SUPPORTING INFORMATION. Aggregation Strength Tuning in Difluorobenzoxadiazole-Based Polymeric

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1 SUPPORTING INFORMATION Aggregation Strength Tuning in Difluorobenzoxadiazole-Based Polymeric Semiconductors for High-Performance Thick-Film Polymer Solar cells Peng Chen, Shengbin Shi, Hang Wang, Fanglong Qiu, Yuxi Wang, Yumin Tang, Jian-Rui Feng, Han Guo,* Xing Cheng and Xugang Guo* Department of Materials Science and Engineering and The Shenzhen Key Laboratory for Printed Organic Electronics, Southern University of Science and Technology of (SUSTech), No. 1088, Xueyuan Road, Shenzhen, Guangdong , China P.C. and S.S. contributed equally to this work. * (H.G.); (X.G.) S-1

2 Table of Contents 1. Materials and Instruments. 2. Thermal, Electrochemical and Optical Properties of Polymers. 3. DFT-Based Theoretical Calculations. 4. Organic Thin-Film Transistor Performance. 5. Fabrication of Polymer Solar Cells with Fullerene Acceptor 6. Fabrication of Polymer Solar Cells with Non-Fullerene Acceptor 7. SCLC Mobility Measurement. 8. Polymer Film Morphology Characterization. 9. NMR Spectra of Compounds S-2

3 1. Materials and Instruments. Monomer ffbx-2tdt-br was synthesized according to the published procedure. 1 Monomers T-Sn, TT-Sn, and DTT-Sn were purchased from Derthon Optoelectronic Materials Science Technology Co., Ltd. (Shenzhen, Chin. Anhydrous toluene was distilled from Na/benzophenone before use. All other reagents and chemicals were used as received without any further purification. The 1 H NMR spectra were measured on the Bruker Ascend 400 MHz spectrometer. Chemical shifts were referenced to residual protio-solvent signals. C, H, N, S elemental analyses (EAs) of the polymers were performed at Shenzhen University (Shenzhen, Chin. Molecular weights of the polymers were measured with high-temperature GPC/SEC system (Agilent PL-GPC220) at 150 ºC versus polystyrene standard using 1,2,4-trichlorobenzene as the eluent. Thermogravimetric analysis (TGA) curves were collected using Mettler STAR e at a heating ramp of 10 ºC min 1 in nitrogen environment. Differential scanning calorimetry (DSC) curves were recorded with Mettler STAR e at a heating rate of 10 ºC min 1 under nitrogen. Room temperature UV-vis spectra of the polymer solutions and films were collected on a Shimadzu UV-3600 UV-VIS-NIR spectrophotometer. Temperature-dependent UV-vis absorption spectra of the polymer solutions were collected on Perkin Elmer Lambda 950 UV/VIS/NIR Spectrometer. Cyclic voltammetry (CV) measurements of the polymer films were carried out under argon atmosphere using a CHI760 Evoltammetric analyzer with 0.1 M tetra-n-butylammoniumhexafluorophosphate (Bu 4 NPF 6 ) in acetonitrile (CH 3 CN) as the supporting electrolyte. A platinum disk working electrode, a platinum wire counter electrode, and a silver wire reference electrode were employed, and S-3

4 ferrocene/ferroceniuum (Fc/Fc + ) redox couple was used as reference for all measurements. The scanning rate was 50 mv s 1. Atomic Force Microscopy (AFM) measurements were conducted using a Dimension Icon Scanning Probe Microscope (Asylum Research, MFP-3D-Stand Alone) in the tapping mode. Transmission Electron Microscopy (TEM) images were obtained on Tecnai Spirit microscope (20 kv). For TEM samples, the films were first casted on PEDOT:PSS covered substrates, then they were floated off in deionized water before being transferred onto TEM copper grids. X-ray diffraction (XRD) measurements were performed on a Rigaku Smartlab diffractometer using standard out-of-plane 2θ technique (thin-film XRD), with monochromated Cu Kɑ radiation (λ = Å). For XRD samples, the films were spin-casted on ZnO covered silicon substrates. The π-π stacking distances were calculated using Bragg s law nλ = 2dsinθ from the corresponding peaks. S-4

