Low Threshold, High Q-Factor Optically Pumped Organic Lasers and Exciton Dynamics in OLEDs under High Current Density: Singlet-Triplet Annihilation Effect and toward Electrical Injection Lasing

The realization of electrically pumped organic semiconductor lasers needs to suppress singlet-triplet annihilation (STA) as much as possible. Generally, organic gain medium materials suffer extensive loss of singlet excitons through STA, resulting in extremely high lasing threshold current density (J(th)) on the order of 10-100 kA cm(-2). Herein, we study the lasing and electroluminescence (EL) properties of a new organic gain material, named PIO, with low STA. As shown, it exhibits remarkable optical gain and EL performance. A low lasing threshold of 0.47 mJ cm(-2) and a high Q-factor of 6000 are well obtained in the microring resonator. In pulse-driven organic light emitting diodes (OLEDs), a high current density of 112.4 A cm(-2) is achieved. Furthermore, a dynamical model is used to analysis exciton dynamics, gain behaviors and singlet exciton loss channels under electrical excitation. It is found that the rate of STA (k(ST)) is at least lower than 1 x 10(-10) cm(3) s(-1) to realize lasing emission with J(th) below the order of 10 kA cm(-2). The k(ST) of the doped PIO is determined to be 6.6 x 10(-12) cm(3) s(-1). Therefore, it can be predicted that the lasing threshold J(th) of PIO is about 1.20 kA cm(-2).