Achieving Extreme Utilization of Excitons by an Efficient Sandwich-Type Emissive Layer Architecture for Reduced Efficiency Roll-Off and Improved Operational Stability in Organic Light-Emitting Diodes

2016 ◽  
Vol 8 (5) ◽  
pp. 3150-3159 ◽  
Author(s):  
Zhongbin Wu ◽  
Ning Sun ◽  
Liping Zhu ◽  
Hengda Sun ◽  
Jiaxiu Wang ◽  
...  
Keyword(s):  
Light Emitting Diodes ◽  
Operational Stability ◽  
Organic Light Emitting Diodes ◽  
Light Emitting ◽  
Emissive Layer ◽  
Organic Light ◽  
Sandwich Type

Electrically and Optically Detected Electron Paramagnetic Resonance in Blue Organic Light Emitting Diodes

2021 ◽  
Author(s):  
◽  
Rebecca Jane Sutton
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Light Emitting Diodes ◽  
Organic Light Emitting Diodes ◽  
Great Promise ◽  
Paramagnetic Resonance ◽  
Light Emitting ◽  
Emissive Layer ◽  
Organic Light ◽  
Optically Detected ◽  
Electron Paramagnetic

<p>Organic light emitting diodes (OLEDs) are an emerging technology based on electrically conducting polymer films, with great promise for large area lighting and flexible ultra-thin displays. However, despite the rapid technological development, there is still a poor understanding of the degradation and spindependent recombination processes that take place inside an OLED. In this thesis, Electron Paramagnetic Resonance (EPR) was used to investigate these processes in blue-emitting OLEDs.  A successful procedure was developed and refined for fabricating OLEDs with the structure ITO/PEDOT:PSS/emissive layer/Al/Ag, with and without the PEDOT:PSS hole-transporting layer. The organic emissive layer was either F8BT, PFO, or PVK:OXD-7:FIrpic (PB). These OLEDs were fabricated in air and with a geometry optimised for EPR experiments. Critical features for satisfactory devices were found to be a sufficiently thick organic layer and minimal exposure to the air.  A compact apparatus was developed for simultaneous light output, current, and voltage measurements on the OLEDs while in an inert glove box environment. Electroluminescence and current-voltage parameters measured for these devices showed predominantly trap-controlled space-charge-limited conduction.   OLEDs with PFO as the emissive layer and with a PEDOT:PSS layer were investigated with conventional, electrically-detected (ED) and optically-detected (OD) EPR techniques. EDEPR and ODEPR signals were observed at ~9.2 GHz and in the low (<50 mT) and high (~330 mT) magnetic field regimes and were found to change markedly with time during operation as the device degraded. The low field signals initially showed a composite broad quenching and superimposed narrow enhancing response centred around zero field strength. These signals were attributed to magneto-resistance (MR) and magneto-electroluminescence (MEL). Following operational ageing, a third, narrow quenching line was observed in the MR and the ratio of the initial two MR responses changed substantially. These effects are tentatively attributed to a hyperfine interaction.  For both EDEPR and ODEPR, quenching high field resonances with a g-value (gyromagnetic ratio) of 2.003±0.001 were observed. The current-quenching resonance gradually diminished during operation and after 4–5 hours was replaced by a current-enhancing resonance. The appearance of this latter resonance could be explained by chemical changes in the OLED due to the diffusion of oxygen through the device from the oxygen-plasma-treated ITO. A working model is proposed which can explain this observed change as spindependent trapping and recombination at free radicals, although the model requires further experimentation to test its validity.</p>

Color stable phosphorescent white organic light-emitting diodes with double emissive layer structure

2013 ◽  
Vol 14 (4) ◽  
pp. 1183-1188 ◽  
Author(s):  
Young Hoon Son ◽  
Mi Jin Park ◽  
Young Jae Kim ◽  
Joong Hwan Yang ◽  
Jung Soo Park ◽  
...  
Keyword(s):  
Light Emitting Diodes ◽  
Layer Structure ◽  
Organic Light Emitting Diodes ◽  
Light Emitting ◽  
Emissive Layer ◽  
Organic Light

Orange phosphorescent organic light-emitting diodes with high operational stability

2012 ◽  
Vol 13 (9) ◽  
pp. 1506-1510 ◽  
Author(s):  
Enrico Orselli ◽  
Jonathan Maunoury ◽  
Dominique Bascour ◽  
Jean-Pierre Catinat
Keyword(s):  
Light Emitting Diodes ◽  
Operational Stability ◽  
Organic Light Emitting Diodes ◽  
Light Emitting ◽  
Organic Light
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