Remarkable enhancement in the photoelectric performance of uniform

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Remarkable enhancement in the photoelectric performance of uniform flowerlike mesoporous Fe3O4 wrapped in nitrogen-doped graphene networks Jixin Yao, Kang Zhang, Wen Wang, Xueqin Zuo, Qun Yang, Huaibao Tang, Mingzai Wu, and Guang Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b01240 • Publication Date (Web): 18 May 2018 Downloaded from http://pubs.acs.org on May 19, 2018

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ACS Applied Materials & Interfaces

Remarkable enhancement in the photoelectric performance of uniform flower-like mesoporous Fe3O4 wrapped in nitrogen-doped graphene networks

Jixin Yaoa, Kang Zhanga, Wen Wanga, Xueqin Zuoa, Qun Yanga, Huaibao Tanga b, Mingzai Wua b, Guang Lia b∗

a

School of Physics and Materials Science, Anhui University, Hefei 230601, China

b

Anhui Key Laboratory of Information Materials and Devices, Hefei 230601, China

Abstract The porous structure and excellent specific surface area are superior for use as a counter electrode (CE) material. In addition, N-doped graphene possesses a remarkable electron-transfer pathway and many active sites. Therefore, a novel idea is to wrap uniform flower-like mesoporous Fe3O4 (Fe3O4UFM) in a N-doped graphene (N-RGO) network structure to enhance the power conversion efficiency (PCE). The hybrid materials of Fe3O4UFM@N-RGO are first used as a CE in dye-sensitized solar cells (DSSCs), showing a preeminent conductive interconnected 3D porous structure with more catalytic activity sites and a better ability for and a faster reaction rate of charge transfer, resulting in quicker reduction of than Pt. A 9.26% photoelectric conversion efficiency has been achieved for the DSSCs with Fe3O4UFM@N-RGO as the CE, which is beyond the value of Pt (7.72%). The positive synergetic effect between Fe3O4 and N-RGO is mainly responsible for the remarkable photoelectric property enhancement of this uniform flower-like mesoporous Fe3O4 wrapped in N-doped

graphene

networks,

as demonstrated

by

the

Tafel

polarization,

electrochemical impedance spectra (EIS), and CV curves. These methods will provide a simple way to effectively reproduce CE materials. KEYWORDS: Fe3O4UFM@N-RGO, photoelectric performance, Electrochemistry, Counter electrode, DSSCs

∗Corresponding author. Tel: (+86) 0551 63861867, Fax: (+86) 0551 63861992 e-mail address: [email protected] (G. Li), [email protected]

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1. Introduction Energy is an important foundation for economic development and improvement of human living standards. Traditional fossil-fuel based energy is continuing to run out of sources, and the existing energy structure has a great impact on the climate, environment, and human health. Changing the existing energy structure and developing sustainable, clean energy have become the main concerns of all countries in the world.1-3 Solar energy is the most plentiful, renewable and clean energy resource with great application in energy conversion into electricity. Great attention has been paid to DSSCs due to their simple structure, easy assembly, low cost of production, high power conversion efficiency (PCE), and short-term period.4-8 In general, DSSC devices are made up of three parts: porous titanium dioxide (TiO2) sensitized by dye, a photocathode (CE), and a redox mediator (e.g., iodide electrolyte).9-12 As the significant component of DSSCs, the CE plays two main functions: one is to collect external circuit electrons, while the other is to catalyze the reduction of oxidation-reduction couples / .3 Pt is recognized as an optimal counter electrode due to its excellent electrocatalytic performance.13, 14 However, Pt is very expensive due to its scarce resource reserve. For CE materials, the high price is not suitable for mass production and commercial application of DSSCs. Pt is also subject to corrosiveness in iodine solution to form PtI4 and H2PtI6. Iron (Fe) is one of the rich elements in the world, and Fe3O4 has been widely prepared and studied in ORR and supercapacitors. 15, 16 However, the PCE obtained with Fe3O4 as the CE in DSSCs is not ideal.17 In addition, Fe3O4 is vulnerable to corrosion by the electrolyte in DSSCs, which leads to the gradual attenuation of catalytic activity. How to maintain a stable catalytic activity is an urgent issue. As we know, carbon materials,18,

19

polymer conductive materials,20,

21

and inorganic materials22-24 are

frequently used in ORR, lithium ion batteries, and electrocatalysis. Many kinds of carbon materials exist, e.g., graphene,25,

