RESUMO
Multi-organic light-emitting devices comprising two light-emitting units stacked in series through a charge-generation layer are fabricated by solution processes. A zinc oxide nanoparticles/polyethylene-imine bilayer is used as the electron-injection layer and phosphomolybdic acid is used as the charge-generation layer. Appropriate choice of solvents during spin-coating of each layer ensures the nine-layered structure fabricated by solution processes.
RESUMO
Recent developments in the field of π-conjugated polymers have led to considerable improvements in the performance of solution-processed organic light-emitting devices (OLEDs). However, further improving efficiency is still required to compete with other traditional light sources. Here we demonstrate efficient solution-processed multilayer OLEDs using small molecules. On the basis of estimates from a solvent resistance test of small host molecules, we demonstrate that covalent dimerization or trimerization instead of polymerization can afford conventional small host molecules sufficient resistance to alcohols used for processing upper layers. This allows us to construct multilayer OLEDs through subsequent solution-processing steps, achieving record-high power efficiencies of 36, 52 and 34 lm W(-1) at 100 cd m(-2) for solution-processed blue, green and white OLEDs, respectively, with stable electroluminescence spectra under varying current density. We also show that the composition at the resulting interface of solution-processed layers is a critical factor in determining device performance.
