Porous Tin Oxide Nanosheets with Enhanced Conversion Efficiency

Article pubs.acs.org/JPCC

Porous Tin Oxide Nanosheets with Enhanced Conversion Efficiency as Dye-Sensitized Solar Cell Electrode Xiaoqian Xu,† Fangjian Qiao,‡ Liyun Dang,† Qingyi Lu,*,† and Feng Gao*,‡ †

State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute, Nanjing National Laboratory of Microstructures, and ‡Department of Materials Science and Engineering, Nanjing University, Nanjing 210093, People’s Republic of China S Supporting Information *

ABSTRACT: In this study, porous SnO2 nanosheets composed of SnO2 nanoparticles were prepared by calcining SnS2 nanosheets. The SnO2 nanoparticles have an average diameter of 15−20 nm and porous SnO2 nanosheets have a large specific surface area of 37.39 m2/g. As photoanodes, the dye-sensitized solar cell (DSSCs) based on porous SnO2 nanosheets show a superior power conversion efficiency of 0.562%, improved by 134.2% compared to pure SnO2 nanoplate (0.240%). The efficiency improvement could be attributed to the unique porous architecture, which provides efficient electron channels and excellent ability of light scattering.

1. INTRODUCTION Compared to nonrenewable energy sources relying on fossil fuels with limited reserves, solar energy has attracted great attention because of its cleanness and inexhaustibility.1,2 Solar cells are regarded as promising renewable energy sources as they can utilize sunlight as an unlimited energy source to convert to electricity. In consideration of low-cost and lowenergy consumption solar cells, dye-sensitized solar cells (DSSCs) are quite conspicuous, which meet future energy demands.3,4 Since Michael Grätzel made the big breakthrough on DSSC in 1991,5 enormous research interests have been focusing on developing DSSCs.6−11 Typically, DSSCs are composed of photoanode, electrolyte, and Pt counter electrode.12 Among them, photoanode is considered to be an important part of DSSCs, related to dye loading, light scattering, electron injection, transport and recombination, and have great effects on the power conversion efficiency.12 As a stable, n-type, and wide band gap semiconductor, TiO2 has been broadly investigated as photoanode for DSSCs based on its relevant band gap position and many successes have been accomplished. However, after intensive researches of the last two decades, DSSCs still suffer from relatively low conversion efficiencies.13,14 Semiconducting metal oxides including ZnO, SnO2, Nb2O5, and SrTiO3 were investigated as potential alternatives to TiO2 in DSSCs.15−17 Tin oxide (SnO2), a typical n-type semiconductor with a band gap of 3.8 eV, is one of the most important and extensively used metal oxide materials for conducting electrodes of solar cells due to its high visible optical transparent property.18 Compared to TiO2 photoanode, SnO2 displays higher electron mobility (∼100−200 cm2 V−1 S1−),19 suggesting a faster diffusion transport of photoinduced © 2014 American Chemical Society

electrons in SnO2 than in TiO2 and larger band gap (3.8 eV), creating fewer oxidative holes in the valence band to facilitate the long-term stability of DSSCs.16 However, SnO2-based DSSCs were developed with lower success, and the conversion efficiencies of SnO2 photoelectrodes reported so far are much less than those of TiO2,20 which makes it necessary to explore effective ways to improve the performances of SnO2 in DSSCs. Nanoparticles are considered to be promising to increase the energy conversion efficiency of DSSCs, since they have large specific surface areas which can not only provide active sites for the photochemical and electrochemical reactions, but have important effects on efficient charge transportation.21 However, although nanoparticles can provide high surface areas, they still have a key disadvantage that such nanoparticle-based cells exhibit poor interconnectivity between particles which leads to high recombination losses and low fill factor.22,23 Networks organized by nanoparticles would increase the interconnectivity and offer faster electron transport paths, enhance light scattering and facilitate infiltration of the electrolyte solution, which would be promising for DSSCs.12 In this study, porous SnO2 nanosheets were prepared by calcining SnS2 nanosheets. The obtained SnO2 nanosheets are composed of self-organized SnO2 nanoparticles. This self-organized structure as we called porous structure would not only provide large specific surface area but also exhibit good interconnectivity, which would benefit for enhancing the conversion efficiency of dye-sensitized Special Issue: Michael Grätzel Festschrift Received: January 13, 2014 Revised: May 12, 2014 Published: May 14, 2014 16856

