p-type Dye-Sensitized Solar Cells Based on Delafossite CuGaO 2 Nanoplates with Saturation Photovoltages Exceeding 460 mv

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1 SI Page 1 Supporting Information p-type Dye-Sensitized Solar Cells Based on Delafossite CuGaO 2 Nanoplates with Saturation Photovoltages Exceeding 460 mv Mingzhe Yu, Gayatri Natu, Zhiqiang Ji and Yiying Wu* Department of Chemistry & Biochemistry, The Ohio State University, 100 West 18 th Avenue, Columbus, Ohio *To whom correspondence should be addressed. Phone: (+1) , Fax: (+1) , wu@chemistry.ohio-state.edu

2 SI Page 2 1: Experimental details 1.1 Reagents and Materials All chemicals were used as received: gallium nitrate hydrate (Ga(NO 3 ) 3 ixh 2 O,99.9% ), copper nitrate penta-hydrate ( Gu(NO 3 ) 2 i2.5h 2 O, % ), cobalt chloride hydrate ( CoCl 2 i6h 2 O, AR ) and potassium hydroxide ( KOH ) from Alfa Aesar; ethylene glycol ( EG, 99% ), hexadecyltrimethylammonium bromide (CTAB, 99%), lithium iodide ( LiI,99.9%), iodine ( I 2,99.99% ), 4,4 -Di-tert-butyl-2,2 -dipyridyl (98%), acetonitrile and 3- methoxypropionitrile (MPN) from Sigma-Aldrich; ammonia hydroxide( NH4OH ), acetic acid(hac), 200 proof ethyl alcohol and ACS grade isopropyl alcohol from Fisher Scientific; deionized water (resistivity = 18MΩ.cm) from the Barnstead E-Pure system. FTO (fluorine-doped 3 tin oxide) glass pieces ( cm ) from Hartford Glass Co. were used for the solar cell construction. The organic donor-π-accepotor type chromophore P1 dye was synthesized as described by Qin et.al. 1 The Co 3+/2+ (dtb-bpy) compounds were synthesized as described by Gibson et.al CuGaO 2 Nanoplates Synthesis In a typical synthesis, 0.24mmol gallium nitrate and copper nitrate and 0.05g CTAB were dissolved in 6mL de-ionized water. 6mL 0.4M KOH solution was added drop-wisely into the former solution to get a homogenous colloid solution; 2mL EG was added into the solution as the reducing reagent. The solution (14mL in total) with a ph about 5 was stirred overnight, later poured to a 23mL Teflon cup and sealed with the outside bomb. The autoclave was heated at 190 o C for 52 hours for the hydrothermal reaction. The light-colored CuGaO 2 precipitate was

3 SI Page 3 collected after discarding the upper-liquid and washed with iso-propanol, diluted ammonia hydroxide (1M) and de-ionized water for 3-5 times respectively. 1.3 Material Characterizations The CuGaO 2 was characterized by powder X-ray diffraction (XRD, Cu Kα, Rigaku Inc.), scanning electron microscopy (SEM, Sirion, FEI Company) and transmission electron microscopy (TEM, Tecnai TF-20, FEI Company). 1.4 Saturation Open-circuit Voltage (V oc ) Measurements The saturation-v oc measurements were designed to get the solar cell s saturation-v oc under extremely high illumination intensity. An Oriel mercury-vapor lamp was used as the illumination source and a Newport 1916-c optical power meter was used to determine the illumination intensity. A CV-50W volatmmetric analyzer was used to record the solar cell s V oc. 1.5 Adsorption Isotherm Measurements The method used here was described in detail in another paper by Natu et.al from our group. 3 The tests were designed to get the dye adsorption information for the CuGaO 2 nanoplate films. The amount of the P1 organic dye molecules absorbed on CuGaO 2 films were compared with NiO films at the same conditions. The Sips model 4-5 of adsorption was used to fit the adsorption isotherm data: q= q m b ( ac ) 1 + ( ac ) b where q m is the maximum amount of adsorbed dye molecules on the particles surface, c is concentration of the dye solution, a and b are constant parameters. 1.6 Fabrication and Tests of Dye-Sensitized Solar Cells CuGaO 2 films with different thickness were fabricated with the CuGaO 2 paste. A typical paste was made by adding 30µL 0.6% (v/v) acetic acid and 30µL 1% (v/v) Triton-100

