Alloying of platinum and molybdenum for transparent counter electrodes. A strategy of enhancing power output for bifacial dye-sensitized solar cells

Abstract

Designing a cost-effective counter electrode (CE) with no sacrifice of photovoltaic performances and power output for a bifacial dye-sensitized solar cell (DSSC) is a persistent objective in photovoltaic power generation. We present here the fabrication of a novel transparent binary Pt-Mo alloy CE by an electrochemical strategy for bifacial DSSC application with an aim of bringing down the cost for solar-to-electric conversion. Electrochemical, and therefore photovoltaic performances, are optimized by adjusting stoichiometries of Pt-Mo alloys. Due to high charge-transfer ability, electrocatalytic activity, and optical transparency, maximum power conversion efficiencies of 6.75% and 2.89% are recorded under front and rear irradiation, respectively, which are comparable to 6.74% and 2.47% from a pristine Pt electrode-based solar cell. Due to the compensation effect of light from a transparent alloy CE to the incident light from the anode, the maximum power output of a solar cell has been markedly enhanced under simultaneous irradiation in comparison with either side. The enhanced efficiency along with enhanced power output, fast start-up, multiple start capability, simple preparation, and low Pt dosage highlights the potential application of these cost-effective transparent Pt-Mo alloy CEs in bifacial DSSCs.

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1. Introduction

Since the first prototype of a dye-sensitized solar cell (DSSC) created by Grätzel in 1991,¹ DSSC has attracted growing interest because it is considered as an electrochemical device with zero environmental emission, simple fabrication process, and scalable components.^2–6 A typical DSSC device comprises of a dye-sensitized TiO₂ anode, a Pt counter electrode (CE), and a liquid electrolyte containing I⁻/I₃⁻ redox couples. Although research on DSSC has continued for more than twenty years, it is still premature for its commercialization due to remaining problems which include leakage of liquid electrolyte, high expense of a Pt CE, etc. By addressing the issue of electrolyte leakage, we have imbibed the liquid electrolyte having I⁻/I₃⁻ redox couples into a three-dimensional framework of amphiphilic hydrogel matrices to form conducting gel electrolytes.⁷ With an aim of reducing CE cost, conducting polymers (PANi, PPy, etc.),⁸ carbonaceous materials (graphene, carbon nanotubes, etc.),⁹ or their composites¹⁰ have been widely utilized as CE candidates. In comparison to DSSC with a pristine Pt electrode, the expense has been markedly reduced and the photovoltaic performances have also been elevated after versatile avenues of modifications. Remaining problems are unsatisfactory stabilities and catalytic activities.

Alloy materials have been established as robust electrocatalyst candidates for energy conversion. More recently, we pioneerly reported the design of cost-effective binary alloy CEs by a mild solution strategy.^2a,11 A golden rule in fabricating such alloy CEs is to select a suitable transition metal having unfilled valence in a d orbital. The alloying of transition metals with other metallic or nonmetallic species can form coordinated intermediates, which is a prerequisite for robust CE materials. With further reducing the cost of solar-to-electric conversion, a class of metal selenide alloy CEs were synthesized by the same mild solution method.^2b,12 Except for rapid charge-transfer ability, high electrocatalytic activity, and cost-effectiveness, another superiority is their high optical transparencies in the visible-light region. Therefore, electricity-generation can be realized in the resultant DSSCs with transparent metal selenide alloy electrodes from both front (TiO₂ anode) and rear (transparent CE) sides. Although there are follow-up studies on bifacial DSSCs irradiated either from front or rear side,¹³ the dilemma in decreased electron distribution on a TiO₂ network, and therefore low maximum power output (P_max), remains unchanged.

In the search for a new class of low-Pt binary alloy CEs, we report here the synthesis of transparent Pt-Mo alloy CEs by an electrochemical method with an aim of elevating P_max of DSSC. To the best of our knowledge, there is no report on transparent Pt-Mo alloy CEs for bifacial DSSC applications. Incident light from the alloy CE is expected to compensate for the incident light from the anode, leading to an enhanced electron density on the conduction band (CB) of TiO₂ nanocrystallite and P_max of the DSSC. In the current work, we present the structural, electrochemical, and therefore preliminary photovoltaic characterizations of these Pt-Mo alloys and their DSSC devices.

