Investigation on spacers and structures: A simple but effective approach toward high-performance hybrid white organic light emitting diodes

A simple but effective way to achieve high-performance hybrid white organic light emitting diodes (WOLEDs) has been successfully presented. First, by optimizing the thickness of 4,4-N,N-dicarbazolebiphenyl (CBP) spacer, it is demonstrated that 3 nm spacer is the most efficient for obtaining balanced white color. Then, to further enhance the efficiency of the device, mixed spacers CBP:bis(10-hydroxybenzo[h]quinolinato)beryllium complex (Bebq2) with different codoped ratios of 9:1, 7:3 and 5:5 have been explored. Finally, by combining the optimized mixed spacer and a more efficient architecture, the device exhibits a maximum forward-viewing current efficiency and power efficiency of 15.4 cd/A and 16.2 lm/W, respectively. Compared with the device only containing 3 nm CBP spacer (7.4 cd/A, 6.0 lm/W), the optimized device performs 108% higher current efficiency and 170% higher power efficiency. A peak brightness of 35,178 cd/m2, a Commission International de l’Eclairage chromaticity coordinate of (0.30, 0.35) and high color rendering index of 75 are also obtained. Undoubtedly, the results will be beneficial to the design of both material and device architecture for high-performance WOLEDs and next-generation solid-state lighting sources.