Bulk heterojunction solar cells utilizing soluble phthalocyanine derivative, 1,4,8,11,15,18,22,25-o (C6PcH(2)) have been investigated. The active layer was fabricated by spin-coating the mixed solution of C6PcH(2) and 1-(3-methoxy-carbonyl)-propyl-1-1-phenyl-(6,6)C61 (PCBM). The photovoltaic properties of the solar cell with bulk heterojunction of C6PcH(2) and PCBM demonstrated the strong dependence of active layer thickness, and the optimized active layer thickness was clarified to be 120 nm. By inserting MoO(3) hole transport buffer layer between the positive electrode and active layer, the FF and energy conversion efficiency were improved to be 0.50 and 3.2%, respectively. The tandem organic thin-film solar cell has also been studied by utilizing active layer materials of C6PcH(2) and poly(3-hexylthiophene) and the interlayer of LiF/Al/MoO(3) structure, and a high V(oc) of 1.27 V has been achieved. (C) 2011 Elsevier B.V. All rights reserved.