Effect of UV-Light Irradiation on Charge-Accumulation States in PTzBT Polymer Solar Cells

Ternary polymer solar cells based on a polymer PTzBT have received a lot of attention because their power conversion efficiency (PCE) and thermal stability have been greatly improved by adding a small amount of an oligomer ITIC. However, the charge-accumulation states of the PTzBT ternary polymer solar cells have not yet been completely clarified. Here, we report electron spin resonance (ESR) spectroscopy of the PTzBT ternary polymer solar cells to investigate the charge-accumulation states from a microscopic viewpoint with examining the effect of UV-light irradiation. We observed a slight increase in the ESR intensity of the PTzBT cells and layered film samples under simulated solar irradiation with a UV-cut filter. Multiple signals were observed in the PTzBT cells under solar irradiation when the UV-cut filter was removed. Interestingly, no decrease was observed in the ESR signal of ZnO under solar irradiation with the UV-cut filter, although holes in ZnO in the PTzBT cells are known to decrease under solar irradiation. These findings will contribute to a deep understanding of the material properties of polymer solar cells.