Design and optimization of a Blue fluorescent Microcavity-Organic Light-Emitting Diode (MOLED) for an algae excitation light source application

Abstract

International audienceIn this work, we present simultaneous organic light-emitting diode (OLED) stack optimization and optical modelling for a blue microcavity-OLED (MOLED) to be used as algae excitation light source in an optical bio-sensor. Fluorescent materials (MADN and DPAVBi) were used as host/guest for the doped emissive layer due their known stability (compared to phosphorescent and TADF materials). The MOLED modelling was performed by targeting 470 nm as the maximal excitation wavelength and suppressing the emission in the algae fluorescence bandwidth (600-800 nm) in order to fulfil the sensor requirements. By using a bilayer hole transport layer/electron blocking layer (HTL/EBL) instead of a single HTL, the total thickness was adjusted to meet the resonance wavelength condition without loss of efficiency, while at the same time preserving a maximum electric field intensity in the emissive layer (EML at antinode position).MOLED devices were fabricated by evaporation on three different distributed Bragg reflectors (DBRs) with 1.5, 2.5 and 3.5 pairs of TiO2/SiO2 (high-index/low-index) respectively and aluminium-doped zinc oxide electrode (AZO) as low-cost, nontoxic and relative abundant alternative anode to indium tin oxide (ITO). Devices with 1.5 pairs as DBR showed not only an improved external quantum efficiency (+12%) compared to a standard OLED but also an increase of about 3 times the intensity of the peak at 470 nm combined to a lower emission in the 600-800 nm bandwidth, as aimed. This increase in the peak intensity should lead to a longer device lifetime, as the current density necessary to excite at 470 nm is significantly lower due to the microcavity effect. On the other hand, 2.5 and 3.5 pairs devices had a slightly higher intensity peak than the classic OLED at 470 nm. This is because the electric field in the EML of these two MOLEDs was not as high as in the 1.5 pairs case