Photostability and morphological stability of hole transporting materials used in organic electroluminescence

Abstract N , N ′-biphenyl- N , N ′-bis-(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine (TPD) and N , N ′-biphenyl- N , N ′-bis-(1-naphenyl)-[1,1′-biphenyl]-4,4′-diamine (NPB) are typical hole transporting materials, which are widely used in current organic eletroluminescence (EL) research. NPB is regarded as a better hole transporting material than TPD, since it has a higher glass transition temperature ( T g ). In this paper, the photostability and morphological stability of TPD and NPB have been studied in film states. It is concluded that NPB thin film is a better hole transporting material for organic EL than TPD, not only because it has a higher T g , but also because it is more photostable and has a better morphological stability in thin film state.