4 SI Page 4 polymer in isopropanol as surfactant into 0.5g CuGaO 2 aqueous solution. The films were fabricated by dropping a certain amount of the paste on the central region of the FTO glass whose edges were covered by Scotch tapes. After dried in the air, the films were sintered under 350 o C for 30minutes. The thickness of the films was later measured by imaging the film crosssections with SEM. The dye sensitization was accomplished by immersing the films into 0.40mM P1 dye in dry acetonitrile under dark for 24 hours. In a P1 organic dye molecule, the triphenylamine moiety acts as the electron donor and anchoring group; the malononitrile moiety acts as the electron acceptor and the thiophene unit acts as the conjugated chain. 1 A typical solar cell was assembled by attaching a platinum-coated FTO glass with a drilled hole to the dye-sensitized film with a polymer spacer by heating under 120 o C for 1 minute. The 1.0M LiI/0.1M I 2 /MPN or 0.1M Co 3+ (dtb-bpy)/0.1m Co 2+ (dtb-bpy)/mecn electrolyte was injected into the cell through the drilled hole via vacuum back-filling technique. The hole was later sealed with meltonix spacer. The dye sensitized solar cell performance was tested under 1 sun AM 1.5G simulated sunlight (Small-Area Class-B Solar Simulator, PV Measurements). The CV-50W volatmmetric analyzer was used here to record the solar cell s J-V curve 2. Performance of CuGaO 2 -based p-dsscs as a function of CuGaO 2 film thickness P-type DSSCs were fabricated with CuGaO 2 nanoplates as photo-cathodes with different film thicknesses. The 1.0M LiI/0.1M I 2 /MPN and P1 were used as electrolyte and sensitizing dye, respectively; J-V curves were measured under AM 1.5 sun illumination.

5 SI Page 5 Photocathode Film Electrolyte & Solvent Sensitizing-Dye V oc /mv Ref./year NiO LiI/I 2 in propylene carbonate TPPC /1999 Nanoporous-NiO LiI/I 2 electrolyte PN50 MC 93 7 /2005 Nanostructured-NiO LiI/I 2 in propylene carbonate P /2008 P105 precusor-nio LiI/I 2 in acetonitrile NK /2008 Mesoporous-NiO LiI/I 2 in propylene carbonate Erythrosin /2008 Nanoporous-NiO LiI/I 2 C Double-layered-NiO LiI/I 2 in acetonitrile P1 106 Screen-printing NiO N-methyl-N-butyl imidazolium iodide/4-t - butylpyridine/guanadiniu m thiocyanate/iodine in acetonitrile/valeronitrile Dye F108 precusor-nio LiI/I 2 in acetonitrile O6 97 Nanocrystalline-NiO LiI/I 2 in acetontitrile Ru-based dye / / / / /2011 Mesoporous-NiO Co(dtb-bpy) 3 2+/3+ in MeCN PMI-NDI /2011 Nanocrystalline-NiO I 2 / 4-terbutylpyridine /1- butyl-3- methylimidazolium iodide/guanidinium thiocyanate in acetonitrile/valeronitrile Dye /2011 Table. S1 a brief summary of V oc in NiO-based p-dsscs under AM 1.5sun illumination

6 SI Page 6 Film Thickness / µm V oc / mv J sc / (ma/cm2) FF / % Efficiency / % Table. S2 Solar cell parameters with different thick CuGaO 2 films Fig. S1, (a) the J-V curves with different CuGaO 2 films thicknesses with LiI/I 2 redox couple; (b) the best J-V performance of CuGaO 2 p-dsscs with LiI/I 2 redox couple

7 SI Page 7 Fig. S2 Results of control experiments. We have carried out two control experiments to verify the photocurrent is from the dye sensitization of CuGaO 2. The blank test with dye adsorbed fluorine-doped tin oxide (FTO) substrate (without CuGaO 2 ) cell showed negligible photocurrent (blue curve); the photocurrent from CuGaO 2 without dye-sensitizing (red curve) is also almost negligible compared to the dye-sensitized CuGaO 2 cell(green curve). These results clarify that the photocurrent comes from the dye-sensitized CuGaO 2.

8 SI Page 8 Fig.S3, dye adsorption as a function of the dye concentration for CuGaO 2 (blue) and NiO (red). References (1) Qin, P.; Zhu, H.; Edvinsson, T.; Boschloo, G.; Hagfeldt, A.; Sun, L. J. Am. Chem. Soc. 2008, 130, (2) Gibson, E. A.; Smeigh, A. L.; Le Pleux, L. c.; Hammarström, L.; Odobel, F.; Boschloo, G.; Hagfeldt, A. The Journal of Physical Chemistry C 2011, 115, (3) Natu, G.; Huang, Z.; Ji, Z.; Wu, Y. Langmuir 2011, 28, 950. (4) Sips, R. J. Chem. Phys. 1950, 18, (5) Sips, R. J. Chem. Phys. 1948, 16, 490. (6) He, J.; Lindstrom, H.; Hagfeldt, A.; Lindquist, S.-E. J. Phys. Chem. B 1999, 103, (7) Nakasa, A.; Usami, H.; Sumikura, S.; Hasegawa, S.; Koyama, T.; Suzuki, E. Chem. Lett. 2005, 34, 500. (8) Sumikura, S.; Mori, S.; Shimizu, S.; Usami, H.; Suzuki, E. Journal of Photochemistry and Photobiology A: Chemistry 2008, 199, 1. (9) Andrew, N.; Michael, F.; Robert, K.; Yi-Bing, C.; Udo, B. Nanotechnology 2008, 19, (10) Lepleux, L. c.; Chavillon, B.; Pellegrin, Y.; Blart, E.; Cario, L.; Jobic, S. p.; Odobel, F. Inorg. Chem. 2009, 48, (11) Li, L.; Gibson, E. A.; Qin, P.; Boschloo, G.; Gorlov, M.; Hagfeldt, A.; Sun, L. Advanced Materials 2010, 22, 1759.

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