The Study Of Interface Modification For Small Molecular Organic Solar Cells

The effect of interface on the performance of organic solar cells and the effect of traps on the energy loss of organic solar cells has been studied in our research. Our effort focused on two parts:1. The effect of energy cascade energy alignment of anode modification layer on the performance of C60-based organic solar cellsWhen a C60-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(C60)/tr is-(8-hydroxyquinoline) aluminum (Alq3)/aluminum (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 C6o device. In this study, a5nm 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 C60into NPB and hole transportation from NPB to ITO. The power conversion efficiency (PCE) of the C60-based device with MoO3is enhanced to0.976%. which is3.92times that of the device without MoO3. When MoO3is replaced by copper phthalocyanine or rubrene, which has higher mobility than NPB and forms a cascade energy structure with NPB. the PCE of C60-based devices is improved to0.539%and0.529%respectively, which is2.16and2.12times that of devices without such treatments.2. The effect of traps on the energy loss of organic solar cells studied by transient techniquesBy investigating the turn-on and turn-off photovoltage dynamics as a function of aging time, we reported the roles of traps on the energy loss in organic solar cells composing of CuPc/C60.Illuminating the device with square pulses of light, a peak of transient photovoltage after turn-on was observed after device degradation. After turn-off, the transient photovoltage first goes to the negative before settling back to zero, which is the result of electron trapping in the C60layer before being neutralized by re-injected holes. Furthermore, by adding a tris (8-hydroxyquinolinato) aluminum buffer to prevent the traps from propagating into C60layer, the peak after turn-on is greatly suppressed and the negative peak after turn-off vanishes, supporting the trapped electrons in the C60layer play the critical role in the appearance of peak of the transient photovoltage.