P-type sensitized organic solar cells with cascade energy alignment

When a C-60-based device with the structure indium tin oxide (ITO)/N,N'-di-[(1-naphthyl)-N,N'-diphenyl]-1,1'-biphenyl)-4,4'-diamine (NPB)/fullerene (C-60)/tris-(8-hydroxyquinoline) aluminium (Alq(3))/aluminium (Al) is treated as a p-type sensitized solar cell, some methods for improving charge transportation and suppressing charge backflow in dye-sensitized solar cells can be applied to increase the performance of the C-60 device. In this study, a 5 nm layer of molybdenum oxide (MoO3) is inserted between ITO and NPB to realize this idea. This thin layer with higher mobility and higher dielectric constant than NPB forms a cascade energy alignment with NPB, improving hole injection from C-60 into NPB and hole transportation from NPB to ITO. The power conversion efficiency (PCE) of the C-60-based device with MoO3 is enhanced to 0.976%, which is 3.92 times that of the device without MoO3. When MoO3 is replaced by copper phthalocyanine or rubrene, which has higher mobility than NPB and forms a cascade energy structure with NPB, the PCE of C-60-based devices is improved to 0.539% and 0.529% respectively, which is 2.16 and 2.12 times that of devices without such treatments.