dx.doi.org/10.1021/jp500364v | J. Phys. Chem. C 2014, 118, 16856−16862

The Journal of Physical Chemistry C

Article

and ground well in order to obtain a paste. FTO conducting glass was used as substrate after cleaned ultrasonically with acetone and alcohol. Then the paste was coated on FTO conducting glass plates by automatic film applicator coater (ZEHNTNER ZAA 2300) with a controllable thickness to obtain a thin film of SnO2. After drying in a temperature humidity chamber, the FTO glass was sintered at 400 °C for 30 min. The photoelectrodes were soaked in N719 dye solution (24.3 mg of N719 in 100 mL of ethanol) under a vacuum atmosphere for 12 h at room temperature and then washed with ethanol and dried in air. To prepare the counter electrode, a hole (0.8 mm in diameter) was drilled in the FTO glass. Then the FTO glass was cleaned ultrasonically by acetone and alcohol. After being dried in air, a Pt catalyst of about 3 nm in thickness was spattered on the FTO glass by a precision etching coating system (Model 682, Gatan). The dye adsorbed SnO2 electrode and Pt-counter electrode were assembled into a sandwich-type cell and sealed with a hot-melt film (ionomer Surlyn 1702, Dupont) of 60 μm in thickness.26 Then the electrolyte (0.1 M of LiI, 0.05 M of I2, 0.5 M of 4tertbutylpyridine in acetonitrile) was filled in and the hole was sealed using the hot-melt ionomer film made of Surlyn 1702 and a cover glass. 2.4. Characterizations. The crystal structures of the products were characterized by powder X-ray diffraction (XRD) using a Bruker D8 Advance diffractometer with Cu Kα radiation (scanning from 2θ = 10−70°). Scanning electron microscopy (SEM) characterizations were performed on Hitachi S-4800 scanning electron microscopy at 10 kV. Transmission electron microscopy (TEM), high-resolution TEM (HRTEM) images, and selected area electronic diffraction patterns were obtained using a JEOL JEM-2100 transmission electron microscope operating at 200 kV. UV−vis absorbance spectra were measured by a Shimadzu 3600 UV− vis spectrophotometer. Photocurrent−voltage characteristics of solar cells were measured using a voltage−current source monitor (Orzel Sol 3A Newport) under illumination by a Newport solar simulator (AM 1.5, 100 mW·cm−2) with a scan rate of 10 mV·s−1.

solar cells. By comparison of the porous SnO2 nanosheets and single-crystalline SnO2 nanoplates, the specific surface area of the porous SnO2 nanosheets is about five times of that of single-crystalline SnO2 nanosheet, which leads to 134.2% improvement of the conversion efficiency. On the other hand, by comparing the porous SnO2 nanosheets with dispersive nanoparticles of SnO2 with a high specific surface area of 161.84 m2/g, SnO2 nanosheets composed of selforganized nanoparticles also exhibit a higher conversion efficiency, which testifies the point of view that good connectivity between the nanoparticles is important in improving the conversion efficiency.

