5 heteronanostructures was investigated by transmission electron microscopy (TEM) and highresolution transmission electron microscopy (HRTEM, FEI Tecnai G2S-Twin). Elemental mapping images were acquired at the same instrument. Energy dispersive spectroscopy (EDS) was performed on a JEOL JSM-6700F microscope operated at 10 kV. X-ray photoelectron spectroscopy (XPS) was detected by ESCALAB 250 with Mg Kα as Xray source. Absorbance spectra of samples were measured on a UV−vis/ NIR spectrometer (Shimadzu UV-3600 spectrophotometer). Ultraviolet photoelectron spectroscopy (UPS) was collected on VG ESCALAB MK II with monochromatized HeI radiation at 21.22 eV. Thermogravimetric analysis (TGA) and phase transition temperature test were carried out on a thermal gravimetric analyzer (TGA Q500) and differential scanning calorimeter (DSC Q100) of America TA Instruments. Current−voltage (J−V) curves of DSSCs were recorded using a Keithley 2440 workstation system under AM 1.5G solar simulator (Newport Oriel Sol3A Class AAA). Surface structures of Cu3InSnSe5 nanoparticles before and after annealing were determined by infrared spectroscopy (IR) (IFS-66 V/S, Bruker, Germany).

preparation of multicomponent metal sulfides remains a challenge owing to the technical difficulty in regulating the relative activity of various precursors that coexist in a same synthetic system. Through the exploration of the influence of reaction kinetics on morphology and size of Cu3InSnSe5 nanoparticle, the optimal processing parameters were established. Subsequently, high-quality Pt/Au−Cu3InSnSe5 heteronanostructures were produced on the epitaxial growth of previously synthesized Pt/Au nanocrystals that acted as seeds in the precursor solution. The growth of heterostructured nanomaterial can form a new Fermi level equilibrium and achieve a swift and efficient charge transfer. It is feasible to employ Pt/ Au−Cu3InSnSe5 heteronanostructures as a major constituent of counter electrode of DSSCs to improve the photovoltaic performance of dye-sensitized solar cells.25−29 Herein, we employed spin-coating method to produce pristine Cu3InSnSe5, Pt− and Au−Cu3InSnSe5 nanoparticle films onto Mo-coated glass substrate as counter electrodes for DSSCs. As a result, the counter electrodes made of Cu3InSnSe5 nanoparticles films, Pt−Cu3InSnSe5 and Au−Cu3InSnSe5 heteronanostructured films achieved a power conversion efficiency of 5.8%, 7.6%, and 6.5%, respectively (the power conversion efficiency of Ptbased counter electrode was 7.9% under the same condition). It should be noted that the power conversion efficiency of Au− Cu3InSnSe5 and Cu3InSnSe5 materials was stable at 5.0% and 4.4% after 20 days. Therefore, we believe that as-prepared Cu3InSnSe5 NPs have a great application potential as counter electrodes for DSSCs, and the construction of the metal− semiconductor heterostructures imposes a substantial effect on optimization of the performance of the DSSCs.

■

EXPERIMENTAL SECTION

Chemicals. Oleylamine (OLA, 70%) was purchased from SigmaAldrich. Diphenyl diselenide (98%), tin chloride dehydrate (SnCl2), and dodecanethiol (DDT, 98%) were obtained from Alfa Aesar. Copper chloride (CuCl), indium chloride (InCl3), ethanol, toluene, chloroplatinic acid hexahydrate (H2PtCl6·6H2O AR), and hydrogen tetrachloroaurate hydrate (HAuCl4, AR) were purchased from Shanghai Chemical Reagents Company. All reagents were directly used without any purifying treatments. Terpineol slurry, Surlyn 1760−200, and Commercial P25 TiO2 nanoparticles were provided by Dalian Heptachroma Solartech Co., Ltd. Preparation of Cu3InSnSe5 Nanocrystals. Diphenyl diselenide/ OLA solution was first prepared by dissolving diphenyl diselenide (1 mmol) in OLA (10 mL) at room temperature with magnetic stirring under nitrogen gas protection. In terms of a typical synthesis of quasihexagon Cu3InSnSe5 nanocrystals, CuCl (0.3 mmol), SnCl2 (0.1 mmol), InCl3 (0.1 mmol), OLA (8 mL), and DDT (1 mL) were mixed together in a 50 mL three-neck flask. The mixture was degassed at room temperature for several minutes followed by purging with Ar gas under magnetic stirring. Subsequently, the mixture was heated to 230 °C under nitrogen gas protection to yield bright yellow solution. Then diphenyl diselenide/OLA solution (2.5 mL) was swiftly injected into the mixture to see a rapid change into black color, which indicated the formation of nuclei. Temperature was raised up to 240 °C and held for 12 min. Finally, the yielded compounds were respectively washed with ethanol and toluene three times and dispersed into toluene for further characterization. For spherical Cu3InSnSe5 nanocrystals, 1.5 mL/2 mL of DDT was added, while the other experimental conditions were maintained. Preparation of Pt−Cu3InSnSe5 Nanocrystals. Spherical Pt nanocrystals were first prepared as seeds. H2PtCl6·6H2O (40 mg) was dissolved into OLA (4 mL) with magnetic stirring under nitrogen gas protection, and then the solution was heated and held at 200 °C for 30 min to yield black solution containing Pt nanocrystals. Subsequently, Pt/OLA solution (4 mL) was mixed with CuCl (0.075 mmol), SnCl2

