The preparation and characterization of novel electron donor compounds with two (D1) and four (D2) quaterthiophene-containing arms attached to the flexible carbosilane-siloxane core are described. These materials were investigated in organic field effect transistors and photovoltaic cells. A power conversion efficiency of similar to 0.9% obtained for D1:[70]PCBM blends is one of the highest values achieved up to now for solution-processible small molecular bulk heterojunction solar cells with large band-gap oligothiophene-based donor materials comprising no other chromophore units. (C) 2010 Elsevier B.V. All rights reserved.