26

carbon nanotubes,18,

27-30

and carbon

black.31 Especially, graphene has a high surface area, excellent stabilization, and noble electrical conductivity for electron transfer.32-34 However, its reduction catalytic activities are not as good as those of Pt, and this is another issue worth solving. ACS Paragon Plus Environment

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Herein, we report a new strategy for controlled growth of a composite material based on Fe3O4. Uniform flower-like mesoporous Fe3O4 (Fe3O4UFM) was wrapped in a N-doped graphene network structure to form an Fe3O4UFM@N-RGO composite. Fe3O4UFM ensures the interconnected porous channels, providing many short-distance diffusion paths for electrolyte ions in diverse directions, which would produce good performance. The PCE of a cell with Fe3O4UFM as the CE reaches 8.16%, much better than the value for Pt (7.72%). Once RGO is successfully introduced to wrap Fe3O4UFM, it can further improve the electronic migration due to its special layer structure. Meanwhile, the photoelectric conversion performance should be further improved. Our results showed that the cell with Fe3O4UFM@RGO as the CE displayed fairly high PCE (8.64%). Moreover, doping RGO with heteroatoms can introduce more catalytic active sites, such as N-doped RGO.10 The cell with Fe3O4UFM@N-RGO as the CE reaches a high PCE (9.26%), much higher than that for Pt-based cells (7.72%). Recently, the PCE of cells increased up to 13% due to advances in the design of dyes and electrolytes.35-37 It is worth noting here that we only focus on the strategy and building of CEs, while the photoanode, dyes, and electrolytes used in this work are available on the market. As far as we know, this is the first attempt to put Fe3O4UFM@N-RGO composites into application in DSSCs as a CE.

2. Experimental 2.1. Preparation of Fe3O4UFM Fe3O4 flower-like spheres were produced through a simple hydrothermal method. Under magnetic stirring, ferric chloride (FeCl3⋅6H2O, 1.6 g) and urea (0.6 g) were slowly poured into 80 mL of ethylene glycol. A total of 1 g of C7H5NaO3 was then put into the solution, and strong magnetic stirring was maintained for 1 h. Later, the homogeneous mixed solution was transferred to domestic Teflon-lined stainless-steel autoclaves. The autoclaves were maintained at 200 °C for 16 h. The Fe3O4UFM precursor was then obtained, washed with water four times, and later dried in a vacuum oven at 60 °C for 12 h. The powders were then burned at 600 °C for 1 h in Ar ACS Paragon Plus Environment


gas to form Fe3O4UFM. 2.2. Synthesis of Fe3O4UFM@RGO and Fe3O4UFM@N-RGO hybrids The impressive synthetic routes for Fe3O4UFM@RGO and Fe3O4UFM@N-RGO are presented in Scheme 1. The synthesis route of Fe3O4UFM@RGO is introduced in Scheme 1A. Graphene oxide (GO) nanosheets were produced by an improved Hummers procedure.38 Briefly, Fe3O4UFM precursor (0.1 g) was gently poured into a homogeneous GO solution (30 mL, 0.03 g), and ultrasound was applied for 60 min to obtain a well-distributed mixture. CTAB was then added into this homogeneous mixture using magnetic stirring for 24 h. Subsequently, the sample was collected by high-speed centrifugation and freeze dried to make the sample loose and delicate. Finally, the samples were annealed at 600 °C in an Ar atmosphere to form Fe3O4UFM@RGO. The synthesis of Fe3O4UFM@N-RGO is shown in Scheme 1B. Pure Fe3O4UFM was poured into GO solution. Then, NaOH was added to this solution step-by-step until pH=12. The solution was heated to 85 °C in a water bath, and 1.5 mL of hydrazine hydrate was poured into the solution and constantly stirred to form a black color solution. After being rapidly stirred for 8 h, the solution was cooled to 27 °C. A black sample was gathered with centrifugation and washed with water and acetone three times. Then, the sample was dried under vacuum at 100 °C for 12 h to obtain the Fe3O4UFM@N-RGO composite powder.

