Vadim Trepalin1,Yang Ding1,Masaru Kuno1
University of Notre Dame1
Vadim Trepalin1,Yang Ding1,Masaru Kuno1
University of Notre Dame1
Over the last decade the interest in 2D and quasi-2D perovskites has been growing rapidly thanks to their superior stability and unique optoelectronic properties as compared to the more commonly studied 3D perovskites. Spatially separated layers of metal-halide octahedra in these materials naturally form quantum wells with strongly pronounced excitonic effects due to both quantum and dielectric confinements. Exciton binding energies of up to several hundred millielectronvolts facilitate formation of stable multiexcitonic complexes such as biexcitons and even triexcitons under relatively low excitation intensities at cryogenic temperatures. Multiexciton radiative recombination enables a highly efficient pathway for light amplification and thus, these materials show a great potential in cost-efficient laser applications as optical gain media. Moreover, existence of stable triexcitons makes 2D perovskites a unique platform to study the exotic world of many-body physics.<br/>In the present work we investigate the formation and radiative recombination of single excitons and multiexcitonic complexes, including rarely observed triexcitons, in the single crystals of phase-pure quasi-2D Ruddlesden-Popper perovskites (PEA)<sub>2</sub>MAPb<sub>2</sub>I<sub>7</sub> and (n-BuA)<sub>2</sub>MAPb<sub>2</sub>I<sub>7</sub> (PEA = phenethylammonium, MA = methylammonium, n-BuA = n-butylammonium). By means of time-integrated and time-resolved photoluminescence spectroscopies we confirm the existence of stable triexcitons at cryogenic temperatures after high-energy femtosecond pulsed laser excitation. We also support our experimental findings with a developed kinetic model of a dynamic equilibrium between excitonic species that qualitatively explains different laser fluence-dependent behaviors of each excitonic transition. Additionally, we observe Amplified Spontaneous Emission on single crystals of (PEA)<sub>2</sub>MAPb<sub>2</sub>I<sub>7</sub> with threshold fluences as low as ~2 μJ cm<sup>-2</sup> and estimate optical gain coefficient of ~1100 cm<sup>-1</sup> using the Variable Stripe Length method. These promising lasing characteristics and strong excitonic effects together with low-cost solution-based synthetic methods, compositional tunability and enhanced stability make 2D perovskites a unique class of materials for future light-emitting applications and studies of higher order exciton physics.