Transport Layer Engineering Towards Lower Threshold for Perovskite Lasers

Lead halide perovskites are promising candidates for future lasers as they are proven good gain medium, low-cost solution processable, and exhibit bandgap-tunable luminescence with high color purity and photoluminescence quantum yields. Sandwiching the perovskite layer into transport layers is inevitable during the integration of electrical devices for electrically pumped perovskite lasers. However, the appearance of perovskite/transport layer interfaces is absent in most reported optically pumped perovskite lasers, and is usually considered as detrimental factors to lasing actions. This is why the electrically pumped perovskite lasers are still not realized even with the realization of high injection current densities (> 1 kA/cm²) and achievement of optically pumped continuous wave (CW) perovskite lasers at room temperature. Here we report the treatment of perovskite polycrystal thin films with different transport layers effect of transport layers, and the amplified spontaneous emission (ASE) threshold are studied to investigate the influence of perovskite/transport interfaces on lasing actions. We demonstrate largely reduced ASE threshold (22.0%) and enhanced ASE intensity (18.6%) with introducing an additional hole transport layer poly(triaryl amine) (PTAA) on top of perovskite layer. We show that the key role of PTAA layer is to accelerate the hot carrier cooling process from 488 fs to 422 fs by extracting the excess hot holes of perovskites. With suppressed hot holes, the Auger recombination loss is largely reduced, which in turn reduces the ASE threshold. Our work for the first time exemplifies how to further reduce ASE threshold with transport layer engineering. This is critical to maintain the good gain medium properties of perovskites when integrating perovskites into electrical devices and could also have a broader impact on paving the way for future electrically pumped laser fabrication.