New Processable Phenanthridinone‐Based Polymers for Organic Solar Cell Applications

Abstract

anionic form under the alkylation conditions. This same trend was observed for the alkylation of pyrido [2,3,4,5-lmn ]phenanthridine under basic conditions. [ 24 ] Owing to the different functional groups, M1 and M2 can be easily separated on a chromatographic column or purifi ed by recrystallization. To obtain low band gap and processable materials, these monomers were copolymerized with 2,5-bis(2-octyldodecyl)-3,6-di(thien-2-yl)pyrrolo [3,4-c ]pyrrole-1,4-dione ( M3 ) (see the Supporting Information). [ 25 ] The polymerization reactions are also described in Scheme 1 . Two alternating copolymers ( P1 and P2 ) and one random terpolymer ( P3 ) were synthesized via simple direct (hetero)arylation polymerization (DHAP) (see the Supporting Information), a "greener" method which has rapidly developed in recent years. [26][27][28] The advantages of DHAP are manifold, and include a reduction in the number of reaction steps and the elimination of toxic organometallic by-products. The polymerization conditions utilized here are based on a recent report which has shown a high selectivity between aryl-bromide and non-substituted thiophene units. [ 29 ] Suzuki cross-coupling polymerization reactions were also performed for comparison purposes (see the Supporting Information). All polymers are soluble in common chlorinated solvents, such as chloroform (CF) and o -dichlorobenzene (ODCB), as well as chlorine-free solvents such as o -xylene. Interestingly, it has been noted that P2 ( M n = 60 kDa, PDI = 4.0) always afforded higher molecular weights than P1 ( M n = 43 kDa, PDI = 4.0). This could be explained by the greater solubility of P2 . Finally, a terpolymer P3 was obtained by copolymerizing the resulting 35:65 mixture of M1 and M2 with one equivalent of M3 . With a high ratio (65%) of monomer M2 into the structure of the random terpolymer P3 , this polymer ( M n = 57 kDa, PDI = 2.9) displays a good solubility in common solvents. The electrochemical properties of the polymers were investigated by cyclic voltammetry (CV) and are reported in Figure 1 b and Table S1 (Supporting Information). The occupied and unoccupied molecular orbital (HOMO/ LUMO) levels of P1 , P2 , and P3 are −5.48/−3.93, −5.46/−3.95, and −5.43/−3.92 eV, respectively, which indicate good stability in air and similar electronic properties between polymers. As reported in Figure 1 , the pristine green polymers ( P1 , P2 , and P3 ) exhibit broad UV-vis absorption spectra with an optical band gap ( E g opt ) of 1.64-1.65 eV, which is in agreement with the measured electrochemical band gap ( E g elect = 1.51-1.55 eV). Thermogravimetric analyses revealed that all polymers are stable up to 400 °C ( Figure S11, Supporting Information). Also, differential scanning calorimetry (DSC) measurements indicate that all these non-symmetric polymers are amorphous, as no glass transition temperature is observed between 25 and 250 °C. The DSC results are corroborated by X-ray diffraction (XRD) measurements (see the Supporting Information).Organic solar cells (OSC) have attrac...

CH Activation as a Shortcut to Conjugated Polymer Synthesis

“…Thiophene‐based heterocycles in particular are used due to their desirable electronic features, potential for functionalization, and steric role as spacers between larger monomer cores, in which they reduce the torsion angle between repeating units and improve polymer π‐conjugation. For these reasons, the monomers which undergo coupling in a DHAP reaction are often dithienyl‐flanked derivatives of C 6 arenes or other bulky units, such as diketopyrrolopyrrole (DPP), benzothiadiazole (BT), and dialkylphenylene (as shown in Figure ) . Thiophene‐flanked monomers possess three pairs of available C aryl H bonds: the CH bond adjacent to the sulfur atom (the α‐position), the neighboring C β H bond, and the C γ H bond adjacent to the monomer core.…”

Direct arylation polymerization toward a narrow bandgap donor–acceptor conjugated polymer of alternating 5,6‐difluoro‐2,1,3‐benzothiadiazole and alkyl‐quarternarythiophene: From synthesis, optoelectronic properties to devices

“…This result indicates that M n of PDFBT‐Th 4 polymer obtained by DAP is still lower than that of Stille polymerization method. However, this work indicates that it could be possible to synthesize PDFBT‐Th 4 polymer via DAP and an extensive DAP reaction optimization could lead to further increase in its molecular weight …”

“…organo‐tin) . Therefore, DAP is an economically efficient and environmentally benign approach compared with the traditional coupling methods (such as Stille and Suzuki couplings) …”

Conjugated Random Terpolymer Donors towards High‐Efficiency Polymer Solar Cells

“…The best performance was achieved by using TD13a as donor and PC 71 BM ( A3 ) as acceptor with the maximum PCE of 7.20%, which was ascribed to optimized morphology with high hole mobility of 4.24 cm 2 ·V −1 ·cm −1 measured from organic field‐effect transistors (OFETs). In addition, Leclerc and co‐workers synthesized terpolymer donor TD14 with two phenanthridinone derivatives as D monomers and thiophene‐capped DPP as A unit . The parental copolymers were also prepared for comparison.…”