Low Bandgap Polymers Based on Silafluorene Containing Multifused Heptacylic Arenes for Photovoltaic Applications

Abstract

A series of donor−acceptor copolymers based on a new silafluorene containing multifused heptacylic arenes have been designed and synthesized in order to further modulate and optimize their electronic and optical properties. Polymer solar cells based on a blend of these polymers and PC 61 BM exhibited high open circuit voltages of up to 0.86 V. Through simple and straightforward engineering of molecular structures, the devices based on the PSiFDCTBT:PC 61 BM (1:3.5 in wt %) blend provided, on average, a V oc of 0.86 V, a J sc of 8.8 mA/cm 2 , a FF of 56%, delivering a PCE of 4.2%.

Evidence for the Chain-Growth Synthesis of Statistical π-Conjugated Donor-Acceptor Copolymers

“…The donor–acceptor approach to spectral engineering π‐conjugated polymers was first demonstrated by Havinga and co‐workers,, and has since gained popularity as a means to narrow the bandgap of conjugated copolymers . Utilizing an electron‐rich donor with a high‐lying highest occupied molecular orbital (HOMO) level in combination with an electron‐deficient acceptor with a low‐lying lowest unoccupied molecular orbital (LUMO) level, copolymerization of donor and acceptor monomers shifts optical absorbance to a lower energy compared to constituent donor and acceptor polymers.…”

“…Utilizing an electron‐rich donor with a high‐lying highest occupied molecular orbital (HOMO) level in combination with an electron‐deficient acceptor with a low‐lying lowest unoccupied molecular orbital (LUMO) level, copolymerization of donor and acceptor monomers shifts optical absorbance to a lower energy compared to constituent donor and acceptor polymers. The majority of donor–acceptor copolymers consist of alternating donor and acceptor moieties in a one to one ratio that are prepared by Stille or Suzuki polycondensation, yielding well‐defined structures with a known polymer backbone sequence . Several studies have recently reported the synthesis of semirandom donor–acceptor copolymers by cross‐coupling polymerizations, allowing for the donor–acceptor ratio to be controlled in a single step during polymerization .…”

“…In both alternating and semirandom donor–acceptor copolymers, the relative composition of donor and acceptor moieties tunes the bandgap of the copolymer, adjusting optical absorption features resulting from donor–acceptor effects . For this reason, donor–acceptor copolymers are important for the active layer of polymer solar cells as they maximize the optical absorption within the solar spectrum, and allow tuning of the frontier molecular orbitals …”

Ladder‐type Diindenopyrazine Based Conjugated Copolymers for Organic Solar Cells with High Open‐circuit Voltages

“…[2,6,8] In the past decade, great research effort has been devoted to design and synthesize new conjugated polymers for organic photovoltaic (OPV) applications. [24][25][26][27][28][29][30][31][32][33] The ladder-type aromatic molecules have a planar aromatic structure constructed by linking different aromatic units such as benzene or thiophene via a bridging atom, which enables enhanced π-conjugation, π-π intermolecular interactions and improved charge-carrier mobility. [14,21,23] Recently, one kind of aromatic structure, namely ladder-type molecule, was chosen as a building block for materials for organic field effect transistor (OFET) and photovoltaic applications.…”

“…[14,21,23] Recently, one kind of aromatic structure, namely ladder-type molecule, was chosen as a building block for materials for organic field effect transistor (OFET) and photovoltaic applications. [25,28,32,34,35] By replacing the middle benzene ring of indenofluorene with pyrazine, a heteroaromatic ladder-type structure, 6,12-dihydro-diindeno[1,2-b;10,20-e]pyrazine (diindenopyrazine, IPY, Scheme 1) was formed, which can be used as a building block for p-type conjugated polymers for OFET and PSC applications. Besides, various alkyl chains can be easily introduced into the polymer backbone to get good solubility of the target polymers in common organic solvents.…”