Control of electron injection barriers at the interface of a cathode/light-emitting polymer is a key factor to improve the device properties of polymer light-emitting diodes. In this study, to investigate the relationship between electron injection and the structure of the interface, we carried out the simulation of carrier injection for the interface model of Ca/poly(9,9'-dioctylfluorene) (PDOF) by using tight-binding quantum chemistry and Monte Carlo simulations. We found that the height of electron injection barriers strongly depends on the interfacial structure; the distance between Ca atoms and aromatic rings of PDOF. The carrier injection property is discussed on the basis of the interaction between C 2p and Ca 4p orbitals. (C) 2011 The Japan Society of Applied Physics