■

RESULTS AND DISCUSSION In this study, we adopted the simple hot injection method to synthesize quaternary wurtzite Cu3InSnSe5 nanocrystals with B

DOI: 10.1021/acsami.7b03117 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces delicate controls over morphology for the first time. As shown in Figure 1a, crystallographic structures of the as-synthesized

(103), and (112) crystal planes of the wurtzite crystals, in agreement with the corresponding 2θ in the simulated XRD pattern. The calculated lattice parameters of as-synthesized Cu3InSnSe5 nanocrystals are a = b = 3.996 Å and c = 6.626 Å. Therefore, we determine that new quaternary Cu3InSnSe5 nanocrystals exhibit wurtzite structural characteristics. It is challenging to produce such multicomponent selenide with metastable kinetics in this reaction that is associated with selenium source diphenyl diselenide, capping agent DDT, and processing temperature.31,32 Highly active diphenyl diselenide can react with thiolate over a short period of time to trigger a rapid nanocrystal growth toward the formation of metastable kinetic products. DDT adheres well to the surface of nanocrystals to reduce surface free-energy and passivate crystalline facets of the wurtzite-derived phase, which stabilizes the metastable phase. Moreover, reaction temperature also plays a key role in phaseselective syntheses to regulate final crystal phases.33,34 In addition, controls over chemical reaction kinetics can also determine the shape of nanocrystals products. Here, we further explored the shape control on Cu3InSnSe5 nanocrystals by tuning OLA/DDT ratio of the reaction system. Size and morphology of the Cu3InSnSe5 nanocrystals were characterized by TEM. As shown in a typical TEM micrograph in Figure 1c and e, the quasi-hexagon geometry nanocrystals with an average size of 12 nm and the spherical nanocrystals with an average size of 13 nm are highly monodisperse. The corresponding selected-area electron diffraction (SEAD) patterns (insets of Figure 1c,e) are consistent with the XRD patterns, which confirm the presence of wurtzite structure. High-resolution TEM images (Figure 1d,f) depict high crystallinity of as-prepared Cu3InSnSe5 nanocrystals with a distance of atomic lattice fringes of 0.35 nm, which is consistent with the calculation results of its Fourier transform (insets of Figure 1d and 1f). In addition, we investigated the elemental composition of the Cu3InSnSe5 nanocrystals using SEM equipped with an EDS detector. The EDS spectra (Supporting Information, Figure S1) reveal that mole ratio of the four essential elements (i.e., Cu, In, Sn, Se) was close to the stoichiometric ratio of Cu3InSnSe5. In this reaction, mole ratio of OLA and DDT, capping agent, imposes an effect on the morphology of nanoparticles. By increasing the quantity of DDT, the passivation of the crystal plane is strengthened, and it tends to yield nanocrystals with spherical morphology. Moreover, as shown in Figure S2, the size of the spherical particles presented a decreasing trend (about 10 nm) when we increased the amount of DDT to 2 mL. To elucidate band structure of these new

Figure 1. (a) XRD pattern of quaternary Cu3InSnSe5 nanoparticles; (b) crystal structure of wurtzite Cu3InSnSe5 nanoparticle; (c, d) TEM image and HRTEM image of quasi-hexagon Cu3InSnSe5 nanoparticles, inset of panel c is selected-area SAED pattern, and inset of panel d is selectedarea FFT; (e, f) TEM image and HRTEM image of spherical Cu3InSnSe5 nanoparticles in the presence of 1.5 mL of DDT, inset of panel e is selected-area SAED pattern, and inset of panel f is selectedarea FFT. Scale bars of panels c and e are 50 nm. Scale bars of the insets of panels c and e are 21 nm. Scale bars of panels d and f are 5 nm.