2. Experimental

2.1 Preparation of binary Pt-Mo alloy CEs

The feasibility of this strategy was confirmed by following experimental procedures: cleaned FTO glass substrate (sheet resistance of 12 Ω sq⁻¹, purchased from Hartford Glass Co., USA) was immersed in a mixing aqueous solution consisting of 1 mM MoCl₅, 1 mM H₂PtCl₆, and 0.5 mM HCl aqueous solutions at a Mo/Pt (mol/mol) ratio of 1 : 1, 1 : 5, 1 : 10, 1 : 15, and 1 : 20. The total volume of mixed solution was 30 mL. The Pt-Mo alloy CEs were electrochemically co-deposited by a cyclic voltammetry method using a traditional three-electrode system: FTO glass was the working electrode, Pt foil was a counter electrode, and Ag/AgCl was a reference electrode. The scan started from −0.8 V to 0.8 V and back to −0.8 V for 10 cycles. The resultant Pt-Mo alloys synthesized at stoichiometric Pt/Mo ratio of Mo/Pt (mol/mol) ratio of 1 : 1, 1 : 5, 1 : 10, 1 : 15, and 1 : 20 were named PtMo, PtMo_0.2, PtMo_0.1, PtMo_0.067, PtMo_0.05, respectively. As a reference, pure Mo CE was also prepared according to the above approach with 30 mL MoCl₅ (1 mM) in 1 mM HCl aqueous solution. The catalyst thickness was controlled by confirming the deposition time. Measurement of the exact thickness of a catalyst layer was impossible for thin films on the very rough surface of FTO glass substrate.¹⁴ The planar Pt CEs were purchased from Dalian HepatChroma SolarTech Co., Ltd and used as a standard.

2.2 Assembly of DSSCs

A layer of TiO₂ nanocrystal anode film with a thickness of ∼10 μm was prepared by a sol-hydrothermal method.¹⁵ Resultant anodes were further sensitized by immersing into a 0.50 mM ethanol solution of N719 dye. The DSSC was fabricated by sandwiching redox electrolyte between a dye-sensitized TiO₂ anode and a CE. A redox electrolyte consisted of 100 mM of tetraethylammonium iodide, 100 mM of tetramethylammonium iodide, 100 mM of tetrabutylammonium iodide, 100 mM of NaI, 100 mM of KI, 100 mM of LiI, 50 mM of I₂, and 500 mM of 4-tert-butyl-pyridine in 50 mL acetonitrile. Surlyn film (30 μm) was utilized to seal the device through hot-pressing.

2.3 Electrochemical characterizations

Electrochemical performances were recorded on a conventional CHI660E setup comprised of an Ag/AgCl reference electrode, a CE of Pt sheet, and a working electrode of FTO glass supported Pt-Mo alloy. The CV curves were recorded in a supporting electrolyte consisting of 50 mM LiI, 10 mM I₂, and 500 mM LiClO₄ in acetonitrile. EIS measurements were also carried out in a frequency range of 2 × 10⁻² Hz to 1 × 10⁵ kHz and an ac amplitude of 10 mV at room temperature. Tafel polarization curves were recorded by assembling a symmetric dummy cell consisting of CE|redox electrolyte|CE.

2.4 Photovoltaic measurements

The photovoltaic test of the DSSC with an active area of 0.25 cm² was carried out by measuring the photocurrent–voltage (J–V) characteristic curves using a CHI660E Electrochemical Workstation under irradiation of a simulated solar light from a 100 W Xenon arc lamp (XQ-500 W) in ambient atmosphere. Incident light intensity was controlled at 100 mW cm⁻² (calibrated by a standard silicon solar cell). A black mask with an aperture area of around 0.25 cm² was applied on the surface of DSSCs to avoid stray light. Each J–V curve was measured for at least five times and a compromising curve was utilized.

2.5 Other characterizations

X-ray diffraction (XRD) profiles of the resultant alloys were recorded on an X-ray powder diffractometer (X'pert MPD Pro, Philips, Netherlands) with Cu Kα radiation (λ = 1.542 Å) in the 2θ range from 10 to 70° operating at 40 kV accelerating voltage and 40 mA current. Optical transmission spectra of resultant CEs were recorded on a UV-vis spectrophotometer at room temperature using pristine FTO glass as a baseline. Morphologies of the resultant PtMo alloy were observed with a scanning electron microscope (SEM, S4800). Compositions of the alloy CEs were detected by inductively coupled plasma-atomic emission spectra (ICP-AES).

