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- 96 - Device fabrication and characterization
The OPVs were fabricated with a configuration of ITO/PEDOT: PSS/active layer/PDINO/Al. PEDOT:
PSS (Bayer Baytron 4083) was spin-coated at 4000 rpm onto ITO substrate, followed by annealing at 140 oC for 20 min in air. The active layer was spin-coated from blend solutions with a central amount of donor/acceptor weight ratio, followed by a thermal annealing treatment. Then methanol solution of PDINO (1.0 mg ml-1) was then deposited onto the active layer with a spin rate of 3000 rpm for 60 s.
Finally, 100 nm aluminum was thermally evaporated under vacuum (<5.0 10-5 Pa). The active area of each sample was 13.0 mm2. The J-V characteristics were recorded on Keithley 2400 source under illumination of an AM1.5G solar simulator with an intensity of 100 mW cm-2. The EQE measurements were conducted using Model QEX7 by PV measurements Inc. (Boulder, Colorado) in ambient air. The thickness of the active layers was measured using a stylus profilometer (P6, KLA Tencor). The hole and electron mobilities were measured via using the space charge limited current (SCLC) method. Device structures are ITO/PEDOT: PSS/active layer/Au for hole-only devices and ITO/ZnO/active layer/PDINO/Al for electron-only devices, respectively. The SCLC mobilities were calculated by MOTT-Gurney equation:
(1) Where εr is the relative dielectric constant of organic semiconductor, ε0 is the permittivity of empty space, μ is the mobility of zero-field, L is the thickness of the active layer, and V = Vapplied – Vbuilt-in – Vseries-resistance (the Vbi values are 0.2 V and 0V for the hole-only and the electron-only devices, respectively), where Vapplied is the voltage applied, and Vbuilt-in is the built-in voltage from the relative work function difference between the two electrodes. Vseries-resistance is the voltage caused by the series and contact resistance potential drop (Vseries-resistance = J×Rseries-resistance). For convenience, the voltage drop caused by this resistance (Rseries-resistance) was ignored.
Material Characterization Chapter 2
Synthesis of Compound 1
To a solution of 2-(tributylstannyl)thiophene (9.0 g, 24 mmol) and diethyl 2,5-dibromoterephthalate (3.70 g, 10 mmol) in anhydrous toluene (50 ml), Pd(PPh3)4 (0.58g, 0.5 mmol) was added under nitrogen.
The resulting mixture was kept at 110 oC for 24 h and then quenched with water and extracted with diethyl ether. The diethyl ether solution was dried over MgSO4. After removing the solvent, the crude compound 1 was purified by silica gel chromatography using a mixture of dichloromethane and hexane
3 2 0 r
8 9
L J V
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(1:1) as the eluent to afford a colorless solid (3.3 g, 82%). 1H NMR (400 MHz, CDCl3, δ): 7.80 (s, 2H), 7.39 (dd, 2H), 7.11 (m, 4H), 4.21 (d, 4H), 1.15 (t, 6H).
Synthesis of 4-Bromo-1-(2-ethylhexyl)oxy)-2-fluorobenzene
To a solution of 4-bromo-2-fluorophenol (10.0 g, 52.5 mmol), K2CO3 (8.5 g, 62.8 mmol) in DMF (50 ml), 1-bromo-2-ethylhexane (10.0 g, 52.4 mmol) was added and the stirred mixture was kept at 130 oC for 12h. And then cooled to room temperature and extracted with ethyl acetate. The combined organic phase was dried over MgSO4. After removing the solvent, the resulting crude compound was purified by silica gel chromatography using hexane as the eluent to afford a colorless oil (13.0 g, 81%). 1H NMR (400 MHz, CDCl3, δ): 7.24 (dd, 1H), 7.16 (d, 1H), 6.88 (t, 1H), 3.92 (d, 2H), 1.78 (m, 1H), 1.59-1.32 (m, 8H), 0.92-0.86 (m, 6H).
