MetalâOrganic Framework Derived Hierarchical Porous Anatase TiO2

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Metal–organic framework derived hierarchical porous anatase TiO2 as a photoanode for dye-sensitized solar cell Jie Dou, Yafeng Li, Fengyan Xie, Xiaokun Ding, and Mingdeng Wei Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.5b01003 • Publication Date (Web): 23 Nov 2015 Downloaded from http://pubs.acs.org on November 28, 2015

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Crystal Growth & Design

Metal–organic

framework

derived

hierarchical

porous anatase TiO2 as a photoanode for dyesensitized solar cell Jie Dou a, b, Yafeng Li a, b, *, Fengyan Xiea, b, Xiaokun Ding b, and Mingdeng Wei a, b, * a

State Key Laboratory of Photocatalysis on Energy and Environment, Fuzhou University,

Fuzhou, Fujian 350002, China. b

Institute of Advanced Energy Materials, Fuzhou University, Fuzhou, Fujian 350002, China.

E-mail: [email protected]; [email protected]. Fax/Tel.: +86-591-83753180. KEYWORDS: Metal–organic frameworks; MIL-125; Titanium dioxide; Dye-sensitized solar cells

ABSTRACT: Metal–organic frameworks (MOFs) have been generating a great deal of interest due to their high specific surface area, regular pore structure and adjustable aperture. However, only a few studies explored their application in the field of photovoltaic devices. In the present work, MIL-125(Ti), one kind of MOFs, was investigated as the precursor for TiO2 photoanode of dye-sensitized solar cells for the first time. Herein, pure anatase TiO2 with hierarchical structure was synthesized through the decomposition of MIL-125(Ti), which avoids the use of templates

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and fussy operation of sol-gel methods. The obtained TiO2 have a specific surface area of 147 m2g-1 and a mean pore size value of 10 nm. When used as photoanode material in dye-sensitized solar cells, the device gave rise to an overall energy conversion efficiency of 7.20%, which is better than the performance of P25 based photoanode.

1. Introduction

Dye-sensitized solar cells (DSCs) based on porous anatase TiO2 are regarded as a regenerative low-cost alternative to conventional devices. Currently, this kind of device reaches an efficiency exceeding 13%,1 offering a realistic option for converting light to clean energy in the future. As well known, DSCs were composed of photoanode, sensitizer, electrolyte and counter-electrode, and their performance was significantly influenced by the interaction among them. In the past decades, a great deal of attention has been paid to the development of new photoanodes with different nanostructures,2-5 new dyes with broad absorption spectra,2 new electrolytes with different redox composites3 and new counter-electrodes with a highly catalytic activity.4,5 Specifically, the photoanodes play the dual roles of adsorbing dyes and transporting electrons. Therefore, many efforts are devoted to the design and fabrication of semiconductors with favorable energy band structure. To date, a large number of oxides including ZnO,6 SnO2,7,8 Nb2O5,9 Zn2SnO410 and TiO211 have been applied in DSCs as the photoanodes, among them TiO2 with anatase phase exhibits the highest efficiencies.1 To fabricate DSCs with high photovoltaic performance, TiO2 photoanodes must have the following characteristics: (i) the material has a large surface area to adsorb sufficient dye, resulting in the generation of a high photocurrent density; (ii) the interconnected particles provide a pathway for the transport of electrons; (iii) the TiO2 nanoparticles have the favorable


