Supplementary Information
Hydrogen bonding in bulk heterojunction solar cells: A case study
Zeyun Xiao, Kuan Sun, Jegadesan Subbiah, Shaomin Ji, David J. Jones, Wallace W. H. Wong
School of Chemistry, Bio21 Institute, the University of Melbourne, 30 Flemington Road, Parkville, Victoria 3010, Australia.
Table of contents
Generalexperimental information2
Synthesis of compounds3
1H NMR dilution of PC61MBA7
Cyclic voltammograms of the donors and acceptors8
Calculated frontier orbitals of M1 and M29
Fabrication of the BHJ solar cells10
Additional photovoltaic performance of the devices11
Space charge limited current measurements12
1D plot of GIWAX data13
1H NMR spectra of new compounds14
General Experimental Information
Unless noted, all materials were reagent grade and used as received without further purification. Chromatographic separations were performed using standard column methods with silica gel (Merck 9385 Kieselgel 60). Thin layer chromatography was performed on Merck Kieselgel 60 silica gel on glass (0.25 mm thick).
IR spectra were obtained on a Perkin Elmer Spectrum One FT-IR spectrometer and UV-vis spectra were recorded using a Cary 50 UV-Vis spectrometer. Photoluminescence was measured with a Varian Cary Eclipse fluorimeter.
Melting points were determined on a Büchi 510 melting point apparatus for precursor compounds. Differential scanning calorimetry (DSC) experiments were performed on a Perkin-Elmer Sapphire DSC to obtain thermal behavior data (melting point and crystallization point) on the electron donor materials (M1 and M2).
1H NMR and 13C NMR spectra were carried out on a 400 MHz spectrometer. All NMR data was referenced to the chloroform signal and peak multiplicity was reported as follows: s = singlet, d = doublet, t = triplet, q = quartet, p = pentet, dd = doublets of doublets, m = multiplet, br = broad).
All high resolution mass spectrometry experiments were conducted with use of a commercially available hybrid linear ion trap and Fourier-transform ion cyclotron resonance mass spectrometer, equipped with ESI.
Cyclic voltammetry (CV) experiments were performed at a sweep rate of 100 mV/s. CVs were carried out in a three-electrode cell consisting of a glassy carbon working electrode, a platinum wire auxiliary electrode, and a Ag/Ag+ reference electrode. The supporting electrolyte was 0.10 M tetrabutylammonium hexafluorophosphate (Bu4NPF6). The solutions were deoxygenated by sparging with argon prior to each scan and blanketed with argon during the scans. The platinum disc working electrode was polished with 0.05 mm alumina and washed well with deionized water and dry CH3CN prior to each scan.
Synthesis
Compound 2. To a stirred solution of compound 1 (3.7 g, 8.3 mmol) in chloroform (10 mL) and acetic aicid (10 mL) at 0℃ was added NBS (1.47 g, 8.3 mmol) slowly. The resulting mixture was stirred at 0℃ under dark for 1.5 h and then diluted with hexane (100 mL). Then organic phase was washed with H2O, saturated NaHCO3, brine and H2O. After removal of the solvent, the product was purified with column chromatography (silica gel, dichloromethane/petroleum spirits 1:2) to afford a yellow oil (3.5 g, 80%). Rf 0.35 (petroleum spirits/ ethyl acetate 20:1); IR (neat) ν 2928, 2856, 1666, 1436, 1225, 1056 cm-1; 1H NMR (δ, CDCl3) 9.89 (s, 1 H), 7.71 (d, J = 4.0 Hz, 1 H), 7.22 (d, J = 4.0 Hz, 1 H), 6.91 (s, 1 H), 6.90 (s, 1 H), 2.80 (t, J = 8.0 Hz, 2 H), 2.71 (t, J = 7.6 Hz, 2 H), 1.57-1.71 (m, 4 H), 1.26-1.45 (m, 12 H), 0.88 (m, 6 H); 13C NMR (δ, CDCl3) 182.6, 145.9, 142.4, 142.3, 140.9, 136.8, 135.1, 132.9, 131.3, 129.7, 129.4, 126.0, 111.1, 31.6, 31.5, 30.5, 30.2, 29.7, 29.3, 29.2, 29.1, 22.6, 22.5, 14.1, 14.0; MS (ESI+) m/z 525 [M + H] +; HRMS (ESI+) m/z calcd. for C25H32BrOS3 523.0793, found 523.0800.
