Importance of Compact Blocking Layers to the Performance of Dye

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The Importance of Compact Blocking Layers to the Performance of Dye-Sensitized Solar Cells under Ambient Light Conditions I-Ping Liu, Wei-Hsun Lin, Chih-Mei Tseng-Shan, and Yuh-Lang Lee ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b13181 • Publication Date (Web): 19 Oct 2018 Downloaded from http://pubs.acs.org on October 21, 2018

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ACS Applied Materials & Interfaces

The Importance of Compact Blocking Layers to the Performance of Dye-Sensitized Solar Cells under Ambient Light Conditions I-Ping Liu,† Wei-Hsun Lin,† Chih-Mei Tseng-Shan,† and Yuh-Lang Lee*†‡ †Department

of Chemical Engineering, National Cheng Kung University, Tainan 70101, Taiwan

(R. O. C.) E-mail: [email protected] ‡Hierarchical

Green-Energy Materials (Hi-GEM) Research Center, National Cheng Kung

University, Tainan 70101, Taiwan (R. O. C.)

1 Environment ACS Paragon Plus

ACS Applied Materials & Interfaces 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

Abstract Power generation in indoor environments is the next step in dye-sensitized solar cell (DSSC) evolution. To achieve this goal, a critical recombination route which is usually inhibited by the TiCl4-derived blocking layers (BLs), i.e., charge transfer at the fluorine-doped tin oxide (FTO) substrate/electrolyte interface, is of concern. In this study, we demonstrate that due to low surface coverage, the conventional TiCl4 BLs are unable to suppress such electron leakage, thus limiting the photovoltaic performance of Co(bpy)32+/3+-mediated DSSCs (bpy = 2,2′-bipyridine) under ambient lighting. On the other hand, by introducing compact BLs prepared by spray pyrolysis, the DSSCs show lower dark current and operate efficiently not only under high-intensity sunlight, but also under ambient light conditions. The better blocking function of the compact BL is verified by the cyclic voltammetry; other thin film preparation methods, except for the common TiCl4 treatment, are anticipated to realize a similar blocking effect. This study illustrates that dense thin film with predominant blocking function is highly required as the BL for DSSCs under low-light conditions, and this concept will pave the way for more development of indoor DSSC.

Keywords: underlayer, charge recombination, indoor, low light, cobalt electrolyte

1. INTRODUCTION The rapid development of the Internet of Things (IoT) is gradually influencing our lives to an ever greater degree, which means that a large number of wireless sensors, controllers, actuators


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and network systems will become ubiquitous.1,2 At the same time, the use of wearable and portable electronics has also continued to grow to a striking degree in recent years. Both of these trends suggest a strong requirement for a tiny, reliable and efficient power source. Among various power technologies, converting photons from either outdoor or indoor environments into electricity is deemed a practical and sustainable method. Dye-sensitized solar cells (DSSCs), featuring low production cost and environmental friendliness, have emerged as an alternative photovoltaic technology;3,4 importantly, in comparison with other photovoltaics, they demonstrate enormous potential for low-light applications.5-7 As a result, the direction of some DSSC research has recently altered, with much attention being paid to power generation under ambient light conditions.8-11 After decades of progress, the conversion efficiencies of DSSCs have exceeded 13.0% at standard one sun (AM 1.5G, 100 mW cm–2), resulting mainly from the assistance of robust dyes and cobalt complex redox couples.12,13 Very recently, Hagfeldt’s and Grätzel’s groups reported on DSSCs using copper complexes as redox shuttles; by introducing dye co-sensitization and novel device architecture, they both achieved outstanding efficiencies under both sunlight and ambient light conditions.14,15 Apart from the two as-mentioned works, the DSSC research on the low-light power generation so far has primarily been based on the adoption of iodide-related electrolytes.8-11,16 In the past few years, cobalt complexes have become the most promising alternative to conventional iodide/triiodide redox shuttles, due to their less light absorption and low thermodynamic redox potential.17,18 On the other hand, in order to inhibit electron leakage at the FTO substrate/electrolyte interface, the blocking layer (BL), usually made of metal oxides, is an essential component in DSSCs.19 Various materials and methods have been reported for the fabrication of BLs, but the related studies were usually carried out with iodide-based