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structure to allow the sufficient diffusion of electrolyte solution. Therefore, the high photovoltaic properties of DSCs could be achieved by the introduction of TiO2 with hierarchical or mesoporous nanostructure. For example, Kim et al. used the electrostatic spray technique to prepare the hierarchically structured TiO2 sphere.12 Wei et al. fabricated mesoporous TiO2 via template approach, which delivered an efficiency of 10%.13 Grätzel et al. prepared hierarchical TiO2 beads with high surface areas and controllable pore sizes via solvothermal method.14 However, the above approaches involve either the strict control over the samples or the use of template, which is unfavourable for the large scale production of DSCs and the reduction of fabrication cost. In the present work, hierarchical porous TiO2 was prepared via a facile approach, which used metal-organic frameworks (MOFs) as a precursor. MOFs are porous crystalline materials constructed by alternatively connecting metal-ion with organic linkers in a three dimensional space, and have attracted much attention in recent years due to their large surface area and tunable pore structure.15-22 The intriguing features of MOFs enable investigations in the fields of gas storage and separation,15-18 catalysis,19 sensor,20 drug delivery21,22 and so on. More recently, the exploration of MOFs has been extended into the energy related area, including lithium-ion batteries,23,24 supercapacitors,25-27 solar cells28,29 and photocatalytic water splitting.30,31 However, only a handful of investigations have explored MOFs in photovoltaic devices.32,33 For example, ZIF-8, as one kind of MOFs, was introduced into DSCs system as a coating layer on the surface of TiO2 photoanode in our previous work for the first time, and it was found that the charge recombination can be efficiently suppressed.34 Afterwards a new strategy was adopted for the interfacial modification using ZIF-8, which improved the short-circuit photocurrent and the open-circuit voltage in DSCs simultaneously.29 As an another illustration, the solar cell based on


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Al2(BDC)3 only gave rise to a short-circuit current of 23.35 µA/cm2.35 Structurally, MOFs possess the highly ordered porous structures with abundant organic ligands, which would be good candidates for use as a precursor to give highly porous carbon or oxide materials under proper thermolysis conditions.36 These results encouraged us to extend our studies to the synthesis of porous TiO2 derived from MOFs and its applications in DSCs. In the present work, MIL-125(Ti), a kind of MOFs, was utilized as a precursor for synthesizing hierarchical porous anatase TiO2 with a large surface area, which was then used as the photoanode of DSCs for the first time and exhibited an efficiency of 7.20%. 2. Experimental The synthesis and characterization of the samples The precursor MIL-125 (Ti) was obtained according to previously reported procedure [24]. In a typical process, 1.5g of 1,4-benzenedicarboxylic acid (Aldrich, 99%) and 0.78 mL of titanium isoproproxide (Ti(OiPr)4, Aldrich, 95%) were introduced into the mixture solution of N,Ndimethylmethanamide (DMF, Sinopharm, 99%) and methanol (Sinopharm, 99%) with a volume ratio of 9:1. The mixed solution with a total volume of around 30 mL was transferred into a 50 mL Teflon lined autoclave and was kept at 150 °C for 24 h. After cooled to room temperature, the precipitate was separated by centrifugation, and then washed by DMF and methanol for 2 and 1 time, respectively. For the preparation of porous anatase TiO2, the as-synthesized MIL-125(Ti) was heated to 380 °C at a speed of 5 °C min-1 and kept at 380 °C for 5 h in air. After cooled to room temperature, the white powder TiO2 was collected.


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The samples were characterized by scanning electron microscope (S4800 instrument), transmission electron microscope (TEM, FEI F20 S-TWIN instrument) and X-ray diffraction (Axios Petro, PANalytical, CoKα, λ=1.79021Å). DSSC fabrication and measurements Fabrication of the DSCs was executed by screen printing method on FTO (14 Ω/sq2, Nippon sheet glass) using the TiO2 powder with ethyl cellulose (10 wt%) and a solution compose of ethanol and α-terpineol (5 wt%), followed by calcination at 525 °C for 2 h. Before and after this step, the TiO2 electrode were dipped into a 50 mM aqueous TiCl4 solution at 70°C for 30 min and calcined at 450 °C for 30min. For the sensitization of TiO2 film, the electrode with an active area of 0.25 cm2 was immersed into a solution containing 0.5 mM N719 dye in isopropyl alcohol and acetonitrile (v/v=1:1) for 24 h. The Pt-coated FTO glass as a counter electrode was prepared by dropping H2PtCl6 (5 mM) solution on the FTO glass followed by heating at 400 °C for 20 min in air. To prevent the DSC from short-circuiting, the polyethylene spacer with a film thickness of 38 µm was placed between the working electrode and the counter electrode. The electrolyte composed of 0.6 M 1,2-dimethyl-3-n-propylimidazolium iodide, 0.1 M LiI, and 0.05 M I2 in acetonitrile with 0.5 M 4-tertbutylpyridine. The photovoltaic performance tests for DSCs were performed using a source meter (Keithley 2400). A PEC-L11 AM 1.5 solar simulator (Peccell, with a 100 W Xe lamp and an AM 1.5 filter) was used as the light source (100 mW cm-2).The spectra of IPCE were collected using a PEC-S20 (Peccell, Technology Co. Ltd.).The EIS experiments were measured in the dark using an electrochemical workstation (IM6, Zahner). The frequency range of EIS experiments was from 100 mHz to 1 MHz with an AC modulation signal of 10 mV and a bias DC voltage of -0.70