Cu3InSnSe5 nanocrystals were characterized by XRD. A XRD pattern of pure wurtzite ZnSe crystals was simulated for comparison (Figure 1b), where, that is, in the space lattice, Cu+, In3+, and Sn4+ ions are randomly replaced with Zn2+ ions.30,31 We observed that major XRD diffraction peaks at 2θ = 25.62°, 26.90°, 29.04°, 37.52°, 45.23°, 48.80°, and 53.42°, which can be indexed as (100), (002), (101), (102), (110),

Figure 2. (a) UV−vis/NIR absorption spectrum of as-synthesized Cu3InSnSe5 nanoparticles. (b) UPS spectra of as-synthesized Cu3InSnSe5 nanoparticles. C

DOI: 10.1021/acsami.7b03117 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces semiconductor nanoparticles, UV−vis/NIR absorption spectrum and UPS data of Cu3InSnSe5 nanocrystals were recorded (Figure 2a). It demonstrates that Cu3InSnSe5 nanocrystals display a broad absorption range in the visible region between 400 and 780 nm. Band gap value of Cu3InSnSe5 nanocrystals was measured by converting UV−vis/NIR absorption spectra into a graph of the related plot of (αhv)2 as a function of photo energy (hv) to give a value of 1.54 eV (inset of Figure 2a). Through the information on band gap and UPS data, we calculated conduction band (CB) and valence band (VB) edges of the asprepared Cu3InSnSe5 nanocrystals. WF is defined by the secondary electron cutoff. WF value of Cu3InSnSe5 nanocrystals is 21.22 − 15.94 = 5.28 eV. Value of the valence band (VB) edges is −(5.28 + 0.09) = −5.37 eV. Conduction band (CB) edges of Cu3InSnSe5 nanocrystals were then estimated using the corresponding the band gap value and valence band edges. Value of the conduction band (CB) edges is −3.83 eV.35,36 So far, metal−semiconductor heterostructures have not been used as counter electrode of DSSCs, though it is a feasible strategy to incorporate a number of distinct catalytic segments in one individual nanostructure to explore their synergistic effect on the performance of DSSC devices. As such, we chose Pt or Au as seeds to synthesize Pt/Au−Cu3InSnSe5 heterostructures and carried out electrochemical evaluations to study the influence of embedding precious metals. Here, we choose Pt/Au nanoseeds obtained from the reduction reaction of H2PtCl6 or HAuCl4 in OLA solution. The use of same capping agent and solvent OLA created a similar growth environment to the two different nanoparticles. It facilitated absorption of the precursor on the surface of the nanoseeds and nucleation and growth of Cu3InSnSe5 on the surface of metal nanocrystals. In addition, regarding the synthesis of Pt/Au−Cu3InSnSe5 heterostructures, the key factor to avoid preferential growth of Cu3InSnSe5 nanocrystals is the appropriate addition of dodecanethiol. Excess dodecanethiol is favorable to the preparation of neat Cu3InSnSe5 nanoparticles. As shown in Figures 3 and 4, the interfaces of Pt− Cu3InSnSe5 and Au−Cu3InSnSe5 heterostructures are very clear. Pt−Cu3InSnSe5 heterostructure exhibits a homogeneous core− shell structure. Pt core nanocrystals are about 38 nm, and Cu3InSnSe5 shell is about 8 nm. Au−Cu3InSnSe5 heterostructure also presents a heterogeneous core−shell structure. Au core nanocrystals are about 14 nm and contain one thin side (approximately 3 nm) and one thick side (approximately 9 nm). HRTEM images (insets of Figures 3c and 4c) depict high crystallinity of Cu3InSnSe5 nanocrystal shell with a distance of atomic lattice fringes of 0.35 nm, which is consistent with the Cu3InSnSe5 nanocrystals. XRD patterns (Figures 3d and 4d) indicate that the metal−semiconductor heterostructures were synthesized, in which the Au and Pt were both in the cubic phase. STEM-EDS mapping images (Figures 3e and 4e) of Pt− Cu3InSnSe5 and Au−Cu3InSnSe5 heterostructures reveal the distribution of Cu, In, Sn, Se, and Pt/Au elements, which verifies the presence of uniformly alloyed as-synthesized Cu3InSnSe5 nanocrystals and high-quality Pt/Au−Cu3InSnSe5 heteronanostructures. Elemental oxidation state of Cu3InSnSe5 nanocrystals was analyzed made by XPS (Figure 5) in comparison to that of Pt− Cu3InSnSe5 and Au−Cu3InSnSe5 heterostructures. XPS survey spectra of Cu3InSnSe5 nanocrystals show Cu 2p, In 3d, Sn 3d, and Se 3d core levels. Two characteristic peaks of Cu 2p appeared at 932.1 and 951.9 eV with a peak separation of 19.8 eV, which suggested the presence of Cu (I). For In 3d, two intense peaks were located at 444.7 and 452.2 eV, which indicated In (+3) 3d

Figure 3. (a−c) TEM image and HRTEM image of Pt−Cu3InSnSe5 heteronanostructured nanoparticles. (d) XRD pattern of Pt− Cu3InSnSe5 heteronanostructured nanoparticles. Bottom red lines indicate the XRD peak positions of wurtzite Cu3InSnSe5, and blue lines correspond to cubic Pt (JCPDS 65−2868). (e) EDS elemental mapping images of Pt−Cu3InSnSe5 heteronanostructured nanoparticles.

