Phosphorescent and thermally activated delayed fluorescence (TADF) blue organic light-emitting diodes (OLEDs) have been developed to overcome the low efficiency of fluorescent OLEDs. However, device instability, originating from triplet excitons and polarons, limits blue OLED applications. Here, we develop a phosphor-sensitized TADF emission system with TADF emitters to achieve high efficiency and long operational lifetime. Peripheral carbazole moieties are introduced in conventional multi-resonance–type emitters containing one boron atom. The triplet exciton density of the TADF emitter is reduced by facilitating reverse intersystem crossing, and the Förster resonant energy transfer rate from phosphor sensitizer is enhanced by high absorption coefficient of the emitters. The emitter exhibited an operational lifetime of 72.9 hours with Commission Internationale de L’Eclairage chromaticity coordinate
y
= 0.165, which was 6.6 times longer than those of devices using conventional TADF emitters.
Chip-on-glass (COG) interconnection using anisotropic conductive film (ACF) is susceptible to open failures. Open failures can be induced by the absence of conductive particles or an insufficient contact. Experimental results as well as statistical approaches were used to understand the conditions for open failures in COG bonding. The binomial distribution was used to predict the probability of the open failure due to the deficiency of conductive particles. The probability of an open failure decreased with increasing bump area and decreasing particle size. The bump height variation was also an important factor that affected the probability of the open failure together with the bump-to-electrode gap and the particle size. The variation in bump height should be minimized to avoid open failures in fine-pitch applications where a smaller particle size is required.
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