Synthesis of Compounds M1
To a solution of 4-bromo-1-(2-ethylhexyl)oxy)-2-fluorobenzene (3.0 g, 12.5 mmol) in THF (25 mL) at -78 oC was added n-BuLi (5.5 mL, 2.5 M in hexane, 13.75 mmol), the mixture was kept at -78 oC for 1 h, then a solution of compound 1 (0.8 g, 2.1 mmol) in THF (15 mL) was added slowly. After the addition, the mixture was stirred at room temperature overnight and then quenched with water and extracted with ethyl acetate. The combined organic phase was dried over MgSO4. After removing the solvent, the crude product was directly dissolved in acetic acid (100mL) and conc. H2SO4 (2 mL) was added. The mixture was refluxed for 4 h and cooled to room temperature. After pouring into water, the mixture was extracted with ethyl acetate and dried over MgSO4. The resulting crude compound was purified by silica gel chromatography using a mixture of hexane/dichloromethane (5:1) as the eluent to afford a yellow solid (1.6 g, 68%). 1H NMR (400 MHz, CDCl3, δ): 7.36 (s, 2H), 7.29-7.28 (d, 2H), 6.97- 6.94 (m, 6H), 6.93-6.89 (d, 4H), 6.88-6.79 (m, 4H), 3.86-3.84 (m, 8H), 1.75-1.52 (m, 4H), 1.46-1.27 (m, 34H), 0.92-0.86 (m, 24H). 13C NMR (100 MHz, CDCl3, δ): 155.1, 153.5, 153.1, 151.1, 146.4, 141.2, 136.8, 135.0, 128.1, 123.3, 122.6, 117.2, 116.0, 114.3, 71.8, 39.3, 30.3, 28.9, 23.7, 23.0, 14.0. Anal.
calcd for C72H86F4O4S2: C 74.83, H 7.50, O 5.54, S 5.55; found: C 74.65, H 7.61, O 5.64, S 5.60.
Synthesis of Compounds M2
To a solution of M1 (1.1 g, 1.0 mmol) in THF (20mL) at -78 oC was added n-BuLi (1 ml, 2.5M, 2.5 mmol). After addition, the mixture was kept at -78 oC for another 1h and then trimethyltin chloride (1.0 M, 4.0 mmol) was added. The resulting mixture was stirred overnight at room temperature overnight and then quenched with water and extracted with diethyl ether. The diethyl ether solution was dried over MgSO4. Recrystallization from methanol afford a yellow solid (0.9 g, 65%). 1H NMR (400 MHz, CDCl3, δ): 7.35 (s, 2H), 7.25-6.98 (m, 6H), 6.97-6.89 (d, 4H), 6.84-6.80 (m, 4H), 3.89-3.83 (m, 8H),
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1.80-1.56 (m, 4H), 1.45-1.23 (m, 38H), 0.99-0.88 (m, 27H), 0.44-0.30 (t, 18H). 13C NMR (100 MHz, CDCl3, δ): 156.8, 153.5, 153.3, 151.0, 146.3, 142.2, 137.3, 134.7, 129.9, 123.4, 117.5, 116.2, 114.3, 71.8, 39.3, 30.3, 29.7, 23.7, 23.0, 14.0, -8.0. Anal. calcd for C78H102F4O4S2Sn2: C 63.25, H 6.94, O 4.32, S 4.33; found: C 64.69, H 7.46, O 4.24, S 4.11.
Stille-Coupling Polymerization
The compound M2 (150.0 mg, 0.112 mmol), TQ (95.9 mg, 0.112 mmol), Pd2(dba)3 (2.0 mg, 0.002 mmol ) and P(o-Tol )3 (3.4 mg, 0.010 mmol) were put into a Schlenk flask, purged with argon for 10min. Then 5ml of anhydrous toluene was added and the mixture was heated at 110 oC for 72h. After cooling to room temperature, the mixture was poured into methanol. The crude product was collected by filtration and washed by Soxhlet extraction in methanol, acetone, and hexane. Finally, the chloroform-soluble fraction was re-precipitated in methanol to afford a dark purple solid.