5/2 and In 3d (+3) 3/2, respectively. Sn 3d peaks were split into 486.2 and 494.6 eV with a splitted binding energy of 8.4 eV, which can be ascribed to Sn (IV). Se 3d peaks were located at 54.1 eV, which is consistent with the reported results.28,30 The valence state of Cu, In, Sn and Se is +1, + 3, + 4 and −2 respectively. This situation matches the result that mole ratio of Cu, In, Sn and Se was 3:1:1:5. Cu 2p, In 3d, Sn 3d, and Se 3d core levels of Pt−Cu3InSnSe5 and Au−Cu3InSnSe5 heterostructures basically agree with those of Cu3InSnSe5 nanocrystals, which indicate that the generation of heterostructures incurred a slight change in chemical state of the elements of the two materials and no alloy is formed. The absence of Pt peaks in the XPS survey spectra of Pt−Cu3InSnSe5 heterostructure indicates the Pt metal cores were totally embedded in the Cu3InSnSe5 shells and separate metal impurity does not exist since the XPS analysis is a test for the surface of materials.28 On the contrary, peak of Au cores (Figure S3) can be detected because the probing depth of the XPS instrument can reach 5 nm inward from surface. One side of the Cu3InSnSe5 shell is too thin to detect Au signal. To demonstrate the potential application of the as-prepared Cu3InSnSe5 nanocrystals, Pt−/Au−Cu3InSnSe5 heterostrucD

DOI: 10.1021/acsami.7b03117 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

elemental composition of Pt−Cu 3InSnSe5 heteronanostructured counter electrodes and Au−Cu 3InSnSe5 heteronanostructured counter electrodes before annealing by EDS (Figure S7). Results demonstrate that the precious metal dosage was only 6.0% for Pt and 9.1% for Au (both in mass percentage, wt %). Sulfur content was around 9%, which was from the capping agents of 1-DT before annealing. Selection of Mo-coated glass instead of high-cost FTO-based conducting material as substrate can lower the cost and employ the good conductivity of Mo glass, which contributes to high power conversion efficiency.37 We fabricated replicate devices (n = 3−4) to obtain reproducible results for each counter electrode material. Photocurrent density−voltage ( J−V) curves and the photovoltaic device parameters of these DSSCs are depicted in Figures 6 and S7 and Table 1 for comparison. Obviously, we can find that neat Mocoated glass is not a functional counter electrode. When quasihexagon Cu3InSnSe5@Mo and spherical Cu3InSnSe5@Mo were used as counter electrodes, power conversion efficiencies of 5.8% and 5.9% were acquired, which validated the use of Cu3InSnSe5 nanocrystals as an efficient counter electrode material in DSSCs. In addition, the morphology of Cu3InSnSe5 nanoparticle has little effect on the power conversion efficiency of DSSCs devices. The power conversion efficiency of the DSSC devices was significantly enhanced to 7.6% and 6.5%, respectively, when Pt− Cu 3InSnSe5@Mo and Au−Cu 3InSnSe5@Mo counter electrodes were used. For comparison, power conversion efficiencies of 6.2% and 5.7% were acquired when Pt nanoseeds@Mo and Au nanoseeds@Mo counter electrodes were used. The construction of metal/semiconductor hybrid structure greatly enhanced JSC, which should be related to the improved rate of hole recovery at the electrode−electrolyte interface. The high JSC and FF values demonstrate that the construction of metal−semiconductor heterostructures reduces the internal resistances and thereby improve the conductivity and electrocatalytic activity.20,38 In addition, we monitored the variation of their PCE over time. In general, properties of the particles, stability and dispersion of nanocrystals-ink, and film quality all contribute greatly to the performance of DSSCs. We observed that the power conversion efficiencies of Au−Cu 3InSnSe5 and Cu3InSnSe5 materials remained at 5.0% and 4.4% after 20 days’ exposure to the air at room temperature, which is desired for counter electrode materials. In contrast, PCE of Pt−Cu 3InSnSe5 dropped quickly. This may be attributed to the difference in chemical properties of the nanoseeds, which affects the dispersity of the as-synthesized heterostructure nanoparticles. The poor dispersion of the nanocrystals in slurry led to the formation of less stable films, which deteriorates the lifespan of DSSC devices.

