Supporting information. Bilayer Chlorophyll-Based Bio-Solar Cells Inspired from the Z-

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1 Supporting information Bilayer Chlorophyll-Based Bio-Solar Cells Inspired from the Z- Scheme Process of Oxygenic Photosynthesis Shengnan Duan a, Chunxiang Dall Agnese a, Gang Chen a, Xiao-Feng Wang a*, Hitoshi Tamiaki b, Yuya Yamamoto c, Toshitaka Ikeuchi c, Shin-ichi Sasaki b,c a Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), College of Physics, Jilin University, Changchun , P. R. China b Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga , Japan c Nagahama Institute of Bio-Science and Technology, Nagahama, Shiga , Japan Corresponding Author *Xiao-Feng Wang. xf_wang@jlu.edu.cn S1

2 Experimental section Materials Chl-A, 1 Chl-D3, 2 and Chl-D4 3 were synthesized as reported before. Zinc acetate dihydrate (Zn(CH3COO)2 2H2O) and MoO3 were purchased from Sinopharm Chemical Reagent Co., Ltd. 2-Methoxyethanol (CH3OCH2CH2OH), tetrahydrofuran (THF) and ethanolamine (NH2CH2CH2OH) were purchased from Aladdin. Chloroform was purchased from BEIJING SHIJI Co., Ltd. ITO was purchased from Dongguan City Everest Display Technology Co., Ltd. Zinc-metalation of free-base chlorins Chls-D3/D4 was done according to the reported procedure 4 to afford Chls-D1/D2 in a quantitative yield. The synthetic compounds were characterized by the following data with NMR spectra. Zinc methyl 3 2,3 2 -dicyano-pyropheophorbide-a (Chl-D1): Dark green solid; mp C; VIS (THF) max 698 (, 50000), 458 (36000), 388 nm (60000); Flu (THF, ex = 458 nm) em = 728 nm; 1 H-NMR (3% pyridine-d5/cdcl3, 500 MHz, see Chart S1) = 9.64 (1H, s, 10-H), 9.34 (1H, s, 3-CH), 9.17 (1H, s, 5-H), 8.60 (1H, s, 20-H), 5.23, 5.11 (each 1H, d, J = 20 Hz, CH2), 4.48 (1H, dq, J = 2, 8 Hz, 18-H), 4.27 (1H, ddd, J = 9, 2, 2 Hz, 17-H), 3.77 (2H, q, J = 8 Hz, 8-CH2), 3.70 (3H, s, 12-CH3), 3.58 (3H, s, COOCH3), 3.48 (3H, s, 2-CH3), 3.30 (3H, s, 7-CH3), , (each 1H, m, 17-CH2), , (each 1H, m, CH2), 1.74 (3H, d, J = 8 Hz, 18-CH3), 1.72 (3H, t, J = 8 Hz, 8 1 -CH3); 13 C-NMR (3% pyridine-d5/cdcl3, 125 MHz, see Chart S2) = 196.7, 173.3, 166.6, 161.2, 158.0, 150.6, 150.2, 149.8, 147.6, 143.9, 143.8, 140.6, 136.4, 134.9, 133.5, 131.4, 114.6, 113.8, 106.0, 84.9 (C1, 2, 3, 3 2, 3 3 2, 4, 6, 7, 8, 9, 11, S2

