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A systematic study has been conducted on microcavity organic light emitting diodes (OLEDs) based on green, red and blue phosphorescent emitters to elucidate the microcavity effects for different color emitters. We found that the luminance output is determined by the reflectivity of the semitransparent electrode and the photopic response of the green, red and blue emitters. While the luminance enhancements of blue and red phosphorescent microcavity devices are small, a current efficiency as high as 224 cd A−1 is obtained in the green phosphorescent microcavity OLEDs. The role that microcavities play in the output of an organic light-emitting device (OLED) has now been studied in detail. Chaoyu Xiang and co-workers from the University of Florida in the USA and Yamagata University in Japan investigated the efficiency and spectral characteristics of phosphorescent green, red and blue microcavity OLEDs. They concluded that the luminance output of a device is strongly affected by the reflectivity of its semitransparent electrode and its spectral match to the organic material’s electroluminescence. They fabricated device electrodes from indium-tin-oxide-coated distributed Bragg reflectors comprising two separated stacks of alternating layers of titanium oxide and silicon dioxide. They recorded a luminous efficiency of up 224 cd A–1 for an optimized green microcavity device, with smaller values achieved for blue and red devices.
Xiang et al. (Fri,) studied this question.