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V. The curves were fitted by the Zman software. UV-vis spectra were investigated using a Lambda-950(Perkin-Elmer). To compare the loading amount of dyes, the sensitized photoanode was immersed in the 0.1 M NaOH solution with water and ethanol (v/v =1/1) as solvents. The dyes could be desorbed from the TiO2 photoanode completely after immersion for about 1 h.The thickness of the film was determined using a Surfcom 130A (Tokyo Seimitsu). 3. The results and discussion Fig. 1 shows the XRD patterns of the as-prepared MIL-125(Ti) and hierarchically porous TiO2. As depicted in Fig. 1a, the XRD pattern of MIL-125(Ti) sample via a solvothermal method was in good agreement with the simulated one of MIL-125.37 Fig. 1b shows a typical XRD pattern of anatase TiO2 sample. The diffraction peaks at 25.28, 37.93, and 48.38 degree can be indexed to (101), (004) and (200) crystal planes of anatase TiO2, respectively. The pattern of Fig. 1b has no any peaks coming from MIL-125(Ti), indicating the successful and complete transformation of MIL-125 into anatase TiO2 aggregates due to its decomposition. The relatively low intensity of as-prepared TiO2 aggregates may be attributed to their small size, but it can also be caused by their weak crystallinity, which is unfavorable for the charge transport and collection. Herein, the crystallinity of thus fabricated TiO2 could be enhanced due to the following calcination in the process of photoanode preparation, which was beneficial for the charge harvesting. As a matter of fact, the charge collection efficiency of hierarchical porous TiO2 was better than that of P25, as can be found in the below discussion.


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Fig. 1 XRD patterns of (a) MIL-125(Ti) and (b) hierarchically porous TiO2.

The SEM images shown in Fig. 2 reveal the MIL-125(Ti) crystal is the well-defined truncated octahedron morphology. Fig. 2a shows the sample of MIL-125(Ti) with a whole size of about 5 µm. After calcination, the size of as-synthesized TiO2 crystal was reduced to around 2.7 µm as presented in Fig. 2b-c. The prepared TiO2 has been shrunken compared with MIL-125(Ti) due to the loss of H and C atoms during the calcinations process. The detailed morphology of the mesoporous nanocrystal TiO2 was observed by TEM measurement and was shown in Fig. 2d. As can be seen from Fig. 2c-d, hierarchically porous TiO2 octahedrons were formed due to the decomposition of MIL-125(Ti). It can also been found that the octahedrons were composed of nanocrystal TiO2, which has a size of about 10 nm. At the same time, a large number of pores could also be found, as depicted in Fig. 2d. The lattice fringe of 0.352 nm can be observed from Fig. 2e, which corresponds to (101) face of TiO2. Moreover, the selected-area electron diffraction (SAED) image delivered some typical crystal planes of anatase TiO2, which was in good agreement with XRD pattern of anatase TiO2, as discussed above.


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Fig. 2 (a) SEM image of as-synthesized MIL-125(Ti), (b) SEM, (c-d) TEM and (e) HRTEM images of hierarchically porous TiO2. (f) the corresponding SAED image.

To display the hierarchical structure of as-prepared TiO2 better, the size distribution of hierarchical porous TiO2 was shown in Fig. 3. The size distribution of MIL-125(Ti) were also shown in Fig. S1 for comparison. As depicted in Fig. 3, the average diameter of hierarchically porous TiO2 is about 2.6 µm. The particles with the size of 2.4-2.8 µm accounted for more than 50% of the total particles. Although the aggregates of as-prepared TiO2 seem to be larger than P25 (Fig. S2a), they composed TiO2 nanoparticles with small size. Hence, the as-prepared hierarchically porous TiO2 could have large active area and good adsorption ability to dyes.