3. Results and discussion 3.1 Composition and morphology analysis The crystal phases, compositions, and crystallographic structures of the corresponding samples were examined by X-ray photoelectron spectroscopy (XPS) X-ray diffraction (XRD), and Raman spectroscopy. XRD patterns of all samples are displayed in Fig. 1a. The typical Fe3O4UFM diffraction peaks are similar to those of Fe3O4UFM@RGO or Fe3O4UFM@N-RGO and can be assigned to the (111), (220), (311), (222), (440), (422), (511), (440), and (642) crystal planes of Fe3O4 (JCPDS card, file no. 89-4319).39 Compared with those of Fe3O4UFM, it can be clearly found that the peaks of Fe3O4UFM in the two composites are weak, suggesting that the ACS Paragon Plus Environment

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formation of the RGO layer weakens the intensity of the peaks.40 Although there is no obvious

difference

in

XRD

patterns

between

Fe3O4UFM@RGO

and

Fe3O4UFM@N-RGO, the existence of N can be further mirrored in the Raman and XPS detections. In Fig. 1b, for the pristine Fe3O4UFM@RGO, a strong graphitic G band appears at approximately 1580 cm-1, and a relatively weak D band at 1350 cm-1 is observed. In contrast, the D band of N-RGO at 1350 cm-1 is significantly stronger than the G band, indicating that more defects have been generated.41 The chemical composition of Fe3O4UFM@N-RGO is further examined by the XPS test. As shown in Fig. 1c, the typical signals of carbon, oxygen, nitrogen and iron elements are found. Fig. 1d demonstrates that C=C peaks dominate at 284.7 eV, C-N/C-H at 285.3 eV, C-O at 286.5 eV, and C=O at 287.5 eV.42 The main peaks of Fig. 1e corresponding to Fe 2p3/2 and Fe 2p1/2 are located at 711.5 eV and 725.6 eV, while the Fe 2p3/2 peak of Fe3+ centers at 713.1 eV, and that of Fe2+ locates at 711.3 eV.43 Lastly, in Fig. 1f, N functionalities are divided into four types that are discovered in the powders of Fe3O4UFM@N-RGO, which can be assigned to pyridinic N, pyrrolic N, graphitic N, and oxidized N; the four major peaks are at 398.7 eV, 399.6 eV, 401.2 eV, and 403.5 eV, respectively. The heteroatom (N) could provide further defects to modify the surface electronic structure of RGO so that the corresponding conductivity is enhanced. Therefore, it can speed up the reduction of ,44 which will be further confirmed by electrochemical research. The evolutions of N adsorption and desorption of Fe3O4UFM, Fe3O4UFM@RGO and Fe3O4UFM@N-RGO are displayed in Fig. 1(g-i). The specific surface area of Fe3O4UFM@N-RGO is approximately 88 m2⋅g−1 according to BET, which is similar to that of Fe3O4UFM@RGO but higher than that of Fe3O4UFM (65 m2⋅g−1). The pore size distributions were estimated via BJH, and the corresponding plots were inserted in Fig. 1(g-i). The pore size distribution of each sample is approximately 13.64 nm, 16.86 nm, and 16.33 nm. The flexible porous architecture with flower-like spheres can potentially be used as a CE because the large pore volume allows penetration of / and the higher surface area can produce higher dispersion of iodide ions and effectively promote electronic transport. ACS Paragon Plus Environment


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The evolvement of morphologies and microstructures with/without N-RGO wrapping can be clearly identified via electron microscopy image observations. As shown in Fig. 2 and Fig. 3, the N-RGO wrapping does not destroy the primary flower-like spherical architectures of Fe3O4 particles. The pores are mainly in the macropore size range. Mesopores may be determined by BET characterization. Therefore, Fe3O4UFM@N-RGO has hierarchical structures, which will also accelerate the electrolyte diffusion and penetration. According to the TEM images in Fig. 2(c and d) and Fig. 3(c and d), Fe3O4 flower-like spheres are made of very thin flakes. Furthermore, it is worth noting that the Fe3O4 spherical flowers are uniformly surrounded by flexible and thin N-RGO sheets, leading to the dual-structure interconnected frameworks, which are presented in Fig. 3(a and b) and Fig. S5. Fe3O4UFM is wrapped by N-RGO to form a Fe3O4UFM@N-RGO composite, which is further verified by TEM and consistent with the above SEM results. It is clearly observed that the Fe3O4 spherical flower is hollow with a large specific surface area; see Fig. 2(c and d), Fig. 3(c and d). Such a multipurpose porous architecture flower-like sphere with a great surface area is beneficial for DSSCs when it is used as a CE because it ensures rapid diffusion of , as the interrelated porous networks with diverse orientations in the three-dimensional structure offer many diffusion routes for electrolyte ions. 3.2 Electrochemical performances For DSSCs, the catalytic activity of all equipped CEs and Pt are initially evaluated using CV measurements to verify an excellent CE that displays extraordinary catalytic activity of / .45,46 The working diagram is shown in Fig. 4a. The measurements were executed in a 3-electrode system with a step of 25 mV⋅s-1. It is worth mentioning that all CV curves (Fig. 4b) exhibit 2 pairs of oxidation and reduction peaks, corresponding to Ox1/Red1 and Ox2/Red2. The catalytic reactions for / can be disclosed by the two couples of oxidation and reduction peaks according to Eqs. 3 and 4: +2 =3