Figure 4. (a−c) TEM image and HRTEM image of Au−Cu3InSnSe5 heteronanostructured nanoparticles. (d) XRD pattern of Au− Cu3InSnSe5 heteronanostructured nanoparticles. Bottom red lines indicate the XRD peak positions of wurtzite Cu3InSnSe5, and blue lines correspond to cubic Au (JCPDS 04−0784). (e) EDS elemental mapping images of Au−Cu3InSnSe5 heteronanostructured nanoparticles.

tures in dye-sensitized solar cells, we deposited them on Mocoated glass followed by annealing at 400 °C for 1 h with nitrogen protection to evaluate their performance as counter electrode in DSSCs. The annealing temperature of 400 °C was determined by TGA and DSC (Figure S4). The results indicate that the organic ligand decomposed at about 200 °C and no phase transition of quaternary Cu3InSnSe5 nanoparticles occurred below 400 °C. We tested annealed samples by XRD and IR spectroscopy. As shown in Figure S5, XRD pattern of Cu3InSnSe5 nanoparticles after annealing demonstrate that the original crystal structure was retained. As shown in IR spectroscopy (Figure S6), sharp peaks near 2900 cm−1 attributed to C−H stretching vibration absorption and weak peaks near 1460 cm−1 ascribed to S-CH2 formation vibration absorption were apparent. After annealing, these two peaks disappeared because the annealing process removed the capping agents of 1-DT and OLA. DSSC devices were fabricated with different counter electrodes based on conventional Pt, net Mo-coated glass, and Mo-coated glass with thin films of Pt−Cu3InSnSe5, Au−Cu3InSnSe5, quasi-hexagon Cu3InSnSe5, spherical Cu3InSnSe5, Pt nanoseeds, and Au nanoseeds, respectively. In addition, we investigated the

■

CONCLUSIONS In summary, we introduced a colloidal synthesis of quaternary Cu3InSnSe5 nanoparticles. The synthetic parameters could be optimized to yield particles with controlled crystallographic and morphological characteristics. Such preparation strategy has also been validated to produce Pt−Cu3InSnSe5 and Au−Cu3InSnSe5 heteronanostructures through the seed growth approach. Such nanoparticles were transformed into counter electrode of DSSC devices in the form of thin films to test their power conversion efficiency. The Cu3InSnSe5 nanoparticle based DSSC device exhibited power conversion efficiency of 5.8%, which was improved to be 7.6% and 6.5% through the use of Pt-/Au− Cu3InSnSe5 heterostructured counterparts. All these values were comparative to that of the DSSC component with pure Pt madecounter electrode (7.9%). This study provides a new multiE

DOI: 10.1021/acsami.7b03117 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

Figure 5. XPS spectra of as-synthesized Cu3InSnSe5 nanoparticles and Pt/Au−Cu3InSnSe5 heteronanostructures: (a) Cu 2p, (b) In 3d, (c) Sn 3d, and (d) Se 3d core levels.

Figure 6. (a) J−V characteristics of DSSCs devices with counter electrodes made of conventional Pt, neat Mo-coated glass, and Mo-coated glass with Pt−Cu3InSnSe5, Au−Cu3InSnSe5, and Cu3InSnSe5 nanoparticle films, respectively. (b) Plots of PCE of DSSCs devices with counter electrodes made of Mo-coated glass with Pt−Cu3InSnSe5, Au−Cu3InSnSe5, and Cu3InSnSe5 nanoparticle films as a function of time, respectively.

Table 1. Photovoltaic Parameters of Dye-Sensitized Solar Cells with Counter Electrodes Made of Different Nanomaterialsa counter electrodes

VOC [V]

JSC [mA cm−2]

FF [%]

PCE [%]

Pt−Cu3InSnSe5 Au−Cu3InSnSe5 quasi-hexagon Cu3InSnSe5 spherical Cu3InSnSe5 Pt Pt nanoparticles Au nanoparticles

0.74 ± 0.02 0.71 ± 0.03 0.72 ± 0.02 0.74 ± 0.03 0.79 ± 0.02 0.75 ± 0.04 0.69 ± 0.02

17.64 ± 0.40 14.80 ± 0.54 13.51 ± 0.41 13.62 ± 0.45 13.76 ± 0.22 13.88 ± 0.52 12.40 ± 0.49

58.03 ± 0.06 61.99 ± 0.03 59.64 ± 0.04 59.32 ± 0.03 72.84 ± 0.02 59.06 ± 0.04 65.59 ± 0.04

7.59 ± 0.30 6.50 ± 0.32 5.84 ± 0.33 5.92 ± 0.35 7.88 ± 0.28 6.20 ± 0.40 5.66 ± 0.23

a

The device statistics were generated by testing independently fabricated devices (n = 3−4) made of each counter electrodes materials in different batches, and the same substrate was tested three times repeatedly.