2. EXPERIMENTAL SECTION 2.1. Materials. FTO conducting glass, N719 dye (Dyesol), tin(IV) chloride pentahydrate, L-cysteine, tin(II) chloride dehydrate, sodium hydroxide, hydrochloric acid, urea, ethanol, isopropyl alcohol, acetic acid, and Triton X-100. All the reagents are of analytical grade and used without further purification. 2.2. Synthesis of Porous SnO2 Nanosheets. Porous SnO2 nanosheets were prepared by a precursor method with single crystalline SnS2 nanosheets as the precursor. The single crystalline SnS2 nanosheets were prepared through hydrothermal technique with L-cysteine as sulfur source and structure director.24 Typically, appropriate amounts of SnCl4·5H2O and L-cysteine were mixed in 40 mL of deionized water under magnetic stirring. After 5 min of stirring, the mixture was transferred to and sealed in a Teflon-lined autoclave (50 mL), kept at 180 °C for 8 h, and finally cooled to room temperature. The precipitate was collected by centrifugation (8000 rpm, 3 min), washed alternatively with deionized water and ethanol, and dried in air under ambient conditions. Then, the obtained precipitates were heated to 400 °C with a ramping rate of 5 °C/ min and kept at 400 °C for 3 h under air atmosphere. For comparison, we also prepared single-crystalline SnO2 nanosheets by a hydrothermal method. The single-crystalline SnO2 nanosheets were prepared as follows.25 First 1.35 g of SnCl2·2H2O was dissolved into 20 mL water under magnetic stirring. After 15 min of stirring, NaOH solution was dropwise added into SnCl2 solution until the pH value of the mixed solution reached 13. Then the resulting mixture was transferred into a 25 mL Teflon-lined stainless autoclave, sealed, maintained at 180 °C for 48 h, and cooled down to room temperature naturally. The obtained precipitates were centrifuged and washed with water and ethanol for several times until Cl ions could not be detected. Finally, the products were dried in air at 70 °C for 4 h. The SnO2 nanoparticles were also synthesized by a hydrothermal method.26 A total of 65.13 g SnCl4 was dissolved in a 1 M HCl solution, and then the solution was transferred to a 250 mL flask with 1 M HCl and homogenized. A total of 10 mL of the above SnCl4−HCl stock solution was transferred to a 25 mL Teflon container and a total of 1.8 g urea was added. After sealed, the autoclave was treated at 100 °C for 8 h. The products were collected by centrifugation and washed with water and ethanol each three times and dried at 70 °C. 2.3. Preparation of Electrode and Fabrication of DSSCs. The typical procedure of the paste making and DSSC assembling was followed to fabricate the SnO 2 nanostructure-based DSSCs. A total of 2.0 g SnO2 powders, two drops of Triton X-100, 0.05 mL of acetic acid, 1 mL of isopropyl alcohol, and 3.5 mL of deionized water were mixed

3. RESULTS AND DISCUSSION By reacting with O2, SnS2 can be transferred to SnO2 with the release of SO2 gas. The release of SO2 would leave pores in SnO2, as shown in Figure 1. In this study, SnS2 nanosheets were

Figure 1. Scheme of the synthesis process of the porous SnO2 nanosheets.

prepared by hydrothermally treating the mixed solution of SnCl4·5H2O and L-cysteine. Figure 2a displays a XRD pattern of the obtained product and the diffraction peaks are in good agreement with JCPDS Card No. 23-0677, indicating the formation of hexagonal SnS2. The SEM image of the obtained SnS2 is shown in Figure 2b, from which it can be seen that the 16857



Article

Figure 2. XRD pattern and SEM image of the precursor SnS2 nanosheets.

Figure 3. (a) XRD pattern; (b, c) SEM images; (d) TEM image; (e) HRTEM image; and (f) SAED pattern of the porous SnO2 nanosheets.

16858



Article

Figure 4. (a) XRD pattern; (b) SEM image; (c) TEM image, SAED pattern (inset c); and (d) HRTEM image of the single-crystalline SnO2 nanoplates.

