[en] Highlights: • Chemical composition of the multilayer organic-based devices incorporating an ultrathin LiF cathode underlayer was analyzed using the time-of-flight secondary ion mass spectrometry (ToF-SIMS) with depth profiling. • LiF layer is partly decomposed due to diffusion of lithium in the bulk of the device. • Lithium diffuses down to the substrate surface, with accumulation at the interfaces. - Abstract: In this work we investigate the chemical composition of an archetypal thin-film organic device with the Ag/LiF cathode using the time-of-flight secondary ion mass spectrometry (ToF-SIMS) with depth profiling. The LiF cathode underlayer is partly decomposed because a significant amount of lithium is released into the bulk of the multilayer device. The released lithium diffuses all the way to the substrate, accumulating, as revealed by ToF-SIMS depth profiles, at the interfaces rather than uniformly doping the underlying layers. Particularly, the bottom anode becomes chemically modified.