4-Hydroxy-8-methyl-1,5-naphthyridine aluminium chelate: a morphologically stable and efficient exciton-blocking material for organic photovoltaics with prolonged lifetime

A stable exciton-blocking layer (EBL) with rigid ball-like 4-hydroxy-8-methyl-1,5-naphthyridine aluminium chelate (AlmND(3)) has been newly developed for organic photovoltaics (OPVs) based on a double-heterostructure of pentacene/C-60/EBL. Unlike the common EBL materials, such as tris-(8-hydroxyquinoline) aluminium (Alq(3)) and bathocuproine (BCP), AlmND(3) exhibits a relatively high electron mobility (similar to 10(-4) cm(2) V-1 s(-1) at the electric field of 6.4 x 10(5) V cm(-1)) and a wide band gap energy (similar to 3.3 eV) in addition to a high glass transition temperature (T-g similar to 194 degrees C). Having such EBL between active region (pentacene/C-60) and the metal cathode, pristine device performances were comparable with those of BCP-based OPV due to its high mobility and wide band gap energy. Moreover, due to its significantly higher Tg than that of BCP, an extended lifetime performance was observed for AlmND(3)-based OPV, compared with the BCP-based OPV aged at the elevated temperature of 75 degrees C.