Enhanced device efficiency in organic light-emitting diodes by dual oxide buffer layer

Jesuraj, P. Justin,Hafeez, Hassan,Rhee, Sang Ho,Kim, Dong Hyun,Lee, Jong Chan,Lee, Won Ho,Choi, Dae Keun,Song, Aeran,Chung, Kwun-Bum,Song, Myungkwan,Kim, Chang Su,Ryu, Seung Yoon Elsevier 2018 ORGANIC ELECTRONICS Vol.56 No.-

<P><B>Abstract</B></P> <P>We have demonstrated an improvement in device performance of fluorescent organic light-emitting diodes (OLEDs) by inserting a dual anode buffer layer composed of tungsten oxide (WO<SUB>3</SUB>) and molybdenum oxide (MoO<SUB>3</SUB>). The advantage of adding dual anode buffer layers with different deposition sequences over individual and composite oxide buffer layers has been systematically analyzed based on their electronic and optical properties. The incorporation of single and composite buffer layers has been revealed to induce a very low injection barrier for holes in tri-layer fluorescent OLEDs which results in a charge imbalance in the emission layer. In contrast, a proper sequence of buffer layers (WO<SUB>3</SUB>/MoO<SUB>3</SUB>) exhibiting higher contact angle (lower surface energy) and higher surface roughness, together with a step-wise increment of potential barrier leads to a better overall charge balance in the active emission layer. Therefore, an enhanced current efficiency and power efficiency of ∼5.8 cd/A and ∼5.2 lm/W respectively were recorded for the WO<SUB>3</SUB>/MoO<SUB>3</SUB> buffer unit, which was better than the insertion of individual and composite layers.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The dual oxide buffer layers in fluorescent OLEDs have been explored. </LI> <LI> A dual buffer layer consists of tungsten oxide (WO<SUB>3</SUB>)/Molybdenum oxide (MoO<SUB>3</SUB>). </LI> <LI> The increment in hole interface barrier, higher contact angle and surface roughness of dual oxide layers is beneficial to achieve improved charge balance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Enhanced device efficiency in organic light-emitting diodes by dual oxide buffer layer

Jesuraj, P. Justin,Hafeez, Hassan,Rhee, Sang Ho,Kim, Dong Hyun,Lee, Jong Chan,Lee, Won Ho,Choi, Dae Keun,Song, Aeran,Chung, Kwun-Bum,Song, Myungkwan,Kim, Chang Su,Ryu, Seung Yoon Elsevier Science B.V., Amsterdam. 2018 ORGANIC ELECTRONICS Vol.2018 No.56

Recombination Zone Control without Sensing Layer and the Exciton Confinement in Green Phosphorescent OLEDs by Excluding Interface Energy Transfer

Jesuraj, P. Justin,Hafeez, Hassan,Kim, Dong Hyun,Lee, Jong Chan,Lee, Won Ho,Choi, Dae Keun,Kim, Chul Hoon,Song, Myungkwan,Kim, Chang Su,Ryu, Seung Yoon American Chemical Society 2018 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.122 No.5

<P>We report the confinement of recombination zone (RZ) in green phosphorescent organic light-emitting diodes (Ph-OLEDs) for enhanced efficiency by varying the emission layer (EML) thickness and through quantum well (QW) insertion. At low thickness of EML, the efficiency is reduced owing to the diffusion of the RZ toward the EML/hole transport layer interface, which was revealed through the presence of exciton blocking layer [TCTA: tris(4-carbazoyl-9-ylphenyl)amine] excitation accompanied by a blue-shift in electroluminescence (EL). Further increase in the thickness of the EML caused the RZ to move toward the cathode, which was determined based on the disappearance of TCTA emission and the corresponding red-shift observed in EL spectra. The solid-state and time-resolved area normalized photoluminescence emission spectra investigations further corroborate the RZ movement tactics along with TCTA excimer generation and exciplex generation between TCTA and tris[2-phenylpyridinato-C2,N]iridium(III) Ir(ppy)<SUB>3</SUB>. The superior quantum and current efficiency of 14.4% and 50 cd/A, respectively, were determined for the device with an EML thickness of 15 nm due to the confinement of the RZ in the EML. The addition of (EML/interlayer/EML) QW facilitates improved charge balance in the Ph-OLED and further assists in the confinement of the RZ in the EML. Because of QW, a slight increment in quantum (14.6%) and current efficiency (52 cd/A) was observed. Without using any sensing layers, movement of the RZ was successfully monitored and confined in the EML to realize enhanced efficiency in green Ph-OLEDs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2018/jpccck.2018.122.issue-5/acs.jpcc.7b11039/production/images/medium/jp-2017-11039h_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp7b11039'>ACS Electronic Supporting Info</A></P>

Improved charge balance in phosphorescent organic light-emitting diodes by different ultraviolet ozone treatments on indium tin oxide

Kim, Dong Hyun,Lee, Won Ho,Jesuraj, P. Justin,Hafeez, Hassan,Lee, Jong Chan,Choi, Dae Keun,Song, Aeran,Chung, Kwun-Bum,Bae, Tae-Sung,Song, Myungkwan,Kim, Chang Su,Ryu, Seung Yoon Elsevier 2018 ORGANIC ELECTRONICS Vol.61 No.-

