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

Abstract

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 × 10–10 cm3 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 × 10–12 cm3 s–1. Therefore, it can be predicted that the lasing threshold J th of PIO is about 1.20 kA cm–2.

Extremely Low Threshold Quasi‐CW Amplified Spontaneous Emission Achieving and Its Mechanism Study

“…The high radiative rate represents the large, stimulated emission cross section. A formula is used to estimate the stimulated emission cross section (𝜎 SE (𝜆)), as shown below: [19] 𝜎…”

“…Based on the good basic photophysical results, the gain properties of PIO, PIPhDPO, and PI2PhDPO were studied by ASE measurements. Because of the high Förster energy transfer rate between mCP and PPI derivatives, [19] we prepared the doped thin films by doping PIO, PIPhDPO, and PI2PhDPO in mCP with a concentration of 8% by spin-coated method. The thin films were produced on preclean silica substrates and the thickness is in the region of 140-160 nm.…”

“…[18] The phenanthroimidazole derivatives have advantages of weak spectral overlap between triplet absorption and amplified spontaneous emission (ASE), short triplet exciton lifetime, and weak intersystem crossing (ISC), which may have great potential to handle triplet quenching effect. [19] As for photostability, the improvement of operating lifetime is based on the intrinsic photostability of the gain media. Therefore, the development of promising lasing materials owing low lasing threshold, long operating lifetime and negligible pile-up effect from triplet excitons are much significant.…”

Effect of intramolecular charge transfer processes on amplified spontaneous emission of D–π–A type aggregation-enhanced emission molecules

“…6–8 Great effort has been expended to solve the previous issues. 8–12 Recently, Nakanotani et al . first observed the amplified spontaneous emission (ASE) in a thermally activated delayed fluorescence (TADF) material, DABNA-2.…”

“…[6][7][8] Great effort has been expended to solve the previous issues. [8][9][10][11][12] Recently, Nakanotani et al first observed the amplified spontaneous emission (ASE) in a thermally activated delayed fluorescence (TADF) material, DABNA-2. Thus, the study of TADF gain media has become a research hotspot because the reverse intersystem crossing (RISC) process can utilize triplet excitons, and in turn suppress the 'pile-up' effect from triplet excitons.…”