Poly(p-phenylenevinylene) derivatives with conjugated thiophene side chains: Synthesis, photophysics and photovoltaics

Three novel poly(p-phenylenevinylene) (PPV) derivatives with conjugated thiophene side chains, P1, P2 and P3, were designed and synthesized for application in polymer solar cells (PSCs). The effects of the conjugated side chains on the thermal, photophysical, electrochemical and photovoltaic properties of these polymers were investigated. The polymers exhibited good thermal stability and film-forming ability. The absorption spectra indicated that the short conjugated side chains have slight influence on the UV-region spectra of PPVs; whereas with increasing the length of conjugated side chains, the absorption of the UV-region red-shifted. The photoluminescence spectra reveal that complete exciton energy transfer occur from the conjugated side chains to the main chains of the polymers. The polymers emitted yellow-orange light with the emission maximum peaks in the region of 525–550 nm in chloroform solution and 611–616 nm in thin films. Cyclic voltammograms displayed that the band gaps were reduced effectively by the attachment of the conjugated thiophene side chains. The bulk heterojunction solar cells were fabricated based on the blend of the polymers and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in a 1:4 weight ratio. The maximum power conversion efficiency (PCE = 0.53%) was obtained by using P3 as the electron donor under the illumination of AM 1.5, 100 mW/cm2.