Highly Efficient Mesoscopic Dye-Sensitized Solar Cells Based on Donor-Acceptor-Substituted Porphyrins

Solar Cells

DOI: 10.1002/anie.201002118

Highly Efficient Mesoscopic Dye-Sensitized Solar Cells Based on

Donor–Acceptor-Substituted Porphyrins**

Takeru Bessho, Shaik M. Zakeeruddin, Chen-Yu Yeh,* Eric Wei-Guang Diau,* and

Michael Grtzel*

Dye-sensitized solar cells (DSCs) are currently attracting

considerable attention because of their high

light-to-electric-ity conversion efficiencies, ease of fabrication, and low

production costs.

_{Many recent efforts have been devoted}

to the development of new and efficient sensitizers that are

suitable for practical use. Among the investigated

com-pounds, ruthenium sensitizers have been distinguished by

attaining more than 11 % efficiencies.

_{Organic sensitizers}

have also attracted great interest because of their modest cost,

ease of synthesis and modification, large molar absorption

coefficients, and satisfactory stability. Organic dyes with

conversion efficiencies in the range of 5–10 % have been

reported.

_{Porphyrins show strong absorption and}

emis-sion in the visible region as well as tunable redox potentials.

These properties lead to promising applications in many

areas, such as optoelectronics, chemosensors, and catalysis.

Self-assembled porphyrin molecular structures play a key

role in solar energy research as the photosynthetic systems of

bacteria and plants contain chromophores based on

light-harvesting porphyrins,

_{which collect solar energy and}

convert it efficiently into chemical energy. Various artificial

photosynthetic model systems have been designed and

synthesized in order to elucidate the factors that control the

photoinduced electron-transfer reaction.

_{Inspired by the}

efficient energy transfer in naturally occurring photosynthetic

reaction centers, numerous porphyrins

_and

phthalocya-nines

_{have been synthesized and tested in dye-sensitized}

solar cells. The best-performing porphyrin dyes have been

reported to have conversion efficiencies in DSCs in the range

of 5–7 %.

_{A recently reported series of porphyrin dyes with}

donor–acceptor (D–A) substituents exhibit promising

photo-voltaic properties.

Herein we report the achievement of an 11 %

solar-to-electric

power

conversion

efficiency

under

standard

(AM 1.5G, 100 mW cm

_{intensity) reporting conditions by}

using a judiciously tailored porphyrin dye, YD-2. To the best

of our knowledge, this is the first time such a high efficiency

has been obtained with a ruthenium-free sensitizer.

The structure of the YD-2 porphyrin used in this study is

shown in Scheme 1. A diarylamino donor group attached to

the porphyrin ring acts as an electron donor, and the

ethynylbenzoic acid moiety serves as an acceptor. The

porphyrin chromophore itself constitutes the p bridge in this

particular D–p–A structure.

_{In a first set of experiments,}

2.4 mm thick transparent TiO

films loaded with a monolayer

of YD-2 were employed in order to accurately measure the

spectral response and the internal quantum efficiency of the

device. Figure 1 shows the incident photon to current

conversion efficiency (IPCE) as a function of the light

excitation wavelength. The features of the spectral response

of the photocurrent closely match the absorption spectrum of

the YD-2 dye. At 460 nm, near the Soret band maximum, the

IPCE reaches its highest value of 85 %; a second maximum

was obtained near 655 nm, where the IPCE is 80 %. The value

of the absorbance at the latter wavelength was 0.57, thus

implying that the sensitizer absorbed 73 % of the photons with

a wavelength of 655 nm that arrived at the film. By taking into

account the light reflection by the counter electrode, the

internal quantum efficiency for the generation of an electric

current by YD-2 at this wavelength is approximately 100 %.

Table 1 shows the short-circuit photocurrent density (J

),

open-circuit photovoltage (V

), fill factor (FF), and power

conversion efficiency (PCE) obtained with YD-2 sensitized

Scheme 1. Molecular structure of YD-2.