3 12, 13, 13 1, 14, 15, 16, 17 3, 19), (C3 1 ), (C10), 99.1 (C5), 93.8 (C20), 51.6 (C17 5 ), 51.1 (C17), 48.4 (C13 2 ), 48.3 (C18), 30.3 (C17 1 ), 29.6 (C17 2 ), 23.6 (C18 1 ), 19.5 (C8 1 ), 17.4 (C8 2 ), 15.2 (C2 1 ), 12.9 (C12 1 ), 11.1 (C7 1 ); MS (APCI) m/z (MH + ), calcd for C36H33N6O3Zn, Zinc methyl deoxo dicyanomethylene-pyropheophorbide-a (Chl-D2): Green solid; mp C; VIS (THF) max 703 (, 98000), 649 (24000), 457 (48000), 437 (56000), 387 (52000), 353 nm (49000); Flu (THF, ex = 437 nm) em = 723 nm; 1 H- NMR (3% pyridine-d5/cdcl3, 500 MHz, see Chart S3) = 9.30 (1H, s, 10-H), 9.00 (1H, s, 5-H), 8.15 (1H, s, 20-H), 7.87 (1H, dd, J = 18, 12 Hz, 3-CH), 6.13 (1H, dd, J = 18, 2 Hz, 3 1 -CH trans to 3-C H), 5.99 (1H, dd, J = 12, 2 Hz, 3 1 -CH cis to 3-C H), 5.56, 5.45 (each 1H, d, J = 21 Hz, CH2), 4.26 (1H, dq, J = 2, 8 Hz, 18-H), 4.05 (1H, ddd, J = 8, 2, 2 Hz, 17-H), 3.77 (3H, s, 12-CH3), 3.61 (2H, q, J = 8 Hz, 8-CH2), 3.59 (3H, s, COOCH3), 3.24 (3H, s, 2-CH3), 3.11 (3H, s, 7-CH3), , (each 1H, m, 17-CH2), , (each 1H, m, CH2), 1.65 (3H, d, J = 8 Hz, 18-CH3), 1.64 (3H, t, J = 8 Hz, 8 1 -CH3); 13 C-NMR (3% pyridine-d5/cdcl3, 125 MHz, see Chart S4) = 173.2, 169.2, 168.7, 160.1, 155.9, 155.4, 153.3, 149.4, 148.4, 146.4, 144.5, 139.2, 135.5, 133.8, 133.7, 131.6, 117.1, 116.3, 103.9, 67.7 (C1, 2, 3, 4, 6, 7, 8, 9, 11, 12, 13, 13 1, 13 2, , 14, 15, 16, 17 3, 19), (C3 1 ), (C3 2 ), (C10), 98.6 (C5), 92.2 (C20), 51.6 (C17 5 ), 50.2 (C17), 48.6 (C18), 46.0 (C13 2 ), 30.3 (C17 1 ), 29.8 (C17 2 ), 23.1 (C18 1 ), 19.3 (C8 1 ), 17.3 (C8 2 ), 14.7 (C12 1 ), 12.2 (C2 1 ), 10.8 (C7 1 ); MS (APCI) m/z (MH + ), calcd for C37H35N6O2Zn, S3

4 Chart S1. 1 H-NMR spectrum of Chl-D1 in 3% pyridine-d5/cdcl3. Chart S2. 13 C-NMR spectra of Chl-D1 in 3% pyridine-d5/cdcl3 (lower, black). Primary and tertiary carbon signals are shown upwards while secondary ones appear downwards in the DEPT spectrum (upper, red). S4

5 Chart S3. 1 H-NMR spectrum of Chl-D2 in 3% pyridine-d5/cdcl3. Chart S4. 13 C-NMR spectra of Chl-D2 in 3% pyridine-d5/cdcl3 (lower, black). Primary and tertiary carbon signals are shown upwards while secondary ones appear downwards in the DEPT spectrum (upper, red). S5

6 Device fabrication The device, ITO/ZnO/Chl-A/Chl-Ds/MoO3/Ag, was fabricated as follows. An ITO substrate was precleaned in the ultrasound machine by the following sequence: ITO glass detergent, deionized water, ethanol, acetone, isopropanol for each step 30 minutes twice. A ZnO precursor solution was prepared by mixing 0.2 g of zinc acetate dihydrate into 2 ml of 2-methoxyethanol and adding 56 µl of ethanolamine as a stabilizer, then stirred overnight. Chl-A was dissolved into THF with the concentration of 5 mg/ml. The Chl-Ds was dissolved into chloroform with the same concentration. The cleaned ITO substrate was exposed under ultraviolet-ozone for 30 minutes. Then the ZnO precursor solution was spin-coated onto the substrate with the spin speed of 3000 rpm and annealed immediately at 200 C for 30 minutes in air. After the substrate was transferred into a glove box, the Chl-A solution was spin-coated onto the ZnO substrate with the spin speed of 3000 rpm, followed by spin-coating the Chl-D1, -D2, -D3, or -D4 solution at the speed of 3000 rpm. The resulting substrate was sent into high vacuum chamber where MoO3 (10 nm) and Ag (100 nm) were thermal deposited orderly. The single layer devices were fabricated as ITO/ZnO/Chl-A, Chl-D1, Chl-D2, Chl-D3, or Chl-D4/MoO3/Ag under the same conditions. For the Chl-A based single layer device, the film was spin coated at 4000 rpm using 5 mg/ml of Chl-A solution in THF to get the optimized power conversion efficiency (PCE). For the Chl-Ds based single layer device, the films were spin coated at 2000 rpm using 5 mg/ml of Chl-Ds solution in chloroform to get the best PCEs. The films which were used for atomic force microscopy (AFM) measurement and absorbance on film as well as photo-electron spectroscopy measurement were made under the same conditions of 3000 rpm from each solution (5 mg/ml). S6

