Femtosecond transient spectroscopy has proven to be an important tool for investigating the optical transitions of hybrid perovskites with different dimensionalities, morphologies, and architectures. In this article, we present transient absorption measurements on two-dimensional perovskites to elucidate the nature of optical transitions in these materials and subsequent relaxation.

In particular, the transient signals enabled the observation of electronic transitions involved in the formation of excitons with principal quantum numbers of 1s and 2s. The interpretation of the data was supported by theoretical calculations related to electronic structure and excitonic transitions. Analysis of the decay of the transient signal also demonstrated that the exciton-exciton annihilation mechanism is dominant under the excitation conditions studied.