Quantum dot (QD) LEDs of high color purity, and low turn-on voltage and leakage current are prepared using a solvent free method. First, a monolayer of QDs is formed at the air/water interface, which is then transferred with a PDMS stamp onto the device. The method is applicable to large substrates and reduces materials consumption as compared to other deposition techniques.
Solution-based printing and coating processes have the potential to
dramatically reduce the production costs of Organic Light Emitting Diodes.
This is particularly true for Quantum Dots Light Emitting Diode (QDLEDs),
the newborn in the field of LEDs, due to quantum dots price prohibiting
wastage. Here, we report our latest results on the development of
solutionprocessed QDLEDs. We have implemented a layer by layer strategy,
from a whole evaporated small molecule based OLED to a hybrid QDLED
developed by wet deposition techniques for the first layers and by
evaporation for the last ones. Intermediate steps are discussed in this
paper.First, we have worked on a poly(3,4-ethylenedioxythiophene
poly(styrenesulfonate) (PEDOT:PSS) layer. The PEDOT:PSS formulation for
inkjet printing and spin coating were optimised: wettability on an ITO
substrate, jettability of the inkjet formulation and baking conditions were
studied. Additives as surfactant and ethylene glycol were added to the
commercial inkjet grade solution to improve the deposition process. As a
consequence to this study, anisotropic conductivity of PEDOT:PSS was
observed and is reported here. In particular, ethylene glycol demonstrated a
strong ability to increase the parallel conductivity by several orders of
magnitude, but not the vertical one.Then, inkjet-printed and spin-coated device performances are compared to
complete this first study. Hybrid devices with an efficacy of 12cd/A at 4V
were obtained, with 2.17 % of EQE, and a luminance of 4000 cd/m2
at 4V.Finally, we succeeded in the development of our first QDLED based on CdSe
core/ CdSZnS shell quantum dots emitting at a wavelength of 600nm. Quantum
dots were inkjet printed, in order to waste as little as possible this very
expensive material.
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