Cyclopentadithiophene (CPDT) derivatives have been widely used as active layer in optoelectronic devices. The optical and electronic properties of CPDT can be tuned with the substituents at the thiophene position or at the bridgehead position. However, CPDT containing electron deficient unit such as ketone group have low optical absorption in the long wavelength region. Thus, device performance is limited due to the incomplete light harvesting. The low absorptivity could be related to the anti-conformation of CPDT where the bridgehead and the sulfur atoms are located on the opposite side, thus; electronic conjugation cannot extend to the bridgehead group. To increase the low energy absorption, we have created syn-CPDT isomer, where the bridgehead group and sulfur atoms are located on the same side. In this work, anti and syn-CPDT functionalized with ketone and imine groups at the bridgehead position were synthesized to study the effect of heteroatom conformation on optoelectronic properties. We found that the syn-CPDT can increase absorptivity. However, syn-isomers result in significantly decreased mobilities in 3 orders. Next, CPDT have been copolymerized with benzodithiophene (BDT) using microwave-assisted Stille coupling reaction. Similar to the CPDT small molecules, the absorption spectra of the polymer containing syn-CPDT showed increasing of absorption intensity at the low energy band. Moreover, polymers have been used as active layer for photovoltaic devices. We found that pBDTCPDT-anti-imine showed the highest PCE of 0.2 %.

Effect of anti and syn-conformation on optical properties, charge mobilities and photovoltaic performances of cyclopentadithiophene derivatives

252nd National Meeting (2016)

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