Compound 4. Compound 2 (524 mg, 1.0 mmol) and compound 3 (388 mg, 0.5 mmol) were dissolved in toluene (15 mL) and the solution was degassed with N2 for 5 min. Pd(PPh3)4 (10 mg) was added and the mixture was degassed for another 10 min. After stirring at 100℃for 15 h, the reaction mixture was cooled to room temperature. Solvent was removed and the residue was purified with column chromatography (silica gel, dichloromethane/petroleum spirits 1:1) to give compound 4 as a dark red solid (323 mg, 60%). Rf 0.40 (dichloromethane); mp 105-107 oC;IR(neat) ν 2921, 2853, 1658, 1429, 1379, 1224, 1056 cm-1;1H NMR (δ, CDCl3) 9.88 (s, 2 H), 7.70 (d, J = 4.0 Hz, 2 H), 7.31 (s, 2 H), 7.23 (d, J = 4.0 Hz, 2 H), 7.04 (s, 2 H), 7.00 (s, 2 H), 2.82 (t, J = 8.0 Hz, 4 H), 2.77 (t, J = 7.6 Hz, 4 H), 1.60-1.75 (m, 8 H), 1.26-1.45 (m, 24 H), 0.88 (m, 12 H); 13C NMR (δ, CDCl3) 182.5, 146.1, 142.6, 142.2, 141.8, 141.2, 137.7, 136.8, 135.9, 135.5, 129.6, 129.5, 129.4, 129.0, 126.8, 125.8, 116.9, 31.6, 30.4, 30.2, 29.8, 29.6, 29.3, 29.2, 28.3, 27.8, 26.8, 22.6, 22.5, 17.5, 17.3, 14.1, 13.6; MS (ESI+) m/z 1080 [M ] +;HRMS (ESI+) m/z calcd. for C58H64O2S91080.2387, found 1080.2385.
Compound M1. A solution of compound 4 (108 mg, 0.1 mmol), octyl cyanoacetate (200 mg, 1.0 mmol) and 3 drops of triethylamine in chloroform (15 mL) was stirred at 60℃for 2 days. After cooling to room temperature, ethanol (100 mL) was added and the resulting precipitate was collected by filtration and purified with column chromatography (silica gel, dichloromethane/petroleum spirits 3:1) to give a dark solid. The dark solid was dissolved in chloroform and precipitates in ethanol again. Compound 13 was obtained as a dark solid (101 mg, 71%). Rf 0.80 (dichloromethane); Melting point 168 °C;IR(neat) ν 2923, 2854, 1708, 1571, 1417, 1200, 1066, 796 cm-1;1H NMR (δ, CDCl3) 8.25 (s, 2 H), 7.76 (d, J = 4.0 Hz, 2 H), 7.34 (s, 2 H), 7.25 (d, J = 4.0 Hz, 2 H), 7.06 (s, 2 H), 7.02 (s, 2 H), 4.29 (t, J = 6.8 Hz, 4 H), 2.85 (t, J = 8.0 Hz, 4 H), 2.79 (t, J = 7.6 Hz, 4 H), 1.65-1.70 (m, 12 H), 1.26-1.45 (m, 44 H), 0.88 (m, 18 H); 13C NMR (δ, CDCl3) 163.1, 145.8, 143.0, 141.9, 141.3, 137.9, 137.7, 136.3, 134.8, 129.6, 129.5, 129.4, 129.0, 126.9, 126.1, 117.0, 116.1, 97.6, 66.5, 31.8, 31.6, 30.3, 30.2, 29.9, 29.3, 29.2, 29.1, 29.0, 28.6, 25.8, 22.6, 22.5, 14.1, 14.0; MS (MALDI-TOF) m/z 1439 [M + H] +;Elemental analysis calcd (%) for C80H98N2O4S9: C 66.72, H 6.86, N, 1.95; found: C 66.81, H 6.74, N, 1.82.
