Organic Solar Cells Using Cyanine Dyes
Over the last years, we achieved considerable improvements in the performance of cyanine dye / C60 bilayer heterojunction solar cells. We optimized the performance by oxidative doping of the cyanine layer. Doping increased the film conductivity and induced a steep rise in the short-circuit current and the open-circuit voltage. We argued that cyanine aggregates may be responsible for efficient charge transport to the heterointerface. We described a simple process to match the electrode energy to the low-lying cyanine HOMO level by using a thin organic salt layer or doped polyaniline as anode buffer layer. Thereby, hole injection was facilitated and good-performing devices (efficiency = 3%) with a high fill factor (FF = 60%) were fabricated. We demonstrated inverted bilayer cell architectures with an efficiency of 3.7% and cyanine / cyanine tandem devices with over 4% performance. We studied the dynamics of free charge formation during the dissociation of interfacial charge transfer states in planar cyanine dye/fullerene organic solar cells. Recently, we observed surprisingly efficient photoinduced charge generation in the bulk of pristine cyanine dye films with efficiency exceeding >40%, indicating that a donor/acceptor interface for exciton splitting is not really required in these systems.
The figure shows the architecture of an inverted cyanine solar cell and the J-V characteristics under 1 sun illumination with Jsc = 6.2 mA cm-2, Voc = 0.88 V, FF = 67.8% and efficiency = 3.7%.
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