9 research outputs found
High-efficiency perovskite–polymer bulk heterostructure light-emitting diodes
Perovskite-based optoelectronic devices have gained significant attention due
to their remarkable performance and low processing cost, particularly for solar
cells. However, for perovskite light-emitting diodes (LEDs), non-radiative
charge carrier recombination has limited electroluminescence (EL) efficiency.
Here we demonstrate perovskite-polymer bulk heterostructure LEDs exhibiting
record-high external quantum efficiencies (EQEs) exceeding 20%, and an EL
half-life of 46 hours under continuous operation. This performance is achieved
with an emissive layer comprising quasi-2D and 3D perovskites and an insulating
polymer. Transient optical spectroscopy reveals that photogenerated excitations
at the quasi-2D perovskite component migrate to lower-energy sites within 1 ps.
The dominant component of the photoluminescence (PL) is primarily bimolecular
and is characteristic of the 3D regions. From PL quantum efficiency and
transient kinetics of the emissive layer with/without charge-transport
contacts, we find non-radiative recombination pathways to be effectively
eliminated. Light outcoupling from planar LEDs, as used in OLED displays,
generally limits EQE to 20-30%, and we model our reported EL efficiency of over
20% in the forward direction to indicate the internal quantum efficiency (IQE)
to be close to 100%. Together with the low drive voltages needed to achieve
useful photon fluxes (2-3 V for 0.1-1 mA/cm2), these results establish that
perovskite-based LEDs have significant potential for light-emission
applications
Control of exciton spin statistics through spin polarization in organic optoelectronic devices
Highly efficient inverted polymer light-emitting diodes using surface modifications of ​ZnO layer
Organic light-emitting diodes have been recently focused for flexible display and solid-state lighting applications and so much effort has been devoted to achieve highly efficient organic light-emitting diodes. Here, we improve the efficiency of inverted polymer light-emitting diodes by introducing a spontaneously formed ripple-shaped nanostructure of ​ZnO and applying an amine-based polar solvent treatment to the nanostructure of ​ZnO. The nanostructure of the ​ZnO layer improves the extraction of the waveguide modes inside the device structure, and a ​2-ME+​EA interlayer enhances the electron injection and hole blocking in addition to reducing exciton quenching between the polar-solvent-treated ​ZnO and the emissive layer. Therefore, our optimized inverted polymer light-emitting diodes have a luminous efficiency of 61.6 cd A−1 and an external quantum efficiency of 17.8%, which are the highest efficiency values among polymer-based fluorescent light-emitting diodes that contain a single emissive layer.close