(3)

3 +2 =2 .

(4)


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Generally, the peaks of Ox1 and Red1 occur in response to the redox reaction of / , which is far more important than Ox2 and Red2 relating to the oxidation and reduction of / on the CE surface. The catalytic behaviors of Fe3O4UFM, Fe3O4UFM@RGO, Fe3O4UFM@N-RGO and Pt CEs are assessed via the two important parameters of the gap between peaks (Epp) and the peak current density. A shorter distance between the Ox1 and Red1 peaks, specified as Epp, suggests higher catalytic activities for CEs. The Epp of 0.20 V for Fe3O4UFM@N-RGO is smaller in comparison with that of Pt, 0.35 V, indicating that the smaller value of Epp gave rise to the more reversible redox reaction for / and the electrochemical polarization,47 and all CV curves are shown in Fig. 4c. The parameter Epp for each CE is listed in Table 1. It can be clearly noted that the peak current density of Fe3O4UFM@N-RGO related to the reduction reaction for to is greater than that of Pt, signifying an excellent catalytic activity for . Meanwhile, the CV curves of RGO and N-RGO at the same scan rate are shown in Fig. S7. A schematic structure of a symmetric cell assembled by two identical electrodes is shown in Fig 5a, which is widely used for EIS and testing the Tafel polarization. To further assess the catalytic performance for / transfer on the electrode surface, Tafel polarization curves based on all samples and Pt are recorded and shown in Fig. 5b. Tafel curves of RGO and N-RGO are also tested and displayed in Fig. S8. Under normal conditions, the Tafel curve includes three regions: the polarization area, the Tafel area, and the diffusion area. 48-51 In theory, the catalytic activity of all CEs in reduction can be evaluated using the Tafel and diffusion zones, from which the corresponding exchange current density (J0) and the limiting diffusion current density (Jlim) can be obtained. The slope of the cathode branch can be assessed in the Tafel zone. J0 can be clearly attained by the deduction of the Tafel curves, and it reflects the catalytic activity between the counter electrode materials and electrolytes.52-54 Meanwhile, Jlim is another key parameter for evaluating DSSCs’ efficiency.55, 56 J0 and Jlim can be obtained according to Eqs. 5 and 6 and are listed in Table 1.

=


(5)


=

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(6)

In Eq. 5, R is the gas constant, T is temperature, F represents the Faraday constant, and n represents the number of electrons exchanged in the reaction at the interface of the CE and the electrolyte. In Eq. 6, e is electronic charge, C is the concentration of triiodide, D is the diffusion coefficient of triiodide, NA represents Avogadro’s constant, and l represents the electrode spacing. 57 EIS is also executed via two identical CEs (CE/electrolyte/CE, also termed a symmetric cell). The corresponding equivalent circuits of the Nyquist diagrams are shown in Fig. 5c. EIS results an effectively show the electronic conductivity and the interfacial charge transfer situation. The results for RGO and N-RGO as a comparison are presented in Fig. S9. It is worth noting that there are two semicircles in the picture, in which the equivalent series resistance (Rs) is mirrored in the intercept of the real axis. The charge transfer resistance (Rct) is specified as the left semicircle (the high frequency region), disclosing the catalysis of at the electrode/electrolyte interface and the related constant phase element (CPE). Moreover, the Nernst diffusion impedance (ZN) is reflected in the right semicircle (low frequency region) in the Nyquist diagram to assess the oxidation-reduction reaction and coupled transport in the electrolyte.58 The corresponding equivalent circuit is exhibited in Fig. 5c. The parameters for Rs and Rct are recorded in Table 1. The smallest value of Rct for Fe3O4UFM@N-RGO is approximately 0.19 Ω, much less than those of Pt (0.51 Ω), Fe3O4UFM@RGO (0.21 Ω) and Fe3O4UFM (0.31 Ω). The lowest Rct is closely related to the quickest charge transfer, indicating that the electro-catalytic activity area of the CE can be increased as well as revealing that more additional active sites were obtained through the introduction of N. The fine contact between electrodes and electrolytes is very valuable, leading to useful and fast charge transfer.59,60 Impactful reduction of to can expedite the regeneration of anodized dyes, resulting in an enhancement of the photocurrent density (Jsc). Moreover, the relatively smaller Rct could produce lower series resistance, contributing to the rise of energy conversion efficiency via the enhancement of the fill factor in DSSCs.61


