Continuous wave amplified spontaneous emission in phase-stable triple cation lead halide perovskite thin films

Perovskite thin films possess excellent light absorption and light emission properties, as well as a high defect tolerance and high charge carrier mobilities [1]. These properties founded their rapid development in solar cell applications and established this new class of materials as a strong candidate for solution-processed light-emitting applications and on-chip laser sources [2]. So far, the focus has been on investigating the laser behaviour under short pulsed excitation, given the laser death phenomenon observed after a few hundreds of nanoseconds of excitation [3]. Clear CW lasing in perovskites still remains a challenge: It was only observed in a single cation perovskite at a specific temperature of 100 K, where the optical gain originates from small inclusions of a pump-induced crystal phase [3], an unviable approach for practical applications. In contrast, we found that sustained CW operation is possible over a temperature range of ~80-130 K if the methylammonium (MA) cation is partially replaced by formamidinium (FA) and Caesium.