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

Abstract

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 ( C 22 F n H 14 - 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 C 22 F n H 14 - 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 C 22 F n H 14 - n ( n ⩽ 8 ) with Cu electrodes for efficient electron injection.