Tailoring the Optoelectronic Properties of Benzylammonium PbI₄ Hybrid Perovskites

We present a joint theoretical–experimental study of perovskites formed by benzylammonium derivatives and PbI4. The materials were synthesized with a slow evaporation method and subsequently characterized by combining three experimental techniques: X-ray diffraction, X-ray photoemission spectroscopy, and ultraviolet photoemission spectroscopy. Changes in the electronic structure in response to stimulation with visible light were also studied. Simulations were carried out within the framework of density functional theory. In the structural characterization, we have seen that these are layered materials showing alternating organic and inorganic planes with stoichiometry of (XBA)2PbI4, where XBA is a benzylammonium derivative. The ammonium salt varies from one perovskite to another, considering several functional groups in the para position of the benzylamine ring (X = −H, −CH3, −OCH3, and −CF3). We have observed shifts in the Pb 4f, I 3d, C 1s, and N 1s photoemission spectra near the Fermi level, which allow to identify changes in the electronic structure of the perovskites with different organic parts. We attribute such observed changes to the nature of the functional group, in particular, to the permanent dipole exerted by the benzylammonium derivative, and therefore, we conclude that the optoelectronic properties of hybrid perovskites can be modified on demand by altering the electron-withdrawing nature of the organic substituent. Furthermore, the layered structure, separation of charges over long distances (large interplanar distance), and semiconducting properties make it a material in which two-dimensional electron confinement effects are expected to appear after photoexcitation, thus exhibiting a large transient photocurrent effect under visible light illumination and making it an optimal material for optoelectronic devices.