Polytechnique Fédérale de Lausanne, Chemin des Alambics, Station 6, CH-1015, Lausanne, Switzerland

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1 Supporting Information. A Novel Blue Organic Dye for Dye-Sensitized Solar Cells Achieving High Efficiency in Cobalt-based Electrolytes and by Co-sensitization Yan Hao, a Yasemin Saygili, b Jiayan Cong, c Anna Eriksson, a Wenxing Yang, a Jinbao Zhang, a Enrico Polanski, b Kazuteru Nonomura, b Shaik Mohammed Zakeeruddin, d,e Michael Grätzel, d Anders Hagfeldt, a,b,e and Gerrit Boschloo* a a Department of Chemistry-Ångström Laboratory, Center of Molecular Devices, Uppsala University, SE , Uppsala, Sweden b Laboratory of Photomolecular Science, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, Chemin des Alambics, Station 6, CH-1015, Lausanne, Switzerland c Applied Physical Chemistry, School of Chemical Science and Engineering, Department of Chemistry, KTH, Royal Institute of Technology, Teknikringen 30, SE , Stockholm, Sweden d Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, Chemin des Alambics, Station 6, CH-1015, Lausanne, Switzerland e Center of Excellence for Advanced Materials Research (CEAMR), King Abdulaziz University, Jeddah 21589, Saudi Arabia *Address correspondence to gerrit.boschloo@kemi.uu.se S-1

2 1. Synthesis of DB dye 3-(4-bromophenyl)-6-(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (A) was obtained from Dyenamo AB. 3-(4-bromophenyl)-2,5-bis(2-ethylhexyl)-6-(thiophen-2-yl)-2,5- dihydropyrrolo[3,4-c]pyrrole-1,4-dione (B) was synthesized in an analogous method to what was reported in PCT Int. Appl. (2011), WO A and PCT Int. Appl. (2010), WO A , both by BASF SE. 5-(4-(2,5-bis(2-ethylhexyl)-3,6-dioxo-4-(thiophen-2-yl)-2,3,5,6- tetrahydropyrrolo[3,4-c]pyrrol-1-yl)phenyl)furan-2-carbaldehyde (C) and 5-(4-(4- (5-bromothiophen-2-yl)-2,5-bis(2-ethylhexyl)-3,6-dioxo-2,3,5,6- tetrahydropyrrolo[3,4-c]pyrrol-1-yl)phenyl)furan-2-carbaldehyde (D) were synthesized according to the method reported by Jun-Ho Yum, Thomas W. Holcombe etc (4-(4-(5-(4-(bis(2',4'-dibutoxy-[1,1'-biphenyl]-4-yl)amino)phenyl)thiophen-2-yl)- 2,5-bis(2-ethylhexyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol-1- yl)phenyl)furan-2-carbaldehyde (E) 600 mg D (0.87 mmol), 1.08 g of 2',4'-dibutoxy-N-(2',4'-dibutoxy-[1,1'-biphenyl]- 4-yl)-N-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-[1,1'-biphenyl]-4- amine (D35-D) (1.33 mmol), and 550 mg of potassium phosphate tribasic (2.59 mmol) were added in a 50 ml single-neck round-bottom flask. Then 18 ml of toluene, 1.5 ml tamyloh, and 0.75 ml water were added into the flask to dissolve the reactants. The solution was degassed with a stream of N 2 for 20 minutes, and then 10 mg of Pd 2 dba 3, 20 mg of X-Phos and 10 mg XPhos Pd G3 ((2-Dicyclohexylphosphino-2,4,6 -triisopropyl-1,1 -biphenyl)[2-(2 -amino-1,1 - biphenyl)]palladium(ii) methanesulfonate) were added into the solution simultaneously, in one batch. After another 10 minutes degassing, the reaction was brought to 80 C for 6 hours. When to reaction cooled down to room temperature, DCM was added and plugged the solution through a layer of Mg 2 SO 4. Crude product was rotovapped and then loaded onto a silica column and eluted S-2

