White-light emission from HMIMBF4–TiO4(A) colloidal hybrid electrolyte and surface modification of TiO2 using ionic liquid in hybrid optoelectronic devices

Abstract

White-light emission from the colloidal hybrid electrolyte 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF₄)–TiO₂(A) is discussed herein. The HMIMBF₄–TiO₂(A) hybrid electrolyte showed an increase in the lifetime as compared to bare anatase TiO₂ (TiO₂(A)). The blue emission at 420 nm from HMIMBF₄ is attributed to the π–π* transition of the imidazolium moiety, and strong green and yellow emissions at 517 and 568 nm, respectively, are due to defect emissions of TiO₂ NPs. In the HMIMBF₄–TiO₂(A) colloidal hybrid electrolyte, the combination of blue emission from the ionic liquid and defect emission from TiO₂ NPs produced intense white light. Fabricated HyLEDs showed enhanced device efficiency by the surface modification of rutile TiO₂ (TiO₂(R)) using HMIMBF₄ ionic liquid. HMIMBF₄, with a thickness of 250/850 nm, exhibited maximum current efficiency (η_c – cd A⁻¹) of 322.22/361.53, power efficiency (η_p – lm W⁻¹) of 6.2/7.1, external quantum efficiency (η_ex – %) of 322.22/361.53 and luminance (η_L – cd m⁻²) of 70.14/1490.95. Spontaneously aligned dipole polarization within the ionic liquid HMIMBF₄ layer reduced the electron injection barrier and led to enhanced device efficiencies.