3. Results and discussion

3.1 XRD analysis and morphology observation

The resultant CEs were subjected to X-ray diffraction (XRD) characterization, as shown in Fig. 1a. Two pronounced peaks at 2θ = 40.2° and 46.2° correspond to characteristic (111) and (200) planes of metallic Pt with a face centered cubic crystal structure. When increasing Pt/Mo stoichiometry from 1 : 1 to 1 : 0.05, the diffraction peak of Pt (111) shifts to higher angle positions (from 39.9° to 40.2°). To reveal how to alloy Pt with Mo, we compared the electronegativities and lattice constants of Mo and Pt; they are 2.16/3.15 Å for metallic Mo and 2.28/3.92 Å for metallic Pt. Therefore, an electron deviation from Mo to Pt occurs in the alloyed Pt-Mo, making the electron redistribution on the Pt surface and catalytic sites “hotter” in comparison with pristine Pt. However, the Mo atom having a lower lattice constant may enter the face centered cubic Pt lattice to tune the binding strength between Pt and I and to create more active sites for electrolyte adsorption. Some diffraction peaks corresponding to unreacted Pt, Mo, and FTO glass are also detected. Compositions of the Pt-Mo alloys on FTO glass substrates were determined by ICP-AES. The results show that the atomic ratios of PtMo, PtMo_0.2, PtMo_0.1, PtMo_0.067, and PtMo_0.05 are 1.000 : 1.016, 1.000 : 0.188, 1.000 : 0.094, 1.000 : 0.061, and 1.000 : 0.053, respectively. The measured atomic ratios are close to the stoichiometries of PtMo, PtMo_0.2, PtMo_0.1, PtMo_0.067, and PtMo_0.05; therefore, the chemical formulae of the alloy electrodes can be expressed according to their stoichiometric ratios. To realize the bifacial irradiation from both front and rear sides, high optical transparency is crucial in designing such peculiar bifacial DSSCs. The optical transmission spectra in Fig. 1b reveal high optical transparency (>80%) for the resultant alloy CEs in a wavelength range of 320–1100 nm. All the UV-vis spectra are obtained using bared FTO glass as a benchmark. As a reference, the standard Pt electrode has a transparency of only ∼60% due to a reflection function of the metallic surface. The high optical transparencies of resultant Pt-Mo alloy electrodes demonstrate that they are preferred for bifacial DSSCs.

Fig. 1 (a) XRD patterns and (b) optical transmission spectra of various alloys. The UV-vis spectra were obtained using bared FTO glass as a benchmark. The peaks marked by (*) correspond to FTO glass.

The SEM photograph in Fig. 2a suggests a high surface coverage and loading of PtMo alloy nanoparticles on FTO glass substrate. With alternation of Pt/Mo stoichiometry from 1 : 1 to 0.05 : 1 (Fig. 2a–e), the nanoparticle size gradually increases to around 200–300 nm. The large nanoparticle size for alloy material is expected to a give low specific surface area for I₃⁻ reduction. Additionally, the tiny cracks on the top surface of PtMo alloy electrode can also provide an elevated active area for electrolyte diffusion and redox reactions. From the energy-dispersive X-ray spectrum (EDS), as shown in Fig. 2f, Pt and Mo elements as well as the elements from FTO glass are detected, indicating that Pt and Mo have been successfully alloyed on the conductive glass substrate.

Fig. 2 Top-view SEM photographs of (a) PtMo, (b) PtMo_0.2, (c) PtMo_0.1, (d) PtMo_0.067, and (e) PtMo_0.05. (f) EDS spectrum of PtMo alloy.

