PEA ₂ SnI ₄ Perovskite Thin Films for Photonics: Linear and Nonlinear Optical Properties and Waveguided Photoluminescence

Abstract In this work, 2D PEA 2 SnI 4 (PEA: 2‐phenylethanaminium) perovskite thin films, formed with the reducing agent NaBH 4 to control the Sn +4 defects are investigated. Optical characterization of the films reveals idoneous properties for the development of photon sources, particularly an extraordinarily high absorption coefficient at the exciton resonance > 10 µm −1 , the ability to enhance the light‐matter interaction due to the high refractive index. These linear optical properties are complemented with impressive nonlinear optical characteristics, involving a giant nonlinear absorption β = 7–10 cm MW −1 and a remarkably high nonlinear refractive coefficient, n 2 = 1.5–4 cm 2 GW −1 . The integration of PEA 2 SnI 4 films into rigid and flexible waveguides further enhances the generation of waveguided photoluminescence (PL), which is also obtained under the two‐photon absorption mechanism. The efficient generation of PL is validated by the reabsorption effect, resulting in the propagation of recycled photons over distances longer than 3 mm with an increased effective lifetime from 3 to 8.5 ns. These findings pave the way for the development of novel photonic functionalities based on these innovative low‐dimensional semiconductors.