Processible Cyclopentadithiophene Copolymers for Photovoltaic Applications

Abstract

We designed and synthesized a series of conjugated polymers containing alternating 4H-cyclopenta[2,1-b:3,4-b ]dithiophene units and comonomers consisting of 2,2'-bithiophene, 3 ,4 -dihexyl-α-pentathiophene, 3,4-ethylenedioxythiophene and 5,5 -bis(2-thienyl)-4,4 -dihexyl-2,2 -bithiazole. These polymers possess optical bandgaps in the range of 1.75 to 2.0 eV. The desirable absorption attributes of these materials make then excellent candidates for use in photovoltaic cells. Electrochemical studies indicate desirable HOMO-LUMO levels for use with fullerene derivatives as electron transporters. Field effect transistors made of these materials show hole mobilities in the range of 7.5 × 10 −4 cm 2 /Vs to 2.0 × 10 −3 cm 2 /Vs. Due to the combination of these characteristics, power conversion efficiencies up to 3.1% were achieved on devices made of bulk heterojunction composites of these materials with soluble fullerene derivatives.

Bithiazole-bridged dyes for dye-sensitized solar cells with high open circuit voltage performance

“…18 Thiazole is well-known electron-deficient unit because it contains one electron-withdrawing nitrogen of the imine (-C] N) in place of the carbon atom at the 3-position of thiophene. 19 Alkyl chain-substituted bithiazole with two thiazole rings connected together have also been used as acceptor unit to copolymerize with the donor unit of oligothiophene 20,21 or cyclopentadithiophene, 22 and present unique electronic and optical properties. Therefore, bithiazole-based polymers have been widely employed in thin film transistors, photovoltaic cells, and light-emitting diodes applications, in which solar cells based on the bithiazole copolymers show high open circuit voltage and a power conversion efficiency of around 3%, 22b, 23 suggesting that bithiazole-based polymers could be promising photovoltaic donor materials.…”

Synthesis and characterization of light‐absorbing cyclopentadithiophene‐based donor–acceptor copolymers

“…Among thiophene‐based polymers, poly(3‐hexylthiophene) with an energy gap of around 1.9 eV was long considered to be the best donor material for use in OPVs with reported PCEs in the range 4–6% . However, to enhance light absorption, it was necessary to look for alternative materials with smaller energy gap and broader absorption spectra .…”

“…The alternating copolymer of CPDT and BT, poly[4,4‐bis(hexadecyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl‐ alt ‐2,1,3‐benzothiadiazole‐4,7‐diyl] (PCPDTBT), possesses high hole mobility (10 −1 cm 2 V −1 s −1 ) in an organic field effect transistor device . The optical energy gap of PCPDTBT is ca 1.4 eV making it suitable for solar light harvesting .…”