SnO2 nanosheets are polycrystalline and sets of crystalline lattices can be observed. The interplane distances are calculated to be ∼0.264 nm, corresponding to that of (101) facet of rutile SnO2. Further evidence for the polycrystallinity of the SnO2 nanosheets can be obtained from SAED pattern of a single nanosheet (Figure 3f), in which the polycrystalline diffraction rings can be indexed (200), (101) and (211) planes of rutile SnO2 crystal. All the results confirm that after calcining SnS2 nanosheets, porous SnO2 nanosheets can be obtained and the obtained SnO2 nanosheets are porous and composed of SnO2 nanoparticles. These SnO2 nanoparticles connect to each other and form networks with a porous structure, which would result in high surface area and benefit the energy conversion as DSSC electrode. For comparison, single-crystalline SnO2 nanosheets were also prepared to be studied as DSSC electrode. Figure 4 presents XRD pattern and SEM, TEM, and HRTEM images, along with SAED pattern of the single-crystalline SnO2 nanosheets prepared by hydrothemal treatment of SnCl2·2H2O in alkali solution. XRD pattern in Figure 4a demonstrates the synthesis of rutile SnO2. By comparing the XRD patterns in Figures 3a and 4a, the diffraction peaks of single crystalline SnO2 nanosheets are relatively stronger and narrower than those of the porous SnO2 nanosheets, indicating porous SnO2 nanosheets have relatively smaller crystal size. Figure 4b−d displays SEM, TEM, and HRTEM images of single-crystalline SnO2 nanosheets. It can be seen that the sample is composed of 2D nanoplates with thickness of 50−200 nm and length of about 1 μm. SAED pattern in Figure 4c inset and HRTEM image in Figure 4d reveal the single-crystalline nature of the SnO2 nanoplates. Compared with porous SnO2 nanosheets, the

obtained SnS2 is composed of many sheet-like particles. The SnS2 nanosheets are several nanometers in thickness and with smooth surfaces. After calcining the SnS2 precursor in the air at 400 °C for 3 h, the SnS 2 nanosheets were transferred to porous SnO 2 nanosheets. The XRD pattern of the calcined product is shown in Figure 3a, in which all the diffraction peaks can be indexed to the tetragonal rutile structure of SnO2 with lattice constants of a, b = 4.738 Å and c = 3.187 Å, which match well with the reported values (JCPDS card, No. 41-1445). No impurity diffraction peaks can be observed in the XRD pattern, indicating the high purity of the final product and the complete transformation of SnS2 to SnO2. The XRD peaks are very broad, suggesting that the SnO2 nanocrystallites are in the range of the nanometer scale. The sheet-like morphology is maintained on a large scale, as evidenced by SEM image in Figure 3b. But unlike the precursor, these 2D nanosheets do not have smooth surfaces and are composed of a lot of nanoparticles. Figure 3c displays an SEM image with a higher magnification, confirming that the product is two-dimensional nanosheets with rough surfaces composed by SnO2 nanoparticles. The diameter of the SnO2 nanoparticles is about 20 nm. The nanoparticles connect to each other to form the selforganized SnO2 nanosheets and leave voids between them, as we call it self-organized porous structure. Figure 3d−f shows TEM and HRTEM images with SAED pattern of the porous SnO2 nanosheets. The TEM image shown in Figure 3d confirms the results obtained from SEM observations that the calcined product is nanosheets and the nanosheets are porous and composed of SnO2 nanoparticles with an average size of 20 nm. The HRTEM image (Figure 3e) illustrates that the porous 16859



Article

improvement could be attributed to the nanoparticle-assembled porous architecture, which provides a highly efficient electron channel and excellent ability of light scattering. The amounts of loaded dyes in porous SnO2 and dense SnO2 were compared by measuring elute dye concentration with UV−vis absorption spectroscopy. Interestingly, the amount of loaded dyes in dense SnO2 (2.179 × 10−7 mol·cm−2) is higher than that in the porous SnO2 (0.868 × 10−7 mol·cm−2), which further confirms that the self-organized network structure of porous SnO2 have play a decisive role in the conversion efficiency. In order to further confirm the advantage of the self-organized porous structures, we also synthesized SnO2 nanoparticles and used them as photoanode. The characterization results (TEM, Figure S2, SI) show that SnO2 particles are uniform with sizes smaller than 10 nm and have a high specific surface area of 161.84 m 2 /g, much higher than that of porous SnO 2 nanosheets. However, the conversion efficiency of the SnO2 nanoparticles is 0.414%, lower than that of the porous selforganized SnO2 nanosheets, proving our assumption that not only the large specific surface area but also the self-organized porous nanostructures will enhance the conversion efficiency of dye-sensitized solar cells. External quantum efficiency (EQE) is the ratio of the number of charge carriers of solar cell and photons of certain energy which are incident to the surface of solar cell from the outside. Figure 6a shows that the EQE% of solar cell based on porous SnO2 nanosheets is higher than that of single crystalline one, which could explain the higher convention efficiency of solar cell based on porous SnO2 nanosheets. UV−vis diffuse reflectance spectrum can evaluate the light scattering ability of a photoanode. Figure 6b shows the UV−vis diffuse reflectance spectra of the two photoanodes in the wavelength range of 300−800 nm without dye adsorption. The porous SnO2 nanosheets show an absorption edge at around 300 nm, slightly blue-shifted compared to single-crystalline SnO2 nanosheets that has an absorption edge at around 350 nm. The reflectance of the porous SnO2 nanosheets is higher than the single-crystalline SnO2 nanosheets throughout the visible range, revealing an improved light scattering ability of the porous SnO2 nanosheets. Therefore, the higher conversion efficiency and JSC of the porous SnO2 nanosheet photoanode compared with the single-crystalline SnO2 nanosheet photoanode may be attributed to the enhanced light scattering abilities, resulted from the porous structure.