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Fig. 3 (a) SEM image and (b) size distribution of hierarchically porous TiO2.

MIL-125(Ti) is constructed by Ti4+ ions and terephthalate (BDC) to form the 3D truncated octahedron morphology. By using it as precursor, hierarchically porous TiO2 could be synthesized due to the decomposition of MIL-125(Ti) and the combustion of organic ligand. Brunauer–Emmett–Teller (BET) specific surface area measurement was performed to investigate the pore structures of thus prepared TiO2, and the result was illustrated in Fig. 4. In the case of the hierarchically porous TiO2 sample, the specific surface area is 147 m2 g-1, which is larger than many reported results prepared by sol-gel and solvothermal methods12,13 and beneficial to the dye adsorption. The pore size distribution suggests that the obtained TiO2 has a mean pore size value of about 10 nm, which is consistent with the results of TEM measurement. However, the specific surface area of P25 is only 52 m2 g-1 in Fig. S2b. In the process of photoanode preparation, the specific surface area of TiO2 slightly decreased to 135 m2 g-1 due to higher calcination temperature, but it is still much larger than that of P25 (Fig. S3a). Hence, the large dye adsorption amount could be guaranteed. Moreover, the SEM image of TiO2 calcined at 525 o

C was also determined and shown in Fig. S3b. The average diameter of hierarchically porous

TiO2 and the morphology of TiO2 almost keep the same with the sample obtained at 380 oC.


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Hence, the higher calcination temperature in the process of photoanode preparation had little worse effect on the dye adsorption amount, but the crystallinity of TiO2 and thereby the charge harvesting ability could be greatly improved. Such a large BET surface area of hierarchical porous TiO2 should be inherited from the porous MIL-125(Ti) precursor. It needs to be mentioned that such mesoporous TiO2 is difficult to achieve through conventional methods without templates. For MIL-125(Ti), each Ti atom is surrounded by six O atoms forming octahedron clusters and the conversion to TiO2 does not need long-range atomic migration. The porous structure within MIL-125(Ti) can be kept inside porous TiO2 in some certain. However, it should be paid attention that the temperature of calcination is a key factor to control the porosity of the resulting TiO2. If the temperature is too low, MIL-125(Ti) could not transform completely into anatase TiO2 aggregates. For example, after oxidization at 370 oC, the peaks from MIL125(Ti) could still be observed in XRD pattern (Fig. S4a). If the temperature is too high, small particles will grow into big ones with reduced surface area (Fig. S4b) and pores will connect with each other to result in “dead pores”.24 Therefore, for the purpose of complete transformation and high amount of dye adsorption, the TiO2 was fabricated at 380 oC. The large specific surface area of as-prepared mesoporous TiO2 is helpful to the adsorption of dyes, and the widely used TiO2 P25 was chosen as a reference. To verify the advantage of hierarchical porous TiO2 in anchoring dyes, the N719 dyes were desorbed from the P25 and hierarchical porous TiO2 films and the results were shown in Fig. 4b. Comparing the hierarchical porous TiO2 film with P25, it was found that the surface concentration of adsorbed N719 dye increases from 2.37 × 10−7 to 3.26 ×10−7 mol cm-2 by 37% for the former. This might be attributed to the increased specific surface area. The increased dye adsorption will facilitate the light harvesting and thereby the performance of corresponding solar cells.


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Fig. 4 (a) N2 adsorption-desorption isotherms of hierarchically porous TiO2. Inset: Pore size distributions from the adsorption branch through the BJH method. (b) UV-vis absorption spectra of N719 dyes desorbed from the P25 and hierarchically porous TiO2 films.