3.2 Electrochemical behaviours

The CV curve has been widely utilized to evaluate electrocatalytic activity towards a liquid electrolyte having I⁻/I₃⁻ redox couples. The CV curves in Fig. 3a recorded at a scan rate of 50 mV s⁻¹ show two pairs of redox peaks corresponding to I⁻ ↔ I₃⁻ interconversion [Red₁ (I₃⁻ + 2e = 3I⁻)/Ox₁ (3I⁻ − 2e = I₃⁻); Red₂ (3I₂ + 2e = 2I₃⁻)/Ox₂ (2I₃⁻ − 2e = 3I₂)].¹⁶ The shapes and peak positions are similar to that from pristine Pt CE, indicating that the Pt-Mo alloy electrodes display electrocatalytic activities for a liquid electrolyte having I⁻/I₃⁻ redox couples. Since a typical CE will collect electrons from an external circuit and reduce I₃⁻ to I⁻ species, therefore the peak current density of Red₁ and peak-to-peak separation (E_pp) between Red₁ and Ox₁ can be employed to evaluate its catalytic activity. Apparently, the PtMo alloy electrode has comparable catalytic activity to pristine Pt. With increasing Mo dosage, the J_Red1 (a parameter of evaluating catalytic kinetics) decreases and E_pp (a standard of reflecting overpotential loss) elevates. After comprehensive evaluation, the catalysis follows an order of PtMo > Pt > PtMo_0.2 > PtMo_0.1 > PtMo_0.067 > PtMo_0.05. Additionally, the ratio of J_Ox1/|J_Red1| is another parameter of evaluating the reversibility of the redox reaction toward I⁻/I₃⁻ redox couples.¹⁷ The obtained values from pristine Pt (1.18) and PtMo alloy CEs are closer to 1.0 than other alloys, indicating a more reversible redox reaction for I₃⁻ ↔ I⁻. The result indicates the overpotential loss of the PtMo alloy electrode is lower than other CEs in a solar cell. Higher peak current density, lower E_pp, and good reversibility suggest that the PtMo alloy electrode presents high catalytic activity in the reduction of I₃⁻ ions, which is a paramount prerequisite for a robust CE in DSSC applications.¹⁸ From an outward extension of the peak positions in stacking CV curves of PtMo alloy electrodes and linear relationships between square roots of scan rates and peak current densities, as shown in Fig. 4, we can conclude the redox reaction is a diffusion-controlled mechanism on alloy CEs.¹⁹ In order to better estimate the catalytic activity of an alloy electrode, Bode EIS spectra recorded from the symmetric dummy cells are shown in Fig. 3b and the electron lifetimes (τ) are listed in Table 1. The function of an alloy CE is to collect electrons from an external circuit to an alloy/FTO interface and reduce I₃⁻ into I⁻ species (I₃⁻ + 2e = 3I⁻). Therefore, the lifetime of electrons at a CE can be utilized to assess the catalytic kinetics of an alloy electrode. As shown in Table 1, the τ values are calculated to be PtMo (149 μs) < Pt (238 μs) < PtMo_0.2 (293 μs) < PtMo_0.1 (430 μs) < PtMo_0.067 (526 μs) < PtMo_0.05 (610 μs). A lower τ value means that the electrons at the CE/electrolyte interface can rapidly participate in the reduction reaction of I₃⁻ + 2e = 3I⁻. In this fashion, the result from Bode EIS characterization is in an agreement with CV analysis.

Fig. 3 (a) CV curves of various CEs recorded at a scan rate of 50 mV s⁻¹; (b) Bode and (c) Nyquist EIS plots and (d) Tafel polarization curves for symmetric dummy cells fabricated by two identical CEs. The inset shows an equivalent circuit simulated by Z-view software. R_s: series resistance, R_ct: charge-transfer resistance, CPE: constant phase angle element, W: Nernst diffusion impedance.

Fig. 4 (a) CV curves of the PtMo alloy electrode in liquid electrolyte recorded at various scan rates. (b) Relationship between square root of scan rate and peak current densities.

Table 1 Electrochemical parameters extracted from CV curves and Bode EIS spectra

CEs	JRed1 (mA cm^−2)	Epp (V)	JOx1/|JRed1|	Dn (cm^−2 s^−1)	τ (μs)	Rct (Ω cm^2)	W (Ω cm^2)	Rs (Ω cm^2)
Pt	−5.56	0.51	1.18	1.05 × 10^−5	238	0.49	2.86	0.47
PtMo	−5.80	0.48	1.21	1.23 × 10^−5	149	0.28	1.72	0.43
PtMo0.2	−4.01	0.54	1.36	1.43 × 10^−6	293	0.84	3.12	0.65
PtMo0.1	−3.55	0.68	1.31	3.10 × 10^−6	430	0.98	3.86	0.77
PtMo0.067	−3.15	0.72	1.34	2.89 × 10^−6	526	1.07	4.81	0.79
PtMo0.05	−3.77	0.68	1.38	3.69 × 10^−6	610	1.78	4.91	0.82

