Vertical stratification and its impact on device performance in a polycarbazole

Transcription

1 Electronic Supplementary Material (ESI) for Journal of Materials Chemistry C. This journal is The Royal Society of Chemistry 2015 Vertical stratification and its impact on device performance in a polycarbazole based copolymer solar cells Tao Wang 1,2*, Nicholas W. Scarratt 1, Hunan Yi 3, Iain F. Coleman 3, Yiwei Zhang 1, Richard T. Grant 1, Jizhong Yao 4, Maximilian W. A. Skoda 5, Alan D. F. Dunbar 6, Richard A. L. Jones 1, Ahmed Iraqi 3*, David G. Lidzey 1* 1 Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, UK 2 School of Materials Science & Engineering, Wuhan University of Technology, Wuhan, , China 3 Department of Chemistry, University of Sheffield, Sheffield, S3 7HF, UK 4 Centre for Plastic Electronics and Department of Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, UK 5 ISIS Pulsed Neutron and Muon Source; Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot OX11 0QX, UK 6 Department of Chemical and Biological Engineering, University of Sheffield, Sheffield S1 3JD, UK twang@whut.edu.cn, a.iraqi@sheffield.ac.uk, d.g.lidzey@sheffield.ac.uk 1

2 1. Synthesis of monomers and macromolecules 9-(Heptadecan-9-yl)-2,7-bis-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-9Hcarbazole 1 and 1,2-dimethoxy-4,5-diaminobenzene 2 were prepared according to literature procedures. The preparation of 5,6-dimethoxy-4,7-di(thiophen-2- yl)benzo[c][1,2,5] thiadiazole is shown in Scheme S1. Scheme S1. (i) SOCl 2, NEt 3, dichloromethane, reflux. (ii) Br 2, dichloromethane/acetic acid. (iii) Pd(PPh 3 ) 2 Cl 2, toluene, reflux. (iv) NBS, chloroform. 5,6-Dimethoxybenzo[c][1,2,5]thiadiazole A solution of thionyl chloride (4.92 g, mmol) in dichloromethane (40 cm 3 ) was slowly added to a mixture of 1,2-dimethoxy-4,5-diaminobenzene (3.1 g, mmol) and triethylamine (25 cm 3 ) in dichloromethane (300 cm 3 ). After addition, the reaction mixture was heated to reflux for 6 hours. The solution was cooled and concentrated in vacuum followed by trituration in water (100 cm 3 ) and the product was extracted with dichloromethane (300 cm 3 ). The solvent was removed under reduced pressure and the crude product was recrystallized from ethanol then solubilised in chloroform (30 cm 3 ) and passed through a plug of silica gel to afford 5,6-dimethoxybenzo[c][1,2,5]thiadiazole as a white solid after evaporation of the solvent. (2.3 g, 64 % yield). M.p C. 1 H NMR (CDCl 3 ): (δ H /ppm) 7.21 (s, 2H); 4.02 (s, 6H). 13 C NMR (CDCl 3 ): (δ C /ppm) 154.5, 151.3, 98.0, FT-IR (ATR): (cm -1 ) 3040 (Ar-H), 2995 (OCH 3 ) 1494 (C=N), 1168 (C-O). Mass (EI+): (m/z) 196 (M + ). Anal. Calcd. for C 8 H 8 N 2 O 2 S: C, 48.97; H, 4.11; N, 14.28; S, Found: C, 48.9; H, 3.9; N, 14.0; S,

3 4,7-Dibromo-5,6-dimethoxybenzo[c][1,2,5]thiadiazole Bromine (12.40 g, mmol) was added to a solution of 5,6- dimethoxybenzo[c][1,2,5] thiadiazole (2.3 g, mmol) in a mixture of dichloromethane (300 cm 3 ) and acetic acid (150 cm 3 ), and the reaction mixture was stirred in the dark for 48 hours at room temperature. The mixture was then poured into water (400 cm 3 ) and extracted with dichloromethane (3 200 cm 3 ). The combined organic phase was washed with water (200 cm 3 ), saturated NaHCO 3 (aq) (200 cm 3 ), 1M Na 2 SO 3 (aq) (200 cm 3 ) and then dried with MgSO 4. The solvent was evaporated under reduced pressure and the crude product was recrystallized from ethanol then solubilised in chloroform (30 cm 3 ), and passed through a plug of silica gel to afford 4,7- dibromo-5,6-dimethoxybenzo[c][1,2,5]thiadiazole as an off-white solid (2.8 g, 67 % yield). M.p C. 1 H NMR (CDCl 3 ): (δ H /ppm) 4.05 (s, 6H). 13 C NMR (CDCl 3 ): (δ C /ppm) 154.9, 106.2, FT-IR (ATR): (cm -1 ) 3100 (Ar-H), 2930 (OCH 3 ) 750 (C- Br), 1100 (C-O). Mass (EI+): (m/z) 352, 354, 356 (M + ). Anal. Calcd. for C 8 H 6 O 2 N 2 Br 2 S: C, 27.14; H, 1.71; N, 7.91; Br, 45.14; S, Found: C, 27.3; H, 1.5; N, 7.6; Br, 45.0; S, 9.4 5,6-Dimethoxy-4,7-di(thiophen-2-yl)benzo[c][1,2,5] thiadiazole 2-(Tributylstannyl)thiophene (8.20 g, mmol) was added to a solution of 4,7- dibromo-5,6-dimethoxybenzo[c][1,2,5]thiadiazole (2.50 g, 7.06 mmol) and bis(triphenylphosphine) palladium(ii) dichloride (0.1 g, 0.14 mmol) in dry toluene (5 cm 3 ) and the reaction mixture was heated to reflux for 48 hours under argon. The solvent was removed under reduced pressure and the crude product was purified via silica gel column chromatography, eluting with toluene/petroleum ether (1:1, v:v) to afford 5,6-dimethoxy-4,7-di(thiophen-2-yl)benzo[c][1,2,5] thiadiazole as an orange 3

