Dynamical optical investigation of polymer/fullerene composite solar cells

We investigate organic polymer/fullerene (P3HT/PCBM) bulk heterojunction solar cells by means of photoinduced absorption spectroscopy (PIA). The dynamic properties of the charge carriers are studied in the temperature range of 5 K to 200 K by recording the PIA signal in the frequency domain. The mobility and the lifetime of the positive polarons are de- termined. The dependence of the short circuit current on the incident light intensity is also investigated. Finally, the properties of annealed and not annealed solar cells are compared. As the most interesting result, the appearance of two polaron species on different time scales is observed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)