SUPPLEMENTARY INFORMATION

Transcription

1 Supplementary Information for Wideband dye-sensitized solar cells by efficient spin-forbidden transition Table of Contents 1. Theoretical section 1.1 Computation Methods 1.2 Molecular orbital of DX1 and BD 1.3 Calculated excitation energies of DX1E 2. Experimental section 2.1 Materials 2.2 Measurements 2.3 Photophysical analysis 2.4 Absorption specta change in CH 2 X 2 solution 2.5 Experimental absorption and TD-DFT calculation of DX1E 2.6 Electrochemical analysis of DX1 2.7 Photocurrent density-voltage (J-V) characteristics 3. Reference for Supplementary Information NATURE PHOTONICS 1

2 1. Theoretical section 1.1 Computation Methods The calculation was performed by the Gaussian 09 program (31) using the B1LYP exchange correlations functional (32). Geometry optimizations were performed in ethanol solution using Double-ζ quality basis sets were employed for the ligands (6-31G**) (33) and the Ru (LanL2DZ) (34). A relativistic effective core potential (ECP) (34) on Ru replaced the inner core electrons leaving the outer core [(4s) 2 (4p) 6 ] electrons and the (4d) 6 valence electrons of Ru(II). The geometries were fully optimized without symmetry constraints. TD-DFT (35) excited states calculations of the lowest singlet-singlet and singlet-triplet excitations were performed in ethanol solution using the same 6-31G** and LanL2DZ basis set used for geometry optimizations. Typically the lowest 15 triplet and 15 singlet roots of the nonhermitian eigenvalue equations were obtained to the vertical excitation energies. 2 NATURE PHOTONICS

3 1.2 Molecular orbital of DX1 and BD x y z LUMO LUMO HOMO HOMO HOMO-1 HOMO-1 HOMO-2 HOMO-2 DX1E BDE NATURE PHOTONICS 3

4 Figure S1. Calculated molecular orbitals of DX1 and BD. Highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals of DX1 (left) and BD (right) as calculated using density functional theory (DFT) at the B1LYP/6-31G** and Lanl2DZ (Ru) level. Carbon, oxygen, nitrogen, phosphorus, chlorine, hydrogen, sulfur and ruthenium atoms are shown as grey, red, blue, orange, green, white, yellow and light-blue spheres, respectively. Red and green shading distinguishes the positive and negative phases of the molecular orbitals, respectively, displayed with an isovalue of 0.02e Å -3. Table S1. Molecular orbitals with dominant character (%) for DX1 and BD DX1 orbital Ru (%) Cl (%) tcterpy (%) Phosphine (%) HOMO 63 (d yz ), 1 (d xz ) H-1 54 (d xz ) H-2 66 (d xy ) BD orbital Ru (%) NCS (%) tcterpy (%) HOMO 26 (d xz ) H-1 27 (d yz ) 69 4 H-2 19 (d xy ) NATURE PHOTONICS

5 1.3 Calculated excitation energies of DX1E Table S2. Excitation Characteristics of complex DX1E. Singlet states energy / ev oscillator strength character a ( c > 0.1) HOMO LUMO H-1 LUMO 0.26 HOMO L H-1 L HOMO L HOMO L H-1 LUMO 0.22 H-1 L HOMO L H-2 LUMO 0.12 H-4 LUMO HOMO L HOMO L HOMO L H-7 L HOMO L HOMO L HOMO L H-1 L HOMO L H-1 L HOMO L H-1 L H-1 L HOMO L H-1 L H-1 L H-2 L H-3 LUMO 0.29 H-1 L H-1 L H-3 LUMO 0.44 H-2 L H-1 L H-2 L H-1 L H-3 LUMO 0.16 H-1 L H-4 LUMO 0.12 H-2 LUMO H-3 L+1 NATURE PHOTONICS 5

6 Triplet states energy / ev character a ( c > 0.1) HOMO LUMO 0.14 H-1 LUMO H-1 LUMO 0.14 HOMO LUMO HOMO L H-7 L HOMO L HOMO L H-7 L H-1 L H-2 LUMO 0.12 H-4 LUMO H-1 L H-1 L H-10 L H-5 L HOMO L HOMO L HOMO L H-1 L HOMO L H-1 L HOMO L H-1 L H-2 L H-3 LUMO 0.12 H-9 L H-4 L H-3 LUMO 0.29 H-2 L H-9 L H-7 L H-1 L H-10 LUMO H-3 LUMO 0.24 H-9 L H-7 L H-5 LUMO 0.14 H-9 L H-12 LUMO 0.12 H-10 LUMO 0.12 H-1 L HOMO L HOMO L H-7 L HOMO L+8 (a) The H and L in the character column denote the HOMO and LUMO, respectively. Transition contribution coefficients are included. 6 NATURE PHOTONICS