[*] Dr. T. Bessho, Dr. S. M. Zakeeruddin, Prof. Dr. M. Grtzel Laboratory of Photonics and Interfaces

Institute of Chemical Sciences and Engineering Ecole Polytechnique Fdrale de Lausanne (EPFL) Station 6, 1050 Lausanne (Switzerland)

Fax: (+ 41) 21-693-6100 E-mail: [email protected] Prof. Dr. C.-Y. Yeh

Department of Chemistry, National Chung Hsing University Taichung 402 (Taiwan)

E-mail: [email protected] Prof. Dr. E. W.-G. Diau

Department of Applied Chemistry, National Chiao Tung University Hsinchu 300 (Taiwan)

E-mail: [email protected]

[**] Financial support of this work by the Swiss National Science Foundation and the European Research Council (Advanced Grant no 247404 to M.G.) is gratefully acknowledged. We thank Dr. Carole Grtzel for valuable discussions and editorial help with the manuscript. We also thank Prof. S. Ito and Prof. S. Uchida for the gift of the dye D-205, which was developed and prepared in collabo-ration with Dr. M. Takata, Dr. H. Miura and Dr. K. Sumioka.

Communications

transparent nanocrystalline TiO

films, the thickness of which

varied from 2.4 to 11.5 mm. Even the thinnest films gave an

impressive PCE of 5.6 % under illumination by standard

AM 1.5G simulated sunlight (100 mW cm

_{). The PCE}

reached 8.8 % at 11.5 mm mainly because of the increase in

J

from 10.5 to 16.7 mA cm

2

_{, which is accompanied by a}

small drop in the V

value of 20 mV. The fill factor remained

remarkably stable at a value of around 0.7, despite a 60 %

increase in photocurrent and a more than fourfold increase in

film thickness, thus showing that any losses in fill factor

caused by contributions from the internal resistance of the

device must be small. These results are promising for the

practical use of YD-2 type sensitizers in transparent

dye-sensitized solar cell panels. The sensitizers exhibit a beautiful

green color for windows and glass facades that produce solar

electricity.

Although aesthetically pleasing, the green coloration of

the YD-2 sensitized TiO

films results in a lack of light

harvesting in the 480–630 nm range, which leads to the

reduction of the J

and PCE values of the device. This result

is clearly apparent from the IPCE spectrum, which shows a

pronounced dip with a minimum at around 530 nm, where the

IPCE value decreases to a mere 20 % (Figure 1). Hence,

cosensitization by the D-205 dye, which shows

complemen-tary spectral responses in the visible spectral range was

attempted in order to increase the light harvesting in the

green-wavelength region. The D-205 dye has an absorption

maximum at 532 nm that coincides with the minimum of the

IPCE response of the YD-2 dye. The absorption maxima of

D-205 in THF and for YD-2 in ethanol are 532 nm

(53 000 m

_cm

₎

_and

_{644 nm}

_{(31 200 m}

_cm

_),

respec-tively.

_{The photovoltaic performance of cosensitized}

dyes was enhanced in comparison to that of a solar cell

containing a single dye. The IPCEs of devices made with

individual dyes and by cosensitization are shown in Figure 1 a.

For cosensitization, the TiO

surface was initially coated with

a monolayer of the YD-2 dye by dipping the TiO

into a

solution of the dye for 16 hours, followed by immersion of the

electrode in a solution of the D-205 dye for 30 minutes and

then washing with acetonitrile to remove any excess dye. The

peaks corresponding to two different dyes are clearly shown

in the IPCE spectra of the cosensitized devices. The

cosensi-tization of the TiO

electrode by D-205 results in a dramatic

enhancement of the photocurrent response in the spectral

region of 480–580 nm, where the IPCE spectrum of the YD-2

dye shows a dip.

The photovoltaic parameters of these solar cells are given

in Table 2. It is emphasized that the D-205 and YD-2 dyes

gave almost identical efficiencies and J

values when

measured seperately. Devices based on the coadsorbed dyes

D-205 and YD-2 showed a 20 % increase in J

values with a

concomitant 20 % increase in efficiency (Figure 1). These

enhanced values result from filling the dip in the IPCE

spectrum of the YD-2 device. The PCE attains a value close to

7 % for the cosensitized device, which is the highest reported

to date for a 2.4 mm thick transparent titania film, hence

showing that effective panchromatic light harvesting is

achieved by the combination of the two sensitizers despite

the short optical path length. This approach reveals an

Figure 1. a) IPCE action spectra and b) J–V characteristics of DSC fabricated with YD-2 or D-205 and cosensitized with a YD-2/D-205 mixture. TheJ–V curves were measured under 100 % sun (AM 1.5G) for YD-2 (a), D-205 (b), YD-2/D-205 (c).

