Determining Optimal Crystallinity of Diketopyrrolopyrrole-based. Terpolymers for Highly Efficient Polymer Solar Cells and Transistors

Transcription

1 Determining Optimal Crystallinity of Diketopyrrolopyrrole-based Terpolymers for Highly Efficient Polymer Solar Cells and Transistors Supporting Information Ki-Hyun Kim,,a Sunhee Park,,a Hojeong Yu, b,c Hyunbum Kang, a Inho Song, b Joon Hak Oh, b and Bumjoon J. Kim *,a a Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 35-71, Korea b Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang , Republic of Korea c School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan , Republic of Korea S1

2 1. Materials and Characterization Methods Materials All reactions were performed under an argon atmosphere. 2,5-bis(2-hexyldecyl)-3,6-bis(5- bromothiophen-2-yl)pyrrolo[3,4-c]-pyrrole-1,4-dione and PC71BM were purchased from SunaTech and Nano-C Inc., respectively, and used as received without purification. Unless otherwise stated, all of the chemicals were purchased from Aldrich and used as received. Characterization Methods 1 H-NMR spectra were measured on a Liquid 4 NB NMR instrument with CDCl3 as the d-solvent. The peaks are given in ppm, relative to CDCl3 (7.26 ppm). Molecular weights were measured with GPC at 8 C (flow rate: 1 ml/min.) assembled with a Waters 1515 Isocratic HPLC pump, a temperature control module, and a Waters 2414 refractive index detector. o-dichlorobenzene (o-dcb) was used as the eluent against polystyrene standards. Elemental analysis was conducted with a Thermo Scientific Flash 2 Series. UV-visible (UV-vis) absorption spectra were obtained using a UV-18 spectrophotometer (Shimadzu Scientific Instruments) at room temperature. Electrochemical cyclic voltammetry (CV) (CHI 6C electrochemical analyzer) was conducted with a Pt disk working electrode, a Pt counter electrode, and an Ag wire quasi-reference electrode in anhydrous acetonitrile containing.1 M tetrabutylammonium hexafluorophosphate (Bu4NPF6) at a potential scan rate of 5 mv/s. For electrochemical measurements, the polymer films were coated from chloroform solution with a concentration of approximately 1 mg/ml. Differential scanning calorimetry (DSC) analysis was performed on a TA Instruments DSC Q2. The samples ( 5 mg) were heated from 25 to 35 C at a scan rate of 1 C min 1 under N2 atmosphere. Grazing incidence X-ray scattering (GIXS) measurements were performed at beamline 3C in the Pohang Accelerator Laboratory (South Korea). GIXS samples were prepared by spin coating with optimized active layer condition onto a S2

3 PEDOT:PSS/Si substrate. X-rays with a wavelength of A were used. The incidence angle (~.12 ) was chosen to allow for complete penetration of X-rays into the film. TEM measurements were performed with a JEM-311 JEOL Ltd. The optimized active layer were spun cast on PEDOT:PSS/Si substrate, then the thin films were floated onto the air/water interface and transferred to a TEM grid. 2. Synthesis 2,5-bis(trimethylstannyl)selenophene n-buli (1.5 ml of 2.5 M solution in Hexane, 26.3 mmol) was added dropwise to a solution of selenophene (1.5 g, 11.5 mmol) in THF (4 ml) at -78 C with stirring. After stirring for 3 min at -78 C, the reaction mixture was gradually warmed to room temperature and stirred for additional 2 hr. Trimethyltinchloride (26.9 ml of 1 M solution in THF) was slowly added and then stirred overnight at room temperature. The mixture was poured into ice/water, and the product was extracted with ether. The organic layer was washed several times with water and dried over MgSO4, and the solvent was removed by rotary evaporation. Recrystallization from ethanol afforded desired products as white crystals (3.9 g, 8.63 mmol, yield 75%). 1 H-NMR (4 MHz, CDCl3, TMS): δ (ppm) 7.65 (s, 2H, -Th),.34 (s, 18H, - CH3). General polymerization procedure by the Stille coupling reaction All of the polymers were synthesized by microwave-assisted stille coupling reaction. Three monomers were weighed and added to a microwave vial equipped with a magnetic stirrer. Dry toluene and dry DMF were added and the solution was degassed with argon for 2 min. After triphenylphosphine (PPh3, 8 mol%) and tris(dibenzylideneacetone)dipalladium (Pd2(dba)3, 2 mol%) were added, the cap was sealed. This mixture was degassed for an additional 2 min, and then the vial was placed in a S3