3 with 20:3 of DCM:EtOAc eluent. 594 mg blue solid was obtained, and the yield is 52.8%. 1 H NMR (400 MHz, Acetone) δ 9.59 (d, J = 4.0 Hz, 1H), 9.01 (d, J = 4.1 Hz, 1H), (m, 5H), 7.58 (d, J = 8.7 Hz, 2H), 7.49 (d, J = 4.1 Hz, 1H), 7.42 (dd, J = 10.8, 6.1 Hz, 5H), 7.18 (d, J = 3.7 Hz, 1H), 7.14 (d, J = 8.4 Hz, 2H), (m, 6H), (m, 4H), (m, 12H), 1.82 (s, 2H), 1.61 (dt, J = 14.3, 7.5 Hz, 8H), 1.23 (dddd, J = 36.3, 29.0, 19.1, 12.7 Hz, 24H), (m, 24H). 3-(5-(4-(4-(5-(4-(bis(2',4'-dibutoxy-[1,1'-biphenyl]-4-yl)amino)phenyl)thiophen-2- yl)-2,5-bis(2-ethylhexyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol-1- yl)phenyl)furan-2-yl)-2-cyanoacrylic acid (DB) 550 mg E (0.42 mmol), 330 mg cyanoacetic acid (3.88 mmol) were added in a 25 ml single-neck round-bottom flask and dissolve the reactants with 40 ml solvent of 5:3 MeCN:CHCl 3. Then 40 drops of piperidine was added into the flash and heat it to 80 C and keep reflux for 2 hours. Cooled down the reaction and add 1M HCl water solution to adjust the PH to 1. Then the reaction mixture was extracted with DCM, and rotovapped to get crude product. The silica column chromatography was used with a eluent of DCM:EtOAc:Acetic acid:methanol = 50:8:1: mg dark blue solid was obtained, and the yield is 43.7%. 1 H NMR (400 MHz, Acetone) δ 9.16 (d, J = 4.2 Hz, 1H), (m, 5H), 7.75 (d, J = 8.7 Hz, 2H), 7.66 (d, J = 4.1 Hz, 1H), 7.58 (dd, J = 13.9, 6.1 Hz, 5H), 7.45 (d, J = 3.7 Hz, 1H), 7.30 (d, J = 8.4 Hz, 2H), 7.19 (dd, J = 16.5, 8.6 Hz, 6H), 6.65 (dd, J = 18.8, 5.2 Hz, 4H), (m, 12H), 1.94 (d, J = 25.8 Hz, 2H), 1.76 (td, J = 14.5, 6.7 Hz, 8H), (m, 24H), 0.95 (ddd, J = 31.4, 19.4, 7.0 Hz, 18H), 0.77 (dd, J = 13.0, 5.6 Hz, 6H). 13 C NMR (126 MHz, Acetone) δ , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , 99.04, 68.82, 68.34, 40.09, 32.18, 32.06, 31.08, 24.52, 23.74, S-3

4 23.49, 20.06, 19.96, 14.33, 14.33, 14.16, 14.14, 10.87, C 86 H 98 N 4 O 9 S [M + ] Exact Mass = , MS (ESI) = (Shown in Figure S8). 2. Photo-physical and electro-chemical Characterizations: Figure S1. Uv-vis spectra of DB dye with different concentration in tert-butanol: acetonitrile (1:1 v/v) (up) and the calculated extinction coefficient by the fitted curve (down). S-4

5 Figure S2. Normalized Uv-vis absorption and emission spectrum of DB dye in tert-butanol: acetonitrile (1:1 v/v). Figure S3. UV-vis absorbance spectra of the two dyes in 0.05 M TBAOH (1:1 tert-butanol: acetonitrile). S-5

6 y = 34040x R² = E E E E y = 52880x R² = E E E E-05 Figure S4. Standard curves of D35 (up) respectively Dyenamo blue (down) to calculate the extinction coefficient of dyes in 0.05 M TBAOH (1:1 ACN:tBuOH). S-6

7 Figure S5. UV-vis spectra of Co-sensitized (D35:DB=4:1, 8:1, 2:1 and 4:3) dyes attached to TiO 2 surface (up) and desorbed in 0.05 M TBAOH (1:1 tert-butanol: acetonitrile) (down). 3. Photovoltaic performance of solar cells S-7

8 Table S1. Optimized performance of co-sensitized DSSCs with different ratios of D35 and DB dye. DB:D35 ratio (concentration, mm) Voc (mv) Jsc (ma/cm 2 ) FF (%) PCE (%) 1:1 (0.025:0.025) :4 (0.025:0.1) :8 (0.025:0.2) :1 (0.1:0.1) :4 (0.075:0.1) :2 (0.05:0.1) S-8

9 Figure S6. Spectra of incident photon-to current conversion efficiency (IPCE) for DSSCs based on co-sensitized dyes with different ratio of D35 and DB. S-9

10 4. Photo induced and transient absorption spectroscopy Figure S7. PIA spectra of TiO 2 sensitized with (red) D35, (blue) DB and Co-sensitized dyes (DB:D35=3:4), employing inert electrolyte. S-10

11 Figure S8. The EIS Full Mass Spectroscopy of Dyenamo blue dye. S-11