Long-term stability of tandem solar cells containing small organic molecules

In this paper, we discuss long-term stability measurements of tandem solar cells with mixed phthalocyanine: fullerene photoactive layers that exhibit an initial power conversion efficiency of about 4 % . These devices are remarkably stable against exposure to halogen light as their power conversion efficiency decreases by less than 3 % within more than 1400 h of permanent illumination at an intensity of approximately 185 mW/cm 2 at 50 ∘ C . In addition, long-term stability measurements at an elevated temperature of 85 ∘ C are performed. In comparison to the illumination experiment, the cells show a much faster degradation which is attributed to the low glass transition temperature of the hole transport layer.