Total charge amount as indicator for the degradation of small molecule organic solar cells

We show that the number of extracted charge carriers is a suitable measure to compare lifetime measurements on organic solar cells at different intensities. In detail, we used pin-structures with active layers containing a bulk heterojunction of Zincphthalocyanine (ZnPc) and C60. Extended lifetime measurements under constant monochromatic or white illumination at defined temperatures of 50 °C or 90 °C are done. On the one hand, we show that the number of extracted charge carriers is important to determine the degree of degradation. On the other hand, our results show that the energy of irradiated photons is significant for accelerated measurements. This is an major advantage for the realisation of accelerated lifetime measurements. Additionally, we find that not single charge carriers, but excitons cause the degradation of the observed solar cells.

Graphical AbstractFigure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► increased intensity leads to accelerated degradation of small molecule solar cells. ► integration of extracted charges gives a new scale for degradation progress. ► samples at different intensities show same behaviour on this scale. ► for monochromatic light, different wavelength lead to different slopes.