Efficient hybrid bulk heterojunction solar cells based on phenylenevinylene copolymer, perylene bisimide and TiO2

A soluble alternating phenylenevinylene copolymer P containing a side anthracene, which was attached to the thiophene ring via a vinylene bridge, was synthesized by Heck coupling. The copolymer had relatively low glass transition temperature (61 degrees C) and decomposed above 400 degrees C. The absorption maximum of P was located at 387-402 nm with an optical band gap of 2.32 eV. The emission spectra of P indicated that an intramolecular energy transfer from the side anthracene to the main chain took place via the vinylene bridge. In addition, a new symmetrical compound A based on perylene-anthracene was synthesized and used as electron acceptor in the device. Photovoltaic devices were fabricated using a blend of copolymer P as donor and compound A as acceptor, as photoactive layer film sandwiched between indium tin oxide-coated glass and AI electrodes. This device showed a power conversion efficiency of 0.72%. However. when TiO2 nanoparticles were incorporated on the pristine P:A blend, the power conversion efficiency of the device was enhanced up to 1.32%, which is attributed to the enhanced photoinduced excitons due to the increase of the interfacial area and improved charge carrier mobility. The power conversion efficiency of the P:A:TiO2 based photovoltaic device was further improved up to 2.64%, when the hybrid composite was treated with a mixture of Li salt and 4-tert-butylpyridine, which is attributed to the reduction in the recombination of charge carriers. (C) 2009 Elsevier B.V. All rights reserved.