Single- and two-photon excited photoluminescence of 2D perovskite thin films with different organic spacer cations†

Studying the fundamental optical properties of two-dimensional (2D) perovskites is a prerequisite for developing related applications. In this work, we have prepared A₂PbBr₄ (A = EA⁺, PA⁺, and BA⁺) (EA⁺ = ethylammonium, PA⁺ = propylammonium, and BA⁺ = butylammonium) polycrystalline thin films with different alkylamine chain lengths by a spin-coating and annealing method, and we investigate the effect of the organic spacer cation chain length on optical properties. Our experimental results show that the length of the amine chain can significantly affect the temperature-dependent photoluminescence (PL) properties. Specifically, short amine chains will result in dominance of the thermal expansion effect, while long amine chains can enhance electron–phonon coupling strength. Meanwhile, we confirm that the amine chain length can also effectively regulate the two-photon excited PL properties of 2D perovskite films. Among the three samples, the (PA)₂PbBr₄ film with a medium chain length exhibits the largest two-photon absorption coefficient, attributed to its large density of states and the strongest electron–phonon coupling strength. Our study not only deepens the understanding of the regulation of PL properties in 2D perovskites but also provides an important theoretical basis for the development of high-performance luminescent devices.