Degradation of electrical characteristics in low-bandgap polymer solar cells associated with light-induced aging

Abstract

Abstract As the efficiency of organic solar cells has been consistently improved, interest is being raised to understand degradation mechanisms inside the solar cells. Among many factors that affect solar cell deterioration, light is the most crucial factor in the degradation mechanism. Here we report degradation under the continuous light-induced conditions for PTB7:PC70BM organic solar cells during the first 24 h with maintaining the temperature at 25 °C. It revealed 30% of initial performance drop after 24 h of light-induced aging, mostly through a decrease in JSC and FF. The morphological and electrical characteristics of the active layer and devices were investigated by atomic force microscopy, impedance spectroscopy, and temperature-dependent current density–voltage characteristics to figure out the origin of the photo-induced degradation. As a result, the light-induced traps were found to be a primary cause of loss. Furthermore, this trap formation was observed with an energy of 78 meV leading to trapped charge limited conduction properties and electrical degradation of solar cells.