Table 1: Photovoltaic parameters of DSCs based on YD-2.[a] Thickness [mm] Voc [mV] Jsc [mA cm 2 ] FF [%] PCE [%] 2.4 755 10.5 71.2 5.6 4.5 750 13.3 69.8 6.9 6.7 739 15.0 70.9 7.9 8.9 732 16.3 71.0 8.4 11.5 735 16.7 71.5 8.8

[a] DSCs made from YD-2 sensitized transparent nanocrystalline TiO2 films of various thicknesses by employing a volatile electrolyte (Z960) at full sunlight intensity.

Table 2: Photovoltaic parameters of DSCs based on YD-2 and d-205.[a] Sensitizer Voc [mV] Jsc [mA cm 2 ] FF [%] PCE [%] YD-2/D-205 742 12.6 73.2 6.9 d-205 720 10.8 73.2 5.7 YD-2 755 10.5 71.2 5.6

[a] DSCs made from YD-2 and D-205 as cosensitizers under full sunlight intensity by employing a volatile electrolyte (Z960) and a 2.4 mm thick film.

Angewandte

Chemie

6647

important feature for solid-state DSCs where the diffusion

length of the device becomes a limiting factor.

To further increase the light-harvesting capacity of these

devices, an 11 mm transparent TiO

film was coated with a

5 mm thin layer of 400 nm reflecting particles. The

character-istic J–V curve of the solar cell containing YD-2 is shown in

Figure 2 a. The IPCE spectrum of the YD-2 device exhibits a

broad absorption from 400 nm to 750 nm with a peak

maximum over 90 % at 675 nm (Figure 2 b). A J

of

18.6 mA cm

_{, a V}

OC

of 0.77 V, and a FF of 0.764 were derived

from the J–V curve, thus giving an overall power conversion

efficiency (h) of 11 % under illumination with standard

AM 1.5G simulated sunlight (100 mW cm

_{). The J}

SC

value

obtained from integrating the product of the IPCE spectrum

with

the

AM 1.5G

spectral

solar

photon

flux

was

17.6 mA cm

_{. This value lies within 5 % of the measured}

J

value, thus showing that any spectral mismatch of the

simulated sunlight with regard to standard AM 1.5G emission

is small.

In conclusion, the integration of a porphyrin

chromo-phore as p bridge into a D–p–A dye resulted in a new

conjugated porphyrin dye that exhibits an unprecedented

efficiency of 11 % when used as a photosensitizer on a

double-layer TiO

film under standard illumination test conditions. It

has also been demonstrated that this novel porphyrin dye

shows a greatly enhanced photovoltaic performance when

cosensitized on a thin TiO

film (2.4 mm) with a metal-free

dye that has a complementary spectral response. Testing of

cosensitization for various TiO

film designs are the next step

in our investigation. The present study has opened new

possibilities for the improvement of photovoltaic

perfor-mance through a judicious design of the donor–acceptor

substitution on porphyrin dyes.

Experimental Section

Device fabrication: Screen-printed layers of TiO2 films were pre-pared as previously reported.[3c]_{The transparent film was prepared} with a TiO2nanoparticle paste (DSL-18NRT) obtained from Dysol, Australia. After sintering at 500 8C and cooling to 80 8C, the sintered TiO2electrodes were sensitized by immersion in a solution of the YD-2 dye (0.2 mm in ethanol with 0.4 mm chenodeoxycholic acid, CDCA) for 18 h, and then assembled using a thermally platinized FTO/glass (Tec 7) counter electrode. For the cosensitization experi-ments, TiO2electrodes were first immersed in a solution of YD-2 (0.2 mm in ethanol with 0.4 mm CDCA) for 18 h, rinsed with acetonitrile, and then immersed in a solution of D-205 (0.2 mm in tert-butanol/acetonitrile (1:1) with 0.4 mm CDCA) for 30 min. Following the immersion procedure, the dye-sensitized electrode was rinsed with acetonitrile and dried in air. The working and counter electrodes were separated by a 25 mm thick hot melt ring (Surlyn, DuPont) and sealed by heating. The cell internal space was filled with a volatile electrolyte (Z960: 1.0 m 1,3-dimethylimidazolium iodide, 0.03 m iodine, 0.5 m tert-butylpyridine, 0.05 m LiI, 0.1 m guanidinium thiocyanate), in an 85:15 acetonitrile/valeronitrile mixture through a pre-drilled hole using a vacuum pump. The electrolyte injection hole on the thermally platinized FTO glass counter electrode was finally sealed with a Surlyn sheet and a thin glass cover by heating.