Compound M2. A solution of compound 4 (108 mg, 0.1 mmol), octyl cyanoacetamide (200 mg, 1.0 mmol) and 3 drops of DBU in THF (15 mL) was stirred at reflux for 24 h. After cooling to room temperature, ethanol (100 mL) was added and the resulting precipitate was collected by filtration. The precipitate was washed with ethanol and small amount of acetone and then dissolved dichloromethane and precipitate in methanol. Compound 14 was obtained as a dark solid (71 mg, 49%). Rf 0.45 (dichloromethane); Melting point 148 °C;IR(neat) ν 3358, 2923, 2853, 1738, 1664, 1578, 1424, 1218, 1065, 795 cm-1;1H NMR (δ, CDCl3) 8.33 (s, 2 H), 7.66 (d, J = 4.0 Hz, 2 H), 7.31 (s, 2 H), 7.20 (d, J = 4.0 Hz, 2 H), 7.04 (s, 2 H), 7.00 (s, 2 H), 6.24 (t, J = 5.6 Hz, 2 H), 3.40 (m, 4 H), 2.83 (t, J = 7.6 Hz, 4 H), 2.77 (t, J = 7.6 Hz, 4 H), 1.55-1.75 (m, 12 H), 1.25-1.50 (m, 44 H), 0.88 (m, 18 H); 13C NMR (δ, CDCl3) 160.6, 145.0, 143.9, 142.6, 141.9, 141.2, 137.7, 137.2, 136.0, 135.5, 135.2, 129.6, 129.5, 129.4, 129.0, 126.9, 126.0, 117.5, 116.9, 99.0, 40.6, 31.8, 31.7, 31.6, 30.3, 30.2, 29.9, 29.6, 29.5, 29.4, 29.3, 29.1, 29.0, 28.9, 26.9, 22.6, 22.5, 14.1, 14.0; MS (ESI+) m/z 1436 [M ] +;HRMS (ESI+) m/z calcd. for C80H100N4O2S9 1436.5327, found 1436.5362.Elemental analysis calcd (%) for C80H100N4O2S9: C 66.81, H 7.01, N, 3.90; found: C 66.70, H 7.12, N, 3.69.
Compound 6. To a stirred suspension of compound 5 (1.92 g, 10 mmol) in dry CH2Cl2 (20 mL) was added SOCl2 (2 mL) and 1 drop of dry DMF. The resulting mixture was stirred at r. t. for 2 hrs. After removal of solvent under vacuum, 20 mL of dry CH2Cl2 was added. Excess methyl amine was bubbled to the solution slowly and the solution was stirred at r. t for another 1 hr. Solvent was evaporated under vacuum and the residue was purified with short column chromatography (silica gel, chloroform) to give compound 6 as a white solid (1.47 g, 72%). Rf 0.10 (CH2Cl2/EtOAc 4:1); mp 93-95oC;IR(neat) ν 3317, 1673, 1643,1550, 1446, 1403, 1284, 1200, 690cm-1;1H NMR (δ, CDCl3) 7.95 (m, 2 H), 7.55 (m, 1 H), 7.44 (m, 2 H), 5.73 (s, 1 H), 3.05 (t, J = 6.8 Hz, 2 H), 2.80 (d, J = 4.4 Hz, 3 H), 2.28 (t, J = 7.2 Hz, 4 H), 2.07 (m, 2 H); 13C NMR (δ, CDCl3) 200.0, 173.2, 136.7, 133.1, 128.6, 128.1, 37.4, 35.3, 26.3, 20.2; MS (ESI+) m/z 228 [M + Na ] +;HRMS (ESI+) m/z calcd. for C12H15NO2228.0995, found 228.0996.
Compound 7. A solutionof compound 6 (410 mg, 2.0 mmol) and p-tosylhydrazide (559 mg, 3.0 mmol) in dry methanol (50 mL) was stirred at reflux overnight. After cooling to r. t., all the solvent was evaporated under vacuum and the residue was recrystalliized from methanol to give compound 7 as a white solid (605mg, 81%). Rf 0.20 (CH2Cl2/EtOAc 4:1); mp 165-168oC;IR(neat) ν 3367, 1637, 1566, 1303, 1153, 699, 662 cm-1;1H NMR (δ, CD3CN) 11.08 (s, 1 H), 7.84 (d, J = 8.4 Hz, 2 H), 7.62 (m, 2 H), 7.38 (m, 5 H), 6.60 (s, 1 H), 2.77(d, J = 4.8 Hz, 3 H), 2.73 (t, J = 7.6 Hz, 2 H), 2.41 (s, 3 H), 1.90 (m, 2 H), 1.59 (m, 2 H); 13C NMR (δ, CDCl3) 174.4, 154.8, 143.9, 136.6, 133.3, 129.5, 129.4, 128.5, 127.6, 126.2, 32.6, 25.7, 25.5, 21.8, 20.6; MS (ESI+) m/z396 [M + Na ] +;HRMS (ESI+) m/z calcd. for C19H23N3O3SNa396.1352, found 396.1352.