F

DOI: 10.1021/acsami.7b03117 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

(7) Roy-Mayhew, J. D.; Bozym, D. J.; Punckt, C.; Aksay, I. A. Functionalized Graphene as a Catalytic Counter Electrode in Dyesensitized Solar Cells. ACS Nano 2010, 4, 6203−6211. (8) Chen, H.; Liu, T.; Ren, J.; He, H.; Cao, Y.; Wang, N.; Guo, Z. Synergistic Carbon Nanotube aerogel - Pt Nanocomposites toward Enhanced Energy Conversion in Dye-sensitized Solar Cells. J. Mater. Chem. A 2016, 4, 3238−3244. (9) Trevisan, R.; Döbbelin, M.; Boix, P. P.; Barea, E. M.; Tena-Zaera, R.; Mora-Seró, I.; Bisquert, J. PEDOT Nanotube Arrays as High Performing Counter Electrodes for Dye Sensitized Solar Cells. Study of the Interactions among Electrolytes and Counter Electrodes. Adv. Energy Mater. 2011, 1, 781−784. (10) Sun, W.; Peng, T.; Liu, Y.; Xu, S.; Yuan, J.; Guo, S.; Zhao, X.-Z. Hierarchically Porous Hybrids of Polyaniline Nanoparticles Anchored on Reduced Graphene Oxide Sheets as Counter Electrodes for Dyesensitized Solar Cells. J. Mater. Chem. A 2013, 1, 2762−2768. (11) Jiang, S.; Yin, X.; Zhang, J.; Zhu, X.; Li, J.; He, M. Vertical Ultrathin MoS2 Nanosheets on a Flexible Substrate as an Efficient Counter Electrode for Dye-sensitized Solar Cells. Nanoscale 2015, 7, 10459−10464. (12) Kim, J.; Jung, C. L.; Kim, M.; Kim, S.; Kang, Y.; Lee, H. S.; Park, J.; Jun, Y.; Kim, D. Electrocatalytic Activity of NiO on Silicon Nanowires with a Carbon Shell and its Application in Dye-sensitized Solar Cell Counter Electrodes. Nanoscale 2016, 8, 7761−7767. (13) Zhang, Z.; Zhang, X.; Xu, H.; Liu, Z.; Pang, S.; Zhou, X.; Dong, S.; Chen, X.; Cui, G. CuInS2 Nanocrystals/PEDOT: PSS Composite Counter Electrode for Dye-sensitized Solar Cells. ACS Appl. Mater. Interfaces 2012, 4, 6242−6246. (14) Luan, X.; Wang, Y. Plasmon-enhanced Performance of Dyesensitized Solar Cells Based on Electrodeposited Ag Nanoparticles. J. Mater. Sci. Technol. 2014, 30, 1−7. (15) Theerthagiri, J.; Senthil, R. A.; Buraidah, M. H.; Madhavan, J.; Arof, A. K. Synthesis of α-Mo2C by Carburization of α-MoO3 Nanowires and Its Electrocatalytic Activity towards Tri-iodide Reduction for Dye-Sensitized Solar Cells. J. Mater. Sci. Technol. 2016, 32, 1339−1344. (16) Kukunuri, S.; Karthick, S. N.; Sampath, S. Robust, Metallic Pd17Se15 and Pd7Se4 Phases from a Single Source Precursor and their Use as Counter Electrodes in Dye Sensitized Solar Cells. J. Mater. Chem. A 2015, 3, 17144−17153. (17) Wang, X.; Batter, B.; Xie, Y.; Pan, K.; Liao, Y.; Lv, C.; Li, M.; Sui, S.; Fu, H. Highly Crystalline, Small Sized, Monodisperse α-NiS Nanocrystal Ink as an Efficient Counter Electrode for Dye-sensitized Solar Cells. J. Mater. Chem. A 2015, 3, 15905−15912. (18) Chen, B.; Chang, S.; Li, D.; Chen, L.; Wang, Y.; Chen, T.; Zou, B.; Zhong, H.; Rogach, A. L. Template Synthesis of CuInS2 Nanocrystals from In2S3 Nanoplates and their Application as Counter Electrodes in Dye-sensitized Solar Cells. Chem. Mater. 2015, 27, 5949−5956. (19) Yi, L.; Liu, Y.; Yang, N.; Tang, Z.; Zhao, H.; Ma, G.; Su, Z.; 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. (20) Chen, S.-L.; Xu, A.-C.; Tao, J.; Tao, H.-J.; Shen, Y.-Z.; Zhu, L.-M.; Jiang, J.-J.; Wang, T.; Pan, L. In Situ Synthesis of Two-dimensional Leaflike Cu2ZnSnS4 Plate Arrays as a Pt-free Counter Electrode for Efficient Dye-sensitized Solar Cells. Green Chem. 2016, 18, 2793−2801. (21) Liu, M.; Li, G.; Chen, X. One-pot Controlled Synthesis of Sponge Like CuInS2 Microspheres for Efficient Counter Electrode with Graphene Assistance in Dye-sensitized Solar Cells. ACS Appl. Mater. Interfaces 2014, 6, 2604−2610. (22) Mali, S. S.; Patil, P. S.; Hong, C. K. Low-cost Electrospun Highly Crystalline Kesterite Cu2ZnSnS4 Nanofiber Counter Electrodes for Efficient Dye-sensitized Solar Cells. ACS Appl. Mater. Interfaces 2014, 6, 1688−1696. (23) Yao, R. Y.; Zhou, Z. J.; Hou, Z. L.; Wang, X.; Zhou, W. H.; Wu, S. X. Surfactant-free CuInS2 Nanocrystals: an Alternative Counterelectrode Material for Dye-sensitized Solar Cells. ACS Appl. Mater. Interfaces 2013, 5, 3143−3148.

