Two new small molecule dyes for the donor material, named IDTT-OX and IDTT-EPMP-IDC have been successfully synthesized and characterized for solution-processed bulk heterojunction organic solar cells (OSCs). These dyes are containing indacedithieno[3,2-b]thiophene (IDTT) as the donor moiety, phenylisoxazolone (OX) and malononitrile derivatives (EPMP-IDC) as the acceptor. IDTT-OX exhibits a strong self-aggregation behavior and broad absorption with an optical band gap of 1.88 eV. While IDTT-EPMP-IDC shows different behavior, the self-aggregation of IDTT-EPMP was efficiently restricted by the presence of the alkyl group at EPMP-IDC functional group in the molecule and it has 1.60 eV optical bandgap. The inverted-type OSCs based on the blend of IDTT-OX (or IDTT-EPMP-IDC) as a donor, PC71BM as an acceptor are fabricated. The power conversion efficiencies (PCEs) of the optimized OSCs are reached up to 0.29% for IDTT-OX and 2.07% for IDTT-EPMP-IDC.