7 2.Experimental section: 2.1 Materials All organic solvents used were of puriss grade from Wako Pure Chemical Industries, Ltd, Japan. DMF was distilled with BaO (Wako) in vacuum, and treatmented with molecular sieves 3A (Wako) for 1day. After deaeration the solvent was stored under Ar and used as soon as possible. Other compounds used were: trimethyl-2,2 :6,2 -terpyridine- 4,4,4 -tricarboxylate (Aldrich), RuCl 3 (Tokyo Chemical Industry Co., Ltd.), phenyldimethoxyphosphine (Wako), NEt 3 (Wako), NaNCS (Wako), TBACl (Wako), Sephadex LH-20 (GE Healthcare), 1,2-dimethyl-3-propylimidazolium iodide (DMPII) (Shikoku Chemicals Co., Ltd.), Black Dye (Dyesol). Synthesis of esterified DX1 (DX1E). RuCl 3 was dissolved in dehydrated EtOH, and trimethyl-2,2 :6,2 -terpyridine-4,4,4 -tricarboxylate was then added. The reaction mixture was refluxed under argon for 3 h. The reaction solvent was removed, and the residue was dissolved into CHCl 3 at 0 C. To the reaction solution was then added NEt 3 and phenyldimethoxyphosphine, and the reaction mixture was heated at 70 C for 5 min. After cooling, most of solvent was removed under vacuum. The brown product was precipitated NATURE PHOTONICS 7

8 with diethylether. This brown product was isolated by suction filtration and washed with diethylether. It was purified on a silica gel column using CH 3 Cl:CH 3 CN = 3:7 as the eluent. 1 H NMR (400MHz, δ/ p.p.m. in CDCl 3 ), 9.22 (d, J=5.5Hz, 2H), 8.77 (d, J=1.4Hz, 2H), 8.63 (s, 2H), 8.13 (m, 2H), 7.73 (d, J=5.5Hz, 2H), 7.50 (m, 3H), 4.13 (s, 3H), 4.02 (s, 6H), 3.92 (d, 10.1Hz, 6H). FAB-MS (m/z): [M]+ calcd for C 29 H 28 Cl 2 N 3 O 8 PRu, ; found, Synthesis of esterified BD (BDE). RuCl 3 was dissolved in dehydrated EtOH, and trimethyl-2,2 :6,2 -terpyridine-4,4,4 -tricarboxylate was then added. The reaction mixture was refluxed under argon for 3 h. The reaction solvent was removed, and the residue was dissolved into distilled DMF. To the reaction solution was then added excess NaNCS solution and the reaction mixture was refluxed for 24 h. After cooling, most of the solvent was removed under vacuum. The dark green product was dissolved into water, and to the solution was added TBACl solution. The dark green product was isolated by suction filtration and washed with water and acetone / diethylether. It was purified on a Sephadex LH-20 column using methanol as the eluent. 1 H NMR (400MHz, δ/ p.p.m. in CDCl 3 ), 9.12 (d, J=5.9Hz, 2H), 8.66 (d, J=1.4Hz, 2H), 8.64 (s, J=1.4Hz, 2H), 8.03 (dd, J=5.9Hz, J=1.4Hz, 2H), 4.12 (s, 3H), 4.08 (s, 6H), 3.38 (t, J=8.4Hz, 16H), 1.75 (m, 16H), 1.42 (m, 16H), 0.96 (t, 8 NATURE PHOTONICS

9 J=7.3Hz, 24H). FAB-MS (m/z): [M]- calcd for C 24 H 17 N 6 O 6 RuS 3, ; found, Measurements UV-vis absorption spectra were measured using a JASCO V-570 spectrometer. The steady-state emission and time-resolved emission spectra were measured by exciting the sample with a pulse from an active modelocked Nd:YAG laser, using the frequency doubled line at 532 nm. The emitted light was detected with a Hamamatsu R photomultiplier operated in single-photon counting mode. The emission lifetimes were measured using a time-correlated single photon counting system (Hamamatsu C7990). The emission lifetime data were analyzed using the deconvolution method with an instrumental response function (IRF). A Dewar vessel was used for the measurements at 77K. 1 H NMR spectra were recorded with a JEOL JNM-ECS400 spectrometer. 14 N NMR spectra were recorded with a Bruker DMX 500 MHz NMR spectrometer. CH 3 NO 2 was used as internal reference and DMSO-d 6 was used as a solvent. 31 P NMR spectra were recorded with a Bruker Avance 600 MHz NMR spectrometer. 85% H 3 PO 4 solution was used as external reference and DMSO-d 6 was used as a solvent. Electrochemical data were obtained by differential pulse voltammetry using a three-electrode cell and a BAS100B/W electrochemical analyzer. The counter NATURE PHOTONICS 9