surface of the SnO2 nanoplates is really smooth, which would result in smaller specific surface area than the porous SnO2 nanosheets. The BET surface areas of the porous and singlecrystalline SnO2 nanosheets and SnS2 nanosheets were studied by nitrogen adsorption−desorption measurements. The N2 physisorption isotherms and pore size distributions of both SnS2 and porous SnO2 nanosheets are presented in the Figure S1 (Supporting Information (SI)). The results show that the surface area of porous SnO2 nanosheets is 37.39 m2/g, which is about 5× that of single-crystalline SnO2 nanosheet (7.67 m2/g). The pore volumes of the porous SnO2 nanosheets, the singlecrystalline SnO2 nanoplates and SnS2 are 0.089, 0.030, and 0.055 cm3/g, respectively. The performances of porous and single-crystalline SnO2 nanosheets in DSSCs were both investigated in this study. The dye sensitization time was 6 h for all cells. The resulting DSSCs were characterized by measuring the current−voltage (I−V) behavior under AM1.5 simulated sunlight (100 mW/ cm2). The photocurrent density−voltage (J−V) characteristics of DSSCs based on porous and single-crystalline SnO2 nanosheets are shown in Figure 5 and the detailed photovoltaic

Figure 5. Photocurrent density−voltage curves of DSSCs based on (a) the porous SnO 2 nanosheets and (b) single-crystalline SnO 2 nanoplates.

parameters such as Voc, Jsc, η, and FF (fill factor) are summarized in Table 1. As the said, electron transport property Table 1. Detailed Photovoltaic Parameters (Voc, Jsc, FF, and η) of Dye-Sensitized Solar Cells with Different SnO2 Photoelectrodes cells porous SnO2 nanosheets single-crystalline SnO2 nanoplates SnO2 nanoparticles

Voc (mV)

Jsc (mA· cm−2)

FF

η%

417 348

2.35 1.93

57.25 35.75

0.562 0.240

414

1.97

50.61

0.414

4. CONCLUSIONS In summary, we have successfully prepared porous SnO2 nanosheets with high specific surface area through a precursor method with SnS2 nanosheets as precursor. By calcining SnS2 nanosheets, SnO2 nanosheets were obtained. The SnO2 nanosheets are composed of SnO2 nanoparticles with an average diameter of 20 nm, which interconnect to each other to form porous networks, resulting in a large specific surface area of 37.39 m2/g. As photoanodes, the DSSCs based on the porous SnO2 nanosheets show a superior power conversion efficiency of 0.562%, improved by 134.2% compared to pure SnO2 nanoplate. The efficiency improvement could be attributed to the unique porous architecture, which provides a highly efficient electron channel and excellent ability of light scattering.

makes difference to the convention efficiency.23 In our study, it clearly shows that the power convention efficiency of DSSC based on porous SnO2 nanosheets (0.562%) exhibits a significant enhancement compared to that of DSSC based on single-crystalline SnO2 nanosheets (0.240%), with the improvement of Voc (from 348 to 417 mV), FF (from 35.75 to 52.25), and Jsc (from 1.93 to 2.35 mA·cm−2). The efficiency 16860



Article

Figure 6. (a) EQE of DSSCs based on the porous SnO2 nanosheets and single-crystalline SnO2 nanosheets; (b) Diffuse reflectance spectra of the porous SnO2 nanosheets and single-crystalline SnO2 nanoplates.

