Electroluminescence and contact formation of 1-(pyridin-2-yl)-3-(quinolin-2-yl)imidazo[1,5-a]quinoline thin films

Abstract

Abstract Contact formation was investigated for the recently introduced organic light emitting molecule 1-(pyridin-2-yl)-3-(quinolin-2-yl)imidazo[1,5-a]quinoline (PCIC) by in situ atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) during physical vapor deposition (PVD). The hole conductors poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and poly(9-vinylcarbazole) (PVK), as well as the electron conductor bathocuproine (BCP) were used. Different growth modes were found for PCIC films and charge carrier injection barriers were identified. Based on these findings, electroluminescent layer structures with an imidazo[1,5-a]quinoline were prepared for the first time and effects of contact formation on radiative recombination were studied. Depending on the chosen contact material, blue PCIC electroluminescence or significantly red-shifted emission presumably caused by electroplex formation could be obtained. Using PCIC in a host-guest system within a matrix of PVK and 1,3-bis[5-(4-tert-butylphenyl)-2-[1,3,4]oxadiazolyl]benzene (Oxd-7), led to blue emission at improved luminescence. The studied interactions of PCIC with typical contact materials reveal the potential and limitations to use PCIC as an electroluminescent material.