component metal selenide and semiconductor heterostructured material with controls over crystal phase and morphology for future commercialization of DSSCs.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b03117. EDS spectrum, TGA, DSC of Cu3InSnSe5 nanoparticles; TEM and HRTEM images of spherical Cu3InSnSe5 nanoparticles; XPS spectra of Au 4f of Au−Cu3InSnSe5 heteronanostructure; XRD pattern of Cu3InSnSe5 nanoparticle; IR spectra of Cu3InSnSe5 nanoparticles; EDS spectrum of Pt−Cu3InSnSe5 heteronanostructured counter electrodes and Au−Cu3InSnSe5 heteronanostructured counter electrodes; J−V characteristics of DSSCs devices (PDF)

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Phone: +86-431 85168662. Fax: +86-431 85168662. *E-mail: [email protected]. ORCID

Zhan Shi: 0000-0001-9717-1487 Xiao-Bo Chen: 0000-0002-4508-5971 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the Natural Science Foundation of China (Grant Nos. 21621001 and 21371069), the National Key Research and Development Program of China (Grant No. 2016YFB0701100), and the S&T Development Program of Jilin Province of China (No. 20160101325JC). X.C. and Z.S. gratefully acknowledge the financial support from the Natural Science Foundation of China through Research Fund for International Young Scientists scheme (21550110190).

■

REFERENCES

(1) Briscoe, J.; Dunn, S. The Future of Using Earth-abundant Elements in Counter Electrodes for Dye-sensitized Solar Cells. Adv. Mater. 2016, 28, 3802−3813. (2) Ye, M.; Wen, X.; Wang, M.; Iocozzia, J.; Zhang, N.; Lin, C.; Lin, Z. Recent Advances in Dye-sensitized Solar Cells: from Photoanodes, Sensitizers and Electrolytes to Counter Electrodes. Mater. Today 2015, 18, 155−162. (3) Liu, Z.; Hu, Z.; Huang, H.; Zhang, Q.; Zhang, T.; Zhai, J.; Jiang, L. Heterogeneous 3-D Nanotubular Arrays of CdS-TiO2: Efficient Collections of Reflection Light for Enhanced Photoelectric Output. J. Mater. Chem. 2012, 22, 22120−22125. (4) Liu, J.; Liu, Z.; Zhang, T.; Zhai, J.; Jiang, L. Low-temperature Crystallization of Anodized TiO2 Nanotubes at the Solid-gas Interface and their Photoelectrochemical Properties. Nanoscale 2013, 5, 6139− 6144. (5) Huang, Y.; Cheng, K.; Liu, J.; Xue, M.; Kuang, Z.; Du, Z. Size Dependence of Photovoltaic Properties and Surface States Modulation in ZnO Nanowire/poly(3-hexylthiophene) Hybrid Nanostructures. Sci. Bull. 2016, 61, 245−251. (6) Xin, X.; He, M.; Han, W.; Jung, J.; Lin, Z. Low-cost Copper Zinc Tin Sulfide Counter Electrodes for High-efficiency Dye-sensitized Solar Cells. Angew. Chem., Int. Ed. 2011, 50, 11739−11742. G