■

Nanoporous SnO2 Layers for Dye-Sensitized Solar Cells. ACS Appl. Mater. Interfaces 2011, 3, 1485−1491. (9) Magne, C.; Moehl, T.; Urien, M.; Grätzel, M.; Pauporté, T. Effects of ZnO Film Growth Route and Nanostructured on Electron Transport and Recombination in Dye-Sensitized Solar Cells. J. Mater. Chem. A 2013, 1, 2079−2088. (10) Zhang, Q. F.; Chou, T. P.; Russo, B.; Jenekhe, S. A.; Cao, G. Z. Aggregation of ZnO Nanocrystallites for High Conversion Efficiency in Dye-Sensitized Solar Cells. Angew. Chem., Int. Ed. 2008, 47, 2402− 2406. (11) Chen, J.; Lu, L.; Wang, W. Zn2SnO4 Nanowires as Photoanode for Dye-Sensitized Solar Cells and the Improvement on Open-Circuit Voltage. J. Phys. Chem. C 2012, 116, 10841−10847. (12) Li, K. N.; Wang, Y. F.; Xu, Y. F.; Chen, H. Y.; Su, C. Y.; Kuang, D. B. Macroporous SnO2 Synthesized via a Template-Assisted Reflux Process for Efficient Dye-Sensitized Solar Cells. ACS Appl. Mater. Interfaces 2013, 5, 5105−5111. (13) Pagliaro, M.; Palmisano, G.; Ciriminna, R.; Loddo, V. Nanochemistry Aspects of Titania in Dye-Sensitized Solar Cells. Energy Environ. Sci. 2009, 2, 838−844. (14) Grätzel, M. Corrigendum to “Conversion of Sunlight to Electric Power by Nanocrystalline Dye-Sensitized Solar Cells. J. Photochem. Photobiol. 2004, 164, 3−14. (15) Law, M.; Greene, L. E.; Johnson, J. C.; Saykally, R.; Yang, P. Nanowire Dye-Sensitized Solar Cells. Nat. Mater. 2005, 4, 455−459. (16) Qian, J.; Liu, P.; Xiao, Y.; Jiang, Y.; Cao, Y.; Ai, X.; Yang, H. TiO2-Coated Multilayered SnO2 Hollow Microspheres for DyeSensitized Solar Cells. Adv. Mater. 2009, 21, 3663−3667. (17) Ramasamy, E.; Lee, J. Ordered Mesoporous SnO2-Based Photoanodes for High-Performance Dye-Sensitized Solar Cells. J. Phys. Chem. C 2010, 114, 22032−22037. (18) Sahana, M. B.; Sudakar, C.; Dixita, A.; Thakur, J. S.; Naik, R.; Naik, V. M. Quantum Confinement Effects and Band Gap Engineering of SnO2 Nanocrystals in a MgO Matrix. Acta Mater. 2012, 60, 1072− 1078. (19) Zukalová, M.; Zukal, A.; Kavan, L.; Nazeeruddin, M. K.; Liska, P.; Grätzel, M. Organized Mesoporous TiO2 Films Exhibiting Greatly Enhanced Performance in Dye-Sensitized Solar Cells. Nano Lett. 2005, 5, 1789−1792. (20) Prasittichai, C.; Hupp, J. T. Surface Modification of SnO2 Photoelectrodes in Dye-Sensitized Solar Cells:Significant Improvements in Photovoltage via Al2O3 Atomic Layer Deposition. J. Phys. Chem. Lett. 2010, 1, 1611−1615. (21) Birkel, A.; Lee, Y. G.; Koll, D.; Van Meerbeek, X.; Frank, S.; Choi, M. J.; Kang, Y. S.; Char, K.; Tremel, W. Highly Efficient and Stable Dye-Sensitized Solar Cells Based on SnO2 Nanocrystals Prepared by Microwave-Assisted Synthesis. Energy Environ. Sci. 2012, 5, 5392−5400.