electrolytes.20-23 There is little DSSC research investigating the BL function in cobalt complex electrolytes.24,25 It is also worth noting that so far the BL-related studies have mainly been conducted for the DSSC operation under conventional sunlight irradiation, and not under specific indoor low-light conditions. Herein, the BL effect on Co(bpy)32+/3+-mediated DSSCs are systematically investigated under both simulated sunlight and ambient light conditions. Besides the traditional TiCl4-derived BL, a compact TiO2 BL was introduced for comparison. The photovoltaic behaviors of the two types of cells were comparable in conventional sunlight, while under ambient lighting, the DSSC with a TiCl4 BL performed much worse than the other did. The compact BL can notably suppress the charge recombination occurring at the FTO surface, resulting in a DSSC with conversion efficiencies beyond 14.5% over a broad range of low-light intensities. This article, for the first time, demonstrates power generation by cobalt-mediated DSSCs under ambient lighting; furthermore, it stresses the importance of compact BLs to the performance of such devices in indoor low-light environments.

2. RESULTS AND DISCUSSION The TiCl4 treatment is considered as the most conventional method for fabricating BLs for liquid-junction DSSCs. In this work, the TiCl4-derived BLs were fabricated according to commonly used procedures, including the immersion of FTO substrates in 40 mM aqueous TiCl4 solution (70ºC, 30 min), followed by a sintering process in air. In addition, in view of the simplicity and the effective blocking function of the resultant films, spray pyrolysis was executed to fabricate compact BLs.26 Sprayed compact layers are commonly utilized in solid-state DSSCs; they are considered as high-coverage thin films without pin holes.27-29 In this work, the spray


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pyrolysis was conducted manually at 450ºC, and the thin film properties of the resultant BLs were directly controlled by the spraying cycles. Figure 1a-c display the SEM images related to the surface morphology of pristine and BL-coated FTO substrates. It is obvious that the pristine FTO surface exhibits many crystalline grains and sharp facets of tin oxides. After the TiCl4 treatment, numerous tiny TiO2 particles appear, while the surface topography remains constant, thus illustrating that the TiO2 coverage on the FTO surface is rather low; due to their low surface coverage and non-uniformity, it is difficult to precisely determine the thickness of TiCl4 BLs. Furthermore, after coating a compact BL on the bare FTO with 12 spraying cycles, the crystalline facets become gentle and the surface reveals a smoother morphology. The experimental results also show that the thickness of the compact BL is proportional to the employed spraying cycles (Figure S1); due to the ultra-low thickness of prepared BLs, the corresponding AFM images demonstrate highly comparable surface characteristics and their roughness is almost uniform (Figure S2). Figure 1d exhibits X-ray diffraction patterns which indicate that except for the FTO characteristics, an additional diffraction peak is detected at 25.2° in the substrate with a sprayed BL, corresponding to the (101) lattice plane of anatase TiO2 (JCPDS card #21-1272). In addition, Figure 1e shows that the TiCl4 treatment hardly influences the optical transmittance of the substrate, while the coating of compact BLs causes a distinct decrease in the light transparency. The greater the number of spraying cycles, the lower the optical transmittances of the resultant samples! A photograph illustrating the comparison of the pristine and sprayed BL-coated FTO substrates is shown in Figure 1f. To render the most photons available for power generation, the compact BLs indicated in the following paragraphs were prepared by 12 fixed spraying cycles (roughly equivalent to 250 μL precursor solution) unless noted otherwise.



