Density-functional theoretical study of fluorination effect on organic/metal interfaces

Density-functional theory with a semi-empirical dispersion correction was used to systematically examine how the number of fluorine (F) atoms affects atomic and electronic structures of fluorinated pentacene (C22FnH14-n) adsorbed on Cu(1 1 1) surfaces. The fluorination effect on the carrier injection efficiency at organic/metal interfaces was investigated. We found that as the number of F atoms decreases, the electron affinity of isolated molecules decreases, suggesting that the molecule becomes less reactive. However, for adsorbed systems, as the number of F atoms decreases, molecular orbitals of C22FnH14-n strongly hybridize with the substrate states while retaining the n-type energy level alignment, resulting in lowering the barrier height of the carrier injection. Based on the calculation results, we propose using C22FnH14-n (n <= 8) with Cu electrodes for efficient electron injection. (C) 2010 Elsevier B.V. All rights reserved.