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A schematic diagram of the working principle of the complete battery is presented in Fig. 6a. The explanation of the working principle is introduced in supporting information Fig. S10(a and b) in detail. To verify the outstanding photovoltaic property of Fe3O4UFM@N-RGO as a CE in a whole cell, J–V curves of the cell equipped with the as-prepared CEs, irradiated at AM 1.5 (100 mW⋅cm-2), are recorded and displayed in Fig. 6b and 6c. RGO and N-RGO are used as CEs, shown in Fig. S10c. The full parameters of the J–V curves are listed in Table 2. It is noteworthy that the cell equipped with Fe3O4UFM@N-RGO achieves a high PCE (9.26%), which is much greater than the values for Fe3O4UFM and Fe3O4UFM@RGO and even much beyond that for Pt (7.72%). This result is due to the fact that the Fe3O4UFM@N-RGO composites achieve 17.5 mA⋅cm-2 for Jsc, 0.795 V for Voc, and 66.64% for FF. The high efficiency can be ascribed to the 3D flower-like nanostructures that are encapsulated by N-graphene and have a larger surface area and more surface reaction sites. Thus, the combination of Fe3O4UFM and N-RGO generates a positive synergistic effect. The electrochemical stability of Fe3O4UFM@N-RGO is presented in Fig. S11 at the same scanning rate of 25 mV/s. It is clear that the electrochemical stability of Fe3O4UFM@N-RGO is almost the same as that of N-RGO after 25 cycles of scanning, as shown in Fig. S11(b and c). However, the photovoltaic performance of N-RGO as a CE is not as good as that of Fe3O4UFM@N-RGO. Fe3O4 and Pt CEs are also presented in the Supporting Information, shown in Fig. S11(a and d). From the perspectives of charge resistance, catalytic activity, photovoltaic performance, and electrochemical stability, Fe3O4UFM@N-RGO is the best choice among them. Therefore, Fe3O4UFM@N-RGO has the potential to replace conventional Pt CEs in DSSCs. The above results demonstrate the improvement of the PCE performance of CEs from Fe3O4UFM to Fe3O4UFM@N-RGO. The gradual enrichment of performance may be ascribed to several reasons. An analytical diagram of the counter electrode material performance is plotted in Fig. 7. Importantly, Fe3O4 has a hollow structure and a large number of pores in the surface, which increases the contact area between ACS Paragon Plus Environment


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Fe3O4 and the electrolyte. With the shortening of the diffusion lengths for charges and ions, the catalytic availability is improved as well. Then, RGO is introduced to improve the exchange current between Fe3O4 and the electrolyte, speeding up the charge transfer at the CE/electrolyte interface. Additionally, heteroatom (nitrogen) doping has been shown to improve conductivity and interface hydrophilicity, thereby promoting the charge transfer and the interaction of electrodes and electrolytes and even promoting electrocatalytic activity.62, 63

4. Conclusions In summary, nanocomposites of Fe3O4UFM@N-RGO are designed by using delicate nitrogen from hydrazine hydrate to embellish RGO as an electrocatalyst for a triiodide reduction reaction. Depending on the three-dimensional structure of Fe3O4, N-RGO convolves Fe3O4UFM to form a double construction of metallic oxide and modified carbon material. This study provides new insight into Fe3O4-based electrocatalysts by studying the composition dependency of their electrocatalytic property. The findings highlight the significance of controlling the surface properties of combined metal oxide and N-doped RGO-based electrocatalysts and call attention to an approach for improving the interaction at the surface of electrolytes and CEs, which can assist the strategy for and building of CE material 5. ASSOCIATED CONTENT Supporting Information SEM images of non-porous globular flowers and porous globular flowers of Fe3O4; SEM images of the Fe3O4 UFM precursor and Fe3O4UFM@RGO; TEM images of Fe3O4UFM@N-RGO; Composition analysis of RGO and N-RGO; Determination of electrochemical

parameters;

