Tuning Color Temperature of White OLEDs in Parallel Tandems

Abstract

Color‐temperature tunable white organic light emitting diodes (WOLEDs) in parallel tandem configuration were fabricated by using TFB:MEH‐PPV (yellow emitter) in the bottom subunit and TBADN (blue emitter) in the top subunit. In this parallel tandem architecture, a thin film of silver was an active common anode, which permitted to inject holes into top and bottom subunits simultaneously. This common injection electrode also allowed to tune the color temperature (CCT) and CIE coordinates of white light emission from cool (CIE: 0.33, 0.25; CCT = 5218 K) to warm (CIE: 0.38, 0.39; CCT = 3926 K) by controlling the brightness of the yellow light and blue light emitted in the bottom and top subunits respectively. The performance of the parallel tandem was compared with that of in‐series tandems and additional advantages of the parallel architecture such as tunable chromaticity, lower turn on voltage (4 V compared to 7 V in the in‐series tandem) and higher brightness (∼15%) were found. The closest CIE coordinate obtained for white light was (0.35, 0.35), which is near to the ideal coordinate of (0.33, 0.33) for pure white light. Thus, the results indicate that these white OLEDs in parallel configuration can be potentially useful for displays and lighting applications.