10 electrode and the working electrode were platinum electrodes, and the reference electrode was a saturated calomel electrode (SCE), and the supporting electrolyte was 0.1 M tetrabutylammonium hexafluorophosphate. 10 NATURE PHOTONICS

11 2.3 Photophysical analysis (a) MeO O - TBA + MeO O O MeO SCN N N Ru N NCS NCS O MeO Cl N Cl N Ru P N OMe OMe MeO O MeO O (b) absorption phosphorescence absorption phosphorescence Intensity / arb. units Intensity / arb. units Energy / ev Energy / ev (c) Extinction coefficient / M -1 cm -1 x absorption at 298 K Energy / ev Extinction coefficient / M -1 cm -1 x absorption at 298 K Energy / ev Fig. S2 Chemical structures of esterified BD (BDE) and esterified DX1 (DX1E) and low temperature absorption and phosphorescence spectra of BDE and DX1E in toluene. (a) Chemical structures of esterified BD (left) and esterified DX1 (right). TBA + is NATURE PHOTONICS 11

12 n-tetrabutylammonium cation. (b) Low temperature (77K) absorption (blue) and phosphorescence (red) spectra of BDE (left) and DX1E (right) in toluene. Filled curve parts in the absorption spectra indicate the overlap region of both absorption and phosphorescence spectra. (c) Absorption spectra of BDE (left) and DX1E (right) in toluene at 298 K. 12 NATURE PHOTONICS

13 2.4 Absorption specta change in CH 2 X 2 solution (a) Extinciton coefficient / M -1 cm -1 x DX1E X=Cl Br I Wavelength / nm 1100 (c) ΔO.D. / arb. units DX1E Δ(Br-Cl) Δ(I-Cl) Wavelength / nm 1100 (b) Extinciton coefficient / M -1 cm -1 x BDE X=Cl Br I Wavelength / nm 1050 (d) ΔO.D. / arb. units BDE Δ(Br-Cl) Δ(I-Cl) Wavelength / nm Fig. S3 Enhancement of the absorption band of BDE and DX1E in CH 2 X 2 containing different external heavy atoms (X=Cl, Br, I). (a), (b) Absorption spectra on the overlapped NATURE PHOTONICS 13

14 region with the emission spectra of DX1E (a) and BDE (b) in methylene dihalide (CH 2 X 2 : X=Cl, Br, I) solutions at 298 K (c), (d) Enhancement of absorption spectra of DX1E (c) and BDE (d) in methylene dihalide (CH 2 X 2 : X=Cl, Br, I) solutions at 298 K. Table S3. Enhancements of the absorption band on the overlapped region with emission spectrum of DX1E and BDE by CH 2 X 2 (X=Cl, Br, I) DX1E CH 2 X 2 (X=) f a Δf b (vs. Cl) τ c /ns Cl Br I BDE CH 2 X 2 (X=) f a Δf b (vs. Cl) τ c /ns Cl Br I a The integrated absorption intensity is defined as f d(ev ), where is extinction coefficient. b The integrated difference of intensity is defined as f d(ev ), where is difference of the extinction coefficient ( Br ). or I Cl c Measured at 77K. 14 NATURE PHOTONICS

15 Table S4. The ratio between the increase in absorption intensity caused by the CH 2 X 2 solvent containing heavy atom (X=Br, I) and absorption intensity in CH 2 Cl 2 of BDE and DX1E Complex Δf Br-Cl / f Cl Δf I-Cl / f Cl BDE DX1E NATURE PHOTONICS 15

16 2.5 Experimental absorption and TD-DFT calculation of DX1E Intensity / arb. units absorption (77K) phosphorescence (77K) calc. (singlet-singlet) calc. (singlet-triplet) Energy / ev Fig. S4 Comparison chart of low temperature absorption and phosphorescence spectra and TD-DFT calculation results of DX1E. The absorption and phosphorescence spectra of DX1E (top) were measured in toluene at 77K. The calculation results are obtained by TD-DFT. Since the oscillator strengths are calculated with the non-spin orbital coupled model, the oscillator strength values of the singlet-triplet transitions can not be obtained. 16 NATURE PHOTONICS

17 2.6 Electrochemical analysis of DX1 Figure S5 exhibited the differential pulse voltammetry (DPV) of DX1 and BD in DMF which showed a reversible wave at 0.68 V vs. SCE (standard calomel electrode) for the anodic region, which can be readily assigned to the Ru(II)/(III) redox couple. For the cathodic region, a quasi-reversible wave at V vs. SCE assigned to the reduction of the tcterpy ligand was observed. Under similar conditions in DMF, the DPV of BD shows an oxidation wave at 0.72 V and a reduction wave at V vs. SCE. Thus, both sensitizers have similar HOMO-LUMO energy levels and are in good accordance with the small difference between the phosphorescence maxima of the two compounds of ~0.03 ev. Therefore, DX1 is expected to have comparable driving forces with BD for both electron injection to TiO 2 and regeneration of the dye through electron transfer to the electrolyte. NATURE PHOTONICS 17