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The charge-transfer resistance (R_ct) can be extracted from the EIS Nyquist plots for assessing the charge-transfer capabilities of alloy electrodes. Fig. 3c shows the impedance characteristics of various CEs and an equivalent circuit is depicted in the insert. There is an increasing tendency in R_ct values at elevated Mo dosage, indicating an enhanced resistance for charge transportation within alloy electrodes and therefore reduced catalytic activity. Tafel polarization curves in Fig. 3d can combine CV and EIS characterizations. The exchange current density (J₀) generated from the slopes for anodic or cathodic branches are in the order of PtMo > Pt > PtMo_0.2 > PtMo_0.1 > PtMo_0.067 > PtMo_0.05. J₀ is inversely proportional to R_ct:^10c J₀ = RT/nFR_ct, where R is the gas constant, T is absolute temperature, and F is Faraday's constant. Apparently, the calculated R_ct values from Tafel polarization curves match the order in EIS analysis. In addition, the limiting diffusion current density (J_lim) extracted from the intersection of the cathodic branch with the Y-axis is a parameter that depends on the diffusion coefficient (D_n) of I⁻/I₃⁻ of redox couples at the CE/electrolyte interface. J_lim is in proportion to D_n:²⁰ J_lim = 2nFCD_n/l, where l is the distance between electrodes in a symmetric dummy cell, n is the number of electrons involved in the reduction of I₃⁻, and C is the I₃⁻ concentration. Alternatively, the D_n can also be described by Randles–Sevcik theory:²¹ J_Red = Kn^1.5ACD_n^0.5v^0.5, where J_Red is the peak current density of Red₁, K is a constant, A is the active area of the dummy cell, and v is the scan rate for CV curves. Apparently, the D_n values from CV curves and Tafel polarization curves follow the same sequence.

3.3 Photovoltaic performances

Fig. 5a compares the J–V curves of solar cells with various CEs under front irradiation and the photovoltaic parameters are summarized in Table 2. Due to high catalytic activity and charge-transfer ability, the cell with the PtMo alloy CE yields a maximum front η of 6.75% (J_sc = 15.48 mA cm⁻², V_oc of 0.697 V, and FF of 62.6%) at simulated air mass 1.5 (AM1.5) global sunlight; this is comparable to the cell from pristine Pt (6.74%). In regard to high optical transparency in visible and near-infrared regions, simulated light can penetrate the rear side of DSSC devices and generate electricity. As shown in Fig. 5b, an optimal rear η of 2.89% was also recorded in the cell with the PtMo alloy electrode, which is higher than 2.47% from a pristine Pt-based cell and ∼2% for other DSSCs. Pristine Pt has a metallic luster and therefore the incident light can be reflected by luminous surfaces, leading to a low optimal transparency and dye excitation; this is supported by a lower rear J_sc in comparison with front ones.

Fig. 5 Characteristic J–V curves of bifacial DSSCs from varied CEs for (a) front, (b) rear, and (c) both irradiation under one sun illumination, and (d) in the dark.

Table 2 Photovoltaic parameters of DSSCs with varied CEs. V_oc: open-circuit voltage; J_sc: short-circuit current density, FF: fill factor; η: power conversion efficiency; P_max: maximum power output. For the simultaneous irradiation from both front and rear sides, the η and P_max are calculated using a P_in of 200 mW cm⁻², whereas they are obtained using a P_in of 100 mW cm⁻² at front or rear irradiation

CEs	Irradiation	η (%)	Voc (V)	Jsc (mA cm^−2)	FF (%)	Pmax (mW cm^−2)
PtMo	Both	4.05	0.707	18.05	63.4	8.09
	Front	6.75	0.697	15.48	62.6	6.75
	Rear	2.89	0.696	6.51	63.9	2.89
PtMo0.2	Both	3.82	0.692	18.84	58.5	7.63
	Front	6.35	0.714	12.57	70.7	6.35
	Rear	2.29	0.664	5.91	58.4	2.29
PtMo0.1	Both	3.68	0.703	16.43	63.7	7.36
	Front	6.11	0.730	11.87	70.5	6.11
	Rear	2.23	0.676	5.23	63.1	2.23
PtMo0.067	Both	3.56	0.703	15.61	64.8	7.11
	Front	5.74	0.725	12.36	64.1	5.74
	Rear	1.91	0.636	5.95	50.5	1.91
PtMo0.05	Both	3.43	0.736	15.15	61.4	6.85
	Front	5.58	0.732	11.11	68.6	5.58
	Rear	1.83	0.592	5.87	52.7	1.83
Pt	Both	4.03	0.726	16.31	68.1	8.06
	Front	6.74	0.696	15.47	62.6	6.74
	Rear	2.47	0.635	7.24	53.7	2.47