DAP
The compound M1 (100.0 mg, 0.069 mmol), TQ (74.5 mg, 0.069 mmol), Pd(OAc)2 (0.3 mg, 0.002 mmol) and K2CO3 (23.9 mg, 0.173 mmol ) were put into a microwave vessel, purged with argon for 10min. Then 5ml of anhydrous DMAc was added and the mixture was heated at 100 oC by using either conventional or microwave tool for each reaction time noticed in Table 1. After cooling to room temperature, the mixture was poured into methanol. The crude product was collected by filtration and washed by Soxhlet extraction in methanol, acetone, and hexane. Finally, the chloroform-soluble fraction was re-precipitated in methanol to afford a dark purple solid.
Chapter 3.1
Synthesis of donor polymers
The monomers TPTI-Br2 (80 mg, 0.0859 mmol), T, and 2T were mixed in 12 mL of anhydrous toluene.
After degassing under argon for 10 min, Pd2(dba)3 (2.359 mg, 2.57 µmol) and P(o-tolyl)3 (3.13 mg, 10.28 µmol) were added as the catalyst and ligand. The reaction mixture was stirred at 100 oC for 3 days under argon. Then, 2-(tributylstannyl)thiophene and 2-bromothiophene were added to end-cap the polymer chain. The reaction mixture was cooled to room temperature and precipitated into methanol.
The precipitate was purified by Soxhlet extraction in the sequences of methanol, acetone, hexane, and chloroform. The chloroform fraction was re-precipitated using methanol and dried. Finally, PTPTI-T series terpolymers were obtained as a dark purple solid.
PTPTI-T100: Isolated yield = 82.3% (60.3 mg). 1H NMR (400 MHz, CDCl3, δ): 8.6-7.71(br, Ar–H), 6.84-6.00 (br, Ar–H), 5.25-4.5 (br, N–CH2), 1.56-1.00 (m, br, –CH, –CH3), 0.97-0.4 (m, br, –CH3). Anal.
calcd for C52H72N2O2S3: C 73.19, H 8.50, N 3.28, S 11.27; found: C 73.17, H 8.29, N 3.01, S 11.10.
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PTPTI-T70: Isolated yield = 95.9 % (72.3 mg). 1H NMR (400 MHz, CDCl3, δ): 8.6-7.71(br, Ar–H), 6.84-6.00 (br, Ar–H), 5.25-4.5 (br, N–CH2), 1.56-1.00 (m, br, –CH, –CH3), 0.97-0.4 (m, br, –CH3). Anal.
calcd for [(C52H72N2O2S3)0.7 + (C56H74N2O2S4)0.3]: C 72.80, H 8.34, N 3.19, S 12.00; found: C 72.12, H 8.30, N 2.68, S 11.50.
PTPTI-T50:Isolated yield = 90.6 % (69.7 mg). 1H NMR (400 MHz, CDCl3, δ): 8.6-7.71(br, Ar–H), 6.84-6.00 (br, Ar–H), 5.25-4.5 (br, N–CH2), 1.56-1.00 (m, br, –CH, –CH3), 0.97-0.4 (m, br, –CH3). Anal.
calcd for [(C52H72N2O2S3)0.5 + (C56H74N2O2S4)0.5]: C 72.54, H 8.23, N 3.13, S 12.49; found: C 72.03, H 8.24, N 2.66, S 12.34.
PTPTI-T30: Isolated yield = 81 % (63.4 mg). 1H NMR (CDCl3, 400 MHz): δ (ppm) 8.6-7.71(br, Ar–
H), 6.84-6.00 (br, Ar–H), 5.25-4.5 (br, N–CH2), 1.56-1.00 (m, br, –CH, –CH3), 0.97-0.4 (m, br, –CH3).