7 Material characterization UV/Vis/NIR absorption spectra of Chls on the solid film and in THF solution were recorded by a Shimadzu UV-3100 spectrophotometer. Photo-electron spectroscopic data of the five Chls were measured by ionization energy photoelectron yield spectroscopy in the vacuum (IPS). The morphologies of all the Chls films were analyzed through AFM in tapping mode under ambient conditions using a Bruker instrument. Device characterization The photocurrent density voltage (J-V) characteristics of solar cells were measured by a computer-controlled Keithley 2400 source meter measurement system with an AM1.5G filter at a calibrated intensity of 100 mw/cm 2 illumination, as corrected by a standard silicon reference cell (91150V Oriel Instruments). Incident photon-to-electron conversion efficiency (IPCE) measurements were carried out using a commercial IPCE setup equipped with a 100W Xe arc lamp, a filter wheel, and a monochromator (CrowntechQTest Station 1000AD, SOFN INSTRUMENTS CO., LTD). Monochromatic light chopped at a frequency of 80 Hz and photocurrents were measured using a lock-in amplifier. The device area of 0.04 cm 2 was controlled by a metal mask. The performance data were averaged from four independently fabricated solar cells. S7

8 Figure S1. Absorption spectra of bilayer devices, which were made by spin-coating Chl- A and Chl-Ds in sequence. From the absorption spectra, we can clearly see that both sublayer Chl-A (PSI simulator) and upper layer Chl-Ds (PSII simulator) contribute to the final absorbance spectra. S8

9 Figure S2. Device structure of the present bilayer Chls-based bio-solar cell, in which the Chl-D layer involves either Chl-D1, Chl-D2, Chl-D3, or Chl-D4. Figure S3. Absorption spectra of Chl-A film (black line) and the already formed Chl-A film with chloroform dropped onto it (red line) (PS: the operation is the same as that for the device fabrication, except without Chl-Ds spin-coated from chloroform). From the intensity of absorption spectra, we can clearly see that it shows no change on the absorption of already formed Chl-A film when chloroform is dropped onto the film. This result proves that the process of spin-coating the upper layer Chl-Ds would not affect the sublayer Chl-A film, indicating that the device is bilayer structure. S9

10 Figure S4. The HOMO energy levels of the specific five Chls measured by ionization energy photoelectron yield spectroscopy in vacuum. S10

11 Figure S5. a) J-V curves of ITO/ZnO/Chl-A or Chl-D1 or Chl-D2 or Chl-D3 or Chl- D4/MoO3/Ag single layer-based devices under standard AM mw/cm 2 sunlight, and b) corresponding IPCE responses of the devices. S11

12 Table S1. Energy levels of the Chls. [a] HOMO (ev) LUMO (ev) Eg (ev) Chl-A Chl-D Chl-D Chl-D Chl-D [a] HOMO levels are calculated from the photo-electron spectroscopy. Band gap Eg are derived from the absorption spectra: Eg (ev) = 1240 / λ (nm). LUMO levels are estimated from HOMO + Eg. S12

13 Table S2. Photovoltaic performances of ITO/ZnO/ Chl-A or Chl-D1 or Chl-D2 or Chl- D3 or Chl-D4/MoO3/Ag based single layer devices under standard AM mw/cm 2 sunlight. Jsc (ma/cm 2 ) Voc (V) FF IPCE (%) Chl-A Chl-D Chl-D Chl-D Chl-D Figure S5a and Table S2 show the photovoltaic performances of single layer-based devices following the order: Chl-D4 > Chl-D2 > Chl-A > Chl-D3 > Chl-D1. The Voc varies with the order: Chl-D4 > Chl-D2 > Chl-D3 > Chl-D1 > Chl-A, which is generally the same trend as for the PCE except for Chl-A. The much lower Voc value of Chl-A might be due to decreased charge separation owing to a decrease in charge delocalization, as reflected in the absorption spectra in solution. The clear increase in the Jsc may be originated from better charge transfer. The variation in Jsc is consistent with the IPCE responses. S13

14 References (1) Tamiaki, H.; Amakawa, M.; Shimono, Y.; Tanikaga, R.; Hotzwarth, A. R.; Schaffner, K. Synthetic Zinc and Magnesium Chlorin Aggregates as Models for Supramolecular Antenna Complexes in Chlorosomes of Green Photosynthetic Bacteria. Photochem. Photobiol. 1996, (2) Tamiaki, H.; Kouraba, M. Synthesis of Chlorophyll-a Homologs by Wittig and Knoevenagel Reactions with Methyl Pyropheophorbide-d. Tetrahedron 1997, 53, (3) Sasaki, S.; Yoshizato, M.; Kunieda, M.; Tamiaki, H. Cooperative C3- and C13- Substituent Effects on Synthetic Chlorophyll Derivatives. Eur. J. Org. Chem. 2010, (4) Tamiaki, H.; Takeuchi, S; Tsudzuki, S.; Miyatake, T.; Tanikaga, R. Self-Aggregation of Synthetic Zinc Chlorins with a Chiral 1-Hydroxyethyl Group as a Model for in Vivo Epimeric Bacteriochlorophyll-c and d Aggregates. Tetrahedron 1998, 54, S14