Articles written in Journal of Chemical Sciences
Volume 130 Issue 12 December 2018 Article ID 0167
We report on the optimization of organic light emitting diode (OLED) devices using 1,8-di-(4-trifluromethylphenyl)-anthracene (CF3-DPA) as the active emissive layer. CF3-DPA emits in the deep blue region with an emission peak at 432 nm in solution which showed a slight red shift in thin films. CF3-DPA hashigh reported fluorescence quantum efficiency,~67%, as compared to 9,10-diphenyl anthracene (9,10-DPA).We optimized the OLED devices with different hole transporting layers (HTLs). Bilayer devices formed with N,N' -di(1-naphthyl)-N,N' -diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPD) as the HTL gave a reasonable light output. We observed that trilayer or multilayer devices with the inclusion of poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) and/or copper phthalocyanine as an additional HTL reduced the turn on voltage by ~5 to 9 V, though the brightness of the light emission also decreased. Including suitable carrier (electron or hole) transporting layers like 2, 2' ,2''' -(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi)and 4,4' -Bis(N-carbazolyl)-1,1' -biphenyl (CBP) increases the efficiency of the devices. From our studies, we conclude that though NPD/CF3-DPA interface is crucial for light emission, the performance of the devices is limited by the mismatch of the hole and electron mobilities and the low internal quantum efficiency of CF3-DPA in the solid state. Devices having ITO/NPD/CF3-DPA/TPBi/LiF-Al geometry were observed to be the most efficient.
Volume 131 Issue 9 September 2019 Article ID 0094
Acridone (acceptor) and naphthylamine (donor) based Donor-Acceptor-Donor (D-A-D) compound (1) was synthesised, characterised and its thermally-activated delayed fluorescence (TADF) properties were studied in detail. Compound 1 is fluorescent and emits in the green region (550 nm). The energy gapbetween the ground and the lowest excited singlet (S1) state is estimated to be 2.55 eV. The energy gap between the CT singlet and triplet states (ΔEST) was found to be ~0.3 eV. Small ΔES1-T1 is one of the important criteria for TADF to take place in a molecule and thus detailed photophysics has been studied.Transient lifetime measurements showed an increase in the fluorescence lifetime (s) on purging with N2, as compared with that in air-saturated solution, indicating the involvement of the triplet state in emission. Emission at 550 nm was also observed with a delay of 100 ls which corresponded to the delayed fluorescencein 1. The lifetime of TADF was found to be 176 ls. Applications of TADF materials in organic lightemitting devices (OLEDs) has gotten attention as TADF materials utilise the triplet excitons which helps in increasing internal quantum efficiency of device. Air-saturated based on 1 were fabricated and their intensity was found to be nearly as high as 17,000 Cd/m2 at 25 mA/cm2 which was comparable to many of the known TADF emitters.
Volume 134, 2022
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