Porphyrin sensitized solar cells: TiO2 sensitization with a π-extended porphyrin possessing two anchoring groups

Article abstract of DOI:10.1039/c0cc00257g

A π-extended porphyrin possessing two anchoring groups has been synthesized and successfully applied to dye-sensitized solar cells with a power conversion efficiency of 5.5%, rendering it comparable to the performance of N719-sensitized solar cells under the conditions employed here.

Full text of DOI:10.1039/c0cc00257g

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Supporting Information for
Porphyrin Sensitized Solar Cells: TiO2 Sensitization With a Π-
Extended Porphyrin Possessing Two Anchoring Groups
by
Chang Yeon Lee, Chunxing She, Nak Cheon Jeong and Joseph T. Hupp*
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA
*To whom correspondence should be addressed. E-mail: j-hupp@northwestern.edu
Tel: (847) 491-3504. Fax: (847) 491-7713
Experimental Section
Materials and General Procedures
All chemicals were obtained from commercial sources and used without further purification.
All of the reactions and manipulations were carried out under N2 with the use of standard inert-
atmosphere and Schlenk techniques. Solvents used in reactions were dried by standard
procedures. Absorbance spectra were obtained using a Varian Cary 5000 UV-Vis-NIR
spectrophotometer. Nuclear magnetic resonance (NMR) spectra for all the synthesized
1
compounds were recorded on a Varian INOVA 500 NMR spectrometer (499.773 MHz for H
NMR, 125.669 MHz for 13C NMR). Matrix-assisted laser desorption ionization time-of-flight
(MALDI-TOF) mass spectrometry was performed on a PE Voyager DE-Pro MALDI-TOF mass
spectrometer in positive, reflector ionization mode, using dithranol as a matrix. Atomic layer
deposition (ALD) was performed with a Savannah 100 instrument (Cambridge Nanotech Inc.).
Compounds 1 and 2 were synthesized according to the published procedures.1
Porphyrin Synthesis
Details of the synthetic method are displayed in Scheme 1.

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C12H25
O
O
OC12H25
C12H25
O
O
OC12H25
N
N
N
N
N
N
N
N
Zn
Zn
Si(C6H13 3
)
C12H25
OC12H25
C12H25
OC12H25
1
2
3, PPh3, CuI, Pd2(dba)3
3, PPh3, CuI, Pd2(dba)3
TEA, Toluene, r.t, 12h.
TEA, Toluene, r.t, 12h.
C12H25
O
OC12H25
C12H25
O
OC12H25
HOOC
N
N
N
N
N
N
N
CN
Zn
Si(C6H13 3
)
Zn
HOOC
HOOC
N
CN
CN
C12H25
O
OC12H25
C12H25
O
OC12H25
ZnPCA
ZnPDCA
COOH
O
H
NC
CNCH2COOH, NH4Ac
Acetic acid, 80oC, 3h.
I
I
3
Scheme 1. Synthetic procedures for ZnPCA and ZnPDCA.
2-Cyano-3-(4-iodophenyl)acrylic Acid 3. 4-Iodobenzaldehyde (100 mg, 0.43 mmol) and
cyanoacetic acid (44 mg, 0.52 mmol) were added to a stirred solution of ammonium acetate (11
mg, 0.14 mmol) in 1 ml of acetic acid and the resulting solution was refluxed for 12 h. After
cooling to room temperature, the desired product was crystallized from the solution. The
precipitate was filtered, washed by distilled water. Recrystallization from methylene chloride and
hexane yielded the compound 3 as white solid (77 mg, 60% yield). 1H NMR (DMSO) δ 8.29 (s,
13
1H), 7.97 (d, J = 8.5 Hz, 2H), 7.78 (d, J = 8.5 Hz, 2H). C NMR (DMSO) δ 163.09, 153.38,
138.21, 131.97, 130.91, 115.94, 104.45, 101.42.
ZnPCA. A solution of 1 (112 mg, 0.070 mmol), 3 (21 mg, 0.070 mmol), CuI (7 mg, 0.037
mmol), and PPh3 (18 mg, 0.069 mmol) in 10 ml of TEA/Toluene (1:5 v/v) was degassed with N2

