Ultrafast Studies of Charge Generation in PCBM:P3HT Blend Films following Excitation of the Fullerene PCBM

In order to better understand the limits of [6,6]phenyl C-61-butyric acid methyl ester/poly(3-hexylthiophene) (PCBM:P3HT) organic solar cell device performance, ultrafast transient absorption spectroscopy has been used to probe the dynamics of charge creation in films of PCBM:P3HT following excitation of the fullerene. The time scale for splitting of the PCBM singlet excited state and hole transfer across the polymer-fullerene donor-acceptor interface is found to be faster than the system resolution of 250 fs and is calculated to occur with near unity efficiency. Ironically, this very quick electron transfer is discussed as being inefficient with regard to organic solar cell device power conversion efficiency as an excess amount of energy is used up in the electron transfer step.