55 巻 (2016) 2 号 p. 143-148
Thermally activated delayed fluorescence (TADF) has attracted much attention for realization of highly-efficient and low-cost organic light emitting diodes (OLEDs). OLEDs based on 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), which is one of highly-efficient TADF emitters, have been demonstrated to exhibit external quantum efficiency more than 19%. To study the decay rates from excited states of 4CzIPN, the temperature dependence of photoluminescence quantum efficiency (PLQE) has been measured in the weak photoexcitation limit in 4CzIPN-doped 1,3-bis(9-carbazolyl)benzene thin films. Characteristic features of the temperature dependence of PLQE in the weak photoexcitation limit are found, and examined by using rate equations of singlet and triplet densities.