The synthesis of new soluble tetrasubstituted quater- and quinquethiophenesilanes and their application as donor materials in bulk heterojunction solar cells and photodetectors has been described. The solubility of these compounds is governed by their 3D molecular structure, solubilizing linear n-hexyl (for quaterthiophenesilane), and branched 2-ethylhexyl groups (for quinquethiophenesilane). It was demonstrated that oligothiophenesilanes blended with fullerene derivatives can be used as promising active layer materials in organic bulk heterojunction solar cells. The maximum power conversion efficiency of the devices increased proportionally with the conjugation length of the oligothiophene units and reached 1.0% and 1.4% for quater- and quinquethiophenesilane respectively. Photodetectors based on the oligothiophenesilane/fullerene composites showed unusually high speeds of operation, which suggests another direction for the practical implementation of the three-dimensional organic semiconductor family designed herein.