The photovoltaic properties of mesoporous TiO2 were further investigated. Fig. 5a shows the photocurrent–voltage (I–V) curves of solar cells based on mesoporous TiO2 and P25 and the corresponding photovoltaic parameters were listed in Table 1. The optimum film thickness was found to be 27.1 µm in this system (Table S1). The result denoted that the photoanode of mesoporous TiO2 presented higher Jsc and higher energy conversion efficiency compared with P25. The enhanced Jsc and η could be attributed to the increased dye adsorption amount of mesoporous TiO2 photoanode as discussed above, which was beneficial for the absorption of incident light. The incident photo-to-electric conversion efficiency (IPCE) spectrum of hierarchical porous TiO2 and P25 were measured in the wavelength range from 300 to 800 nm. For mesoporous TiO2 photoanode, it had a maximum value of 58% at around 530 nm. As can be seen from Fig.5b, the mesoporous TiO2 prepared here showed much higher IPCE value than that of P25, which was consistent with the result of I-V measurements. As well known, the higher light harvesting


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efficiency ηlh could be enhanced by the increased dye amount.38,39 Therefore, the higher IPCE could also be ascribed to the improved dye adsorption amount of mesoporous TiO2 photoanode. Electrochemical impedance spectra (EIS) were shown in Fig.5c-d. An equivalent circuit (the inset in Fig. 5c) was given to fit the series resistance (Rs) and charge-transfer resistance (Rf and Rct). Resistance (Rs) is mainly related to resistance of the FTO glass substrate, contact resistance, counter electrode material and the resistance of external circuits. The semicircle in the high frequency region (Rf) related with the interfacial resistance of the Pt/FTO substrate and redox reaction of I-/I3- at the values related to the identical FTO substrate. The semicircle in the intermediate frequency semicircle (Rct) corresponded to the electron transfer at the TiO2/dye/electrolyte interface. It shows that the Rs and Rf of the two electrodes show no significant difference as presented in Table 1, but the fitting values of Rct corresponding to P25 and mesoporous TiO2 are 88.7 Ω and 73.6 Ω. This result also suggests that the charge transport in the latter is easier than the P25, which can qualitatively estimate that τd in DSCs is in the order of hierarchical P25 > TiO2. For DSCs, the electron lifetime (τn) could be expressed as follows: τn = 1 / 2πfmax, where fmax is the frequency at which the low frequency peak appears in the Bode plot.38 As shown in Fig. 5d, the fmax of the P25 and hierarchically porous TiO2 cells are 10.03 and 3.86 Hz, and the electron lifetime (τn) are estimated to be 15.9 and 41.2 ms, respectively. The longer electron lifetime means that the photo induced electron-hole recombination was effectively suppressed, which is also favorable for the performance improvement of DSCs based on hierarchically porous TiO2 photoanode. Charge collection efficiency (ηcc) can be estimated by comparing the charge transport and recombination time constants, and calculated by the expression: ηcc = 1-τd /τn, where τd is the electron transit time and τn is the electron lifetime. 40.41 Because τd of P25 is larger than that of hierarchical TiO2, and the former has a less τn,


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hierarchical TiO2 has the larger the charge collection efficiency (ηcc) than P25, which may also contributed to the better performance of the former.

Fig. 5 (a) I–V curves, (b) IPCE spectra, (c) Nyquist plots and (d) Bode phase plots of the DSCs based on hierarchically mesoporous TiO2 and P25 sensitized by N719. The inset in (c) is the equivalent circuit used for fit the impedance data. Table 1 Photovoltaic parameters of the DSCs based on the hierarchically TiO2 and P25. CE

Jsc (mA cm-2)

Voc (V)

Fill Factor

η (%)

Rs (Ω)

Rf (Ω)

Rct (Ω)

