Regioregularity and Electron Deficiency Control of Unsymmetric Diketopyrrolopyrrole Copolymers for Organic Photovoltaics

Abstract

Manipulating the electron deficiency and controlling the regioregularity of π-conjugated polymers are important for the fine-tuning of their electronic and electrochemical properties to make them suitable for an organic solar cell. Here, we report such a molecular design of unsymmetric diketopyrrolopyrrole (DPP) based copolymers with different aromatic side units of either thiophene (Th), pyridine (Py), or fluorobenzene (FBz). The unsymmetric electron acceptors of Th–DPP–Py and Th–DPP–FBz were polymerized with the electron donor of two-dimensional benzobisthiophene (BDT-Th), affording two regiorandom DPP copolymers. They exhibited contrasting molecular orbital levels and bulk heterojunction morphology in methanofullerene-blended films, leading to power conversion efficiencies of 3.75 and 0.18%, respectively. We further synthesized a regioregular DPP copolymer via sandwiching the centrosymmetric BDT-Th unit by two Th–DPP–Py units in an axisymmetric manner. The extensive characterization through morphology observation, X-ray diffraction, and space-charge-limited current mobilities highlight the case-dependent positive/negative effects of regioregularity and electron deficiency control.

Regioregularity-control of conjugated polymers: from synthesis and properties, to photovoltaic device applications

“…Lastly, many D-A alternating copolymers can exhibit sequential RR. [45][46][47][48][49][50] Most of the recent high-performance CPs used in organic electronics are based on D-A molecular structures, where D and A are alternately coupled along the CP backbones. In general, D-A copolymers are prepared via multiple coupling reactions between D and A moieties in an alternating sequence of D-A structures.…”

“…Moreover, different monomer sequences can be introduced in conjugated terpolymers (D-A1-D-A2) or tetrapolymers (D1-A1-D2-A2). [45][46][47][48][49] Sequentially rre terpolymers or tetrapolymers comprise repeating (D1-A1) and (D2-A2) sequences (or (D-A1) and (D-A2)) that alternate throughout the polymer chain. In contrast, rra polymers comprise a random sequence of donors (D1 or D2) and acceptors (A1 or A2) in the conjugated terpolymers or tetrapolymers.…”

Synthesis of conjugated polymers via cyclopentannulation reaction: promising materials for iodine adsorption

“…The design of new conjugated polymers has become one of the chief topics of interest for scientific endeavors because of the importance of this latter class of materials in diverse applications, namely, light-emitting diodes (LEDs), [1][2][3] organic solar cells, [4][5][6][7] field-effect transistors (FETs), [8][9][10][11][12][13][14][15][16] sensors, 17 optical switches, [18][19][20][21][22] batteries, 23 and thermoelectrics. 24 In addition to the hitherto mentioned applications, conjugated microporous polymers (CMP) have become exceptionally eminent due to many reasons, notably their extended π-conjugation skeleton, high stability, synthesis versatility, large surface area, and excellent gas sorption properties.…”

Recent structural evolution of lactam- and imide-functionalized polymers applied in organic field-effect transistors and organic solar cells

“…Such changes could make polymer lms adopt different packing states, let alone their photoelectric performances. 57,58 Besides, compared with DPPs with the same anking rings, those asymmetrically bridged DPP units are relatively harder to obtain due to the multiple synthetic steps, low yield, and difficulties in the purication process. It is noted that the backbone randomness of asymmetrically anked DPPbased polymers should not be neglected, which potentially affected the physicochemical properties or device performance.…”