4 microwave reactor and stirred at 15 C for 3 hr. After then, trimethylstannyl- and bromo-terminal groups in polymers were capped with 2-bromothiophene (.2 ml) and 2-(tributylstannyl)thiophene (.25 ml), respectively, in microwave reactor at 15 C for 1 hr. After cooling to room temperature, the resulting gel was diluted with chloroform and refluxed with ethylenediaminetetraacetic acid (EDTA, 3 mg) in water at 11 C for 1 hr. The organic layer was washed with water and dried over MgSO4. The solvent was removed in vacuo and precipitated into methanol after which the resulting solids were purified via Soxhlet extraction sequentially with methanol, acetone, hexane, dichloromethane, chloroform, and chlorobenzene (if necessary). The filtrate in the each fraction was concentrated under reduced pressure and precipitated into cold methanol. The polymer was dried under vacuum for 24 hr. Polymerization for PDPT-Th1 (P1). A mixture of 2,5-bis(2-hexyldecyl)-3,6-bis(5- bromothiophen-2-yl)pyrrolo[3,4-c]-pyrrole-1,4-dione (2. mg, 1. eq), 2,5-bis(trimethylstannyl) thiophene (9.35 mg, 1. eq), PPh3 (4.6 mg), and Pd2(dba)3 (4. mg) were taken in Toluene (3. ml) and DMF (.3 ml) to synthesize P1 according to the procedure described above. (Chloroform fraction: 147 mg, yield 8%). GPC (Mn= 78.4K, Mw= 27K, PDI= 3.45). Elem. Anal. Calcd.: C, 72.41; H, 8.78; N, 3.38; S, 11.58; O, Found: C, 72.43; H, 8.85; N, 3.38; S, Polymerization for PDPT-Se1-Th9 (). A mixture of 2,5-bis(2-hexyldecyl)-3,6-bis(5- bromothiophen-2-yl)pyrrolo[3,4-c]-pyrrole-1,4-dione (3. mg, 1. eq), 2,5-bis(trimethylstannyl) thiophene (122.1 mg,.9 eq), 2,5-bis(trimethylstannyl)selenophene (15.12 mg,.1 eq), PPh3 (7. mg), and Pd2(dba)3 (6.1 mg) were taken in Toluene (2.5 ml) and DMF (.3 ml) to synthesize according to the procedure described above. (Chloroform fraction: 162 mg, yield 6%). GPC (Mn= 164K, Mw= 698K, PDI= 4.25). Elem. Anal. Calcd.: C, 71.99; H, 8.73; N, 3.36; S, 11.13; O, 3.84; Se,.96. Found: C, 71.62; H, 8.81; N, 3.3; S, Polymerization for PDPT-Se3-Th7 (P3). A mixture of 2,5-bis(2-hexyldecyl)-3,6-bis(5- bromothiophen-2-yl)pyrrolo[3,4-c]-pyrrole-1,4-dione (4. mg, 1. eq), 2,5-bis(trimethylstannyl) thiophene (126.5 mg,.7 eq), 2,5-bis(trimethylstannyl)selenophene (6.4 mg,.3 eq), PPh3 (9.3 mg), S4

5 and Pd2(dba)3 (8.1 mg) were taken in Toluene (3. ml) and DMF (.3 ml) to synthesize P3 according to the procedure described above. (Chloroform fraction: 37 mg, yield 83%). GPC (Mn= 119K, Mw= 531K, PDI= 4.45). Elem. Anal. Calcd.: C, 71.18; H, 8.63; N, 3.32; S, 1.24; O, 3.79; Se, Found: C, 71.4; H, 8.68; N, 3.33; S, Polymerization for PDPT-Se5-Th5 (). A mixture of 2,5-bis(2-hexyldecyl)-3,6-bis(5- bromothiophen-2-yl)pyrrolo[3,4-c]-pyrrole-1,4-dione (4. mg, 1. eq), 2,5-bis(trimethylstannyl) thiophene (9.35 mg,.5 eq), 2,5-bis(trimethylstannyl)selenophene (1.7 mg,.5 eq), PPh3 (9.3 mg), and Pd2(dba)3 (8.1 mg) were taken in Toluene (3. ml) and DMF (.3 ml) to synthesize according to the procedure described above. (Chloroform fraction: 252 mg, yield 67%). GPC (Mn= 86.3K, Mw= 387K, PDI= 4.48). Elem. Anal. Calcd.: C, 7.37; H, 8.53; N, 3.28; S, 9.37; O, 3.75; Se, Found: C, 7.55; H, 8.56; N, 3.3; S, Polymerization for PDPT-Se1 (). A mixture of 2,5-bis(2-hexyldecyl)-3,6-bis(5- bromothiophen-2-yl)pyrrolo[3,4-c]-pyrrole-1,4-dione (4. mg, 1. eq), 2,5- bis(trimethylstannyl)selenophene (21.4 mg, 1. eq), PPh3 (9.3 mg), and Pd2(dba)3 (8.1 mg) were taken in Toluene (3. ml) and DMF (.3 ml) to synthesize according to the procedure described above. (Chlorobenzene fraction: 2 mg, yield 52%). GPC (Mn=22.7K, Mw= 93.4K, PDI= 4.12). Elem. Anal. Calcd.: C, 68.45; H, 8.3; N, 3.19; S, 7.3; O, 3.65; Se, Found: C, 67.82; H, 8.25; N,3.16; S, Device Fabrication and Measurements OFET device fabrication and measurements PDPT-Se-Th terpolymers based OFETs were fabricated with a heavily n-doped Si wafers (<.4 Ω cm) covered with a 3 nm-thick SiO2 dielectric (Ci = 1 nf cm -2 ). The SiO2/Si wafers were treated with n-octadecyltrimethoxysilane (OTS) in solution phase. 3 mm OTS solution in trichloroethylene (TCE) was spin-coated onto a UV/ozone treated SiO2/Si wafer after cleaning with piranha solution (7:3 mixture of H2SO4 and H2O2 by volume ratio). Then, the wafer was exposed to ammonia vapor in a S5

6 vacuum desiccator for 12 hr at room temperature. The substrates were then rinsed with toluene, acetone and isopropyl alcohol, followed by drying with N2 blowing. The solution-shearing thin films of terpolymers were deposited onto the OTS-treated SiO2/Si substrates using chlorobenzene solutions (2 mg ml -1 ). In solution-shearing step, the shearing speed was optimized to.12 mm s -1. Then, terpolymer films were annealed on a hot plate at 2 C for 1 min under N2 atmosphere. The 4 nm gold electrode was thermally evaporated through a shadow mask onto the semiconductor layer. The current voltage (I V) characteristics of the devices were measured in a N2-filled glovebox using a Keithley 42 semiconductor parametric analyzer. The field-effect mobility was calculated in the saturation regime using the following equation: ID W 2L μc i (V G V T ) 2 where ID is the drain current, W and L are the semiconductor channel width and length, respectively, μ is the mobility, Ci is the capacitance per unit area of the gate dielectric, and VG and VT are the gate voltage and threshold voltage, respectively. Fabrication of inverted type PSCs To investigate the photovoltaic properties of the PDPT-Se-Th terpolymers in inverted type polymer solar cells, bulk heterojunction (BHJ) photovoltaic cells were fabricated using an ITO/ZnO/terpolymers:PC71BM/MoO3/Ag structure. The ZnO sol-gel was prepared using a sol-gel procedure by dissolving zinc acetate dihydrate (Zn(O2CCH3)2 (H2O)2, 99.9%, 1 g) and ethanolamine (HOCH2CH2NH2, 99.5%,.28 g) in anhydrous 2-methoxy ethanol (CH3OCH2CH2OH, > 99.8%, 1 ml) under vigorous stirring for more than 24 hr for hydrolysis reaction and aging. ZnO thin films with a thickness of ca. 4 nm were prepared by spin-coating the sol-gel precursor solution at 4 rpm on top of the ITO substrate. The films were heated at 2 C for 1 hr in air. After application of the ZnO layer, all subsequent procedures were performed in a glove box under a N2 atmosphere. Then, each active blending solution (terpolymer:pc71bm = 1:2 w/w, polymer concentration= 5 mg/ml) was spin-cast S6

7 onto an ITO/ZnO substrate at 12 rpm for 9 sec. The thicknesses of the optimized active layers were 13 nm (P1), 135 nm (), 13 nm (P3), 15 nm (), and 12 nm (). Finally, to complete the devices, the top electrodes of 7 nm MoO3/1 nm Ag film was thermally evaporated under high vacuum (less than 1-6 Torr). The active area of the fabricated devices was.9 cm 2. Inverted type PSC devices were characterized using a solar simulator (Newport Oriel Solar Simulators) with an air mass (AM) 1.5 G filter. The intensity of the solar simulator was calibrated carefully using an AIST-certified silicon photodiode. The current-voltage behavior was measured using a Keithley 24 SMU. EQE measurements The EQE curves were obtained by a spectral measurement system (K31 IQX, McScience Inc.). The light source (a 3-W xenon arc lamp) was used with a monochromator (Newport) and an optical chopper (MC 2 Thorlabs). S7

8 4. Supporting Data Table S1. Elemental analysis of PDPT-Se-Th terpolymers used in this study Se:Th N C H S PDPT-Th1 (P1) PDPT-Se1-Th9 () PDPT-Se3-Th7 (P3) PDPT-Se5-Th5 () PDPT-Se1 () Measured Calculated : Measured Calculated 1: Measured Calculated 3: Measured Calculated 5: Measured Calculated 1: S8

9 P1 Current (ma) =.43 V ox Current (ma) =.42 V ox = V red = V red Potential (V vs. Fc/Fc + ) Potential (V vs. Fc/Fc + ) P3 Current (ma) =.43 V ox Current (ma) =.39 V ox = V red = V red Potential (V vs. Fc/Fc + ) Potential (V vs. Fc/Fc + ) Current (ma) =.35 V ox = V red Potential (V vs. Fc/Fc + ) Figure S1. Cyclic voltammograms of PDPT-Se-Th terpolymers S9

10 (-ID )1/2 (X1-4 A 1/2 ) (-ID )1/2 (X1-4 A 1/2 ) (-ID )1/2 (X1-4 A 1/2 ) (-ID )1/2 (X1-4 A 1/2 ) (-ID )1/2 (X1-4 A 1/2 ) (ID )1/2 (X1-4 A 1/2 ) (ID )1/2 (X1-4 A 1/2 ) (ID )1/2 (X1-4 A 1/2 ) (ID )1/2 (X1-4 A 1/2 ) (ID )1/2 (X1-4 A 1/2 ) P1 = -1V = -1V P3 = -1V = -1V = -1V P1 = 1V = 1V P3 V 1-4 DS = 1V = 1V = 1V Figure S2. Transfer characteristics of OFETs with P1- films prepared by solution shearing and annealed at 2 C. Hole-enhancement operation (top line), and electron-enhancement operations (bottom line) with VDS= -1 V and +1 V, respectively. The average hole and electron mobilities were calculated from the I-V data set obtained using the range of ~1 V in the gate voltage sweep: i.e., hole enhancement mode: VGS ranges from -24 to -34 V for P1, -26 to -36 V for, -24 to -34 V for P3, -22 to -32 V for, and -14 to -24 V for ; electron enhancement mode: VGS ranges from 132 to 142 V for P1, 114 to 124 V for, 134 to 144 V for P3, 134 to 144 V for, and 114 to 124 V for S1

11 - (ma) P1 V G =6 V 4 V 2 V V -2 V -4 V -6 V -8 V -1 V - ( A) V G =6 V 4 V 2 V V -2 V -4 V -6V -8V -1V - ( A) P3 V G =6 V 4 V 2 V V -2 V -4 V -6V -8V -1V - ( A) V G =6 V 4 V 2 V V -2 V -4 V -6V -8V -1V - ( A) V G =2 V V -2 V -4 V -6 V -8 V -1 V (ma) P1 V G = V 2 V 4 V 6 V 8 V 1 V 12 V 14 V ( A) V G = V 2 V 4 V 6 V 8 V 1 V 12V 14V ( A) P3 V G = V 2 V 4 V 6 V 8 V 1 V 12V 14V ( A) V G = V 2 V 4 V 6 V 8 V 1 V 12V 14V ( A) V G = V 2 V 4 V 6 V 8 V 1 V 12V 14V Figure S3. Output characteristics of OFETs with P1- films prepared by solution shearing and annealed at 2 C. Hole-enhancement operation (top line), and electron-enhancement operations (bottom line), respectively S11

12 Table S2. Average device performance of the optimized inverted PSCs based on P1- a Terpolymer/PC 71 BM b J SC (ma/cm 2 ) V OC FF PCE (%) P1 c 14.6 ± ±.7.68 ± ±.2 d ± ±.2.66 ± ±.4 P3 c 15.2 ± ±.3.66 ± ±.6 d ±.2.66 ±.1.64 ± ±.2 c ± ±.2.62 ± ±.9 a Values are averages of more than 12 devices with active area of.9 cm 2. b The blend ratio (w/w) = 1:2 with 1,8-diiodooctane (3 vol%) as additive. c The mixing ratio of solvent o-dcb/cf (v/v) = 4:1. d The mixing ratio of solvent o-dcb/cf (v/v) = 3:1. S12

13 Normalized absorption (a.u.) Wavelength (nm) P1 P3 Figure S4. UV-vis absorption spectra of PDPT-Se-Th:PC71BM film at the optimized PSC device condition S13

14 (a) Intensity (a.u.) P1 P q z (Å -1 ) (b) Intensity (a.u.) P1 P q xy (Å -1 ) Figure S5. (a) Out-of-plane and (b) in-plane GIXS patterns of PDPT-Se-Th:PC71BM film at the optimized PSC device condition S14

15 Table S3. Full-width at half-maximum (FWHM) data of scattering peaks from GIXS measurements Terpolymer/PC 71 BM FWHM 1 (Å -1 ) a FWHM 1 (Å -1 ) b P P FWHM data of a (1) and b (1) peaks in in-plane and outof-plane direction, respectively. S15

16 Figure S6. GIXS patterns of pristine polymer (P1-) films S16

17 (a) Intensity (a.u.) P1 P q z (Å -1 ) (b) Intensity (a.u.) P1 P q xy (Å -1 ) Figure S7. (a) Out-of-plane and (b) in-plane GIXS patterns of pristine polymer (P1-) films S17

18 Table S4. Crystalline characteristics of pristine polymer (P1-) films Terpolymer d 1 (nm) a d 1 (nm) b FWHM 1 (Å -1 ) c Lc 1 (nm) d FWHM 1 (Å -1 ) e LC 1 (nm) f P P Domain spacings of a lamellar and b π-π stackings calculated from 2D GIXS in-plane and out-of-plane components, respectively. FWHM data of c (1) and d (1) reflection peaks in in-plane and out-of-plane directions, respectively. The correlation lengths of e lamellar and f π-π stacking crystals were estimated by using the Scherrer equation. S18