TiO2

13.99

0.768

0.67

7.20

15.53

7.5

73.6

P25

12.01

0.776

0.68

6.37

15.89

6.0

88.7

4. Conclusion


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In summary, a novel approach for the application of MOFs in the field of DSCs was proposed. The hierarchically porous TiO2 can be straightforwardly prepared through the calcination of highly porous MIL-125(Ti) in an air atmosphere, which delivered a larger BET surface area of 147 m2 g-1, and a pore size value of 10 nm. The cell made of hierarchically porous TiO2 showed a higher efficiency of 7.20% than that of P25, which may be ascribed to the enhanced dye adsorption, faster electron transport and better charge collection efficiency. This study shows an interesting example for the applications of MOFs in the field of the DSCs, and as-prepared porous TiO2 could be optimized for better device performance. ACKNOWLEDGMENT The authors gratefully acknowledge financial support from National Natural Science Foundation of China (91433104, 21303020), Research Fund for the Doctoral Program of Higher Education of China (20123514120004, 20133514110002), Independent Research Project of State Key Laboratory of Photocatalysis on Energy and Environment and Key Laboratory of Novel Thin Film Solar Cells, CAS. REFERENCES [1] S. Mathew, A. Yella, P. Gao, R. Humphry-Baker, B. Curchod, N. Ashari-Astani, I. Tavernelli, U. Rothlisberger, K. NazeeruddinMd and M. Grätzel, Nat. Chem., 2014, 6, 242-247. [2] A. Mishra, M. K. R. Fischer and P. Bäuerle, Angew. Chem. Int. Ed., 2009, 48, 2474-2499. [3] P. Wang, S. M. Zakeeruddin, J. E. Moser, M. K. Nazeeruddin, T. Sekiguchi and M. Grätzel, Nat. Mater., 2003, 2, 402-407. [4] Z. Huang, X. Liu, K. Li, D. Li, Y. Luo, H. Li, W. Song, L. Chen and Q. Meng, Electrochem. Commun., 2007, 9, 596-598.


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


[5] J.-H. Yum, E. Baranoff, S. Wenger, M. K. Nazeeruddin and M. Grätzel, Energy Environ. Sci., 2011, 4, 842-857. [6] Q. Zhang, C. S. Dandeneau, X. Zhou and G. Cao, Adv. Mater., 2009, 21, 4087-4108. [7] S. Gubbala, V. Chakrapani, V. Kumar and M. K. Sunkara, Adv. Funct. Mater., 2008, 18, 2411-2418. [8] H. J. Snaith and C. Ducati, Nano Lett., 2010, 10, 1259-1265. [9] J. Z. Ou, R. A. Rani, M.-H. Ham, M. R. Field, Y. Zhang, H. Zheng, P. Reece, S. Zhuiykov, S. Sriram, M. Bhaskaran, R. B. Kaner and K. Kalantar-zadeh, ACS Nano , 2012, 6, 4045-4053. [10] C. Chen, Y. Li, X. Sun, F. Xie and M. Wei, New J. Chem., 2014, 38, 4465. [11] S. Yang, Y. C. Zheng, Y. Hou, X. H. Yang and H. G. Yang, Phys. Chem. Chem. Phys., 2014, 16, 23038-23043. [12] D. Hwang, H. Lee, S. Y. Jang, S. M. Jo, D. Kim, Y. Seo and D. Y. Kim, ACS Appl. Mater. Interfaces, 2011, 3, 2719-2725. [13] M. Wei, Y. Konishi, H. Zhou, M. Yanagida, H. Sugihara, H. Arakawa, J. Mater. Chem., 2006, 16, 1287-1293. [14] F. Sauvage, D. Chen, P. Comte, F. Huang, L.-P. Heiniger, Y.-B. Cheng, R. A. Caruso and M. Grätzel, ACS Nano , 2010, 4, 4420-4425. [15] L. J. Murray, M. Dinca and J. R. Long, Chem. Soc. Rev., 2009, 38, 1294-1314. [16] T. A. Makal, J.-R. Li, W. Lu and H.-C. Zhou, Chem. Soc. Rev., 2012, 41, 7761-7779. [17] F. Pina, M. J. Melo, C. A. T. Laia, A. J. Parola and J. C. Lima, Chem. Soc. Rev., 2012, 41, 869-908. [18] P. Nugent, Y. Belmabkhout, S. D. Burd, A. J. Cairns, R. Luebke, K. Forrest, T. Pham, S. Ma, B. Space, L. Wojtas, M. Eddaoudi and M. J. Zaworotko, Nature , 2013, 495, 80-84.