PC61MBA. A mixture of compound7 (373 mg, 1 mmol), sodium methoxide (54 mg, 1 mmol) and dry pyridine (15 mL)was placed under nitrogen and stirred at room temperature for30 min. Then a solution of C60 (720 mg, 1 mmol) in 1,2-dichlorobenzene(50 mL) was added. The mixture was stirred at 80 °Cfor 24 h and then removed solvent under vacuum. The crudeproduct was chromatographed on silica gel by 0-50% ethylacetate in toluene as eluent. The mono portion was collectedand then resolved in 1,2-dichlorobenzene and refluxed for 24 h to ensurecompletely change from [5,6] open shell to [6,6] close shellmethanofullerenes. After the removal of1,2-dichlorobenzene in vacuum, theproduct was precipitated with methanol,centrifuged, and decanted.The remaining pellet was washed twice with methanol and thendried under vacuum to give PCMBA as a brown solid (102mg, 11%). Rf 0.35 (toluene/EtOAc 3:1); mp > 250oC;IR(neat) ν 3299, 2934, 1643, 1541, 1428, 1187, 753, 698cm-1;1H NMR (δ, CDCl3) 7.92 (d, J = 7.2 Hz, 2 H), 7.54 (t, J = 7.2 Hz, 2 H), 7.46 (m, 1 H), 5.45 (s, 1 H), 2.90 (m, 2 H), 2.81 (d, J = 4.8 Hz, 3 H), 2.36 (t, J = 7.6 Hz, 4 H), 2.02 (m, 2 H); 13C NMR (δ, CDCl3) 148.8, 147.8, 145.2, 145.1, 145.0, 144.8, 144.6, 144.5, 144.4, 144.0, 143.8, 143.0, 142.9, 142.8, 142.1, 142. 1, 142.0, 141.0, 140.8, 138.0, 137.6, 136.8, 132.1, 128.4, 128.2, 52.0, 36.4, 33.9, 26.4, 23.2; MS (ESI+) m/z909 [M + H ] +;HRMS (ESI+) m/z calcd. for C72H16NO910.1226, found 910.1228.
Characterisation data of compounds
FigureS1. Chemical shift of amide proton (N-H) of PC61MBA at different concentration in CDCl3.
Figure S2.Differential scanning calorimetry (DSC) traces for compounds M1 and M2 showing melting and crystallization processes.
Figure S3.Photoluminescence (PL) spectrum for (a) compounds M1 and M2 in chloroform solution (excitation wavelength 500 nm) and in film state (excitation wavelength 550 nm) and (b) for blend films of M1 and M2 with PC61BM and PC71BM (excitation wavelength 550 nm).
Figure S4.UV-vis spectrum of blend films of of M1 and M2 with PC61BM and PC71BM.
Figure S5.Cyclic voltammograms of (a) M1 and M2, (b) PC61BM and PC61MBA. Cyclic voltammetry (CV) experiments were performed at a sweep rate of 100 mV/s and were carried out in a three-electrode cell consisting of a glassy carbon working electrode, a platinum wire auxiliary electrode, and a Ag/Ag+ reference electrode. The supporting electrolyte was 0.10 M tetrabutylammonium hexafluorophosphate (Bu4NPF6).
a)M1 HOMO
b)M1 LUMO
c)M2 HOMO
d)M2 LUMO
Figure S6. The molecular frontier orbitals ofM1 and M2 calculated by DFT at the B3LYP/6-31G level using Gaussian 09.