Anal. calcd for [(C52H72N2O2S3)0.3 + (C56H74N2O2S4)0.7]: C 72.28, H 8.12, N 3.07, S 12.97; found: C 71.88, H 7.85, N 2.60, S 12.88.
Chapter 3.2
Synthesis of donor polymers
The dibrominated monomer (M2, M3, and M4, respectively) (0.10 mmol) and distannylated M1 (0.10 mmol) were taken in a long Schlenk tube under argon condition with 3 mL of anhydrous toluene and 1 mL of dimethylformamide. The mixture was degassed for 10 min, followed by addition of a solution of Pd(PPh3)4 (2.0 mol) in 1 mL of toluene to the tube. The reaction mixture was stirred vigorously at 120
oC for 1 day. After cooling to room temperature, it was poured into methanol (200 mL) and the precipitate was formed. The filtered polymer was then purified by Soxhlet extraction using methanol (1 d), acetone (1 d), hexane (1 d) and chloroform (1 d). The chloroform fraction was concentrated and reprecipitated in acetone. The purified polymer was collected by using membrane filter (pore size, 0.45
m) and dried under high vacuum oven at room temperature.
PJ1: Isolated yield = 89%. 1H NMR (CDCl3, 400 MHz, 298 K) ppm 7.69 (s, 2H), 7.58 (s, 2H), 7.39 (s, 2H), 7.21 (s, 2 H), 3.52 (br, 2H), 2.79 (br, 4H), 1.86 (br, 1H), 1.66 (br, 4H), 1.57-1.47 (m, 12H), 1.39-1.18 (br, 60H), 1.09-1.00(m, 18H), 0.96-0.81 (m, 24H). Anal.calc. for C90H135NO2S7Si2: C, 70.03;
H, 8.81; N, 0.91; S, 14.54; Found: C, 70.06; H, 9.24; N, 1.06; S, 14.38. Mn = 87.8 kDa, PDI = 1.58.
PJ2: Isolated yield = 75%. 1H NMR (CDCl3, 400 MHz, 298 K) ppm 7.77-7.40 (br, 6H), 7.21-6.78 (br, 4H), 3.50-3.11 (br, 4H), 1.88-0.57 (br, 72 H). Anal.calc. for C70H88O2S8Si2: C, 65.99; H, 6.96; S, 20.13;
Found: C, 65.55; H, 6.95; S, 20.95. Mn = 80.1 kDa, PDI = 1.44.
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PJ3: Isolated yield = 77%. 1H NMR (CDCl3, 400 MHz, 298 K) ppm 8.05-7.71 (br, 2H), 7.62-7.30 (br, 4H), 7.08-6.80 (br, 2H) 3.17-2.76 (br, 4H), 1.99-0.65 (br, 88 H). Anal.calc. for C90H134F2N2S7Si2: C, 69.17; H, 8.64; N, 1.79; S, 14.36; Found: C, 68.26; H, 8.36; N, 1.81; S, 14.28. Mn = 79.2 kDa, PDI = 1.56.
Chapter 4
Synthesis of donor polymers
In a Schlenk flask, TT (a mol), BDT (b mol), and BDD (a + b mol) were dissolved in anhydrous toluene (4 mL) and purged with argon for 15 min. Then, Pd(PPh3)4 (0.07 equiv. of BDD) was added and purged again with argon for 10 min. After that, the reaction mixture was stirred at 120°C for 12 h. Afterward, small amounts of 2-bromothiophene and 2-(trimethylstannyl)thiophene were used as the end-capping agent, respectively. And then, the mixture was cooled down and precipitated to methanol. The precipitated crude product was purified via sequential Soxhlet extraction with methanol, acetone, hexane, and chloroform. The chloroform fraction was concentrated and precipitated to methanol. The purified copolymers were collected by using membrane filter (pore size, 0.45 m) and dried under high vacuum oven.