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stream for 10 min. Pd2(dba)3 (16 mg, 0.017 mmol) was added all at once and then stirred for 12 h.
Solvent was evaporated in vacuo and then dark residue was purified by silica-gel column
chromatography silica-gel column chromatography (dichloromethane/methanol (95:5 v/v)) to
afford pure ZnPCA, (74 mg, 60% yield). 1H NMR (CDCl3) δ 9.69 (d, J = 4.5 Hz, 2H), 9.61 (d, J
= 4.5 Hz, 2H), 8.93 (d, J = 4.5 Hz, 2H), 8.83 (d, J = 4.5 Hz, 2H), 8.36(s, 1H), 8.23 (br, 2H), 8.10
(br, 2H), 7.61 (br, 2H), 6.95 (d, J = 7 Hz 4H), 3.81 (br, 8H) 1.76-1.79 (m, 6H), 1.54-1.57 (m, 6H),
1.39-1.44 (m, 12H), 0.73-1.19 (br, 75H), 0.37-0.58 (br, 32H). MS (MALDI-TOF) m/z 1763 (M +
H+).
ZnPDCA A solution of 2 (90 mg, 0.070 mmol), 3 (46 mg, 0.15 mmol), CuI (6 mg, 0.071
mmol), and PPh3 (37 mg, 0.140 mmol) in 10 ml of TEA/Toluene (1:5 v/v) was degassed with N2
stream for 10min. Pd2(dba)3 (32 mg, 0.035 mmol) was added all at once and then stirred for 12h.
Solvent was evaporated in vacuo and then dark residue was purified by silica-gel column
chromatography silica-gel column chromatography (dichloromethane/methanol (2:1 v/v)) to
afford pure ZnPDCA, (63 mg, 55% yield). 1H NMR (CDCl3/CD3OD) δ 9.40 (d, J = 4.5 Hz, 4H),
8.59 (d, J = 4.5 Hz, 4H), 8.03 (s, 2H), 7.93 (d, J = 8 Hz, 4H), 7.86 (d, J = 8 Hz, 4H), 7.49 (t, J =
8.5 Hz, 2H), 6.81 (d, J = 8.5 Hz, 4H), 3.66 (t, J = 6.0 Hz, 8H), 0.92-0.97 (m, 10H), 0.65-0.87 (br,
38H), 0.56-0.63 (br, 20H) 0.40-0.45 (m, 8H), 0.23-0.29 (m, 16H), 0.15-0.17 (m, 8H), (MALDI-
TOF) m/z 1652 (M + H+).
Preparation of dye-sensitized solar cells. Photoelectrodes were prepared on 12 Ω cm-2 FTO-
coated glass (Hartford glass). Blocking layers of TiO2 were deposited using 400 ALD cycles of
titanium isopropoxide (Aldrich), TIP, and water as precursors. TiO2 was grown at 200 °C using
reactant exposure times of 1 and 0.02 s for TIP and H2O, respectively, and nitrogen purge times
of 10 s between exposures. A transparent TiO2 nanoparticle layer (12 μm, measured using a
Tencor P10 profilometer) was prepared by doctor blading a paste of TiO2 nanoparticles (DSL
18NR-T, Dyesol) on the FTO. A scattering layer (4 μm) of TiO2 nanoparticles (WER4-O,
Dyesol) was subsequently deposited on top of the transparent layer. The resulting electrodes
were annealed at 500 °C in air for 30 min. After annealing, the TiO2 electrodes were
immediately immersed in a 0.5 mM solution of ZnPCA and ZnPDCA in chloroform/ethanol
(3:1). After 2 h, they were rinsed with chloroform/ethanol and dried with N2. A Surlyn frame (25
μm) was sandwiched between the open-pore side of the membrane and a platinized FTO
electrode. Light pressure was applied to seal the cell while heating the cell at 130 °C. A solution

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of 0.60 M butylmethylimidazolium iodide, 0.03 M I2, 0.10 M guanidinium thiocyanate, 0.50 M
4-tert-butylpyridine and 0.1 M LiI in 3 mL acetonitrile:valeronitrile (85:15) was introduced into
the TiO2 cells. Additional Surlyn and a microscope cover slide sealed the electrolyte into the cell.
Cells were illuminated through an Oriel 81092 filter by a Xe lamp in a Jobin Yvon fluorimeter
(Fluorolog 3). Broadband excitation using the grating at zeroth order was 98 mW cm-2. Optical
power was measured with an Ophir 3A-SH radiometer. A CH Instruments 1200A potentiostat
was used to measure current-voltage curves.
Electrochemical measurements. Cyclic voltammetry was carried out on a CH Instruments
CH900 Electrochemical Analyzer using a conventional three-electrode system consisting of a
ZnPCA/TiO2 or ZnPDCA/TiO2 as the working electrode, a platinum wire electrode, and a
pseudo Ag/AgCl reference electrode. Ferrocene/ferrocenium (+0.64 V vs NHE) was used as an
internal reference. All measurements were performed at ambient temperature under a nitrogen
atomosphere in dry deoxygenated 0.1 M tetrabutylammonium hexafluorophosphate solution in
CH2Cl2.
Fig. S1. UV-Vis spectra of 2, ZnPCA and ZnPDCA in chloroform-ethanol (3:1).

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Fig. S2. Light harvesting efficiency (LHE) for ZnPCA and ZnPDCA on 12 μm TiO2 films.
(Reflection by FTO and scattering by 400 nm particles are not taken into account.)
Fig. S3. Cyclic voltammograms of ZnPCA (a) and ZnPDCA (b) on TiO2 (scan rate = 0.1 V/s).

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HOMO of ZnPDCA
LUMO of ZnPDCA
HOMO of ZnPCA
LUMO of ZnPCA
Fig. S4. Molecular orbitals of ZnPCA and ZnPDCA calculated at the B3LYP/6-31G* level.
Fig. S5. Charge lifetimes vs. photovoltage for ZnPDCA and ZnPCA sensitized TiO2 cells.

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Fig. S6. MALDI-TOF of ZnPCA

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Fig. S7. Expanded MALDI-TOF of ZnPCA

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Fig. S8. MALDI-TOF of ZnPDCA

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Fig. S9. Expanded MALDI-TOF of ZnPDCA

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Fig. S10. 1H-NMR of ZnPCA

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Fig. S11. 1H-NMR of ZnPDCA
Reference:
1. C. Y. Lee and J. T. Hupp, Langmuir, 2010, 26, 3760.

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Caption for TOC figure: A dye-sensitized solar cell based on a π-extended
porphyrin possessing two anchoring groups achieves a power conversion
efficiency of 5.5 %.