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[19] J. Zhang, A. V. Biradar, S. Pramanik, T. J. Emge, T. Asefa and J. Li, Chem. Commun., 2012, 48, 6541-6543. [20] B. Liu, J. Mater. Chem., 2012, 22, 10094-10101. [21] P. Horcajada, T. Chalati, C. Serre, B. Gillet, C. Sebrie, T. Baati, J. F. Eubank, D. Heurtaux, P. Clayette, C. Kreuz, J.-S. Chang, Y. K. Hwang, V. Marsaud, P.-N. Bories, L. Cynober, S. Gil, G. Ferey, P. Couvreur and R. Gref, Nat. Mater., 2010, 9, 172-178. [22] J. Della Rocca, D. Liu and W. Lin, Accounts. Chem. Res., 2011, 44, 957-968. [23] H. B. Wu, S. Wei, L. Zhang, R. Xu, H. H. Hng and X. W. Lou, Chem.-Eur. J., 2013, 19, 10804-10808. [24] Z. Wang, X. Li, H. Xu, Y. Yang, Y. Cui, H. Pan, Z. Wang, B. Chen and G. Qian, J. Mater. Chem. A, 2014, 2, 12571. [25] B. Liu, H. Shioyama, H. Jiang, X. Zhang and Q. Xu, Carbon, 2010, 48, 456-463. [26] J. Yang, P. Xiong, C. Zheng, H. Qiu and M. Wei, J. Mater. Chem. A, 2014, 2, 16640-16644. [27] J. Yang, C. Zheng, P. Xiong, Y. Li and M. Wei, J. Mater. Chem. A, 2014, 2, 19005-19010. [28] Y. Li, C. Chen, X. Sun, J. Dou and M. Wei, Chem. Commun., 2014, 50, 9769-9772. [29] Y. Li, C. Chen, X. Sun, J. Dou and M. Wei, ChemSusChem., 2014, 7, 2469-2472. [30] C. Gomes Silva, I. Luz, F. X. Llabrés i Xamena, A. Corma and H. García, Chem.-Eur. J., 2010, 16, 11133-11138. [31] F. del Valle, A. Ishikawa, K. Domen, J. A. Villoria de la Mano, M. C. Sánchez-Sánchez, I. D. González, S. Herreras, N. Mota, M. E. Rivas, M. C. Álvarez Galván, J. L. G. Fierro and R. M. Navarro, Catal. Today, 2009, 143, 51-56. [32] S.-L. Li and Q. Xu, Energy. Environ. Sci., 2013, 6, 1656.


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[33] D. Y. Lee, C. Y. Shin, S. J. Yoon, H. Y. Lee, W. Lee, N. K. Shrestha, J. K. Lee and S. Han, Sci. Rep., 2014, 4, 3930 [34] Y. Li, A. Pang, C. Wang and M. Wei, J. Mater. Chem., 2011, 21, 17259. [35] H. A. Lopez, A. Dhakshinamoorthy, B. Ferrer, P. Atienzar, M. Alvaro and H. Garcia, J. Phys. Chem. C, 2011, 115, 22200-22206. [36] A. V. Vinogradov, H. Zaake-Hertling, E. Hey-Hawkins, A. V. Agafonov, G. A. Seisenbaeva, V. G. Kessler and V. V. Vinogradov, Chem. Commun., 2014, 50, 10210-10213. [37] M. Dan-Hardi, C. Serre, T. Frot, L. Rozes, G. Maurin, C. Sanchez and G. Ferey, J. Am. Chem. Soc., 2009, 131, 10857- 10859. [38] K. Zhu, N. R. Neale, A. Miedaner and A. J. Frank, Nano Lett.,2007, 7, 69–74. [39] Q. Wang, J.E. Moser and M. Grätzel, J. Phys. Chem. B, 2005, 109, 14945-14953 [40] G. Schlichthorl, N. G. Park and A. J. Frank, J. Phys. Chem. B,1999, 103, 782–791. [41] A. Hagfeldt, G. Boschloo, L. C. Sun, L. Kloo and H. Pettersson, Chem. Rev., 2010, 110, 6595–6663.


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For Table of Contents Use Only

Metal–organic framework derived hierarchical porous anatase TiO2 as a photoanode for dye-sensitized solar cell Jie Dou, Yafeng Li*, Fengyan Xie, Xiaokun Ding, and Mingdeng Wei* The hierarchical porous TiO2 was prepared through the decomposition of MIL-125(Ti) and exhibited much larger specific surface area than commercially available P25. When used as photoanode of dye-sensitized solar cells, thus prepared TiO2 yielded an energy conversion efficiency of 7.20%.


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MetalâOrganic Framework Derived Hierarchical Porous Anatase TiO2

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MetalâOrganic Framework Derived Hierarchical Porous Anatase TiO2