PBDB-TT0: On basis of the procedure described above, the reference PBDB-TT0 copolymer was prepared by using BDT (100 mg, 0.111 mmol) and BDD (84.8 mg, 0.111 mmol). Yield = 96.7%. Mn = 15.3 kDa, PDI = 3.21.
PBDB-TT5: On basis of the procedure described above, BDT (95.4 mg, 0.105 mmol), TT (2.6 mg, 0.00555 mmol), and BDD (84.8 mg, 0.111 mmol) were used for copolymerization. Yield = 95.2%. Mn
= 24.8 kDa, PDI = 2.50. 1H NMR (400 MHz, CDCl3), δ (ppm): 8.50-7.30 (br), 7.25-6.00 (br), 4.10-2.50 (br), 2.30-1.25 (br), 1.20-0.25 (br). Elemental analysis calculated for [C666H761O20S79]: C, 68.64; H, 6.74; S, 21.84; Found: C, 68.45; H, 6.72; S, 21.86.
PBDB-TT10: On basis of the procedure described above, BDT (90.3 mg, 0.0998 mmol), TT (5.2 mg, 0.0111 mmol), and BDD (84.8 mg, 0.111 mmol) were used for copolymerization. Yield = 94.9%. Mn = 18.6 kDa, PDI = 3.50. 1H NMR (400 MHz, CDCl3), δ (ppm): 8.50-7.30 (br), 7.25-6.00 (br), 4.10-2.50 (br), 2.30-1.25 (br), 1.20-0.25 (br). Elemental analysis calculated for [C652H742O20S78]: C, 68.41; H, 6.69; S, 22.04; Found: C, 68.43; H, 6.71; S, 22.11.
PBDB-TT20: On basis of the procedure described above, BDT (80.2 mg, 0.0887 mmol), TT (10.3 mg, 0.0222 mmol), and BDD (84.8 mg, 0.111 mmol) were used for copolymerization. Yield = 83.9%. Mn =
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11.7 kDa, PDI = 4.12. 1H NMR (400 MHz, CDCl3), δ (ppm): 8.50-7.30 (br), 7.25-6.00 (br), 4.10-2.50 (br), 2.30-1.25 (br), 1.20-0.25 (br). Elemental analysis calculated for [C624H704O20S76]: C, 67.96; H, 6.57; S, 22.45; Found: C, 67.95; H, 6.58; S, 22.51.
Chapter 5
Synthesis of donor polymers
5,8-dibromo-2,3-bis(3-(octyloxy)phenyl)quinoxaline (0.32 mmole), 5,8-dibromo-6-fluoro-2,3-bis(3- (octyloxy)phenyl)quinoxaline or 5,8-dibromo-6,7-difluoro-2,3-bis(3-(octyloxy)phenyl) quinoxaline (0.320 mmol) and 2,5-bis(trimethylstannyl) thiophene (0.320 mmol) were taken in a Schlenk tube under argon atmosphere. 10 mL of anhydrous toluene was added and the mixture was degassed for 20 min followed by addition of Pd2(dba)3 (9 mg, 9.8 mol) and P(o-tolyl)3 (15 mg, 49 mol). The mixture was heated at 110°C for 72 h. After cooling to room temperature, it was poured into vigorously stirred methanol (300 mL) together with 30 mL of 30% aqueous NH4OH solution and the resulting precipitate was filtered and washed with methanol (2 x 200 mL). The polymer was purified by Soxhlet extraction using methanol (12 h), acetone (12 h) and hexane (12 h), and finally extracted with chloroform. The chloroform solution was then concentrated by evaporation and re-precipitated in methanol. The resulting dark-colored solid was collected and dried overnight under vacuum.
TQ: 1H NMR (400 MHz, CDCl3, δ): 7.83 (br, 2H), 7.35 (br, 2H), 7.21-7.10 (br, 6H), 6.85 (br, 2H), 3.70 (br, 4H), 1.55 (br, 4H), 1.17 (br, 20H), 0.80 (br, 6H). Mn = 30.7 kDa, PDI = 2.95.