5 2. Thermal, Electrochemical and Optical Properties of Polymers. Figure S1. ( TGA and (b) DSC curves of polymers PffBX-T, PffBX-TT, and PffBX-DTT. Figure S2. Cyclic voltammograms of PffBX-T, PffBX-TT, and PffBX-DTT polymer films in 0.1 M (n-bu) 4 N PF 6 acetonitrile solution (the Fc/Fc + redox couple is used as the internal standard). Figure S3. Temperature-dependent absorption spectra of ( PffBX-T; (b) PffBX-TT; and (c) PffBX-DTT in diluted o-dcb solutions from high temperature to low temperature. S-5

6 3. DFT-Based Theoretical Calculations. Figure S4. DFT calculated frontier molecular orbitals for the trimers of the repeating unit of PffBX-T, PffBX-TT, and PffBX-DTT under the optimized geometries. Table S1. DFT calculated energy levels for the trimers of the repeating unit of PffBX-T, PffBX-TT, and PffBX-DTT under the optimized geometries. Polymer HOMO (ev) LUMO (ev) E g (ev) PffBX-T PffBX-TT PffBX-DTT S-6

7 4. Organic Thin-Film Transistor Performance Table S2. Device performance parameters of TGBC organic thin-film transistors containing PffBX-T as the active layer fabricated at various annealing temperatures. Average mobilities and standard deviations are based on at least 5 devices. Polymer T anneal ( C) µ h,sat (cm 2 V 1 s 1 ) µ h,sat max (cm 2 V 1 s 1 ) V T,avg (V) I on /I off as-cast ± ± ± ± PffBX-T ± ± ± ± ± ± ± ± Table S3. Device performance parameters of TGBC organic thin-film transistors containing PffBX-TT as the active layer fabricated at various annealing temperatures. Average mobilities and standard deviations are based on at least 5 devices. Polymer T anneal ( C) µ h,sat (cm 2 V 1 s 1 ) µ h,sat max (cm 2 V 1 s 1 ) V T,avg (V) I on /I off as-cast 0.17 ± ± ± ± PffBX-TT ± ± ± ± ± ± ± ± S-7

8 Table S4. Device performance parameters of TGBC organic thin-film transistors containing PffBX-DTT as the active layer fabricated at various annealing temperatures. Average mobilities and standard deviations are based on at least 5 devices. Polymer T anneal ( C) µ h,sat (cm 2 V 1 s 1 ) µ h,sat max (cm 2 V 1 s 1 ) V T,avg (V) I on /I off as-cast 0.52 ± ± ± ± PffBX-DTT ± ± ± ± ± ± ± ± S-8

9 5. Fabrication of Polymer Solar Cells with Fullerene Acceptor Polymer solar cells with conventional structure: Indium tin oxide (ITO)-coated glass substrates (10 Ω/square) were cleaned as above for the inverted cells. PEDOT:PSS (Clevios P VP A1 4083) was used as hole injection layer, and it was spin-coated at 3000 rpm for 20 s on the active layer forming approximately 30 nm film onto the UV-ozone treated ITO substrates and then annealed at 150 C for 15 min in air before being transferred into a N 2 -filled glove-box. The polymer active layers were spin-casted in the same manner as for the inverted cells. Finally, 5 nm perylene diimide functionalized with amino Noxide (PDINO) 2 (1.5 mg ml 1 in ethanol) was spin-coated at 3000 rpm for 20 s on the active layer followed by the deposition of 100 nm Al cathode under high vacuum (3E 6 Torr) in thermal evaporator. The solar cell device characterization was performed in a N 2 filled glovebox using a Xeno-lamp-based solar simulator (Newport, Oriel AM1.5G, 100 mw cm 2 ). The effective area for the devices is cm 2. For device characterization, J-V curves were measured under AM 1.5G light (100 mw cm 2 ) with a computerized Keithley 2400 source meter. The light intensity is calibrated using an NREL-certified monocrystalline Si diode coupled to a KG3 filter to bring the spectral mismatch to unity. External quantum efficiency (EQE) was collected on a QE-R3011 measurement system (Enli Technology, Inc.) S-9

10 Table S5. Device performance parameters of PffBX-based inverted PSCs using various amount of DIO additives. (polymer:pc 71 BM = 1:1.5, weight ratio; CB:o-DCB solvent (1:1, volume ratio) for PffBX-TT and PffBX-DTT; chloroform solvent for PffBX-T) Polymer Additive V oc J sc FF PCE PCE max (V) (ma cm -2 ) (%) (%) (%) w/o 0.86 ± ± ± ± PffBX-TT 0.5% DIO 0.85 ± ± ± ± % DIO 0.85 ± ± ± ± % DIO 0.86 ± ± ± ± PffBX-T w/o 0.84 ± ± ± ± % DIO 0.99 ± ± ± ± PffBX-DTT w/o 0.82 ± ± ± ± % DIO 0.82 ± ± ± ± The average values and standard deviations of the device parameters are based on 10 devices. Table S6. Device performance parameters of PffBX-based inverted PSCs using various solvents. (polymer:pc 71 BM = 1:1.5, weight ratio; donor: 8 mg ml 1 for PffBX-TT and PffBX-DTT, 6 mg ml 1 for PffBX-T; 1% DIO, volume percentage) Polymer Solvent V oc J sc FF PCE PCE max (V) (ma cm -2 ) (%) (%) (%) CB 0.83 ± ± ± ± PffBX-TT PffBX-T o-dcb 0.85 ± ± ± ± CB/o-DCB (1:1) 0.85 ± ± ± ± CB/o-DCB (1:1) 0.99 ± ± ± ± CF 0.99 ± ± ± ± PffBX-DTT CB 0.80 ± ± ± ± CB/o-DCB (1:1) 0.82 ± ± ± ± The average values and standard deviations of the device parameters are based on 10 devices. S-10

11 Table S7. Device performance parameters of PffBX-TT-based inverted PSCs using various polymer:pc 71 BM ratios. (solvent: CB:o-DCB = 1:1, volume ratio; donor: 8 mg ml 1 ; 1 % DIO, volume percentage) Polymer:PC 71 BM Polymer (w:w) V oc J sc FF PCE PCE max (V) (ma cm -2 ) (%) (%) (%) 1: ± ± ± ± PffBX-TT 1: ± ± ± ± : ± ± ± ± The average values and standard deviations of the device parameters are based on 10 devices. Table S8. Device performance parameters of PffBX-TT-based inverted PSCs using various fullerene acceptors. (D:A weight ratio 1:1.5; solvent: CB:o-DCB = 1:1, volume ratio; donor: 8 mg ml 1 ; 1 % DIO, volume ratio) Polymer Acceptor V oc J sc FF PCE PCE max (V) (ma/cm 2 ) (%) (%) (%) PffBX-TT PC 61 BM 0.87 ± ± ± ± PC 71 BM 0.85 ± ± ± ± The average values and standard deviations of the device parameters are based on 10 devices. Table S9. Device performance parameters of PffBX-TT-based PSCs with different device structures. (D:A weight ratio 1:1.5; donor: 8 mg ml 1 ; solvent: CB:o-DCB = 1:1, volume ratio; 1 % DIO, volume ratio) Device Polymer structure d) d) V oc J sc FF d) PCE d) PCE max (V) (ma cm -2 ) (%) (%) (%) Conventional 0.86 ± ± ± ± PffBX-TT Conventional b) 0.87 ± ± ± ± Inverted c) 0.85 ± ± ± ± ITO/PEDOT:PSS/polymer:PC 71 BM/PDINO/Al; b) ITO/MoO 3 /Polymer:PC 71 BM/PDINO/Al; c) ITO/ZnO/Polymer:PC 71 BM/MoO 3 /Ag. d) The average values and standard deviations of the device parameters are based on 10 devices. S-11

12 6. Fabrication of Polymer Solar Cells with Non-Fullerene Acceptor Indium tin oxide (ITO)-coated glass substrates (10 Ω sq 1 ) were cleaned as described above for fullerene solar cells. PEDOT:PSS (Clevios P VP A1 4083) was spin-coated onto the UV-ozone treated ITO substrates, at 3000 rpm for 20 s then annealed at 150 C for 15 min in air, forming ~30 nm film. The PEDOT:PSS-coated ITO substrates were transferred into a N 2 -filled glove box for subsequent steps. For PffBX-TT and PffBX-DTT donor polymers, the polymer:it-4f (1:1 weight ratio) active layer solutions were prepared at a concentration of 8 mg ml 1 (for PffBX-TT ) or 10 mg ml 1 (for PffBX-DTT ) in 1,2-dichlorobenene with 0.5% volume ratio of 1,8-diiodooctane (DIO) as the processing additive. The solutions were stirred and heated at 130 C overnight to be completely dissolved. The ITO substrates were pre-heated on a hot plate at 130 C before spin-coating the active layers at 2000 rpm. For PffBX-T, the polymer:it-4f (1:1 weight ratio) active layer solution was prepared at a concentration of 7 mg ml 1 (for the donor polymer) in chloroform (CF) with 0.5% volume ratio of DIO as the additive. The active layer solution was stirred at room temperature for 3 h before spin-coating at 2000 rpm. All active layers were thermally annealed at 125 C for 5 min. Finally, 5 nm perylene diimide functionalized with amino N-oxide (PDINO) (1.5 mg ml 1 in ethanol) was spin-coated at 3000 rpm for 20 s on the active layer followed by the deposition of 100 nm Al cathode under a high vacuum (3E 6 Torr) using thermal evaporation. S-12

13 Figure S5. ( J-V curves, (b) EQE spectra of the best-performing conventional PSCs with the polymer:it-4f active layers. Table S10. Device performance parameters of PSCs containing polymer:it-4f blend as the active layer. (polymer:it-4f = 1:1, weight ratio; donor: 7 mg ml 1 for PffBX-T; 8 mg ml 1 for PffBX-TT, 10 mg ml 1 and PffBX-DTT; 0.5% DIO, volume percentage) Polymer Thickness (nm) V oc (V) J sc (ma cm -2 ) Integrated J sc b) (ma cm -2 ) FF (%) PCE (%) PCE max (%) PffBX-T ± ± ± ± PffBX-TT ± ± ± ± PffBX-DTT ± ± ± ± The average values and standard deviations of the device parameters are based on 10 devices; b) Integrated from EQE curves. S-13

14 7. SCLC Mobility Measurement. Space charge limited current (SCLC) measurements were performed on both hole-only and electron-only devices. The structure of the hole-only device is ITO/PEDOT:PSS/polymer:PC 71 BM/MoO 3 /Ag and the structure of the electron-only device is ITO/ZnO/polymer:PC 71 BM/PDINO/Al. The device fabrication conditions are the same as the PSCs described above. The SCLC mobility is extracted using Mott-Gurney equation 3 : = where J is the current density, ε 0 is the vacuum permittivity ( F m 1 ), ε r is the relative dielectric constant of the active layer (assumed to be 3), µ is the hole or electron mobility, d is the thickness of the active layer, V is the potential within the device given by V = V appl V bi, where V appl is the voltage applied to the device and V bi is the build-in potential across the active layer and the electrode interface. V bi is taken to be zero for these hole-only and electron-only devices. Table S11. The SCLC mobility measurements of the polymer:pc 71 BM blend films under the same conditions as for optimal solar cell performance Polymer µ e,sclc (cm 2 V 1 s 1 ) µ h,sclc (cm 2 V 1 s 1 ) µ h,sclc /µ e,sclc PffBX-T PffBX-TT PffBX-DTT S-14

