Synthesis of All-Conjugated ABA and AB-type Donor-Acceptor Block Copolymers and Their Application in All-Polymer Solar C
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In this work, systematic investigations on the crystalline behaviors of the block copolymers based on PNDI are carried out by grazing incidence wide-angle X-ray scattering (GIWAXS) measurement. For this purpose, a series of all-conjugated block copolymers comprised of PNDI and P3HT are synthesized by the newly developed KCTP method.12,13 The chemical structures and abbreviations of these AB and ABA-type block copolymers are illustrated in Scheme 1. Here, we investigate the crystalline behaviors as a function of thermal annealing, as well as the differences between the polymers with different number of thiophene units (P2 and P3). In addition, the chain orientation of the block copolymers are compared to that of the physical blends of P3HT and PNDI homopolymers. Finally, all-polymer solar cells using P1 as the single active materials are reported. EXPERIMENT Materials. All reagents were purchased from commercial sources and used without further purification unless otherwise noted. N,N’-Bis(2-decyltetradecyl)-2,6dibromonaphthalene-1,4,5,8-bis(dicarboximide) (NDI-Br2) and 2,5Bis(trimethylstannyl)thiophene (1) were prepared according to literature procedures.14,15 5,5’Bis(trimethylstannyl)-2,2’-bithiophene (2) and 2,5-dibromo-3-hexylthiophene (3) were purchased from Sigma-Aldrich, Japan, and used as received. P1 was prepared as reported in previous work.12,13 Characterization. 1H NMR spectra were recorded on a Bruker DPX (300 MHz) in CDCl3 (25 oC) using tetramethylsilane as the internal standard. GIWAXS experiments were conducted at the Spring-8 on beamline BL 19B2. The samples were irradiated at a fixed incident angle on the order of 0.12o through a Huber diffractometer, and the GIWAXS patterns were recorded with a 2D image detector (Pilatus 300K) and with an X-ray energy of 12.39 keV (λ=1Å). The samples for GIWAXS were prepared by drop-casting the polymer solution in dichlorobenzene on the Si/SiO2 substrate and dried in air. Thermo-annealing of the samples was carried out at 150 and 230 oC, respectively, under vacuum for 1 h. Synthesis of PNDI macroinitiators. The preparation of PDNI macroinitiators for ABA triblock copolymers were carried out according to the literature.12,13 The preparation of PNDI macroinitiators for AB diblock copolymers is as follow: To a flask, 1.0 equiv of NDI-Br2 and 1.0 equiv of monomer 1 or 2 were placed under nitrogen followed by adding 0.025 equiv of Pd(PPh3)2Cl2. The flask and its contents were subjected to three pump/purge cycles with nitrogen followed by addition of anhydrous and degassed toluene (6 ml) via a syringe. The reaction mixture was stirred at 100 oC for 2 days, followed by adding 2-bromothiophene. After cooling to room temperature, the deeply colored mixture was dripped into 100 mL of vigorously stirred methanol (containing 5 ml of 12 M hydrochloric acid). After stirring for 3 h, the precipitated solid was collected by filtration under reduced pressure, and subjected to sequential Soxhlet extraction with methanol, acetone, and chloroform. Finally, the polymer solution in ch
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