<P><B>Abstract</B></P> <P>Ultraviolet ozone (UVO) treatment of indium tin oxide (ITO) is a well-known technique to realize improved performance in organic light-emitting diodes (OLEDs). Herein, we report the comparison of UVO treatments on ITO at different energies (187 and 254 nm) in varying the charge balance in green phosphorescent OLEDs (Ph-OLEDs). The amounts and types of removed organic contaminants (such as -OH, C-C, C≡C, C=C, O=O, etc.) were observed to differ for each UVO energy. The 254-nm UVO treatment could not remove all the contaminants from the ITO surface, causing a decrease in hole injection (observed by hole-only device trends), due to the decrease in work function (WF) compared to the 187-nm-treated ITO. Moreover, the presence of large negatively charged O=O groups on the surface of 254-nm-treated ITO induced electronic repulsion (observed by electron-only device trends). However, remarkably, a suitable charge balance was attained by ITO treated with 254-nm UVO source over un-treated ITO, as well as with samples exposed to the higher-energy source (187 nm). The devices utilizing ITO treated with 254-nm UVO demonstrated the enhanced current efficiency of 67 cd/A, while the 187-nm UVO-treated and untreated ITO anodes exhibit those of 47 cd/A and 57 cd/A, respectively, at 5000 cd/m<SUP>2</SUP>. The variation in the WF of ITO with respect to different UVO sources and its role in the charge transport behaviors of the Ph-OLEDs were investigated in detail with contact angle measurements and interface barrier calculations through hole-only devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effects of UVO treatment wavelength on ITO for Ph-OLED have investigated. </LI> <LI> Improved Charge balance achieved with 254 nm rather than 187 nm UVO treated ITO. </LI> <LI> Changes in work function and hole interface barrier in Ph-OLED have calculated. </LI> <LI> Superior EQE and current efficiency of 19.31% & 67.4 cd/A obtained with 254 nm UVO. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Phytochemical analysis and antioxidant potential of the crude extract of Allium oschaninii scape

Seenivasaperumal Alagarsamy,Pandiselvam Chellappan,Michel Thomas Jesuraj,Manoj Saravana Guru Mohan,Rengesh Balakrishnan 경희대학교 융합한의과학연구소 2018 Oriental Pharmacy and Experimental Medicine Vol.18 No.4

The present study focuses on the antioxidant potential of aqueous and ethanolic extracts of the scape of Allium oschaninii. Phytochemical analysis and total phenolic content for both the extracts and Total flavonoid content for ethanolic extract were determined. Anti-microbial activity of different concentrations of both the extracts against Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, and Bacillus cereus was investigated. The total antioxidant power (TAP), 2,2′-azinobis( 3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH) and Ferric reducing ability of plasma (FRAP) assays were carried out. IC50 values of aqueous and ethanolic extract to scavenge ABTS and DPPH free radical were determined as 0.2524, 0.5467 and 0.6155, 0.9591 (mg/mL) respectively. FRAP and TAP results of both aqueous and ethanolic extracts were determined to be 2530.972 and 1199.86 (μmol of Fe2+ per 1000 μg of extract) and 84.13 ± 5.51 and 141.88 ± 40.49 (equivalent mg of ferulic acid per 150 mg dried sample) respectively. These results signify the antioxidant power potential of the scape of A.oschaninii.

Improved stability of silver nanowire (AgNW) electrode for high temperature applications using selective photoresist passivation

Lee, Jong Chan,Min, Jeongho,Justin Jesuraj, P.,Hafeez, Hassan,Kim, Dong Hyun,Lee, Won Ho,Choi, Dae Keun,Cha, Jun Hwan,Lee, Chang Min,Song, Myungkwan,Kim, Chang Su,Ryu, Seung Yoon Elsevier 2019 MICROELECTRONIC ENGINEERING Vol.206 No.-

<P><B>Abstract</B></P> <P>Metal nanostructure arrays have been progressed as an alternative to the conventional oxides-based transparent conductive electrodes. Herein, we demonstrate the improved reliability of silver nanowire (AgNW) electrodes by photoresist encapsulation. The incorporation of photoresist followed by photolithography is beneficial to selectively pattern the AgNWs on poly[ether sulfone]. By varying the development or removal time of the ultraviolet (UV)-exposed photoresist, the properties of the AgNWs in the electrode are significantly varied. The optical parameters such as transmittance, haziness, and the yellow index of the electrodes have been extensively studied to reveal the advantage of the selective photoresist patterning. The AgNW electrodes patterned under 120 s of development time explored superior optical and electrical properties with high durability. The electrical properties of the AgNW electrodes at high temperatures (250 °C) demonstrate the photoresist-induced stability as compared to bare samples. Further, the morphological examination after the high temperature treatment reveals the reduced Rayleigh instability effects in 120 s developed AgNWs that facilitate the reliability under harsh conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Selective passivation of AgNWs electrode achieved with a photoresist. </LI> <LI> Haze/yellow index variation of AgNW electrode with various developing time revealed. </LI> <LI> AgNW passivated with 120 s developing time show high reliability until 250 °C. </LI> <LI> Selective passivation of AgNWs suppressed thermally induced Rayleigh instability. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>