Photovoltaic characterization: A 450 W xenon light source (Oriel, USA) was used to characterize the solar cells. The spectral output of the lamp was matched in the region of 350–750 nm with the aid of a Schott K113 Tempax sunlight filter (Przisions Glas & Optik GmbH, Germany) so as to reduce the mismatch between the simulated and true solar spectra to less than 2 %. The current– voltage characteristics of the cell measured under these conditions were obtained by applying external potential bias to the cell and by measuring the generated photocurrent with a Keithley model 2400 digital source meter (Keithley, USA). The devices were masked to attain an illuminated active area of 0.16 cm2_.

Received: April 9, 2010 Published online: August 4, 2010

.

Keywords: donor–acceptor systems · dyes/pigments ·

energy conversion · porphyrinoids · solar cells

[1] B. ORegan, M. Grtzel, Nature 1991, 353, 737 – 740.

[2] a) M. Nazeeruddin, F. De Angelis, S. Fantacci, A. Selloni, G. Viscardi, P. Liska, S. Ito, B. Takeru, M. Grtzel, J. Am. Chem. Soc. 2005, 127, 16835 – 16847; b) Y. Chiba, A. Islam, Y. Watanabe, R. Komiya, N. Koide, L. Han, Jpn. J. Appl. Phys. Part 2 2006, 45, L638 – L640; c) F. Gao, Y. Wang, D. Shi, J. Zhang, M. Wang, X. Jing, R. Humphry-Baker, P. Wang, S. Zakeeruddin, M. Grtzel, J. Am. Chem. Soc. 2008, 130, 10720 – 10728; d) C. Chen, M. Wang, J. Li, N. Pootrakulchote, L. Alibabaei, C. Ngoc-le, J.-D. Decoppet, J. H. Tsai, C. Grtzel, C.-G. Wu, S. M. Zakeeruddin, M. Grtzel, ACS Nano 2009, 3, 3103 – 3109. [3] a) T. Horiuchi, H. Miura, S. Uchida, Chem. Commun. 2003,

3036; b) T. Horiuchi, H. Miura, K. Sumioka, S. Uchida, J. Am. Chem. Soc. 2004, 126, 12218; c) S. Ito, S. M. Zakeeruddin, R. Humphry-Baker, P. Liska, R. Charvet, P. Comte, M. K. Nazeer-Figure 2. a) Photocurrent density–voltage (J–V) characteristics of a

device (2.4 mm thick film) using YD-2 as sensitizer under AM 1.5G illumination (100 mWcm2

). Values for dark current (a) and 100 % sun (c) are shown. b) Incident photon-to-current conversion effi-ciency (IPCE) spectrum of the same device.

Communications

uddin, P. Pchy, M. Takata, H. Miura, S. Uchida, M. Grtzel, Adv. Mater. 2006, 18, 1202 – 1205.

[4] a) T. Kitamura, M. Ikeda, K. Shigaki, T. Inoue, N. A. Anderson, X. Ai, T. Lian, S. Yanagida, Chem. Mater. 2004, 16, 1806; b) K. Hara, T. Sato, R. Katoh, A. Furabe, T. Yoshihara, M. Murai, M. Kurashige, S. Ito, A. Shinpo, S. Suga, H. Arakawa, Adv. Funct. Mater. 2005, 15, 246.

[5] a) S. Kim, H. Choi, D. Kim, K. Song, S. O. Kang, J. Ko, Tetrahedron 2007, 63, 9206; b) S. Kim, H. Choi, C. Baik, K. Song, S. O. Kang, J. Ko, Tetrahedron 2007, 63, 11436; c) I. Jung, J. K. Lee, K. H. Song, K. Song, S. O. Kang, J. Ko, J. Org. Chem. 2007, 72, 3652.

[6] a) M. Velusamy, K. R. J. Thomas, J. T. Lin, Y. Hsu, K. Ho, Org. Lett. 2005, 7, 1899; b) D. P. Hagberg, T. Edvinsson, T. Marinado, G. Boschloo, A. Hagfeldt, L. Sun, Chem. Commun. 2006, 2245; c) M. Liang, W. Xu, F. Cai, P. Chen, B. Peng, J. Chen, Z. Li, J. Phys. Chem. C 2007, 111, 4465.