The blocking function of prepared BLs was first evaluated by cyclic voltammetry with the Fe(CN)63−/4− model redox probe.26 As exhibited in Figure 2, the reversible voltammogram was clearly detected for a pristine FTO substrate, which corresponds to the redox reaction of Fe(CN)63−/4− occurring at the naked FTO surface. In terms of the FTO substrate treated by TiCl4, its voltammogram is different, revealing the decrease in the peak current densities together with markedly enhanced peak-to-peak separation; it represents that the TiCl4 BL possesses somewhat blocking function, causing a larger charge transfer resistance towards the Fe(CN)63−/4− redox reaction. In addition, an irreversible voltammogram was detected for the substrate coated by a sprayed compact BL; the oxidation of Fe(CN)64− was fully suppressed, while the reduction of Fe(CN)63− was triggered because of the quasi-metallic nature of TiO2 occurring at this negative potential.26 In short, the compact BL displays much better blocking function compared to the TiCl4 one. The two kinds of BLs are further compared in terms of the photovoltaic performance of DSSCs using commercial organic MK-2 dye in conjunction with Co(bpy)32+/3+ as redox couples. Figure 3 depicts the J−V characteristics of MK-2 DSSCs separately under ambient light and simulated sunlight irradiation, and the corresponding cell parameters are summarized in Table 1 and S1, respectively. The ambient light was generated using typical T5 fluorescent tubes, and its spectrum (Figure S3) and intensity were measured with a calibrated spectroradiometer. Clearly, under sunlight conditions, DSSCs applying TiCl4 or compact BLs present comparable photovoltaic performance. Although the cell with a compact BL reveals slightly higher fill factors (FF), the discrepancies in the conversion efficiencies (η) between these two DSSCs are simply within 0.3%. On the other hand, under ambient light conditions, the cell incorporating a TiCl4 BL displays inferior J−V characteristics, as it suffers from considerable decreases in both


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open-circuit voltage (Voc) and FF; this result implies tremendous electron leakage taking place inside the solar cell. The DSSC using a sprayed compact BL, however, still operates smoothly, offering outstanding efficiencies beyond 14.5% over a wide lighting range (from 250 lux to 1001 lux, where lux represents the unit of illuminance). Due to the lower optical transmittance, a cell with a much thicker compact BL (prepared by 48 spraying cycles) reveals a slightly inferior performance (Table S2). These results therefore enable us to conclude that the BLs markedly affect the overall performance of cobalt-mediated DSSCs, in particular, under low-light conditions. Several analyses were carried out to interpret the effect of BL on suppressing electron leakage at the substrate/electrolyte interface. Dark current measurement can provide helpful information on the back electron transfer in solar cells.30 When applying low bias on a DSSC in the dark, due to the large charge transport resistance in the TiO2, the dark current results mainly from the reduction of Co(bpy)33+ species at the exposed FTO surface. As can be observed in the low voltage domain (< 0.4 V) in Figure 4a, the dark current of the TiCl4-based device is at least an order of magnitude higher than that of the cell using a compact BL, suggesting that the compact BL prepared by spray pyrolysis is more effective in hindering electron leakage at the FTO surface. In addition, a simple technique, open-circuit voltage decay (OCVD), was also conducted to assess the electron lifetime in the two DSSCs.31,32 In this measurement, the variation of Voc as a function of time was traced and recorded after the simulated sunlight (standard 1 sun) was switched off. As illustrated in Figure 4b, the Voc sharply decays to 0 V in only a few seconds for the TiCl4-treated solar cell. However, for the DSSC with a compact BL, the result is somewhat different; the Voc decays drastically only in the initial period, and the decay unmistakably slows down when the voltage is below 0.5 V. A faster decay of Voc towards 0 V indicates a more



pronounced recapture of electrons by the oxidized species in the electrolyte. The effective electron lifetime can be further derived from the Voc decay rate (see more details in the Experimental section in the SI). As shown in Figure 4c, in the high voltage region (> 0.7 V), the lifetimes in the two DSSCs are seemingly comparable, while the discrepancy between them becomes more significant with the decrease in voltage. At 0.63 V, the lifetime in the solar cell using a compact BL is ca. double that in the TiCl4-based device, and at 0.55 V, the difference in lifetime becomes an order of magnitude. According to the aforementioned analyses, the DSSC with a compact BL exhibits smaller dark currents and longer electron lifetimes in the moderate voltage region. It is worth noting that under indoor light conditions, the DSSC works at moderate voltages. Therefore, a more effective suppression of electron recapture by a compact BL leads to a much better photovoltaic performance of the solar cells under ambient lighting. Due to the low surface coverage, however, the blocking function of the TiCl4 BL is worse than that of the compact one, causing higher dark currents and shorter electron lifetimes for the corresponding solar cell. These results illustrate that under indoor low-light conditions, the charge recombination occurring at the FTO surface plays a key role in determining the performance of cobalt-mediated DSSCs. In DSSCs, three routes related to the electron recombination with oxidized species in the electrolyte are often of concern: the charge transfer from the nanocrystalline TiO2 either via the conduction band or via surface states, and from the FTO substrate. The first route is known to dominate the performance of DSSCs under conventional sunlight irradiation, while the third route is often neglected. If the recombination takes place through the first route only, the DSSC can be considered as an ideal diode, demonstrating a slope of 59 mV/decade at 298 K in the semilogarithmic plot of Voc versus the incident light intensity.24,33 The voltages of the two studied