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All the V_oc values generated from front irradiation are higher than that from rear side. Fig. 6 represents the diagrammatic sketch for decreased incident light intensity and electron distribution on the TiO₂ anode, aiming to reveal the potential mechanism. Due to a step-wised decrease in light intensity within the TiO₂ film, the electron distribution generated from excited dyes is therefore also diminished. From this point of view, the electron recombination with I₃⁻ species (I₃⁻ + 2e_CB⁻(TiO₂) = 3I⁻) from front irradiation is retarded in comparison with rear irradiation. The maximum V_oc is determined by the difference between quasi Fermi energy of electrons in TiO₂ and redox potential energy of electrolyte,²² whereas the real V_oc of the DSSCs is smaller than this theoretical limit because of a backward reaction between photogenerated electron and I₃⁻ species.²³ Therefore, there is a low electron loss for front irradiation and a high V_oc.

Fig. 6 Schemes representing incident light evolution and electron density on the conduction band of TiO₂ with irradiation from (a) front, (b) rear, and (c) both. The incident light intensity is controlled at 100 mW cm⁻² (calibrated by a standard silicon solar cell) on either side.

When applied as windows, roof panels, or portable sources, the solar panels should be expected to have superiorities of fast start-up behavior, multiple start/stop capability, and photocurrent stability.²⁴ To evaluate these performances, we measured the start–stop switches by alternatively illuminating (100 mW cm⁻²) and darkening (0 mW cm⁻²) the DSSCs with PtMo and Pt CEs. As shown in Fig. 7a, the abrupt increase in current density under irradiation means a fast start-up on the solar cell; meanwhile, no delay in starting the cell suggests a high catalytic activity of the PtMo alloy toward redox couples. After six cycles, 93.96% of photocurrent density remained, signifying a high multiple start capability. Additionally, the photocurrent density stabilities of the solar cells with PtMo and pristine Pt CEs over 3000 s are shown in Fig. 7b; 88.5% of initial photocurrent density remained for the PtMo-based DSSC, whereas it was 93.8% for the Pt-based solar cell. These results demonstrate that the cell with the PtMo alloy electrode has comparable stability to that with a pristine Pt electrode under durative irradiation.

Fig. 7 (a) Start–stop plots with irradiation from the front side were achieved by alternately irradiating (100 mW cm⁻²) and darking (0 mW cm⁻²) the DSSC with PtMo alloy and Pt electrodes at an internal of 50 s and 0 V. (b) Photocurrent stabilities of the DSSC devices with PtMo and Pt electrodes under front irradiation.

4. Conclusions

In summary, transparent and cost-effective Pt-Mo binary alloys were fabricated by an electrochemical strategy free of any surfactant or template and were employed as CE materials in bifacial DSSCs. PtMo alloy CE displays higher electrocatalytic activity and lower charge-transfer resistance than other alloy electrodes, and has similar performances in comparison with a pristine Pt electrode. The DSSC employing a PtMo alloy CE displays front and rear efficiencies of 6.75% and 2.89%, respectively, similar to cell performances from the pristine Pt electrode. Additionally, the P_max has been markedly enhanced due to the compensation effect of incident light from the alloy electrode to the light from the anode. The merits on fast start-up, high multiple-start capability and good photocurrent stability also motivate the potential applications of such cost-effective Pt-Mo alloys in bifacial DSSCs.

Acknowledgements

The authors would like to acknowledge financial support from Fundamental Research Funds for the Central Universities (201313001, 201312005), Shandong Province Outstanding Youth Scientist Foundation Plan (BS2013CL015), Shandong Provincial Natural Science Foundation (ZR2011BQ017), and Research Project for the Application Foundation in Qingdao (13-4-198-jch).

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