Solution-processed, top-emitting, microcavity polymer light-emitting diodes for the pure red, green, blue and near white emission

Top-emitting microcavity polymer light-emitting diodes (TMPLEDs) are of great significance for active matrix PLED displays with high color purity. However, the complex device structures of highly efficient microcavity organic light-emitting diodes fabricated by the full vapor deposition technology are not suitable for solution-processed PLEDs. Solution-processed TMPLEDs with simple device structures are promising candidates for large-area, mass production display techniques. In this work, three strategies were used to apply microcavity into PLEDs: (1) double Ag electrodes performed as the mirrors of cavity, instead of a multi-layer Bragg reflector, which simplified the device structure and fabrication process; (2) three solution-processed functional layers were specially designed for avoiding the inter-infiltration between the different solutions and to improve the interface contacts; (3) high order microcavities were utilized according to the optical simulation results, in which thick EMLs benefited from thickness control and reproductivity. As a result, the full-color emission including pure red, green, blue was realized, and quasi-white light was also achieved from a single polymer emitting material. The achievement of color purity always requires the sacrifice of part of the current efficiency due to the spectra narrowing, while the higher current efficiency of green TMPLED (10.08 cd A−1) compared to that of non-cavity PLED (~8.60 cd A−1) cast a light on future improvements.