DOI: 10.1021/acsami.7b03117 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces (24) Du, Y. F.; Fan, J. Q.; Zhou, W. H.; Zhou, Z. J.; Jiao, J.; Wu, S. X. One-step Synthesis of Stoichiometric Cu2ZnSnSe4 as Counter Electrode for Dye-sensitized Solar Cells. ACS Appl. Mater. Interfaces 2012, 4, 1796−1802. (25) Yu, X.; Shavel, A.; An, X.; Luo, Z.; Ibanez, M.; Cabot, A. Cu2ZnSnS4-Pt and Cu2ZnSnS4-Au Heterostructured Nanoparticles for Photocatalytic Water Splitting and Pollutant Degradation. J. Am. Chem. Soc. 2014, 136, 9236−9239. (26) Patra, B. K.; Guria, A. K.; Dutta, A.; Shit, A.; Pradhan, N. Au-SnS Hetero Nanostructures: Size of Au Matters. Chem. Mater. 2014, 26, 7194−7200. (27) Wang, W.; Ding, T.; Chen, G.; Zhang, L.; Yu, Y.; Yang, Q. Synthesis of Cu2SnSe3-Au Heteronanostructures with Optoelectronic and Photocatalytic Properties. Nanoscale 2015, 7, 15106−15110. (28) Ha, E.; Lee, L. Y.; Wang, J.; Li, F.; Wong, K. Y.; Tsang, S. C. Significant Enhancement in Photocatalytic Reduction of Water to Hydrogen by Au/Cu2ZnSnS4 Nanostructure. Adv. Mater. 2014, 26, 3496−3500. (29) Wang, P.; Minegishi, T.; Ma, G.; Takanabe, K.; Satou, Y.; Maekawa, S.; Kobori, Y.; Kubota, J.; Domen, K. Photoelectrochemical Conversion of Toluene to Methylcyclohexane as an Organic Hydride by Cu2ZnSnS4-based Photoelectrode Assemblies. J. Am. Chem. Soc. 2012, 134, 2469−2472. (30) Bai, T.; Xing, S.; Lou, Y.; Chen, C.; Huang, H.; Li, C.; Shi, Z.; Feng, S. Colloidal Synthesis of Quaternary Wurtzite Cu3AlSnS5 Nanocrystals and their Photoresponsive Properties. ChemPlusChem 2015, 80, 652−655. (31) Norako, M. E.; Greaney, M. J.; Brutchey, R. L. Synthesis and Characterization of Wurtzite-phase Copper Tin Selenide Nanocrystals. J. Am. Chem. Soc. 2012, 134, 23−26. (32) Fan, F.-J.; Wu, L.; Yu, S.-H. Energetic I-III-VI2 and I2-II-IV-VI4 Nanocrystals: Synthesis, Photovoltaic and Thermoelectric Applications. Energy Environ. Sci. 2014, 7, 190−208. (33) Batabyal, S. K.; Tian, L.; Venkatram, N.; Ji, W.; Vittal, J. J. PhaseSelective Synthesis of CuInS2 Nanocrystals. J. Phys. Chem. C 2009, 113, 15037−15042. (34) Fan, F.-J.; Wu, L.; Gong, M.; Chen, S. Y.; Liu, G. Y.; Yao, H.-B.; Liang, H.-W.; Wang, Y.-X.; Yu, S.-H. Linearly Arranged Polytypic CZTSSe Nanocrystals. Sci. Rep. 2012, 2, 952. (35) Du, J.; Du, Z.; Hu, J. S.; Pan, Z.; Shen, Q.; Sun, J.; Long, D.; Dong, H.; Sun, L.; Zhong, X.; Wan, L. J. Zn-Cu-In-Se Quantum Dot Solar Cells with a Certified Power Conversion Efficiency of 11.6%. J. Am. Chem. Soc. 2016, 138, 4201−4209. (36) Cheng, X.; Sun, S.; Chen, Y.; Gao, Y.; Ai, L.; Jia, T.; Li, F.; Wang, Y. A Water-soluble Metallophthalocyanine Derivative as a Cathode Interlayer for Highly Efficient Polymer Solar Cells. J. Mater. Chem. A 2014, 2, 12484−12491. (37) He, J.; Lee, L. T.; Yang, S.; Li, Q.; Xiao, X.; Chen, T. Printable Highly Catalytic Pt- and TCO-free Counter Electrode for Dyesensitized Solar Cells. ACS Appl. Mater. Interfaces 2014, 6, 2224−2229. (38) Kim, H. J.; Kim, S. W.; Gopi, C. V. V. M.; Kim, S. K.; Rao, S. S.; Jeong, M. S. Improved Performance of Quantum Dot-sensitized Solar Cells Adopting a Highly Efficient Cobalt Sulfide/nickel Sulfide Composite Thin Film Counter Electrode. J. Power Sources 2014, 268, 163−170.

H

DOI: 10.1021/acsami.7b03117 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX