The research paper published by IJSER journal is about Fabrication and Characterization of Dye Sensitized Solar Cell Using Nanostructured TiO2 Photoelectrode 1

ISSN 2229-5518

Fabrication and Characterization of Dye

Sensitized Solar Cell Using Nanostructured TiO2

Photoelectrode

Abel. F. Ole, Gil Nonato C. Santos, Reuben V. Quiroga

Abstract- Dye Sensitized Solar Cells (DSSCs) with photoelectrodes synthesized via Horizontal Vapor Phase Crystal (HVPC) Growth Technique were fabricated and characterized in the present study. Nanostructured TiO 2 was first synthesized on glass substrates at growth temperatures of 1000 oC, 1100 oC, and 1200 oC with varying substrate distance from the bulk powder. Flourine-

doped Tin Oxide (FTO) was used to deposit nanostructured TiO2 for the photoelectrodes of the DSSCs employing the optimum substrate distance identified by SEM analysis. Bixin dye extracted from Annatto was utilized as a low -cost sensitizer and a graphite coated FTO as counter-electrode. All the DSSCs with photoelectrode fabricated by HVPC growth technique achieved a relatively large open-circuit voltage (Voc) of 387 mV, 427 mV, and 412 mV for growth temperature of 1000 oC, 1100 oC, and 1200 oC respectively.

Keywords- Nanostructured Titanium oxide (TiO2), Dye Sensitized Solar Cell (DSSC), Photoelectrode, Annatto

1 INTRODUCTION

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comparable conversion efficiency using low-cost fabrication
techniques and the other advantages mentioned above
ne of the most promising types of solar cell that has attracted much of attention in the scientific community already belongs to the third generation of photovoltaics (PVs). Unlike the common solid state solar cells based on crystalline silicon, the dye-sensitized solar cell (DSSC) does not depend on the principle of a p-n junction for its basic operation (Aydil 2007) [1]. The DSSC can be classified as a photoelectrochemical (PEC) solar cell due to its utilization of photons, charges, and electrolyte for its basic operation (Yu & Chen 2009) *34+. Since its invention by O’Regan and Grätzel in 1991, it has attracted widespread academic and industrial interest because it offers some advantages over the traditional photovoltaic cells. Based on the reports in the literature, the group of Y. Zhang et al. (2009) [35] said that DSSCs are easily fabricated, low-cost, environmentally benign, and have relatively high energy conversion efficiency. Another advantage of DSSCs over competing technologies is that
temperature changes do not
degrade their performance in contrast with conventional
silicon solar cells (Gratzel 2004) [9]. This photovoltaic cell is one of the leading candidates as a substitute for the traditional and expensive silicon solar cell because of its

————————————————

Abel F. Ole, Master of Science in Physics, De La Salle University-Manila, Philippines. E-mail: Abel.Ole@dlsu.edu.ph
Gil Nonato C. Santos, Doctor of Philosophy in Materials Science, Professor, De La Salle University-Manila, Philippines. E-mail: santosg@dlsu.edu.ph

Reuben V. Quiroga, Doctor of Philosophy in Physic, De La

Salle University-Manila, Philippines. E-mail:

quirogar@dlsu.edu.
(Gratzel 2003) [10].
Another interesting characteristic of DSSCs is the
incorporation of nanomaterials among its components. So far,
among all the emerging PVs that employ nanotechnology, DSSCs are the most efficient (Aydil 2007) [1]. Based on the original design of Gratzel, the cell is basically composed of a working electrode made up of nanocrystalline TiO2 typically
5-10 nm in diameter deposited on a transparent conducting
oxide (TCO), a dye sensitizer usually Ruthenium based, an Iodide/Triiodide redox couple electrolyte, and a Platinum or Carbon coated counter-electrode (Gratzel 2003) [10]. For almost two decades, many investigators have tried various combinations of nanocrystalline TiO2, dye sensitizers, electrolytes, and assembly methods to optimize the solar cell performance (Aydil 2007) [1].
The most common aspect of the DSSC that has been extensively studied to improve its efficiency is the design and fabrication of the photoelectrode using TiO2 nanomaterials (Y. Zhang et al. 2009) [35]. The unique characteristics of nanomaterials such as their very large surface areas per unit volume or per unit mass (Aydil 2007) [1] can potentially improve the solar cell’s efficiency. The large surface and interfacial areas found in nanostructured materials is also said to present significant advantages on the two critical steps in solar-to-electric energy conversion such as light absorption and charge separation (Aydil 2007) [1]. Hence, the

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The research paper published by IJSER journal is about Fabrication and Characterization of Dye Sensitized Solar Cell Using Nanostructured TiO2 Photoelectrode 2

ISSN 2229-5518

present work will mainly concentrate on trying to fabricate nanostructured TiO2 as working electrode of a standard
DSSC and study whether the novel method of synthesis can be effectively employed in the process of DSSC assembly. In this paper, nanostructured TiO2 synthesized via Horizontal Vapor Phase Crystal (HVPC) Growth Technique [6] will be introduced as the photoelectrode of Dye-Sensitized Solar Cells (DSSCs).

2 EXPERIMENTAL DETAILS

2.1 Synthesis of Nanostructured TiO2

First, an amorphous silica tube with an inner diameter of
8.5 mm, outer diameter of 11 mm, and length of 290 mm was sealed at one end using the flame torch which is an approximate mixture of LPG and oxygen. Three different tubes was dented at about 50 mm, 80 mm, and 110 mm, respectively from the sealed end to prevent the substrate from reaching the region where the TiO2 powder will be located. The sealed amorphous silica tubes were cleaned using an ultrasonic cleanser for 30 minutes and were washed and dried. Approximately 0.035 g of high purity (99.99%) P25
Degussa TiO2 powder was loaded into the tube sealed at one
end. The glass, with approximate dimensions of 25 mm by 7 mm, was placed inside each tube to serve as a substrate. Finally, the quartz tube with the TiO2 powder and the substrate was connected to the Thermionic High Vacuum System until it reached the desired pressure of around 10 -5 to
10-6 Torr. Once it acquired the right pressure range, the tube was sealed and detached carefully at approximately 140 mm from the sealed end using the flame torch.
The as-prepared amorphous silica tube containing the
TiO2 powder and the substrate was placed inside the
Thermolyne Horizontal Tube Furnace to facilitate the synthesis of the TiO2 nanomaterial via the Vapor-Solid (VS) growth or evaporation-condensation technique. The furnace was set at varying growth temperature from 1000 °C to 1200
°C in increments of 100 °C and fixed dwell time of 6 h for
three separate sets of vacuum-sealed tubes. A constant ramp rate of 10o C per minute was used for the furnace to go from the ambient to the desired temperature. In order to create a thermal gradient that will serve as the transport mechanism for the vapor during the deposition process, the completely sealed tubes were inserted halfway through the furnace. Before retrieving the synthesized TiO2, the whole system, including the amorphous silica tube must be allowed to cool
down naturally to room temperature. The nanostructured
TiO2 were retrieved by breaking the amorphous silica tube
carefully without damaging the substrate.

2.2 Characterization of Nanostructured TiO2

Nanostructured TiO2 grown on the glass substrate was
subjected to a series of characterization. Surface and
morphological characteristics were examined with the aid of JEOL JSM-5310 scanning electron microscope (SEM). The elemental composition of the TiO2 nanomaterial was also analyzed using the same instrument but under the Energy Dispersive X-ray (EDX) mode.
Two empty or blank glass substrates, one baked without TiO2 powder while the other unbaked, was also characterized so that the researcher had an idea about the morphology and composition of the substrate that served as a background.

2.3 DSSC Fabrication

After determining the optimum substrate distance for
each growth temperatures, FTO was used as substrate instead of ordinary glass in growing TiO2 nanomaterials to serve as photoelectrode of the DSSC.
The nanostructured TiO2 grown on the FTO substrate was soaked in a dye solution of Bixin, extracted from Annatto by boiling water, for a period of 24 h to adsorb enough amount of dye as sensitizer. Twenty-four hours later, the FTO with the TiO2 nanomaterial and the sensitizer was rinsed with water to remove the excess dyes that were not completely adsorbed to the nanostructured TiO2 [2], [9], [10].
Once the working electrode has totally dried, two small drops of an electrolyte containing an Iodide/Triiodide redox couple was applied on the side with the TiO2 nanomaterials and dye. Finally, a graphite-coated FTO was placed on top of the working electrode which served as its counter-electrode [2], [9], [10].
The two electrodes were fixed one on top of the other
using a pair of alligator clips. An offset of about 2.5 mm on
opposite electrodes was included to serve as electrical contacts. The fabricated DSSC was sealed on all its sides to prevent the leakage of the electrolyte.

2.4 Assessment of the DSSCs’ Photovoltaic Performance

The photovoltaic performance of the DSSC based on nanostructured TiO2 produced via HVPC growth technique was evaluated. The DSSC was connected to a series of potentiometers with resistance ranging from very low (70 Ω) to very high (2.93 MΩ) resistance values.

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Using a very sensitive digital voltmeter (Fluke, 0.1 mV), the open-circuit voltage (Voc) was determined by setting the
resistance high enough. Next is the measurement of the short-circuit current (Isc) which was accomplished with the aid of a very sensitive ammeter (Newstar UT33D, 1 μA) and the resistance set at a very low value. The artificial light source in the set-up is a 120 W OMNI lamp available in the laboratory. An I-V curve was obtained by varying the resistance from very low to a very high value while measuring the particular current and voltage for each amount of load. The maximum power point was identified from the I-V curve and the maximum power point voltage (Vmp) and current (Imp) was consequently determined. From the values obtained for Voc, Isc, Vmp, and Imp; the fill factor (FF) and therefore the overall energy conversion efficiency (η) were calculated using the equations presented below [2].

Figure 2: SEM micrographs of S1100-80

Pm a x

Pin

where :

100

( I scVoc FF)

Pin

100

Figure 3: SEM micrographs of S1200-80

Based on the SEM micrographs and the summary of the

FF I mpVmp

I scVoc

3 RESULTS AND DISCUSSION

3.1 Nanomaterial Characterization

3.1.1 Surface Morphology

The following figures are the representative SEM micrographs for each sample utilized in the fabrication of DSSC photoelectrodes.

Figure 1: SEM micrographs of S1000-80

grown TiO2 nanostructures and microstructures, the researcher chose the substrate distance that will more likely produce a greater amount of nanostructured TiO2 suitable for DSSC application. The first consideration was the size of the synthesized TiO2, the smaller the size the better. Therefore, substrate distance of 50 mm was immediately excluded from the options because majority of the deposited TiO2 were microstructures. Another deciding factor considered by the author was the amount as well as the distribution of the nanomaterials. Since monodispersed nanomaterials promote an increase in the interfacial surface area compared to agglomerated ones, the substrate distance with the greatest amount of monodispersed nanostructures was chosen to be used in the synthesis of the photoelectrodes for the DSSCs [30]. Large interfacial surface area of nanomaterials favor greater dye loading ability for the TiO2 which promotes a higher light absorption capability for the photoelectrode of DSSCs [2]. As illustrated by the SEM micrographs, the most favorable substrate distance to be used for all growth temperatures was 80 mm from the bulk powder.

3.1.2 Elemental Composition

The Energy Dispersive X-ray analysis results shown below strongly suggest that indeed, TiO2 nanomaterials were successfully synthesized on the glass substrate at different growth temperatures. Other elements present in the X-ray
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The research paper published by IJSER journal is about Fabrication and Characterization of Dye Sensitized Solar Cell Using Nanostructured TiO2 Photoelectrode 4

ISSN 2229-5518

spectra were attributed to the composition of the substrate that served as a background in the deposition of
nanostructured TiO2.

C o u n t s

1500

1000 Si

500 Ti

O

Ti Ti

0

0 5 10 15 20

E n e r g y ( k e V )

3.2 DSSC Characterization

The fabricated DSSCs were characterized inside the laboratory using a 120 W lamp that emits a mean intensity of
18 049 .82 lux. This light intensity was converted to the amount of W/cm2 to serve as the input power density on the DSSC which was calculated to be 2.64 mW/cm2. Actual sunlight characterization was also conducted for the fabricated DSSCs at approximately 11:00 am. From the measured average amount of light intensity (4396.48 lux), the power density input on the DSSC was computed to be
643.6μW/cm2.

Figure 4: EDX result for nanostructured TiO2 synthesized via HVPC

growth technique

Table 1: Summary of the DSSC Photovoltaic Performance under Artificial and Actual Sunlight Illumination

Table 1, revealed that even under sunlight illumination, the performance of DSSC-1000 and DSSC-1100 were still comparable with each other while DSSC-1200 demonstrated a relatively larger efficiency as before. There were some variations in the values of the average FF and η of the first two DSSCs in actual sunlight characterization suggesting that their performance has a degree of instability affected by light intensity. On the other hand, DSSC-1200 exhibited a consistent performance in terms of both the quality and the efficiency of the cell as indicated by its unchanged FF and largest η both in artificial light and actual sunlight testing. Therefore, among the three DSSCs with photoelectrodes fabricated by HVPC growth technique, DSSC-1200 has the optimum performance and reliability. These positive results were attributed to the thicker deposition of TiO2 nanostructures on its photoelectrode as a consequence of the higher growth temperature during fabrication via HVPC growth technique [6].
All the DSSCs with photoelectrode fabricated by HVPC
growth technique achieved a relatively large open-circuit voltage (Voc) of 387 mV, 427 mV, and 412 mV for growth temperature of 1000 oC, 1100 oC, and 1200 oC; respectively. Among the fabricated DSSCs with photoelectrodes grown at different temperatures, DSSC-1200 exhibited the largest short-circuit photocurrent (Isc) of 45 μA compared to 40 μA for DSSC-1000 and 39 μA for DSSC 1100. As a consequence, DSSC-1200 demonstrated the largest recorded fill-factor of
0.24 and efficiency of 0.12 % among the three during
artificial light characterization.
When the photoelectrode of a DSSC fabricated by solution-based method was first subjected to HVPC growth technique, a very large enhancement in open-circuit voltage (Voc) was achieved. The DL-DSSC-1200 resulted to the following cell parameters; Isc = 290 μA, Voc = 488 mV, Imp
= 119 μA, Vmp = 269 mV, FF = 0.23, and η= 0.87 % making it
the best performing DSSC in the present study.

4 CONCLUSION

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From the research findings discussed in the previous section, it can be said that nanostructured TiO2 was effectively grown on glass substrate via HVPC growth technique. Substrate distance from the bulk powder aside from the growth temperature also influenced the synthesis of TiO2 nanomaterials. When the substrate distance was fixed, increase in growth temperature resulted to a thicker deposition of TiO2 nanomaterials on the substrate [6]. Greater amount of nanostructured TiO2 was deposited because the increase in growth temperature caused an increase in the amount of TiO2 vapour producing a greater number of nucleation sites [6].
The presence of nanostructured TiO2 was considered as the determining factor of the relatively large open-circuit voltage (Voc) of the fabricated DSSCs due to the smaller particle size of the TiO2 nanomaterials on the photoelectrode [30]. On the other hand, the photocurrent values were limited by the low-cost natural organic dye sensitizer [27] and the thickness of TiO2 deposition utilized in the DSSC. Better performance of the DSSC could be achieved by maximizing both the Voc and Isc which was accomplished through an optimized deposition of nanostructured TiO2 if availability of the best sensitizer was lacking. Therefore, the highest growth temperature should be employed in the fabrication of photoelectrode via HVPC growth technique for DSSC application.
In conclusion, HVPC growth technique could be
incorporated in the fabrication of photoelectrode for DSSC either by itself or in conjunction with the solution based technique. Independently, it can be used to grow nanostructured TiO2 on FTO to serve as photoelectrode but an efficient sensitizer should be used in order to enhance its light absorption ability When used in conjunction with solution based technique, a low-cost sensitizer like Bixin extract from Annatto used in the present study will be sufficient to demonstrate an enhancement in DSSC performance as a result of the relatively high open-circuit voltage (Voc) when its photoelectrode was first subjected to HVPC growth technique.

REFERENCES

1. Aydil E (2007), Nanomaterials for Solar Cells, Nanotechnology

Law & Business Volume 4 No. 3 pp. 275-291.

2. Brammer T (2004), Nanostructured Titania Dye Sensitised Solar Cells: Study of the effects of variations in the TiO2 Film Thickness and Dyeing Times, Thesis Paper, Australia Research Council Centre for Functional Nanomaterials, Division of Chemical Engineering School of Engineering, The University of Queensland.

3. Campbell, W , Burrel A, Officer D, and Jolley K (2004), Porphyrins as light harvesters in the dye-sensitised TiO2 solar cell, Coordination Chemistry Reviews 248 pp. 1363-1379.

4. Chen Y, Loc Y, Huang C, Cai Y, and Hsu M (2010), Anode growth of DSSCs by flat-flame chemical vapor deposition method,

Materials Chemistry and Physics 120 pp. 181–186.

5. Chen Y, Hsu M, and Cai Y (2010), Preparation of TiO2 films using nanopowder synthesized by flat-flame chemical vapor condensation method for DSSCs, Journal of Alloys and

Compounds 490 pp. 493–498.

6. [De Los Reyes R (2009), Growth and Thermal Properties of Tin

Oxide (SnO2) Nanomaterials Prepared via Horizontal Vapor Phase

Growth (HVPG) Deposition, Master’s Thesis,

7. De La Salle University.

8. Dhungel S, and Park J (2010), Optimization of paste formulation

for TiO2 nanoparticles with wide range of size distribution for its application in dye sensitized solar cells, Renewable Energy 35 pp.

2776-2780.

9. Gong Y (2009), Nanomaterials for the Conversion of Solar Energy,

Department of Electrical Engineering, Stanford University, Stanford, CA 94305.

10. Gratzel M (2004), Conversion of sunlight to electric power by nanocrystalline dye-sensitized solar cells, Journal of

Photochemistry and Photobiology A: Chemistry 164 pp. 3–14.

11. Gratzel M (2003), Dye-sensitized solar cells, Journal of

Photochemistry and Photobiology C: Photochemistry Reviews 4 pp. 145–153.

12. Grätzel M , Ito S, Murakami T, Comte P, Liska P, Grätzel C, and Nazeeruddin M (2008), Fabrication of thin film dye sensitized solar cells with solar to electric power conversion efficiency over 10%, Thin Solid Films 516 pp. 4613–4619.

13. Gupta N, Alapatt G, Podila R, Singh R, and Poole K (2009), Prospects of Nanostructure-Based Solar Cells for Manufacturing Future Generations of Photovoltaic Modules, International Journal

of Photoenergy Volume 2009 pp. 1-13.

14. Jensen H (2006), ZnO and TiO2 dye-sensitized Graetzel cells, Thesis Paper, Dartmouth REU.

15. Johnson G (2009), Plugging Into the Sun, National Geographic,

Retrieved from:

http://ngm.nationalgeographic.com/2009/09/solar/carroll-text, May

2010.

16. Lai W , Su Y, Teoh L, and Hon M (2008), Commercial and natural

dyes as photosensitizers for a water-based dye-sensitized solar

cell loaded with gold nanoparticles, Journal of Photochemistry and

Photobiology A: Chemistry 195 pp. 307–313.

17. Lee K, Suryanarayanan V, and Ho K (2009), Influences of different

TiO2 morphologies and solvents on the photovoltaic performance of dye-sensitized solar cells, Journal of Power Sources 188 pp.

635–641.

18. Lee Y, Chae J, and Kang M (2010), Comparison of the photovoltaic efficiency on DSSC for nanometer sized TiO2 using a conventional sol–gel and solvothermal methods, Journal of

Industrial and Engineering Chemistry 16 pp. 609–614.

19. Lee Y and Kang M (2010), The optical properties of nanoporous

structured titanium dioxide and the photovoltaic efficiency on

DSSC, Materials Chemistry and Physics 122 pp. 284–289.

20. Lehtinen K, and Kulmala M (2002), A model for particle formation and growth in the atmosphere with molecular resolution in size,

Atmospheric Chemistry and Physics Discussions 2, pp. 1791

1807.

21. Meng L, Ren T, and Li C (2010), The control of the diameter of the

nanorods prepared by dc reactive magnetron sputtering and the

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The research paper published by IJSER journal is about Fabrication and Characterization of Dye Sensitized Solar Cell Using Nanostructured TiO2 Photoelectrode 6

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applications for DSSC, Applied Surface Science 256 pp. 3676–

3682.

22. Paulose M, Shankar K, Varghese O, Mor G, Hardin, B and Grimes C (2006), Backside illuminated dye-sensitized solar cells based on titania nanotube array electrodes, Nanotechnology 17 pp. 1446–

1448.

23. Phan T, Pham H, Cuong T, Kim E, Kim S, and Shin E (2009), A

simple hydrothermal preparation of TiO2 nanomaterials using concentrated hydrochloric acid, Journal of Crystal Growth 312 pp.

79–85.

24. Pradhan B, Batabyal S, and Pal A (2007), Vertically aligned ZnO

nanowire arrays in Rose Bengal-based dye-sensitized solar cells,

Solar Energy Materials & Solar Cells 91 pp. 769–773.

25. Quinonez C, Vallejoa W , and Gordillo G (2010), Structural, optical

and electrochemical properties of TiO2 thin films grown byAPCVD

method, Applied Surface Science 256 pp. 4065–4071.

26. Saji V and Pyo M (2010), Dye sensitized solar cell of TiO2

nanoparticle/nanorod composites prepared via low-temperature synthesis in oleic acid, Thin Solid Films.

27. Tsakalakos L (2008), Nanostructures for photovoltaics, Materials

Science and Engineering Reviews 62 pp. 175–189.

28. Turkevych I, Hara K, and Kondo M, Nanostructured TiO2

photoelectrodes for Dye Sensitized Solar Cells, National Institute

of Advanced Industrial Science and Technology 1-1-1 Umezono, Tsukuba, Ibaraki, 305-8568, Japan.

29. W ongcharee K., Meeyoo V., and Chavadej S. (2007), Dye-

sensitized solar cell using natural dyes extracted from rosella and blue pea flowers, Solar Energy Materials & Solar Cells 91 pp. 566-

571.

30. W ong M, Lee M, Chen C, and Huang C (2010), Vapor deposited sculptured nano-porous titania films by glancing angle deposition for efficiency enhancement in dye-sensitized solar cells, Thin Solid

Films pp. 1-6.

31. Xiao Y, W u J, Yue G, Xie G, Lin J, and Huang M (2010), The

preparation of titania nanotubes and its application in flexible dye-

sensitized solar cells, Electrochimica Acta 55 pp. 4573–4578.

32. Xiaobo C (2009), Titanium Dioxide Nanomaterials and Their

Energy Applications, Chinese Journal of Catalysis 30(8) pp. 839–

851.

33. Xu H, Tao X, W ang D, Zheng Y, and Chen J (2010), Enhanced efficiency in dye-sensitized solar cells based on TiO2 nanocrystal/nanotube double-layered films, Electrochimica Acta 55

pp. 2280–2285.

34. Yang H, Lee M, Huang C, Lo Y, Chen Y, and W ong M (2009),

Glancing angle deposited titania films for dye-sensitized solar

cells, Thin Solid Films 518 pp. 1590–1594.

35. [33] Yianoulis P and Giannouli M (2008), Thin Solid Films and

Nanomaterials for Solar Energy Conversion and Energy Saving

Applications, Journal of Nano Research Vol. 2 pp. 49-60.

36. Yu K and Chen J (2009), Enhancing Solar Cell Efficiencies through 1-D Nanostructures, Nanoscale Res Lett 4 pp. 1–10.

37. Zhang Y, W u L, Xie E, Duan H, Han W , and Zhao J (2009), A simple method to prepare uniform-size nanoparticle TiO2 electrodes for dye-sensitized solar cells, Journal of Power Sources 189 pp. 1256–1263.

38. Zhang Y, Zhang J, W ang P, Yang G, Sun Q, Zheng J, and Zhu Y (2010), Anatase TiO2 hollow spheres embedded TiO2 nanocrystalline photoanode for dye-sensitized solar cells,

Materials Chemistry and Physics 123 pp. 595–600.

39. Zhu K, Neale N, Miedaner A, and Frank A, Oriented TiO2

Nanotube Arrays for Dye-Sensitized Solar Cells: Effect of Nanostructure Order on Transport, Recombination, and Light Harvesting, National Renewable Energy Laboratory, Golden, CO.

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