Impact of excitonic and photonic loss mechanisms on the threshold and slope efficiency of organic semiconductor lasers

Abstract

We investigated the impact of various excitonic and photonic losses on the lasing threshold and slope efficiency of organic semiconductor lasers (OSLs) under optical and electrical excitations. The rate equations are solved numerically using the Euler method for an OSL and an organic semiconductor laser diode (OSLD), including 4,4′-bis[(N-carbazole)styryl]biphenyl (BSB-Cz) as a gain medium. The results showed that the loss mechanisms that affect the exciton and photon densities cause an increase in the laser threshold and a decrease in the slope efficiency. Further, we demonstrated that by using a thermally activated delayed fluorescence (TADF) emitter as a gain medium, the triplet excitons could be harvested by increasing the reverse intersystem crossing rate (kRISC), resulting in an appreciable decrease of the laser threshold and an increase of the slope efficiency. Accordingly, the TADF emitters with a fast kRISC are expected to significantly reduce the current density required for electrical excitation.

Progress and Perspective toward Continuous‐Wave Organic Solid‐State Lasers

“…Long-lived triplets generated via ISC or spin statistics are important for lasing, especially under long-pulsed excitation. [109] Triplet accumulation will result in annihilations through multiple channels, as shown in Figure 10. [110][111][112]…”

“…Theoretically, a fast RISC process would be potential to decrease the triplet density and generate the singlets for a lower lasing threshold. [109] Electrical excitation will be much more complex because of the large number of generated triplets via the spin-statistic rule, and singlet-polaron annihilation, and tripletpolaron annihilation also would occur during carrier injection, transporting, and recombination.…”

Quantum Dynamical Approach to Predicting the Optical Pumping Threshold for Lasing in Organic Materials

“…. 42,43 The relevant results are listed in Table 1. The exciton−photon coupling strength is shown in Table 3.…”

“…Excellent laser performance usually corresponds to a low laser threshold. On the basis of phenomenological theory, Adachi’s group has studied the influence of different excitonic losses and photon leakage on the organic laser threshold of organic lasers under optical and electrical excitations. , However, the phenomenological method cannot directly connect the laser threshold and cavity parameters and molecular electronic structure parameters. In this paper, we directly relate the input variable and the output variable of organic lasers to obtain the lasing threshold based on the quantum dynamical method and then investigate the structure–property relationships between the laser threshold and the cavity parameters (including intracavity photon leakage rate and cavity volume) and molecular electronic structure parameters (including the energy of the molecular excited state, the transition dipole, and the organization energy).…”

“…We set the characteristic frequency of the photon environment outside the cavity ω P c to 1450 cm –1 . According to spectral density J P (ω), we can calculate the corresponding leakage rate of the intracavity photon normalΓ normalP = 1 τ normalP = 2 J normalP ( ω P ) 1 − normale − β ω normalP , where τ c is the intracavity photon lifetime and β = 1 k normalB T with the Boltzmann constant k B and temperature T (300 K), and then obtain the quality of the cavity ( Q value) Q = 1 2 ω normalP normalΓ normalP . , The relevant results are listed in Table . The exciton–photon coupling strength is shown in Table .…”