[7] a) S. Ferrere, A. Zaban, B. A. Greg, J. Phys. Chem. B 1997, 101, 4490; b) S. Ferrere, B. A. Greg, New J. Chem. 2002, 26, 1155; c) Y. Shibano, T. Umeyama, Y. Matano, H. Imahori, Org. Lett. 2007, 9, 1971.

[8] a) A. Ehret, L. Stuhl, M. T. Spitler, J. Phys. Chem. B 2001, 105, 9960; b) S. Ushiroda, N. Ruzycki, Y. Lu, M. T. Spitler, B. A. Parkinson, J. Am. Chem. Soc. 2005, 127, 5158.

[9] S. Tatay, S. A. Haque, B. ORegan, J. R. Durrant, W. J. H. Verhees, J. M. Kroon, A. Vidal-Ferran, P. Gavia, E. Palomares, J. Mater. Chem. 2007, 17, 3037.

[10] a) Q.-H. Yao, L. Shan, F.-Y. Li, D.-D. Yin, C.-H. Huang, New J. Chem. 2003, 27, 1277; b) Y.-S. Chen, C. Li, Z.-H. Zeng, W.-B. Wang, X.-S. Wang, B.-W. Zhang, J. Mater. Chem. 2005, 15, 1654. [11] a) K. Hara, T. Sato, R. Katoh, A. Furube, Y. Ohga, A. Shinpo, S. Suga, K. Sayama, H. Sugihaa, H. Arakawa, J. Phys. Chem. B 2003, 107, 597; b) A. Morandeira, G. Boschloo, A. Hagfeldt, L. Hammarstrm, J. Phys. Chem. B 2005, 109, 19403; c) N. Koumura, Z.-S. Wang, S. Mori, M. Miyashita, E. Suzuki, K. Hara, J. Am. Chem. Soc. 2006, 128, 14256.

[12] a) The Porphyrin Handbook (Eds.: K. Kadish, K. Smith, R. Guilard), Academic, New York, 2000; b) A. Burrell, D. Officer, P. Plieger, D. Reid, Chem. Rev. 2001, 101, 2751.

[13] The Photosynthetic Reaction (Eds.: J. Deisenhofer, J. R. Norris), Academic Press, New York, 1993.

[14] a) J.-P. Collin, A. Harriman, V. Heitz, F. Odobel, J.-P. Sauvage, J. Am. Chem. Soc. 1994, 116, 5679; b) J. Seth, V. Palaniappan, R. W. Wagner, T. E. Johnson, J. S. Lindsey, D. F. Bocian, J. Am. Chem. Soc. 1996, 118, 11194; c) D.-L. Jiang, T. Aida, J. Am. Chem. Soc. 1998, 120, 10895; d) D. Gust, T. A. Moore, A. L. Moore, Acc. Chem. Res. 2001, 34, 40; e) H. S. Cho, H. Rhee, J. K. Song, C. K. Min, M. Takase, N. Aratani, S. Cho, A. Osuka, T. Joo, D. Kim, J. Am. Chem. Soc. 2003, 125, 5849; f) T. V. Duncan, S. P. Wu, M. J. Therien, J. Am. Chem. Soc. 2006, 128, 10423; g) H. Imahori, Bull. Chem. Soc. Jpn. 2007, 80, 621; h) M. U. Winters, J. Krnbratt, H. E. Blades, C. J. Wilson, M. J. Frampton, H. L. Anderson, B. Albinsson, Chem. Eur. J. 2007, 13, 7385.

