Efficient and chromaticity stable green and white organic light-emitting devices with organic-inorganic hybrid...

Efficient inverted bottom emissive organic light emitting diodes (IBOLEDs) with tin dioxide and/or Cd-doped SnO₂ nanoparticles as an electron injection layer at the indium tin oxide cathode:electron transport layer interface have been fabricated. The SnO₂ NPs promote electron injection efficiently because their conduction band (-3.6 eV) lies between the work function (W _f) of ITO (4.8 eV) and the LUMO of the electron-transporting molecule (-3.32 eV), leading to enhanced efficiency at low voltage. The 2.0% SnO₂ NPs (25 nm) with Ir(ddsi)₂(acac) emissive material (SnO₂ NPs/ITO) have an enhanced current efficiency (η _c, cd A^-1) of 52.3/24.3, power efficiency (η _p, lm W^-1) of 10.9/3.4, external quantum efficiency (η _ex, %) of 16.4/7.5 and luminance (L, cd m^-2) of 28 182/1982. A device with a 2.0% Cd-doped SnO₂ layer shows higher η _c (60.6 cd A^-1), η _p (15.4 lm W^-1), η _ex (18.3%) and L (26 858 cd m^-2) than SnO₂ devices or control devices. White light emission was harvested from a mixture of Cd-SnO₂ NPs and homoleptic blue phosphor Ir(tsi)₃; the combination of blue emission (λ _EL = 428 nm) from Ir(tsi)₃ and defect emission from Cd-SnO₂ NPs (λ _EL = 568 nm) gives an intense white light with CIE of (0.31, 0.30) and CCT of 6961 K. The white light emission [CIE of (0.34, 0.35) and CCT of 5188 K] from colloid hybrid electrolyte BMIMBF₄-SnO₂ is also discussed.