Exciton Dynamics and Optically Pumped Lasing in 1‐Naphthylmethylamine‐Based Quasi‐2D Perovskite Films

Abstract

Films of the quasi‐2D perovskite based on 1‐naphthylmethylamine (NMA) are promising as the gain medium for optically pumped lasing and future electrically pumped lasing because of its low lasing threshold and small electroluminescence efficiency rolloff. However, reasons for the low threshold and small efficiency rolloff are still unclear. Therefore, exciton dynamics are investigated in NMA‐based quasi‐2D perovskite films. It is found that quenching of bright excitons by other excitons or charge carriers is unlikely in NMA‐based quasi‐2D perovskite films, which is one reason for the low lasing threshold and small efficiency rolloff. Moreover, thermally stimulated current measurements reveal that the defect levels inside the band gap of the NMA‐based quasi‐2D perovskite are shallow, with a depth of ≈0.3 eV, causing a decrease in nonradiative exciton recombination through the defects. Therefore, population inversion can be easily achieved, leading to the low lasing threshold as well. For fabrication of NMA‐based quasi‐2D perovskite laser devices with even lower lasing thresholds, a circular‐shaped optical resonator, and small‐molecule‐based defect passivation are used. Optically pumped lasing can be obtained from these devices, with a threshold of ≈1 µJ cm−2, which is one of the lowest values ever reported in any perovskite lasers.

Improved Photoluminescence, Electroluminescence, and Laser Characteristics of 1-Naphthylmethylamine-Based Quasi-Two-Dimensional Perovskite Films at Lower Temperatures

“…Qin et al realized CW lasing from quasi-2D perovskite films fabricated using NMA or PEA as the B -site large organic cation in air at room temperature, along with excellent laser intensity durability under intense photoexcitation . Especially, NMA-based quasi-2D perovskite films had lower ASE and laser thresholds and very small external quantum efficiency (EQE) roll-off than PEA-based quasi-2D perovskite films did. , Further, we showed that the laser threshold of NMA-based quasi-2D perovskite films was lowered to ∼1 μJ/cm 2 by introducing a circular-shaped DFB resonator . Note that, in NMA-based quasi-2D perovskite films, quenching of bright excitons by other excitons or charge carriers is unlikely, making NMA-based quasi-2D perovskite films a promising candidate for future electrical lasing.…”

“…These spectra agree well with the report. 11 SEM and AFM images shown in Figure S2 (Supporting Information) indicated that NMA-based quasi-2D perovskite films had a featureless surface morphology with a small surface roughness R a of ∼0.3 nm.…”

“…In our laser study, a second-order circular-shaped DFB structure (m = 2) was used, enabling surface-emitting laser oscillation with lower thresholds. 11,45 The λ Bragg value was 530 nm. The n eff value was 1.92, which was obtained using variable angle spectroscopic ellipsometry.…”

“…This EQE is not so high but consistent with the report. 11 Then, these perovskite LEDs were operated under electrical pulse excitation to avoid degradation, which may be associated with Joule heating and ion migration. 19 While using the electrical pulses at a higher voltage of 15 V resulted in a gradual decrease in EL intensity with time, no EL decrease was observed with a lower voltage of 5 or 10 V (Figure S9, Supporting Information).…”

2D and quasi-2D hybrid perovskites containing organic cations with an extended conjugated system: opportunities and challenges

“…In a recent follow-up paper, Adachi and co-workers showed that quenching of bright excitons by other excitons or charge carriers does not happen in NMA-based quasi-2D perovskite films and that such films possess shallower defect levels inside the bandgap as compared to PEA-based ones. 24…”