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

Abstract

A stable exciton-blocking layer (EBL) with rigid ball-like 4-hydroxy-8-methyl-1,5-naphthyridine aluminium chelate (AlmND₃) has been newly developed for organic photovoltaics (OPVs) based on a double-heterostructure of pentacene/C₆₀/EBL. Unlike the common EBL materials, such as tris-(8-hydroxyquinoline)aluminium (Alq₃) and bathocuproine (BCP), AlmND₃ exhibits a relatively high electron mobility (∼10⁻⁴ cm² V⁻¹ s⁻¹ at the electric field of 6.4 × 10⁵ V cm⁻¹) and a wide band gap energy (∼3.3 eV) in addition to a high glass transition temperature (T_g ∼ 194 °C). Having such EBL between active region (pentacene/C₆₀) 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 T_g than that of BCP, an extended lifetime performance was observed for AlmND₃-based OPV, compared with the BCP-based OPV aged at the elevated temperature of 75 °C.