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MK-2 DSSCs under various irradiation intensities are depicted in Figure 5 as a logarithmic function of irradiance. The solar cell using a compact BL exhibits an almost-ideal linear behavior across a wide irradiance range, from simulated sunlight to the ambient lighting region. A slope of 69 mV/decade is also measured, which is highly comparable with those reported in BL-related studies.21,24,25,34 The small deviation in the measured slope from the ideal value is probably due to the electron recombination via the surface states. On the other hand, the TiCl4-based cell does not present a linear feature in the whole irradiance range. At low irradiance, the voltages deviate significantly from the linear feature that expresses in the sunlight region, and a slope of 290 mV/decade is obtained. In Figure 5, a nearly identical slope in the sunlight region is observed in the two DSSCs studied, which suggests similar recombination behaviors. Under high-intensity lighting conditions, the TiO2 in DSSCs becomes electronically conducting; therefore, most of the electron recombination takes place through the TiO2. By contrast, the TiO2 behaves like an insulator under ambient lighting, so the recombination behavior might change. The high slope observed in the TiCl4-based solar cell is clear evidence of the different charge transfer behaviors. Moreover, it implies a severe electron leakage occurring at the FTO surface. In terms of the DSSC with a compact BL, however, the slope is consistent throughout the whole irradiance range; this result suggests not only a uniform behavior of electron recombination but also predominant blocking function of compact BLs. Consequently, the aforementioned device analyses all indicate that in order to achieve high performance under low-light conditions for DSSCs, a BL with powerful blocking function has to be introduced. Besides the spray pyrolysis adopted in this work, other materials and methods are anticipated to obtain a similar blocking effect, but the conventional



TiCl4 treatment is not highly recommended; this concept will facilitate the progress of indoor DSSCs. In the literature, an organic dye coded as Y123 has been widely used to fabricate DSSCs with cobalt complex redox couples.12,35,36 In this study, the Y123 dye was also employed to harvest photons in the indoor environments. The assembled Y123 cells with sprayed compact BLs were tested under five different ambient light irradiances (Figure 6a); the extracted parameters are listed in Table S3. As exhibited in Figure 6b, under these light intensities, the conversion efficiencies of the Y123 cells are within the 17.6~18.0% range, and the output power almost amplifies linearly with the increase in light irradiance, showing good charge extraction under these low-light conditions. It is worth noting that compared to the previous MK-2 cells, the better performance of the Y123 devices mainly results from the enhanced short-circuit current density (Jsc) and Voc values. The higher voltages are possibly due to the distinct recombination mechanism that originates from the structure of dye itself.37 Moreover, the Y123 dye has better light-absorbing ability than the MK-2 dye in the wavelength range from 500 to 600 nm.35,38 It illustrates that the Y123 dye can harvest more photons in the fluorescent tube lighting; the increased currents of related solar cells were thereby measured. This result demonstrates that on a basis of using compact BLs, better photovoltaic performance under ambient lighting can be realized by introducing appropriate dye molecules for more efficient light harvesting.

3. CONCLUSIONS This study demonstrates that a compact BL with powerful blocking function is eminently required for the operation of cobalt-mediated DSSCs under indoor low-light conditions. The DSSCs using traditional TiCl4-derived BLs work efficiently in normal sunlight, while the severe


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electron transfer from the FTO to electrolyte under ambient lighting restrains the performance of such cells. To overcome this situation, compact TiO2 BLs were introduced, and their robust blocking function was electrochemically verified. The experimental results reveal that the compact BL is able to inhibit electron leakage over a wide intensity range, enabling the DSSCs to operate efficiently in low-light environments. It is anticipated that besides the spray pyrolysis, other thin film fabrication methods can achieve a similar blocking function. The relevant blocking effect elucidated in this study is beneficial for the DSSC progress towards efficient indoor power generation.

