Estimate of singlet diffusion lengths in PCBM films by time-resolved emission studies

Diffusion lengths for singlet states in PCBM films were estimated from analysis of annihilation rates in time-resolved emission studies. Results show the onset of singlet annihilation in PCBM films at absorbed photon densities above 1 × 1018 per cm3 and the singlet annihilation is well described by a time-independent value for the singlet annihilation rate constant ( γ ) of 0.5 × 10−9 cm3 s−1. Limitations in our method means that our calculated value for the PCBM singlet diffusion length of 5 nm is likely to be a lower bound.