[15] a) J. N. Clifford, G. Yahioglu, L. R. Milgrom, J. R. Durrant, Chem. Commun. 2002, 1260; b) T. Hasobe, H. Imahori, P. V. Kamat, T. K. Ahn, S. K. Kim, D. Kim, A. Fujimoto, T. Hirakawa, S. Fukuzumi, J. Am. Chem. Soc. 2005, 127, 1216; c) T. Hasobe, P. V. Kamat, V. Troiani, N. Solladi, T. K. Ahn, S. K. Kim, D. Kim, A. Kongkanand, S. Kuwabata, S. Fukuzumi, J. Phys. Chem. B 2005, 109, 19; d) M. Borgstrm, E. Blart, G. Boschloo, E. Mukhtar, A. Hagfeldt, L. Hammarstrm, F. Odobel, J. Phys. Chem. B 2005, 109, 22928; e) L. Luo, C.-F. Lo, C.-Y. Lin, I.-J. Chang, E. W.-G. Diau, J. Phys. Chem. B 2006, 110, 410; f) A. Huijser, T. J. Savenije, A. Kotlewski, S. J. Picken, L. D. A. Siebbeles, Adv. Mater. 2006, 18, 2234; g) O. Hagemann, M. Jørgensen, F. C. Krebs, J. Org. Chem. 2006, 71, 5546; h) G. M. Hasselman, D. F. Watson, J. R. Stromberg, D. F. Bocian, D. Holten, J. S. Lindsey, G. J. Meyer, J. Phys. Chem. B 2006, 110, 25430; i) S. Eu, S. Hayashi, T. Umeyama, A. Oguro, M. Kawasaki, N. Kadota, Y. Matano, H. Imahori, J. Phys. Chem. C 2007, 111, 3528.

[16] a) B. C. ORegan, I. Lpez-Duarte, M. V. Martnez-Daz, A. Forneli, J. Albero, A. Morandeira, E. Palomares, T. Torres, J.R. Durrant, J. Am. Chem. Soc. 2008, 130, 2906 – 2907; b) J. Cid, J.-H. Yum, S.-R. Jang, M. K. Nazeeruddin, E. Martnez-Ferrero, E. Palomares, J. Ko, M. Grtzel, T. Torres, Angew. Chem. 2007, 119, 8510; Angew. Chem. Int. Ed. 2007, 46, 8358; c) P. Y. Reddy, L. Giribabu, C. Lyness, H. J. Snaith, C. Vijaykumar, M. Chandra-sekharam, M. Lakshmikantam, J.-H. Yum, K. Kalyanasundaram, M. Grtzel, M. K. Nazeer, Angew. Chem. 2007, 119, 377; Angew. Chem. Int. Ed. 2007, 46, 373; d) J. He, G. Benk, F. Korodi, T. Polvka, R. Lomoth, B. kermark, L. Sun, A. Hagfeldt, V. Sundstrm, J. Am. Chem. Soc. 2002, 124, 4922; e) E. Palomares, M. V. Martinez-Diaz, S. A. Haque, T. Torres, J. R. Durrant, Chem. Commun. 2004, 2112.

[17] a) W. M. Campbell, A. K. Burrell, D. L. Officer, K. W. Jolley, Coord. Chem. Rev. 2004, 248, 1363; b) Q. Wang, W. M. Camp-bell, E. E. Bonfantani, K. W. Jolley, D. L. Officer, P. J. Walsh, K. Gordon, R. Humphry-Baker, M. K. Nazeeruddin, M. Grtzel, J. Phys. Chem. B 2005, 109, 15 397; c) L. Schmidt-Mende, W. M. Campbell, Q. Wang, K. W. Jolley, D. L. Officer, M. K. Nazeer-uddin, M. Grtzel, ChemPhysChem 2005, 6, 1253; d) W. M. Campbell, K. W. Jolley, P. Wagner, K. Wagner, P. J. Walsh, K. C. Gordon, L. Schmidt-Mende, M. K. Nazeeruddin, Q. Wang, M. Grtzel, D. L. Officer, J. Phys. Chem. C 2007, 111, 11760. [18] a) H.-P. Lu, C.-Y. Tsai, W.-N. Yen, C.-P. Hsieh, C.-W. Lee, C.-Y.

Yeh, E. W.-G. Diau, J. Phys. Chem. C 2009, 113, 20990; b) C.-P. Hsieh, H.-P. Lu, C.-L. Chiu, C.-W. Lee, S.-H. Chuang, C.-L. Mai, W.-N. Yen, S.-J. Hsu, E. W.-G. Diau, C.-Y. Yeh, J. Mater. Chem. 2010, 20, 1127.

[19] D. Kuang, S. Uchida, R. Humphry-Baker, S. M. Zakeeruddin, M. Grtzel, Angew. Chem. 2008, 120, 1949; Angew. Chem. Int. Ed. 2008, 47, 1923.

[20] C. Li, J.-Y. Yum, S.-J. Moon, A. Hermann, F. Eickemeyer, N. G. Pschirer, P. Erk, J. Schneboom, K. Mllen, M. Grtzel, M. K. Nazeeruddin, ChemSusChem 2008, 1, 699.

Angewandte

Chemie

6649