Associated Content Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: Experimental section, thickness of sprayed compact BLs, AFM images, spectra of lighting sources, IPCE results, photovoltaic parameters.

Author Information Corresponding Author *E-mail: [email protected]. Tel: +886-6-2757575 ext. 62693. ORICD I-Ping Liu: 0000-0002-7380-4777 Yuh-Lang Lee: 0000-0002-0469-5896 Notes The authors declare no competing financial interest.



Acknowledgements Financial grants by the Ministry of Science and Technology of Taiwan under the projects MOST 106-2119-M-006-003, 106-2221-E-006-197-MY3 and 107-2811-M-006-012 are acknowledged. The authors would like to thank Chiao-Wei Li and Yi-Chen Hou for fruitful discussions, as well as the Center for Micro/Nano Science and Technology for the AFM and ellipsometry measurements.

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[34] Fisher, A. C.; Peter, L. M.; Ponomarev, E. A.; Walker, A. B.; Wijayantha, K. G. U. Intensity Dependence of the Back Reaction and Transport of Electrons in Dye-Sensitized Nanocrystalline TiO2 Solar Cells. J. Phys. Chem. B 2000, 104, 949–958. [35] Tsao, H. N.; Yi, C.; Moehl, T.; Yum, J.-H.; Zakeeruddin, S. M.; Nazeeruddin, M. K.; Grätzel, M. Cyclopentadithiophene Bridged Donor–Acceptor Dyes Achieve High Power Conversion Efficiencies in Dye-Sensitized Solar Cells Based on the tris-Cobalt Bipyridine Redox Couple. ChemSusChem 2011, 4, 591–594. [36] Tsao, H. N.; Burschka, J.; Yi, C.; Kessler, F.; Nazeeruddin, M. K.; Grätzel, M. Influence of the Interfacial Charge-Transfer Resistance at the Counter Electrode in Dye-Sensitized Solar Cells Employing Cobalt Redox Shuttles. Energy Environ. Sci. 2011, 4, 4921–4924. [37] Liu, Y.; Jennings, J. R.; Zakeeruddin, S. M.; Grätzel, M.; Wang, Q. Heterogeneous Electron Transfer from Dye-Sensitized Nanocrystalline TiO2 to [Co(bpy)3]3+: Insights Gained from Impedance Spectroscopy. J. Am. Chem. Soc. 2013, 135, 3939–3952. [38] Koumura, N.; Wang, Z.-S.; Mori, S.; Miyashita, M.; Suzuki, E.; Hara, K. Alkyl-Functionalized Organic Dyes for Efficient Molecular Photovoltaics. J. Am. Chem. Soc. 2006, 128, 14256–14257.



Figure 1. Top-view SEM images with scale bars of 200 nm: (a) pristine FTO surface and FTO substrates coated with BLs fabricated by (b) TiCl4 treatment and (c) 12 spraying cycles. (d) XRD patterns of the FTO samples without and with a sprayed compact BL; the circle and squares indicate phases of anatase TiO2 (JCPDS 21-1272) and tetragonal rutile SnO2 (JCPDS 41-1445), respectively. (e) Transmittance spectra of FTO substrates coated without and with different BLs; the sample with a BL fabricated by n spraying cycles is denoted as Spray-n. (f) A digital photograph of bare FTO substrates with two kinds of sprayed BLs.


Page 16 of 23

2

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


Current Density (mA cm )

Page 17 of 23

0.09 0.06 0.03

FTO FTO/TiCl4 BL FTO/Compact BL

0.00 -0.03 -0.06 -0.09 -0.4 -0.2 0.0

0.2

0.4

0.6

0.8

Potential (V vs. Ag/AgCl)

1.0

Figure 2. Cyclic voltammograms of the bare and different BL-coated FTO substrates. The aqueous electrolyte solution contains 0.5 mM K4Fe(CN)6, 0.5 mM K3Fe(CN)6 and 0.5 M KCl (pH = 2.5), and the scan rate is 20 mV s−1.


