The triplet-charge annihilation in copolymer-based organic light emitting diodes: through the “Scattering Channel” or the “Dissociation Channel”?

Jia

Xiang

et al. 2016

Organic Electronics

Self Cite

Although it is known that triplet excitons can be quenched via triplet-charge interaction (TQI), it is still unclear how this process occurs in rubrene-based devices. We found that magneto-conductance (MC) can be used to probe the detailed mechanism of TQI in rubrene-based organic light-emitting diodes and observed the coexistence of negative and positive MC responses in the high-field region when holes and electrons were the dominant charged species at different interfaces adjoining the rubrene layer, respectively. Further analysis suggests that the negative MC response was originated from the dissociation of triplet excitons by holes, while the positive MC response was due to electron scattering by triplet excitons. The MC responses of the devices were examined under different injection currents and temperatures to confirm our hypothesis. This work gives significant insight into mechanisms of TQI in organic semiconductors, which will allow for the design of new and improved devices.

Section: ．Introductionmentioning

confidence: 88%

Identify triplet-charge interaction in rubrene-based diodes using magneto-conductance: Coexistence of dissociation and scattering channels

Jia

Xiang

et al. 2016

Organic Electronics

Self Cite

“…It has been demonstrated experimentally that both SF and TTA are sensitive to an external magnetic field ( B ), and that their organic magneto-electroluminescence (MEL) responses exhibit diagnostic “fingerprints” 13 15 16 17 18 19 . To date, MEL has proven to be an effective means to explore the underlying dynamics in organic semiconductors 16 19 20 21 22 23 24 25 26 . Several models describing MEL have been proposed based on both experimental and theoretical analyses, including intersystem crossing 18 22 24 25 , reverse intersystem crossing 21 , SF 15 16 , TTA 11 17 and triplet-charge annihilation (TCA) 20 23 .…”

mentioning

confidence: 99%

Determining the Origin of Half-bandgap-voltage Electroluminescence in Bifunctional Rubrene/C60 Devices

Jia

et al. 2016

Sci Rep

Self Cite

Lowering the driving voltage of organic light-emitting diodes (OLEDs) is an important approach to reduce their energy consumption. We have fabricated a series of bifunctional devices (OLEDs and photovoltaics) using rubrene and fullerene (C60) as the active layer, in which the electroluminescence threshold voltage(~1.1 V) was half the value of the bandgap of rubrene. Magneto-electroluminescence (MEL) response of planner heterojunction diodes exhibited a small increase in response to a low magnetic field strength (<20 mT); however, a very large decay was observed at a high magnetic field strength (>20 mT). When a hole-transport layer with a low mobility was included in these devices, the MEL response reversed in shape, and simultaneously, the EL threshold voltage became larger than the bandgap voltage. When bulk heterojunction device was examined, the amplitude of MEL curves presented an anomalous voltage-dependence. Following an analysis of the MEL responses of these devices, we proposed that the EL of half-bandgap-voltage device originated from bimolecular triplet-triplet annihilation in the rubrene film, rather than from singlet excitons that formed via an interface auger recombination. This work provides critical insight into the mechanisms of OLED emission and will help advance the applications of bifunctional devices.

Physica Status Solidi (a)

“…The values of HOMO and LUMO of each organic and inorganic layer were taken from the literature of Refs. . In this diagram, the negative signs indicate that ITO and Al are the cathodes while Ag is the positive anode.…”

Section: Resultsmentioning

confidence: 99%

Tuning Color Temperature of White OLEDs in Parallel Tandems

Oliva

Papadimitratos

Rosa

et al. 2017

Color-temperature tunable white organic light emitting diodes (WOLEDs) in parallel tandem configuration were fabricated by using TFB:MEH-PPV (yellow emitter) in the bottom subunit and TBADN (blue emitter) in the top subunit. In this parallel tandem architecture, a thin film of silver was an active common anode, which permitted to inject holes into top and bottom subunits simultaneously. This common injection electrode also allowed to tune the color temperature (CCT) and CIE coordinates of white light emission from cool (CIE: 0.33, 0.25; CCT ¼ 5218 K) to warm (CIE: 0.38, 0.39; CCT ¼ 3926 K) by controlling the brightness of the yellow light and blue light emitted in the bottom and top subunits respectively. The performance of the parallel tandem was compared with that of in-series tandems and additional advantages of the parallel architecture such as tunable chromaticity, lower turn on voltage (4 V compared to 7 V in the in-series tandem) and higher brightness ($15%) were found. The closest CIE coordinate obtained for white light was (0.35, 0.35), which is near to the ideal coordinate of (0.33, 0.33) for pure white light. Thus, the results indicate that these white OLEDs in parallel configuration can be potentially useful for displays and lighting applications.