TQ-F: 1H-NMR (400 MHz, C2D2Cl4, δ): 8.20 (br, 2H), 7.41-6.87 (br, 9H), 3.68 (br, 4H), 1.44-1.19 (br, 24H), 0.85 (br, 6H). Mn = 32.0 kDa, PDI = 2.63.
TQ-FF: 1H-NMR (400 MHz, C2D2Cl4, δ): 8.35 (br, 2H), 7.34-7.09 (br, 6H), 6.81 (br, 2H), 3.61 (br, 4H), 1.40-1.14 (br, 24H), 0.82 (br, 6H). Mn = 29.8 kDa, PDI = 2.71.
Synthesis of acceptor polymers
All P(NDI2OD-T2)-based polymers were also synthesized by a Stille coupling followed by carefully controlling the reaction conditions to isolate the polymers with different Mns as follows: Polymerization with Pd2(dba)3 (1.5 mol%) and tri-o-tolylphosphine to palladium ligand ratio (Pd/P(o-tolyl)3 of 1:5) in at 100 °C for 2 days was carried out. The concentration was 25 mg ml-1 of anhydrous toluene. The crude polymer was purified by Soxhlet extraction with methanol, acetone, and hexane. The resulting polymer was further fractionated by Soxhlet extraction with MC and then with chloroform, giving two fractions, M-P(NDI2OD-T2) and H-P(NDI2OD-T2. On the other hand, the polymerization procedure for L-
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P(NDI2OD-T2) involved a slightly higher amount of Pd2(dba)3 (3 mol%) and (Pd/P(o-tolyl)3 of 1:4 at 100 °C for 2 days. The concentration was 10 mg ml-1 of anhydrous toluene. After sequential Soxhlet extraction, the fraction extracted in chloroform was re-precipitated into methanol to generate L- P(NDI2OD-T2). All the acceptor polymers were supported by 1H NMR spectroscopy, in agreement with the literature report.
L-P(NDI2OD-T2): 1H NMR (400 MHz, CDCl3, δ): 8.52-8.82 (m, br, 2H), 7.20-7.34 (br, 4H), 4.12 (s, br, 2H), 2.00 (s, br, 4H), 1.04-1.45 (s, br, 64H), 0.80-0.87 (s, br, 12H). Mn = 20.4 kDa, PDI = 3.67.
M-P(NDI2OD-T2): 1H NMR (400 MHz, CDCl3, δ): 8.52-8.83 (m, br, 2H), 7.20-7.34 (br, 4H), 4.12 (s, br, 2H), 2.01 (s, br, 4H), 1.09-1.45 (br, 64H), 0.80-0.87 (s, br, 12H). Mn = 31.7 kDa, PDI = 3.08.
H-P(NDI2OD-T2): 1H NMR (400 MHz, CDCl3, δ): 8.52-8.83 (m, br, 2H), 7.20-7.34 (br, 4H), 4.12 (s, br, 2H), 2.04 (s, br, 4H), 1.04-1.45 (s, br, 64H), 0.80-0.87 (s, br, 12H). Mn = 63.3 kDa, PDI = 2.70.
Chapter 6
Synthesis of PDMS-S
Poly(methylhydrosiloxane) macroinitiator (5 ml) and drops of Karstedt’s catalyst were taken in a Schlenk tube under argon atmosphere. Styrene (84.8 mg, 0.111 mmol) was added and the mixture was degassed for 20 min followed by heating at 80°C for 24 h. After cooling to room temperature, it was poured into water and extracted with CHCl3. The chloroform solution was then concentrated by evaporation and dried overnight under vacuum. Yield = 96%. Mn = 3338 Da, PDI = 1.44. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.25 − 7.00 (br), 2.75 – 2.55 (br), 1.45 – 1.25 (br), 2.30 − 1.25 (br), 0.20 − 0.00 (br)
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