Thermally Induced Dewetting in Ultrathin C₆₀ Films on Copper Phthalocyanine

The evolution of thermally annealed ultrathin fullerene–C 60 layers on copper phthalocyanine is examined by atomic force microscopy and near-edge X-ray absorption fine structure spectroscopy. Annealing causes C 60 films to dewet the copper phthalocyanine substrate surface via lateral surface mass transport. Coarsening of C 60 clusters is observed that creates mounds that exceed the nominal C 60 thickness by more than an order of magnitude and is consistent with surface diffusion-mediated mass transport. Implications for thermal morphology control in organic solar cells, such as the destabilization of multilayered C 60:CuPc with individual layers only ∼5–10 nm thick, are discussed.