2

12

(a)

10 8 6

Page 18 of 23

1 sun

0.491 sun

Blocking Layer Compact TiCl4

4 2

0.098 sun

0 0.0

0.2

0.4

0.6

0.8

Voltage (V)

0.10

(b)

1001 lux

2


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



0.08 0.06

601 lux

0.04 0.02

251 lux

0.00 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Voltage (V) Figure 3. J−V characteristics of the cobalt-mediated MK-2 DSSCs with compact and TiCl4 BLs recorded under (a) simulated sunlight and (b) ambient T5 lighting conditions.


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Table 1. Photovoltaic parameters obtained under different T5 lighting illuminance from the MK-2 DSSCs using compact and TiCl4 BLs.a Illuminance

Pinb [μW cm−2]

Blocking layer

Jsc [μA cm−2]

Voc [V]

FF

η [%]

1001 lux

319

TiCl4 Compact

83.47 ± 0.45 84.60 ± 1.63

0.641 ± 0.010 0.703 ± 0.003

0.511 ± 0.009 0.820 ± 0.002

8.56 ± 0.34 15.26 ± 0.19

601 lux

188

TiCl4 Compact

48.85 ± 0.21 49.06 ± 1.06

0.589 ± 0.017 0.684 ± 0.002

0.487 ± 0.002 0.817 ± 0.002

7.46 ± 0.24 14.59 ± 0.24

251 lux

78.8

TiCl4 Compact

21.90 ± 0.11 22.76 ± 0.06

0.472 ± 0.019 0.652 ± 0.002

0.472 ± 0.004 0.803 ± 0.006

6.19 ± 0.22 15.12 ± 0.13

aParameters

are expressed as average values together with standard deviations based on four

cells. The efficiencies were calculated with equation: Jsc  Voc  FF  Pin  100%. bIncident

power of the fluorescent light measured by a calibrated spectroradiometer.


10

0

10

-1

10

Blocking Layer TiCl4 Compact

-2

10

-3

10

-4

10

-5

10

0.0

0.2

0.4

0.6

Voltage (V)

0.8

1.0

(b)

Light Off

0.8 0.6 0.4 0.2 0.0

Page 20 of 23

Electron Lifetime (sec)

(a)

1

Open-Circuit Voltage (V)

2

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

Dark Current Density (mA cm )


(c)

1

10

Compact TiCl4

0

10

-1

10

-2

0

10

20

30

40

Time (sec)

50

10

0.0

0.2

0.4

0.6

Figure 4. Charge transfer properties of the MK-2 DSSCs with compact and TiCl4 BLs: (a) Dark current measurement results, (b) open-circuit voltage decay analyses and (c) effective electron lifetime derived from the Voc decay rate.


0.8

Open-Circuit Voltage (V)

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


Open-Circuit Voltage (mV)

Page 21 of 23

900 800

Ambient Lighting

Sunlight

Compact BL slope = 69.2 mV/decade

700 600 TiCl4 BL

500

slope = 289.5 mV/decade

400 0.1

1

10

2

Irradiance (mW cm )

100

Figure 5. Open-circuit voltages of the MK-2 DSSCs with compact and TiCl4 BLs under simulated sunlight and ambient lighting conditions plotted as a logarithmic function of irradiance.



250

3156 lux

200 150 100

(a) Compact BL Y123 Dye

2003 lux

1002 lux

50

601 lux 0 251 lux 0.0

0.2

3

10

0.4

0.6

0.8

Voltage (V)

19

2

(b) 18

2

10

17 16

Efficiency (%)

2

Current Density (A cm )

300

Output Power (W cm )

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

Page 22 of 23

1

10

0.1

2

Irradiance (mW cm )

1

15

Figure 6. Photovoltaic characteristics of the cobalt-mediated DSSC using a compact BL in conjunction with the Y123 dye: (a) J−V curves recorded under different ambient T5 lighting and (b) plots of output power and efficiency vs. irradiance.


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Table of contents


Importance of Compact Blocking Layers to the Performance of Dye

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