4 solid (1.60 g, 63 % yield). M.p C. 1 H NMR (CDCl 3 ): (δ H /ppm) 8.65 (m, 2H); 7.55 (m, 2H) 7.30 (m, 2H) (s, 6H), 13 C NMR (CDCl 3 ): (δ C /ppm) 150.8, 130.7, 127.6, 127.0, 117.2, FT-IR (ATR): (cm -1 ) 3092 (Ar-H), 2929 (OCH 3 ), 1082 (C- O). Mass (EI+): (m/z) 360 (M + ). Anal. Calcd. for C 16 H 12 S 3 N 2 O 2 : C, 53.31; H, 3.36; N, 7.77; S, Found: C, 53.1; H, 3.1; N, 7.7; S, ,7-Bis(5-bromothiophen-2-yl)-5,6-dimethoxybenzo[c][1,2,5]thiadiazole NBS (2.20 g, mmol) was added to a solution of 5,6-dimethoxy-4,7- di(thiophen-2-yl) benzo[c][1,2,5]thiadiazole (2.20 g, 6.10 mmol) in chloroform (250 cm 3 ). The mixture was stirred at room temperature for 48 hours in the dark. The chloroform layer was washed with water (3 x 100 cm 3 ). The combined organic phase was dried with MgSO 4 and the solvent was removed under reduced pressure. The crude product was purified via silica gel column chromatography, eluting with petroleum ether/dichloromethane (4:1, v:v) to afford 4,7-bis(5-bromothiophen-2-yl)-5,6- dimethoxybenzo[c]1,2,5] thiadiazole as an orange solid (2.50 g, 79 % yield). M.p C. 1 H NMR (CDCl 3 ): (δ H /ppm) 8.5 (m, 2H,). 7.2 (m, 2H), 4.00 (s, 6H). FT-IR (ATR): (cm -1 ) 3100 (Ar-H), 1041 (C-O), 704 (C-Br). Anal. Calcd. for C 16 H 10 S 3 N 2 O 2 Br 2 : C, 37.08; H, 1.94; N, 5.41; Br, 30.84; S, Found C, 37.1; H, 1.8; N, 5.3; Br 30.6; S, Poly[9-(heptadecan-9-yl)-9H-carbazole-2,7-diyl-alt-(5,6-bis(methyloxy)-4,7- di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole-5,5-diyl] (PCDTBT1) 4

5 Scheme S1. (i) Pd(OAc) 2, P(o-tolyl) 3, NEt 4 OH, toluene. To a degassed solution of 9-(heptadecan-9-yl)-2,7-bis(4,4,5,5-tetramethyl-1,3,2- dioxaborolan-2-yl)-9h-carbazole (1.118 g, 1.7 mmol), and 4,7-bis(5- bromothiophen-2-yl)-5,6-dimethoxybenzo[c]1,2,5]thiadiazole (0.881 g, 1.7 mmol) in toluene (24 cm 3 ) was added a degassed solution of tetraethylammonium hydroxide (8.0 cm 3 of a 20 wt% solution, mmol). Pd(OAc) 2 (9.6 mg, mmol) and tri(o-tolyl)phosphine (26 mg, mmol) were then added to the mixture and the system was degassed under argon and heated to 90 C for 48 hours. The mixture was cooled to room temperature then bromobenzene (0.1 ml) was added followed by heating the mixture to 90 C for 1 hour. Again, the mixture was cooled to room temperature and phenylboronic acid (120 mg) was added, the mixture degassed and heated to 90 C for 3 hours. After cooling to room temperature, the mixture was dissolved in CHCl 3 (200 cm 3 ) and to this solution was added an ammonium hydroxide solution (28% in H 2 O, 50 cm 3 ) then the mixture was stirred overnight. The organic phase was separated and washed with distilled water (100 cm 3 ), concentrated to approximately 50 cm 3 and poured into degassed methanol/water (10:1, 300 cm 3 ). The resulting mixture was then stirred overnight and filtered through a membrane filter. The collected solid was cleaned and fractionated using Soxhlet extraction with solvents in order methanol, acetone, hexane and toluene. The toluene fraction was concentrated to approximately 50 cm 3 5

