Vapor-deposition of naphthalene diimide derivatives and interface control between aluminum cathode

Two types of naphthalenediimide derivatives, N,N'-bis(benzyl)naphthalenediimide (Bzl-NDI) and N,N'-bis(p-vinylbenzyl)naphthalenediimide (PVB-NDI), were vapor-deposited either on a bare aluminum or an aluminum modified with a self-assembled monolayer (SAM) of (3-mercaptopropyl) trimethoxysilane. The deposition on the SAM-modified surface was achieved under UV irradiation to enhance thiol-ene reaction of the SAM with vinyl groups of the deposited molecules. The films of Bzl-NDI gradually crystallized, while PVB-NDI formed stable amorphous films. Electron-only devices were prepared with combinations of Bzl- and PVB-NDIs with bare and the SAM-modified aluminum cathodes. PVB-NDI was less conductive than Bzl-NDI due to the amorphous nature of the film. The SAM modification on the cathode was effective to increase the electron current of the PVB-NDI device, whereas the SAM modification did not increase the current of the Bzl-NDI device. The implication is that the thiol-terminated SAM can bind with PVB-NDI that has the vinyl group, leading to an improvement of the organic/cathode interface. (C) 2020 The Japan Society of Applied Physics