Triplet-triplet annihilation (TTA) will change the ratio between fluorescence and phosphorescence in the photoluminescence spectrum of a thermally activated delayed fluorescence emitter at very low temperature. Using the resultant spectral blueshift, this study investigated the nature of TTA in 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) doped in a host material. The spectral blueshift is not caused by singlet-triplet annihilation and the emitter saturation effect and is less influenced by the emitter aggregates, particularly for the case of a lower doping concentration. Using these features, it is possible to focus on TTA. For 4CzIPN, the spectral blueshift due to TTA is recognized even in samples with the doping concentration as low as 1 wt. %.
References
This data is presented in the supplementary material of Ref. 19.
The physical constants used here, including γST and γTT, were chosen to closely reproduce the experimental results. However, kT was taken from Ref. 19, and kS and kISC are close to those in Ref. 1. In the simulations, we have set α to be zero. However, the discussions would not change qualitatively if α ≠ 0; in that case, the estimated γTT would be simply 1 + α times larger. According to the lattice gas model34 with a lattice constant of 1 nm, the emitter density is estimated to be 5 × 1019 cm−3 for 5 wt%. We, however, used half of this value as n for a better reproduction of experimental results.