Fabrication of the BHJ polymer solar cells
BHJ solar cells were processed on pre-patterned indium tin oxide (ITO) coated glass substrates with a sheet resistance of 15 Ω per square. First a thin layer (30 nm) of poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS; Baytron AI 4083 from HC Starck) was spin-coated on a UV-Ozone cleaned ITO substrates, followed by baking on a hot plate at 140 °C for 10 min. An active layer of the device was deposited by spin coating a chloroform solution containing 10 mg of donor and 20 mg of PCBM. The thickness of the active layer was 75 nmas determined by Veeco Dektak 150+ Surface Profiler. A thin layer of ZnO nanopaticle was deposited on the active layer by spin-coating (3000 rpm) to form a 25nm thick ZnO layer.The films were then transferred to a metal evaporation chamber and aluminum (100 nm) were deposited through a shadow mask (active area was 0.1 cm2) at approximately 1 x 10-6 torr. Film thickness was determined by Veeco Dektak 150+Surface Profiler. The current density-voltage measurements of the devices were carried out using a 1 kW Oriel solar simulator with an AM 1.5G filter as the light source in conjunction with a Keithley 2400 source measurement unit. Solar measurements were carried out under 1000 W/m2 AM 1.5G illumination conditions. For accurate measurement, the light intensity was calibrated using a reference silicon solar cell (PV measurements Inc.) certified by the National Renewable Energy Laboratory. Device fabrication and characterizations were performed in an ambient environment without any encapsulation.
Figure S4Schematic diagram of the BHJ solar cells.
Figure S7.J-V curves of BHJ solar cells based onM1 and M2.
Table S1Summary ofdevice parameters of small molecular solar cells based on M2/PC61BM.
Active layer / VOC (V) / JSC (mA cm–2) / FF(%) / PCE(%)M2 : PC61BM 2:1 / 0.60 / -0.53 / 29.01 / 0.09
M2 : PC61BM1:1 / 0.60 / -0.90 / 27.32 / 0.16
M2 : PC61BM 1:2 / 0.60 / -1.10 / 27.50 / 0.18
M2 : PC61BM1:4 / 0.62 / -0.98 / 43.02 / 0.26
M2 : PC61BM 1:6 / 0.58 / -0.61 / 43.07 / 0.15
Table S2Summary ofdevice parameters of small molecule solar cells based on M1/PC61BM.
Active layer / VOC (V) / JSC (mA cm–2) / FF(%) / PCE(%)M1 : PC61BM 2:1 / 0.66 / 0.53 / 0.32 / 0.11
M1 : PC61BM 1:0.8 / 0.67 / 1.29 / 0.37 / 0.32
M1 : PC61BM 1:4 / 0.63 / 1.23 / 0.42 / 0.32
M1 : PC61BM 1:6 / 0.66 / 0.92 / 0.46 / 0.28
Table S3Summary ofdevice parameters of small molecule solar cells based on M1/PC61MBAand M2/PC71MBA.
Active layer / VOC (V) / JSC (mA cm–2) / FF(%) / PCE(%)M1 : PC61MBA 2:1 / 0.62 / -0.38 / 28 / 0.06
M1 : PC61MBA 1:1 / 0.45 / -0.37 / 28 / 0.05
M2 : PC61MBA 2:1 / 0.65 / -0.21 / 27 / 0.04
M2 : PC61MBA 1:1 / 0.58 / -0.46 / 28 / 0.08
Space Charge Limited Current (SCLC) Measurements
The space charge limited current (SCLC) of M1 and M2 were studied using hole-only devices to find the charge-transport properties. The hole-only devices, consisting of active layer sandwiched between a PEDOT:PSS coated ITO electrode and Au counter-electrode as the electron-blocking contact, were fabricated as shown in figure XX. From the current density as a function of voltage data, the hole mobility in the space-charge limited current (SCLC) region can be estimated using the Mott-Gurney equation, J=9 (εrε0μ)/8 x (V2/d3), where J is the current density, V = Vappl – Vbi, V appl is the applied potential, Vbi is the built-in potential resulting from workfunction difference between two electrodes, εr is the dielectric constant of the polymer, ε0 is the permittivity of vacuum, μ is the hole mobility, d is the sample thickness.
Figure S8.(a) Device geometry of hole-only device for SCLC measurement; (b) current density vs. voltage data and table of calculated hole mobilities for compounds M1 and M2 in blends with PC61BM.
Grazing incidence wide-angle X-ray scattering data
Figure S9.1D-plot (out of plane) of the GIWAXS data: (a)M1, (b) M2, (c) M1:PC61BM, and (d) M2:PC61BM. The scattering vector is defined as q = 4π sin(θ)/λ, where λ is the incident X-ray wavelength and θ is half the scattering angle.
NMR Spectra
1H NMR of compound 1.
1H NMR of compound 2.
1H NMR of compound 4.
1H NMR of compound M1.
1H NMR of compound M2.
1H NMR of compound 6.
1H NMR of compound 7.
1H NMR of compound 8.
1