15 research outputs found
A numerical study on the relationship between the doping and performance in P3HT:PCBM organic bulk heterojunction solar cells
Abstract In this study, we perform a simulation analysis to investigate the influence of p-type and n-type doping concentration in BHJ SCs using the drift-diffusion model. Specifically, we investigate the effect of doping on the charge carrier transport and calculate the above-mentioned device parameters. We show that doping the active layer can increase the cell characteristic parameters, that the results are in an excellent agreement with the experimental results previously reported in the literature. We also show that doping causes space charge effects which subsequently lead to redistribution of the internal electric field in the device. Our results reveal that higher doping levels lead to screening the electrical field in the P3HT:PCBM active region. This in turn forces the charge carrier transport to be solely dominated by the diffusion, consequently decreasing the performance of the device. We also show that doping of the active layer to an optimum level can effectively improve the charge transport. Moreover, we show that doping can create an Ohmic contact between the organic and cathode interface. Additionally, the charge carrier concentration profile shows that by increasing the dopant concentration, the J sc can be improved remarkably. Upon doping the active layer, this indicates that illumination can simply reduce the series resistance in the device
An Investigation on the Cyclic Temperature-Dependent Performance Behaviors of Ultrabright Air-Stable QLEDs
The aerobic and thermal stability of quantum-dot light-emitting diodes
(QLEDs) is an important factor for the practical applications of these devices
under harsh environmental conditions. In this paper, we demonstrate
all-solution-processed amber QLEDs with an external quantum efficiency (EQE) of
>14% with almost negligible efficiency roll-off (droop) and a peak brightness
of >600,000 cd/m2, unprecedented for QLEDs fabricated under ambient air
conditions. We investigate the device efficiency and brightness level at a
temperature range between -10 C to 85 C in a 5-step cooling/heating cycle.
Unlike previous studies reported in the literature, we conducted the
experiments at relatively high brightness levels, required for outdoor lighting
applications. The results reveal that the device performance increases slightly
at sub-zero temperatures (-10 C) and drops slightly at very high temperatures
(85 C), proving acceptable thermal stability. Overall, the performance
parameters do not change dramatically over the temperature range within the
experimental uncertainty range. Interestingly, the device efficiency parameters
recover to the initial values upon returning to room temperature. The
variations in the performance are correlated with the modification of charge
transport characteristics and induced radiative/non-radiative exciton
relaxation dynamics at different temperatures. Being complementary to previous
studies on the subject, the present work is expected to shed light on the
potential feasibility of realizing aerobic-stable ultrabright droop-free QLEDs
and encourage further research for solid-state lighting applications.Comment: 21 pages, 6 figure
Structural Engineering of Colloidal Quantum Dots: Towards Realization of Highly Efficient, Aerobic-Stable, and Droop-Free QLEDs
Quantum dot light-emitting diodes (QLEDs) are promising building blocks for
prospective lighting and display applications. Despite the significant
advancements achieved towards increasing the efficiency and brightness levels
of QLEDs, the unavoidable demand for an inert atmosphere during the fabrication
process restrains their potential for large-scale manufacturing. Here, we
demonstrate ZnCdSe/ZnSe/ZnSeS/ZnS core/multi-shell QDs with ultra-thick shell
(14 monolayers), significantly suppressing the diffusion of moisture and
oxidative species to realize efficient all solution-processed QLED devices
fully fabricated under ambient air conditions. The lattice-mismatch-engineered
shell growth in the synthesized QDs leads to the strong confinement of charge
carriers inside the core and near-unity photoluminescence quantum yield (PLQY)
in the amber-to-red wavelength region (595-625 nm). The best amber-emitting
QLED devices exhibit an external quantum efficiency (EQE) of 14.8%, a current
efficiency (CE) of 41.1 cd/A, and a luminance of 5.6 x 105 cd/m2 at 12 V. To
the best of our knowledge, these are the highest efficiency levels achieved in
air-fabricated QLEDs. Importantly, the demonstrated devices show significant
suppression of non-radiative Auger recombination and optimal charge balance,
leading to negligible EQE roll-off (i.e., droop-free behavior) at the maximum
luminance level. Furthermore, employing a refractive-index-matched optical
compound to enhance light out-coupling increases the EQE to 26.6%, which is
comparable to the best devices fabricated in an inert atmosphere. Collectively,
these advances will greatly facilitate the large-scale industrial fabrication
of air-stable QLEDs.Comment: 22 pages, 5 figure
Efficient Solution-Processed Hyperfluorescent OLEDs with Spectrally Narrow Emission at 840 nm
Near infrared electroluminescence from Nd(TTA) 3 phen in solution-processed small molecule organic light-emitting diodes
International audienceWe report on the near infrared electroluminescence properties of a Nd3+ complex with thenoyltrifluoroacetone and 1,10-phenantroline ligands in solution-processed organic light-emitting diodes. Spin-coated blends containing a 1,3-bis(9-carbazolyl)benzene host doped with the Nd3+ complex were found to exhibit a photoluminescence quantum yield of about 0.5%, regardless of the doping concentration level. Electroluminescent devices based on these small molecule blends showed the characteristic emission of Nd3+ at 890, 1060 and 1330 nm with an external quantum efficiency as high as 0.022%. These improved performances were mainly attributed to direct charge trapping and exciton formation on the near infrared emitter. Importantly, the efficiency roll-off at high current densities due to triplet-triplet exciton annihilation in the device containing 20 wt% of the complex was lower than what is typically observed in lanthanide complex-based electroluminescent devices. This is presumably due to the high triplet energy of the host material, which prevents guest-to-host energy-back transfer and thus host-guest triplet-triplet exciton annihilation
Enhanced near-infrared electroluminescence from a neodymium complex in organic light-emitting diodes with a solution-processed exciplex host
International audienc