Lead-free PEA
2
SnI
4
-based perovskite
LEDs
are successfully inkjet-printed on rigid and flexible substrates.
Red-emitting devices (λ
max
= 633 nm) exhibit, under
ambient conditions, a maximum external quantum efficiency (EQE
max
) of 1% with a related brightness of 30 cd/m
2
at 10 mA/cm
2
.
Metal halide perovskites (MHPs) have shown outstanding optical emissive properties and can be employed in several optoelectronics devices. In contrast with materials of well‐established technologies, which are prone to degradation or require expensive processes, MHPs can be obtained by solution processing methods and increase stability. Inkjet printing is proposed as an industrial friendly technique to deposit MHPs. The inks have been developed from colloidal CsPbBr3 nanocrystals and printing procedures that allow the deposition of thin layers with intense green emission. High emissive printed layers are assured by carrying out thermal annealing in vacuum oven, which is demonstrated to promote compact layers with low roughness, corroborated by SEM and AFM. XRD measurements show CsPbBr3 crystalline layers with cubic symmetry and XPS provides insight into the stoichiometric composition and local bonding. Optical properties of inkjet‐printed CsPbBr3 films have been analyzed by UV–vis absorbance and photoluminescence (PL), to extract the bandgap energy and photoluminescence quantum yield (PLQY). CsPbBr3 printed layers emit at 524 nm with a narrow emission (FWHM ≈ 15 nm), exhibiting a PLQY up to 20%. These results enabled the large‐scale fabrication by inkjet printing of CsPbBr3 color conversion layers (CCLs) and pave the way for flexible LEDs.
By using ZnO thin films doped with Ce, Tb or Eu, deposited via RF magnetron sputtering, we have developed monochromatic (blue, green and red, respectively) light emitting devices. The rare earth ions introduced with doping rates lower than 2% exhibit narrow and intense emission peaks due to electronic transitions in relaxation processes induced after electrical excitation. This study proves zinc oxide to be a good host for these elements; its high conductivity and optical transparency in the visible range being as well exploited as top transparent electrode. After structural characterization of the different doped layers, a device structure with intense electroluminescence is presented, modelled, and electrically and optically characterized. The different emission spectra obtained are compared in a chromatic diagram, providing a reference for future works with similar devices. The results hereby presented demonstrate three operating monochromatic light emitting devices, as well as a combination of the three species into another one, with a simply-designed structure compatible with current Si technology and demonstrating an integrated RGB emission.
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