15 Figure S6. J V characteristics of (a, b, c) the electron-only devices and (d, e,f) the hole-only devices. Experimental data was in black and the SCLC fitting was shown in red. For the electron-only device, the device structure is ITO/ZnO/polymer:PC 71 BM/PDINO/Al; while for hole-only device, the device structure is ITO/PEDOT:PSS/polymer:PC 71 BM/MoO 3 /Ag. S-15

16 8. Polymer Film Morphology Characterization. Figure S7. Tapping-mode AFM height images of polymer:pc 71 BM blend films: ( PffBX-T:PC 71 BM with DIO; (b) PffBX-TT:PC 71 BM with DIO; (c) PffBX-DTT:PC 71 BM with DIO; (d) PffBX-TT:PC 71 BM without DIO; (e) PffBX-TT:PC 71 BM without DIO; (f) PffBX-DTT:PC 71 BM without DIO. Table S12. AFM measured root mean square (RMS) roughness values of the polymer:pc 71 BM blend films. Blend w/ DIO (nm) w/o DIO (nm) PffBX-T:PC 71 BM PffBX-TT:PC 71 BM PffBX-DTT:PC 71 BM S-16

17 Figure S8. TEM images of polymer:pc71bm blend films prepared without DIO (a, b, c) and with DIO (d, e, f) additives under the optimal conditions for the PSC devices. Figure S9. Out-of-plane 2θ XRD scattering patterns of ( the neat polymer films, (b) the neat polymer films with thermal annealing treatment, and (c) the polymer:pc71bm blend films. S-17

18 9. NMR Spectra of Compounds. Figure S10. 1 H NMR spectrum of monomer ffbx-2tdt-br (r.t., in CDCl 3 ). Figure S C NMR spectrum of monomer ffbx-2tdt-br (r.t., in CDCl 3 ). S-18

19 Figure S F NMR spectrum of monomer ffbx-2tdt-br (r.t., in CDCl 3 ). 4 Figure S13. 1 H NMR spectrum of polymer PffBX-T (80 ºC in Toluene-d 8 ). S-19

20 Figure S14. 1 H NMR spectrum of polymer PffBX-TT (80 ºC in 1,2-C 6 D 4 Cl 2 ). Figure S15. 1 H NMR spectrum of polymer PffBX-DTT (80 ºC in 1,2-C 6 D 4 Cl 2 ). S-20

21 References 1. Zhao, J.; Li, Y.; Hunt, A.; Zhang, J.; Yao, H.; Li, Z.; Zhang, J.; Huang, F.; Ade, H.; Yan, H. A Difluorobenzoxadiazole Building Block for Efficient Polymer Solar Cells. Adv. Mater. 2016, 28, Zhang, Z.-G.; Qi, B.; Jin, Z.; Chi, D.; Qi, Z.; Li, Y.; Wang, J. Perylene Diimides: A Thickness-Insensitive Cathode Interlayer for High Performance Polymer Solar Cells. Energy Environ. Sci. 2014, 7, Murgatroyd, P. Theory of Space-Charge-Limited Current Enhanced by Frenkel Effect. J. Phys. D: Appl. Phys. 1970, 3, Shi, S.; Wang, Y.; Uddin, M. A.; Zhou, X.; Guo, H.; Liao, Q.; Zhu, X.; Cheng, X.; Woo, H. Y.; Guo, X. Difluorobenzoxadiazole-Based Polymer Semiconductors for High-Performance Organic Thin-Film Transistors with Tunable Charge Carrier Polarity. Adv. Electron. Mater. 2017, 3, S-21