ASSOCIATED CONTENT

S Supporting Information *

N2 physisorption isotherms and pore size distributions of both SnS2 and porous SnO2 nanosheets; TEM image of SnO2 nanoparticles. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work is supported by the National Basic Research Program of China (Grant No. 2013CB922102) and the National Natural Science Foundation of China (Grant Nos. 21071076, 51172106, and 21021062).

■

REFERENCES

(1) Winter, M.; Brodd, R. J. What Are Batteries, Fuel Cells, and Supercapacitors? Chem. Rev. 2004, 104, 4245−4269. (2) Chen, D. H.; Huang, F. Z.; Cheng, Y. B.; Caruso, R. A. Mesoporous Anatase TiO2 Beads with High Surface Areas and Controllable Pore Sizes: A Superior Candidate for High-Performance Dye-Sensitized Solar Cells. Adv. Mater. 2009, 21, 2206−2210. (3) Xu, F.; Sun, L. T. Solution-derived ZnO nanostructures for photoanodes of dye-sensitized solar cells. Energy Environ. Sci. 2011, 4, 818−841. (4) Snaith, H. J.; Ducati, C. SnO2-Based Dye-Sensitized Hybrid Solar Cells Exhibiting Near Unity Absorbed Photon-to-Electron Conversion Efficiency. Nano Lett. 2010, 10, 1259−1265. (5) O’ Regan, B.; Grätzel, M. A Low-Cost, High-Efficiency Solar Cell Based on Dye-Sensitized Colloidal TiO2 Films. Nature 1991, 353, 737−740. (6) Yella, A.; Lee, H. W.; Taso, H. N.; Yi, C.; Chandiran, A. K.; Nazeeruddin, M. K.; Diau, E. W. G.; Yeh, C. Y.; Zakeeruddin, S. M.; Grätzel, M. Porphyrin-Sensitized Solar Cells with Cobalt (II/III)Based Redox Electrolyte Exceed 12% Efficiency. Science 2011, 334, 629−634. (7) Sauvage, F.; Di Fonzo, F.; Bassi, A. L.; Casari, C. S.; Russo, V.; Divitini, G.; Ducati, C.; Bottani, C. E.; Comte, P.; Grätzel, M. Hierarchical TiO2 Photoanode for Dye-Sensitized Solar Cells. Nano Lett. 2010, 10, 2562−2567. (8) Teddy, Z.; Uddin, T.; Nicolas, Y.; Olivier, C.; Toupance, T.; Labrugère, C.; Hirsch, L. Low-Temperature UV Processing of 16861



Article

(22) Gubbala, S.; Chakrapani, V.; Kumar, V.; Sunkara, M. K. BandEdge Engineered Hybrid Structured for Dye-Sensitized Solar Cells Based on SnO2 Nanowires. Adv. Funct. Mater. 2008, 18, 2411−2418. (23) Zhu, K.; Neale, N. R.; Miedaner, A.; Frank, A. J. Enhanced Charge-Collection Efficiencies and Light Scattering in Dye-Sensitized Solar Cells Using Oriented TiO2 Nanotubes Arrays. Nano Lett. 2007, 7, 69−74. (24) Ma, L.; Li, H.; Chang, K.; Li, H.; Chen, W. X. Synthesis of SnS2 Nanosheets and Their Electrochemical Performances Used as Anode Materials of Li-Ion Battery. J. Zhejiang Univ. Eng. Sci. 2011, 45, 354− 357. (25) Li, Y.; Guo, Y. Q.; Tan, R. Q.; Cui, P.; Li, Y.; Song, W. J. Synthesis of SnO2 Nano-Sheets by a Template-Free Hydrothermal Method. Mater. Lett. 2009, 63, 2085−2088. (26) Krishna, M.; Komarneni, S. Conventional- vs MicrowaveHydrothermal Synthesis of Tin Oxide Nanoparticles. Ceram. Int. 2009, 35, 3375−3379.

16862


Porous Tin Oxide Nanosheets with Enhanced Conversion Efficiency

Recommend Documents