Consecutive

25

CV

for

Fe3O4,

N-RGO,

Fe3O4UFM@N-RGO and Pt. 6. Acknowledgments We acknowledge the financial support for this work from the National Key R&D Program of China (2017YFA0403503), National Natural Science Foundation of China (11674001), Anhui Provincial Natural Science Foundation (1708085MA07, ACS Paragon Plus Environment

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1708085QE116), Science Foundation of Anhui Education (No. KJ2013A030), Doctoral research start-up funds projects of Anhui University (J01003206), and Opening Project of the State Key Laboratory of High Performance Ceramics and Superfine Microstructure (SKL201607SIC).



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Scheme 1. Schematic A shows the fabrication of the Fe3O4UFM@RGO composite. Schematic B is the synthetic route for Fe3O4UFM@N-RGO hybrid architecture.



Fig 1. (a) XRD patterns of Fe3O4UFM, Fe3O4UFM@RGO and Fe3O4UFM@N-RGO. (b) Raman spectra of Fe3O4UFM, Fe3O4UFM@RGO, and Fe3O4UFM@N-RGO. (c) Wide XPS spectra of Fe3O4UFM@N-RGO. (d) C1s spectra. (e) Fe 2p spectra. (f) N1s spectra for Fe3O4UFM@N-RGO. (g-i) N2 adsorption-desorption isotherms and corresponding pore size distribution of Fe3O4UFM, Fe3O4UFM@RGO, and Fe3O4UFM@N-RGO.


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Fig 2. SEM (a and b) and TEM (c and d) micrographs of Fe3O4UFM.



Fig 3. SEM (a and b) and TEM (c and d) micrographs of Fe3O4UFM@N-RGO


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Fig 4. (a) Schematic diagram of I2 in Fe3O4UFM@N-RGO adsorption, dissociation, and desorption during CV measurement. (b) Cyclic voltammograms of the Pt, Fe3O4UFM,

Fe3O4UFM@RGO, and Fe3O4UFM@N-RGO nanostructures for the redox of / species. (c) Cyclic voltammograms of Epp for all samples and Pt.



Fig 5. (a) Schematic structure of a symmetric cell used for the measurement of Tafel polarization and EIS. (b) Tafel polarization curves of the Pt thin film and Pt, Fe3O4UFM, Fe3O4UFM@RGO, and Fe3O4UFM@N-RGO nanostructures. (c) Nyquist plots of DSSCs using Pt thin film, Fe3O4UFM, Fe3O4UFM@RGO, and Fe3O4UFM@N-RGO as the CE.


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Fig 6. (a) Schematic structure of a DSSC using Fe3O4UFM@N-RGO as the CE to form a full cell. (b) J−V curves of DSSCs with different CEs. (c) PCE for all samples and Pt.



Fig 7. Analytical diagram of the counter electrode material performance


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Table 1. EIS and Tafel curve results for DSSCs based on Fe3O4UFM, Fe3O4UFM@RGO, Fe3O4UFM@N-RGO, and Pt CEs in the same environment.

CEs

Rs (Ω⋅cm2 )

Rct (Ω⋅cm2 )

lgJ0 lgJlim -2 (mA⋅cm ) (mA⋅cm-2)

Fe3O4UFM

7.52±0.01

0.31±0.01

0.57±0.01

1.49±0.01

0.29±0.01

Fe3O4UFM@RGO

6.06±0.01

0.21±0.01

0.64±0.01

1.58±0.01

0.27±0.01

Fe3O4UFM@N-RGO

5.43±0.01

0.19±0.01

0.73±0.01

1.69±0.01

0.19±0.01

Pt

6.02±0.01

0.51±0.01

0.55±0.01

1.46±0.01

0.34±0.01


EPP (V)


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Table 2. Photovoltaic parameters for DSSCs based on testing of different CEs in the same environment

CEs

JSC (mA⋅cm-2 )

VOC (V)

FF (%)

PEC (%)

Fe3O4UFM

15.4

0.775

68.37

8.16%

Fe3O4UFM@RGO

16.6

0.775

67.16

8.64%

Fe3O4UFM@N-RGO

17.4

0.795

66.95

9.26%

Pt

15.2

0.760

66.82

7.72%


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TOC graphic


Remarkable enhancement in the photoelectric performance of uniform

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