18 3 2 DX1 BD Current / μa Potential / mv vs SCE Fig. S5 Differential pulse voltammograms of DX1 (red) and BD (green) in DMF. 18 NATURE PHOTONICS

19 2.7 Photocurrent density-voltage (J-V) characteristics a IPCE / % Wavelength / nm 900 [TBP] 0.0 M 0.1 M 0.2 M 0.3 M 0.4 M 0.5 M 1000 b Current density / macm [TBP] 0.0 M 0.1 M 0.2 M 0.3 M 0.4 M 0.5 M Voltage / V Fig. S6 Effects of the 4-tert-butyl pyridine (TBP) concentration on device performance. (a) Incident photon-to-current IPCE spectrum of the DSSC made of DX1 using the same electrolyte captioned in Fig. 2b [0.60 M 1,2-dimethyl-3-propylimidazolium iodide (DMPII), 25 mm I 2, and 0.1 M LiI in a mixture of acetonitrile] with various 4-tert-butyl pyridine (TBP) concentrations. (b) Short-circuit current versus voltage curves of the same devices shown in Fig. 2b under solar illumination (AM1.5G, 100mWcm -2 ). NATURE PHOTONICS 19

20 Table S5 Photovoltaic parameters at various concentration of 4-tert-butyl pyridine (TBP). [TBP] / M V OC / V J SC / macm -2 FF η / % (best) η / % (average) Short-circuit photocurrent density (J SC ), Open-circuit voltage (V OC ), fill factor (FF) and over all conversion efficiency (η). Measurements were carried out under an AM1.5G one sun intensity of 100 mwcm -2. The photoelectric conversion properties depend strongly on the surface condition of the titanium oxide particles. However the photoelectric parameter dispersion can be relatively stabilized by titanium tetrachloride treatment. 20 NATURE PHOTONICS

21 mw/cm 2 Current density / macm Int V OC J SC FF η mw/cm 2 7 mw/cm 2 0 dark Voltage / V Fig. S7 Photocurrent voltage characteristics of DSSCs sensitized with DX1 under different incident light intensities. Short-circuit current versus the voltage curve characteristics of DSSC with DX1 under different light intensity, with the spectral distribution matching the standard AM 1.5 solar radiation: 100 mw cm -2 (red line), 34 mw cm -2 (blue line), 7.4 mw cm -2 (green line), and dark (red dashed line). The electrolyte solution contained 0.1 M 4-tert-butylpyridine (TBP), 0.60 M 1,2-dimethyl-3-propylimidazolium iodide (DMPII), 25 mm I 2, and 0.1 M LiI in a mixture of acetonitrile. Inset: V OC, open-circuit voltage (V); J SC, short-circuit current density (macm -2 ); FF, fill factor; η, energy conversion efficiency (%). NATURE PHOTONICS 21

22 Current density / macm mwcm mwcm mwcm mwcm -2 dark Voltage / V Fig. S8 Photocurrent voltage characteristics of the tandem-dssc under different incident light intensities. Short-circuit current versus the voltage curve characteristics of tandem-dssc under different light intensity, with the spectral distribution matching the standard AM 1.5G solar radiation: 100 mw cm -2 (red line), 59 mw cm -2 (brown line), 34 mw cm -2 (green line), 7.4 mw cm -2 (blue line), and dark (purple line). Table S6 Photovoltaic parameters of the tandem-dssc under different incident light intensities. Intensity / mwcm -2 V OC / V J SC / macm -2 FF η / % NATURE PHOTONICS

23 3. Reference for Supplementary Information (31) Frisch, M. J., et al. Gaussian 09, revision A.02; Gaussian, Inc.:Wallingford, CT, (32) Becke, A. D. Density-functional thermochemistry. IV. A new dynamical correlation functional and implications for exact-exchange mixing. J. Chem. Phys., 104, 1040 (1996). (33) Ditchfield, R., Hehre, W. J., Pople, J. A. Self consistent molecular orbital methods. IX. An extended gaussian type basis for molecular orbital studies of organic molecules. J. Chem. Phys. 54, 724 (1971) (34) Hay, P. J., Wadt, W. R. Ab initio effective core potentials for molecular calculations. potentials for the transition metal atoms Sc to Hg. J. Chem. Phys. 82, 270 (1985) (35) Bauernschmitt, R. & Ahlrichs, R. Treatment of electronic excitations within the adiabatic approximation of time dependent density functional theory. Chem. Phys. Lett. 256, 454 (1996) NATURE PHOTONICS 23