6 and then poured into degassed methanol (200 cm 3 ). The resulting mixture was stirred overnight and the solid was collected by filtration through a membrane filter to afford the polymer as a red powder (1.08 g, 83 % yield). GPC (1,2,4- trichlorobenzene at 100 C): M n = 28,400, M w = 57,300, PD = H NMR (C 2 D 2 Cl 4 ): (δ H / ppm) 8.62 (m, 2H), 8.11 (m, 2H), 7.83 (s, 2H), 7.63 (m, 2H), 7.52 (m, 2H), 4.66 (br, 1H), 4.15 (s, 6H), 2.39 (br, 2H), 2.07 (br, 2H), (m, 24H), 0.79 (m, 6H). 13 C NMR (C 2 D 2 Cl 4 ): (δ C / ppm) , , , , , , , , , 60.94, 34.29, 31.92, 29.63, 29.52, 29.30, 27.17, 22.70, Anal. Calcd. for (C 45 H 51 N 3 O 2 S 3 ) n : C, 70.92; H, 6.75; N, 5.51; Br, 0. Found: C, 70.97; H, 6.68; N, 5.44; Br, Measurements Nuclear magnetic resonance (NMR) spectra were recorded on Bruker 250 MHz, AMX MHz or DRX MHz NMR spectrometers at 22 C in chloroform-d solutions with TMS as the internal standard. Polymer solutions in 1,2,4-trichlorobenzene at 100 C were used as samples for GPC analysis. The GPC curves were obtained by the RI-detection method, which was calibrated with a series of polystyrene narrow standards (Polymer Laboratories). Elemental analyses were carried out by the Perkin Elmer 2400 CHN Elemental Analyser for CHN analysis and by the Schöniger oxygen flask combustion method for anion analysis. UV visible absorption spectra were measured by Hitachi U-2010 Double Beam UV/Visible Spectrophotometer. The absorbance of polymers was measured in solution in chloroform (spectrophotometric grade) at ambient temperature using rectangular quartz cuvettes (light path length = 10 mm) purchased from Sigma- Aldrich. Samples of pristine polymer thin films for UV visible absorption spectra measurements were prepared by dip coating quartz plates into 1 mg cm 3 polymer 6

7 solutions in chloroform (HPLC grade); and the measurements were carried out at ambient temperature. Cyclic voltammograms were recorded using a Princeton Applied Research Model 263A Potentiostat/Galvanostat. Measurements were carried out under argon at 25±2 C. 10 ml of tetrabutylammonium hexafluorophosphate solution in acetonitrile (0.1 mol dm 3 ) was used as the electrolyte solution. A three electrode system was used consisting of an Ag/Ag + reference electrode (silver wire in 0.01 mol dm 3 silver nitrate solution in the electrolyte solution), a platinum working electrode (2 mm-diameter smooth platinum disc, area = cm 2 ), and a platinum counter electrode (platinum wire). Polymer thin films were formed by drop casting 1.0 mm 3 of polymer solutions in chloroform (HPLC grade) (1 mg cm 3 ) onto the working electrode, then dried in air. Ferrocene was employed as a reference redox system according to IUPAC's recommendation Effect of blend ratio and film thickness on the PCEs of OPV devices (a) J (ma cm -2 ) :1-10 PCDTBT1:PC 71 BM 1:2 1:3 1: (c) Bias (V) 2.2 (b) Refractive index (n) (d) Wavelength (nm) Excinction coefficient (k) Photocurrent (ma/cm 2 ) Photocurrent (ma/cm 2 ) Modeling Experimental Photocurrent (ma/cm 2 ) Thickness of the active layer (nm) Thickness of the active layer (nm) 7

8 Figure S1. (a) J-V curves of spin-cast PCDTBT1:PC 71 BM solar cells at different blend ratios, with the active layers having a similar thickness. (b) Optical constants of PCDTBT1:PC 71 BM 1:4 blend cast from CB. (c) Maximum photocurrent modeled from transfer matrix reflectivity model with the thickness of the active layer ranging from 0 to 300 nm. (d) A comparison of maximum photocurrents obtained from experiments and modeling. 4. Light ideality factors of PCDTBT1:PC 71 BM devices using PEDOT:PSS and smoox as the HTLs (a) (b) Figure S2. (a) Open-circuit voltage versus light intensity of PCDTBT1:PC 71 BM devices using PEDOT:PSS and smoox as the HTLs. (b) Plot of light ideality factors versus voltage determined differentially from the plot in (a). The thickness of the active layer was ca. 60 nm. References [1] G. Gritzner, Pure Appl. Chem., 1990, 62, [2] N. Blouin, A. Michaud, M. Leclerc, Adv. Mater., 2007, 19, [3] L. Perrin, P. Hudhomme, Eur. J. Org. Chem., 2011, 28,